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/DerivedTypes.h"
18 #include "llvm/GlobalVariable.h"
19 #include "llvm/Instructions.h"
20 #include "llvm/IntrinsicInst.h"
21 #include "llvm/LLVMContext.h"
22 #include "llvm/Metadata.h"
23 #include "llvm/Operator.h"
24 #include "llvm/Type.h"
25 #include "llvm/Analysis/InstructionSimplify.h"
26 #include "llvm/Analysis/ValueTracking.h"
27 #include "llvm/Target/TargetData.h"
28 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
29 #include "llvm/ADT/DenseMap.h"
30 #include "llvm/ADT/SetVector.h"
31 #include "llvm/ADT/SmallVector.h"
32 #include "llvm/ADT/SmallPtrSet.h"
33 #include "llvm/ADT/Statistic.h"
34 #include "llvm/ADT/STLExtras.h"
35 #include "llvm/Support/CFG.h"
36 #include "llvm/Support/CommandLine.h"
37 #include "llvm/Support/ConstantRange.h"
38 #include "llvm/Support/Debug.h"
39 #include "llvm/Support/IRBuilder.h"
40 #include "llvm/Support/MDBuilder.h"
41 #include "llvm/Support/NoFolder.h"
42 #include "llvm/Support/raw_ostream.h"
48 static cl::opt<unsigned>
49 PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(1),
50 cl::desc("Control the amount of phi node folding to perform (default = 1)"));
53 DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false),
54 cl::desc("Duplicate return instructions into unconditional branches"));
56 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
59 class SimplifyCFGOpt {
60 const TargetData *const TD;
62 Value *isValueEqualityComparison(TerminatorInst *TI);
63 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
64 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases);
65 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
67 IRBuilder<> &Builder);
68 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
69 IRBuilder<> &Builder);
71 bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder);
72 bool SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder);
73 bool SimplifyUnreachable(UnreachableInst *UI);
74 bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
75 bool SimplifyIndirectBr(IndirectBrInst *IBI);
76 bool SimplifyUncondBranch(BranchInst *BI, IRBuilder <> &Builder);
77 bool SimplifyCondBranch(BranchInst *BI, IRBuilder <>&Builder);
80 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
81 bool run(BasicBlock *BB);
85 /// SafeToMergeTerminators - Return true if it is safe to merge these two
86 /// terminator instructions together.
88 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
89 if (SI1 == SI2) return false; // Can't merge with self!
91 // It is not safe to merge these two switch instructions if they have a common
92 // successor, and if that successor has a PHI node, and if *that* PHI node has
93 // conflicting incoming values from the two switch blocks.
94 BasicBlock *SI1BB = SI1->getParent();
95 BasicBlock *SI2BB = SI2->getParent();
96 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
98 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
99 if (SI1Succs.count(*I))
100 for (BasicBlock::iterator BBI = (*I)->begin();
101 isa<PHINode>(BBI); ++BBI) {
102 PHINode *PN = cast<PHINode>(BBI);
103 if (PN->getIncomingValueForBlock(SI1BB) !=
104 PN->getIncomingValueForBlock(SI2BB))
111 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
112 /// now be entries in it from the 'NewPred' block. The values that will be
113 /// flowing into the PHI nodes will be the same as those coming in from
114 /// ExistPred, an existing predecessor of Succ.
115 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
116 BasicBlock *ExistPred) {
117 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
120 for (BasicBlock::iterator I = Succ->begin();
121 (PN = dyn_cast<PHINode>(I)); ++I)
122 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
126 /// GetIfCondition - Given a basic block (BB) with two predecessors (and at
127 /// least one PHI node in it), check to see if the merge at this block is due
128 /// to an "if condition". If so, return the boolean condition that determines
129 /// which entry into BB will be taken. Also, return by references the block
130 /// that will be entered from if the condition is true, and the block that will
131 /// be entered if the condition is false.
133 /// This does no checking to see if the true/false blocks have large or unsavory
134 /// instructions in them.
135 static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
136 BasicBlock *&IfFalse) {
137 PHINode *SomePHI = cast<PHINode>(BB->begin());
138 assert(SomePHI->getNumIncomingValues() == 2 &&
139 "Function can only handle blocks with 2 predecessors!");
140 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
141 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
143 // We can only handle branches. Other control flow will be lowered to
144 // branches if possible anyway.
145 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
146 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
147 if (Pred1Br == 0 || Pred2Br == 0)
150 // Eliminate code duplication by ensuring that Pred1Br is conditional if
152 if (Pred2Br->isConditional()) {
153 // If both branches are conditional, we don't have an "if statement". In
154 // reality, we could transform this case, but since the condition will be
155 // required anyway, we stand no chance of eliminating it, so the xform is
156 // probably not profitable.
157 if (Pred1Br->isConditional())
160 std::swap(Pred1, Pred2);
161 std::swap(Pred1Br, Pred2Br);
164 if (Pred1Br->isConditional()) {
165 // The only thing we have to watch out for here is to make sure that Pred2
166 // doesn't have incoming edges from other blocks. If it does, the condition
167 // doesn't dominate BB.
168 if (Pred2->getSinglePredecessor() == 0)
171 // If we found a conditional branch predecessor, make sure that it branches
172 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
173 if (Pred1Br->getSuccessor(0) == BB &&
174 Pred1Br->getSuccessor(1) == Pred2) {
177 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
178 Pred1Br->getSuccessor(1) == BB) {
182 // We know that one arm of the conditional goes to BB, so the other must
183 // go somewhere unrelated, and this must not be an "if statement".
187 return Pred1Br->getCondition();
190 // Ok, if we got here, both predecessors end with an unconditional branch to
191 // BB. Don't panic! If both blocks only have a single (identical)
192 // predecessor, and THAT is a conditional branch, then we're all ok!
