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 /// ComputeSpeculuationCost - 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->getPredicate() == ICmpInst::ICMP_EQ ||
537 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
538 GetConstantInt(ICI->getOperand(1), TD))
539 CV = ICI->getOperand(0);
541 // Unwrap any lossless ptrtoint cast.
542 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
543 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
544 CV = PTII->getOperand(0);
548 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
549 /// decode all of the 'cases' that it represents and return the 'default' block.
550 BasicBlock *SimplifyCFGOpt::
551 GetValueEqualityComparisonCases(TerminatorInst *TI,
552 std::vector<ValueEqualityComparisonCase>
554 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
555 Cases.reserve(SI->getNumCases());
556 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i)
557 Cases.push_back(ValueEqualityComparisonCase(i.getCaseValue(),
558 i.getCaseSuccessor()));
559 return SI->getDefaultDest();
562 BranchInst *BI = cast<BranchInst>(TI);
563 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
564 BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE);
565 Cases.push_back(ValueEqualityComparisonCase(GetConstantInt(ICI->getOperand(1),
568 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
572 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
573 /// in the list that match the specified block.
574 static void EliminateBlockCases(BasicBlock *BB,
575 std::vector<ValueEqualityComparisonCase> &Cases) {
576 Cases.erase(std::remove(Cases.begin(), Cases.end(), BB), Cases.end());
579 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
582 ValuesOverlap(std::vector<ValueEqualityComparisonCase> &C1,
583 std::vector<ValueEqualityComparisonCase > &C2) {
584 std::vector<ValueEqualityComparisonCase> *V1 = &C1, *V2 = &C2;
586 // Make V1 be smaller than V2.
587 if (V1->size() > V2->size())
590 if (V1->size() == 0) return false;
591 if (V1->size() == 1) {
593 ConstantInt *TheVal = (*V1)[0].Value;
594 for (unsigned i = 0, e = V2->size(); i != e; ++i)
595 if (TheVal == (*V2)[i].Value)
599 // Otherwise, just sort both lists and compare element by element.
600 array_pod_sort(V1->begin(), V1->end());
601 array_pod_sort(V2->begin(), V2->end());
602 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
603 while (i1 != e1 && i2 != e2) {
604 if ((*V1)[i1].Value == (*V2)[i2].Value)
606 if ((*V1)[i1].Value < (*V2)[i2].Value)
614 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
615 /// terminator instruction and its block is known to only have a single
616 /// predecessor block, check to see if that predecessor is also a value
617 /// comparison with the same value, and if that comparison determines the
618 /// outcome of this comparison. If so, simplify TI. This does a very limited
619 /// form of jump threading.
620 bool SimplifyCFGOpt::
621 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
623 IRBuilder<> &Builder) {
624 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
625 if (!PredVal) return false; // Not a value comparison in predecessor.
627 Value *ThisVal = isValueEqualityComparison(TI);
628 assert(ThisVal && "This isn't a value comparison!!");
629 if (ThisVal != PredVal) return false; // Different predicates.
631 // TODO: Preserve branch weight metadata, similarly to how
632 // FoldValueComparisonIntoPredecessors preserves it.
634 // Find out information about when control will move from Pred to TI's block.
635 std::vector<ValueEqualityComparisonCase> PredCases;
636 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
638 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
640 // Find information about how control leaves this block.
641 std::vector<ValueEqualityComparisonCase> ThisCases;
642 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
643 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
645 // If TI's block is the default block from Pred's comparison, potentially
646 // simplify TI based on this knowledge.
647 if (PredDef == TI->getParent()) {
648 // If we are here, we know that the value is none of those cases listed in
649 // PredCases. If there are any cases in ThisCases that are in PredCases, we
651 if (!ValuesOverlap(PredCases, ThisCases))
654 if (isa<BranchInst>(TI)) {
655 // Okay, one of the successors of this condbr is dead. Convert it to a
657 assert(ThisCases.size() == 1 && "Branch can only have one case!");
658 // Insert the new branch.
659 Instruction *NI = Builder.CreateBr(ThisDef);
662 // Remove PHI node entries for the dead edge.
663 ThisCases[0].Dest->removePredecessor(TI->getParent());
665 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
666 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
668 EraseTerminatorInstAndDCECond(TI);
672 SwitchInst *SI = cast<SwitchInst>(TI);
673 // Okay, TI has cases that are statically dead, prune them away.
674 SmallPtrSet<Constant*, 16> DeadCases;
675 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
676 DeadCases.insert(PredCases[i].Value);
678 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
679 << "Through successor TI: " << *TI);
681 // Collect branch weights into a vector.
682 SmallVector<uint32_t, 8> Weights;
683 MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
684 bool HasWeight = MD && (MD->getNumOperands() == 2 + SI->getNumCases());
686 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
688 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(MD_i));
690 Weights.push_back(CI->getValue().getZExtValue());
692 for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) {
694 if (DeadCases.count(i.getCaseValue())) {
696 std::swap(Weights[i.getCaseIndex()+1], Weights.back());
699 i.getCaseSuccessor()->removePredecessor(TI->getParent());
703 if (HasWeight && Weights.size() >= 2)
704 SI->setMetadata(LLVMContext::MD_prof,
705 MDBuilder(SI->getParent()->getContext()).
706 createBranchWeights(Weights));
708 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
712 // Otherwise, TI's block must correspond to some matched value. Find out
713 // which value (or set of values) this is.
714 ConstantInt *TIV = 0;
715 BasicBlock *TIBB = TI->getParent();
716 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
717 if (PredCases[i].Dest == TIBB) {
719 return false; // Cannot handle multiple values coming to this block.
720 TIV = PredCases[i].Value;
722 assert(TIV && "No edge from pred to succ?");
724 // Okay, we found the one constant that our value can be if we get into TI's
725 // BB. Find out which successor will unconditionally be branched to.
726 BasicBlock *TheRealDest = 0;
727 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
728 if (ThisCases[i].Value == TIV) {
729 TheRealDest = ThisCases[i].Dest;
733 // If not handled by any explicit cases, it is handled by the default case.
734 if (TheRealDest == 0) TheRealDest = ThisDef;
736 // Remove PHI node entries for dead edges.
737 BasicBlock *CheckEdge = TheRealDest;
738 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
739 if (*SI != CheckEdge)
740 (*SI)->removePredecessor(TIBB);
744 // Insert the new branch.
745 Instruction *NI = Builder.CreateBr(TheRealDest);
748 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
749 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
751 EraseTerminatorInstAndDCECond(TI);
756 /// ConstantIntOrdering - This class implements a stable ordering of constant
757 /// integers that does not depend on their address. This is important for
758 /// applications that sort ConstantInt's to ensure uniqueness.
759 struct ConstantIntOrdering {
760 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
761 return LHS->getValue().ult(RHS->getValue());
766 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
767 const ConstantInt *LHS = *(const ConstantInt*const*)P1;
768 const ConstantInt *RHS = *(const ConstantInt*const*)P2;
769 if (LHS->getValue().ult(RHS->getValue()))
771 if (LHS->getValue() == RHS->getValue())
776 static inline bool HasBranchWeights(const Instruction* I) {
777 MDNode* ProfMD = I->getMetadata(LLVMContext::MD_prof);
778 if (ProfMD && ProfMD->getOperand(0))
779 if (MDString* MDS = dyn_cast<MDString>(ProfMD->getOperand(0)))
780 return MDS->getString().equals("branch_weights");
785 /// Get Weights of a given TerminatorInst, the default weight is at the front
786 /// of the vector. If TI is a conditional eq, we need to swap the branch-weight
788 static void GetBranchWeights(TerminatorInst *TI,
789 SmallVectorImpl<uint64_t> &Weights) {
790 MDNode* MD = TI->getMetadata(LLVMContext::MD_prof);
792 for (unsigned i = 1, e = MD->getNumOperands(); i < e; ++i) {
793 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(i));
795 Weights.push_back(CI->getValue().getZExtValue());
798 // If TI is a conditional eq, the default case is the false case,
799 // and the corresponding branch-weight data is at index 2. We swap the
800 // default weight to be the first entry.
801 if (BranchInst* BI = dyn_cast<BranchInst>(TI)) {
802 assert(Weights.size() == 2);
803 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
804 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
805 std::swap(Weights.front(), Weights.back());
809 /// Sees if any of the weights are too big for a uint32_t, and halves all the
810 /// weights if any are.
811 static void FitWeights(MutableArrayRef<uint64_t> Weights) {
813 for (unsigned i = 0; i < Weights.size(); ++i)
814 if (Weights[i] > UINT_MAX) {
822 for (unsigned i = 0; i < Weights.size(); ++i)
826 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
827 /// equality comparison instruction (either a switch or a branch on "X == c").
828 /// See if any of the predecessors of the terminator block are value comparisons
829 /// on the same value. If so, and if safe to do so, fold them together.
830 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
831 IRBuilder<> &Builder) {
832 BasicBlock *BB = TI->getParent();
833 Value *CV = isValueEqualityComparison(TI); // CondVal
834 assert(CV && "Not a comparison?");
835 bool Changed = false;
837 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
838 while (!Preds.empty()) {
839 BasicBlock *Pred = Preds.pop_back_val();
841 // See if the predecessor is a comparison with the same value.
842 TerminatorInst *PTI = Pred->getTerminator();
843 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
845 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
846 // Figure out which 'cases' to copy from SI to PSI.
847 std::vector<ValueEqualityComparisonCase> BBCases;
848 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
850 std::vector<ValueEqualityComparisonCase> PredCases;
851 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
853 // Based on whether the default edge from PTI goes to BB or not, fill in
854 // PredCases and PredDefault with the new switch cases we would like to
856 SmallVector<BasicBlock*, 8> NewSuccessors;
858 // Update the branch weight metadata along the way
859 SmallVector<uint64_t, 8> Weights;
860 bool PredHasWeights = HasBranchWeights(PTI);
861 bool SuccHasWeights = HasBranchWeights(TI);
863 if (PredHasWeights) {
864 GetBranchWeights(PTI, Weights);
865 // branch-weight metadata is inconsistent here.
866 if (Weights.size() != 1 + PredCases.size())
867 PredHasWeights = SuccHasWeights = false;
868 } else if (SuccHasWeights)
869 // If there are no predecessor weights but there are successor weights,
870 // populate Weights with 1, which will later be scaled to the sum of
871 // successor's weights
872 Weights.assign(1 + PredCases.size(), 1);
874 SmallVector<uint64_t, 8> SuccWeights;
875 if (SuccHasWeights) {
876 GetBranchWeights(TI, SuccWeights);
877 // branch-weight metadata is inconsistent here.
878 if (SuccWeights.size() != 1 + BBCases.size())
879 PredHasWeights = SuccHasWeights = false;
880 } else if (PredHasWeights)
881 SuccWeights.assign(1 + BBCases.size(), 1);
883 if (PredDefault == BB) {
884 // If this is the default destination from PTI, only the edges in TI
885 // that don't occur in PTI, or that branch to BB will be activated.
886 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
887 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
888 if (PredCases[i].Dest != BB)
889 PTIHandled.insert(PredCases[i].Value);
891 // The default destination is BB, we don't need explicit targets.
892 std::swap(PredCases[i], PredCases.back());
894 if (PredHasWeights || SuccHasWeights) {
895 // Increase weight for the default case.
896 Weights[0] += Weights[i+1];
897 std::swap(Weights[i+1], Weights.back());
901 PredCases.pop_back();
905 // Reconstruct the new switch statement we will be building.
906 if (PredDefault != BBDefault) {
907 PredDefault->removePredecessor(Pred);
908 PredDefault = BBDefault;
909 NewSuccessors.push_back(BBDefault);
912 unsigned CasesFromPred = Weights.size();
913 uint64_t ValidTotalSuccWeight = 0;
914 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
915 if (!PTIHandled.count(BBCases[i].Value) &&
916 BBCases[i].Dest != BBDefault) {
917 PredCases.push_back(BBCases[i]);
918 NewSuccessors.push_back(BBCases[i].Dest);
919 if (SuccHasWeights || PredHasWeights) {
920 // The default weight is at index 0, so weight for the ith case
921 // should be at index i+1. Scale the cases from successor by
922 // PredDefaultWeight (Weights[0]).
923 Weights.push_back(Weights[0] * SuccWeights[i+1]);
924 ValidTotalSuccWeight += SuccWeights[i+1];
928 if (SuccHasWeights || PredHasWeights) {
929 ValidTotalSuccWeight += SuccWeights[0];
930 // Scale the cases from predecessor by ValidTotalSuccWeight.
931 for (unsigned i = 1; i < CasesFromPred; ++i)
932 Weights[i] *= ValidTotalSuccWeight;
933 // Scale the default weight by SuccDefaultWeight (SuccWeights[0]).
934 Weights[0] *= SuccWeights[0];
937 // If this is not the default destination from PSI, only the edges
938 // in SI that occur in PSI with a destination of BB will be
940 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
941 std::map<ConstantInt*, uint64_t> WeightsForHandled;
942 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
943 if (PredCases[i].Dest == BB) {
944 PTIHandled.insert(PredCases[i].Value);
946 if (PredHasWeights || SuccHasWeights) {
947 WeightsForHandled[PredCases[i].Value] = Weights[i+1];
948 std::swap(Weights[i+1], Weights.back());
952 std::swap(PredCases[i], PredCases.back());
953 PredCases.pop_back();
957 // Okay, now we know which constants were sent to BB from the
958 // predecessor. Figure out where they will all go now.
959 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
960 if (PTIHandled.count(BBCases[i].Value)) {
961 // If this is one we are capable of getting...
962 if (PredHasWeights || SuccHasWeights)
963 Weights.push_back(WeightsForHandled[BBCases[i].Value]);
964 PredCases.push_back(BBCases[i]);
965 NewSuccessors.push_back(BBCases[i].Dest);
966 PTIHandled.erase(BBCases[i].Value);// This constant is taken care of
969 // If there are any constants vectored to BB that TI doesn't handle,
970 // they must go to the default destination of TI.
971 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
973 E = PTIHandled.end(); I != E; ++I) {
974 if (PredHasWeights || SuccHasWeights)
975 Weights.push_back(WeightsForHandled[*I]);
976 PredCases.push_back(ValueEqualityComparisonCase(*I, BBDefault));
977 NewSuccessors.push_back(BBDefault);
981 // Okay, at this point, we know which new successor Pred will get. Make
982 // sure we update the number of entries in the PHI nodes for these
984 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
985 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
987 Builder.SetInsertPoint(PTI);
988 // Convert pointer to int before we switch.
989 if (CV->getType()->isPointerTy()) {
990 assert(TD && "Cannot switch on pointer without DataLayout");
991 CV = Builder.CreatePtrToInt(CV, TD->getIntPtrType(CV->getContext()),
995 // Now that the successors are updated, create the new Switch instruction.
996 SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault,
998 NewSI->setDebugLoc(PTI->getDebugLoc());
999 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
1000 NewSI->addCase(PredCases[i].Value, PredCases[i].Dest);
1002 if (PredHasWeights || SuccHasWeights) {
1003 // Halve the weights if any of them cannot fit in an uint32_t
1004 FitWeights(Weights);
1006 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
1008 NewSI->setMetadata(LLVMContext::MD_prof,
1009 MDBuilder(BB->getContext()).
1010 createBranchWeights(MDWeights));
1013 EraseTerminatorInstAndDCECond(PTI);
1015 // Okay, last check. If BB is still a successor of PSI, then we must
1016 // have an infinite loop case. If so, add an infinitely looping block
1017 // to handle the case to preserve the behavior of the code.
