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/Constants.h"
17 #include "llvm/Instructions.h"
18 #include "llvm/IntrinsicInst.h"
19 #include "llvm/Type.h"
20 #include "llvm/DerivedTypes.h"
21 #include "llvm/GlobalVariable.h"
22 #include "llvm/Analysis/InstructionSimplify.h"
23 #include "llvm/Analysis/ValueTracking.h"
24 #include "llvm/Target/TargetData.h"
25 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
26 #include "llvm/ADT/DenseMap.h"
27 #include "llvm/ADT/SmallVector.h"
28 #include "llvm/ADT/SmallPtrSet.h"
29 #include "llvm/ADT/Statistic.h"
30 #include "llvm/ADT/STLExtras.h"
31 #include "llvm/Support/CFG.h"
32 #include "llvm/Support/CommandLine.h"
33 #include "llvm/Support/ConstantRange.h"
34 #include "llvm/Support/Debug.h"
35 #include "llvm/Support/IRBuilder.h"
36 #include "llvm/Support/raw_ostream.h"
42 static cl::opt<unsigned>
43 PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(1),
44 cl::desc("Control the amount of phi node folding to perform (default = 1)"));
47 DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false),
48 cl::desc("Duplicate return instructions into unconditional branches"));
50 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
53 class SimplifyCFGOpt {
54 const TargetData *const TD;
56 Value *isValueEqualityComparison(TerminatorInst *TI);
57 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
58 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases);
59 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
61 IRBuilder<> &Builder);
62 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI);
64 bool SimplifyReturn(ReturnInst *RI);
65 bool SimplifyUnwind(UnwindInst *UI, IRBuilder<> &Builder);
66 bool SimplifyUnreachable(UnreachableInst *UI);
67 bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
68 bool SimplifyIndirectBr(IndirectBrInst *IBI);
69 bool SimplifyUncondBranch(BranchInst *BI, IRBuilder <> &Builder);
70 bool SimplifyCondBranch(BranchInst *BI, IRBuilder <>&Builder);
73 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
74 bool run(BasicBlock *BB);
78 /// SafeToMergeTerminators - Return true if it is safe to merge these two
79 /// terminator instructions together.
81 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
82 if (SI1 == SI2) return false; // Can't merge with self!
84 // It is not safe to merge these two switch instructions if they have a common
85 // successor, and if that successor has a PHI node, and if *that* PHI node has
86 // conflicting incoming values from the two switch blocks.
87 BasicBlock *SI1BB = SI1->getParent();
88 BasicBlock *SI2BB = SI2->getParent();
89 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
91 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
92 if (SI1Succs.count(*I))
93 for (BasicBlock::iterator BBI = (*I)->begin();
94 isa<PHINode>(BBI); ++BBI) {
95 PHINode *PN = cast<PHINode>(BBI);
96 if (PN->getIncomingValueForBlock(SI1BB) !=
97 PN->getIncomingValueForBlock(SI2BB))
104 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
105 /// now be entries in it from the 'NewPred' block. The values that will be
106 /// flowing into the PHI nodes will be the same as those coming in from
107 /// ExistPred, an existing predecessor of Succ.
108 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
109 BasicBlock *ExistPred) {
110 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
113 for (BasicBlock::iterator I = Succ->begin();
114 (PN = dyn_cast<PHINode>(I)); ++I)
115 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
119 /// GetIfCondition - Given a basic block (BB) with two predecessors (and at
120 /// least one PHI node in it), check to see if the merge at this block is due
121 /// to an "if condition". If so, return the boolean condition that determines
122 /// which entry into BB will be taken. Also, return by references the block
123 /// that will be entered from if the condition is true, and the block that will
124 /// be entered if the condition is false.
126 /// This does no checking to see if the true/false blocks have large or unsavory
127 /// instructions in them.
128 static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
129 BasicBlock *&IfFalse) {
130 PHINode *SomePHI = cast<PHINode>(BB->begin());
131 assert(SomePHI->getNumIncomingValues() == 2 &&
132 "Function can only handle blocks with 2 predecessors!");
133 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
134 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
136 // We can only handle branches. Other control flow will be lowered to
137 // branches if possible anyway.
138 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
139 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
140 if (Pred1Br == 0 || Pred2Br == 0)
143 // Eliminate code duplication by ensuring that Pred1Br is conditional if
145 if (Pred2Br->isConditional()) {
146 // If both branches are conditional, we don't have an "if statement". In
147 // reality, we could transform this case, but since the condition will be
148 // required anyway, we stand no chance of eliminating it, so the xform is
149 // probably not profitable.
150 if (Pred1Br->isConditional())
153 std::swap(Pred1, Pred2);
154 std::swap(Pred1Br, Pred2Br);
157 if (Pred1Br->isConditional()) {
158 // The only thing we have to watch out for here is to make sure that Pred2
159 // doesn't have incoming edges from other blocks. If it does, the condition
160 // doesn't dominate BB.
161 if (Pred2->getSinglePredecessor() == 0)
164 // If we found a conditional branch predecessor, make sure that it branches
165 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
166 if (Pred1Br->getSuccessor(0) == BB &&
167 Pred1Br->getSuccessor(1) == Pred2) {
170 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
171 Pred1Br->getSuccessor(1) == BB) {
175 // We know that one arm of the conditional goes to BB, so the other must
176 // go somewhere unrelated, and this must not be an "if statement".
180 return Pred1Br->getCondition();
183 // Ok, if we got here, both predecessors end with an unconditional branch to
184 // BB. Don't panic! If both blocks only have a single (identical)
185 // predecessor, and THAT is a conditional branch, then we're all ok!
186 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
187 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
190 // Otherwise, if this is a conditional branch, then we can use it!
191 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
192 if (BI == 0) return 0;
194 assert(BI->isConditional() && "Two successors but not conditional?");
195 if (BI->getSuccessor(0) == Pred1) {
202 return BI->getCondition();
205 /// DominatesMergePoint - If we have a merge point of an "if condition" as
206 /// accepted above, return true if the specified value dominates the block. We
207 /// don't handle the true generality of domination here, just a special case
208 /// which works well enough for us.
210 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
211 /// see if V (which must be an instruction) and its recursive operands
212 /// that do not dominate BB have a combined cost lower than CostRemaining and
213 /// are non-trapping. If both are true, the instruction is inserted into the
214 /// set and true is returned.
216 /// The cost for most non-trapping instructions is defined as 1 except for
217 /// Select whose cost is 2.
219 /// After this function returns, CostRemaining is decreased by the cost of
220 /// V plus its non-dominating operands. If that cost is greater than
221 /// CostRemaining, false is returned and CostRemaining is undefined.
222 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
223 SmallPtrSet<Instruction*, 4> *AggressiveInsts,
224 unsigned &CostRemaining) {
225 Instruction *I = dyn_cast<Instruction>(V);
227 // Non-instructions all dominate instructions, but not all constantexprs
228 // can be executed unconditionally.
229 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
234 BasicBlock *PBB = I->getParent();
236 // We don't want to allow weird loops that might have the "if condition" in
237 // the bottom of this block.
238 if (PBB == BB) return false;
240 // If this instruction is defined in a block that contains an unconditional
241 // branch to BB, then it must be in the 'conditional' part of the "if
242 // statement". If not, it definitely dominates the region.
243 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
244 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB)
247 // If we aren't allowing aggressive promotion anymore, then don't consider
248 // instructions in the 'if region'.
249 if (AggressiveInsts == 0) return false;
251 // If we have seen this instruction before, don't count it again.
252 if (AggressiveInsts->count(I)) return true;
254 // Okay, it looks like the instruction IS in the "condition". Check to
255 // see if it's a cheap instruction to unconditionally compute, and if it
256 // only uses stuff defined outside of the condition. If so, hoist it out.
257 if (!I->isSafeToSpeculativelyExecute())
262 switch (I->getOpcode()) {
263 default: return false; // Cannot hoist this out safely.
264 case Instruction::Load:
265 // We have to check to make sure there are no instructions before the
266 // load in its basic block, as we are going to hoist the load out to its
268 if (PBB->getFirstNonPHIOrDbg() != I)
272 case Instruction::GetElementPtr:
273 // GEPs are cheap if all indices are constant.
274 if (!cast<GetElementPtrInst>(I)->hasAllConstantIndices())
278 case Instruction::Add:
279 case Instruction::Sub:
280 case Instruction::And:
281 case Instruction::Or:
282 case Instruction::Xor:
283 case Instruction::Shl:
284 case Instruction::LShr:
285 case Instruction::AShr:
286 case Instruction::ICmp:
287 case Instruction::Trunc:
288 case Instruction::ZExt:
289 case Instruction::SExt:
291 break; // These are all cheap and non-trapping instructions.
293 case Instruction::Select:
298 if (Cost > CostRemaining)
301 CostRemaining -= Cost;
303 // Okay, we can only really hoist these out if their operands do
304 // not take us over the cost threshold.
305 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
306 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining))
308 // Okay, it's safe to do this! Remember this instruction.
309 AggressiveInsts->insert(I);
313 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
314 /// and PointerNullValue. Return NULL if value is not a constant int.
315 static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
316 // Normal constant int.
317 ConstantInt *CI = dyn_cast<ConstantInt>(V);
318 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
321 // This is some kind of pointer constant. Turn it into a pointer-sized
322 // ConstantInt if possible.
323 const IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
325 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
326 if (isa<ConstantPointerNull>(V))
327 return ConstantInt::get(PtrTy, 0);
329 // IntToPtr const int.
330 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
331 if (CE->getOpcode() == Instruction::IntToPtr)
332 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
333 // The constant is very likely to have the right type already.
