1 //===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Peephole optimize the CFG.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "simplifycfg"
15 #include "llvm/Transforms/Utils/Local.h"
16 #include "llvm/ADT/DenseMap.h"
17 #include "llvm/ADT/STLExtras.h"
18 #include "llvm/ADT/SetVector.h"
19 #include "llvm/ADT/SmallPtrSet.h"
20 #include "llvm/ADT/SmallVector.h"
21 #include "llvm/ADT/Statistic.h"
22 #include "llvm/Analysis/InstructionSimplify.h"
23 #include "llvm/Analysis/TargetTransformInfo.h"
24 #include "llvm/Analysis/ValueTracking.h"
25 #include "llvm/IR/Constants.h"
26 #include "llvm/IR/DataLayout.h"
27 #include "llvm/IR/DerivedTypes.h"
28 #include "llvm/IR/GlobalVariable.h"
29 #include "llvm/IR/IRBuilder.h"
30 #include "llvm/IR/Instructions.h"
31 #include "llvm/IR/IntrinsicInst.h"
32 #include "llvm/IR/LLVMContext.h"
33 #include "llvm/IR/MDBuilder.h"
34 #include "llvm/IR/Metadata.h"
35 #include "llvm/IR/Module.h"
36 #include "llvm/IR/Operator.h"
37 #include "llvm/IR/Type.h"
38 #include "llvm/Support/CFG.h"
39 #include "llvm/Support/CommandLine.h"
40 #include "llvm/Support/ConstantRange.h"
41 #include "llvm/Support/Debug.h"
42 #include "llvm/Support/NoFolder.h"
43 #include "llvm/Support/raw_ostream.h"
44 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
50 static cl::opt<unsigned>
51 PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(1),
52 cl::desc("Control the amount of phi node folding to perform (default = 1)"));
55 DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false),
56 cl::desc("Duplicate return instructions into unconditional branches"));
59 SinkCommon("simplifycfg-sink-common", cl::Hidden, cl::init(true),
60 cl::desc("Sink common instructions down to the end block"));
63 HoistCondStores("simplifycfg-hoist-cond-stores", cl::Hidden, cl::init(true),
64 cl::desc("Hoist conditional stores if an unconditional store preceeds"));
66 STATISTIC(NumBitMaps, "Number of switch instructions turned into bitmaps");
67 STATISTIC(NumLookupTables, "Number of switch instructions turned into lookup tables");
68 STATISTIC(NumSinkCommons, "Number of common instructions sunk down to the end block");
69 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
72 /// ValueEqualityComparisonCase - Represents a case of a switch.
73 struct ValueEqualityComparisonCase {
77 ValueEqualityComparisonCase(ConstantInt *Value, BasicBlock *Dest)
78 : Value(Value), Dest(Dest) {}
80 bool operator<(ValueEqualityComparisonCase RHS) const {
81 // Comparing pointers is ok as we only rely on the order for uniquing.
82 return Value < RHS.Value;
85 bool operator==(BasicBlock *RHSDest) const { return Dest == RHSDest; }
88 class SimplifyCFGOpt {
89 const TargetTransformInfo &TTI;
90 const DataLayout *const TD;
92 Value *isValueEqualityComparison(TerminatorInst *TI);
93 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
94 std::vector<ValueEqualityComparisonCase> &Cases);
95 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
97 IRBuilder<> &Builder);
98 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
99 IRBuilder<> &Builder);
101 bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder);
102 bool SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder);
103 bool SimplifyUnreachable(UnreachableInst *UI);
104 bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
105 bool SimplifyIndirectBr(IndirectBrInst *IBI);
106 bool SimplifyUncondBranch(BranchInst *BI, IRBuilder <> &Builder);
107 bool SimplifyCondBranch(BranchInst *BI, IRBuilder <>&Builder);
110 SimplifyCFGOpt(const TargetTransformInfo &TTI, const DataLayout *TD)
111 : TTI(TTI), TD(TD) {}
112 bool run(BasicBlock *BB);
116 /// SafeToMergeTerminators - Return true if it is safe to merge these two
117 /// terminator instructions together.
119 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
120 if (SI1 == SI2) return false; // Can't merge with self!
122 // It is not safe to merge these two switch instructions if they have a common
123 // successor, and if that successor has a PHI node, and if *that* PHI node has
124 // conflicting incoming values from the two switch blocks.
125 BasicBlock *SI1BB = SI1->getParent();
126 BasicBlock *SI2BB = SI2->getParent();
127 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
129 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
130 if (SI1Succs.count(*I))
131 for (BasicBlock::iterator BBI = (*I)->begin();
132 isa<PHINode>(BBI); ++BBI) {
133 PHINode *PN = cast<PHINode>(BBI);
134 if (PN->getIncomingValueForBlock(SI1BB) !=
135 PN->getIncomingValueForBlock(SI2BB))
142 /// isProfitableToFoldUnconditional - Return true if it is safe and profitable
143 /// to merge these two terminator instructions together, where SI1 is an
144 /// unconditional branch. PhiNodes will store all PHI nodes in common
147 static bool isProfitableToFoldUnconditional(BranchInst *SI1,
150 SmallVectorImpl<PHINode*> &PhiNodes) {
151 if (SI1 == SI2) return false; // Can't merge with self!
152 assert(SI1->isUnconditional() && SI2->isConditional());
154 // We fold the unconditional branch if we can easily update all PHI nodes in
155 // common successors:
156 // 1> We have a constant incoming value for the conditional branch;
157 // 2> We have "Cond" as the incoming value for the unconditional branch;
158 // 3> SI2->getCondition() and Cond have same operands.
159 CmpInst *Ci2 = dyn_cast<CmpInst>(SI2->getCondition());
160 if (!Ci2) return false;
161 if (!(Cond->getOperand(0) == Ci2->getOperand(0) &&
162 Cond->getOperand(1) == Ci2->getOperand(1)) &&
163 !(Cond->getOperand(0) == Ci2->getOperand(1) &&
164 Cond->getOperand(1) == Ci2->getOperand(0)))
167 BasicBlock *SI1BB = SI1->getParent();
168 BasicBlock *SI2BB = SI2->getParent();
169 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
170 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
171 if (SI1Succs.count(*I))
172 for (BasicBlock::iterator BBI = (*I)->begin();
173 isa<PHINode>(BBI); ++BBI) {
174 PHINode *PN = cast<PHINode>(BBI);
175 if (PN->getIncomingValueForBlock(SI1BB) != Cond ||
176 !isa<ConstantInt>(PN->getIncomingValueForBlock(SI2BB)))
178 PhiNodes.push_back(PN);
183 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
184 /// now be entries in it from the 'NewPred' block. The values that will be
185 /// flowing into the PHI nodes will be the same as those coming in from
186 /// ExistPred, an existing predecessor of Succ.
187 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
188 BasicBlock *ExistPred) {
189 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
192 for (BasicBlock::iterator I = Succ->begin();
193 (PN = dyn_cast<PHINode>(I)); ++I)
194 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
198 /// GetIfCondition - Given a basic block (BB) with two predecessors (and at
199 /// least one PHI node in it), check to see if the merge at this block is due
200 /// to an "if condition". If so, return the boolean condition that determines
201 /// which entry into BB will be taken. Also, return by references the block
202 /// that will be entered from if the condition is true, and the block that will
203 /// be entered if the condition is false.
205 /// This does no checking to see if the true/false blocks have large or unsavory
206 /// instructions in them.
207 static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
208 BasicBlock *&IfFalse) {
209 PHINode *SomePHI = cast<PHINode>(BB->begin());
210 assert(SomePHI->getNumIncomingValues() == 2 &&
211 "Function can only handle blocks with 2 predecessors!");
212 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
213 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
215 // We can only handle branches. Other control flow will be lowered to
216 // branches if possible anyway.
217 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
218 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
219 if (Pred1Br == 0 || Pred2Br == 0)
222 // Eliminate code duplication by ensuring that Pred1Br is conditional if
224 if (Pred2Br->isConditional()) {
225 // If both branches are conditional, we don't have an "if statement". In
226 // reality, we could transform this case, but since the condition will be
227 // required anyway, we stand no chance of eliminating it, so the xform is
228 // probably not profitable.
229 if (Pred1Br->isConditional())
232 std::swap(Pred1, Pred2);
233 std::swap(Pred1Br, Pred2Br);
236 if (Pred1Br->isConditional()) {
237 // The only thing we have to watch out for here is to make sure that Pred2
238 // doesn't have incoming edges from other blocks. If it does, the condition
239 // doesn't dominate BB.
240 if (Pred2->getSinglePredecessor() == 0)
243 // If we found a conditional branch predecessor, make sure that it branches
244 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
245 if (Pred1Br->getSuccessor(0) == BB &&
246 Pred1Br->getSuccessor(1) == Pred2) {
249 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
250 Pred1Br->getSuccessor(1) == BB) {
254 // We know that one arm of the conditional goes to BB, so the other must
255 // go somewhere unrelated, and this must not be an "if statement".
259 return Pred1Br->getCondition();
262 // Ok, if we got here, both predecessors end with an unconditional branch to
263 // BB. Don't panic! If both blocks only have a single (identical)
264 // predecessor, and THAT is a conditional branch, then we're all ok!
265 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
266 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
269 // Otherwise, if this is a conditional branch, then we can use it!
270 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
271 if (BI == 0) return 0;
273 assert(BI->isConditional() && "Two successors but not conditional?");
274 if (BI->getSuccessor(0) == Pred1) {
281 return BI->getCondition();
284 /// ComputeSpeculationCost - Compute an abstract "cost" of speculating the
285 /// given instruction, which is assumed to be safe to speculate. 1 means
286 /// cheap, 2 means less cheap, and UINT_MAX means prohibitively expensive.
287 static unsigned ComputeSpeculationCost(const User *I) {
288 assert(isSafeToSpeculativelyExecute(I) &&
289 "Instruction is not safe to speculatively execute!");
290 switch (Operator::getOpcode(I)) {
292 // In doubt, be conservative.
294 case Instruction::GetElementPtr:
295 // GEPs are cheap if all indices are constant.
296 if (!cast<GEPOperator>(I)->hasAllConstantIndices())
299 case Instruction::Load:
300 case Instruction::Add:
301 case Instruction::Sub:
302 case Instruction::And:
303 case Instruction::Or:
304 case Instruction::Xor:
305 case Instruction::Shl:
306 case Instruction::LShr:
307 case Instruction::AShr:
308 case Instruction::ICmp:
309 case Instruction::Trunc:
310 case Instruction::ZExt:
311 case Instruction::SExt:
312 return 1; // These are all cheap.
314 case Instruction::Call:
315 case Instruction::Select:
320 /// DominatesMergePoint - If we have a merge point of an "if condition" as
321 /// accepted above, return true if the specified value dominates the block. We
322 /// don't handle the true generality of domination here, just a special case
323 /// which works well enough for us.
325 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
326 /// see if V (which must be an instruction) and its recursive operands
327 /// that do not dominate BB have a combined cost lower than CostRemaining and
328 /// are non-trapping. If both are true, the instruction is inserted into the
329 /// set and true is returned.
331 /// The cost for most non-trapping instructions is defined as 1 except for
332 /// Select whose cost is 2.
334 /// After this function returns, CostRemaining is decreased by the cost of
335 /// V plus its non-dominating operands. If that cost is greater than
336 /// CostRemaining, false is returned and CostRemaining is undefined.
337 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
338 SmallPtrSet<Instruction*, 4> *AggressiveInsts,
339 unsigned &CostRemaining) {
340 Instruction *I = dyn_cast<Instruction>(V);
342 // Non-instructions all dominate instructions, but not all constantexprs
343 // can be executed unconditionally.
344 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
349 BasicBlock *PBB = I->getParent();
351 // We don't want to allow weird loops that might have the "if condition" in
352 // the bottom of this block.
353 if (PBB == BB) return false;
355 // If this instruction is defined in a block that contains an unconditional
356 // branch to BB, then it must be in the 'conditional' part of the "if
357 // statement". If not, it definitely dominates the region.
358 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
359 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB)
362 // If we aren't allowing aggressive promotion anymore, then don't consider
363 // instructions in the 'if region'.
364 if (AggressiveInsts == 0) return false;
366 // If we have seen this instruction before, don't count it again.
367 if (AggressiveInsts->count(I)) return true;
369 // Okay, it looks like the instruction IS in the "condition". Check to
370 // see if it's a cheap instruction to unconditionally compute, and if it
371 // only uses stuff defined outside of the condition. If so, hoist it out.
372 if (!isSafeToSpeculativelyExecute(I))
375 unsigned Cost = ComputeSpeculationCost(I);
377 if (Cost > CostRemaining)
380 CostRemaining -= Cost;
382 // Okay, we can only really hoist these out if their operands do
383 // not take us over the cost threshold.
384 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
385 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining))
387 // Okay, it's safe to do this! Remember this instruction.
388 AggressiveInsts->insert(I);
392 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
393 /// and PointerNullValue. Return NULL if value is not a constant int.
394 static ConstantInt *GetConstantInt(Value *V, const DataLayout *TD) {
395 // Normal constant int.
396 ConstantInt *CI = dyn_cast<ConstantInt>(V);
397 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
400 // This is some kind of pointer constant. Turn it into a pointer-sized
401 // ConstantInt if possible.
402 IntegerType *PtrTy = cast<IntegerType>(TD->getIntPtrType(V->getType()));
404 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
405 if (isa<ConstantPointerNull>(V))
406 return ConstantInt::get(PtrTy, 0);
408 // IntToPtr const int.
409 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
410 if (CE->getOpcode() == Instruction::IntToPtr)
411 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
412 // The constant is very likely to have the right type already.
413 if (CI->getType() == PtrTy)
416 return cast<ConstantInt>
417 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
422 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
423 /// collection of icmp eq/ne instructions that compare a value against a
424 /// constant, return the value being compared, and stick the constant into the
427 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
428 const DataLayout *TD, bool isEQ, unsigned &UsedICmps) {
429 Instruction *I = dyn_cast<Instruction>(V);
430 if (I == 0) return 0;
432 // If this is an icmp against a constant, handle this as one of the cases.
433 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
434 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
435 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
438 return I->getOperand(0);
441 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
444 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
446 // If this is an and/!= check then we want to optimize "x ugt 2" into
449 Span = Span.inverse();
451 // If there are a ton of values, we don't want to make a ginormous switch.
452 if (Span.getSetSize().ugt(8) || Span.isEmptySet())
455 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
456 Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
458 return I->getOperand(0);
463 // Otherwise, we can only handle an | or &, depending on isEQ.
464 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
467 unsigned NumValsBeforeLHS = Vals.size();
468 unsigned UsedICmpsBeforeLHS = UsedICmps;
469 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
471 unsigned NumVals = Vals.size();
472 unsigned UsedICmpsBeforeRHS = UsedICmps;
473 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
477 Vals.resize(NumVals);
478 UsedICmps = UsedICmpsBeforeRHS;
481 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
482 // set it and return success.
483 if (Extra == 0 || Extra == I->getOperand(1)) {
484 Extra = I->getOperand(1);
488 Vals.resize(NumValsBeforeLHS);
489 UsedICmps = UsedICmpsBeforeLHS;
493 // If the LHS can't be folded in, but Extra is available and RHS can, try to
495 if (Extra == 0 || Extra == I->getOperand(0)) {
496 Value *OldExtra = Extra;
497 Extra = I->getOperand(0);
498 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
501 assert(Vals.size() == NumValsBeforeLHS);
508 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
509 Instruction *Cond = 0;
510 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
511 Cond = dyn_cast<Instruction>(SI->getCondition());
512 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
513 if (BI->isConditional())
514 Cond = dyn_cast<Instruction>(BI->getCondition());
515 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
516 Cond = dyn_cast<Instruction>(IBI->getAddress());
519 TI->eraseFromParent();
520 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
523 /// isValueEqualityComparison - Return true if the specified terminator checks
524 /// to see if a value is equal to constant integer value.
525 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
527 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
528 // Do not permit merging of large switch instructions into their
529 // predecessors unless there is only one predecessor.
530 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
531 pred_end(SI->getParent())) <= 128)
532 CV = SI->getCondition();
533 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
534 if (BI->isConditional() && BI->getCondition()->hasOneUse())
535 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
536 if (ICI->isEquality() && GetConstantInt(ICI->getOperand(1), TD))
537 CV = ICI->getOperand(0);
539 // Unwrap any lossless ptrtoint cast.
540 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
541 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
542 CV = PTII->getOperand(0);
546 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
547 /// decode all of the 'cases' that it represents and return the 'default' block.
548 BasicBlock *SimplifyCFGOpt::
549 GetValueEqualityComparisonCases(TerminatorInst *TI,
550 std::vector<ValueEqualityComparisonCase>
552 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
553 Cases.reserve(SI->getNumCases());
554 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i)
555 Cases.push_back(ValueEqualityComparisonCase(i.getCaseValue(),
556 i.getCaseSuccessor()));
557 return SI->getDefaultDest();
560 BranchInst *BI = cast<BranchInst>(TI);
561 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
562 BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE);
563 Cases.push_back(ValueEqualityComparisonCase(GetConstantInt(ICI->getOperand(1),
566 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
570 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
571 /// in the list that match the specified block.