1018 BasicBlock *InfLoopBlock = 0;
1019 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
1020 if (NewSI->getSuccessor(i) == BB) {
1021 if (InfLoopBlock == 0) {
1022 // Insert it at the end of the function, because it's either code,
1023 // or it won't matter if it's hot. :)
1024 InfLoopBlock = BasicBlock::Create(BB->getContext(),
1025 "infloop", BB->getParent());
1026 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1028 NewSI->setSuccessor(i, InfLoopBlock);
1037 // isSafeToHoistInvoke - If we would need to insert a select that uses the
1038 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
1039 // would need to do this), we can't hoist the invoke, as there is nowhere
1040 // to put the select in this case.
1041 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
1042 Instruction *I1, Instruction *I2) {
1043 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
1045 for (BasicBlock::iterator BBI = SI->begin();
1046 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1047 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1048 Value *BB2V = PN->getIncomingValueForBlock(BB2);
1049 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
1057 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
1058 /// BB2, hoist any common code in the two blocks up into the branch block. The
1059 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
1060 static bool HoistThenElseCodeToIf(BranchInst *BI) {
1061 // This does very trivial matching, with limited scanning, to find identical
1062 // instructions in the two blocks. In particular, we don't want to get into
1063 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
1064 // such, we currently just scan for obviously identical instructions in an
1066 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
1067 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
1069 BasicBlock::iterator BB1_Itr = BB1->begin();
1070 BasicBlock::iterator BB2_Itr = BB2->begin();
1072 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
1073 // Skip debug info if it is not identical.
1074 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
1075 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
1076 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
1077 while (isa<DbgInfoIntrinsic>(I1))
1079 while (isa<DbgInfoIntrinsic>(I2))
1082 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
1083 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
1086 // If we get here, we can hoist at least one instruction.
1087 BasicBlock *BIParent = BI->getParent();
1090 // If we are hoisting the terminator instruction, don't move one (making a
1091 // broken BB), instead clone it, and remove BI.
1092 if (isa<TerminatorInst>(I1))
1093 goto HoistTerminator;
1095 // For a normal instruction, we just move one to right before the branch,
1096 // then replace all uses of the other with the first. Finally, we remove
1097 // the now redundant second instruction.
1098 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
1099 if (!I2->use_empty())
1100 I2->replaceAllUsesWith(I1);
1101 I1->intersectOptionalDataWith(I2);
1102 I2->eraseFromParent();
1106 // Skip debug info if it is not identical.
1107 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
1108 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
1109 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
1110 while (isa<DbgInfoIntrinsic>(I1))
1112 while (isa<DbgInfoIntrinsic>(I2))
1115 } while (I1->isIdenticalToWhenDefined(I2));
1120 // It may not be possible to hoist an invoke.
1121 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
1124 // Okay, it is safe to hoist the terminator.
1125 Instruction *NT = I1->clone();
1126 BIParent->getInstList().insert(BI, NT);
1127 if (!NT->getType()->isVoidTy()) {
1128 I1->replaceAllUsesWith(NT);
1129 I2->replaceAllUsesWith(NT);
1133 IRBuilder<true, NoFolder> Builder(NT);
1134 // Hoisting one of the terminators from our successor is a great thing.
1135 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
1136 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
1137 // nodes, so we insert select instruction to compute the final result.
1138 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
1139 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
1141 for (BasicBlock::iterator BBI = SI->begin();
1142 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1143 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1144 Value *BB2V = PN->getIncomingValueForBlock(BB2);
1145 if (BB1V == BB2V) continue;
1147 // These values do not agree. Insert a select instruction before NT
1148 // that determines the right value.
1149 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
1151 SI = cast<SelectInst>
1152 (Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,
1153 BB1V->getName()+"."+BB2V->getName()));
1155 // Make the PHI node use the select for all incoming values for BB1/BB2
1156 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
1157 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
1158 PN->setIncomingValue(i, SI);
1162 // Update any PHI nodes in our new successors.
1163 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
1164 AddPredecessorToBlock(*SI, BIParent, BB1);
1166 EraseTerminatorInstAndDCECond(BI);
1170 /// SinkThenElseCodeToEnd - Given an unconditional branch that goes to BBEnd,
1171 /// check whether BBEnd has only two predecessors and the other predecessor
1172 /// ends with an unconditional branch. If it is true, sink any common code
1173 /// in the two predecessors to BBEnd.
1174 static bool SinkThenElseCodeToEnd(BranchInst *BI1) {
1175 assert(BI1->isUnconditional());
1176 BasicBlock *BB1 = BI1->getParent();
1177 BasicBlock *BBEnd = BI1->getSuccessor(0);
1179 // Check that BBEnd has two predecessors and the other predecessor ends with
1180 // an unconditional branch.
1181 pred_iterator PI = pred_begin(BBEnd), PE = pred_end(BBEnd);
1182 BasicBlock *Pred0 = *PI++;
1183 if (PI == PE) // Only one predecessor.
1185 BasicBlock *Pred1 = *PI++;
1186 if (PI != PE) // More than two predecessors.
1188 BasicBlock *BB2 = (Pred0 == BB1) ? Pred1 : Pred0;
1189 BranchInst *BI2 = dyn_cast<BranchInst>(BB2->getTerminator());
1190 if (!BI2 || !BI2->isUnconditional())
1193 // Gather the PHI nodes in BBEnd.
1194 std::map<Value*, std::pair<Value*, PHINode*> > MapValueFromBB1ToBB2;
1195 Instruction *FirstNonPhiInBBEnd = 0;
1196 for (BasicBlock::iterator I = BBEnd->begin(), E = BBEnd->end();
1198 if (PHINode *PN = dyn_cast<PHINode>(I)) {
1199 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1200 Value *BB2V = PN->getIncomingValueForBlock(BB2);
1201 MapValueFromBB1ToBB2[BB1V] = std::make_pair(BB2V, PN);
1203 FirstNonPhiInBBEnd = &*I;
1207 if (!FirstNonPhiInBBEnd)
1211 // This does very trivial matching, with limited scanning, to find identical
1212 // instructions in the two blocks. We scan backward for obviously identical
1213 // instructions in an identical order.
1214 BasicBlock::InstListType::reverse_iterator RI1 = BB1->getInstList().rbegin(),
1215 RE1 = BB1->getInstList().rend(), RI2 = BB2->getInstList().rbegin(),
1216 RE2 = BB2->getInstList().rend();
1218 while (RI1 != RE1 && isa<DbgInfoIntrinsic>(&*RI1)) ++RI1;
1221 while (RI2 != RE2 && isa<DbgInfoIntrinsic>(&*RI2)) ++RI2;
1224 // Skip the unconditional branches.
1228 bool Changed = false;
1229 while (RI1 != RE1 && RI2 != RE2) {
1231 while (RI1 != RE1 && isa<DbgInfoIntrinsic>(&*RI1)) ++RI1;
1234 while (RI2 != RE2 && isa<DbgInfoIntrinsic>(&*RI2)) ++RI2;
1238 Instruction *I1 = &*RI1, *I2 = &*RI2;
1239 // I1 and I2 should have a single use in the same PHI node, and they
1240 // perform the same operation.
1241 // Cannot move control-flow-involving, volatile loads, vaarg, etc.
1242 if (isa<PHINode>(I1) || isa<PHINode>(I2) ||
1243 isa<TerminatorInst>(I1) || isa<TerminatorInst>(I2) ||
1244 isa<LandingPadInst>(I1) || isa<LandingPadInst>(I2) ||
1245 isa<AllocaInst>(I1) || isa<AllocaInst>(I2) ||
1246 I1->mayHaveSideEffects() || I2->mayHaveSideEffects() ||
1247 I1->mayReadOrWriteMemory() || I2->mayReadOrWriteMemory() ||
1248 !I1->hasOneUse() || !I2->hasOneUse() ||
1249 MapValueFromBB1ToBB2.find(I1) == MapValueFromBB1ToBB2.end() ||
1250 MapValueFromBB1ToBB2[I1].first != I2)
1253 // Check whether we should swap the operands of ICmpInst.
1254 ICmpInst *ICmp1 = dyn_cast<ICmpInst>(I1), *ICmp2 = dyn_cast<ICmpInst>(I2);
1255 bool SwapOpnds = false;
1256 if (ICmp1 && ICmp2 &&
1257 ICmp1->getOperand(0) != ICmp2->getOperand(0) &&
1258 ICmp1->getOperand(1) != ICmp2->getOperand(1) &&
1259 (ICmp1->getOperand(0) == ICmp2->getOperand(1) ||
1260 ICmp1->getOperand(1) == ICmp2->getOperand(0))) {
1261 ICmp2->swapOperands();
1264 if (!I1->isSameOperationAs(I2)) {
1266 ICmp2->swapOperands();
1270 // The operands should be either the same or they need to be generated
1271 // with a PHI node after sinking. We only handle the case where there is
1272 // a single pair of different operands.
1273 Value *DifferentOp1 = 0, *DifferentOp2 = 0;
1274 unsigned Op1Idx = 0;
1275 for (unsigned I = 0, E = I1->getNumOperands(); I != E; ++I) {
1276 if (I1->getOperand(I) == I2->getOperand(I))
1278 // Early exit if we have more-than one pair of different operands or
1279 // the different operand is already in MapValueFromBB1ToBB2.
1280 // Early exit if we need a PHI node to replace a constant.
1282 MapValueFromBB1ToBB2.find(I1->getOperand(I)) !=
1283 MapValueFromBB1ToBB2.end() ||
1284 isa<Constant>(I1->getOperand(I)) ||
1285 isa<Constant>(I2->getOperand(I))) {
1286 // If we can't sink the instructions, undo the swapping.
1288 ICmp2->swapOperands();
1291 DifferentOp1 = I1->getOperand(I);
1293 DifferentOp2 = I2->getOperand(I);
1296 // We insert the pair of different operands to MapValueFromBB1ToBB2 and
1297 // remove (I1, I2) from MapValueFromBB1ToBB2.
1299 PHINode *NewPN = PHINode::Create(DifferentOp1->getType(), 2,
1300 DifferentOp1->getName() + ".sink",
1302 MapValueFromBB1ToBB2[DifferentOp1] = std::make_pair(DifferentOp2, NewPN);
1303 // I1 should use NewPN instead of DifferentOp1.
1304 I1->setOperand(Op1Idx, NewPN);
1305 NewPN->addIncoming(DifferentOp1, BB1);
1306 NewPN->addIncoming(DifferentOp2, BB2);
1307 DEBUG(dbgs() << "Create PHI node " << *NewPN << "\n";);
1309 PHINode *OldPN = MapValueFromBB1ToBB2[I1].second;
1310 MapValueFromBB1ToBB2.erase(I1);
1312 DEBUG(dbgs() << "SINK common instructions " << *I1 << "\n";);
1313 DEBUG(dbgs() << " " << *I2 << "\n";);
1314 // We need to update RE1 and RE2 if we are going to sink the first
1315 // instruction in the basic block down.
1316 bool UpdateRE1 = (I1 == BB1->begin()), UpdateRE2 = (I2 == BB2->begin());
1317 // Sink the instruction.
1318 BBEnd->getInstList().splice(FirstNonPhiInBBEnd, BB1->getInstList(), I1);
1319 if (!OldPN->use_empty())
1320 OldPN->replaceAllUsesWith(I1);
1321 OldPN->eraseFromParent();
1323 if (!I2->use_empty())
1324 I2->replaceAllUsesWith(I1);
1325 I1->intersectOptionalDataWith(I2);
1326 I2->eraseFromParent();
1329 RE1 = BB1->getInstList().rend();
1331 RE2 = BB2->getInstList().rend();
1332 FirstNonPhiInBBEnd = I1;
1339 /// \brief Determine if we can hoist sink a sole store instruction out of a
1340 /// conditional block.
1342 /// We are looking for code like the following:
1344 /// store i32 %add, i32* %arrayidx2
1345 /// ... // No other stores or function calls (we could be calling a memory
1346 /// ... // function).
1347 /// %cmp = icmp ult %x, %y
1348 /// br i1 %cmp, label %EndBB, label %ThenBB
1350 /// store i32 %add5, i32* %arrayidx2
1354 /// We are going to transform this into:
1356 /// store i32 %add, i32* %arrayidx2
1358 /// %cmp = icmp ult %x, %y
1359 /// %add.add5 = select i1 %cmp, i32 %add, %add5
1360 /// store i32 %add.add5, i32* %arrayidx2
1363 /// \return The pointer to the value of the previous store if the store can be
1364 /// hoisted into the predecessor block. 0 otherwise.
1365 static Value *isSafeToSpeculateStore(Instruction *I, BasicBlock *BrBB,
1366 BasicBlock *StoreBB, BasicBlock *EndBB) {
1367 StoreInst *StoreToHoist = dyn_cast<StoreInst>(I);
1371 // Volatile or atomic.
1372 if (!StoreToHoist->isSimple())
1375 Value *StorePtr = StoreToHoist->getPointerOperand();
1377 // Look for a store to the same pointer in BrBB.
1378 unsigned MaxNumInstToLookAt = 10;
1379 for (BasicBlock::reverse_iterator RI = BrBB->rbegin(),
1380 RE = BrBB->rend(); RI != RE && (--MaxNumInstToLookAt); ++RI) {
1381 Instruction *CurI = &*RI;
1383 // Could be calling an instruction that effects memory like free().
1384 if (CurI->mayHaveSideEffects() && !isa<StoreInst>(CurI))
1387 StoreInst *SI = dyn_cast<StoreInst>(CurI);
1388 // Found the previous store make sure it stores to the same location.
1389 if (SI && SI->getPointerOperand() == StorePtr)
1390 // Found the previous store, return its value operand.
1391 return SI->getValueOperand();
1393 return 0; // Unknown store.
1399 /// \brief Speculate a conditional basic block flattening the CFG.
1401 /// Note that this is a very risky transform currently. Speculating
1402 /// instructions like this is most often not desirable. Instead, there is an MI
1403 /// pass which can do it with full awareness of the resource constraints.
1404 /// However, some cases are "obvious" and we should do directly. An example of
1405 /// this is speculating a single, reasonably cheap instruction.
1407 /// There is only one distinct advantage to flattening the CFG at the IR level:
1408 /// it makes very common but simplistic optimizations such as are common in
1409 /// instcombine and the DAG combiner more powerful by removing CFG edges and
1410 /// modeling their effects with easier to reason about SSA value graphs.
1413 /// An illustration of this transform is turning this IR:
1416 /// %cmp = icmp ult %x, %y
1417 /// br i1 %cmp, label %EndBB, label %ThenBB
1419 /// %sub = sub %x, %y
1422 /// %phi = phi [ %sub, %ThenBB ], [ 0, %EndBB ]
1429 /// %cmp = icmp ult %x, %y
1430 /// %sub = sub %x, %y
1431 /// %cond = select i1 %cmp, 0, %sub
1435 /// \returns true if the conditional block is removed.
1436 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB) {
1437 // Be conservative for now. FP select instruction can often be expensive.