334 if (CI->getType() == PtrTy)
337 return cast<ConstantInt>
338 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
343 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
344 /// collection of icmp eq/ne instructions that compare a value against a
345 /// constant, return the value being compared, and stick the constant into the
348 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
349 const TargetData *TD, bool isEQ, unsigned &UsedICmps) {
350 Instruction *I = dyn_cast<Instruction>(V);
351 if (I == 0) return 0;
353 // If this is an icmp against a constant, handle this as one of the cases.
354 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
355 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
356 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
359 return I->getOperand(0);
362 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
365 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
367 // If this is an and/!= check then we want to optimize "x ugt 2" into
370 Span = Span.inverse();
372 // If there are a ton of values, we don't want to make a ginormous switch.
373 if (Span.getSetSize().ugt(8) || Span.isEmptySet() ||
374 // We don't handle wrapped sets yet.
378 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
379 Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
381 return I->getOperand(0);
386 // Otherwise, we can only handle an | or &, depending on isEQ.
387 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
390 unsigned NumValsBeforeLHS = Vals.size();
391 unsigned UsedICmpsBeforeLHS = UsedICmps;
392 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
394 unsigned NumVals = Vals.size();
395 unsigned UsedICmpsBeforeRHS = UsedICmps;
396 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
400 Vals.resize(NumVals);
401 UsedICmps = UsedICmpsBeforeRHS;
404 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
405 // set it and return success.
406 if (Extra == 0 || Extra == I->getOperand(1)) {
407 Extra = I->getOperand(1);
411 Vals.resize(NumValsBeforeLHS);
412 UsedICmps = UsedICmpsBeforeLHS;
416 // If the LHS can't be folded in, but Extra is available and RHS can, try to
418 if (Extra == 0 || Extra == I->getOperand(0)) {
419 Value *OldExtra = Extra;
420 Extra = I->getOperand(0);
421 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
424 assert(Vals.size() == NumValsBeforeLHS);
431 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
432 Instruction* Cond = 0;
433 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
434 Cond = dyn_cast<Instruction>(SI->getCondition());
435 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
436 if (BI->isConditional())
437 Cond = dyn_cast<Instruction>(BI->getCondition());
438 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
439 Cond = dyn_cast<Instruction>(IBI->getAddress());
442 TI->eraseFromParent();
443 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
446 /// isValueEqualityComparison - Return true if the specified terminator checks
447 /// to see if a value is equal to constant integer value.
448 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
450 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
451 // Do not permit merging of large switch instructions into their
452 // predecessors unless there is only one predecessor.
453 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
454 pred_end(SI->getParent())) <= 128)
455 CV = SI->getCondition();
456 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
457 if (BI->isConditional() && BI->getCondition()->hasOneUse())
458 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
459 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
460 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
461 GetConstantInt(ICI->getOperand(1), TD))
462 CV = ICI->getOperand(0);
464 // Unwrap any lossless ptrtoint cast.
465 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
466 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
467 CV = PTII->getOperand(0);
471 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
472 /// decode all of the 'cases' that it represents and return the 'default' block.
473 BasicBlock *SimplifyCFGOpt::
474 GetValueEqualityComparisonCases(TerminatorInst *TI,
475 std::vector<std::pair<ConstantInt*,
476 BasicBlock*> > &Cases) {
477 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
478 Cases.reserve(SI->getNumCases());
479 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
480 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
481 return SI->getDefaultDest();
484 BranchInst *BI = cast<BranchInst>(TI);
485 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
486 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD),
487 BI->getSuccessor(ICI->getPredicate() ==
488 ICmpInst::ICMP_NE)));
489 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
493 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
494 /// in the list that match the specified block.
495 static void EliminateBlockCases(BasicBlock *BB,
496 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
497 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
498 if (Cases[i].second == BB) {
499 Cases.erase(Cases.begin()+i);
504 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
507 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
508 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
509 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
511 // Make V1 be smaller than V2.
512 if (V1->size() > V2->size())
515 if (V1->size() == 0) return false;
516 if (V1->size() == 1) {
518 ConstantInt *TheVal = (*V1)[0].first;
519 for (unsigned i = 0, e = V2->size(); i != e; ++i)
520 if (TheVal == (*V2)[i].first)
524 // Otherwise, just sort both lists and compare element by element.
525 array_pod_sort(V1->begin(), V1->end());
526 array_pod_sort(V2->begin(), V2->end());
527 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
528 while (i1 != e1 && i2 != e2) {
529 if ((*V1)[i1].first == (*V2)[i2].first)
531 if ((*V1)[i1].first < (*V2)[i2].first)
539 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
540 /// terminator instruction and its block is known to only have a single
541 /// predecessor block, check to see if that predecessor is also a value
542 /// comparison with the same value, and if that comparison determines the
543 /// outcome of this comparison. If so, simplify TI. This does a very limited
544 /// form of jump threading.
545 bool SimplifyCFGOpt::
546 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
548 IRBuilder<> &Builder) {
549 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
550 if (!PredVal) return false; // Not a value comparison in predecessor.
552 Value *ThisVal = isValueEqualityComparison(TI);
553 assert(ThisVal && "This isn't a value comparison!!");
554 if (ThisVal != PredVal) return false; // Different predicates.
556 // Find out information about when control will move from Pred to TI's block.
557 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
558 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
560 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
562 // Find information about how control leaves this block.
563 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
564 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
565 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
567 // If TI's block is the default block from Pred's comparison, potentially
568 // simplify TI based on this knowledge.
569 if (PredDef == TI->getParent()) {
570 // If we are here, we know that the value is none of those cases listed in
571 // PredCases. If there are any cases in ThisCases that are in PredCases, we
573 if (!ValuesOverlap(PredCases, ThisCases))
576 if (isa<BranchInst>(TI)) {
577 // Okay, one of the successors of this condbr is dead. Convert it to a
579 assert(ThisCases.size() == 1 && "Branch can only have one case!");
580 // Insert the new branch.
581 Instruction *NI = Builder.CreateBr(ThisDef);
584 // Remove PHI node entries for the dead edge.
585 ThisCases[0].second->removePredecessor(TI->getParent());
587 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
588 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
590 EraseTerminatorInstAndDCECond(TI);
594 SwitchInst *SI = cast<SwitchInst>(TI);
595 // Okay, TI has cases that are statically dead, prune them away.
596 SmallPtrSet<Constant*, 16> DeadCases;
597 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
598 DeadCases.insert(PredCases[i].first);
600 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
601 << "Through successor TI: " << *TI);
603 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
604 if (DeadCases.count(SI->getCaseValue(i))) {
605 SI->getSuccessor(i)->removePredecessor(TI->getParent());
609 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
613 // Otherwise, TI's block must correspond to some matched value. Find out
614 // which value (or set of values) this is.
615 ConstantInt *TIV = 0;
616 BasicBlock *TIBB = TI->getParent();
617 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
618 if (PredCases[i].second == TIBB) {
620 return false; // Cannot handle multiple values coming to this block.
621 TIV = PredCases[i].first;
623 assert(TIV && "No edge from pred to succ?");
625 // Okay, we found the one constant that our value can be if we get into TI's
626 // BB. Find out which successor will unconditionally be branched to.
627 BasicBlock *TheRealDest = 0;
628 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
629 if (ThisCases[i].first == TIV) {
630 TheRealDest = ThisCases[i].second;
634 // If not handled by any explicit cases, it is handled by the default case.
635 if (TheRealDest == 0) TheRealDest = ThisDef;
637 // Remove PHI node entries for dead edges.
638 BasicBlock *CheckEdge = TheRealDest;
639 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
640 if (*SI != CheckEdge)
641 (*SI)->removePredecessor(TIBB);
645 // Insert the new branch.
646 Instruction *NI = Builder.CreateBr(TheRealDest);
649 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
650 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
652 EraseTerminatorInstAndDCECond(TI);
657 /// ConstantIntOrdering - This class implements a stable ordering of constant
658 /// integers that does not depend on their address. This is important for
659 /// applications that sort ConstantInt's to ensure uniqueness.
660 struct ConstantIntOrdering {
661 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
662 return LHS->getValue().ult(RHS->getValue());
667 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
668 const ConstantInt *LHS = *(const ConstantInt**)P1;
669 const ConstantInt *RHS = *(const ConstantInt**)P2;
670 if (LHS->getValue().ult(RHS->getValue()))
672 if (LHS->getValue() == RHS->getValue())
677 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
678 /// equality comparison instruction (either a switch or a branch on "X == c").
679 /// See if any of the predecessors of the terminator block are value comparisons
680 /// on the same value. If so, and if safe to do so, fold them together.
681 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
682 BasicBlock *BB = TI->getParent();
683 Value *CV = isValueEqualityComparison(TI); // CondVal
684 assert(CV && "Not a comparison?");
685 bool Changed = false;
687 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
688 while (!Preds.empty()) {
689 BasicBlock *Pred = Preds.pop_back_val();
691 // See if the predecessor is a comparison with the same value.
692 TerminatorInst *PTI = Pred->getTerminator();
693 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
695 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
696 // Figure out which 'cases' to copy from SI to PSI.
697 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
698 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
700 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
701 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
703 // Based on whether the default edge from PTI goes to BB or not, fill in
704 // PredCases and PredDefault with the new switch cases we would like to
706 SmallVector<BasicBlock*, 8> NewSuccessors;
708 if (PredDefault == BB) {
709 // If this is the default destination from PTI, only the edges in TI
710 // that don't occur in PTI, or that branch to BB will be activated.
711 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
712 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
713 if (PredCases[i].second != BB)
714 PTIHandled.insert(PredCases[i].first);
716 // The default destination is BB, we don't need explicit targets.
717 std::swap(PredCases[i], PredCases.back());
718 PredCases.pop_back();
722 // Reconstruct the new switch statement we will be building.