572 static void EliminateBlockCases(BasicBlock *BB,
573 std::vector<ValueEqualityComparisonCase> &Cases) {
574 Cases.erase(std::remove(Cases.begin(), Cases.end(), BB), Cases.end());
577 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
580 ValuesOverlap(std::vector<ValueEqualityComparisonCase> &C1,
581 std::vector<ValueEqualityComparisonCase > &C2) {
582 std::vector<ValueEqualityComparisonCase> *V1 = &C1, *V2 = &C2;
584 // Make V1 be smaller than V2.
585 if (V1->size() > V2->size())
588 if (V1->size() == 0) return false;
589 if (V1->size() == 1) {
591 ConstantInt *TheVal = (*V1)[0].Value;
592 for (unsigned i = 0, e = V2->size(); i != e; ++i)
593 if (TheVal == (*V2)[i].Value)
597 // Otherwise, just sort both lists and compare element by element.
598 array_pod_sort(V1->begin(), V1->end());
599 array_pod_sort(V2->begin(), V2->end());
600 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
601 while (i1 != e1 && i2 != e2) {
602 if ((*V1)[i1].Value == (*V2)[i2].Value)
604 if ((*V1)[i1].Value < (*V2)[i2].Value)
612 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
613 /// terminator instruction and its block is known to only have a single
614 /// predecessor block, check to see if that predecessor is also a value
615 /// comparison with the same value, and if that comparison determines the
616 /// outcome of this comparison. If so, simplify TI. This does a very limited
617 /// form of jump threading.
618 bool SimplifyCFGOpt::
619 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
621 IRBuilder<> &Builder) {
622 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
623 if (!PredVal) return false; // Not a value comparison in predecessor.
625 Value *ThisVal = isValueEqualityComparison(TI);
626 assert(ThisVal && "This isn't a value comparison!!");
627 if (ThisVal != PredVal) return false; // Different predicates.
629 // TODO: Preserve branch weight metadata, similarly to how
630 // FoldValueComparisonIntoPredecessors preserves it.
632 // Find out information about when control will move from Pred to TI's block.
633 std::vector<ValueEqualityComparisonCase> PredCases;
634 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
636 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
638 // Find information about how control leaves this block.
639 std::vector<ValueEqualityComparisonCase> ThisCases;
640 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
641 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
643 // If TI's block is the default block from Pred's comparison, potentially
644 // simplify TI based on this knowledge.
645 if (PredDef == TI->getParent()) {
646 // If we are here, we know that the value is none of those cases listed in
647 // PredCases. If there are any cases in ThisCases that are in PredCases, we
649 if (!ValuesOverlap(PredCases, ThisCases))
652 if (isa<BranchInst>(TI)) {
653 // Okay, one of the successors of this condbr is dead. Convert it to a
655 assert(ThisCases.size() == 1 && "Branch can only have one case!");
656 // Insert the new branch.
657 Instruction *NI = Builder.CreateBr(ThisDef);
660 // Remove PHI node entries for the dead edge.
661 ThisCases[0].Dest->removePredecessor(TI->getParent());
663 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
664 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
666 EraseTerminatorInstAndDCECond(TI);
670 SwitchInst *SI = cast<SwitchInst>(TI);
671 // Okay, TI has cases that are statically dead, prune them away.
672 SmallPtrSet<Constant*, 16> DeadCases;
673 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
674 DeadCases.insert(PredCases[i].Value);
676 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
677 << "Through successor TI: " << *TI);
679 // Collect branch weights into a vector.
680 SmallVector<uint32_t, 8> Weights;
681 MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
682 bool HasWeight = MD && (MD->getNumOperands() == 2 + SI->getNumCases());
684 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
686 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(MD_i));
688 Weights.push_back(CI->getValue().getZExtValue());
690 for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) {
692 if (DeadCases.count(i.getCaseValue())) {
694 std::swap(Weights[i.getCaseIndex()+1], Weights.back());
697 i.getCaseSuccessor()->removePredecessor(TI->getParent());
701 if (HasWeight && Weights.size() >= 2)
702 SI->setMetadata(LLVMContext::MD_prof,
703 MDBuilder(SI->getParent()->getContext()).
704 createBranchWeights(Weights));
706 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
710 // Otherwise, TI's block must correspond to some matched value. Find out
711 // which value (or set of values) this is.
712 ConstantInt *TIV = 0;
713 BasicBlock *TIBB = TI->getParent();
714 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
715 if (PredCases[i].Dest == TIBB) {
717 return false; // Cannot handle multiple values coming to this block.
718 TIV = PredCases[i].Value;
720 assert(TIV && "No edge from pred to succ?");
722 // Okay, we found the one constant that our value can be if we get into TI's
723 // BB. Find out which successor will unconditionally be branched to.
724 BasicBlock *TheRealDest = 0;
725 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
726 if (ThisCases[i].Value == TIV) {
727 TheRealDest = ThisCases[i].Dest;
731 // If not handled by any explicit cases, it is handled by the default case.
732 if (TheRealDest == 0) TheRealDest = ThisDef;
734 // Remove PHI node entries for dead edges.
735 BasicBlock *CheckEdge = TheRealDest;
736 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
737 if (*SI != CheckEdge)
738 (*SI)->removePredecessor(TIBB);
742 // Insert the new branch.
743 Instruction *NI = Builder.CreateBr(TheRealDest);
746 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
747 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
749 EraseTerminatorInstAndDCECond(TI);
754 /// ConstantIntOrdering - This class implements a stable ordering of constant
755 /// integers that does not depend on their address. This is important for
756 /// applications that sort ConstantInt's to ensure uniqueness.
757 struct ConstantIntOrdering {
758 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
759 return LHS->getValue().ult(RHS->getValue());
764 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
765 const ConstantInt *LHS = *(const ConstantInt*const*)P1;
766 const ConstantInt *RHS = *(const ConstantInt*const*)P2;
767 if (LHS->getValue().ult(RHS->getValue()))
769 if (LHS->getValue() == RHS->getValue())
774 static inline bool HasBranchWeights(const Instruction* I) {
775 MDNode* ProfMD = I->getMetadata(LLVMContext::MD_prof);
776 if (ProfMD && ProfMD->getOperand(0))
777 if (MDString* MDS = dyn_cast<MDString>(ProfMD->getOperand(0)))
778 return MDS->getString().equals("branch_weights");
783 /// Get Weights of a given TerminatorInst, the default weight is at the front
784 /// of the vector. If TI is a conditional eq, we need to swap the branch-weight
786 static void GetBranchWeights(TerminatorInst *TI,
787 SmallVectorImpl<uint64_t> &Weights) {
788 MDNode* MD = TI->getMetadata(LLVMContext::MD_prof);
790 for (unsigned i = 1, e = MD->getNumOperands(); i < e; ++i) {
791 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(i));
793 Weights.push_back(CI->getValue().getZExtValue());
796 // If TI is a conditional eq, the default case is the false case,
797 // and the corresponding branch-weight data is at index 2. We swap the
798 // default weight to be the first entry.
799 if (BranchInst* BI = dyn_cast<BranchInst>(TI)) {
800 assert(Weights.size() == 2);
801 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
802 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
803 std::swap(Weights.front(), Weights.back());
807 /// Sees if any of the weights are too big for a uint32_t, and halves all the
808 /// weights if any are.
809 static void FitWeights(MutableArrayRef<uint64_t> Weights) {
811 for (unsigned i = 0; i < Weights.size(); ++i)
812 if (Weights[i] > UINT_MAX) {
820 for (unsigned i = 0; i < Weights.size(); ++i)
824 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
825 /// equality comparison instruction (either a switch or a branch on "X == c").
826 /// See if any of the predecessors of the terminator block are value comparisons
827 /// on the same value. If so, and if safe to do so, fold them together.
828 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
829 IRBuilder<> &Builder) {
830 BasicBlock *BB = TI->getParent();
831 Value *CV = isValueEqualityComparison(TI); // CondVal
832 assert(CV && "Not a comparison?");
833 bool Changed = false;
835 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
836 while (!Preds.empty()) {
837 BasicBlock *Pred = Preds.pop_back_val();
839 // See if the predecessor is a comparison with the same value.
840 TerminatorInst *PTI = Pred->getTerminator();
841 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
843 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
844 // Figure out which 'cases' to copy from SI to PSI.
845 std::vector<ValueEqualityComparisonCase> BBCases;
846 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
848 std::vector<ValueEqualityComparisonCase> PredCases;
849 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
851 // Based on whether the default edge from PTI goes to BB or not, fill in
852 // PredCases and PredDefault with the new switch cases we would like to
854 SmallVector<BasicBlock*, 8> NewSuccessors;
856 // Update the branch weight metadata along the way
857 SmallVector<uint64_t, 8> Weights;
858 bool PredHasWeights = HasBranchWeights(PTI);
859 bool SuccHasWeights = HasBranchWeights(TI);
861 if (PredHasWeights) {
862 GetBranchWeights(PTI, Weights);
863 // branch-weight metadata is inconsistent here.
864 if (Weights.size() != 1 + PredCases.size())
865 PredHasWeights = SuccHasWeights = false;
866 } else if (SuccHasWeights)
867 // If there are no predecessor weights but there are successor weights,
868 // populate Weights with 1, which will later be scaled to the sum of
869 // successor's weights
870 Weights.assign(1 + PredCases.size(), 1);
872 SmallVector<uint64_t, 8> SuccWeights;
873 if (SuccHasWeights) {
874 GetBranchWeights(TI, SuccWeights);
875 // branch-weight metadata is inconsistent here.
876 if (SuccWeights.size() != 1 + BBCases.size())
877 PredHasWeights = SuccHasWeights = false;
878 } else if (PredHasWeights)
879 SuccWeights.assign(1 + BBCases.size(), 1);
881 if (PredDefault == BB) {
882 // If this is the default destination from PTI, only the edges in TI
883 // that don't occur in PTI, or that branch to BB will be activated.
884 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
885 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
886 if (PredCases[i].Dest != BB)
887 PTIHandled.insert(PredCases[i].Value);
889 // The default destination is BB, we don't need explicit targets.
890 std::swap(PredCases[i], PredCases.back());
892 if (PredHasWeights || SuccHasWeights) {
893 // Increase weight for the default case.
894 Weights[0] += Weights[i+1];
895 std::swap(Weights[i+1], Weights.back());
899 PredCases.pop_back();
903 // Reconstruct the new switch statement we will be building.
904 if (PredDefault != BBDefault) {
905 PredDefault->removePredecessor(Pred);
906 PredDefault = BBDefault;
907 NewSuccessors.push_back(BBDefault);
910 unsigned CasesFromPred = Weights.size();
911 uint64_t ValidTotalSuccWeight = 0;
912 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
913 if (!PTIHandled.count(BBCases[i].Value) &&
914 BBCases[i].Dest != BBDefault) {
915 PredCases.push_back(BBCases[i]);
916 NewSuccessors.push_back(BBCases[i].Dest);
917 if (SuccHasWeights || PredHasWeights) {
918 // The default weight is at index 0, so weight for the ith case
919 // should be at index i+1. Scale the cases from successor by
920 // PredDefaultWeight (Weights[0]).
921 Weights.push_back(Weights[0] * SuccWeights[i+1]);
922 ValidTotalSuccWeight += SuccWeights[i+1];
926 if (SuccHasWeights || PredHasWeights) {
927 ValidTotalSuccWeight += SuccWeights[0];
928 // Scale the cases from predecessor by ValidTotalSuccWeight.
929 for (unsigned i = 1; i < CasesFromPred; ++i)
930 Weights[i] *= ValidTotalSuccWeight;
931 // Scale the default weight by SuccDefaultWeight (SuccWeights[0]).
932 Weights[0] *= SuccWeights[0];
935 // If this is not the default destination from PSI, only the edges
936 // in SI that occur in PSI with a destination of BB will be
938 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
939 std::map<ConstantInt*, uint64_t> WeightsForHandled;
940 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
941 if (PredCases[i].Dest == BB) {
942 PTIHandled.insert(PredCases[i].Value);
944 if (PredHasWeights || SuccHasWeights) {
945 WeightsForHandled[PredCases[i].Value] = Weights[i+1];
946 std::swap(Weights[i+1], Weights.back());
950 std::swap(PredCases[i], PredCases.back());
951 PredCases.pop_back();
955 // Okay, now we know which constants were sent to BB from the
956 // predecessor. Figure out where they will all go now.
957 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
958 if (PTIHandled.count(BBCases[i].Value)) {
959 // If this is one we are capable of getting...
960 if (PredHasWeights || SuccHasWeights)
961 Weights.push_back(WeightsForHandled[BBCases[i].Value]);
962 PredCases.push_back(BBCases[i]);
963 NewSuccessors.push_back(BBCases[i].Dest);
964 PTIHandled.erase(BBCases[i].Value);// This constant is taken care of
967 // If there are any constants vectored to BB that TI doesn't handle,
968 // they must go to the default destination of TI.
969 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
971 E = PTIHandled.end(); I != E; ++I) {
972 if (PredHasWeights || SuccHasWeights)
973 Weights.push_back(WeightsForHandled[*I]);
974 PredCases.push_back(ValueEqualityComparisonCase(*I, BBDefault));
975 NewSuccessors.push_back(BBDefault);
979 // Okay, at this point, we know which new successor Pred will get. Make
980 // sure we update the number of entries in the PHI nodes for these
982 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
983 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
985 Builder.SetInsertPoint(PTI);
986 // Convert pointer to int before we switch.
987 if (CV->getType()->isPointerTy()) {
988 assert(TD && "Cannot switch on pointer without DataLayout");
989 CV = Builder.CreatePtrToInt(CV, TD->getIntPtrType(CV->getContext()),
993 // Now that the successors are updated, create the new Switch instruction.
994 SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault,
996 NewSI->setDebugLoc(PTI->getDebugLoc());
997 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
998 NewSI->addCase(PredCases[i].Value, PredCases[i].Dest);
1000 if (PredHasWeights || SuccHasWeights) {
1001 // Halve the weights if any of them cannot fit in an uint32_t
1002 FitWeights(Weights);
1004 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
1006 NewSI->setMetadata(LLVMContext::MD_prof,
1007 MDBuilder(BB->getContext()).
1008 createBranchWeights(MDWeights));
1011 EraseTerminatorInstAndDCECond(PTI);
1013 // Okay, last check. If BB is still a successor of PSI, then we must
1014 // have an infinite loop case. If so, add an infinitely looping block
1015 // to handle the case to preserve the behavior of the code.
1016 BasicBlock *InfLoopBlock = 0;
1017 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
1018 if (NewSI->getSuccessor(i) == BB) {
1019 if (InfLoopBlock == 0) {
1020 // Insert it at the end of the function, because it's either code,
1021 // or it won't matter if it's hot. :)
1022 InfLoopBlock = BasicBlock::Create(BB->getContext(),
1023 "infloop", BB->getParent());
1024 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1026 NewSI->setSuccessor(i, InfLoopBlock);
1035 // isSafeToHoistInvoke - If we would need to insert a select that uses the
1036 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
1037 // would need to do this), we can't hoist the invoke, as there is nowhere
1038 // to put the select in this case.
1039 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
1040 Instruction *I1, Instruction *I2) {
1041 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
1043 for (BasicBlock::iterator BBI = SI->begin();
1044 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1045 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1046 Value *BB2V = PN->getIncomingValueForBlock(BB2);
1047 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
1055 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
1056 /// BB2, hoist any common code in the two blocks up into the branch block. The
1057 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
1058 static bool HoistThenElseCodeToIf(BranchInst *BI) {
1059 // This does very trivial matching, with limited scanning, to find identical
1060 // instructions in the two blocks. In particular, we don't want to get into
1061 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
1062 // such, we currently just scan for obviously identical instructions in an
1064 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
1065 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
1067 BasicBlock::iterator BB1_Itr = BB1->begin();
1068 BasicBlock::iterator BB2_Itr = BB2->begin();
1070 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
1071 // Skip debug info if it is not identical.
1072 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
1073 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
1074 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
1075 while (isa<DbgInfoIntrinsic>(I1))
1077 while (isa<DbgInfoIntrinsic>(I2))
1080 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
1081 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
1084 BasicBlock *BIParent = BI->getParent();
1086 bool Changed = false;
1088 // If we are hoisting the terminator instruction, don't move one (making a
1089 // broken BB), instead clone it, and remove BI.
1090 if (isa<TerminatorInst>(I1))
1091 goto HoistTerminator;
1093 // For a normal instruction, we just move one to right before the branch,
1094 // then replace all uses of the other with the first. Finally, we remove
1095 // the now redundant second instruction.
1096 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
1097 if (!I2->use_empty())
1098 I2->replaceAllUsesWith(I1);
1099 I1->intersectOptionalDataWith(I2);
1100 I2->eraseFromParent();
1105 // Skip debug info if it is not identical.
1106 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
1107 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
1108 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
1109 while (isa<DbgInfoIntrinsic>(I1))
1111 while (isa<DbgInfoIntrinsic>(I2))
1114 } while (I1->isIdenticalToWhenDefined(I2));
1119 // It may not be possible to hoist an invoke.
1120 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
1123 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
1125 for (BasicBlock::iterator BBI = SI->begin();
1126 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1127 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1128 Value *BB2V = PN->getIncomingValueForBlock(BB2);
1132 if (isa<ConstantExpr>(BB1V) && !isSafeToSpeculativelyExecute(BB1V))
1134 if (isa<ConstantExpr>(BB2V) && !isSafeToSpeculativelyExecute(BB2V))
1139 // Okay, it is safe to hoist the terminator.