1438 Value *BrCond = BI->getCondition();
1439 if (isa<FCmpInst>(BrCond))
1442 BasicBlock *BB = BI->getParent();
1443 BasicBlock *EndBB = ThenBB->getTerminator()->getSuccessor(0);
1445 // If ThenBB is actually on the false edge of the conditional branch, remember
1446 // to swap the select operands later.
1447 bool Invert = false;
1448 if (ThenBB != BI->getSuccessor(0)) {
1449 assert(ThenBB == BI->getSuccessor(1) && "No edge from 'if' block?");
1452 assert(EndBB == BI->getSuccessor(!Invert) && "No edge from to end block");
1454 // Keep a count of how many times instructions are used within CondBB when
1455 // they are candidates for sinking into CondBB. Specifically:
1456 // - They are defined in BB, and
1457 // - They have no side effects, and
1458 // - All of their uses are in CondBB.
1459 SmallDenseMap<Instruction *, unsigned, 4> SinkCandidateUseCounts;
1461 unsigned SpeculationCost = 0;
1462 Value *SpeculatedStoreValue = 0;
1463 StoreInst *SpeculatedStore = 0;
1464 for (BasicBlock::iterator BBI = ThenBB->begin(),
1465 BBE = llvm::prior(ThenBB->end());
1466 BBI != BBE; ++BBI) {
1467 Instruction *I = BBI;
1469 if (isa<DbgInfoIntrinsic>(I))
1472 // Only speculatively execution a single instruction (not counting the
1473 // terminator) for now.
1475 if (SpeculationCost > 1)
1478 // Don't hoist the instruction if it's unsafe or expensive.
1479 if (!isSafeToSpeculativelyExecute(I) &&
1480 !(HoistCondStores &&
1481 (SpeculatedStoreValue = isSafeToSpeculateStore(I, BB, ThenBB,
1484 if (!SpeculatedStoreValue &&
1485 ComputeSpeculationCost(I) > PHINodeFoldingThreshold)
1488 // Store the store speculation candidate.
1489 if (SpeculatedStoreValue)
1490 SpeculatedStore = cast<StoreInst>(I);
1492 // Do not hoist the instruction if any of its operands are defined but not
1493 // used in BB. The transformation will prevent the operand from
1494 // being sunk into the use block.
1495 for (User::op_iterator i = I->op_begin(), e = I->op_end();
1497 Instruction *OpI = dyn_cast<Instruction>(*i);
1498 if (!OpI || OpI->getParent() != BB ||
1499 OpI->mayHaveSideEffects())
1500 continue; // Not a candidate for sinking.
1502 ++SinkCandidateUseCounts[OpI];
1506 // Consider any sink candidates which are only used in CondBB as costs for
1507 // speculation. Note, while we iterate over a DenseMap here, we are summing
1508 // and so iteration order isn't significant.
1509 for (SmallDenseMap<Instruction *, unsigned, 4>::iterator I =
1510 SinkCandidateUseCounts.begin(), E = SinkCandidateUseCounts.end();
1512 if (I->first->getNumUses() == I->second) {
1514 if (SpeculationCost > 1)
1518 // Check that the PHI nodes can be converted to selects.
1519 bool HaveRewritablePHIs = false;
1520 for (BasicBlock::iterator I = EndBB->begin();
1521 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1522 Value *OrigV = PN->getIncomingValueForBlock(BB);
1523 Value *ThenV = PN->getIncomingValueForBlock(ThenBB);
1525 // Skip PHIs which are trivial.
1529 HaveRewritablePHIs = true;
1530 ConstantExpr *CE = dyn_cast<ConstantExpr>(ThenV);
1532 continue; // Known safe and cheap.
1534 if (!isSafeToSpeculativelyExecute(CE))
1536 if (ComputeSpeculationCost(CE) > PHINodeFoldingThreshold)
1539 // Account for the cost of an unfolded ConstantExpr which could end up
1540 // getting expanded into Instructions.
1541 // FIXME: This doesn't account for how many operations are combined in the
1542 // constant expression.
1544 if (SpeculationCost > 1)
1548 // If there are no PHIs to process, bail early. This helps ensure idempotence
1550 if (!HaveRewritablePHIs && !(HoistCondStores && SpeculatedStoreValue))
1553 // If we get here, we can hoist the instruction and if-convert.
1554 DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *ThenBB << "\n";);
1556 // Insert a select of the value of the speculated store.
1557 if (SpeculatedStoreValue) {
1558 IRBuilder<true, NoFolder> Builder(BI);
1559 Value *TrueV = SpeculatedStore->getValueOperand();
1560 Value *FalseV = SpeculatedStoreValue;
1562 std::swap(TrueV, FalseV);
1563 Value *S = Builder.CreateSelect(BrCond, TrueV, FalseV, TrueV->getName() +
1564 "." + FalseV->getName());
1565 SpeculatedStore->setOperand(0, S);
1568 // Hoist the instructions.
1569 BB->getInstList().splice(BI, ThenBB->getInstList(), ThenBB->begin(),
1570 llvm::prior(ThenBB->end()));
1572 // Insert selects and rewrite the PHI operands.
1573 IRBuilder<true, NoFolder> Builder(BI);
1574 for (BasicBlock::iterator I = EndBB->begin();
1575 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1576 unsigned OrigI = PN->getBasicBlockIndex(BB);
1577 unsigned ThenI = PN->getBasicBlockIndex(ThenBB);
1578 Value *OrigV = PN->getIncomingValue(OrigI);
1579 Value *ThenV = PN->getIncomingValue(ThenI);
1581 // Skip PHIs which are trivial.
1585 // Create a select whose true value is the speculatively executed value and
1586 // false value is the preexisting value. Swap them if the branch
1587 // destinations were inverted.
1588 Value *TrueV = ThenV, *FalseV = OrigV;
1590 std::swap(TrueV, FalseV);
1591 Value *V = Builder.CreateSelect(BrCond, TrueV, FalseV,
1592 TrueV->getName() + "." + FalseV->getName());
1593 PN->setIncomingValue(OrigI, V);
1594 PN->setIncomingValue(ThenI, V);
1601 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1602 /// across this block.
1603 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1604 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1607 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1608 if (isa<DbgInfoIntrinsic>(BBI))
1610 if (Size > 10) return false; // Don't clone large BB's.
1613 // We can only support instructions that do not define values that are
1614 // live outside of the current basic block.
1615 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1617 Instruction *U = cast<Instruction>(*UI);
1618 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1621 // Looks ok, continue checking.
1627 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1628 /// that is defined in the same block as the branch and if any PHI entries are
1629 /// constants, thread edges corresponding to that entry to be branches to their
1630 /// ultimate destination.
1631 static bool FoldCondBranchOnPHI(BranchInst *BI, const DataLayout *TD) {
1632 BasicBlock *BB = BI->getParent();
1633 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1634 // NOTE: we currently cannot transform this case if the PHI node is used
1635 // outside of the block.
1636 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1639 // Degenerate case of a single entry PHI.
1640 if (PN->getNumIncomingValues() == 1) {
1641 FoldSingleEntryPHINodes(PN->getParent());
1645 // Now we know that this block has multiple preds and two succs.
1646 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1648 // Okay, this is a simple enough basic block. See if any phi values are
1650 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1651 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1652 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1654 // Okay, we now know that all edges from PredBB should be revectored to
1655 // branch to RealDest.
1656 BasicBlock *PredBB = PN->getIncomingBlock(i);
1657 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1659 if (RealDest == BB) continue; // Skip self loops.
1660 // Skip if the predecessor's terminator is an indirect branch.
1661 if (isa<IndirectBrInst>(PredBB->getTerminator())) continue;
1663 // The dest block might have PHI nodes, other predecessors and other
1664 // difficult cases. Instead of being smart about this, just insert a new
1665 // block that jumps to the destination block, effectively splitting
1666 // the edge we are about to create.
1667 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1668 RealDest->getName()+".critedge",
1669 RealDest->getParent(), RealDest);
1670 BranchInst::Create(RealDest, EdgeBB);
1672 // Update PHI nodes.
1673 AddPredecessorToBlock(RealDest, EdgeBB, BB);
1675 // BB may have instructions that are being threaded over. Clone these
1676 // instructions into EdgeBB. We know that there will be no uses of the
1677 // cloned instructions outside of EdgeBB.
1678 BasicBlock::iterator InsertPt = EdgeBB->begin();
1679 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1680 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1681 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1682 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1685 // Clone the instruction.
1686 Instruction *N = BBI->clone();
1687 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1689 // Update operands due to translation.
1690 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1692 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1693 if (PI != TranslateMap.end())
1697 // Check for trivial simplification.
1698 if (Value *V = SimplifyInstruction(N, TD)) {
1699 TranslateMap[BBI] = V;
1700 delete N; // Instruction folded away, don't need actual inst
1702 // Insert the new instruction into its new home.
1703 EdgeBB->getInstList().insert(InsertPt, N);
1704 if (!BBI->use_empty())
1705 TranslateMap[BBI] = N;
1709 // Loop over all of the edges from PredBB to BB, changing them to branch
1710 // to EdgeBB instead.
1711 TerminatorInst *PredBBTI = PredBB->getTerminator();
1712 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1713 if (PredBBTI->getSuccessor(i) == BB) {
1714 BB->removePredecessor(PredBB);
1715 PredBBTI->setSuccessor(i, EdgeBB);
1718 // Recurse, simplifying any other constants.
1719 return FoldCondBranchOnPHI(BI, TD) | true;
1725 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1726 /// PHI node, see if we can eliminate it.
1727 static bool FoldTwoEntryPHINode(PHINode *PN, const DataLayout *TD) {
1728 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1729 // statement", which has a very simple dominance structure. Basically, we
1730 // are trying to find the condition that is being branched on, which
1731 // subsequently causes this merge to happen. We really want control
1732 // dependence information for this check, but simplifycfg can't keep it up
1733 // to date, and this catches most of the cases we care about anyway.
1734 BasicBlock *BB = PN->getParent();
1735 BasicBlock *IfTrue, *IfFalse;
1736 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1738 // Don't bother if the branch will be constant folded trivially.
1739 isa<ConstantInt>(IfCond))
1742 // Okay, we found that we can merge this two-entry phi node into a select.
1743 // Doing so would require us to fold *all* two entry phi nodes in this block.
1744 // At some point this becomes non-profitable (particularly if the target
1745 // doesn't support cmov's). Only do this transformation if there are two or
1746 // fewer PHI nodes in this block.
1747 unsigned NumPhis = 0;
1748 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1752 // Loop over the PHI's seeing if we can promote them all to select
1753 // instructions. While we are at it, keep track of the instructions
1754 // that need to be moved to the dominating block.
1755 SmallPtrSet<Instruction*, 4> AggressiveInsts;
1756 unsigned MaxCostVal0 = PHINodeFoldingThreshold,
1757 MaxCostVal1 = PHINodeFoldingThreshold;
1759 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1760 PHINode *PN = cast<PHINode>(II++);
1761 if (Value *V = SimplifyInstruction(PN, TD)) {
1762 PN->replaceAllUsesWith(V);
1763 PN->eraseFromParent();
1767 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
1769 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
1774 // If we folded the first phi, PN dangles at this point. Refresh it. If
1775 // we ran out of PHIs then we simplified them all.
1776 PN = dyn_cast<PHINode>(BB->begin());
1777 if (PN == 0) return true;
1779 // Don't fold i1 branches on PHIs which contain binary operators. These can
1780 // often be turned into switches and other things.
1781 if (PN->getType()->isIntegerTy(1) &&
1782 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1783 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1784 isa<BinaryOperator>(IfCond)))
1787 // If we all PHI nodes are promotable, check to make sure that all
1788 // instructions in the predecessor blocks can be promoted as well. If
1789 // not, we won't be able to get rid of the control flow, so it's not
1790 // worth promoting to select instructions.
1791 BasicBlock *DomBlock = 0;
1792 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1793 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1794 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1797 DomBlock = *pred_begin(IfBlock1);
1798 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1799 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1800 // This is not an aggressive instruction that we can promote.
1801 // Because of this, we won't be able to get rid of the control
1802 // flow, so the xform is not worth it.
1807 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1810 DomBlock = *pred_begin(IfBlock2);
1811 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1812 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1813 // This is not an aggressive instruction that we can promote.
1814 // Because of this, we won't be able to get rid of the control
1815 // flow, so the xform is not worth it.
1820 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1821 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1823 // If we can still promote the PHI nodes after this gauntlet of tests,
1824 // do all of the PHI's now.
1825 Instruction *InsertPt = DomBlock->getTerminator();
1826 IRBuilder<true, NoFolder> Builder(InsertPt);
1828 // Move all 'aggressive' instructions, which are defined in the
1829 // conditional parts of the if's up to the dominating block.
1831 DomBlock->getInstList().splice(InsertPt,
1832 IfBlock1->getInstList(), IfBlock1->begin(),
1833 IfBlock1->getTerminator());
1835 DomBlock->getInstList().splice(InsertPt,
1836 IfBlock2->getInstList(), IfBlock2->begin(),
1837 IfBlock2->getTerminator());
1839 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1840 // Change the PHI node into a select instruction.
1841 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1842 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1845 cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, ""));
1846 PN->replaceAllUsesWith(NV);
1848 PN->eraseFromParent();
1851 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1852 // has been flattened. Change DomBlock to jump directly to our new block to
1853 // avoid other simplifycfg's kicking in on the diamond.
1854 TerminatorInst *OldTI = DomBlock->getTerminator();
1855 Builder.SetInsertPoint(OldTI);
1856 Builder.CreateBr(BB);
1857 OldTI->eraseFromParent();
1861 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1862 /// to two returning blocks, try to merge them together into one return,
1863 /// introducing a select if the return values disagree.
1864 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
1865 IRBuilder<> &Builder) {
1866 assert(BI->isConditional() && "Must be a conditional branch");
1867 BasicBlock *TrueSucc = BI->getSuccessor(0);
1868 BasicBlock *FalseSucc = BI->getSuccessor(1);
1869 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1870 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1872 // Check to ensure both blocks are empty (just a return) or optionally empty
1873 // with PHI nodes. If there are other instructions, merging would cause extra
1874 // computation on one path or the other.
1875 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1877 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1880 Builder.SetInsertPoint(BI);
1881 // Okay, we found a branch that is going to two return nodes. If
1882 // there is no return value for this function, just change the
1883 // branch into a return.
1884 if (FalseRet->getNumOperands() == 0) {
1885 TrueSucc->removePredecessor(BI->getParent());
1886 FalseSucc->removePredecessor(BI->getParent());
1887 Builder.CreateRetVoid();
1888 EraseTerminatorInstAndDCECond(BI);
1892 // Otherwise, figure out what the true and false return values are
1893 // so we can insert a new select instruction.
1894 Value *TrueValue = TrueRet->getReturnValue();
1895 Value *FalseValue = FalseRet->getReturnValue();
1897 // Unwrap any PHI nodes in the return blocks.
1898 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1899 if (TVPN->getParent() == TrueSucc)
1900 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1901 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1902 if (FVPN->getParent() == FalseSucc)
1903 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1905 // In order for this transformation to be safe, we must be able to
1906 // unconditionally execute both operands to the return. This is
1907 // normally the case, but we could have a potentially-trapping
1908 // constant expression that prevents this transformation from being
1910 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1913 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1917 // Okay, we collected all the mapped values and checked them for sanity, and
1918 // defined to really do this transformation. First, update the CFG.
1919 TrueSucc->removePredecessor(BI->getParent());
1920 FalseSucc->removePredecessor(BI->getParent());
1922 // Insert select instructions where needed.