723 if (PredDefault != BBDefault) {
724 PredDefault->removePredecessor(Pred);
725 PredDefault = BBDefault;
726 NewSuccessors.push_back(BBDefault);
728 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
729 if (!PTIHandled.count(BBCases[i].first) &&
730 BBCases[i].second != BBDefault) {
731 PredCases.push_back(BBCases[i]);
732 NewSuccessors.push_back(BBCases[i].second);
736 // If this is not the default destination from PSI, only the edges
737 // in SI that occur in PSI with a destination of BB will be
739 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
740 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
741 if (PredCases[i].second == BB) {
742 PTIHandled.insert(PredCases[i].first);
743 std::swap(PredCases[i], PredCases.back());
744 PredCases.pop_back();
748 // Okay, now we know which constants were sent to BB from the
749 // predecessor. Figure out where they will all go now.
750 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
751 if (PTIHandled.count(BBCases[i].first)) {
752 // If this is one we are capable of getting...
753 PredCases.push_back(BBCases[i]);
754 NewSuccessors.push_back(BBCases[i].second);
755 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
758 // If there are any constants vectored to BB that TI doesn't handle,
759 // they must go to the default destination of TI.
760 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
762 E = PTIHandled.end(); I != E; ++I) {
763 PredCases.push_back(std::make_pair(*I, BBDefault));
764 NewSuccessors.push_back(BBDefault);
768 // Okay, at this point, we know which new successor Pred will get. Make
769 // sure we update the number of entries in the PHI nodes for these
771 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
772 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
774 // Convert pointer to int before we switch.
775 if (CV->getType()->isPointerTy()) {
776 assert(TD && "Cannot switch on pointer without TargetData");
777 CV = new PtrToIntInst(CV, TD->getIntPtrType(CV->getContext()),
779 cast<PtrToIntInst>(CV)->setDebugLoc(PTI->getDebugLoc());
782 // Now that the successors are updated, create the new Switch instruction.
783 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
784 PredCases.size(), PTI);
785 NewSI->setDebugLoc(PTI->getDebugLoc());
786 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
787 NewSI->addCase(PredCases[i].first, PredCases[i].second);
789 EraseTerminatorInstAndDCECond(PTI);
791 // Okay, last check. If BB is still a successor of PSI, then we must
792 // have an infinite loop case. If so, add an infinitely looping block
793 // to handle the case to preserve the behavior of the code.
794 BasicBlock *InfLoopBlock = 0;
795 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
796 if (NewSI->getSuccessor(i) == BB) {
797 if (InfLoopBlock == 0) {
798 // Insert it at the end of the function, because it's either code,
799 // or it won't matter if it's hot. :)
800 InfLoopBlock = BasicBlock::Create(BB->getContext(),
801 "infloop", BB->getParent());
802 BranchInst::Create(InfLoopBlock, InfLoopBlock);
804 NewSI->setSuccessor(i, InfLoopBlock);
813 // isSafeToHoistInvoke - If we would need to insert a select that uses the
814 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
815 // would need to do this), we can't hoist the invoke, as there is nowhere
816 // to put the select in this case.
817 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
818 Instruction *I1, Instruction *I2) {
819 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
821 for (BasicBlock::iterator BBI = SI->begin();
822 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
823 Value *BB1V = PN->getIncomingValueForBlock(BB1);
824 Value *BB2V = PN->getIncomingValueForBlock(BB2);
825 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
833 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
834 /// BB2, hoist any common code in the two blocks up into the branch block. The
835 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
836 static bool HoistThenElseCodeToIf(BranchInst *BI) {
837 // This does very trivial matching, with limited scanning, to find identical
838 // instructions in the two blocks. In particular, we don't want to get into
839 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
840 // such, we currently just scan for obviously identical instructions in an
842 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
843 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
845 BasicBlock::iterator BB1_Itr = BB1->begin();
846 BasicBlock::iterator BB2_Itr = BB2->begin();
848 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
849 // Skip debug info if it is not identical.
850 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
851 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
852 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
853 while (isa<DbgInfoIntrinsic>(I1))
855 while (isa<DbgInfoIntrinsic>(I2))
858 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
859 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
862 // If we get here, we can hoist at least one instruction.
863 BasicBlock *BIParent = BI->getParent();
866 // If we are hoisting the terminator instruction, don't move one (making a
867 // broken BB), instead clone it, and remove BI.
868 if (isa<TerminatorInst>(I1))
869 goto HoistTerminator;
871 // For a normal instruction, we just move one to right before the branch,
872 // then replace all uses of the other with the first. Finally, we remove
873 // the now redundant second instruction.
874 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
875 if (!I2->use_empty())
876 I2->replaceAllUsesWith(I1);
877 I1->intersectOptionalDataWith(I2);
878 I2->eraseFromParent();
882 // Skip debug info if it is not identical.
883 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
884 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
885 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
886 while (isa<DbgInfoIntrinsic>(I1))
888 while (isa<DbgInfoIntrinsic>(I2))
891 } while (I1->isIdenticalToWhenDefined(I2));
896 // It may not be possible to hoist an invoke.
897 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
900 // Okay, it is safe to hoist the terminator.
901 Instruction *NT = I1->clone();
902 BIParent->getInstList().insert(BI, NT);
903 if (!NT->getType()->isVoidTy()) {
904 I1->replaceAllUsesWith(NT);
905 I2->replaceAllUsesWith(NT);
909 // Hoisting one of the terminators from our successor is a great thing.
910 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
911 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
912 // nodes, so we insert select instruction to compute the final result.
913 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
914 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
916 for (BasicBlock::iterator BBI = SI->begin();
917 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
918 Value *BB1V = PN->getIncomingValueForBlock(BB1);
919 Value *BB2V = PN->getIncomingValueForBlock(BB2);
920 if (BB1V == BB2V) continue;
922 // These values do not agree. Insert a select instruction before NT
923 // that determines the right value.
924 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
926 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
927 BB1V->getName()+"."+BB2V->getName(), NT);
928 SI->setDebugLoc(BI->getDebugLoc());
930 // Make the PHI node use the select for all incoming values for BB1/BB2
931 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
932 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
933 PN->setIncomingValue(i, SI);
937 // Update any PHI nodes in our new successors.
938 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
939 AddPredecessorToBlock(*SI, BIParent, BB1);
941 EraseTerminatorInstAndDCECond(BI);
945 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
946 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
947 /// (for now, restricted to a single instruction that's side effect free) from
948 /// the BB1 into the branch block to speculatively execute it.
949 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
950 // Only speculatively execution a single instruction (not counting the
951 // terminator) for now.
952 Instruction *HInst = NULL;
953 Instruction *Term = BB1->getTerminator();
954 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
956 Instruction *I = BBI;
958 if (isa<DbgInfoIntrinsic>(I)) continue;
959 if (I == Term) break;
968 // Be conservative for now. FP select instruction can often be expensive.
969 Value *BrCond = BI->getCondition();
970 if (isa<FCmpInst>(BrCond))
973 // If BB1 is actually on the false edge of the conditional branch, remember
974 // to swap the select operands later.
976 if (BB1 != BI->getSuccessor(0)) {
977 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
984 // br i1 %t1, label %BB1, label %BB2
993 // %t3 = select i1 %t1, %t2, %t3
994 switch (HInst->getOpcode()) {
995 default: return false; // Not safe / profitable to hoist.
996 case Instruction::Add:
997 case Instruction::Sub:
998 // Not worth doing for vector ops.
999 if (HInst->getType()->isVectorTy())
1002 case Instruction::And:
1003 case Instruction::Or:
1004 case Instruction::Xor:
1005 case Instruction::Shl:
1006 case Instruction::LShr:
1007 case Instruction::AShr:
1008 // Don't mess with vector operations.
1009 if (HInst->getType()->isVectorTy())
1011 break; // These are all cheap and non-trapping instructions.
1014 // If the instruction is obviously dead, don't try to predicate it.
1015 if (HInst->use_empty()) {
1016 HInst->eraseFromParent();
1020 // Can we speculatively execute the instruction? And what is the value
1021 // if the condition is false? Consider the phi uses, if the incoming value
1022 // from the "if" block are all the same V, then V is the value of the
1023 // select if the condition is false.
1024 BasicBlock *BIParent = BI->getParent();
1025 SmallVector<PHINode*, 4> PHIUses;
1026 Value *FalseV = NULL;
1028 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
1029 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
1031 // Ignore any user that is not a PHI node in BB2. These can only occur in
1032 // unreachable blocks, because they would not be dominated by the instr.
1033 PHINode *PN = dyn_cast<PHINode>(*UI);
1034 if (!PN || PN->getParent() != BB2)
1036 PHIUses.push_back(PN);
1038 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1041 else if (FalseV != PHIV)
1042 return false; // Inconsistent value when condition is false.
1045 assert(FalseV && "Must have at least one user, and it must be a PHI");
1047 // Do not hoist the instruction if any of its operands are defined but not
1048 // used in this BB. The transformation will prevent the operand from
1049 // being sunk into the use block.
1050 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1052 Instruction *OpI = dyn_cast<Instruction>(*i);
1053 if (OpI && OpI->getParent() == BIParent &&
1054 !OpI->isUsedInBasicBlock(BIParent))
1058 // If we get here, we can hoist the instruction. Try to place it
1059 // before the icmp instruction preceding the conditional branch.
1060 BasicBlock::iterator InsertPos = BI;
1061 if (InsertPos != BIParent->begin())
1063 // Skip debug info between condition and branch.
1064 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
1066 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
1067 SmallPtrSet<Instruction *, 4> BB1Insns;
1068 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
1069 BB1I != BB1E; ++BB1I)
1070 BB1Insns.insert(BB1I);
1071 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
1073 Instruction *Use = cast<Instruction>(*UI);
1074 if (!BB1Insns.count(Use)) continue;
1076 // If BrCond uses the instruction that place it just before
1077 // branch instruction.
1083 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
1085 // Create a select whose true value is the speculatively executed value and
1086 // false value is the previously determined FalseV.