1140 Instruction *NT = I1->clone();
1141 BIParent->getInstList().insert(BI, NT);
1142 if (!NT->getType()->isVoidTy()) {
1143 I1->replaceAllUsesWith(NT);
1144 I2->replaceAllUsesWith(NT);
1148 IRBuilder<true, NoFolder> Builder(NT);
1149 // Hoisting one of the terminators from our successor is a great thing.
1150 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
1151 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
1152 // nodes, so we insert select instruction to compute the final result.
1153 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
1154 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
1156 for (BasicBlock::iterator BBI = SI->begin();
1157 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1158 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1159 Value *BB2V = PN->getIncomingValueForBlock(BB2);
1160 if (BB1V == BB2V) continue;
1162 // These values do not agree. Insert a select instruction before NT
1163 // that determines the right value.
1164 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
1166 SI = cast<SelectInst>
1167 (Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,
1168 BB1V->getName()+"."+BB2V->getName()));
1170 // Make the PHI node use the select for all incoming values for BB1/BB2
1171 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
1172 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
1173 PN->setIncomingValue(i, SI);
1177 // Update any PHI nodes in our new successors.
1178 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
1179 AddPredecessorToBlock(*SI, BIParent, BB1);
1181 EraseTerminatorInstAndDCECond(BI);
1185 /// SinkThenElseCodeToEnd - Given an unconditional branch that goes to BBEnd,
1186 /// check whether BBEnd has only two predecessors and the other predecessor
1187 /// ends with an unconditional branch. If it is true, sink any common code
1188 /// in the two predecessors to BBEnd.
1189 static bool SinkThenElseCodeToEnd(BranchInst *BI1) {
1190 assert(BI1->isUnconditional());
1191 BasicBlock *BB1 = BI1->getParent();
1192 BasicBlock *BBEnd = BI1->getSuccessor(0);
1194 // Check that BBEnd has two predecessors and the other predecessor ends with
1195 // an unconditional branch.
1196 pred_iterator PI = pred_begin(BBEnd), PE = pred_end(BBEnd);
1197 BasicBlock *Pred0 = *PI++;
1198 if (PI == PE) // Only one predecessor.
1200 BasicBlock *Pred1 = *PI++;
1201 if (PI != PE) // More than two predecessors.
1203 BasicBlock *BB2 = (Pred0 == BB1) ? Pred1 : Pred0;
1204 BranchInst *BI2 = dyn_cast<BranchInst>(BB2->getTerminator());
1205 if (!BI2 || !BI2->isUnconditional())
1208 // Gather the PHI nodes in BBEnd.
1209 std::map<Value*, std::pair<Value*, PHINode*> > MapValueFromBB1ToBB2;
1210 Instruction *FirstNonPhiInBBEnd = 0;
1211 for (BasicBlock::iterator I = BBEnd->begin(), E = BBEnd->end();
1213 if (PHINode *PN = dyn_cast<PHINode>(I)) {
1214 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1215 Value *BB2V = PN->getIncomingValueForBlock(BB2);
1216 MapValueFromBB1ToBB2[BB1V] = std::make_pair(BB2V, PN);
1218 FirstNonPhiInBBEnd = &*I;
1222 if (!FirstNonPhiInBBEnd)
1226 // This does very trivial matching, with limited scanning, to find identical
1227 // instructions in the two blocks. We scan backward for obviously identical
1228 // instructions in an identical order.
1229 BasicBlock::InstListType::reverse_iterator RI1 = BB1->getInstList().rbegin(),
1230 RE1 = BB1->getInstList().rend(), RI2 = BB2->getInstList().rbegin(),
1231 RE2 = BB2->getInstList().rend();
1233 while (RI1 != RE1 && isa<DbgInfoIntrinsic>(&*RI1)) ++RI1;
1236 while (RI2 != RE2 && isa<DbgInfoIntrinsic>(&*RI2)) ++RI2;
1239 // Skip the unconditional branches.
1243 bool Changed = false;
1244 while (RI1 != RE1 && RI2 != RE2) {
1246 while (RI1 != RE1 && isa<DbgInfoIntrinsic>(&*RI1)) ++RI1;
1249 while (RI2 != RE2 && isa<DbgInfoIntrinsic>(&*RI2)) ++RI2;
1253 Instruction *I1 = &*RI1, *I2 = &*RI2;
1254 // I1 and I2 should have a single use in the same PHI node, and they
1255 // perform the same operation.
1256 // Cannot move control-flow-involving, volatile loads, vaarg, etc.
1257 if (isa<PHINode>(I1) || isa<PHINode>(I2) ||
1258 isa<TerminatorInst>(I1) || isa<TerminatorInst>(I2) ||
1259 isa<LandingPadInst>(I1) || isa<LandingPadInst>(I2) ||
1260 isa<AllocaInst>(I1) || isa<AllocaInst>(I2) ||
1261 I1->mayHaveSideEffects() || I2->mayHaveSideEffects() ||
1262 I1->mayReadOrWriteMemory() || I2->mayReadOrWriteMemory() ||
1263 !I1->hasOneUse() || !I2->hasOneUse() ||
1264 MapValueFromBB1ToBB2.find(I1) == MapValueFromBB1ToBB2.end() ||
1265 MapValueFromBB1ToBB2[I1].first != I2)
1268 // Check whether we should swap the operands of ICmpInst.
1269 ICmpInst *ICmp1 = dyn_cast<ICmpInst>(I1), *ICmp2 = dyn_cast<ICmpInst>(I2);
1270 bool SwapOpnds = false;
1271 if (ICmp1 && ICmp2 &&
1272 ICmp1->getOperand(0) != ICmp2->getOperand(0) &&
1273 ICmp1->getOperand(1) != ICmp2->getOperand(1) &&
1274 (ICmp1->getOperand(0) == ICmp2->getOperand(1) ||
1275 ICmp1->getOperand(1) == ICmp2->getOperand(0))) {
1276 ICmp2->swapOperands();
1279 if (!I1->isSameOperationAs(I2)) {
1281 ICmp2->swapOperands();
1285 // The operands should be either the same or they need to be generated
1286 // with a PHI node after sinking. We only handle the case where there is
1287 // a single pair of different operands.
1288 Value *DifferentOp1 = 0, *DifferentOp2 = 0;
1289 unsigned Op1Idx = 0;
1290 for (unsigned I = 0, E = I1->getNumOperands(); I != E; ++I) {
1291 if (I1->getOperand(I) == I2->getOperand(I))
1293 // Early exit if we have more-than one pair of different operands or
1294 // the different operand is already in MapValueFromBB1ToBB2.
1295 // Early exit if we need a PHI node to replace a constant.
1297 MapValueFromBB1ToBB2.find(I1->getOperand(I)) !=
1298 MapValueFromBB1ToBB2.end() ||
1299 isa<Constant>(I1->getOperand(I)) ||
1300 isa<Constant>(I2->getOperand(I))) {
1301 // If we can't sink the instructions, undo the swapping.
1303 ICmp2->swapOperands();
1306 DifferentOp1 = I1->getOperand(I);
1308 DifferentOp2 = I2->getOperand(I);
1311 // We insert the pair of different operands to MapValueFromBB1ToBB2 and
1312 // remove (I1, I2) from MapValueFromBB1ToBB2.
1314 PHINode *NewPN = PHINode::Create(DifferentOp1->getType(), 2,
1315 DifferentOp1->getName() + ".sink",
1317 MapValueFromBB1ToBB2[DifferentOp1] = std::make_pair(DifferentOp2, NewPN);
1318 // I1 should use NewPN instead of DifferentOp1.
1319 I1->setOperand(Op1Idx, NewPN);
1320 NewPN->addIncoming(DifferentOp1, BB1);
1321 NewPN->addIncoming(DifferentOp2, BB2);
1322 DEBUG(dbgs() << "Create PHI node " << *NewPN << "\n";);
1324 PHINode *OldPN = MapValueFromBB1ToBB2[I1].second;
1325 MapValueFromBB1ToBB2.erase(I1);
1327 DEBUG(dbgs() << "SINK common instructions " << *I1 << "\n";);
1328 DEBUG(dbgs() << " " << *I2 << "\n";);
1329 // We need to update RE1 and RE2 if we are going to sink the first
1330 // instruction in the basic block down.
1331 bool UpdateRE1 = (I1 == BB1->begin()), UpdateRE2 = (I2 == BB2->begin());
1332 // Sink the instruction.
1333 BBEnd->getInstList().splice(FirstNonPhiInBBEnd, BB1->getInstList(), I1);
1334 if (!OldPN->use_empty())
1335 OldPN->replaceAllUsesWith(I1);
1336 OldPN->eraseFromParent();
1338 if (!I2->use_empty())
1339 I2->replaceAllUsesWith(I1);
1340 I1->intersectOptionalDataWith(I2);
1341 I2->eraseFromParent();
1344 RE1 = BB1->getInstList().rend();
1346 RE2 = BB2->getInstList().rend();
1347 FirstNonPhiInBBEnd = I1;
1354 /// \brief Determine if we can hoist sink a sole store instruction out of a
1355 /// conditional block.
1357 /// We are looking for code like the following:
1359 /// store i32 %add, i32* %arrayidx2
1360 /// ... // No other stores or function calls (we could be calling a memory
1361 /// ... // function).
1362 /// %cmp = icmp ult %x, %y
1363 /// br i1 %cmp, label %EndBB, label %ThenBB
1365 /// store i32 %add5, i32* %arrayidx2
1369 /// We are going to transform this into:
1371 /// store i32 %add, i32* %arrayidx2
1373 /// %cmp = icmp ult %x, %y
1374 /// %add.add5 = select i1 %cmp, i32 %add, %add5
1375 /// store i32 %add.add5, i32* %arrayidx2
1378 /// \return The pointer to the value of the previous store if the store can be
1379 /// hoisted into the predecessor block. 0 otherwise.
1380 static Value *isSafeToSpeculateStore(Instruction *I, BasicBlock *BrBB,
1381 BasicBlock *StoreBB, BasicBlock *EndBB) {
1382 StoreInst *StoreToHoist = dyn_cast<StoreInst>(I);
1386 // Volatile or atomic.
1387 if (!StoreToHoist->isSimple())
1390 Value *StorePtr = StoreToHoist->getPointerOperand();
1392 // Look for a store to the same pointer in BrBB.
1393 unsigned MaxNumInstToLookAt = 10;
1394 for (BasicBlock::reverse_iterator RI = BrBB->rbegin(),
1395 RE = BrBB->rend(); RI != RE && (--MaxNumInstToLookAt); ++RI) {
1396 Instruction *CurI = &*RI;
1398 // Could be calling an instruction that effects memory like free().
1399 if (CurI->mayHaveSideEffects() && !isa<StoreInst>(CurI))
1402 StoreInst *SI = dyn_cast<StoreInst>(CurI);
1403 // Found the previous store make sure it stores to the same location.
1404 if (SI && SI->getPointerOperand() == StorePtr)
1405 // Found the previous store, return its value operand.
1406 return SI->getValueOperand();
1408 return 0; // Unknown store.
1414 /// \brief Speculate a conditional basic block flattening the CFG.
1416 /// Note that this is a very risky transform currently. Speculating
1417 /// instructions like this is most often not desirable. Instead, there is an MI
1418 /// pass which can do it with full awareness of the resource constraints.
1419 /// However, some cases are "obvious" and we should do directly. An example of
1420 /// this is speculating a single, reasonably cheap instruction.
1422 /// There is only one distinct advantage to flattening the CFG at the IR level:
1423 /// it makes very common but simplistic optimizations such as are common in
1424 /// instcombine and the DAG combiner more powerful by removing CFG edges and
1425 /// modeling their effects with easier to reason about SSA value graphs.
1428 /// An illustration of this transform is turning this IR:
1431 /// %cmp = icmp ult %x, %y
1432 /// br i1 %cmp, label %EndBB, label %ThenBB
1434 /// %sub = sub %x, %y
1437 /// %phi = phi [ %sub, %ThenBB ], [ 0, %EndBB ]
1444 /// %cmp = icmp ult %x, %y
1445 /// %sub = sub %x, %y
1446 /// %cond = select i1 %cmp, 0, %sub
1450 /// \returns true if the conditional block is removed.
1451 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB) {
1452 // Be conservative for now. FP select instruction can often be expensive.
1453 Value *BrCond = BI->getCondition();
1454 if (isa<FCmpInst>(BrCond))
1457 BasicBlock *BB = BI->getParent();
1458 BasicBlock *EndBB = ThenBB->getTerminator()->getSuccessor(0);
1460 // If ThenBB is actually on the false edge of the conditional branch, remember
1461 // to swap the select operands later.
1462 bool Invert = false;
1463 if (ThenBB != BI->getSuccessor(0)) {
1464 assert(ThenBB == BI->getSuccessor(1) && "No edge from 'if' block?");
1467 assert(EndBB == BI->getSuccessor(!Invert) && "No edge from to end block");
1469 // Keep a count of how many times instructions are used within CondBB when
1470 // they are candidates for sinking into CondBB. Specifically:
1471 // - They are defined in BB, and
1472 // - They have no side effects, and
1473 // - All of their uses are in CondBB.
1474 SmallDenseMap<Instruction *, unsigned, 4> SinkCandidateUseCounts;
1476 unsigned SpeculationCost = 0;
1477 Value *SpeculatedStoreValue = 0;
1478 StoreInst *SpeculatedStore = 0;
1479 for (BasicBlock::iterator BBI = ThenBB->begin(),
1480 BBE = llvm::prior(ThenBB->end());
1481 BBI != BBE; ++BBI) {
1482 Instruction *I = BBI;
1484 if (isa<DbgInfoIntrinsic>(I))
1487 // Only speculatively execution a single instruction (not counting the
1488 // terminator) for now.
1490 if (SpeculationCost > 1)
1493 // Don't hoist the instruction if it's unsafe or expensive.
1494 if (!isSafeToSpeculativelyExecute(I) &&
1495 !(HoistCondStores &&
1496 (SpeculatedStoreValue = isSafeToSpeculateStore(I, BB, ThenBB,
1499 if (!SpeculatedStoreValue &&
1500 ComputeSpeculationCost(I) > PHINodeFoldingThreshold)
1503 // Store the store speculation candidate.
1504 if (SpeculatedStoreValue)
1505 SpeculatedStore = cast<StoreInst>(I);
1507 // Do not hoist the instruction if any of its operands are defined but not
1508 // used in BB. The transformation will prevent the operand from
1509 // being sunk into the use block.
1510 for (User::op_iterator i = I->op_begin(), e = I->op_end();
1512 Instruction *OpI = dyn_cast<Instruction>(*i);
1513 if (!OpI || OpI->getParent() != BB ||
1514 OpI->mayHaveSideEffects())
1515 continue; // Not a candidate for sinking.
1517 ++SinkCandidateUseCounts[OpI];
1521 // Consider any sink candidates which are only used in CondBB as costs for
1522 // speculation. Note, while we iterate over a DenseMap here, we are summing
1523 // and so iteration order isn't significant.
1524 for (SmallDenseMap<Instruction *, unsigned, 4>::iterator I =
1525 SinkCandidateUseCounts.begin(), E = SinkCandidateUseCounts.end();
1527 if (I->first->getNumUses() == I->second) {
1529 if (SpeculationCost > 1)
1533 // Check that the PHI nodes can be converted to selects.
1534 bool HaveRewritablePHIs = false;
1535 for (BasicBlock::iterator I = EndBB->begin();
1536 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1537 Value *OrigV = PN->getIncomingValueForBlock(BB);
1538 Value *ThenV = PN->getIncomingValueForBlock(ThenBB);
1540 // FIXME: Try to remove some of the duplication with HoistThenElseCodeToIf.
1541 // Skip PHIs which are trivial.
1545 HaveRewritablePHIs = true;
1546 ConstantExpr *OrigCE = dyn_cast<ConstantExpr>(OrigV);
1547 ConstantExpr *ThenCE = dyn_cast<ConstantExpr>(ThenV);
1548 if (!OrigCE && !ThenCE)
1549 continue; // Known safe and cheap.
1551 if ((ThenCE && !isSafeToSpeculativelyExecute(ThenCE)) ||
1552 (OrigCE && !isSafeToSpeculativelyExecute(OrigCE)))
1554 unsigned OrigCost = OrigCE ? ComputeSpeculationCost(OrigCE) : 0;
1555 unsigned ThenCost = ThenCE ? ComputeSpeculationCost(ThenCE) : 0;
1556 if (OrigCost + ThenCost > 2 * PHINodeFoldingThreshold)
1559 // Account for the cost of an unfolded ConstantExpr which could end up
1560 // getting expanded into Instructions.
1561 // FIXME: This doesn't account for how many operations are combined in the
1562 // constant expression.
1564 if (SpeculationCost > 1)
1568 // If there are no PHIs to process, bail early. This helps ensure idempotence
1570 if (!HaveRewritablePHIs && !(HoistCondStores && SpeculatedStoreValue))
1573 // If we get here, we can hoist the instruction and if-convert.
1574 DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *ThenBB << "\n";);
1576 // Insert a select of the value of the speculated store.
1577 if (SpeculatedStoreValue) {
1578 IRBuilder<true, NoFolder> Builder(BI);
1579 Value *TrueV = SpeculatedStore->getValueOperand();
1580 Value *FalseV = SpeculatedStoreValue;
1582 std::swap(TrueV, FalseV);
1583 Value *S = Builder.CreateSelect(BrCond, TrueV, FalseV, TrueV->getName() +
1584 "." + FalseV->getName());
1585 SpeculatedStore->setOperand(0, S);
1588 // Hoist the instructions.