1923 Value *BrCond = BI->getCondition();
1925 // Insert a select if the results differ.
1926 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1927 } else if (isa<UndefValue>(TrueValue)) {
1928 TrueValue = FalseValue;
1930 TrueValue = Builder.CreateSelect(BrCond, TrueValue,
1931 FalseValue, "retval");
1935 Value *RI = !TrueValue ?
1936 Builder.CreateRetVoid() : Builder.CreateRet(TrueValue);
1940 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1941 << "\n " << *BI << "NewRet = " << *RI
1942 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1944 EraseTerminatorInstAndDCECond(BI);
1949 /// ExtractBranchMetadata - Given a conditional BranchInstruction, retrieve the
1950 /// probabilities of the branch taking each edge. Fills in the two APInt
1951 /// parameters and return true, or returns false if no or invalid metadata was
1953 static bool ExtractBranchMetadata(BranchInst *BI,
1954 uint64_t &ProbTrue, uint64_t &ProbFalse) {
1955 assert(BI->isConditional() &&
1956 "Looking for probabilities on unconditional branch?");
1957 MDNode *ProfileData = BI->getMetadata(LLVMContext::MD_prof);
1958 if (!ProfileData || ProfileData->getNumOperands() != 3) return false;
1959 ConstantInt *CITrue = dyn_cast<ConstantInt>(ProfileData->getOperand(1));
1960 ConstantInt *CIFalse = dyn_cast<ConstantInt>(ProfileData->getOperand(2));
1961 if (!CITrue || !CIFalse) return false;
1962 ProbTrue = CITrue->getValue().getZExtValue();
1963 ProbFalse = CIFalse->getValue().getZExtValue();
1967 /// checkCSEInPredecessor - Return true if the given instruction is available
1968 /// in its predecessor block. If yes, the instruction will be removed.
1970 static bool checkCSEInPredecessor(Instruction *Inst, BasicBlock *PB) {
1971 if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst))
1973 for (BasicBlock::iterator I = PB->begin(), E = PB->end(); I != E; I++) {
1974 Instruction *PBI = &*I;
1975 // Check whether Inst and PBI generate the same value.
1976 if (Inst->isIdenticalTo(PBI)) {
1977 Inst->replaceAllUsesWith(PBI);
1978 Inst->eraseFromParent();
1985 /// FoldBranchToCommonDest - If this basic block is simple enough, and if a
1986 /// predecessor branches to us and one of our successors, fold the block into
1987 /// the predecessor and use logical operations to pick the right destination.
1988 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1989 BasicBlock *BB = BI->getParent();
1991 Instruction *Cond = 0;
1992 if (BI->isConditional())
1993 Cond = dyn_cast<Instruction>(BI->getCondition());
1995 // For unconditional branch, check for a simple CFG pattern, where
1996 // BB has a single predecessor and BB's successor is also its predecessor's
1997 // successor. If such pattern exisits, check for CSE between BB and its
1999 if (BasicBlock *PB = BB->getSinglePredecessor())
2000 if (BranchInst *PBI = dyn_cast<BranchInst>(PB->getTerminator()))
2001 if (PBI->isConditional() &&
2002 (BI->getSuccessor(0) == PBI->getSuccessor(0) ||
2003 BI->getSuccessor(0) == PBI->getSuccessor(1))) {
2004 for (BasicBlock::iterator I = BB->begin(), E = BB->end();
2006 Instruction *Curr = I++;
2007 if (isa<CmpInst>(Curr)) {
2011 // Quit if we can't remove this instruction.
2012 if (!checkCSEInPredecessor(Curr, PB))
2021 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
2022 Cond->getParent() != BB || !Cond->hasOneUse())
2025 // Only allow this if the condition is a simple instruction that can be
2026 // executed unconditionally. It must be in the same block as the branch, and
2027 // must be at the front of the block.
2028 BasicBlock::iterator FrontIt = BB->front();
2030 // Ignore dbg intrinsics.
2031 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
2033 // Allow a single instruction to be hoisted in addition to the compare
2034 // that feeds the branch. We later ensure that any values that _it_ uses
2035 // were also live in the predecessor, so that we don't unnecessarily create
2036 // register pressure or inhibit out-of-order execution.
2037 Instruction *BonusInst = 0;
2038 if (&*FrontIt != Cond &&
2039 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
2040 isSafeToSpeculativelyExecute(FrontIt)) {
2041 BonusInst = &*FrontIt;
2044 // Ignore dbg intrinsics.
2045 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
2048 // Only a single bonus inst is allowed.
2049 if (&*FrontIt != Cond)
2052 // Make sure the instruction after the condition is the cond branch.
2053 BasicBlock::iterator CondIt = Cond; ++CondIt;
2055 // Ingore dbg intrinsics.
2056 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
2061 // Cond is known to be a compare or binary operator. Check to make sure that
2062 // neither operand is a potentially-trapping constant expression.
2063 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
2066 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
2070 // Finally, don't infinitely unroll conditional loops.
2071 BasicBlock *TrueDest = BI->getSuccessor(0);
2072 BasicBlock *FalseDest = (BI->isConditional()) ? BI->getSuccessor(1) : 0;
2073 if (TrueDest == BB || FalseDest == BB)
2076 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2077 BasicBlock *PredBlock = *PI;
2078 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
2080 // Check that we have two conditional branches. If there is a PHI node in
2081 // the common successor, verify that the same value flows in from both
2083 SmallVector<PHINode*, 4> PHIs;
2084 if (PBI == 0 || PBI->isUnconditional() ||
2085 (BI->isConditional() &&
2086 !SafeToMergeTerminators(BI, PBI)) ||
2087 (!BI->isConditional() &&
2088 !isProfitableToFoldUnconditional(BI, PBI, Cond, PHIs)))
2091 // Determine if the two branches share a common destination.
2092 Instruction::BinaryOps Opc = Instruction::BinaryOpsEnd;
2093 bool InvertPredCond = false;
2095 if (BI->isConditional()) {
2096 if (PBI->getSuccessor(0) == TrueDest)
2097 Opc = Instruction::Or;
2098 else if (PBI->getSuccessor(1) == FalseDest)
2099 Opc = Instruction::And;
2100 else if (PBI->getSuccessor(0) == FalseDest)
2101 Opc = Instruction::And, InvertPredCond = true;
2102 else if (PBI->getSuccessor(1) == TrueDest)
2103 Opc = Instruction::Or, InvertPredCond = true;
2107 if (PBI->getSuccessor(0) != TrueDest && PBI->getSuccessor(1) != TrueDest)
2111 // Ensure that any values used in the bonus instruction are also used
2112 // by the terminator of the predecessor. This means that those values
2113 // must already have been resolved, so we won't be inhibiting the
2114 // out-of-order core by speculating them earlier.
2116 // Collect the values used by the bonus inst
2117 SmallPtrSet<Value*, 4> UsedValues;
2118 for (Instruction::op_iterator OI = BonusInst->op_begin(),
2119 OE = BonusInst->op_end(); OI != OE; ++OI) {
2121 if (!isa<Constant>(V))
2122 UsedValues.insert(V);
2125 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
2126 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
2128 // Walk up to four levels back up the use-def chain of the predecessor's
2129 // terminator to see if all those values were used. The choice of four
2130 // levels is arbitrary, to provide a compile-time-cost bound.
2131 while (!Worklist.empty()) {
2132 std::pair<Value*, unsigned> Pair = Worklist.back();
2133 Worklist.pop_back();
2135 if (Pair.second >= 4) continue;
2136 UsedValues.erase(Pair.first);
2137 if (UsedValues.empty()) break;
2139 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
2140 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
2142 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
2146 if (!UsedValues.empty()) return false;
2149 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
2150 IRBuilder<> Builder(PBI);
2152 // If we need to invert the condition in the pred block to match, do so now.
2153 if (InvertPredCond) {
2154 Value *NewCond = PBI->getCondition();
2156 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
2157 CmpInst *CI = cast<CmpInst>(NewCond);
2158 CI->setPredicate(CI->getInversePredicate());
2160 NewCond = Builder.CreateNot(NewCond,
2161 PBI->getCondition()->getName()+".not");
2164 PBI->setCondition(NewCond);
2165 PBI->swapSuccessors();
2168 // If we have a bonus inst, clone it into the predecessor block.
2169 Instruction *NewBonus = 0;
2171 NewBonus = BonusInst->clone();
2172 PredBlock->getInstList().insert(PBI, NewBonus);
2173 NewBonus->takeName(BonusInst);
2174 BonusInst->setName(BonusInst->getName()+".old");
2177 // Clone Cond into the predecessor basic block, and or/and the
2178 // two conditions together.
2179 Instruction *New = Cond->clone();
2180 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
2181 PredBlock->getInstList().insert(PBI, New);
2182 New->takeName(Cond);
2183 Cond->setName(New->getName()+".old");
2185 if (BI->isConditional()) {
2186 Instruction *NewCond =
2187 cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(),
2189 PBI->setCondition(NewCond);
2191 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
2192 bool PredHasWeights = ExtractBranchMetadata(PBI, PredTrueWeight,
2194 bool SuccHasWeights = ExtractBranchMetadata(BI, SuccTrueWeight,
2196 SmallVector<uint64_t, 8> NewWeights;
2198 if (PBI->getSuccessor(0) == BB) {
2199 if (PredHasWeights && SuccHasWeights) {
2200 // PBI: br i1 %x, BB, FalseDest
2201 // BI: br i1 %y, TrueDest, FalseDest
2202 //TrueWeight is TrueWeight for PBI * TrueWeight for BI.
2203 NewWeights.push_back(PredTrueWeight * SuccTrueWeight);
2204 //FalseWeight is FalseWeight for PBI * TotalWeight for BI +
2205 // TrueWeight for PBI * FalseWeight for BI.
2206 // We assume that total weights of a BranchInst can fit into 32 bits.
2207 // Therefore, we will not have overflow using 64-bit arithmetic.
2208 NewWeights.push_back(PredFalseWeight * (SuccFalseWeight +
2209 SuccTrueWeight) + PredTrueWeight * SuccFalseWeight);
2211 AddPredecessorToBlock(TrueDest, PredBlock, BB);
2212 PBI->setSuccessor(0, TrueDest);
2214 if (PBI->getSuccessor(1) == BB) {
2215 if (PredHasWeights && SuccHasWeights) {
2216 // PBI: br i1 %x, TrueDest, BB
2217 // BI: br i1 %y, TrueDest, FalseDest
2218 //TrueWeight is TrueWeight for PBI * TotalWeight for BI +
2219 // FalseWeight for PBI * TrueWeight for BI.
2220 NewWeights.push_back(PredTrueWeight * (SuccFalseWeight +
2221 SuccTrueWeight) + PredFalseWeight * SuccTrueWeight);
2222 //FalseWeight is FalseWeight for PBI * FalseWeight for BI.
2223 NewWeights.push_back(PredFalseWeight * SuccFalseWeight);
2225 AddPredecessorToBlock(FalseDest, PredBlock, BB);
2226 PBI->setSuccessor(1, FalseDest);
2228 if (NewWeights.size() == 2) {
2229 // Halve the weights if any of them cannot fit in an uint32_t
2230 FitWeights(NewWeights);
2232 SmallVector<uint32_t, 8> MDWeights(NewWeights.begin(),NewWeights.end());
2233 PBI->setMetadata(LLVMContext::MD_prof,
2234 MDBuilder(BI->getContext()).
2235 createBranchWeights(MDWeights));
2237 PBI->setMetadata(LLVMContext::MD_prof, NULL);
2239 // Update PHI nodes in the common successors.
2240 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
2241 ConstantInt *PBI_C = cast<ConstantInt>(
2242 PHIs[i]->getIncomingValueForBlock(PBI->getParent()));
2243 assert(PBI_C->getType()->isIntegerTy(1));
2244 Instruction *MergedCond = 0;
2245 if (PBI->getSuccessor(0) == TrueDest) {
2246 // Create (PBI_Cond and PBI_C) or (!PBI_Cond and BI_Value)
2247 // PBI_C is true: PBI_Cond or (!PBI_Cond and BI_Value)
2248 // is false: !PBI_Cond and BI_Value
2249 Instruction *NotCond =
2250 cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
2253 cast<Instruction>(Builder.CreateBinOp(Instruction::And,
2258 cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
2259 PBI->getCondition(), MergedCond,
2262 // Create (PBI_Cond and BI_Value) or (!PBI_Cond and PBI_C)
2263 // PBI_C is true: (PBI_Cond and BI_Value) or (!PBI_Cond)
2264 // is false: PBI_Cond and BI_Value
2266 cast<Instruction>(Builder.CreateBinOp(Instruction::And,
2267 PBI->getCondition(), New,
2269 if (PBI_C->isOne()) {
2270 Instruction *NotCond =
2271 cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
2274 cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
2275 NotCond, MergedCond,
2280 PHIs[i]->setIncomingValue(PHIs[i]->getBasicBlockIndex(PBI->getParent()),
2283 // Change PBI from Conditional to Unconditional.
2284 BranchInst *New_PBI = BranchInst::Create(TrueDest, PBI);
2285 EraseTerminatorInstAndDCECond(PBI);
2289 // TODO: If BB is reachable from all paths through PredBlock, then we
2290 // could replace PBI's branch probabilities with BI's.
2292 // Copy any debug value intrinsics into the end of PredBlock.
2293 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
2294 if (isa<DbgInfoIntrinsic>(*I))
2295 I->clone()->insertBefore(PBI);
2302 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
2303 /// predecessor of another block, this function tries to simplify it. We know
2304 /// that PBI and BI are both conditional branches, and BI is in one of the
2305 /// successor blocks of PBI - PBI branches to BI.
2306 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
2307 assert(PBI->isConditional() && BI->isConditional());
2308 BasicBlock *BB = BI->getParent();
2310 // If this block ends with a branch instruction, and if there is a
2311 // predecessor that ends on a branch of the same condition, make
2312 // this conditional branch redundant.
2313 if (PBI->getCondition() == BI->getCondition() &&
2314 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
2315 // Okay, the outcome of this conditional branch is statically
2316 // knowable. If this block had a single pred, handle specially.
2317 if (BB->getSinglePredecessor()) {
2318 // Turn this into a branch on constant.
2319 bool CondIsTrue = PBI->getSuccessor(0) == BB;
2320 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
2322 return true; // Nuke the branch on constant.
2325 // Otherwise, if there are multiple predecessors, insert a PHI that merges
2326 // in the constant and simplify the block result. Subsequent passes of
2327 // simplifycfg will thread the block.
2328 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
2329 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
2330 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
2331 std::distance(PB, PE),
2332 BI->getCondition()->getName() + ".pr",
2334 // Okay, we're going to insert the PHI node. Since PBI is not the only
2335 // predecessor, compute the PHI'd conditional value for all of the preds.
2336 // Any predecessor where the condition is not computable we keep symbolic.
2337 for (pred_iterator PI = PB; PI != PE; ++PI) {
2338 BasicBlock *P = *PI;
2339 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
2340 PBI != BI && PBI->isConditional() &&
2341 PBI->getCondition() == BI->getCondition() &&
2342 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
2343 bool CondIsTrue = PBI->getSuccessor(0) == BB;
2344 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
2347 NewPN->addIncoming(BI->getCondition(), P);
2351 BI->setCondition(NewPN);
2356 // If this is a conditional branch in an empty block, and if any
2357 // predecessors is a conditional branch to one of our destinations,
2358 // fold the conditions into logical ops and one cond br.