1089 SI = SelectInst::Create(BrCond, FalseV, HInst,
1090 FalseV->getName() + "." + HInst->getName(), BI);
1092 SI = SelectInst::Create(BrCond, HInst, FalseV,
1093 HInst->getName() + "." + FalseV->getName(), BI);
1094 SI->setDebugLoc(BI->getDebugLoc());
1096 // Make the PHI node use the select for all incoming values for "then" and
1098 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1099 PHINode *PN = PHIUses[i];
1100 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1101 if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent)
1102 PN->setIncomingValue(j, SI);
1109 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1110 /// across this block.
1111 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1112 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1115 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1116 if (isa<DbgInfoIntrinsic>(BBI))
1118 if (Size > 10) return false; // Don't clone large BB's.
1121 // We can only support instructions that do not define values that are
1122 // live outside of the current basic block.
1123 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1125 Instruction *U = cast<Instruction>(*UI);
1126 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1129 // Looks ok, continue checking.
1135 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1136 /// that is defined in the same block as the branch and if any PHI entries are
1137 /// constants, thread edges corresponding to that entry to be branches to their
1138 /// ultimate destination.
1139 static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
1140 BasicBlock *BB = BI->getParent();
1141 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1142 // NOTE: we currently cannot transform this case if the PHI node is used
1143 // outside of the block.
1144 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1147 // Degenerate case of a single entry PHI.
1148 if (PN->getNumIncomingValues() == 1) {
1149 FoldSingleEntryPHINodes(PN->getParent());
1153 // Now we know that this block has multiple preds and two succs.
1154 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1156 // Okay, this is a simple enough basic block. See if any phi values are
1158 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1159 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1160 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1162 // Okay, we now know that all edges from PredBB should be revectored to
1163 // branch to RealDest.
1164 BasicBlock *PredBB = PN->getIncomingBlock(i);
1165 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1167 if (RealDest == BB) continue; // Skip self loops.
1169 // The dest block might have PHI nodes, other predecessors and other
1170 // difficult cases. Instead of being smart about this, just insert a new
1171 // block that jumps to the destination block, effectively splitting
1172 // the edge we are about to create.
1173 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1174 RealDest->getName()+".critedge",
1175 RealDest->getParent(), RealDest);
1176 BranchInst::Create(RealDest, EdgeBB);
1178 // Update PHI nodes.
1179 AddPredecessorToBlock(RealDest, EdgeBB, BB);
1181 // BB may have instructions that are being threaded over. Clone these
1182 // instructions into EdgeBB. We know that there will be no uses of the
1183 // cloned instructions outside of EdgeBB.
1184 BasicBlock::iterator InsertPt = EdgeBB->begin();
1185 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1186 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1187 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1188 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1191 // Clone the instruction.
1192 Instruction *N = BBI->clone();
1193 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1195 // Update operands due to translation.
1196 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1198 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1199 if (PI != TranslateMap.end())
1203 // Check for trivial simplification.
1204 if (Value *V = SimplifyInstruction(N, TD)) {
1205 TranslateMap[BBI] = V;
1206 delete N; // Instruction folded away, don't need actual inst
1208 // Insert the new instruction into its new home.
1209 EdgeBB->getInstList().insert(InsertPt, N);
1210 if (!BBI->use_empty())
1211 TranslateMap[BBI] = N;
1215 // Loop over all of the edges from PredBB to BB, changing them to branch
1216 // to EdgeBB instead.
1217 TerminatorInst *PredBBTI = PredBB->getTerminator();
1218 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1219 if (PredBBTI->getSuccessor(i) == BB) {
1220 BB->removePredecessor(PredBB);
1221 PredBBTI->setSuccessor(i, EdgeBB);
1224 // Recurse, simplifying any other constants.
1225 return FoldCondBranchOnPHI(BI, TD) | true;
1231 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1232 /// PHI node, see if we can eliminate it.
1233 static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD,
1234 IRBuilder<> &Builder) {
1235 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1236 // statement", which has a very simple dominance structure. Basically, we
1237 // are trying to find the condition that is being branched on, which
1238 // subsequently causes this merge to happen. We really want control
1239 // dependence information for this check, but simplifycfg can't keep it up
1240 // to date, and this catches most of the cases we care about anyway.
1241 BasicBlock *BB = PN->getParent();
1242 BasicBlock *IfTrue, *IfFalse;
1243 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1245 // Don't bother if the branch will be constant folded trivially.
1246 isa<ConstantInt>(IfCond))
1249 // Okay, we found that we can merge this two-entry phi node into a select.
1250 // Doing so would require us to fold *all* two entry phi nodes in this block.
1251 // At some point this becomes non-profitable (particularly if the target
1252 // doesn't support cmov's). Only do this transformation if there are two or
1253 // fewer PHI nodes in this block.
1254 unsigned NumPhis = 0;
1255 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1259 // Loop over the PHI's seeing if we can promote them all to select
1260 // instructions. While we are at it, keep track of the instructions
1261 // that need to be moved to the dominating block.
1262 SmallPtrSet<Instruction*, 4> AggressiveInsts;
1263 unsigned MaxCostVal0 = PHINodeFoldingThreshold,
1264 MaxCostVal1 = PHINodeFoldingThreshold;
1266 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1267 PHINode *PN = cast<PHINode>(II++);
1268 if (Value *V = SimplifyInstruction(PN, TD)) {
1269 PN->replaceAllUsesWith(V);
1270 PN->eraseFromParent();
1274 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
1276 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
1281 // If we folded the the first phi, PN dangles at this point. Refresh it. If
1282 // we ran out of PHIs then we simplified them all.
1283 PN = dyn_cast<PHINode>(BB->begin());
1284 if (PN == 0) return true;
1286 // Don't fold i1 branches on PHIs which contain binary operators. These can
1287 // often be turned into switches and other things.
1288 if (PN->getType()->isIntegerTy(1) &&
1289 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1290 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1291 isa<BinaryOperator>(IfCond)))
1294 // If we all PHI nodes are promotable, check to make sure that all
1295 // instructions in the predecessor blocks can be promoted as well. If
1296 // not, we won't be able to get rid of the control flow, so it's not
1297 // worth promoting to select instructions.
1298 BasicBlock *DomBlock = 0;
1299 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1300 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1301 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1304 DomBlock = *pred_begin(IfBlock1);
1305 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1306 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1307 // This is not an aggressive instruction that we can promote.
1308 // Because of this, we won't be able to get rid of the control
1309 // flow, so the xform is not worth it.
1314 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1317 DomBlock = *pred_begin(IfBlock2);
1318 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1319 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1320 // This is not an aggressive instruction that we can promote.
1321 // Because of this, we won't be able to get rid of the control
1322 // flow, so the xform is not worth it.
1327 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1328 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1330 // If we can still promote the PHI nodes after this gauntlet of tests,
1331 // do all of the PHI's now.
1332 Instruction *InsertPt = DomBlock->getTerminator();
1333 Builder.SetInsertPoint(InsertPt);
1335 // Move all 'aggressive' instructions, which are defined in the
1336 // conditional parts of the if's up to the dominating block.
1338 DomBlock->getInstList().splice(InsertPt,
1339 IfBlock1->getInstList(), IfBlock1->begin(),
1340 IfBlock1->getTerminator());
1342 DomBlock->getInstList().splice(InsertPt,
1343 IfBlock2->getInstList(), IfBlock2->begin(),
1344 IfBlock2->getTerminator());
1346 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1347 // Change the PHI node into a select instruction.
1348 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1349 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1352 cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, ""));
1353 PN->replaceAllUsesWith(NV);
1355 PN->eraseFromParent();
1358 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1359 // has been flattened. Change DomBlock to jump directly to our new block to
1360 // avoid other simplifycfg's kicking in on the diamond.
1361 TerminatorInst *OldTI = DomBlock->getTerminator();
1362 Builder.SetInsertPoint(OldTI);
1363 Builder.CreateBr(BB);
1364 OldTI->eraseFromParent();
1368 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1369 /// to two returning blocks, try to merge them together into one return,
1370 /// introducing a select if the return values disagree.
1371 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1372 assert(BI->isConditional() && "Must be a conditional branch");
1373 BasicBlock *TrueSucc = BI->getSuccessor(0);
1374 BasicBlock *FalseSucc = BI->getSuccessor(1);
1375 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1376 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1378 // Check to ensure both blocks are empty (just a return) or optionally empty
1379 // with PHI nodes. If there are other instructions, merging would cause extra
1380 // computation on one path or the other.
1381 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1383 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1386 // Okay, we found a branch that is going to two return nodes. If
1387 // there is no return value for this function, just change the
1388 // branch into a return.
1389 if (FalseRet->getNumOperands() == 0) {
1390 TrueSucc->removePredecessor(BI->getParent());
1391 FalseSucc->removePredecessor(BI->getParent());
1392 ReturnInst::Create(BI->getContext(), 0, BI);
1393 EraseTerminatorInstAndDCECond(BI);
1397 // Otherwise, figure out what the true and false return values are
1398 // so we can insert a new select instruction.
1399 Value *TrueValue = TrueRet->getReturnValue();
1400 Value *FalseValue = FalseRet->getReturnValue();
1402 // Unwrap any PHI nodes in the return blocks.
1403 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1404 if (TVPN->getParent() == TrueSucc)
1405 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1406 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1407 if (FVPN->getParent() == FalseSucc)
1408 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1410 // In order for this transformation to be safe, we must be able to
1411 // unconditionally execute both operands to the return. This is
1412 // normally the case, but we could have a potentially-trapping
1413 // constant expression that prevents this transformation from being
1415 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1418 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1422 // Okay, we collected all the mapped values and checked them for sanity, and
1423 // defined to really do this transformation. First, update the CFG.
1424 TrueSucc->removePredecessor(BI->getParent());
1425 FalseSucc->removePredecessor(BI->getParent());
1427 // Insert select instructions where needed.