1589 BB->getInstList().splice(BI, ThenBB->getInstList(), ThenBB->begin(),
1590 llvm::prior(ThenBB->end()));
1592 // Insert selects and rewrite the PHI operands.
1593 IRBuilder<true, NoFolder> Builder(BI);
1594 for (BasicBlock::iterator I = EndBB->begin();
1595 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1596 unsigned OrigI = PN->getBasicBlockIndex(BB);
1597 unsigned ThenI = PN->getBasicBlockIndex(ThenBB);
1598 Value *OrigV = PN->getIncomingValue(OrigI);
1599 Value *ThenV = PN->getIncomingValue(ThenI);
1601 // Skip PHIs which are trivial.
1605 // Create a select whose true value is the speculatively executed value and
1606 // false value is the preexisting value. Swap them if the branch
1607 // destinations were inverted.
1608 Value *TrueV = ThenV, *FalseV = OrigV;
1610 std::swap(TrueV, FalseV);
1611 Value *V = Builder.CreateSelect(BrCond, TrueV, FalseV,
1612 TrueV->getName() + "." + FalseV->getName());
1613 PN->setIncomingValue(OrigI, V);
1614 PN->setIncomingValue(ThenI, V);
1621 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1622 /// across this block.
1623 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1624 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1627 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1628 if (isa<DbgInfoIntrinsic>(BBI))
1630 if (Size > 10) return false; // Don't clone large BB's.
1633 // We can only support instructions that do not define values that are
1634 // live outside of the current basic block.
1635 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1637 Instruction *U = cast<Instruction>(*UI);
1638 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1641 // Looks ok, continue checking.
1647 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1648 /// that is defined in the same block as the branch and if any PHI entries are
1649 /// constants, thread edges corresponding to that entry to be branches to their
1650 /// ultimate destination.
1651 static bool FoldCondBranchOnPHI(BranchInst *BI, const DataLayout *TD) {
1652 BasicBlock *BB = BI->getParent();
1653 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1654 // NOTE: we currently cannot transform this case if the PHI node is used
1655 // outside of the block.
1656 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1659 // Degenerate case of a single entry PHI.
1660 if (PN->getNumIncomingValues() == 1) {
1661 FoldSingleEntryPHINodes(PN->getParent());
1665 // Now we know that this block has multiple preds and two succs.
1666 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1668 // Okay, this is a simple enough basic block. See if any phi values are
1670 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1671 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1672 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1674 // Okay, we now know that all edges from PredBB should be revectored to
1675 // branch to RealDest.
1676 BasicBlock *PredBB = PN->getIncomingBlock(i);
1677 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1679 if (RealDest == BB) continue; // Skip self loops.
1680 // Skip if the predecessor's terminator is an indirect branch.
1681 if (isa<IndirectBrInst>(PredBB->getTerminator())) continue;
1683 // The dest block might have PHI nodes, other predecessors and other
1684 // difficult cases. Instead of being smart about this, just insert a new
1685 // block that jumps to the destination block, effectively splitting
1686 // the edge we are about to create.
1687 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1688 RealDest->getName()+".critedge",
1689 RealDest->getParent(), RealDest);
1690 BranchInst::Create(RealDest, EdgeBB);
1692 // Update PHI nodes.
1693 AddPredecessorToBlock(RealDest, EdgeBB, BB);
1695 // BB may have instructions that are being threaded over. Clone these
1696 // instructions into EdgeBB. We know that there will be no uses of the
1697 // cloned instructions outside of EdgeBB.
1698 BasicBlock::iterator InsertPt = EdgeBB->begin();
1699 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1700 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1701 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1702 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1705 // Clone the instruction.
1706 Instruction *N = BBI->clone();
1707 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1709 // Update operands due to translation.
1710 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1712 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1713 if (PI != TranslateMap.end())
1717 // Check for trivial simplification.
1718 if (Value *V = SimplifyInstruction(N, TD)) {
1719 TranslateMap[BBI] = V;
1720 delete N; // Instruction folded away, don't need actual inst
1722 // Insert the new instruction into its new home.
1723 EdgeBB->getInstList().insert(InsertPt, N);
1724 if (!BBI->use_empty())
1725 TranslateMap[BBI] = N;
1729 // Loop over all of the edges from PredBB to BB, changing them to branch
1730 // to EdgeBB instead.
1731 TerminatorInst *PredBBTI = PredBB->getTerminator();
1732 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1733 if (PredBBTI->getSuccessor(i) == BB) {
1734 BB->removePredecessor(PredBB);
1735 PredBBTI->setSuccessor(i, EdgeBB);
1738 // Recurse, simplifying any other constants.
1739 return FoldCondBranchOnPHI(BI, TD) | true;
1745 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1746 /// PHI node, see if we can eliminate it.
1747 static bool FoldTwoEntryPHINode(PHINode *PN, const DataLayout *TD) {
1748 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1749 // statement", which has a very simple dominance structure. Basically, we
1750 // are trying to find the condition that is being branched on, which
1751 // subsequently causes this merge to happen. We really want control
1752 // dependence information for this check, but simplifycfg can't keep it up
1753 // to date, and this catches most of the cases we care about anyway.
1754 BasicBlock *BB = PN->getParent();
1755 BasicBlock *IfTrue, *IfFalse;
1756 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1758 // Don't bother if the branch will be constant folded trivially.
1759 isa<ConstantInt>(IfCond))
1762 // Okay, we found that we can merge this two-entry phi node into a select.
1763 // Doing so would require us to fold *all* two entry phi nodes in this block.
1764 // At some point this becomes non-profitable (particularly if the target
1765 // doesn't support cmov's). Only do this transformation if there are two or
1766 // fewer PHI nodes in this block.
1767 unsigned NumPhis = 0;
1768 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1772 // Loop over the PHI's seeing if we can promote them all to select
1773 // instructions. While we are at it, keep track of the instructions
1774 // that need to be moved to the dominating block.
1775 SmallPtrSet<Instruction*, 4> AggressiveInsts;
1776 unsigned MaxCostVal0 = PHINodeFoldingThreshold,
1777 MaxCostVal1 = PHINodeFoldingThreshold;
1779 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1780 PHINode *PN = cast<PHINode>(II++);
1781 if (Value *V = SimplifyInstruction(PN, TD)) {
1782 PN->replaceAllUsesWith(V);
1783 PN->eraseFromParent();
1787 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
1789 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
1794 // If we folded the first phi, PN dangles at this point. Refresh it. If
1795 // we ran out of PHIs then we simplified them all.
1796 PN = dyn_cast<PHINode>(BB->begin());
1797 if (PN == 0) return true;
1799 // Don't fold i1 branches on PHIs which contain binary operators. These can
1800 // often be turned into switches and other things.
1801 if (PN->getType()->isIntegerTy(1) &&
1802 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1803 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1804 isa<BinaryOperator>(IfCond)))
1807 // If we all PHI nodes are promotable, check to make sure that all
1808 // instructions in the predecessor blocks can be promoted as well. If
1809 // not, we won't be able to get rid of the control flow, so it's not
1810 // worth promoting to select instructions.
1811 BasicBlock *DomBlock = 0;
1812 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1813 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1814 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1817 DomBlock = *pred_begin(IfBlock1);
1818 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1819 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1820 // This is not an aggressive instruction that we can promote.
1821 // Because of this, we won't be able to get rid of the control
1822 // flow, so the xform is not worth it.
1827 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1830 DomBlock = *pred_begin(IfBlock2);
1831 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1832 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1833 // This is not an aggressive instruction that we can promote.
1834 // Because of this, we won't be able to get rid of the control
1835 // flow, so the xform is not worth it.
1840 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1841 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1843 // If we can still promote the PHI nodes after this gauntlet of tests,
1844 // do all of the PHI's now.
1845 Instruction *InsertPt = DomBlock->getTerminator();
1846 IRBuilder<true, NoFolder> Builder(InsertPt);
1848 // Move all 'aggressive' instructions, which are defined in the
1849 // conditional parts of the if's up to the dominating block.
1851 DomBlock->getInstList().splice(InsertPt,
1852 IfBlock1->getInstList(), IfBlock1->begin(),
1853 IfBlock1->getTerminator());
1855 DomBlock->getInstList().splice(InsertPt,
1856 IfBlock2->getInstList(), IfBlock2->begin(),
1857 IfBlock2->getTerminator());
1859 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1860 // Change the PHI node into a select instruction.
1861 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1862 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1865 cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, ""));
1866 PN->replaceAllUsesWith(NV);
1868 PN->eraseFromParent();
1871 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1872 // has been flattened. Change DomBlock to jump directly to our new block to
1873 // avoid other simplifycfg's kicking in on the diamond.
1874 TerminatorInst *OldTI = DomBlock->getTerminator();
1875 Builder.SetInsertPoint(OldTI);
1876 Builder.CreateBr(BB);
1877 OldTI->eraseFromParent();
1881 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1882 /// to two returning blocks, try to merge them together into one return,
1883 /// introducing a select if the return values disagree.
1884 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
1885 IRBuilder<> &Builder) {
1886 assert(BI->isConditional() && "Must be a conditional branch");
1887 BasicBlock *TrueSucc = BI->getSuccessor(0);
1888 BasicBlock *FalseSucc = BI->getSuccessor(1);
1889 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1890 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1892 // Check to ensure both blocks are empty (just a return) or optionally empty
1893 // with PHI nodes. If there are other instructions, merging would cause extra
1894 // computation on one path or the other.
1895 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1897 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1900 Builder.SetInsertPoint(BI);
1901 // Okay, we found a branch that is going to two return nodes. If
1902 // there is no return value for this function, just change the
1903 // branch into a return.
1904 if (FalseRet->getNumOperands() == 0) {
1905 TrueSucc->removePredecessor(BI->getParent());
1906 FalseSucc->removePredecessor(BI->getParent());
1907 Builder.CreateRetVoid();
1908 EraseTerminatorInstAndDCECond(BI);
1912 // Otherwise, figure out what the true and false return values are
1913 // so we can insert a new select instruction.
1914 Value *TrueValue = TrueRet->getReturnValue();
1915 Value *FalseValue = FalseRet->getReturnValue();
1917 // Unwrap any PHI nodes in the return blocks.
1918 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1919 if (TVPN->getParent() == TrueSucc)
1920 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1921 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1922 if (FVPN->getParent() == FalseSucc)
1923 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1925 // In order for this transformation to be safe, we must be able to
1926 // unconditionally execute both operands to the return. This is
1927 // normally the case, but we could have a potentially-trapping
1928 // constant expression that prevents this transformation from being
1930 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1933 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1937 // Okay, we collected all the mapped values and checked them for sanity, and
1938 // defined to really do this transformation. First, update the CFG.
1939 TrueSucc->removePredecessor(BI->getParent());
1940 FalseSucc->removePredecessor(BI->getParent());
1942 // Insert select instructions where needed.
1943 Value *BrCond = BI->getCondition();
1945 // Insert a select if the results differ.
1946 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1947 } else if (isa<UndefValue>(TrueValue)) {
1948 TrueValue = FalseValue;
1950 TrueValue = Builder.CreateSelect(BrCond, TrueValue,
1951 FalseValue, "retval");
1955 Value *RI = !TrueValue ?
1956 Builder.CreateRetVoid() : Builder.CreateRet(TrueValue);
1960 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1961 << "\n " << *BI << "NewRet = " << *RI
1962 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1964 EraseTerminatorInstAndDCECond(BI);
1969 /// ExtractBranchMetadata - Given a conditional BranchInstruction, retrieve the
1970 /// probabilities of the branch taking each edge. Fills in the two APInt
1971 /// parameters and return true, or returns false if no or invalid metadata was
1973 static bool ExtractBranchMetadata(BranchInst *BI,
1974 uint64_t &ProbTrue, uint64_t &ProbFalse) {
1975 assert(BI->isConditional() &&
1976 "Looking for probabilities on unconditional branch?");
1977 MDNode *ProfileData = BI->getMetadata(LLVMContext::MD_prof);
1978 if (!ProfileData || ProfileData->getNumOperands() != 3) return false;
1979 ConstantInt *CITrue = dyn_cast<ConstantInt>(ProfileData->getOperand(1));
1980 ConstantInt *CIFalse = dyn_cast<ConstantInt>(ProfileData->getOperand(2));
1981 if (!CITrue || !CIFalse) return false;
1982 ProbTrue = CITrue->getValue().getZExtValue();
1983 ProbFalse = CIFalse->getValue().getZExtValue();
1987 /// checkCSEInPredecessor - Return true if the given instruction is available
1988 /// in its predecessor block. If yes, the instruction will be removed.
1990 static bool checkCSEInPredecessor(Instruction *Inst, BasicBlock *PB) {
1991 if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst))
1993 for (BasicBlock::iterator I = PB->begin(), E = PB->end(); I != E; I++) {
1994 Instruction *PBI = &*I;
1995 // Check whether Inst and PBI generate the same value.
1996 if (Inst->isIdenticalTo(PBI)) {
1997 Inst->replaceAllUsesWith(PBI);
1998 Inst->eraseFromParent();
2005 /// FoldBranchToCommonDest - If this basic block is simple enough, and if a
2006 /// predecessor branches to us and one of our successors, fold the block into
2007 /// the predecessor and use logical operations to pick the right destination.
2008 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
2009 BasicBlock *BB = BI->getParent();
2011 Instruction *Cond = 0;
2012 if (BI->isConditional())
2013 Cond = dyn_cast<Instruction>(BI->getCondition());
2015 // For unconditional branch, check for a simple CFG pattern, where
2016 // BB has a single predecessor and BB's successor is also its predecessor's
2017 // successor. If such pattern exisits, check for CSE between BB and its
2019 if (BasicBlock *PB = BB->getSinglePredecessor())
2020 if (BranchInst *PBI = dyn_cast<BranchInst>(PB->getTerminator()))
2021 if (PBI->isConditional() &&
2022 (BI->getSuccessor(0) == PBI->getSuccessor(0) ||
2023 BI->getSuccessor(0) == PBI->getSuccessor(1))) {
2024 for (BasicBlock::iterator I = BB->begin(), E = BB->end();
2026 Instruction *Curr = I++;
2027 if (isa<CmpInst>(Curr)) {
2031 // Quit if we can't remove this instruction.
2032 if (!checkCSEInPredecessor(Curr, PB))
2041 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
2042 Cond->getParent() != BB || !Cond->hasOneUse())
2045 // Only allow this if the condition is a simple instruction that can be
2046 // executed unconditionally. It must be in the same block as the branch, and
2047 // must be at the front of the block.
2048 BasicBlock::iterator FrontIt = BB->front();
2050 // Ignore dbg intrinsics.
2051 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
2053 // Allow a single instruction to be hoisted in addition to the compare
2054 // that feeds the branch. We later ensure that any values that _it_ uses
2055 // were also live in the predecessor, so that we don't unnecessarily create
2056 // register pressure or inhibit out-of-order execution.
2057 Instruction *BonusInst = 0;
2058 if (&*FrontIt != Cond &&
2059 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
2060 isSafeToSpeculativelyExecute(FrontIt)) {
2061 BonusInst = &*FrontIt;
2064 // Ignore dbg intrinsics.
2065 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
2068 // Only a single bonus inst is allowed.
2069 if (&*FrontIt != Cond)
2072 // Make sure the instruction after the condition is the cond branch.
2073 BasicBlock::iterator CondIt = Cond; ++CondIt;
2075 // Ingore dbg intrinsics.
2076 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
2081 // Cond is known to be a compare or binary operator. Check to make sure that
2082 // neither operand is a potentially-trapping constant expression.
2083 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
2086 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
2090 // Finally, don't infinitely unroll conditional loops.
2091 BasicBlock *TrueDest = BI->getSuccessor(0);
2092 BasicBlock *FalseDest = (BI->isConditional()) ? BI->getSuccessor(1) : 0;
2093 if (TrueDest == BB || FalseDest == BB)
2096 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2097 BasicBlock *PredBlock = *PI;
2098 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
2100 // Check that we have two conditional branches. If there is a PHI node in
2101 // the common successor, verify that the same value flows in from both
2103 SmallVector<PHINode*, 4> PHIs;
2104 if (PBI == 0 || PBI->isUnconditional() ||
2105 (BI->isConditional() &&
2106 !SafeToMergeTerminators(BI, PBI)) ||
2107 (!BI->isConditional() &&
2108 !isProfitableToFoldUnconditional(BI, PBI, Cond, PHIs)))
2111 // Determine if the two branches share a common destination.
2112 Instruction::BinaryOps Opc = Instruction::BinaryOpsEnd;
2113 bool InvertPredCond = false;
2115 if (BI->isConditional()) {
2116 if (PBI->getSuccessor(0) == TrueDest)
2117 Opc = Instruction::Or;
2118 else if (PBI->getSuccessor(1) == FalseDest)
2119 Opc = Instruction::And;
2120 else if (PBI->getSuccessor(0) == FalseDest)
2121 Opc = Instruction::And, InvertPredCond = true;
2122 else if (PBI->getSuccessor(1) == TrueDest)
2123 Opc = Instruction::Or, InvertPredCond = true;
2127 if (PBI->getSuccessor(0) != TrueDest && PBI->getSuccessor(1) != TrueDest)
2131 // Ensure that any values used in the bonus instruction are also used
2132 // by the terminator of the predecessor. This means that those values
2133 // must already have been resolved, so we won't be inhibiting the
2134 // out-of-order core by speculating them earlier.