2359 BasicBlock::iterator BBI = BB->begin();
2360 // Ignore dbg intrinsics.
2361 while (isa<DbgInfoIntrinsic>(BBI))
2367 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
2372 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
2374 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
2375 PBIOp = 0, BIOp = 1;
2376 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
2377 PBIOp = 1, BIOp = 0;
2378 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
2383 // Check to make sure that the other destination of this branch
2384 // isn't BB itself. If so, this is an infinite loop that will
2385 // keep getting unwound.
2386 if (PBI->getSuccessor(PBIOp) == BB)
2389 // Do not perform this transformation if it would require
2390 // insertion of a large number of select instructions. For targets
2391 // without predication/cmovs, this is a big pessimization.
2392 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
2394 unsigned NumPhis = 0;
2395 for (BasicBlock::iterator II = CommonDest->begin();
2396 isa<PHINode>(II); ++II, ++NumPhis)
2397 if (NumPhis > 2) // Disable this xform.
2400 // Finally, if everything is ok, fold the branches to logical ops.
2401 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
2403 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
2404 << "AND: " << *BI->getParent());
2407 // If OtherDest *is* BB, then BB is a basic block with a single conditional
2408 // branch in it, where one edge (OtherDest) goes back to itself but the other
2409 // exits. We don't *know* that the program avoids the infinite loop
2410 // (even though that seems likely). If we do this xform naively, we'll end up
2411 // recursively unpeeling the loop. Since we know that (after the xform is
2412 // done) that the block *is* infinite if reached, we just make it an obviously
2413 // infinite loop with no cond branch.
2414 if (OtherDest == BB) {
2415 // Insert it at the end of the function, because it's either code,
2416 // or it won't matter if it's hot. :)
2417 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
2418 "infloop", BB->getParent());
2419 BranchInst::Create(InfLoopBlock, InfLoopBlock);
2420 OtherDest = InfLoopBlock;
2423 DEBUG(dbgs() << *PBI->getParent()->getParent());
2425 // BI may have other predecessors. Because of this, we leave
2426 // it alone, but modify PBI.
2428 // Make sure we get to CommonDest on True&True directions.
2429 Value *PBICond = PBI->getCondition();
2430 IRBuilder<true, NoFolder> Builder(PBI);
2432 PBICond = Builder.CreateNot(PBICond, PBICond->getName()+".not");
2434 Value *BICond = BI->getCondition();
2436 BICond = Builder.CreateNot(BICond, BICond->getName()+".not");
2438 // Merge the conditions.
2439 Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge");
2441 // Modify PBI to branch on the new condition to the new dests.
2442 PBI->setCondition(Cond);
2443 PBI->setSuccessor(0, CommonDest);
2444 PBI->setSuccessor(1, OtherDest);
2446 // Update branch weight for PBI.
2447 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
2448 bool PredHasWeights = ExtractBranchMetadata(PBI, PredTrueWeight,
2450 bool SuccHasWeights = ExtractBranchMetadata(BI, SuccTrueWeight,
2452 if (PredHasWeights && SuccHasWeights) {
2453 uint64_t PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
2454 uint64_t PredOther = PBIOp ?PredTrueWeight : PredFalseWeight;
2455 uint64_t SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
2456 uint64_t SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
2457 // The weight to CommonDest should be PredCommon * SuccTotal +
2458 // PredOther * SuccCommon.
2459 // The weight to OtherDest should be PredOther * SuccOther.
2460 SmallVector<uint64_t, 2> NewWeights;
2461 NewWeights.push_back(PredCommon * (SuccCommon + SuccOther) +
2462 PredOther * SuccCommon);
2463 NewWeights.push_back(PredOther * SuccOther);
2464 // Halve the weights if any of them cannot fit in an uint32_t
2465 FitWeights(NewWeights);
2467 SmallVector<uint32_t, 2> MDWeights(NewWeights.begin(),NewWeights.end());
2468 PBI->setMetadata(LLVMContext::MD_prof,
2469 MDBuilder(BI->getContext()).
2470 createBranchWeights(MDWeights));
2473 // OtherDest may have phi nodes. If so, add an entry from PBI's
2474 // block that are identical to the entries for BI's block.
2475 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
2477 // We know that the CommonDest already had an edge from PBI to
2478 // it. If it has PHIs though, the PHIs may have different
2479 // entries for BB and PBI's BB. If so, insert a select to make
2482 for (BasicBlock::iterator II = CommonDest->begin();
2483 (PN = dyn_cast<PHINode>(II)); ++II) {
2484 Value *BIV = PN->getIncomingValueForBlock(BB);
2485 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
2486 Value *PBIV = PN->getIncomingValue(PBBIdx);
2488 // Insert a select in PBI to pick the right value.
2489 Value *NV = cast<SelectInst>
2490 (Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName()+".mux"));
2491 PN->setIncomingValue(PBBIdx, NV);
2495 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
2496 DEBUG(dbgs() << *PBI->getParent()->getParent());
2498 // This basic block is probably dead. We know it has at least
2499 // one fewer predecessor.
2503 // SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
2504 // branch to TrueBB if Cond is true or to FalseBB if Cond is false.
2505 // Takes care of updating the successors and removing the old terminator.
2506 // Also makes sure not to introduce new successors by assuming that edges to
2507 // non-successor TrueBBs and FalseBBs aren't reachable.
2508 static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
2509 BasicBlock *TrueBB, BasicBlock *FalseBB,
2510 uint32_t TrueWeight,
2511 uint32_t FalseWeight){
2512 // Remove any superfluous successor edges from the CFG.
2513 // First, figure out which successors to preserve.
2514 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
2516 BasicBlock *KeepEdge1 = TrueBB;
2517 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
2519 // Then remove the rest.
2520 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
2521 BasicBlock *Succ = OldTerm->getSuccessor(I);
2522 // Make sure only to keep exactly one copy of each edge.
2523 if (Succ == KeepEdge1)
2525 else if (Succ == KeepEdge2)
2528 Succ->removePredecessor(OldTerm->getParent());
2531 IRBuilder<> Builder(OldTerm);
2532 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
2534 // Insert an appropriate new terminator.
2535 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
2536 if (TrueBB == FalseBB)
2537 // We were only looking for one successor, and it was present.
2538 // Create an unconditional branch to it.
2539 Builder.CreateBr(TrueBB);
2541 // We found both of the successors we were looking for.
2542 // Create a conditional branch sharing the condition of the select.
2543 BranchInst *NewBI = Builder.CreateCondBr(Cond, TrueBB, FalseBB);
2544 if (TrueWeight != FalseWeight)
2545 NewBI->setMetadata(LLVMContext::MD_prof,
2546 MDBuilder(OldTerm->getContext()).
2547 createBranchWeights(TrueWeight, FalseWeight));
2549 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
2550 // Neither of the selected blocks were successors, so this
2551 // terminator must be unreachable.
2552 new UnreachableInst(OldTerm->getContext(), OldTerm);
2554 // One of the selected values was a successor, but the other wasn't.
2555 // Insert an unconditional branch to the one that was found;
2556 // the edge to the one that wasn't must be unreachable.
2558 // Only TrueBB was found.
2559 Builder.CreateBr(TrueBB);
2561 // Only FalseBB was found.
2562 Builder.CreateBr(FalseBB);
2565 EraseTerminatorInstAndDCECond(OldTerm);
2569 // SimplifySwitchOnSelect - Replaces
2570 // (switch (select cond, X, Y)) on constant X, Y
2571 // with a branch - conditional if X and Y lead to distinct BBs,
2572 // unconditional otherwise.
2573 static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
2574 // Check for constant integer values in the select.
2575 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
2576 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
2577 if (!TrueVal || !FalseVal)
2580 // Find the relevant condition and destinations.
2581 Value *Condition = Select->getCondition();
2582 BasicBlock *TrueBB = SI->findCaseValue(TrueVal).getCaseSuccessor();
2583 BasicBlock *FalseBB = SI->findCaseValue(FalseVal).getCaseSuccessor();
2585 // Get weight for TrueBB and FalseBB.
2586 uint32_t TrueWeight = 0, FalseWeight = 0;
2587 SmallVector<uint64_t, 8> Weights;
2588 bool HasWeights = HasBranchWeights(SI);
2590 GetBranchWeights(SI, Weights);
2591 if (Weights.size() == 1 + SI->getNumCases()) {
2592 TrueWeight = (uint32_t)Weights[SI->findCaseValue(TrueVal).
2593 getSuccessorIndex()];
2594 FalseWeight = (uint32_t)Weights[SI->findCaseValue(FalseVal).
2595 getSuccessorIndex()];
2599 // Perform the actual simplification.
2600 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB,
2601 TrueWeight, FalseWeight);
2604 // SimplifyIndirectBrOnSelect - Replaces
2605 // (indirectbr (select cond, blockaddress(@fn, BlockA),
2606 // blockaddress(@fn, BlockB)))
2608 // (br cond, BlockA, BlockB).
2609 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
2610 // Check that both operands of the select are block addresses.
2611 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
2612 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
2616 // Extract the actual blocks.
2617 BasicBlock *TrueBB = TBA->getBasicBlock();
2618 BasicBlock *FalseBB = FBA->getBasicBlock();
2620 // Perform the actual simplification.
2621 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB,
2625 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
2626 /// instruction (a seteq/setne with a constant) as the only instruction in a
2627 /// block that ends with an uncond branch. We are looking for a very specific
2628 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
2629 /// this case, we merge the first two "or's of icmp" into a switch, but then the
2630 /// default value goes to an uncond block with a seteq in it, we get something
2633 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
2635 /// %tmp = icmp eq i8 %A, 92
2638 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
2640 /// We prefer to split the edge to 'end' so that there is a true/false entry to
2641 /// the PHI, merging the third icmp into the switch.
2642 static bool TryToSimplifyUncondBranchWithICmpInIt(
2643 ICmpInst *ICI, IRBuilder<> &Builder, const TargetTransformInfo &TTI,
2644 const DataLayout *TD) {
2645 BasicBlock *BB = ICI->getParent();
2647 // If the block has any PHIs in it or the icmp has multiple uses, it is too
2649 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
2651 Value *V = ICI->getOperand(0);
2652 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
2654 // The pattern we're looking for is where our only predecessor is a switch on
2655 // 'V' and this block is the default case for the switch. In this case we can
2656 // fold the compared value into the switch to simplify things.
2657 BasicBlock *Pred = BB->getSinglePredecessor();
2658 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
2660 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
2661 if (SI->getCondition() != V)
2664 // If BB is reachable on a non-default case, then we simply know the value of
2665 // V in this block. Substitute it and constant fold the icmp instruction
2667 if (SI->getDefaultDest() != BB) {
2668 ConstantInt *VVal = SI->findCaseDest(BB);
2669 assert(VVal && "Should have a unique destination value");
2670 ICI->setOperand(0, VVal);
2672 if (Value *V = SimplifyInstruction(ICI, TD)) {
2673 ICI->replaceAllUsesWith(V);
2674 ICI->eraseFromParent();
2676 // BB is now empty, so it is likely to simplify away.
2677 return SimplifyCFG(BB, TTI, TD) | true;
2680 // Ok, the block is reachable from the default dest. If the constant we're
2681 // comparing exists in one of the other edges, then we can constant fold ICI
2683 if (SI->findCaseValue(Cst) != SI->case_default()) {
2685 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2686 V = ConstantInt::getFalse(BB->getContext());
2688 V = ConstantInt::getTrue(BB->getContext());
2690 ICI->replaceAllUsesWith(V);
2691 ICI->eraseFromParent();
2692 // BB is now empty, so it is likely to simplify away.
2693 return SimplifyCFG(BB, TTI, TD) | true;
2696 // The use of the icmp has to be in the 'end' block, by the only PHI node in
2698 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
2699 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
2700 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
2701 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
2704 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
2706 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
2707 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
2709 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2710 std::swap(DefaultCst, NewCst);
2712 // Replace ICI (which is used by the PHI for the default value) with true or
2713 // false depending on if it is EQ or NE.
2714 ICI->replaceAllUsesWith(DefaultCst);
2715 ICI->eraseFromParent();
2717 // Okay, the switch goes to this block on a default value. Add an edge from
2718 // the switch to the merge point on the compared value.
2719 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
2720 BB->getParent(), BB);
2721 SmallVector<uint64_t, 8> Weights;
2722 bool HasWeights = HasBranchWeights(SI);
2724 GetBranchWeights(SI, Weights);
2725 if (Weights.size() == 1 + SI->getNumCases()) {
2726 // Split weight for default case to case for "Cst".
2727 Weights[0] = (Weights[0]+1) >> 1;
2728 Weights.push_back(Weights[0]);
2730 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
2731 SI->setMetadata(LLVMContext::MD_prof,
2732 MDBuilder(SI->getContext()).
2733 createBranchWeights(MDWeights));
2736 SI->addCase(Cst, NewBB);
2738 // NewBB branches to the phi block, add the uncond branch and the phi entry.
2739 Builder.SetInsertPoint(NewBB);
2740 Builder.SetCurrentDebugLocation(SI->getDebugLoc());
2741 Builder.CreateBr(SuccBlock);
2742 PHIUse->addIncoming(NewCst, NewBB);
2746 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
2747 /// Check to see if it is branching on an or/and chain of icmp instructions, and
2748 /// fold it into a switch instruction if so.
2749 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const DataLayout *TD,
2750 IRBuilder<> &Builder) {
2751 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
2752 if (Cond == 0) return false;
2755 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2756 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2757 // 'setne's and'ed together, collect them.
2759 std::vector<ConstantInt*> Values;
2760 bool TrueWhenEqual = true;
2761 Value *ExtraCase = 0;
2762 unsigned UsedICmps = 0;
2764 if (Cond->getOpcode() == Instruction::Or) {
2765 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
2767 } else if (Cond->getOpcode() == Instruction::And) {
2768 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
2770 TrueWhenEqual = false;
2773 // If we didn't have a multiply compared value, fail.
2774 if (CompVal == 0) return false;
2776 // Avoid turning single icmps into a switch.
2780 // There might be duplicate constants in the list, which the switch
2781 // instruction can't handle, remove them now.
2782 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
2783 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2785 // If Extra was used, we require at least two switch values to do the
2786 // transformation. A switch with one value is just an cond branch.
2787 if (ExtraCase && Values.size() < 2) return false;
2789 // TODO: Preserve branch weight metadata, similarly to how
2790 // FoldValueComparisonIntoPredecessors preserves it.
2792 // Figure out which block is which destination.
2793 BasicBlock *DefaultBB = BI->getSuccessor(1);
2794 BasicBlock *EdgeBB = BI->getSuccessor(0);
2795 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2797 BasicBlock *BB = BI->getParent();
2799 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
2800 << " cases into SWITCH. BB is:\n" << *BB);
2802 // If there are any extra values that couldn't be folded into the switch
2803 // then we evaluate them with an explicit branch first. Split the block
2804 // right before the condbr to handle it.
2806 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
2807 // Remove the uncond branch added to the old block.
2808 TerminatorInst *OldTI = BB->getTerminator();
2809 Builder.SetInsertPoint(OldTI);
2812 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
2814 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
2816 OldTI->eraseFromParent();
2818 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
2819 // for the edge we just added.