1428 Value *BrCond = BI->getCondition();
1430 // Insert a select if the results differ.
1431 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1432 } else if (isa<UndefValue>(TrueValue)) {
1433 TrueValue = FalseValue;
1435 TrueValue = SelectInst::Create(BrCond, TrueValue,
1436 FalseValue, "retval", BI);
1440 Value *RI = !TrueValue ?
1441 ReturnInst::Create(BI->getContext(), BI) :
1442 ReturnInst::Create(BI->getContext(), TrueValue, BI);
1445 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1446 << "\n " << *BI << "NewRet = " << *RI
1447 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1449 EraseTerminatorInstAndDCECond(BI);
1454 /// FoldBranchToCommonDest - If this basic block is simple enough, and if a
1455 /// predecessor branches to us and one of our successors, fold the block into
1456 /// the predecessor and use logical operations to pick the right destination.
1457 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1458 BasicBlock *BB = BI->getParent();
1459 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1460 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1461 Cond->getParent() != BB || !Cond->hasOneUse())
1464 // Only allow this if the condition is a simple instruction that can be
1465 // executed unconditionally. It must be in the same block as the branch, and
1466 // must be at the front of the block.
1467 BasicBlock::iterator FrontIt = BB->front();
1469 // Ignore dbg intrinsics.
1470 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1472 // Allow a single instruction to be hoisted in addition to the compare
1473 // that feeds the branch. We later ensure that any values that _it_ uses
1474 // were also live in the predecessor, so that we don't unnecessarily create
1475 // register pressure or inhibit out-of-order execution.
1476 Instruction *BonusInst = 0;
1477 if (&*FrontIt != Cond &&
1478 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1479 FrontIt->isSafeToSpeculativelyExecute()) {
1480 BonusInst = &*FrontIt;
1483 // Ignore dbg intrinsics.
1484 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1487 // Only a single bonus inst is allowed.
1488 if (&*FrontIt != Cond)
1491 // Make sure the instruction after the condition is the cond branch.
1492 BasicBlock::iterator CondIt = Cond; ++CondIt;
1494 // Ingore dbg intrinsics.
1495 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
1500 // Cond is known to be a compare or binary operator. Check to make sure that
1501 // neither operand is a potentially-trapping constant expression.
1502 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1505 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1509 // Finally, don't infinitely unroll conditional loops.
1510 BasicBlock *TrueDest = BI->getSuccessor(0);
1511 BasicBlock *FalseDest = BI->getSuccessor(1);
1512 if (TrueDest == BB || FalseDest == BB)
1515 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1516 BasicBlock *PredBlock = *PI;
1517 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1519 // Check that we have two conditional branches. If there is a PHI node in
1520 // the common successor, verify that the same value flows in from both
1522 if (PBI == 0 || PBI->isUnconditional() || !SafeToMergeTerminators(BI, PBI))
1525 // Determine if the two branches share a common destination.
1526 Instruction::BinaryOps Opc;
1527 bool InvertPredCond = false;
1529 if (PBI->getSuccessor(0) == TrueDest)
1530 Opc = Instruction::Or;
1531 else if (PBI->getSuccessor(1) == FalseDest)
1532 Opc = Instruction::And;
1533 else if (PBI->getSuccessor(0) == FalseDest)
1534 Opc = Instruction::And, InvertPredCond = true;
1535 else if (PBI->getSuccessor(1) == TrueDest)
1536 Opc = Instruction::Or, InvertPredCond = true;
1540 // Ensure that any values used in the bonus instruction are also used
1541 // by the terminator of the predecessor. This means that those values
1542 // must already have been resolved, so we won't be inhibiting the
1543 // out-of-order core by speculating them earlier.
1545 // Collect the values used by the bonus inst
1546 SmallPtrSet<Value*, 4> UsedValues;
1547 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1548 OE = BonusInst->op_end(); OI != OE; ++OI) {
1550 if (!isa<Constant>(V))
1551 UsedValues.insert(V);
1554 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1555 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1557 // Walk up to four levels back up the use-def chain of the predecessor's
1558 // terminator to see if all those values were used. The choice of four
1559 // levels is arbitrary, to provide a compile-time-cost bound.
1560 while (!Worklist.empty()) {
1561 std::pair<Value*, unsigned> Pair = Worklist.back();
1562 Worklist.pop_back();
1564 if (Pair.second >= 4) continue;
1565 UsedValues.erase(Pair.first);
1566 if (UsedValues.empty()) break;
1568 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
1569 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1571 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1575 if (!UsedValues.empty()) return false;
1578 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1580 // If we need to invert the condition in the pred block to match, do so now.
1581 if (InvertPredCond) {
1582 Value *NewCond = PBI->getCondition();
1584 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
1585 CmpInst *CI = cast<CmpInst>(NewCond);
1586 CI->setPredicate(CI->getInversePredicate());
1588 NewCond = BinaryOperator::CreateNot(NewCond,
1589 PBI->getCondition()->getName()+".not", PBI);
1592 PBI->setCondition(NewCond);
1593 BasicBlock *OldTrue = PBI->getSuccessor(0);
1594 BasicBlock *OldFalse = PBI->getSuccessor(1);
1595 PBI->setSuccessor(0, OldFalse);
1596 PBI->setSuccessor(1, OldTrue);
1599 // If we have a bonus inst, clone it into the predecessor block.
1600 Instruction *NewBonus = 0;
1602 NewBonus = BonusInst->clone();
1603 PredBlock->getInstList().insert(PBI, NewBonus);
1604 NewBonus->takeName(BonusInst);
1605 BonusInst->setName(BonusInst->getName()+".old");
1608 // Clone Cond into the predecessor basic block, and or/and the
1609 // two conditions together.
1610 Instruction *New = Cond->clone();
1611 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1612 PredBlock->getInstList().insert(PBI, New);
1613 New->takeName(Cond);
1614 Cond->setName(New->getName()+".old");
1616 Instruction *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1617 New, "or.cond", PBI);
1618 NewCond->setDebugLoc(PBI->getDebugLoc());
1619 PBI->setCondition(NewCond);
1620 if (PBI->getSuccessor(0) == BB) {
1621 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1622 PBI->setSuccessor(0, TrueDest);
1624 if (PBI->getSuccessor(1) == BB) {
1625 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1626 PBI->setSuccessor(1, FalseDest);
1629 // Copy any debug value intrinsics into the end of PredBlock.
1630 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
1631 if (isa<DbgInfoIntrinsic>(*I))
1632 I->clone()->insertBefore(PBI);
1639 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1640 /// predecessor of another block, this function tries to simplify it. We know
1641 /// that PBI and BI are both conditional branches, and BI is in one of the
1642 /// successor blocks of PBI - PBI branches to BI.
1643 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1644 assert(PBI->isConditional() && BI->isConditional());
1645 BasicBlock *BB = BI->getParent();
1647 // If this block ends with a branch instruction, and if there is a
1648 // predecessor that ends on a branch of the same condition, make
1649 // this conditional branch redundant.
1650 if (PBI->getCondition() == BI->getCondition() &&
1651 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1652 // Okay, the outcome of this conditional branch is statically
1653 // knowable. If this block had a single pred, handle specially.
1654 if (BB->getSinglePredecessor()) {
1655 // Turn this into a branch on constant.
1656 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1657 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1659 return true; // Nuke the branch on constant.
1662 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1663 // in the constant and simplify the block result. Subsequent passes of
1664 // simplifycfg will thread the block.
1665 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1666 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
1667 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1668 std::distance(PB, PE),
1669 BI->getCondition()->getName() + ".pr",
1671 // Okay, we're going to insert the PHI node. Since PBI is not the only
1672 // predecessor, compute the PHI'd conditional value for all of the preds.
1673 // Any predecessor where the condition is not computable we keep symbolic.
1674 for (pred_iterator PI = PB; PI != PE; ++PI) {
1675 BasicBlock *P = *PI;
1676 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
1677 PBI != BI && PBI->isConditional() &&
1678 PBI->getCondition() == BI->getCondition() &&
1679 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1680 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1681 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1684 NewPN->addIncoming(BI->getCondition(), P);
1688 BI->setCondition(NewPN);
1693 // If this is a conditional branch in an empty block, and if any
1694 // predecessors is a conditional branch to one of our destinations,
1695 // fold the conditions into logical ops and one cond br.
1696 BasicBlock::iterator BBI = BB->begin();
1697 // Ignore dbg intrinsics.
1698 while (isa<DbgInfoIntrinsic>(BBI))
1704 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1709 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1711 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1712 PBIOp = 0, BIOp = 1;
1713 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1714 PBIOp = 1, BIOp = 0;
1715 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1720 // Check to make sure that the other destination of this branch
1721 // isn't BB itself. If so, this is an infinite loop that will
1722 // keep getting unwound.
1723 if (PBI->getSuccessor(PBIOp) == BB)
1726 // Do not perform this transformation if it would require
1727 // insertion of a large number of select instructions. For targets
1728 // without predication/cmovs, this is a big pessimization.
1729 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1731 unsigned NumPhis = 0;
1732 for (BasicBlock::iterator II = CommonDest->begin();
1733 isa<PHINode>(II); ++II, ++NumPhis)
1734 if (NumPhis > 2) // Disable this xform.
1737 // Finally, if everything is ok, fold the branches to logical ops.
1738 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1740 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
1741 << "AND: " << *BI->getParent());
1744 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1745 // branch in it, where one edge (OtherDest) goes back to itself but the other
1746 // exits. We don't *know* that the program avoids the infinite loop
1747 // (even though that seems likely). If we do this xform naively, we'll end up
1748 // recursively unpeeling the loop. Since we know that (after the xform is
1749 // done) that the block *is* infinite if reached, we just make it an obviously
1750 // infinite loop with no cond branch.