2136 // Collect the values used by the bonus inst
2137 SmallPtrSet<Value*, 4> UsedValues;
2138 for (Instruction::op_iterator OI = BonusInst->op_begin(),
2139 OE = BonusInst->op_end(); OI != OE; ++OI) {
2141 if (!isa<Constant>(V))
2142 UsedValues.insert(V);
2145 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
2146 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
2148 // Walk up to four levels back up the use-def chain of the predecessor's
2149 // terminator to see if all those values were used. The choice of four
2150 // levels is arbitrary, to provide a compile-time-cost bound.
2151 while (!Worklist.empty()) {
2152 std::pair<Value*, unsigned> Pair = Worklist.back();
2153 Worklist.pop_back();
2155 if (Pair.second >= 4) continue;
2156 UsedValues.erase(Pair.first);
2157 if (UsedValues.empty()) break;
2159 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
2160 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
2162 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
2166 if (!UsedValues.empty()) return false;
2169 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
2170 IRBuilder<> Builder(PBI);
2172 // If we need to invert the condition in the pred block to match, do so now.
2173 if (InvertPredCond) {
2174 Value *NewCond = PBI->getCondition();
2176 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
2177 CmpInst *CI = cast<CmpInst>(NewCond);
2178 CI->setPredicate(CI->getInversePredicate());
2180 NewCond = Builder.CreateNot(NewCond,
2181 PBI->getCondition()->getName()+".not");
2184 PBI->setCondition(NewCond);
2185 PBI->swapSuccessors();
2188 // If we have a bonus inst, clone it into the predecessor block.
2189 Instruction *NewBonus = 0;
2191 NewBonus = BonusInst->clone();
2192 PredBlock->getInstList().insert(PBI, NewBonus);
2193 NewBonus->takeName(BonusInst);
2194 BonusInst->setName(BonusInst->getName()+".old");
2197 // Clone Cond into the predecessor basic block, and or/and the
2198 // two conditions together.
2199 Instruction *New = Cond->clone();
2200 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
2201 PredBlock->getInstList().insert(PBI, New);
2202 New->takeName(Cond);
2203 Cond->setName(New->getName()+".old");
2205 if (BI->isConditional()) {
2206 Instruction *NewCond =
2207 cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(),
2209 PBI->setCondition(NewCond);
2211 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
2212 bool PredHasWeights = ExtractBranchMetadata(PBI, PredTrueWeight,
2214 bool SuccHasWeights = ExtractBranchMetadata(BI, SuccTrueWeight,
2216 SmallVector<uint64_t, 8> NewWeights;
2218 if (PBI->getSuccessor(0) == BB) {
2219 if (PredHasWeights && SuccHasWeights) {
2220 // PBI: br i1 %x, BB, FalseDest
2221 // BI: br i1 %y, TrueDest, FalseDest
2222 //TrueWeight is TrueWeight for PBI * TrueWeight for BI.
2223 NewWeights.push_back(PredTrueWeight * SuccTrueWeight);
2224 //FalseWeight is FalseWeight for PBI * TotalWeight for BI +
2225 // TrueWeight for PBI * FalseWeight for BI.
2226 // We assume that total weights of a BranchInst can fit into 32 bits.
2227 // Therefore, we will not have overflow using 64-bit arithmetic.
2228 NewWeights.push_back(PredFalseWeight * (SuccFalseWeight +
2229 SuccTrueWeight) + PredTrueWeight * SuccFalseWeight);
2231 AddPredecessorToBlock(TrueDest, PredBlock, BB);
2232 PBI->setSuccessor(0, TrueDest);
2234 if (PBI->getSuccessor(1) == BB) {
2235 if (PredHasWeights && SuccHasWeights) {
2236 // PBI: br i1 %x, TrueDest, BB
2237 // BI: br i1 %y, TrueDest, FalseDest
2238 //TrueWeight is TrueWeight for PBI * TotalWeight for BI +
2239 // FalseWeight for PBI * TrueWeight for BI.
2240 NewWeights.push_back(PredTrueWeight * (SuccFalseWeight +
2241 SuccTrueWeight) + PredFalseWeight * SuccTrueWeight);
2242 //FalseWeight is FalseWeight for PBI * FalseWeight for BI.
2243 NewWeights.push_back(PredFalseWeight * SuccFalseWeight);
2245 AddPredecessorToBlock(FalseDest, PredBlock, BB);
2246 PBI->setSuccessor(1, FalseDest);
2248 if (NewWeights.size() == 2) {
2249 // Halve the weights if any of them cannot fit in an uint32_t
2250 FitWeights(NewWeights);
2252 SmallVector<uint32_t, 8> MDWeights(NewWeights.begin(),NewWeights.end());
2253 PBI->setMetadata(LLVMContext::MD_prof,
2254 MDBuilder(BI->getContext()).
2255 createBranchWeights(MDWeights));
2257 PBI->setMetadata(LLVMContext::MD_prof, NULL);
2259 // Update PHI nodes in the common successors.
2260 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
2261 ConstantInt *PBI_C = cast<ConstantInt>(
2262 PHIs[i]->getIncomingValueForBlock(PBI->getParent()));
2263 assert(PBI_C->getType()->isIntegerTy(1));
2264 Instruction *MergedCond = 0;
2265 if (PBI->getSuccessor(0) == TrueDest) {
2266 // Create (PBI_Cond and PBI_C) or (!PBI_Cond and BI_Value)
2267 // PBI_C is true: PBI_Cond or (!PBI_Cond and BI_Value)
2268 // is false: !PBI_Cond and BI_Value
2269 Instruction *NotCond =
2270 cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
2273 cast<Instruction>(Builder.CreateBinOp(Instruction::And,
2278 cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
2279 PBI->getCondition(), MergedCond,
2282 // Create (PBI_Cond and BI_Value) or (!PBI_Cond and PBI_C)
2283 // PBI_C is true: (PBI_Cond and BI_Value) or (!PBI_Cond)
2284 // is false: PBI_Cond and BI_Value
2286 cast<Instruction>(Builder.CreateBinOp(Instruction::And,
2287 PBI->getCondition(), New,
2289 if (PBI_C->isOne()) {
2290 Instruction *NotCond =
2291 cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
2294 cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
2295 NotCond, MergedCond,
2300 PHIs[i]->setIncomingValue(PHIs[i]->getBasicBlockIndex(PBI->getParent()),
2303 // Change PBI from Conditional to Unconditional.
2304 BranchInst *New_PBI = BranchInst::Create(TrueDest, PBI);
2305 EraseTerminatorInstAndDCECond(PBI);
2309 // TODO: If BB is reachable from all paths through PredBlock, then we
2310 // could replace PBI's branch probabilities with BI's.
2312 // Copy any debug value intrinsics into the end of PredBlock.
2313 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
2314 if (isa<DbgInfoIntrinsic>(*I))
2315 I->clone()->insertBefore(PBI);
2322 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
2323 /// predecessor of another block, this function tries to simplify it. We know
2324 /// that PBI and BI are both conditional branches, and BI is in one of the
2325 /// successor blocks of PBI - PBI branches to BI.
2326 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
2327 assert(PBI->isConditional() && BI->isConditional());
2328 BasicBlock *BB = BI->getParent();
2330 // If this block ends with a branch instruction, and if there is a
2331 // predecessor that ends on a branch of the same condition, make
2332 // this conditional branch redundant.
2333 if (PBI->getCondition() == BI->getCondition() &&
2334 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
2335 // Okay, the outcome of this conditional branch is statically
2336 // knowable. If this block had a single pred, handle specially.
2337 if (BB->getSinglePredecessor()) {
2338 // Turn this into a branch on constant.
2339 bool CondIsTrue = PBI->getSuccessor(0) == BB;
2340 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
2342 return true; // Nuke the branch on constant.
2345 // Otherwise, if there are multiple predecessors, insert a PHI that merges
2346 // in the constant and simplify the block result. Subsequent passes of
2347 // simplifycfg will thread the block.
2348 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
2349 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
2350 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
2351 std::distance(PB, PE),
2352 BI->getCondition()->getName() + ".pr",
2354 // Okay, we're going to insert the PHI node. Since PBI is not the only
2355 // predecessor, compute the PHI'd conditional value for all of the preds.
2356 // Any predecessor where the condition is not computable we keep symbolic.
2357 for (pred_iterator PI = PB; PI != PE; ++PI) {
2358 BasicBlock *P = *PI;
2359 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
2360 PBI != BI && PBI->isConditional() &&
2361 PBI->getCondition() == BI->getCondition() &&
2362 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
2363 bool CondIsTrue = PBI->getSuccessor(0) == BB;
2364 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
2367 NewPN->addIncoming(BI->getCondition(), P);
2371 BI->setCondition(NewPN);
2376 // If this is a conditional branch in an empty block, and if any
2377 // predecessors is a conditional branch to one of our destinations,
2378 // fold the conditions into logical ops and one cond br.
2379 BasicBlock::iterator BBI = BB->begin();
2380 // Ignore dbg intrinsics.
2381 while (isa<DbgInfoIntrinsic>(BBI))
2387 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
2392 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
2394 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
2395 PBIOp = 0, BIOp = 1;
2396 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
2397 PBIOp = 1, BIOp = 0;
2398 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
2403 // Check to make sure that the other destination of this branch
2404 // isn't BB itself. If so, this is an infinite loop that will
2405 // keep getting unwound.
2406 if (PBI->getSuccessor(PBIOp) == BB)
2409 // Do not perform this transformation if it would require
2410 // insertion of a large number of select instructions. For targets
2411 // without predication/cmovs, this is a big pessimization.
2412 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
2414 unsigned NumPhis = 0;
2415 for (BasicBlock::iterator II = CommonDest->begin();
2416 isa<PHINode>(II); ++II, ++NumPhis)
2417 if (NumPhis > 2) // Disable this xform.
2420 // Finally, if everything is ok, fold the branches to logical ops.
2421 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
2423 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
2424 << "AND: " << *BI->getParent());
2427 // If OtherDest *is* BB, then BB is a basic block with a single conditional
2428 // branch in it, where one edge (OtherDest) goes back to itself but the other
2429 // exits. We don't *know* that the program avoids the infinite loop
2430 // (even though that seems likely). If we do this xform naively, we'll end up
2431 // recursively unpeeling the loop. Since we know that (after the xform is
2432 // done) that the block *is* infinite if reached, we just make it an obviously
2433 // infinite loop with no cond branch.
2434 if (OtherDest == BB) {
2435 // Insert it at the end of the function, because it's either code,
2436 // or it won't matter if it's hot. :)
2437 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
2438 "infloop", BB->getParent());
2439 BranchInst::Create(InfLoopBlock, InfLoopBlock);
2440 OtherDest = InfLoopBlock;
2443 DEBUG(dbgs() << *PBI->getParent()->getParent());
2445 // BI may have other predecessors. Because of this, we leave
2446 // it alone, but modify PBI.
2448 // Make sure we get to CommonDest on True&True directions.
2449 Value *PBICond = PBI->getCondition();
2450 IRBuilder<true, NoFolder> Builder(PBI);
2452 PBICond = Builder.CreateNot(PBICond, PBICond->getName()+".not");
2454 Value *BICond = BI->getCondition();
2456 BICond = Builder.CreateNot(BICond, BICond->getName()+".not");
2458 // Merge the conditions.
2459 Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge");
2461 // Modify PBI to branch on the new condition to the new dests.
2462 PBI->setCondition(Cond);
2463 PBI->setSuccessor(0, CommonDest);
2464 PBI->setSuccessor(1, OtherDest);
2466 // Update branch weight for PBI.
2467 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
2468 bool PredHasWeights = ExtractBranchMetadata(PBI, PredTrueWeight,
2470 bool SuccHasWeights = ExtractBranchMetadata(BI, SuccTrueWeight,
2472 if (PredHasWeights && SuccHasWeights) {
2473 uint64_t PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
2474 uint64_t PredOther = PBIOp ?PredTrueWeight : PredFalseWeight;
2475 uint64_t SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
2476 uint64_t SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
2477 // The weight to CommonDest should be PredCommon * SuccTotal +
2478 // PredOther * SuccCommon.
2479 // The weight to OtherDest should be PredOther * SuccOther.
2480 SmallVector<uint64_t, 2> NewWeights;
2481 NewWeights.push_back(PredCommon * (SuccCommon + SuccOther) +
2482 PredOther * SuccCommon);
2483 NewWeights.push_back(PredOther * SuccOther);
2484 // Halve the weights if any of them cannot fit in an uint32_t
2485 FitWeights(NewWeights);
2487 SmallVector<uint32_t, 2> MDWeights(NewWeights.begin(),NewWeights.end());
2488 PBI->setMetadata(LLVMContext::MD_prof,
2489 MDBuilder(BI->getContext()).
2490 createBranchWeights(MDWeights));
2493 // OtherDest may have phi nodes. If so, add an entry from PBI's
2494 // block that are identical to the entries for BI's block.
2495 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
2497 // We know that the CommonDest already had an edge from PBI to
2498 // it. If it has PHIs though, the PHIs may have different
2499 // entries for BB and PBI's BB. If so, insert a select to make
2502 for (BasicBlock::iterator II = CommonDest->begin();
2503 (PN = dyn_cast<PHINode>(II)); ++II) {
2504 Value *BIV = PN->getIncomingValueForBlock(BB);
2505 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
2506 Value *PBIV = PN->getIncomingValue(PBBIdx);
2508 // Insert a select in PBI to pick the right value.
2509 Value *NV = cast<SelectInst>
2510 (Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName()+".mux"));
2511 PN->setIncomingValue(PBBIdx, NV);
2515 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
2516 DEBUG(dbgs() << *PBI->getParent()->getParent());
2518 // This basic block is probably dead. We know it has at least
2519 // one fewer predecessor.
2523 // SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
2524 // branch to TrueBB if Cond is true or to FalseBB if Cond is false.
2525 // Takes care of updating the successors and removing the old terminator.
2526 // Also makes sure not to introduce new successors by assuming that edges to
2527 // non-successor TrueBBs and FalseBBs aren't reachable.
2528 static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
2529 BasicBlock *TrueBB, BasicBlock *FalseBB,
2530 uint32_t TrueWeight,
2531 uint32_t FalseWeight){
2532 // Remove any superfluous successor edges from the CFG.
2533 // First, figure out which successors to preserve.
2534 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
2536 BasicBlock *KeepEdge1 = TrueBB;
2537 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
2539 // Then remove the rest.
2540 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
2541 BasicBlock *Succ = OldTerm->getSuccessor(I);
2542 // Make sure only to keep exactly one copy of each edge.
2543 if (Succ == KeepEdge1)
2545 else if (Succ == KeepEdge2)
2548 Succ->removePredecessor(OldTerm->getParent());
2551 IRBuilder<> Builder(OldTerm);
2552 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
2554 // Insert an appropriate new terminator.
2555 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
2556 if (TrueBB == FalseBB)
2557 // We were only looking for one successor, and it was present.
2558 // Create an unconditional branch to it.
2559 Builder.CreateBr(TrueBB);
2561 // We found both of the successors we were looking for.
2562 // Create a conditional branch sharing the condition of the select.
2563 BranchInst *NewBI = Builder.CreateCondBr(Cond, TrueBB, FalseBB);
2564 if (TrueWeight != FalseWeight)
2565 NewBI->setMetadata(LLVMContext::MD_prof,
2566 MDBuilder(OldTerm->getContext()).
2567 createBranchWeights(TrueWeight, FalseWeight));
2569 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
2570 // Neither of the selected blocks were successors, so this
2571 // terminator must be unreachable.
2572 new UnreachableInst(OldTerm->getContext(), OldTerm);
2574 // One of the selected values was a successor, but the other wasn't.
2575 // Insert an unconditional branch to the one that was found;
2576 // the edge to the one that wasn't must be unreachable.
2578 // Only TrueBB was found.
2579 Builder.CreateBr(TrueBB);
2581 // Only FalseBB was found.
2582 Builder.CreateBr(FalseBB);
2585 EraseTerminatorInstAndDCECond(OldTerm);
2589 // SimplifySwitchOnSelect - Replaces
2590 // (switch (select cond, X, Y)) on constant X, Y
2591 // with a branch - conditional if X and Y lead to distinct BBs,
2592 // unconditional otherwise.
2593 static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
2594 // Check for constant integer values in the select.
2595 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
2596 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
2597 if (!TrueVal || !FalseVal)
2600 // Find the relevant condition and destinations.
2601 Value *Condition = Select->getCondition();
2602 BasicBlock *TrueBB = SI->findCaseValue(TrueVal).getCaseSuccessor();
2603 BasicBlock *FalseBB = SI->findCaseValue(FalseVal).getCaseSuccessor();
2605 // Get weight for TrueBB and FalseBB.
2606 uint32_t TrueWeight = 0, FalseWeight = 0;
2607 SmallVector<uint64_t, 8> Weights;
2608 bool HasWeights = HasBranchWeights(SI);
2610 GetBranchWeights(SI, Weights);
2611 if (Weights.size() == 1 + SI->getNumCases()) {
2612 TrueWeight = (uint32_t)Weights[SI->findCaseValue(TrueVal).
2613 getSuccessorIndex()];
2614 FalseWeight = (uint32_t)Weights[SI->findCaseValue(FalseVal).
2615 getSuccessorIndex()];
2619 // Perform the actual simplification.
2620 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB,
2621 TrueWeight, FalseWeight);
2624 // SimplifyIndirectBrOnSelect - Replaces
2625 // (indirectbr (select cond, blockaddress(@fn, BlockA),
2626 // blockaddress(@fn, BlockB)))
2628 // (br cond, BlockA, BlockB).