2820 AddPredecessorToBlock(EdgeBB, BB, NewBB);
2822 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
2823 << "\nEXTRABB = " << *BB);
2827 Builder.SetInsertPoint(BI);
2828 // Convert pointer to int before we switch.
2829 if (CompVal->getType()->isPointerTy()) {
2830 assert(TD && "Cannot switch on pointer without DataLayout");
2831 CompVal = Builder.CreatePtrToInt(CompVal,
2832 TD->getIntPtrType(CompVal->getContext()),
2836 // Create the new switch instruction now.
2837 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
2839 // Add all of the 'cases' to the switch instruction.
2840 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2841 New->addCase(Values[i], EdgeBB);
2843 // We added edges from PI to the EdgeBB. As such, if there were any
2844 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2845 // the number of edges added.
2846 for (BasicBlock::iterator BBI = EdgeBB->begin();
2847 isa<PHINode>(BBI); ++BBI) {
2848 PHINode *PN = cast<PHINode>(BBI);
2849 Value *InVal = PN->getIncomingValueForBlock(BB);
2850 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2851 PN->addIncoming(InVal, BB);
2854 // Erase the old branch instruction.
2855 EraseTerminatorInstAndDCECond(BI);
2857 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
2861 bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
2862 // If this is a trivial landing pad that just continues unwinding the caught
2863 // exception then zap the landing pad, turning its invokes into calls.
2864 BasicBlock *BB = RI->getParent();
2865 LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI());
2866 if (RI->getValue() != LPInst)
2867 // Not a landing pad, or the resume is not unwinding the exception that
2868 // caused control to branch here.
2871 // Check that there are no other instructions except for debug intrinsics.
2872 BasicBlock::iterator I = LPInst, E = RI;
2874 if (!isa<DbgInfoIntrinsic>(I))
2877 // Turn all invokes that unwind here into calls and delete the basic block.
2878 bool InvokeRequiresTableEntry = false;
2879 bool Changed = false;
2880 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
2881 InvokeInst *II = cast<InvokeInst>((*PI++)->getTerminator());
2883 if (II->hasFnAttr(Attribute::UWTable)) {
2884 // Don't remove an `invoke' instruction if the ABI requires an entry into
2886 InvokeRequiresTableEntry = true;
2890 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
2892 // Insert a call instruction before the invoke.
2893 CallInst *Call = CallInst::Create(II->getCalledValue(), Args, "", II);
2895 Call->setCallingConv(II->getCallingConv());
2896 Call->setAttributes(II->getAttributes());
2897 Call->setDebugLoc(II->getDebugLoc());
2899 // Anything that used the value produced by the invoke instruction now uses
2900 // the value produced by the call instruction. Note that we do this even
2901 // for void functions and calls with no uses so that the callgraph edge is
2903 II->replaceAllUsesWith(Call);
2904 BB->removePredecessor(II->getParent());
2906 // Insert a branch to the normal destination right before the invoke.
2907 BranchInst::Create(II->getNormalDest(), II);
2909 // Finally, delete the invoke instruction!
2910 II->eraseFromParent();
2914 if (!InvokeRequiresTableEntry)
2915 // The landingpad is now unreachable. Zap it.
2916 BB->eraseFromParent();
2921 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
2922 BasicBlock *BB = RI->getParent();
2923 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2925 // Find predecessors that end with branches.
2926 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2927 SmallVector<BranchInst*, 8> CondBranchPreds;
2928 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2929 BasicBlock *P = *PI;
2930 TerminatorInst *PTI = P->getTerminator();
2931 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2932 if (BI->isUnconditional())
2933 UncondBranchPreds.push_back(P);
2935 CondBranchPreds.push_back(BI);
2939 // If we found some, do the transformation!
2940 if (!UncondBranchPreds.empty() && DupRet) {
2941 while (!UncondBranchPreds.empty()) {
2942 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2943 DEBUG(dbgs() << "FOLDING: " << *BB
2944 << "INTO UNCOND BRANCH PRED: " << *Pred);
2945 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
2948 // If we eliminated all predecessors of the block, delete the block now.
2949 if (pred_begin(BB) == pred_end(BB))
2950 // We know there are no successors, so just nuke the block.
2951 BB->eraseFromParent();
2956 // Check out all of the conditional branches going to this return
2957 // instruction. If any of them just select between returns, change the
2958 // branch itself into a select/return pair.
2959 while (!CondBranchPreds.empty()) {
2960 BranchInst *BI = CondBranchPreds.pop_back_val();
2962 // Check to see if the non-BB successor is also a return block.
2963 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2964 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2965 SimplifyCondBranchToTwoReturns(BI, Builder))
2971 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2972 BasicBlock *BB = UI->getParent();
2974 bool Changed = false;
2976 // If there are any instructions immediately before the unreachable that can
2977 // be removed, do so.
2978 while (UI != BB->begin()) {
2979 BasicBlock::iterator BBI = UI;
2981 // Do not delete instructions that can have side effects which might cause
2982 // the unreachable to not be reachable; specifically, calls and volatile
2983 // operations may have this effect.
2984 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2986 if (BBI->mayHaveSideEffects()) {
2987 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
2988 if (SI->isVolatile())
2990 } else if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
2991 if (LI->isVolatile())
2993 } else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(BBI)) {
2994 if (RMWI->isVolatile())
2996 } else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) {
2997 if (CXI->isVolatile())
2999 } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) &&
3000 !isa<LandingPadInst>(BBI)) {
3003 // Note that deleting LandingPad's here is in fact okay, although it
3004 // involves a bit of subtle reasoning. If this inst is a LandingPad,
3005 // all the predecessors of this block will be the unwind edges of Invokes,
3006 // and we can therefore guarantee this block will be erased.
3009 // Delete this instruction (any uses are guaranteed to be dead)
3010 if (!BBI->use_empty())
3011 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
3012 BBI->eraseFromParent();
3016 // If the unreachable instruction is the first in the block, take a gander
3017 // at all of the predecessors of this instruction, and simplify them.
3018 if (&BB->front() != UI) return Changed;
3020 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
3021 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
3022 TerminatorInst *TI = Preds[i]->getTerminator();
3023 IRBuilder<> Builder(TI);
3024 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
3025 if (BI->isUnconditional()) {
3026 if (BI->getSuccessor(0) == BB) {
3027 new UnreachableInst(TI->getContext(), TI);
3028 TI->eraseFromParent();
3032 if (BI->getSuccessor(0) == BB) {
3033 Builder.CreateBr(BI->getSuccessor(1));
3034 EraseTerminatorInstAndDCECond(BI);
3035 } else if (BI->getSuccessor(1) == BB) {
3036 Builder.CreateBr(BI->getSuccessor(0));
3037 EraseTerminatorInstAndDCECond(BI);
3041 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
3042 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
3044 if (i.getCaseSuccessor() == BB) {
3045 BB->removePredecessor(SI->getParent());
3050 // If the default value is unreachable, figure out the most popular
3051 // destination and make it the default.
3052 if (SI->getDefaultDest() == BB) {
3053 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
3054 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
3056 std::pair<unsigned, unsigned> &entry =
3057 Popularity[i.getCaseSuccessor()];
3058 if (entry.first == 0) {
3060 entry.second = i.getCaseIndex();
3066 // Find the most popular block.
3067 unsigned MaxPop = 0;
3068 unsigned MaxIndex = 0;
3069 BasicBlock *MaxBlock = 0;
3070 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
3071 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
3072 if (I->second.first > MaxPop ||
3073 (I->second.first == MaxPop && MaxIndex > I->second.second)) {
3074 MaxPop = I->second.first;
3075 MaxIndex = I->second.second;
3076 MaxBlock = I->first;
3080 // Make this the new default, allowing us to delete any explicit
3082 SI->setDefaultDest(MaxBlock);
3085 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
3087 if (isa<PHINode>(MaxBlock->begin()))
3088 for (unsigned i = 0; i != MaxPop-1; ++i)
3089 MaxBlock->removePredecessor(SI->getParent());
3091 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
3093 if (i.getCaseSuccessor() == MaxBlock) {
3099 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
3100 if (II->getUnwindDest() == BB) {
3101 // Convert the invoke to a call instruction. This would be a good
3102 // place to note that the call does not throw though.
3103 BranchInst *BI = Builder.CreateBr(II->getNormalDest());
3104 II->removeFromParent(); // Take out of symbol table
3106 // Insert the call now...
3107 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
3108 Builder.SetInsertPoint(BI);
3109 CallInst *CI = Builder.CreateCall(II->getCalledValue(),
3110 Args, II->getName());
3111 CI->setCallingConv(II->getCallingConv());
3112 CI->setAttributes(II->getAttributes());
3113 // If the invoke produced a value, the call does now instead.
3114 II->replaceAllUsesWith(CI);
3121 // If this block is now dead, remove it.
3122 if (pred_begin(BB) == pred_end(BB) &&
3123 BB != &BB->getParent()->getEntryBlock()) {
3124 // We know there are no successors, so just nuke the block.
3125 BB->eraseFromParent();
3132 /// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
3133 /// integer range comparison into a sub, an icmp and a branch.
3134 static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
3135 assert(SI->getNumCases() > 1 && "Degenerate switch?");
3137 // Make sure all cases point to the same destination and gather the values.
3138 SmallVector<ConstantInt *, 16> Cases;
3139 SwitchInst::CaseIt I = SI->case_begin();
3140 Cases.push_back(I.getCaseValue());
3141 SwitchInst::CaseIt PrevI = I++;
3142 for (SwitchInst::CaseIt E = SI->case_end(); I != E; PrevI = I++) {
3143 if (PrevI.getCaseSuccessor() != I.getCaseSuccessor())
3145 Cases.push_back(I.getCaseValue());
3147 assert(Cases.size() == SI->getNumCases() && "Not all cases gathered");
3149 // Sort the case values, then check if they form a range we can transform.
3150 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
3151 for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
3152 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
3156 Constant *Offset = ConstantExpr::getNeg(Cases.back());
3157 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases());
3159 Value *Sub = SI->getCondition();
3160 if (!Offset->isNullValue())
3161 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off");
3163 // If NumCases overflowed, then all possible values jump to the successor.
3164 if (NumCases->isNullValue() && SI->getNumCases() != 0)
3165 Cmp = ConstantInt::getTrue(SI->getContext());
3167 Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
3168 BranchInst *NewBI = Builder.CreateCondBr(
3169 Cmp, SI->case_begin().getCaseSuccessor(), SI->getDefaultDest());
3171 // Update weight for the newly-created conditional branch.
3172 SmallVector<uint64_t, 8> Weights;
3173 bool HasWeights = HasBranchWeights(SI);
3175 GetBranchWeights(SI, Weights);
3176 if (Weights.size() == 1 + SI->getNumCases()) {
3177 // Combine all weights for the cases to be the true weight of NewBI.
3178 // We assume that the sum of all weights for a Terminator can fit into 32
3180 uint32_t NewTrueWeight = 0;
3181 for (unsigned I = 1, E = Weights.size(); I != E; ++I)
3182 NewTrueWeight += (uint32_t)Weights[I];
3183 NewBI->setMetadata(LLVMContext::MD_prof,
3184 MDBuilder(SI->getContext()).
3185 createBranchWeights(NewTrueWeight,
3186 (uint32_t)Weights[0]));
3190 // Prune obsolete incoming values off the successor's PHI nodes.
3191 for (BasicBlock::iterator BBI = SI->case_begin().getCaseSuccessor()->begin();
3192 isa<PHINode>(BBI); ++BBI) {
3193 for (unsigned I = 0, E = SI->getNumCases()-1; I != E; ++I)
3194 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
3196 SI->eraseFromParent();
3201 /// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch
3202 /// and use it to remove dead cases.
3203 static bool EliminateDeadSwitchCases(SwitchInst *SI) {
3204 Value *Cond = SI->getCondition();
3205 unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth();
3206 APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
3207 ComputeMaskedBits(Cond, KnownZero, KnownOne);
3209 // Gather dead cases.
3210 SmallVector<ConstantInt*, 8> DeadCases;
3211 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
3212 if ((I.getCaseValue()->getValue() & KnownZero) != 0 ||
3213 (I.getCaseValue()->getValue() & KnownOne) != KnownOne) {
3214 DeadCases.push_back(I.getCaseValue());
3215 DEBUG(dbgs() << "SimplifyCFG: switch case '"
3216 << I.getCaseValue() << "' is dead.\n");
3220 SmallVector<uint64_t, 8> Weights;
3221 bool HasWeight = HasBranchWeights(SI);
3223 GetBranchWeights(SI, Weights);
3224 HasWeight = (Weights.size() == 1 + SI->getNumCases());
3227 // Remove dead cases from the switch.
3228 for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) {
3229 SwitchInst::CaseIt Case = SI->findCaseValue(DeadCases[I]);
3230 assert(Case != SI->case_default() &&
3231 "Case was not found. Probably mistake in DeadCases forming.");
3233 std::swap(Weights[Case.getCaseIndex()+1], Weights.back());
3237 // Prune unused values from PHI nodes.
3238 Case.getCaseSuccessor()->removePredecessor(SI->getParent());
3239 SI->removeCase(Case);
3242 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
3243 SI->setMetadata(LLVMContext::MD_prof,
3244 MDBuilder(SI->getParent()->getContext()).
3245 createBranchWeights(MDWeights));
3248 return !DeadCases.empty();
3251 /// FindPHIForConditionForwarding - If BB would be eligible for simplification
3252 /// by TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated
3253 /// by an unconditional branch), look at the phi node for BB in the successor
3254 /// block and see if the incoming value is equal to CaseValue. If so, return
3255 /// the phi node, and set PhiIndex to BB's index in the phi node.
3256 static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
3259 if (BB->getFirstNonPHIOrDbg() != BB->getTerminator())
3260 return NULL; // BB must be empty to be a candidate for simplification.
3261 if (!BB->getSinglePredecessor())
3262 return NULL; // BB must be dominated by the switch.
3264 BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
3265 if (!Branch || !Branch->isUnconditional())
3266 return NULL; // Terminator must be unconditional branch.
3268 BasicBlock *Succ = Branch->getSuccessor(0);
3270 BasicBlock::iterator I = Succ->begin();
3271 while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
3272 int Idx = PHI->getBasicBlockIndex(BB);
3273 assert(Idx >= 0 && "PHI has no entry for predecessor?");
3275 Value *InValue = PHI->getIncomingValue(Idx);
3276 if (InValue != CaseValue) continue;
3285 /// ForwardSwitchConditionToPHI - Try to forward the condition of a switch
3286 /// instruction to a phi node dominated by the switch, if that would mean that
3287 /// some of the destination blocks of the switch can be folded away.
3288 /// Returns true if a change is made.
3289 static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
3290 typedef DenseMap<PHINode*, SmallVector<int,4> > ForwardingNodesMap;
3291 ForwardingNodesMap ForwardingNodes;
3293 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
3294 ConstantInt *CaseValue = I.getCaseValue();
3295 BasicBlock *CaseDest = I.getCaseSuccessor();
3298 PHINode *PHI = FindPHIForConditionForwarding(CaseValue, CaseDest,
3302 ForwardingNodes[PHI].push_back(PhiIndex);
3305 bool Changed = false;
3307 for (ForwardingNodesMap::iterator I = ForwardingNodes.begin(),
3308 E = ForwardingNodes.end(); I != E; ++I) {
3309 PHINode *Phi = I->first;
3310 SmallVector<int,4> &Indexes = I->second;
3312 if (Indexes.size() < 2) continue;
3314 for (size_t I = 0, E = Indexes.size(); I != E; ++I)
3315 Phi->setIncomingValue(Indexes[I], SI->getCondition());
3322 /// ValidLookupTableConstant - Return true if the backend will be able to handle
3323 /// initializing an array of constants like C.