1751 if (OtherDest == BB) {
1752 // Insert it at the end of the function, because it's either code,
1753 // or it won't matter if it's hot. :)
1754 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1755 "infloop", BB->getParent());
1756 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1757 OtherDest = InfLoopBlock;
1760 DEBUG(dbgs() << *PBI->getParent()->getParent());
1762 // BI may have other predecessors. Because of this, we leave
1763 // it alone, but modify PBI.
1765 // Make sure we get to CommonDest on True&True directions.
1766 Value *PBICond = PBI->getCondition();
1768 PBICond = BinaryOperator::CreateNot(PBICond,
1769 PBICond->getName()+".not",
1771 Value *BICond = BI->getCondition();
1773 BICond = BinaryOperator::CreateNot(BICond,
1774 BICond->getName()+".not",
1776 // Merge the conditions.
1777 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1779 // Modify PBI to branch on the new condition to the new dests.
1780 PBI->setCondition(Cond);
1781 PBI->setSuccessor(0, CommonDest);
1782 PBI->setSuccessor(1, OtherDest);
1784 // OtherDest may have phi nodes. If so, add an entry from PBI's
1785 // block that are identical to the entries for BI's block.
1786 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
1788 // We know that the CommonDest already had an edge from PBI to
1789 // it. If it has PHIs though, the PHIs may have different
1790 // entries for BB and PBI's BB. If so, insert a select to make
1793 for (BasicBlock::iterator II = CommonDest->begin();
1794 (PN = dyn_cast<PHINode>(II)); ++II) {
1795 Value *BIV = PN->getIncomingValueForBlock(BB);
1796 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1797 Value *PBIV = PN->getIncomingValue(PBBIdx);
1799 // Insert a select in PBI to pick the right value.
1800 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1801 PBIV->getName()+".mux", PBI);
1802 PN->setIncomingValue(PBBIdx, NV);
1806 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1807 DEBUG(dbgs() << *PBI->getParent()->getParent());
1809 // This basic block is probably dead. We know it has at least
1810 // one fewer predecessor.
1814 // SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
1815 // branch to TrueBB if Cond is true or to FalseBB if Cond is false.
1816 // Takes care of updating the successors and removing the old terminator.
1817 // Also makes sure not to introduce new successors by assuming that edges to
1818 // non-successor TrueBBs and FalseBBs aren't reachable.
1819 static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
1820 BasicBlock *TrueBB, BasicBlock *FalseBB){
1821 // Remove any superfluous successor edges from the CFG.
1822 // First, figure out which successors to preserve.
1823 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
1825 BasicBlock *KeepEdge1 = TrueBB;
1826 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
1828 // Then remove the rest.
1829 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
1830 BasicBlock *Succ = OldTerm->getSuccessor(I);
1831 // Make sure only to keep exactly one copy of each edge.
1832 if (Succ == KeepEdge1)
1834 else if (Succ == KeepEdge2)
1837 Succ->removePredecessor(OldTerm->getParent());
1840 IRBuilder<> Builder(OldTerm);
1841 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
1843 // Insert an appropriate new terminator.
1844 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
1845 if (TrueBB == FalseBB)
1846 // We were only looking for one successor, and it was present.
1847 // Create an unconditional branch to it.
1848 Builder.CreateBr(TrueBB);
1850 // We found both of the successors we were looking for.
1851 // Create a conditional branch sharing the condition of the select.
1852 Builder.CreateCondBr(Cond, TrueBB, FalseBB);
1853 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
1854 // Neither of the selected blocks were successors, so this
1855 // terminator must be unreachable.
1856 new UnreachableInst(OldTerm->getContext(), OldTerm);
1858 // One of the selected values was a successor, but the other wasn't.
1859 // Insert an unconditional branch to the one that was found;
1860 // the edge to the one that wasn't must be unreachable.
1862 // Only TrueBB was found.
1863 Builder.CreateBr(TrueBB);
1865 // Only FalseBB was found.
1866 Builder.CreateBr(FalseBB);
1869 EraseTerminatorInstAndDCECond(OldTerm);
1873 // SimplifySwitchOnSelect - Replaces
1874 // (switch (select cond, X, Y)) on constant X, Y
1875 // with a branch - conditional if X and Y lead to distinct BBs,
1876 // unconditional otherwise.
1877 static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
1878 // Check for constant integer values in the select.
1879 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
1880 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
1881 if (!TrueVal || !FalseVal)
1884 // Find the relevant condition and destinations.
1885 Value *Condition = Select->getCondition();
1886 BasicBlock *TrueBB = SI->getSuccessor(SI->findCaseValue(TrueVal));
1887 BasicBlock *FalseBB = SI->getSuccessor(SI->findCaseValue(FalseVal));
1889 // Perform the actual simplification.
1890 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB);
1893 // SimplifyIndirectBrOnSelect - Replaces
1894 // (indirectbr (select cond, blockaddress(@fn, BlockA),
1895 // blockaddress(@fn, BlockB)))
1897 // (br cond, BlockA, BlockB).
1898 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
1899 // Check that both operands of the select are block addresses.
1900 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
1901 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
1905 // Extract the actual blocks.
1906 BasicBlock *TrueBB = TBA->getBasicBlock();
1907 BasicBlock *FalseBB = FBA->getBasicBlock();
1909 // Perform the actual simplification.
1910 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB);
1913 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
1914 /// instruction (a seteq/setne with a constant) as the only instruction in a
1915 /// block that ends with an uncond branch. We are looking for a very specific
1916 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
1917 /// this case, we merge the first two "or's of icmp" into a switch, but then the
1918 /// default value goes to an uncond block with a seteq in it, we get something
1921 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
1923 /// %tmp = icmp eq i8 %A, 92
1926 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
1928 /// We prefer to split the edge to 'end' so that there is a true/false entry to
1929 /// the PHI, merging the third icmp into the switch.
1930 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
1931 const TargetData *TD,
1932 IRBuilder<> &Builder) {
1933 BasicBlock *BB = ICI->getParent();
1935 // If the block has any PHIs in it or the icmp has multiple uses, it is too
1937 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
1939 Value *V = ICI->getOperand(0);
1940 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
1942 // The pattern we're looking for is where our only predecessor is a switch on
1943 // 'V' and this block is the default case for the switch. In this case we can
1944 // fold the compared value into the switch to simplify things.
1945 BasicBlock *Pred = BB->getSinglePredecessor();
1946 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
1948 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
1949 if (SI->getCondition() != V)
1952 // If BB is reachable on a non-default case, then we simply know the value of
1953 // V in this block. Substitute it and constant fold the icmp instruction
1955 if (SI->getDefaultDest() != BB) {
1956 ConstantInt *VVal = SI->findCaseDest(BB);
1957 assert(VVal && "Should have a unique destination value");
1958 ICI->setOperand(0, VVal);
1960 if (Value *V = SimplifyInstruction(ICI, TD)) {
1961 ICI->replaceAllUsesWith(V);
1962 ICI->eraseFromParent();
1964 // BB is now empty, so it is likely to simplify away.
1965 return SimplifyCFG(BB) | true;
1968 // Ok, the block is reachable from the default dest. If the constant we're
1969 // comparing exists in one of the other edges, then we can constant fold ICI
1971 if (SI->findCaseValue(Cst) != 0) {
1973 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1974 V = ConstantInt::getFalse(BB->getContext());
1976 V = ConstantInt::getTrue(BB->getContext());
1978 ICI->replaceAllUsesWith(V);
1979 ICI->eraseFromParent();
1980 // BB is now empty, so it is likely to simplify away.
1981 return SimplifyCFG(BB) | true;
1984 // The use of the icmp has to be in the 'end' block, by the only PHI node in
1986 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
1987 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
1988 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
1989 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
1992 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
1994 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
1995 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
1997 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1998 std::swap(DefaultCst, NewCst);
2000 // Replace ICI (which is used by the PHI for the default value) with true or
2001 // false depending on if it is EQ or NE.
2002 ICI->replaceAllUsesWith(DefaultCst);
2003 ICI->eraseFromParent();
2005 // Okay, the switch goes to this block on a default value. Add an edge from
2006 // the switch to the merge point on the compared value.
2007 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
2008 BB->getParent(), BB);
2009 SI->addCase(Cst, NewBB);
2011 // NewBB branches to the phi block, add the uncond branch and the phi entry.
2012 Builder.SetInsertPoint(NewBB);
2013 Builder.SetCurrentDebugLocation(SI->getDebugLoc());
2014 Builder.CreateBr(SuccBlock);
2015 PHIUse->addIncoming(NewCst, NewBB);
2019 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
2020 /// Check to see if it is branching on an or/and chain of icmp instructions, and
2021 /// fold it into a switch instruction if so.
2022 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD) {
2023 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
2024 if (Cond == 0) return false;
2027 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2028 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2029 // 'setne's and'ed together, collect them.
2031 std::vector<ConstantInt*> Values;
2032 bool TrueWhenEqual = true;
2033 Value *ExtraCase = 0;
2034 unsigned UsedICmps = 0;
2036 if (Cond->getOpcode() == Instruction::Or) {
2037 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
2039 } else if (Cond->getOpcode() == Instruction::And) {
2040 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
2042 TrueWhenEqual = false;
2045 // If we didn't have a multiply compared value, fail.
2046 if (CompVal == 0) return false;
2048 // Avoid turning single icmps into a switch.
2052 // There might be duplicate constants in the list, which the switch
2053 // instruction can't handle, remove them now.
2054 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
2055 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2057 // If Extra was used, we require at least two switch values to do the
2058 // transformation. A switch with one value is just an cond branch.
2059 if (ExtraCase && Values.size() < 2) return false;
2061 // Figure out which block is which destination.
2062 BasicBlock *DefaultBB = BI->getSuccessor(1);
2063 BasicBlock *EdgeBB = BI->getSuccessor(0);
2064 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2066 BasicBlock *BB = BI->getParent();
2068 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
2069 << " cases into SWITCH. BB is:\n" << *BB);
2071 // If there are any extra values that couldn't be folded into the switch
2072 // then we evaluate them with an explicit branch first. Split the block
2073 // right before the condbr to handle it.