2629 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
2630 // Check that both operands of the select are block addresses.
2631 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
2632 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
2636 // Extract the actual blocks.
2637 BasicBlock *TrueBB = TBA->getBasicBlock();
2638 BasicBlock *FalseBB = FBA->getBasicBlock();
2640 // Perform the actual simplification.
2641 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB,
2645 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
2646 /// instruction (a seteq/setne with a constant) as the only instruction in a
2647 /// block that ends with an uncond branch. We are looking for a very specific
2648 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
2649 /// this case, we merge the first two "or's of icmp" into a switch, but then the
2650 /// default value goes to an uncond block with a seteq in it, we get something
2653 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
2655 /// %tmp = icmp eq i8 %A, 92
2658 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
2660 /// We prefer to split the edge to 'end' so that there is a true/false entry to
2661 /// the PHI, merging the third icmp into the switch.
2662 static bool TryToSimplifyUncondBranchWithICmpInIt(
2663 ICmpInst *ICI, IRBuilder<> &Builder, const TargetTransformInfo &TTI,
2664 const DataLayout *TD) {
2665 BasicBlock *BB = ICI->getParent();
2667 // If the block has any PHIs in it or the icmp has multiple uses, it is too
2669 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
2671 Value *V = ICI->getOperand(0);
2672 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
2674 // The pattern we're looking for is where our only predecessor is a switch on
2675 // 'V' and this block is the default case for the switch. In this case we can
2676 // fold the compared value into the switch to simplify things.
2677 BasicBlock *Pred = BB->getSinglePredecessor();
2678 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
2680 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
2681 if (SI->getCondition() != V)
2684 // If BB is reachable on a non-default case, then we simply know the value of
2685 // V in this block. Substitute it and constant fold the icmp instruction
2687 if (SI->getDefaultDest() != BB) {
2688 ConstantInt *VVal = SI->findCaseDest(BB);
2689 assert(VVal && "Should have a unique destination value");
2690 ICI->setOperand(0, VVal);
2692 if (Value *V = SimplifyInstruction(ICI, TD)) {
2693 ICI->replaceAllUsesWith(V);
2694 ICI->eraseFromParent();
2696 // BB is now empty, so it is likely to simplify away.
2697 return SimplifyCFG(BB, TTI, TD) | true;
2700 // Ok, the block is reachable from the default dest. If the constant we're
2701 // comparing exists in one of the other edges, then we can constant fold ICI
2703 if (SI->findCaseValue(Cst) != SI->case_default()) {
2705 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2706 V = ConstantInt::getFalse(BB->getContext());
2708 V = ConstantInt::getTrue(BB->getContext());
2710 ICI->replaceAllUsesWith(V);
2711 ICI->eraseFromParent();
2712 // BB is now empty, so it is likely to simplify away.
2713 return SimplifyCFG(BB, TTI, TD) | true;
2716 // The use of the icmp has to be in the 'end' block, by the only PHI node in
2718 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
2719 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
2720 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
2721 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
2724 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
2726 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
2727 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
2729 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2730 std::swap(DefaultCst, NewCst);
2732 // Replace ICI (which is used by the PHI for the default value) with true or
2733 // false depending on if it is EQ or NE.
2734 ICI->replaceAllUsesWith(DefaultCst);
2735 ICI->eraseFromParent();
2737 // Okay, the switch goes to this block on a default value. Add an edge from
2738 // the switch to the merge point on the compared value.
2739 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
2740 BB->getParent(), BB);
2741 SmallVector<uint64_t, 8> Weights;
2742 bool HasWeights = HasBranchWeights(SI);
2744 GetBranchWeights(SI, Weights);
2745 if (Weights.size() == 1 + SI->getNumCases()) {
2746 // Split weight for default case to case for "Cst".
2747 Weights[0] = (Weights[0]+1) >> 1;
2748 Weights.push_back(Weights[0]);
2750 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
2751 SI->setMetadata(LLVMContext::MD_prof,
2752 MDBuilder(SI->getContext()).
2753 createBranchWeights(MDWeights));
2756 SI->addCase(Cst, NewBB);
2758 // NewBB branches to the phi block, add the uncond branch and the phi entry.
2759 Builder.SetInsertPoint(NewBB);
2760 Builder.SetCurrentDebugLocation(SI->getDebugLoc());
2761 Builder.CreateBr(SuccBlock);
2762 PHIUse->addIncoming(NewCst, NewBB);
2766 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
2767 /// Check to see if it is branching on an or/and chain of icmp instructions, and
2768 /// fold it into a switch instruction if so.
2769 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const DataLayout *TD,
2770 IRBuilder<> &Builder) {
2771 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
2772 if (Cond == 0) return false;
2775 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2776 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2777 // 'setne's and'ed together, collect them.
2779 std::vector<ConstantInt*> Values;
2780 bool TrueWhenEqual = true;
2781 Value *ExtraCase = 0;
2782 unsigned UsedICmps = 0;
2784 if (Cond->getOpcode() == Instruction::Or) {
2785 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
2787 } else if (Cond->getOpcode() == Instruction::And) {
2788 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
2790 TrueWhenEqual = false;
2793 // If we didn't have a multiply compared value, fail.
2794 if (CompVal == 0) return false;
2796 // Avoid turning single icmps into a switch.
2800 // There might be duplicate constants in the list, which the switch
2801 // instruction can't handle, remove them now.
2802 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
2803 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2805 // If Extra was used, we require at least two switch values to do the
2806 // transformation. A switch with one value is just an cond branch.
2807 if (ExtraCase && Values.size() < 2) return false;
2809 // TODO: Preserve branch weight metadata, similarly to how
2810 // FoldValueComparisonIntoPredecessors preserves it.
2812 // Figure out which block is which destination.
2813 BasicBlock *DefaultBB = BI->getSuccessor(1);
2814 BasicBlock *EdgeBB = BI->getSuccessor(0);
2815 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2817 BasicBlock *BB = BI->getParent();
2819 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
2820 << " cases into SWITCH. BB is:\n" << *BB);
2822 // If there are any extra values that couldn't be folded into the switch
2823 // then we evaluate them with an explicit branch first. Split the block
2824 // right before the condbr to handle it.
2826 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
2827 // Remove the uncond branch added to the old block.
2828 TerminatorInst *OldTI = BB->getTerminator();
2829 Builder.SetInsertPoint(OldTI);
2832 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
2834 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
2836 OldTI->eraseFromParent();
2838 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
2839 // for the edge we just added.
2840 AddPredecessorToBlock(EdgeBB, BB, NewBB);
2842 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
2843 << "\nEXTRABB = " << *BB);
2847 Builder.SetInsertPoint(BI);
2848 // Convert pointer to int before we switch.
2849 if (CompVal->getType()->isPointerTy()) {
2850 assert(TD && "Cannot switch on pointer without DataLayout");
2851 CompVal = Builder.CreatePtrToInt(CompVal,
2852 TD->getIntPtrType(CompVal->getContext()),
2856 // Create the new switch instruction now.
2857 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
2859 // Add all of the 'cases' to the switch instruction.
2860 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2861 New->addCase(Values[i], EdgeBB);
2863 // We added edges from PI to the EdgeBB. As such, if there were any
2864 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2865 // the number of edges added.
2866 for (BasicBlock::iterator BBI = EdgeBB->begin();
2867 isa<PHINode>(BBI); ++BBI) {
2868 PHINode *PN = cast<PHINode>(BBI);
2869 Value *InVal = PN->getIncomingValueForBlock(BB);
2870 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2871 PN->addIncoming(InVal, BB);
2874 // Erase the old branch instruction.
2875 EraseTerminatorInstAndDCECond(BI);
2877 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
2881 bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
2882 // If this is a trivial landing pad that just continues unwinding the caught
2883 // exception then zap the landing pad, turning its invokes into calls.
2884 BasicBlock *BB = RI->getParent();
2885 LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI());
2886 if (RI->getValue() != LPInst)
2887 // Not a landing pad, or the resume is not unwinding the exception that
2888 // caused control to branch here.
2891 // Check that there are no other instructions except for debug intrinsics.
2892 BasicBlock::iterator I = LPInst, E = RI;
2894 if (!isa<DbgInfoIntrinsic>(I))
2897 // Turn all invokes that unwind here into calls and delete the basic block.
2898 bool InvokeRequiresTableEntry = false;
2899 bool Changed = false;
2900 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
2901 InvokeInst *II = cast<InvokeInst>((*PI++)->getTerminator());
2903 if (II->hasFnAttr(Attribute::UWTable)) {
2904 // Don't remove an `invoke' instruction if the ABI requires an entry into
2906 InvokeRequiresTableEntry = true;
2910 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
2912 // Insert a call instruction before the invoke.
2913 CallInst *Call = CallInst::Create(II->getCalledValue(), Args, "", II);
2915 Call->setCallingConv(II->getCallingConv());
2916 Call->setAttributes(II->getAttributes());
2917 Call->setDebugLoc(II->getDebugLoc());
2919 // Anything that used the value produced by the invoke instruction now uses
2920 // the value produced by the call instruction. Note that we do this even
2921 // for void functions and calls with no uses so that the callgraph edge is
2923 II->replaceAllUsesWith(Call);
2924 BB->removePredecessor(II->getParent());
2926 // Insert a branch to the normal destination right before the invoke.
2927 BranchInst::Create(II->getNormalDest(), II);
2929 // Finally, delete the invoke instruction!
2930 II->eraseFromParent();
2934 if (!InvokeRequiresTableEntry)
2935 // The landingpad is now unreachable. Zap it.
2936 BB->eraseFromParent();
2941 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
2942 BasicBlock *BB = RI->getParent();
2943 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2945 // Find predecessors that end with branches.
2946 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2947 SmallVector<BranchInst*, 8> CondBranchPreds;
2948 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2949 BasicBlock *P = *PI;
2950 TerminatorInst *PTI = P->getTerminator();
2951 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2952 if (BI->isUnconditional())
2953 UncondBranchPreds.push_back(P);
2955 CondBranchPreds.push_back(BI);
2959 // If we found some, do the transformation!
2960 if (!UncondBranchPreds.empty() && DupRet) {
2961 while (!UncondBranchPreds.empty()) {
2962 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2963 DEBUG(dbgs() << "FOLDING: " << *BB
2964 << "INTO UNCOND BRANCH PRED: " << *Pred);
2965 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
2968 // If we eliminated all predecessors of the block, delete the block now.
2969 if (pred_begin(BB) == pred_end(BB))
2970 // We know there are no successors, so just nuke the block.
2971 BB->eraseFromParent();
2976 // Check out all of the conditional branches going to this return
2977 // instruction. If any of them just select between returns, change the
2978 // branch itself into a select/return pair.
2979 while (!CondBranchPreds.empty()) {
2980 BranchInst *BI = CondBranchPreds.pop_back_val();
2982 // Check to see if the non-BB successor is also a return block.
2983 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2984 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2985 SimplifyCondBranchToTwoReturns(BI, Builder))
2991 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2992 BasicBlock *BB = UI->getParent();
2994 bool Changed = false;
2996 // If there are any instructions immediately before the unreachable that can
2997 // be removed, do so.
2998 while (UI != BB->begin()) {
2999 BasicBlock::iterator BBI = UI;
3001 // Do not delete instructions that can have side effects which might cause
3002 // the unreachable to not be reachable; specifically, calls and volatile
3003 // operations may have this effect.
3004 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
3006 if (BBI->mayHaveSideEffects()) {
3007 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
3008 if (SI->isVolatile())
3010 } else if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
3011 if (LI->isVolatile())
3013 } else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(BBI)) {
3014 if (RMWI->isVolatile())
3016 } else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) {
3017 if (CXI->isVolatile())
3019 } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) &&
3020 !isa<LandingPadInst>(BBI)) {
3023 // Note that deleting LandingPad's here is in fact okay, although it
3024 // involves a bit of subtle reasoning. If this inst is a LandingPad,
3025 // all the predecessors of this block will be the unwind edges of Invokes,
3026 // and we can therefore guarantee this block will be erased.
3029 // Delete this instruction (any uses are guaranteed to be dead)
3030 if (!BBI->use_empty())
3031 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
3032 BBI->eraseFromParent();
3036 // If the unreachable instruction is the first in the block, take a gander
3037 // at all of the predecessors of this instruction, and simplify them.
3038 if (&BB->front() != UI) return Changed;
3040 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
3041 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
3042 TerminatorInst *TI = Preds[i]->getTerminator();
3043 IRBuilder<> Builder(TI);
3044 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
3045 if (BI->isUnconditional()) {
3046 if (BI->getSuccessor(0) == BB) {
3047 new UnreachableInst(TI->getContext(), TI);
3048 TI->eraseFromParent();
3052 if (BI->getSuccessor(0) == BB) {
3053 Builder.CreateBr(BI->getSuccessor(1));
3054 EraseTerminatorInstAndDCECond(BI);
3055 } else if (BI->getSuccessor(1) == BB) {
3056 Builder.CreateBr(BI->getSuccessor(0));
3057 EraseTerminatorInstAndDCECond(BI);
3061 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
3062 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
3064 if (i.getCaseSuccessor() == BB) {
3065 BB->removePredecessor(SI->getParent());
3070 // If the default value is unreachable, figure out the most popular
3071 // destination and make it the default.
3072 if (SI->getDefaultDest() == BB) {
3073 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
3074 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
3076 std::pair<unsigned, unsigned> &entry =
3077 Popularity[i.getCaseSuccessor()];
3078 if (entry.first == 0) {
3080 entry.second = i.getCaseIndex();
3086 // Find the most popular block.
3087 unsigned MaxPop = 0;
3088 unsigned MaxIndex = 0;
3089 BasicBlock *MaxBlock = 0;
3090 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
3091 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
3092 if (I->second.first > MaxPop ||
3093 (I->second.first == MaxPop && MaxIndex > I->second.second)) {
3094 MaxPop = I->second.first;
3095 MaxIndex = I->second.second;
3096 MaxBlock = I->first;
3100 // Make this the new default, allowing us to delete any explicit
3102 SI->setDefaultDest(MaxBlock);
3105 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
3107 if (isa<PHINode>(MaxBlock->begin()))
3108 for (unsigned i = 0; i != MaxPop-1; ++i)
3109 MaxBlock->removePredecessor(SI->getParent());
3111 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
3113 if (i.getCaseSuccessor() == MaxBlock) {
3119 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
3120 if (II->getUnwindDest() == BB) {
3121 // Convert the invoke to a call instruction. This would be a good
3122 // place to note that the call does not throw though.
3123 BranchInst *BI = Builder.CreateBr(II->getNormalDest());
3124 II->removeFromParent(); // Take out of symbol table
3126 // Insert the call now...
3127 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
3128 Builder.SetInsertPoint(BI);
3129 CallInst *CI = Builder.CreateCall(II->getCalledValue(),
3130 Args, II->getName());
3131 CI->setCallingConv(II->getCallingConv());
3132 CI->setAttributes(II->getAttributes());
3133 // If the invoke produced a value, the call does now instead.
3134 II->replaceAllUsesWith(CI);
3141 // If this block is now dead, remove it.
3142 if (pred_begin(BB) == pred_end(BB) &&
3143 BB != &BB->getParent()->getEntryBlock()) {
3144 // We know there are no successors, so just nuke the block.
3145 BB->eraseFromParent();
3152 /// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
3153 /// integer range comparison into a sub, an icmp and a branch.
3154 static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
3155 assert(SI->getNumCases() > 1 && "Degenerate switch?");
3157 // Make sure all cases point to the same destination and gather the values.
3158 SmallVector<ConstantInt *, 16> Cases;
3159 SwitchInst::CaseIt I = SI->case_begin();
3160 Cases.push_back(I.getCaseValue());
3161 SwitchInst::CaseIt PrevI = I++;
3162 for (SwitchInst::CaseIt E = SI->case_end(); I != E; PrevI = I++) {
3163 if (PrevI.getCaseSuccessor() != I.getCaseSuccessor())
3165 Cases.push_back(I.getCaseValue());
3167 assert(Cases.size() == SI->getNumCases() && "Not all cases gathered");
3169 // Sort the case values, then check if they form a range we can transform.
3170 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
3171 for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
3172 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
3176 Constant *Offset = ConstantExpr::getNeg(Cases.back());
3177 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases());
3179 Value *Sub = SI->getCondition();
3180 if (!Offset->isNullValue())
3181 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off");
3183 // If NumCases overflowed, then all possible values jump to the successor.
3184 if (NumCases->isNullValue() && SI->getNumCases() != 0)
3185 Cmp = ConstantInt::getTrue(SI->getContext());
3187 Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
3188 BranchInst *NewBI = Builder.CreateCondBr(
3189 Cmp, SI->case_begin().getCaseSuccessor(), SI->getDefaultDest());
3191 // Update weight for the newly-created conditional branch.
3192 SmallVector<uint64_t, 8> Weights;
3193 bool HasWeights = HasBranchWeights(SI);
3195 GetBranchWeights(SI, Weights);
3196 if (Weights.size() == 1 + SI->getNumCases()) {
3197 // Combine all weights for the cases to be the true weight of NewBI.
3198 // We assume that the sum of all weights for a Terminator can fit into 32
3200 uint32_t NewTrueWeight = 0;
3201 for (unsigned I = 1, E = Weights.size(); I != E; ++I)
3202 NewTrueWeight += (uint32_t)Weights[I];
3203 NewBI->setMetadata(LLVMContext::MD_prof,
3204 MDBuilder(SI->getContext()).
3205 createBranchWeights(NewTrueWeight,
3206 (uint32_t)Weights[0]));
3210 // Prune obsolete incoming values off the successor's PHI nodes.