3324 static bool ValidLookupTableConstant(Constant *C) {
3325 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C))
3326 return CE->isGEPWithNoNotionalOverIndexing();
3328 return isa<ConstantFP>(C) ||
3329 isa<ConstantInt>(C) ||
3330 isa<ConstantPointerNull>(C) ||
3331 isa<GlobalValue>(C) ||
3335 /// LookupConstant - If V is a Constant, return it. Otherwise, try to look up
3336 /// its constant value in ConstantPool, returning 0 if it's not there.
3337 static Constant *LookupConstant(Value *V,
3338 const SmallDenseMap<Value*, Constant*>& ConstantPool) {
3339 if (Constant *C = dyn_cast<Constant>(V))
3341 return ConstantPool.lookup(V);
3344 /// ConstantFold - Try to fold instruction I into a constant. This works for
3345 /// simple instructions such as binary operations where both operands are
3346 /// constant or can be replaced by constants from the ConstantPool. Returns the
3347 /// resulting constant on success, 0 otherwise.
3348 static Constant *ConstantFold(Instruction *I,
3349 const SmallDenseMap<Value*, Constant*>& ConstantPool) {
3350 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(I)) {
3351 Constant *A = LookupConstant(BO->getOperand(0), ConstantPool);
3354 Constant *B = LookupConstant(BO->getOperand(1), ConstantPool);
3357 return ConstantExpr::get(BO->getOpcode(), A, B);
3360 if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
3361 Constant *A = LookupConstant(I->getOperand(0), ConstantPool);
3364 Constant *B = LookupConstant(I->getOperand(1), ConstantPool);
3367 return ConstantExpr::getCompare(Cmp->getPredicate(), A, B);
3370 if (SelectInst *Select = dyn_cast<SelectInst>(I)) {
3371 Constant *A = LookupConstant(Select->getCondition(), ConstantPool);
3374 if (A->isAllOnesValue())
3375 return LookupConstant(Select->getTrueValue(), ConstantPool);
3376 if (A->isNullValue())
3377 return LookupConstant(Select->getFalseValue(), ConstantPool);
3381 if (CastInst *Cast = dyn_cast<CastInst>(I)) {
3382 Constant *A = LookupConstant(I->getOperand(0), ConstantPool);
3385 return ConstantExpr::getCast(Cast->getOpcode(), A, Cast->getDestTy());
3391 /// GetCaseResults - Try to determine the resulting constant values in phi nodes
3392 /// at the common destination basic block, *CommonDest, for one of the case
3393 /// destionations CaseDest corresponding to value CaseVal (0 for the default
3394 /// case), of a switch instruction SI.
3395 static bool GetCaseResults(SwitchInst *SI,
3396 ConstantInt *CaseVal,
3397 BasicBlock *CaseDest,
3398 BasicBlock **CommonDest,
3399 SmallVector<std::pair<PHINode*,Constant*>, 4> &Res) {
3400 // The block from which we enter the common destination.
3401 BasicBlock *Pred = SI->getParent();
3403 // If CaseDest is empty except for some side-effect free instructions through
3404 // which we can constant-propagate the CaseVal, continue to its successor.
3405 SmallDenseMap<Value*, Constant*> ConstantPool;
3406 ConstantPool.insert(std::make_pair(SI->getCondition(), CaseVal));
3407 for (BasicBlock::iterator I = CaseDest->begin(), E = CaseDest->end(); I != E;
3409 if (TerminatorInst *T = dyn_cast<TerminatorInst>(I)) {
3410 // If the terminator is a simple branch, continue to the next block.
3411 if (T->getNumSuccessors() != 1)
3414 CaseDest = T->getSuccessor(0);
3415 } else if (isa<DbgInfoIntrinsic>(I)) {
3416 // Skip debug intrinsic.
3418 } else if (Constant *C = ConstantFold(I, ConstantPool)) {
3419 // Instruction is side-effect free and constant.
3420 ConstantPool.insert(std::make_pair(I, C));
3426 // If we did not have a CommonDest before, use the current one.
3428 *CommonDest = CaseDest;
3429 // If the destination isn't the common one, abort.
3430 if (CaseDest != *CommonDest)
3433 // Get the values for this case from phi nodes in the destination block.
3434 BasicBlock::iterator I = (*CommonDest)->begin();
3435 while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
3436 int Idx = PHI->getBasicBlockIndex(Pred);
3440 Constant *ConstVal = LookupConstant(PHI->getIncomingValue(Idx),
3445 // Note: If the constant comes from constant-propagating the case value
3446 // through the CaseDest basic block, it will be safe to remove the
3447 // instructions in that block. They cannot be used (except in the phi nodes
3448 // we visit) outside CaseDest, because that block does not dominate its
3449 // successor. If it did, we would not be in this phi node.
3451 // Be conservative about which kinds of constants we support.
3452 if (!ValidLookupTableConstant(ConstVal))
3455 Res.push_back(std::make_pair(PHI, ConstVal));
3462 /// SwitchLookupTable - This class represents a lookup table that can be used
3463 /// to replace a switch.
3464 class SwitchLookupTable {
3466 /// SwitchLookupTable - Create a lookup table to use as a switch replacement
3467 /// with the contents of Values, using DefaultValue to fill any holes in the
3469 SwitchLookupTable(Module &M,
3471 ConstantInt *Offset,
3472 const SmallVector<std::pair<ConstantInt*, Constant*>, 4>& Values,
3473 Constant *DefaultValue,
3474 const DataLayout *TD);
3476 /// BuildLookup - Build instructions with Builder to retrieve the value at
3477 /// the position given by Index in the lookup table.
3478 Value *BuildLookup(Value *Index, IRBuilder<> &Builder);
3480 /// WouldFitInRegister - Return true if a table with TableSize elements of
3481 /// type ElementType would fit in a target-legal register.
3482 static bool WouldFitInRegister(const DataLayout *TD,
3484 const Type *ElementType);
3487 // Depending on the contents of the table, it can be represented in
3490 // For tables where each element contains the same value, we just have to
3491 // store that single value and return it for each lookup.
3494 // For small tables with integer elements, we can pack them into a bitmap
3495 // that fits into a target-legal register. Values are retrieved by
3496 // shift and mask operations.
3499 // The table is stored as an array of values. Values are retrieved by load
3500 // instructions from the table.
3504 // For SingleValueKind, this is the single value.
3505 Constant *SingleValue;
3507 // For BitMapKind, this is the bitmap.
3508 ConstantInt *BitMap;
3509 IntegerType *BitMapElementTy;
3511 // For ArrayKind, this is the array.
3512 GlobalVariable *Array;
3516 SwitchLookupTable::SwitchLookupTable(Module &M,
3518 ConstantInt *Offset,
3519 const SmallVector<std::pair<ConstantInt*, Constant*>, 4>& Values,
3520 Constant *DefaultValue,
3521 const DataLayout *TD)
3522 : SingleValue(0), BitMap(0), BitMapElementTy(0), Array(0) {
3523 assert(Values.size() && "Can't build lookup table without values!");
3524 assert(TableSize >= Values.size() && "Can't fit values in table!");
3526 // If all values in the table are equal, this is that value.
3527 SingleValue = Values.begin()->second;
3529 // Build up the table contents.
3530 SmallVector<Constant*, 64> TableContents(TableSize);
3531 for (size_t I = 0, E = Values.size(); I != E; ++I) {
3532 ConstantInt *CaseVal = Values[I].first;
3533 Constant *CaseRes = Values[I].second;
3534 assert(CaseRes->getType() == DefaultValue->getType());
3536 uint64_t Idx = (CaseVal->getValue() - Offset->getValue())
3538 TableContents[Idx] = CaseRes;
3540 if (CaseRes != SingleValue)
3544 // Fill in any holes in the table with the default result.
3545 if (Values.size() < TableSize) {
3546 for (uint64_t I = 0; I < TableSize; ++I) {
3547 if (!TableContents[I])
3548 TableContents[I] = DefaultValue;
3551 if (DefaultValue != SingleValue)
3555 // If each element in the table contains the same value, we only need to store
3556 // that single value.
3558 Kind = SingleValueKind;
3562 // If the type is integer and the table fits in a register, build a bitmap.
3563 if (WouldFitInRegister(TD, TableSize, DefaultValue->getType())) {
3564 IntegerType *IT = cast<IntegerType>(DefaultValue->getType());
3565 APInt TableInt(TableSize * IT->getBitWidth(), 0);
3566 for (uint64_t I = TableSize; I > 0; --I) {
3567 TableInt <<= IT->getBitWidth();
3568 // Insert values into the bitmap. Undef values are set to zero.
3569 if (!isa<UndefValue>(TableContents[I - 1])) {
3570 ConstantInt *Val = cast<ConstantInt>(TableContents[I - 1]);
3571 TableInt |= Val->getValue().zext(TableInt.getBitWidth());
3574 BitMap = ConstantInt::get(M.getContext(), TableInt);
3575 BitMapElementTy = IT;
3581 // Store the table in an array.
3582 ArrayType *ArrayTy = ArrayType::get(DefaultValue->getType(), TableSize);
3583 Constant *Initializer = ConstantArray::get(ArrayTy, TableContents);
3585 Array = new GlobalVariable(M, ArrayTy, /*constant=*/ true,
3586 GlobalVariable::PrivateLinkage,
3589 Array->setUnnamedAddr(true);
3593 Value *SwitchLookupTable::BuildLookup(Value *Index, IRBuilder<> &Builder) {
3595 case SingleValueKind:
3598 // Type of the bitmap (e.g. i59).
3599 IntegerType *MapTy = BitMap->getType();
3601 // Cast Index to the same type as the bitmap.
3602 // Note: The Index is <= the number of elements in the table, so
3603 // truncating it to the width of the bitmask is safe.
3604 Value *ShiftAmt = Builder.CreateZExtOrTrunc(Index, MapTy, "switch.cast");
3606 // Multiply the shift amount by the element width.
3607 ShiftAmt = Builder.CreateMul(ShiftAmt,
3608 ConstantInt::get(MapTy, BitMapElementTy->getBitWidth()),
3612 Value *DownShifted = Builder.CreateLShr(BitMap, ShiftAmt,
3613 "switch.downshift");
3615 return Builder.CreateTrunc(DownShifted, BitMapElementTy,
3619 Value *GEPIndices[] = { Builder.getInt32(0), Index };
3620 Value *GEP = Builder.CreateInBoundsGEP(Array, GEPIndices,
3622 return Builder.CreateLoad(GEP, "switch.load");
3625 llvm_unreachable("Unknown lookup table kind!");
3628 bool SwitchLookupTable::WouldFitInRegister(const DataLayout *TD,
3630 const Type *ElementType) {
3633 const IntegerType *IT = dyn_cast<IntegerType>(ElementType);
3636 // FIXME: If the type is wider than it needs to be, e.g. i8 but all values
3637 // are <= 15, we could try to narrow the type.
3639 // Avoid overflow, fitsInLegalInteger uses unsigned int for the width.
3640 if (TableSize >= UINT_MAX/IT->getBitWidth())
3642 return TD->fitsInLegalInteger(TableSize * IT->getBitWidth());
3645 /// ShouldBuildLookupTable - Determine whether a lookup table should be built
3646 /// for this switch, based on the number of caes, size of the table and the
3647 /// types of the results.
3648 static bool ShouldBuildLookupTable(SwitchInst *SI,
3650 const TargetTransformInfo &TTI,
3651 const DataLayout *TD,
3652 const SmallDenseMap<PHINode*, Type*>& ResultTypes) {
3653 if (SI->getNumCases() > TableSize || TableSize >= UINT64_MAX / 10)
3654 return false; // TableSize overflowed, or mul below might overflow.
3656 bool AllTablesFitInRegister = true;
3657 bool HasIllegalType = false;
3658 for (SmallDenseMap<PHINode*, Type*>::const_iterator I = ResultTypes.begin(),
3659 E = ResultTypes.end(); I != E; ++I) {
3660 Type *Ty = I->second;
3662 // Saturate this flag to true.
3663 HasIllegalType = HasIllegalType || !TTI.isTypeLegal(Ty);
3665 // Saturate this flag to false.
3666 AllTablesFitInRegister = AllTablesFitInRegister &&
3667 SwitchLookupTable::WouldFitInRegister(TD, TableSize, Ty);
3669 // If both flags saturate, we're done. NOTE: This *only* works with
3670 // saturating flags, and all flags have to saturate first due to the
3671 // non-deterministic behavior of iterating over a dense map.
3672 if (HasIllegalType && !AllTablesFitInRegister)
3676 // If each table would fit in a register, we should build it anyway.
3677 if (AllTablesFitInRegister)
3680 // Don't build a table that doesn't fit in-register if it has illegal types.
3684 // The table density should be at least 40%. This is the same criterion as for
3685 // jump tables, see SelectionDAGBuilder::handleJTSwitchCase.
3686 // FIXME: Find the best cut-off.
3687 return SI->getNumCases() * 10 >= TableSize * 4;
3690 /// SwitchToLookupTable - If the switch is only used to initialize one or more
3691 /// phi nodes in a common successor block with different constant values,
3692 /// replace the switch with lookup tables.
3693 static bool SwitchToLookupTable(SwitchInst *SI,
3694 IRBuilder<> &Builder,
3695 const TargetTransformInfo &TTI,
3696 const DataLayout* TD) {
3697 assert(SI->getNumCases() > 1 && "Degenerate switch?");
3699 // Only build lookup table when we have a target that supports it.
3700 if (!TTI.shouldBuildLookupTables())
3703 // FIXME: If the switch is too sparse for a lookup table, perhaps we could
3704 // split off a dense part and build a lookup table for that.
3706 // FIXME: This creates arrays of GEPs to constant strings, which means each
3707 // GEP needs a runtime relocation in PIC code. We should just build one big
3708 // string and lookup indices into that.
3710 // Ignore the switch if the number of cases is too small.
3711 // This is similar to the check when building jump tables in
3712 // SelectionDAGBuilder::handleJTSwitchCase.
3713 // FIXME: Determine the best cut-off.
3714 if (SI->getNumCases() < 4)
3717 // Figure out the corresponding result for each case value and phi node in the
3718 // common destination, as well as the the min and max case values.
3719 assert(SI->case_begin() != SI->case_end());
3720 SwitchInst::CaseIt CI = SI->case_begin();
3721 ConstantInt *MinCaseVal = CI.getCaseValue();
3722 ConstantInt *MaxCaseVal = CI.getCaseValue();
3724 BasicBlock *CommonDest = 0;
3725 typedef SmallVector<std::pair<ConstantInt*, Constant*>, 4> ResultListTy;
3726 SmallDenseMap<PHINode*, ResultListTy> ResultLists;
3727 SmallDenseMap<PHINode*, Constant*> DefaultResults;
3728 SmallDenseMap<PHINode*, Type*> ResultTypes;
3729 SmallVector<PHINode*, 4> PHIs;
3731 for (SwitchInst::CaseIt E = SI->case_end(); CI != E; ++CI) {
3732 ConstantInt *CaseVal = CI.getCaseValue();
3733 if (CaseVal->getValue().slt(MinCaseVal->getValue()))
3734 MinCaseVal = CaseVal;
3735 if (CaseVal->getValue().sgt(MaxCaseVal->getValue()))
3736 MaxCaseVal = CaseVal;
3738 // Resulting value at phi nodes for this case value.