2075 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
2076 // Remove the uncond branch added to the old block.
2077 TerminatorInst *OldTI = BB->getTerminator();
2080 BranchInst::Create(EdgeBB, NewBB, ExtraCase, OldTI);
2082 BranchInst::Create(NewBB, EdgeBB, ExtraCase, OldTI);
2084 OldTI->eraseFromParent();
2086 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
2087 // for the edge we just added.
2088 AddPredecessorToBlock(EdgeBB, BB, NewBB);
2090 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
2091 << "\nEXTRABB = " << *BB);
2095 // Convert pointer to int before we switch.
2096 if (CompVal->getType()->isPointerTy()) {
2097 assert(TD && "Cannot switch on pointer without TargetData");
2098 CompVal = new PtrToIntInst(CompVal,
2099 TD->getIntPtrType(CompVal->getContext()),
2101 cast<PtrToIntInst>(CompVal)->setDebugLoc(BI->getDebugLoc());
2104 // Create the new switch instruction now.
2105 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB, Values.size(), BI);
2106 New->setDebugLoc(BI->getDebugLoc());
2108 // Add all of the 'cases' to the switch instruction.
2109 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2110 New->addCase(Values[i], EdgeBB);
2112 // We added edges from PI to the EdgeBB. As such, if there were any
2113 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2114 // the number of edges added.
2115 for (BasicBlock::iterator BBI = EdgeBB->begin();
2116 isa<PHINode>(BBI); ++BBI) {
2117 PHINode *PN = cast<PHINode>(BBI);
2118 Value *InVal = PN->getIncomingValueForBlock(BB);
2119 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2120 PN->addIncoming(InVal, BB);
2123 // Erase the old branch instruction.
2124 EraseTerminatorInstAndDCECond(BI);
2126 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
2130 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI) {
2131 BasicBlock *BB = RI->getParent();
2132 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2134 // Find predecessors that end with branches.
2135 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2136 SmallVector<BranchInst*, 8> CondBranchPreds;
2137 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2138 BasicBlock *P = *PI;
2139 TerminatorInst *PTI = P->getTerminator();
2140 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2141 if (BI->isUnconditional())
2142 UncondBranchPreds.push_back(P);
2144 CondBranchPreds.push_back(BI);
2148 // If we found some, do the transformation!
2149 if (!UncondBranchPreds.empty() && DupRet) {
2150 while (!UncondBranchPreds.empty()) {
2151 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2152 DEBUG(dbgs() << "FOLDING: " << *BB
2153 << "INTO UNCOND BRANCH PRED: " << *Pred);
2154 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
2157 // If we eliminated all predecessors of the block, delete the block now.
2158 if (pred_begin(BB) == pred_end(BB))
2159 // We know there are no successors, so just nuke the block.
2160 BB->eraseFromParent();
2165 // Check out all of the conditional branches going to this return
2166 // instruction. If any of them just select between returns, change the
2167 // branch itself into a select/return pair.
2168 while (!CondBranchPreds.empty()) {
2169 BranchInst *BI = CondBranchPreds.pop_back_val();
2171 // Check to see if the non-BB successor is also a return block.
2172 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2173 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2174 SimplifyCondBranchToTwoReturns(BI))
2180 bool SimplifyCFGOpt::SimplifyUnwind(UnwindInst *UI, IRBuilder<> &Builder) {
2181 // Check to see if the first instruction in this block is just an unwind.
2182 // If so, replace any invoke instructions which use this as an exception
2183 // destination with call instructions.
2184 BasicBlock *BB = UI->getParent();
2185 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2187 bool Changed = false;
2188 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2189 while (!Preds.empty()) {
2190 BasicBlock *Pred = Preds.back();
2191 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
2192 if (II && II->getUnwindDest() == BB) {
2193 // Insert a new branch instruction before the invoke, because this
2194 // is now a fall through.
2195 Builder.SetInsertPoint(II);
2196 BranchInst *BI = Builder.CreateBr(II->getNormalDest());
2197 Pred->getInstList().remove(II); // Take out of symbol table
2199 // Insert the call now.
2200 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
2201 Builder.SetInsertPoint(BI);
2202 CallInst *CI = Builder.CreateCall(II->getCalledValue(),
2203 Args.begin(), Args.end(),
2205 CI->setCallingConv(II->getCallingConv());
2206 CI->setAttributes(II->getAttributes());
2207 // If the invoke produced a value, the Call now does instead.
2208 II->replaceAllUsesWith(CI);
2216 // If this block is now dead (and isn't the entry block), remove it.
2217 if (pred_begin(BB) == pred_end(BB) &&
2218 BB != &BB->getParent()->getEntryBlock()) {
2219 // We know there are no successors, so just nuke the block.
2220 BB->eraseFromParent();
2227 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2228 BasicBlock *BB = UI->getParent();
2230 bool Changed = false;
2232 // If there are any instructions immediately before the unreachable that can
2233 // be removed, do so.
2234 while (UI != BB->begin()) {
2235 BasicBlock::iterator BBI = UI;
2237 // Do not delete instructions that can have side effects, like calls
2238 // (which may never return) and volatile loads and stores.
2239 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2241 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
2242 if (SI->isVolatile())
2245 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
2246 if (LI->isVolatile())
2249 // Delete this instruction (any uses are guaranteed to be dead)
2250 if (!BBI->use_empty())
2251 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
2252 BBI->eraseFromParent();
2256 // If the unreachable instruction is the first in the block, take a gander
2257 // at all of the predecessors of this instruction, and simplify them.
2258 if (&BB->front() != UI) return Changed;
2260 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2261 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2262 TerminatorInst *TI = Preds[i]->getTerminator();
2264 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2265 if (BI->isUnconditional()) {
2266 if (BI->getSuccessor(0) == BB) {
2267 new UnreachableInst(TI->getContext(), TI);
2268 TI->eraseFromParent();
2272 if (BI->getSuccessor(0) == BB) {
2273 BranchInst::Create(BI->getSuccessor(1), BI);
2274 EraseTerminatorInstAndDCECond(BI);
2275 } else if (BI->getSuccessor(1) == BB) {
2276 BranchInst::Create(BI->getSuccessor(0), BI);
2277 EraseTerminatorInstAndDCECond(BI);
2281 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2282 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2283 if (SI->getSuccessor(i) == BB) {
2284 BB->removePredecessor(SI->getParent());
2289 // If the default value is unreachable, figure out the most popular
2290 // destination and make it the default.
2291 if (SI->getSuccessor(0) == BB) {
2292 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
2293 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
2294 std::pair<unsigned, unsigned>& entry =
2295 Popularity[SI->getSuccessor(i)];
2296 if (entry.first == 0) {
2304 // Find the most popular block.
2305 unsigned MaxPop = 0;
2306 unsigned MaxIndex = 0;
2307 BasicBlock *MaxBlock = 0;
2308 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
2309 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2310 if (I->second.first > MaxPop ||
2311 (I->second.first == MaxPop && MaxIndex > I->second.second)) {
2312 MaxPop = I->second.first;
2313 MaxIndex = I->second.second;
2314 MaxBlock = I->first;
2318 // Make this the new default, allowing us to delete any explicit
2320 SI->setSuccessor(0, MaxBlock);
2323 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2325 if (isa<PHINode>(MaxBlock->begin()))
2326 for (unsigned i = 0; i != MaxPop-1; ++i)
2327 MaxBlock->removePredecessor(SI->getParent());
2329 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2330 if (SI->getSuccessor(i) == MaxBlock) {
2336 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2337 if (II->getUnwindDest() == BB) {
2338 // Convert the invoke to a call instruction. This would be a good
2339 // place to note that the call does not throw though.
2340 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2341 II->removeFromParent(); // Take out of symbol table
2343 // Insert the call now...
2344 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2345 CallInst *CI = CallInst::Create(II->getCalledValue(),
2346 Args.begin(), Args.end(),
2348 CI->setCallingConv(II->getCallingConv());
2349 CI->setAttributes(II->getAttributes());
2350 // If the invoke produced a value, the call does now instead.
2351 II->replaceAllUsesWith(CI);
2358 // If this block is now dead, remove it.
2359 if (pred_begin(BB) == pred_end(BB) &&
2360 BB != &BB->getParent()->getEntryBlock()) {
2361 // We know there are no successors, so just nuke the block.
2362 BB->eraseFromParent();
2369 /// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
2370 /// integer range comparison into a sub, an icmp and a branch.
2371 static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
2372 assert(SI->getNumCases() > 2 && "Degenerate switch?");
2374 // Make sure all cases point to the same destination and gather the values.
2375 SmallVector<ConstantInt *, 16> Cases;
2376 Cases.push_back(SI->getCaseValue(1));
2377 for (unsigned I = 2, E = SI->getNumCases(); I != E; ++I) {
2378 if (SI->getSuccessor(I-1) != SI->getSuccessor(I))
2380 Cases.push_back(SI->getCaseValue(I));
2382 assert(Cases.size() == SI->getNumCases()-1 && "Not all cases gathered");
2384 // Sort the case values, then check if they form a range we can transform.
2385 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
2386 for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
2387 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
2391 Constant *Offset = ConstantExpr::getNeg(Cases.back());
2392 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases()-1);
2394 Value *Sub = SI->getCondition();
2395 if (!Offset->isNullValue())
2396 Sub = BinaryOperator::CreateAdd(Sub, Offset, Sub->getName()+".off", SI);
2397 Value *Cmp = new ICmpInst(SI, ICmpInst::ICMP_ULT, Sub, NumCases, "switch");
2398 Builder.CreateCondBr(Cmp, SI->getSuccessor(1), SI->getDefaultDest());
2400 // Prune obsolete incoming values off the successor's PHI nodes.