3211 for (BasicBlock::iterator BBI = SI->case_begin().getCaseSuccessor()->begin();
3212 isa<PHINode>(BBI); ++BBI) {
3213 for (unsigned I = 0, E = SI->getNumCases()-1; I != E; ++I)
3214 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
3216 SI->eraseFromParent();
3221 /// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch
3222 /// and use it to remove dead cases.
3223 static bool EliminateDeadSwitchCases(SwitchInst *SI) {
3224 Value *Cond = SI->getCondition();
3225 unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth();
3226 APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
3227 ComputeMaskedBits(Cond, KnownZero, KnownOne);
3229 // Gather dead cases.
3230 SmallVector<ConstantInt*, 8> DeadCases;
3231 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
3232 if ((I.getCaseValue()->getValue() & KnownZero) != 0 ||
3233 (I.getCaseValue()->getValue() & KnownOne) != KnownOne) {
3234 DeadCases.push_back(I.getCaseValue());
3235 DEBUG(dbgs() << "SimplifyCFG: switch case '"
3236 << I.getCaseValue() << "' is dead.\n");
3240 SmallVector<uint64_t, 8> Weights;
3241 bool HasWeight = HasBranchWeights(SI);
3243 GetBranchWeights(SI, Weights);
3244 HasWeight = (Weights.size() == 1 + SI->getNumCases());
3247 // Remove dead cases from the switch.
3248 for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) {
3249 SwitchInst::CaseIt Case = SI->findCaseValue(DeadCases[I]);
3250 assert(Case != SI->case_default() &&
3251 "Case was not found. Probably mistake in DeadCases forming.");
3253 std::swap(Weights[Case.getCaseIndex()+1], Weights.back());
3257 // Prune unused values from PHI nodes.
3258 Case.getCaseSuccessor()->removePredecessor(SI->getParent());
3259 SI->removeCase(Case);
3262 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
3263 SI->setMetadata(LLVMContext::MD_prof,
3264 MDBuilder(SI->getParent()->getContext()).
3265 createBranchWeights(MDWeights));
3268 return !DeadCases.empty();
3271 /// FindPHIForConditionForwarding - If BB would be eligible for simplification
3272 /// by TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated
3273 /// by an unconditional branch), look at the phi node for BB in the successor
3274 /// block and see if the incoming value is equal to CaseValue. If so, return
3275 /// the phi node, and set PhiIndex to BB's index in the phi node.
3276 static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
3279 if (BB->getFirstNonPHIOrDbg() != BB->getTerminator())
3280 return NULL; // BB must be empty to be a candidate for simplification.
3281 if (!BB->getSinglePredecessor())
3282 return NULL; // BB must be dominated by the switch.
3284 BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
3285 if (!Branch || !Branch->isUnconditional())
3286 return NULL; // Terminator must be unconditional branch.
3288 BasicBlock *Succ = Branch->getSuccessor(0);
3290 BasicBlock::iterator I = Succ->begin();
3291 while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
3292 int Idx = PHI->getBasicBlockIndex(BB);
3293 assert(Idx >= 0 && "PHI has no entry for predecessor?");
3295 Value *InValue = PHI->getIncomingValue(Idx);
3296 if (InValue != CaseValue) continue;
3305 /// ForwardSwitchConditionToPHI - Try to forward the condition of a switch
3306 /// instruction to a phi node dominated by the switch, if that would mean that
3307 /// some of the destination blocks of the switch can be folded away.
3308 /// Returns true if a change is made.
3309 static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
3310 typedef DenseMap<PHINode*, SmallVector<int,4> > ForwardingNodesMap;
3311 ForwardingNodesMap ForwardingNodes;
3313 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
3314 ConstantInt *CaseValue = I.getCaseValue();
3315 BasicBlock *CaseDest = I.getCaseSuccessor();
3318 PHINode *PHI = FindPHIForConditionForwarding(CaseValue, CaseDest,
3322 ForwardingNodes[PHI].push_back(PhiIndex);
3325 bool Changed = false;
3327 for (ForwardingNodesMap::iterator I = ForwardingNodes.begin(),
3328 E = ForwardingNodes.end(); I != E; ++I) {
3329 PHINode *Phi = I->first;
3330 SmallVector<int,4> &Indexes = I->second;
3332 if (Indexes.size() < 2) continue;
3334 for (size_t I = 0, E = Indexes.size(); I != E; ++I)
3335 Phi->setIncomingValue(Indexes[I], SI->getCondition());
3342 /// ValidLookupTableConstant - Return true if the backend will be able to handle
3343 /// initializing an array of constants like C.
3344 static bool ValidLookupTableConstant(Constant *C) {
3345 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C))
3346 return CE->isGEPWithNoNotionalOverIndexing();
3348 return isa<ConstantFP>(C) ||
3349 isa<ConstantInt>(C) ||
3350 isa<ConstantPointerNull>(C) ||
3351 isa<GlobalValue>(C) ||
3355 /// LookupConstant - If V is a Constant, return it. Otherwise, try to look up
3356 /// its constant value in ConstantPool, returning 0 if it's not there.
3357 static Constant *LookupConstant(Value *V,
3358 const SmallDenseMap<Value*, Constant*>& ConstantPool) {
3359 if (Constant *C = dyn_cast<Constant>(V))
3361 return ConstantPool.lookup(V);
3364 /// ConstantFold - Try to fold instruction I into a constant. This works for
3365 /// simple instructions such as binary operations where both operands are
3366 /// constant or can be replaced by constants from the ConstantPool. Returns the
3367 /// resulting constant on success, 0 otherwise.
3368 static Constant *ConstantFold(Instruction *I,
3369 const SmallDenseMap<Value*, Constant*>& ConstantPool) {
3370 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(I)) {
3371 Constant *A = LookupConstant(BO->getOperand(0), ConstantPool);
3374 Constant *B = LookupConstant(BO->getOperand(1), ConstantPool);
3377 return ConstantExpr::get(BO->getOpcode(), A, B);
3380 if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
3381 Constant *A = LookupConstant(I->getOperand(0), ConstantPool);
3384 Constant *B = LookupConstant(I->getOperand(1), ConstantPool);
3387 return ConstantExpr::getCompare(Cmp->getPredicate(), A, B);
3390 if (SelectInst *Select = dyn_cast<SelectInst>(I)) {
3391 Constant *A = LookupConstant(Select->getCondition(), ConstantPool);
3394 if (A->isAllOnesValue())
3395 return LookupConstant(Select->getTrueValue(), ConstantPool);
3396 if (A->isNullValue())
3397 return LookupConstant(Select->getFalseValue(), ConstantPool);
3401 if (CastInst *Cast = dyn_cast<CastInst>(I)) {
3402 Constant *A = LookupConstant(I->getOperand(0), ConstantPool);
3405 return ConstantExpr::getCast(Cast->getOpcode(), A, Cast->getDestTy());
3411 /// GetCaseResults - Try to determine the resulting constant values in phi nodes
3412 /// at the common destination basic block, *CommonDest, for one of the case
3413 /// destionations CaseDest corresponding to value CaseVal (0 for the default
3414 /// case), of a switch instruction SI.
3415 static bool GetCaseResults(SwitchInst *SI,
3416 ConstantInt *CaseVal,
3417 BasicBlock *CaseDest,
3418 BasicBlock **CommonDest,
3419 SmallVector<std::pair<PHINode*,Constant*>, 4> &Res) {
3420 // The block from which we enter the common destination.
3421 BasicBlock *Pred = SI->getParent();
3423 // If CaseDest is empty except for some side-effect free instructions through
3424 // which we can constant-propagate the CaseVal, continue to its successor.
3425 SmallDenseMap<Value*, Constant*> ConstantPool;
3426 ConstantPool.insert(std::make_pair(SI->getCondition(), CaseVal));
3427 for (BasicBlock::iterator I = CaseDest->begin(), E = CaseDest->end(); I != E;
3429 if (TerminatorInst *T = dyn_cast<TerminatorInst>(I)) {
3430 // If the terminator is a simple branch, continue to the next block.
3431 if (T->getNumSuccessors() != 1)
3434 CaseDest = T->getSuccessor(0);
3435 } else if (isa<DbgInfoIntrinsic>(I)) {
3436 // Skip debug intrinsic.
3438 } else if (Constant *C = ConstantFold(I, ConstantPool)) {
3439 // Instruction is side-effect free and constant.
3440 ConstantPool.insert(std::make_pair(I, C));
3446 // If we did not have a CommonDest before, use the current one.
3448 *CommonDest = CaseDest;
3449 // If the destination isn't the common one, abort.
3450 if (CaseDest != *CommonDest)
3453 // Get the values for this case from phi nodes in the destination block.
3454 BasicBlock::iterator I = (*CommonDest)->begin();
3455 while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
3456 int Idx = PHI->getBasicBlockIndex(Pred);
3460 Constant *ConstVal = LookupConstant(PHI->getIncomingValue(Idx),
3465 // Note: If the constant comes from constant-propagating the case value
3466 // through the CaseDest basic block, it will be safe to remove the
3467 // instructions in that block. They cannot be used (except in the phi nodes
3468 // we visit) outside CaseDest, because that block does not dominate its
3469 // successor. If it did, we would not be in this phi node.
3471 // Be conservative about which kinds of constants we support.
3472 if (!ValidLookupTableConstant(ConstVal))
3475 Res.push_back(std::make_pair(PHI, ConstVal));
3482 /// SwitchLookupTable - This class represents a lookup table that can be used
3483 /// to replace a switch.
3484 class SwitchLookupTable {
3486 /// SwitchLookupTable - Create a lookup table to use as a switch replacement
3487 /// with the contents of Values, using DefaultValue to fill any holes in the
3489 SwitchLookupTable(Module &M,
3491 ConstantInt *Offset,
3492 const SmallVector<std::pair<ConstantInt*, Constant*>, 4>& Values,
3493 Constant *DefaultValue,
3494 const DataLayout *TD);
3496 /// BuildLookup - Build instructions with Builder to retrieve the value at
3497 /// the position given by Index in the lookup table.
3498 Value *BuildLookup(Value *Index, IRBuilder<> &Builder);
3500 /// WouldFitInRegister - Return true if a table with TableSize elements of
3501 /// type ElementType would fit in a target-legal register.
3502 static bool WouldFitInRegister(const DataLayout *TD,
3504 const Type *ElementType);
3507 // Depending on the contents of the table, it can be represented in
3510 // For tables where each element contains the same value, we just have to
3511 // store that single value and return it for each lookup.
3514 // For small tables with integer elements, we can pack them into a bitmap
3515 // that fits into a target-legal register. Values are retrieved by
3516 // shift and mask operations.
3519 // The table is stored as an array of values. Values are retrieved by load
3520 // instructions from the table.
3524 // For SingleValueKind, this is the single value.
3525 Constant *SingleValue;
3527 // For BitMapKind, this is the bitmap.
3528 ConstantInt *BitMap;
3529 IntegerType *BitMapElementTy;
3531 // For ArrayKind, this is the array.
3532 GlobalVariable *Array;
3536 SwitchLookupTable::SwitchLookupTable(Module &M,
3538 ConstantInt *Offset,
3539 const SmallVector<std::pair<ConstantInt*, Constant*>, 4>& Values,
3540 Constant *DefaultValue,
3541 const DataLayout *TD)
3542 : SingleValue(0), BitMap(0), BitMapElementTy(0), Array(0) {
3543 assert(Values.size() && "Can't build lookup table without values!");
3544 assert(TableSize >= Values.size() && "Can't fit values in table!");
3546 // If all values in the table are equal, this is that value.
3547 SingleValue = Values.begin()->second;
3549 // Build up the table contents.
3550 SmallVector<Constant*, 64> TableContents(TableSize);
3551 for (size_t I = 0, E = Values.size(); I != E; ++I) {
3552 ConstantInt *CaseVal = Values[I].first;
3553 Constant *CaseRes = Values[I].second;
3554 assert(CaseRes->getType() == DefaultValue->getType());
3556 uint64_t Idx = (CaseVal->getValue() - Offset->getValue())
3558 TableContents[Idx] = CaseRes;
3560 if (CaseRes != SingleValue)
3564 // Fill in any holes in the table with the default result.
3565 if (Values.size() < TableSize) {
3566 for (uint64_t I = 0; I < TableSize; ++I) {
3567 if (!TableContents[I])
3568 TableContents[I] = DefaultValue;
3571 if (DefaultValue != SingleValue)
3575 // If each element in the table contains the same value, we only need to store
3576 // that single value.
3578 Kind = SingleValueKind;
3582 // If the type is integer and the table fits in a register, build a bitmap.
3583 if (WouldFitInRegister(TD, TableSize, DefaultValue->getType())) {
3584 IntegerType *IT = cast<IntegerType>(DefaultValue->getType());
3585 APInt TableInt(TableSize * IT->getBitWidth(), 0);
3586 for (uint64_t I = TableSize; I > 0; --I) {
3587 TableInt <<= IT->getBitWidth();
3588 // Insert values into the bitmap. Undef values are set to zero.
3589 if (!isa<UndefValue>(TableContents[I - 1])) {
3590 ConstantInt *Val = cast<ConstantInt>(TableContents[I - 1]);
3591 TableInt |= Val->getValue().zext(TableInt.getBitWidth());
3594 BitMap = ConstantInt::get(M.getContext(), TableInt);
3595 BitMapElementTy = IT;
3601 // Store the table in an array.
3602 ArrayType *ArrayTy = ArrayType::get(DefaultValue->getType(), TableSize);
3603 Constant *Initializer = ConstantArray::get(ArrayTy, TableContents);
3605 Array = new GlobalVariable(M, ArrayTy, /*constant=*/ true,
3606 GlobalVariable::PrivateLinkage,
3609 Array->setUnnamedAddr(true);
3613 Value *SwitchLookupTable::BuildLookup(Value *Index, IRBuilder<> &Builder) {
3615 case SingleValueKind:
3618 // Type of the bitmap (e.g. i59).
3619 IntegerType *MapTy = BitMap->getType();
3621 // Cast Index to the same type as the bitmap.
3622 // Note: The Index is <= the number of elements in the table, so
3623 // truncating it to the width of the bitmask is safe.
3624 Value *ShiftAmt = Builder.CreateZExtOrTrunc(Index, MapTy, "switch.cast");
3626 // Multiply the shift amount by the element width.
3627 ShiftAmt = Builder.CreateMul(ShiftAmt,
3628 ConstantInt::get(MapTy, BitMapElementTy->getBitWidth()),
3632 Value *DownShifted = Builder.CreateLShr(BitMap, ShiftAmt,
3633 "switch.downshift");
3635 return Builder.CreateTrunc(DownShifted, BitMapElementTy,
3639 Value *GEPIndices[] = { Builder.getInt32(0), Index };
3640 Value *GEP = Builder.CreateInBoundsGEP(Array, GEPIndices,
3642 return Builder.CreateLoad(GEP, "switch.load");
3645 llvm_unreachable("Unknown lookup table kind!");
3648 bool SwitchLookupTable::WouldFitInRegister(const DataLayout *TD,
3650 const Type *ElementType) {
3653 const IntegerType *IT = dyn_cast<IntegerType>(ElementType);
3656 // FIXME: If the type is wider than it needs to be, e.g. i8 but all values
3657 // are <= 15, we could try to narrow the type.
3659 // Avoid overflow, fitsInLegalInteger uses unsigned int for the width.
3660 if (TableSize >= UINT_MAX/IT->getBitWidth())
3662 return TD->fitsInLegalInteger(TableSize * IT->getBitWidth());
3665 /// ShouldBuildLookupTable - Determine whether a lookup table should be built
3666 /// for this switch, based on the number of cases, size of the table and the
3667 /// types of the results.
3668 static bool ShouldBuildLookupTable(SwitchInst *SI,
3670 const TargetTransformInfo &TTI,
3671 const DataLayout *TD,
3672 const SmallDenseMap<PHINode*, Type*>& ResultTypes) {
3673 if (SI->getNumCases() > TableSize || TableSize >= UINT64_MAX / 10)
3674 return false; // TableSize overflowed, or mul below might overflow.
3676 bool AllTablesFitInRegister = true;
3677 bool HasIllegalType = false;
3678 for (SmallDenseMap<PHINode*, Type*>::const_iterator I = ResultTypes.begin(),
3679 E = ResultTypes.end(); I != E; ++I) {
3680 Type *Ty = I->second;
3682 // Saturate this flag to true.
3683 HasIllegalType = HasIllegalType || !TTI.isTypeLegal(Ty);
3685 // Saturate this flag to false.
3686 AllTablesFitInRegister = AllTablesFitInRegister &&
3687 SwitchLookupTable::WouldFitInRegister(TD, TableSize, Ty);
3689 // If both flags saturate, we're done. NOTE: This *only* works with
3690 // saturating flags, and all flags have to saturate first due to the
3691 // non-deterministic behavior of iterating over a dense map.
3692 if (HasIllegalType && !AllTablesFitInRegister)
3696 // If each table would fit in a register, we should build it anyway.
3697 if (AllTablesFitInRegister)
3700 // Don't build a table that doesn't fit in-register if it has illegal types.
3704 // The table density should be at least 40%. This is the same criterion as for
3705 // jump tables, see SelectionDAGBuilder::handleJTSwitchCase.