3739 typedef SmallVector<std::pair<PHINode*, Constant*>, 4> ResultsTy;
3741 if (!GetCaseResults(SI, CaseVal, CI.getCaseSuccessor(), &CommonDest,
3745 // Append the result from this case to the list for each phi.
3746 for (ResultsTy::iterator I = Results.begin(), E = Results.end(); I!=E; ++I) {
3747 if (!ResultLists.count(I->first))
3748 PHIs.push_back(I->first);
3749 ResultLists[I->first].push_back(std::make_pair(CaseVal, I->second));
3753 // Get the resulting values for the default case.
3754 SmallVector<std::pair<PHINode*, Constant*>, 4> DefaultResultsList;
3755 if (!GetCaseResults(SI, 0, SI->getDefaultDest(), &CommonDest,
3756 DefaultResultsList))
3758 for (size_t I = 0, E = DefaultResultsList.size(); I != E; ++I) {
3759 PHINode *PHI = DefaultResultsList[I].first;
3760 Constant *Result = DefaultResultsList[I].second;
3761 DefaultResults[PHI] = Result;
3762 ResultTypes[PHI] = Result->getType();
3765 APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
3766 uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
3767 if (!ShouldBuildLookupTable(SI, TableSize, TTI, TD, ResultTypes))
3770 // Create the BB that does the lookups.
3771 Module &Mod = *CommonDest->getParent()->getParent();
3772 BasicBlock *LookupBB = BasicBlock::Create(Mod.getContext(),
3774 CommonDest->getParent(),
3777 // Check whether the condition value is within the case range, and branch to
3779 Builder.SetInsertPoint(SI);
3780 Value *TableIndex = Builder.CreateSub(SI->getCondition(), MinCaseVal,
3782 Value *Cmp = Builder.CreateICmpULT(TableIndex, ConstantInt::get(
3783 MinCaseVal->getType(), TableSize));
3784 Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest());
3786 // Populate the BB that does the lookups.
3787 Builder.SetInsertPoint(LookupBB);
3788 bool ReturnedEarly = false;
3789 for (size_t I = 0, E = PHIs.size(); I != E; ++I) {
3790 PHINode *PHI = PHIs[I];
3792 SwitchLookupTable Table(Mod, TableSize, MinCaseVal, ResultLists[PHI],
3793 DefaultResults[PHI], TD);
3795 Value *Result = Table.BuildLookup(TableIndex, Builder);
3797 // If the result is used to return immediately from the function, we want to
3798 // do that right here.
3799 if (PHI->hasOneUse() && isa<ReturnInst>(*PHI->use_begin()) &&
3800 *PHI->use_begin() == CommonDest->getFirstNonPHIOrDbg()) {
3801 Builder.CreateRet(Result);
3802 ReturnedEarly = true;
3806 PHI->addIncoming(Result, LookupBB);
3810 Builder.CreateBr(CommonDest);
3812 // Remove the switch.
3813 for (unsigned i = 0; i < SI->getNumSuccessors(); ++i) {
3814 BasicBlock *Succ = SI->getSuccessor(i);
3815 if (Succ == SI->getDefaultDest()) continue;
3816 Succ->removePredecessor(SI->getParent());
3818 SI->eraseFromParent();
3824 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
3825 BasicBlock *BB = SI->getParent();
3827 if (isValueEqualityComparison(SI)) {
3828 // If we only have one predecessor, and if it is a branch on this value,
3829 // see if that predecessor totally determines the outcome of this switch.
3830 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
3831 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
3832 return SimplifyCFG(BB, TTI, TD) | true;
3834 Value *Cond = SI->getCondition();
3835 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
3836 if (SimplifySwitchOnSelect(SI, Select))
3837 return SimplifyCFG(BB, TTI, TD) | true;
3839 // If the block only contains the switch, see if we can fold the block
3840 // away into any preds.
3841 BasicBlock::iterator BBI = BB->begin();
3842 // Ignore dbg intrinsics.
3843 while (isa<DbgInfoIntrinsic>(BBI))
3846 if (FoldValueComparisonIntoPredecessors(SI, Builder))
3847 return SimplifyCFG(BB, TTI, TD) | true;
3850 // Try to transform the switch into an icmp and a branch.
3851 if (TurnSwitchRangeIntoICmp(SI, Builder))
3852 return SimplifyCFG(BB, TTI, TD) | true;
3854 // Remove unreachable cases.
3855 if (EliminateDeadSwitchCases(SI))
3856 return SimplifyCFG(BB, TTI, TD) | true;
3858 if (ForwardSwitchConditionToPHI(SI))
3859 return SimplifyCFG(BB, TTI, TD) | true;
3861 if (SwitchToLookupTable(SI, Builder, TTI, TD))
3862 return SimplifyCFG(BB, TTI, TD) | true;
3867 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
3868 BasicBlock *BB = IBI->getParent();
3869 bool Changed = false;
3871 // Eliminate redundant destinations.
3872 SmallPtrSet<Value *, 8> Succs;
3873 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
3874 BasicBlock *Dest = IBI->getDestination(i);
3875 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
3876 Dest->removePredecessor(BB);
3877 IBI->removeDestination(i);
3883 if (IBI->getNumDestinations() == 0) {
3884 // If the indirectbr has no successors, change it to unreachable.
3885 new UnreachableInst(IBI->getContext(), IBI);
3886 EraseTerminatorInstAndDCECond(IBI);
3890 if (IBI->getNumDestinations() == 1) {
3891 // If the indirectbr has one successor, change it to a direct branch.
3892 BranchInst::Create(IBI->getDestination(0), IBI);
3893 EraseTerminatorInstAndDCECond(IBI);
3897 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
3898 if (SimplifyIndirectBrOnSelect(IBI, SI))
3899 return SimplifyCFG(BB, TTI, TD) | true;
3904 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
3905 BasicBlock *BB = BI->getParent();
3907 if (SinkCommon && SinkThenElseCodeToEnd(BI))
3910 // If the Terminator is the only non-phi instruction, simplify the block.
3911 BasicBlock::iterator I = BB->getFirstNonPHIOrDbgOrLifetime();
3912 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
3913 TryToSimplifyUncondBranchFromEmptyBlock(BB))
3916 // If the only instruction in the block is a seteq/setne comparison
3917 // against a constant, try to simplify the block.
3918 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
3919 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
3920 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
3922 if (I->isTerminator() &&
3923 TryToSimplifyUncondBranchWithICmpInIt(ICI, Builder, TTI, TD))
3927 // If this basic block is ONLY a compare and a branch, and if a predecessor
3928 // branches to us and our successor, fold the comparison into the
3929 // predecessor and use logical operations to update the incoming value
3930 // for PHI nodes in common successor.
3931 if (FoldBranchToCommonDest(BI))
3932 return SimplifyCFG(BB, TTI, TD) | true;
3937 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
3938 BasicBlock *BB = BI->getParent();
3940 // Conditional branch
3941 if (isValueEqualityComparison(BI)) {
3942 // If we only have one predecessor, and if it is a branch on this value,
3943 // see if that predecessor totally determines the outcome of this
3945 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
3946 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
3947 return SimplifyCFG(BB, TTI, TD) | true;
3949 // This block must be empty, except for the setcond inst, if it exists.
3950 // Ignore dbg intrinsics.
3951 BasicBlock::iterator I = BB->begin();
3952 // Ignore dbg intrinsics.
3953 while (isa<DbgInfoIntrinsic>(I))
3956 if (FoldValueComparisonIntoPredecessors(BI, Builder))
3957 return SimplifyCFG(BB, TTI, TD) | true;
3958 } else if (&*I == cast<Instruction>(BI->getCondition())){
3960 // Ignore dbg intrinsics.
3961 while (isa<DbgInfoIntrinsic>(I))
3963 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
3964 return SimplifyCFG(BB, TTI, TD) | true;
3968 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
3969 if (SimplifyBranchOnICmpChain(BI, TD, Builder))
3972 // If this basic block is ONLY a compare and a branch, and if a predecessor
3973 // branches to us and one of our successors, fold the comparison into the
3974 // predecessor and use logical operations to pick the right destination.
3975 if (FoldBranchToCommonDest(BI))
3976 return SimplifyCFG(BB, TTI, TD) | true;
3978 // We have a conditional branch to two blocks that are only reachable
3979 // from BI. We know that the condbr dominates the two blocks, so see if
3980 // there is any identical code in the "then" and "else" blocks. If so, we
3981 // can hoist it up to the branching block.
3982 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
3983 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
3984 if (HoistThenElseCodeToIf(BI))
3985 return SimplifyCFG(BB, TTI, TD) | true;
3987 // If Successor #1 has multiple preds, we may be able to conditionally
3988 // execute Successor #0 if it branches to successor #1.
3989 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
3990 if (Succ0TI->getNumSuccessors() == 1 &&
3991 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
3992 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
3993 return SimplifyCFG(BB, TTI, TD) | true;
3995 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
3996 // If Successor #0 has multiple preds, we may be able to conditionally
3997 // execute Successor #1 if it branches to successor #0.
3998 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
3999 if (Succ1TI->getNumSuccessors() == 1 &&
4000 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
4001 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
4002 return SimplifyCFG(BB, TTI, TD) | true;
4005 // If this is a branch on a phi node in the current block, thread control
4006 // through this block if any PHI node entries are constants.
4007 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
4008 if (PN->getParent() == BI->getParent())
4009 if (FoldCondBranchOnPHI(BI, TD))
4010 return SimplifyCFG(BB, TTI, TD) | true;
4012 // Scan predecessor blocks for conditional branches.
4013 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
4014 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
4015 if (PBI != BI && PBI->isConditional())
4016 if (SimplifyCondBranchToCondBranch(PBI, BI))
4017 return SimplifyCFG(BB, TTI, TD) | true;
4022 /// Check if passing a value to an instruction will cause undefined behavior.
4023 static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
4024 Constant *C = dyn_cast<Constant>(V);
4031 if (C->isNullValue()) {
4032 // Only look at the first use, avoid hurting compile time with long uselists
4033 User *Use = *I->use_begin();
4035 // Now make sure that there are no instructions in between that can alter
4036 // control flow (eg. calls)
4037 for (BasicBlock::iterator i = ++BasicBlock::iterator(I); &*i != Use; ++i)
4038 if (i == I->getParent()->end() || i->mayHaveSideEffects())
4041 // Look through GEPs. A load from a GEP derived from NULL is still undefined
4042 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))
4043 if (GEP->getPointerOperand() == I)
4044 return passingValueIsAlwaysUndefined(V, GEP);
4046 // Look through bitcasts.
4047 if (BitCastInst *BC = dyn_cast<BitCastInst>(Use))
4048 return passingValueIsAlwaysUndefined(V, BC);
4050 // Load from null is undefined.
4051 if (LoadInst *LI = dyn_cast<LoadInst>(Use))
4052 if (!LI->isVolatile())
4053 return LI->getPointerAddressSpace() == 0;
4055 // Store to null is undefined.
4056 if (StoreInst *SI = dyn_cast<StoreInst>(Use))
4057 if (!SI->isVolatile())
4058 return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I;
4063 /// If BB has an incoming value that will always trigger undefined behavior
4064 /// (eg. null pointer dereference), remove the branch leading here.
4065 static bool removeUndefIntroducingPredecessor(BasicBlock *BB) {
4066 for (BasicBlock::iterator i = BB->begin();
4067 PHINode *PHI = dyn_cast<PHINode>(i); ++i)
4068 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
4069 if (passingValueIsAlwaysUndefined(PHI->getIncomingValue(i), PHI)) {
4070 TerminatorInst *T = PHI->getIncomingBlock(i)->getTerminator();
4071 IRBuilder<> Builder(T);
4072 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
4073 BB->removePredecessor(PHI->getIncomingBlock(i));
4074 // Turn uncoditional branches into unreachables and remove the dead
4075 // destination from conditional branches.
4076 if (BI->isUnconditional())
4077 Builder.CreateUnreachable();
4079 Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1) :
4080 BI->getSuccessor(0));
4081 BI->eraseFromParent();
4084 // TODO: SwitchInst.
4090 bool SimplifyCFGOpt::run(BasicBlock *BB) {
4091 bool Changed = false;
4093 assert(BB && BB->getParent() && "Block not embedded in function!");
4094 assert(BB->getTerminator() && "Degenerate basic block encountered!");
4096 // Remove basic blocks that have no predecessors (except the entry block)...
4097 // or that just have themself as a predecessor. These are unreachable.
4098 if ((pred_begin(BB) == pred_end(BB) &&
4099 BB != &BB->getParent()->getEntryBlock()) ||
4100 BB->getSinglePredecessor() == BB) {
4101 DEBUG(dbgs() << "Removing BB: \n" << *BB);
4102 DeleteDeadBlock(BB);
4106 // Check to see if we can constant propagate this terminator instruction
4108 Changed |= ConstantFoldTerminator(BB, true);
4110 // Check for and eliminate duplicate PHI nodes in this block.
4111 Changed |= EliminateDuplicatePHINodes(BB);
4113 // Check for and remove branches that will always cause undefined behavior.
4114 Changed |= removeUndefIntroducingPredecessor(BB);
4116 // Merge basic blocks into their predecessor if there is only one distinct
4117 // pred, and if there is only one distinct successor of the predecessor, and
4118 // if there are no PHI nodes.
4120 if (MergeBlockIntoPredecessor(BB))
4123 IRBuilder<> Builder(BB);
4125 // If there is a trivial two-entry PHI node in this basic block, and we can
4126 // eliminate it, do so now.
4127 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
4128 if (PN->getNumIncomingValues() == 2)
4129 Changed |= FoldTwoEntryPHINode(PN, TD);
4131 Builder.SetInsertPoint(BB->getTerminator());
4132 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
4133 if (BI->isUnconditional()) {
4134 if (SimplifyUncondBranch(BI, Builder)) return true;
4136 if (SimplifyCondBranch(BI, Builder)) return true;
4138 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
4139 if (SimplifyReturn(RI, Builder)) return true;
4140 } else if (ResumeInst *RI = dyn_cast<ResumeInst>(BB->getTerminator())) {
4141 if (SimplifyResume(RI, Builder)) return true;
4142 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
4143 if (SimplifySwitch(SI, Builder)) return true;
4144 } else if (UnreachableInst *UI =
4145 dyn_cast<UnreachableInst>(BB->getTerminator())) {
4146 if (SimplifyUnreachable(UI)) return true;
4147 } else if (IndirectBrInst *IBI =
4148 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
4149 if (SimplifyIndirectBr(IBI)) return true;
4155 /// SimplifyCFG - This function is used to do simplification of a CFG. For
4156 /// example, it adjusts branches to branches to eliminate the extra hop, it
4157 /// eliminates unreachable basic blocks, and does other "peephole" optimization
4158 /// of the CFG. It returns true if a modification was made.
4160 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetTransformInfo &TTI,
4161 const DataLayout *TD) {
4162 return SimplifyCFGOpt(TTI, TD).run(BB);