2401 for (BasicBlock::iterator BBI = SI->getSuccessor(1)->begin();
2402 isa<PHINode>(BBI); ++BBI) {
2403 for (unsigned I = 0, E = SI->getNumCases()-2; I != E; ++I)
2404 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
2406 SI->eraseFromParent();
2411 /// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch
2412 /// and use it to remove dead cases.
2413 static bool EliminateDeadSwitchCases(SwitchInst *SI) {
2414 Value *Cond = SI->getCondition();
2415 unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth();
2416 APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
2417 ComputeMaskedBits(Cond, APInt::getAllOnesValue(Bits), KnownZero, KnownOne);
2419 // Gather dead cases.
2420 SmallVector<ConstantInt*, 8> DeadCases;
2421 for (unsigned I = 1, E = SI->getNumCases(); I != E; ++I) {
2422 if ((SI->getCaseValue(I)->getValue() & KnownZero) != 0 ||
2423 (SI->getCaseValue(I)->getValue() & KnownOne) != KnownOne) {
2424 DeadCases.push_back(SI->getCaseValue(I));
2425 DEBUG(dbgs() << "SimplifyCFG: switch case '"
2426 << SI->getCaseValue(I)->getValue() << "' is dead.\n");
2430 // Remove dead cases from the switch.
2431 for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) {
2432 unsigned Case = SI->findCaseValue(DeadCases[I]);
2433 // Prune unused values from PHI nodes.
2434 SI->getSuccessor(Case)->removePredecessor(SI->getParent());
2435 SI->removeCase(Case);
2438 return !DeadCases.empty();
2441 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
2442 // If this switch is too complex to want to look at, ignore it.
2443 if (!isValueEqualityComparison(SI))
2446 BasicBlock *BB = SI->getParent();
2448 // If we only have one predecessor, and if it is a branch on this value,
2449 // see if that predecessor totally determines the outcome of this switch.
2450 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2451 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
2452 return SimplifyCFG(BB) | true;
2454 Value *Cond = SI->getCondition();
2455 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
2456 if (SimplifySwitchOnSelect(SI, Select))
2457 return SimplifyCFG(BB) | true;
2459 // If the block only contains the switch, see if we can fold the block
2460 // away into any preds.
2461 BasicBlock::iterator BBI = BB->begin();
2462 // Ignore dbg intrinsics.
2463 while (isa<DbgInfoIntrinsic>(BBI))
2466 if (FoldValueComparisonIntoPredecessors(SI))
2467 return SimplifyCFG(BB) | true;
2469 // Try to transform the switch into an icmp and a branch.
2470 if (TurnSwitchRangeIntoICmp(SI, Builder))
2471 return SimplifyCFG(BB) | true;
2473 // Remove unreachable cases.
2474 if (EliminateDeadSwitchCases(SI))
2475 return SimplifyCFG(BB) | true;
2480 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
2481 BasicBlock *BB = IBI->getParent();
2482 bool Changed = false;
2484 // Eliminate redundant destinations.
2485 SmallPtrSet<Value *, 8> Succs;
2486 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2487 BasicBlock *Dest = IBI->getDestination(i);
2488 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2489 Dest->removePredecessor(BB);
2490 IBI->removeDestination(i);
2496 if (IBI->getNumDestinations() == 0) {
2497 // If the indirectbr has no successors, change it to unreachable.
2498 new UnreachableInst(IBI->getContext(), IBI);
2499 EraseTerminatorInstAndDCECond(IBI);
2503 if (IBI->getNumDestinations() == 1) {
2504 // If the indirectbr has one successor, change it to a direct branch.
2505 BranchInst::Create(IBI->getDestination(0), IBI);
2506 EraseTerminatorInstAndDCECond(IBI);
2510 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2511 if (SimplifyIndirectBrOnSelect(IBI, SI))
2512 return SimplifyCFG(BB) | true;
2517 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
2518 BasicBlock *BB = BI->getParent();
2520 // If the Terminator is the only non-phi instruction, simplify the block.
2521 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg();
2522 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
2523 TryToSimplifyUncondBranchFromEmptyBlock(BB))
2526 // If the only instruction in the block is a seteq/setne comparison
2527 // against a constant, try to simplify the block.
2528 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
2529 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
2530 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
2532 if (I->isTerminator()
2533 && TryToSimplifyUncondBranchWithICmpInIt(ICI, TD, Builder))
2541 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
2542 BasicBlock *BB = BI->getParent();
2544 // Conditional branch
2545 if (isValueEqualityComparison(BI)) {
2546 // If we only have one predecessor, and if it is a branch on this value,
2547 // see if that predecessor totally determines the outcome of this
2549 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2550 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
2551 return SimplifyCFG(BB) | true;
2553 // This block must be empty, except for the setcond inst, if it exists.
2554 // Ignore dbg intrinsics.
2555 BasicBlock::iterator I = BB->begin();
2556 // Ignore dbg intrinsics.
2557 while (isa<DbgInfoIntrinsic>(I))
2560 if (FoldValueComparisonIntoPredecessors(BI))
2561 return SimplifyCFG(BB) | true;
2562 } else if (&*I == cast<Instruction>(BI->getCondition())){
2564 // Ignore dbg intrinsics.
2565 while (isa<DbgInfoIntrinsic>(I))
2567 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI))
2568 return SimplifyCFG(BB) | true;
2572 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
2573 if (SimplifyBranchOnICmpChain(BI, TD))
2576 // We have a conditional branch to two blocks that are only reachable
2577 // from BI. We know that the condbr dominates the two blocks, so see if
2578 // there is any identical code in the "then" and "else" blocks. If so, we
2579 // can hoist it up to the branching block.
2580 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
2581 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2582 if (HoistThenElseCodeToIf(BI))
2583 return SimplifyCFG(BB) | true;
2585 // If Successor #1 has multiple preds, we may be able to conditionally
2586 // execute Successor #0 if it branches to successor #1.
2587 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
2588 if (Succ0TI->getNumSuccessors() == 1 &&
2589 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
2590 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
2591 return SimplifyCFG(BB) | true;
2593 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2594 // If Successor #0 has multiple preds, we may be able to conditionally
2595 // execute Successor #1 if it branches to successor #0.
2596 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
2597 if (Succ1TI->getNumSuccessors() == 1 &&
2598 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
2599 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
2600 return SimplifyCFG(BB) | true;
2603 // If this is a branch on a phi node in the current block, thread control
2604 // through this block if any PHI node entries are constants.
2605 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
2606 if (PN->getParent() == BI->getParent())
2607 if (FoldCondBranchOnPHI(BI, TD))
2608 return SimplifyCFG(BB) | true;
2610 // If this basic block is ONLY a setcc and a branch, and if a predecessor
2611 // branches to us and one of our successors, fold the setcc into the
2612 // predecessor and use logical operations to pick the right destination.
2613 if (FoldBranchToCommonDest(BI))
2614 return SimplifyCFG(BB) | true;
2616 // Scan predecessor blocks for conditional branches.
2617 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2618 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2619 if (PBI != BI && PBI->isConditional())
2620 if (SimplifyCondBranchToCondBranch(PBI, BI))
2621 return SimplifyCFG(BB) | true;
2626 bool SimplifyCFGOpt::run(BasicBlock *BB) {
2627 bool Changed = false;
2629 assert(BB && BB->getParent() && "Block not embedded in function!");
2630 assert(BB->getTerminator() && "Degenerate basic block encountered!");
2632 // Remove basic blocks that have no predecessors (except the entry block)...
2633 // or that just have themself as a predecessor. These are unreachable.
2634 if ((pred_begin(BB) == pred_end(BB) &&
2635 BB != &BB->getParent()->getEntryBlock()) ||
2636 BB->getSinglePredecessor() == BB) {
2637 DEBUG(dbgs() << "Removing BB: \n" << *BB);
2638 DeleteDeadBlock(BB);
2642 // Check to see if we can constant propagate this terminator instruction
2644 Changed |= ConstantFoldTerminator(BB);
2646 // Check for and eliminate duplicate PHI nodes in this block.
2647 Changed |= EliminateDuplicatePHINodes(BB);
2649 // Merge basic blocks into their predecessor if there is only one distinct
2650 // pred, and if there is only one distinct successor of the predecessor, and
2651 // if there are no PHI nodes.
2653 if (MergeBlockIntoPredecessor(BB))
2656 IRBuilder<> Builder(BB);
2658 // If there is a trivial two-entry PHI node in this basic block, and we can
2659 // eliminate it, do so now.
2660 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
2661 if (PN->getNumIncomingValues() == 2)
2662 Changed |= FoldTwoEntryPHINode(PN, TD, Builder);
2664 Builder.SetInsertPoint(BB->getTerminator());
2665 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
2666 if (BI->isUnconditional()) {
2667 if (SimplifyUncondBranch(BI, Builder)) return true;
2669 if (SimplifyCondBranch(BI, Builder)) return true;
2671 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
2672 if (SimplifyReturn(RI)) return true;
2673 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
2674 if (SimplifySwitch(SI, Builder)) return true;
2675 } else if (UnreachableInst *UI =
2676 dyn_cast<UnreachableInst>(BB->getTerminator())) {
2677 if (SimplifyUnreachable(UI)) return true;
2678 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
2679 if (SimplifyUnwind(UI, Builder)) return true;
2680 } else if (IndirectBrInst *IBI =
2681 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
2682 if (SimplifyIndirectBr(IBI)) return true;
2688 /// SimplifyCFG - This function is used to do simplification of a CFG. For
2689 /// example, it adjusts branches to branches to eliminate the extra hop, it
2690 /// eliminates unreachable basic blocks, and does other "peephole" optimization
2691 /// of the CFG. It returns true if a modification was made.
2693 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
2694 return SimplifyCFGOpt(TD).run(BB);