3706 // FIXME: Find the best cut-off.
3707 return SI->getNumCases() * 10 >= TableSize * 4;
3710 /// SwitchToLookupTable - If the switch is only used to initialize one or more
3711 /// phi nodes in a common successor block with different constant values,
3712 /// replace the switch with lookup tables.
3713 static bool SwitchToLookupTable(SwitchInst *SI,
3714 IRBuilder<> &Builder,
3715 const TargetTransformInfo &TTI,
3716 const DataLayout* TD) {
3717 assert(SI->getNumCases() > 1 && "Degenerate switch?");
3719 // Only build lookup table when we have a target that supports it.
3720 if (!TTI.shouldBuildLookupTables())
3723 // FIXME: If the switch is too sparse for a lookup table, perhaps we could
3724 // split off a dense part and build a lookup table for that.
3726 // FIXME: This creates arrays of GEPs to constant strings, which means each
3727 // GEP needs a runtime relocation in PIC code. We should just build one big
3728 // string and lookup indices into that.
3730 // Ignore the switch if the number of cases is too small.
3731 // This is similar to the check when building jump tables in
3732 // SelectionDAGBuilder::handleJTSwitchCase.
3733 // FIXME: Determine the best cut-off.
3734 if (SI->getNumCases() < 4)
3737 // Figure out the corresponding result for each case value and phi node in the
3738 // common destination, as well as the the min and max case values.
3739 assert(SI->case_begin() != SI->case_end());
3740 SwitchInst::CaseIt CI = SI->case_begin();
3741 ConstantInt *MinCaseVal = CI.getCaseValue();
3742 ConstantInt *MaxCaseVal = CI.getCaseValue();
3744 BasicBlock *CommonDest = 0;
3745 typedef SmallVector<std::pair<ConstantInt*, Constant*>, 4> ResultListTy;
3746 SmallDenseMap<PHINode*, ResultListTy> ResultLists;
3747 SmallDenseMap<PHINode*, Constant*> DefaultResults;
3748 SmallDenseMap<PHINode*, Type*> ResultTypes;
3749 SmallVector<PHINode*, 4> PHIs;
3751 for (SwitchInst::CaseIt E = SI->case_end(); CI != E; ++CI) {
3752 ConstantInt *CaseVal = CI.getCaseValue();
3753 if (CaseVal->getValue().slt(MinCaseVal->getValue()))
3754 MinCaseVal = CaseVal;
3755 if (CaseVal->getValue().sgt(MaxCaseVal->getValue()))
3756 MaxCaseVal = CaseVal;
3758 // Resulting value at phi nodes for this case value.
3759 typedef SmallVector<std::pair<PHINode*, Constant*>, 4> ResultsTy;
3761 if (!GetCaseResults(SI, CaseVal, CI.getCaseSuccessor(), &CommonDest,
3765 // Append the result from this case to the list for each phi.
3766 for (ResultsTy::iterator I = Results.begin(), E = Results.end(); I!=E; ++I) {
3767 if (!ResultLists.count(I->first))
3768 PHIs.push_back(I->first);
3769 ResultLists[I->first].push_back(std::make_pair(CaseVal, I->second));
3773 // Get the resulting values for the default case.
3774 SmallVector<std::pair<PHINode*, Constant*>, 4> DefaultResultsList;
3775 if (!GetCaseResults(SI, 0, SI->getDefaultDest(), &CommonDest,
3776 DefaultResultsList))
3778 for (size_t I = 0, E = DefaultResultsList.size(); I != E; ++I) {
3779 PHINode *PHI = DefaultResultsList[I].first;
3780 Constant *Result = DefaultResultsList[I].second;
3781 DefaultResults[PHI] = Result;
3782 ResultTypes[PHI] = Result->getType();
3785 APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
3786 uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
3787 if (!ShouldBuildLookupTable(SI, TableSize, TTI, TD, ResultTypes))
3790 // Create the BB that does the lookups.
3791 Module &Mod = *CommonDest->getParent()->getParent();
3792 BasicBlock *LookupBB = BasicBlock::Create(Mod.getContext(),
3794 CommonDest->getParent(),
3797 // Check whether the condition value is within the case range, and branch to
3799 Builder.SetInsertPoint(SI);
3800 Value *TableIndex = Builder.CreateSub(SI->getCondition(), MinCaseVal,
3802 Value *Cmp = Builder.CreateICmpULT(TableIndex, ConstantInt::get(
3803 MinCaseVal->getType(), TableSize));
3804 Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest());
3806 // Populate the BB that does the lookups.
3807 Builder.SetInsertPoint(LookupBB);
3808 bool ReturnedEarly = false;
3809 for (size_t I = 0, E = PHIs.size(); I != E; ++I) {
3810 PHINode *PHI = PHIs[I];
3812 SwitchLookupTable Table(Mod, TableSize, MinCaseVal, ResultLists[PHI],
3813 DefaultResults[PHI], TD);
3815 Value *Result = Table.BuildLookup(TableIndex, Builder);
3817 // If the result is used to return immediately from the function, we want to
3818 // do that right here.
3819 if (PHI->hasOneUse() && isa<ReturnInst>(*PHI->use_begin()) &&
3820 *PHI->use_begin() == CommonDest->getFirstNonPHIOrDbg()) {
3821 Builder.CreateRet(Result);
3822 ReturnedEarly = true;
3826 PHI->addIncoming(Result, LookupBB);
3830 Builder.CreateBr(CommonDest);
3832 // Remove the switch.
3833 for (unsigned i = 0; i < SI->getNumSuccessors(); ++i) {
3834 BasicBlock *Succ = SI->getSuccessor(i);
3835 if (Succ == SI->getDefaultDest()) continue;
3836 Succ->removePredecessor(SI->getParent());
3838 SI->eraseFromParent();
3844 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
3845 BasicBlock *BB = SI->getParent();
3847 if (isValueEqualityComparison(SI)) {
3848 // If we only have one predecessor, and if it is a branch on this value,
3849 // see if that predecessor totally determines the outcome of this switch.
3850 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
3851 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
3852 return SimplifyCFG(BB, TTI, TD) | true;
3854 Value *Cond = SI->getCondition();
3855 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
3856 if (SimplifySwitchOnSelect(SI, Select))
3857 return SimplifyCFG(BB, TTI, TD) | true;
3859 // If the block only contains the switch, see if we can fold the block
3860 // away into any preds.
3861 BasicBlock::iterator BBI = BB->begin();
3862 // Ignore dbg intrinsics.
3863 while (isa<DbgInfoIntrinsic>(BBI))
3866 if (FoldValueComparisonIntoPredecessors(SI, Builder))
3867 return SimplifyCFG(BB, TTI, TD) | true;
3870 // Try to transform the switch into an icmp and a branch.
3871 if (TurnSwitchRangeIntoICmp(SI, Builder))
3872 return SimplifyCFG(BB, TTI, TD) | true;
3874 // Remove unreachable cases.
3875 if (EliminateDeadSwitchCases(SI))
3876 return SimplifyCFG(BB, TTI, TD) | true;
3878 if (ForwardSwitchConditionToPHI(SI))
3879 return SimplifyCFG(BB, TTI, TD) | true;
3881 if (SwitchToLookupTable(SI, Builder, TTI, TD))
3882 return SimplifyCFG(BB, TTI, TD) | true;
3887 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
3888 BasicBlock *BB = IBI->getParent();
3889 bool Changed = false;
3891 // Eliminate redundant destinations.
3892 SmallPtrSet<Value *, 8> Succs;
3893 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
3894 BasicBlock *Dest = IBI->getDestination(i);
3895 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
3896 Dest->removePredecessor(BB);
3897 IBI->removeDestination(i);
3903 if (IBI->getNumDestinations() == 0) {
3904 // If the indirectbr has no successors, change it to unreachable.
3905 new UnreachableInst(IBI->getContext(), IBI);
3906 EraseTerminatorInstAndDCECond(IBI);
3910 if (IBI->getNumDestinations() == 1) {
3911 // If the indirectbr has one successor, change it to a direct branch.
3912 BranchInst::Create(IBI->getDestination(0), IBI);
3913 EraseTerminatorInstAndDCECond(IBI);
3917 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
3918 if (SimplifyIndirectBrOnSelect(IBI, SI))
3919 return SimplifyCFG(BB, TTI, TD) | true;
3924 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
3925 BasicBlock *BB = BI->getParent();
3927 if (SinkCommon && SinkThenElseCodeToEnd(BI))
3930 // If the Terminator is the only non-phi instruction, simplify the block.
3931 BasicBlock::iterator I = BB->getFirstNonPHIOrDbgOrLifetime();
3932 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
3933 TryToSimplifyUncondBranchFromEmptyBlock(BB))
3936 // If the only instruction in the block is a seteq/setne comparison
3937 // against a constant, try to simplify the block.
3938 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
3939 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
3940 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
3942 if (I->isTerminator() &&
3943 TryToSimplifyUncondBranchWithICmpInIt(ICI, Builder, TTI, TD))
3947 // If this basic block is ONLY a compare and a branch, and if a predecessor
3948 // branches to us and our successor, fold the comparison into the
3949 // predecessor and use logical operations to update the incoming value
3950 // for PHI nodes in common successor.
3951 if (FoldBranchToCommonDest(BI))
3952 return SimplifyCFG(BB, TTI, TD) | true;
3957 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
3958 BasicBlock *BB = BI->getParent();
3960 // Conditional branch
3961 if (isValueEqualityComparison(BI)) {
3962 // If we only have one predecessor, and if it is a branch on this value,
3963 // see if that predecessor totally determines the outcome of this
3965 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
3966 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
3967 return SimplifyCFG(BB, TTI, TD) | true;
3969 // This block must be empty, except for the setcond inst, if it exists.
3970 // Ignore dbg intrinsics.
3971 BasicBlock::iterator I = BB->begin();
3972 // Ignore dbg intrinsics.
3973 while (isa<DbgInfoIntrinsic>(I))
3976 if (FoldValueComparisonIntoPredecessors(BI, Builder))
3977 return SimplifyCFG(BB, TTI, TD) | true;
3978 } else if (&*I == cast<Instruction>(BI->getCondition())){
3980 // Ignore dbg intrinsics.
3981 while (isa<DbgInfoIntrinsic>(I))
3983 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
3984 return SimplifyCFG(BB, TTI, TD) | true;
3988 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
3989 if (SimplifyBranchOnICmpChain(BI, TD, Builder))
3992 // If this basic block is ONLY a compare and a branch, and if a predecessor
3993 // branches to us and one of our successors, fold the comparison into the
3994 // predecessor and use logical operations to pick the right destination.
3995 if (FoldBranchToCommonDest(BI))
3996 return SimplifyCFG(BB, TTI, TD) | true;
3998 // We have a conditional branch to two blocks that are only reachable
3999 // from BI. We know that the condbr dominates the two blocks, so see if
4000 // there is any identical code in the "then" and "else" blocks. If so, we
4001 // can hoist it up to the branching block.
4002 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
4003 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
4004 if (HoistThenElseCodeToIf(BI))
4005 return SimplifyCFG(BB, TTI, TD) | true;
4007 // If Successor #1 has multiple preds, we may be able to conditionally
4008 // execute Successor #0 if it branches to successor #1.
4009 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
4010 if (Succ0TI->getNumSuccessors() == 1 &&
4011 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
4012 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
4013 return SimplifyCFG(BB, TTI, TD) | true;
4015 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
4016 // If Successor #0 has multiple preds, we may be able to conditionally
4017 // execute Successor #1 if it branches to successor #0.
4018 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
4019 if (Succ1TI->getNumSuccessors() == 1 &&
4020 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
4021 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
4022 return SimplifyCFG(BB, TTI, TD) | true;
4025 // If this is a branch on a phi node in the current block, thread control
4026 // through this block if any PHI node entries are constants.
4027 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
4028 if (PN->getParent() == BI->getParent())
4029 if (FoldCondBranchOnPHI(BI, TD))
4030 return SimplifyCFG(BB, TTI, TD) | true;
4032 // Scan predecessor blocks for conditional branches.
4033 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
4034 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
4035 if (PBI != BI && PBI->isConditional())
4036 if (SimplifyCondBranchToCondBranch(PBI, BI))
4037 return SimplifyCFG(BB, TTI, TD) | true;
4042 /// Check if passing a value to an instruction will cause undefined behavior.
4043 static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
4044 Constant *C = dyn_cast<Constant>(V);
4051 if (C->isNullValue()) {
4052 // Only look at the first use, avoid hurting compile time with long uselists
4053 User *Use = *I->use_begin();
4055 // Now make sure that there are no instructions in between that can alter
4056 // control flow (eg. calls)
4057 for (BasicBlock::iterator i = ++BasicBlock::iterator(I); &*i != Use; ++i)
4058 if (i == I->getParent()->end() || i->mayHaveSideEffects())
4061 // Look through GEPs. A load from a GEP derived from NULL is still undefined
4062 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))
4063 if (GEP->getPointerOperand() == I)
4064 return passingValueIsAlwaysUndefined(V, GEP);
4066 // Look through bitcasts.
4067 if (BitCastInst *BC = dyn_cast<BitCastInst>(Use))
4068 return passingValueIsAlwaysUndefined(V, BC);
4070 // Load from null is undefined.
4071 if (LoadInst *LI = dyn_cast<LoadInst>(Use))
4072 if (!LI->isVolatile())
4073 return LI->getPointerAddressSpace() == 0;
4075 // Store to null is undefined.
4076 if (StoreInst *SI = dyn_cast<StoreInst>(Use))
4077 if (!SI->isVolatile())
4078 return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I;
4083 /// If BB has an incoming value that will always trigger undefined behavior
4084 /// (eg. null pointer dereference), remove the branch leading here.
4085 static bool removeUndefIntroducingPredecessor(BasicBlock *BB) {
4086 for (BasicBlock::iterator i = BB->begin();
4087 PHINode *PHI = dyn_cast<PHINode>(i); ++i)
4088 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
4089 if (passingValueIsAlwaysUndefined(PHI->getIncomingValue(i), PHI)) {
4090 TerminatorInst *T = PHI->getIncomingBlock(i)->getTerminator();
4091 IRBuilder<> Builder(T);
4092 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
4093 BB->removePredecessor(PHI->getIncomingBlock(i));
4094 // Turn uncoditional branches into unreachables and remove the dead
4095 // destination from conditional branches.
4096 if (BI->isUnconditional())
4097 Builder.CreateUnreachable();
4099 Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1) :
4100 BI->getSuccessor(0));
4101 BI->eraseFromParent();
4104 // TODO: SwitchInst.
4110 bool SimplifyCFGOpt::run(BasicBlock *BB) {
4111 bool Changed = false;
4113 assert(BB && BB->getParent() && "Block not embedded in function!");
4114 assert(BB->getTerminator() && "Degenerate basic block encountered!");
4116 // Remove basic blocks that have no predecessors (except the entry block)...
4117 // or that just have themself as a predecessor. These are unreachable.
4118 if ((pred_begin(BB) == pred_end(BB) &&
4119 BB != &BB->getParent()->getEntryBlock()) ||
4120 BB->getSinglePredecessor() == BB) {
4121 DEBUG(dbgs() << "Removing BB: \n" << *BB);
4122 DeleteDeadBlock(BB);
4126 // Check to see if we can constant propagate this terminator instruction
4128 Changed |= ConstantFoldTerminator(BB, true);
4130 // Check for and eliminate duplicate PHI nodes in this block.
4131 Changed |= EliminateDuplicatePHINodes(BB);
4133 // Check for and remove branches that will always cause undefined behavior.
4134 Changed |= removeUndefIntroducingPredecessor(BB);
4136 // Merge basic blocks into their predecessor if there is only one distinct
4137 // pred, and if there is only one distinct successor of the predecessor, and
4138 // if there are no PHI nodes.
4140 if (MergeBlockIntoPredecessor(BB))
4143 IRBuilder<> Builder(BB);
4145 // If there is a trivial two-entry PHI node in this basic block, and we can
4146 // eliminate it, do so now.
4147 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
4148 if (PN->getNumIncomingValues() == 2)
4149 Changed |= FoldTwoEntryPHINode(PN, TD);
4151 Builder.SetInsertPoint(BB->getTerminator());
4152 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
4153 if (BI->isUnconditional()) {
4154 if (SimplifyUncondBranch(BI, Builder)) return true;
4156 if (SimplifyCondBranch(BI, Builder)) return true;
4158 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
4159 if (SimplifyReturn(RI, Builder)) return true;
4160 } else if (ResumeInst *RI = dyn_cast<ResumeInst>(BB->getTerminator())) {
4161 if (SimplifyResume(RI, Builder)) return true;
4162 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
4163 if (SimplifySwitch(SI, Builder)) return true;
4164 } else if (UnreachableInst *UI =
4165 dyn_cast<UnreachableInst>(BB->getTerminator())) {
4166 if (SimplifyUnreachable(UI)) return true;
4167 } else if (IndirectBrInst *IBI =
4168 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
4169 if (SimplifyIndirectBr(IBI)) return true;
4175 /// SimplifyCFG - This function is used to do simplification of a CFG. For
4176 /// example, it adjusts branches to branches to eliminate the extra hop, it
4177 /// eliminates unreachable basic blocks, and does other "peephole" optimization
4178 /// of the CFG. It returns true if a modification was made.
4180 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetTransformInfo &TTI,
4181 const DataLayout *TD) {
4182 return SimplifyCFGOpt(TTI, TD).run(BB);