193 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
194 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
197 // Otherwise, if this is a conditional branch, then we can use it!
198 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
199 if (BI == 0) return 0;
201 assert(BI->isConditional() && "Two successors but not conditional?");
202 if (BI->getSuccessor(0) == Pred1) {
209 return BI->getCondition();
212 /// ComputeSpeculuationCost - Compute an abstract "cost" of speculating the
213 /// given instruction, which is assumed to be safe to speculate. 1 means
214 /// cheap, 2 means less cheap, and UINT_MAX means prohibitively expensive.
215 static unsigned ComputeSpeculationCost(const User *I) {
216 assert(isSafeToSpeculativelyExecute(I) &&
217 "Instruction is not safe to speculatively execute!");
218 switch (Operator::getOpcode(I)) {
220 // In doubt, be conservative.
222 case Instruction::GetElementPtr:
223 // GEPs are cheap if all indices are constant.
224 if (!cast<GEPOperator>(I)->hasAllConstantIndices())
227 case Instruction::Load:
228 case Instruction::Add:
229 case Instruction::Sub:
230 case Instruction::And:
231 case Instruction::Or:
232 case Instruction::Xor:
233 case Instruction::Shl:
234 case Instruction::LShr:
235 case Instruction::AShr:
236 case Instruction::ICmp:
237 case Instruction::Trunc:
238 case Instruction::ZExt:
239 case Instruction::SExt:
240 return 1; // These are all cheap.
242 case Instruction::Call:
243 case Instruction::Select:
248 /// DominatesMergePoint - If we have a merge point of an "if condition" as
249 /// accepted above, return true if the specified value dominates the block. We
250 /// don't handle the true generality of domination here, just a special case
251 /// which works well enough for us.
253 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
254 /// see if V (which must be an instruction) and its recursive operands
255 /// that do not dominate BB have a combined cost lower than CostRemaining and
256 /// are non-trapping. If both are true, the instruction is inserted into the
257 /// set and true is returned.
259 /// The cost for most non-trapping instructions is defined as 1 except for
260 /// Select whose cost is 2.
262 /// After this function returns, CostRemaining is decreased by the cost of
263 /// V plus its non-dominating operands. If that cost is greater than
264 /// CostRemaining, false is returned and CostRemaining is undefined.
265 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
266 SmallPtrSet<Instruction*, 4> *AggressiveInsts,
267 unsigned &CostRemaining) {
268 Instruction *I = dyn_cast<Instruction>(V);
270 // Non-instructions all dominate instructions, but not all constantexprs
271 // can be executed unconditionally.
272 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
277 BasicBlock *PBB = I->getParent();
279 // We don't want to allow weird loops that might have the "if condition" in
280 // the bottom of this block.
281 if (PBB == BB) return false;
283 // If this instruction is defined in a block that contains an unconditional
284 // branch to BB, then it must be in the 'conditional' part of the "if
285 // statement". If not, it definitely dominates the region.
286 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
287 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB)
290 // If we aren't allowing aggressive promotion anymore, then don't consider
291 // instructions in the 'if region'.
292 if (AggressiveInsts == 0) return false;
294 // If we have seen this instruction before, don't count it again.
295 if (AggressiveInsts->count(I)) return true;
297 // Okay, it looks like the instruction IS in the "condition". Check to
298 // see if it's a cheap instruction to unconditionally compute, and if it
299 // only uses stuff defined outside of the condition. If so, hoist it out.
300 if (!isSafeToSpeculativelyExecute(I))
303 unsigned Cost = ComputeSpeculationCost(I);
305 if (Cost > CostRemaining)
308 CostRemaining -= Cost;
310 // Okay, we can only really hoist these out if their operands do
311 // not take us over the cost threshold.
312 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
313 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining))
315 // Okay, it's safe to do this! Remember this instruction.
316 AggressiveInsts->insert(I);
320 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
321 /// and PointerNullValue. Return NULL if value is not a constant int.
322 static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
323 // Normal constant int.
324 ConstantInt *CI = dyn_cast<ConstantInt>(V);
325 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
328 // This is some kind of pointer constant. Turn it into a pointer-sized
329 // ConstantInt if possible.
330 IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
332 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
333 if (isa<ConstantPointerNull>(V))
334 return ConstantInt::get(PtrTy, 0);
336 // IntToPtr const int.
337 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
338 if (CE->getOpcode() == Instruction::IntToPtr)
339 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
340 // The constant is very likely to have the right type already.
341 if (CI->getType() == PtrTy)
344 return cast<ConstantInt>
345 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
350 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
351 /// collection of icmp eq/ne instructions that compare a value against a
352 /// constant, return the value being compared, and stick the constant into the
355 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
356 const TargetData *TD, bool isEQ, unsigned &UsedICmps) {
357 Instruction *I = dyn_cast<Instruction>(V);
358 if (I == 0) return 0;
360 // If this is an icmp against a constant, handle this as one of the cases.
361 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
362 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
363 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
366 return I->getOperand(0);
369 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
372 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
374 // If this is an and/!= check then we want to optimize "x ugt 2" into
377 Span = Span.inverse();
379 // If there are a ton of values, we don't want to make a ginormous switch.
380 if (Span.getSetSize().ugt(8) || Span.isEmptySet())
383 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
384 Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
386 return I->getOperand(0);
391 // Otherwise, we can only handle an | or &, depending on isEQ.
392 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
395 unsigned NumValsBeforeLHS = Vals.size();
396 unsigned UsedICmpsBeforeLHS = UsedICmps;
397 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
399 unsigned NumVals = Vals.size();
400 unsigned UsedICmpsBeforeRHS = UsedICmps;
401 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
405 Vals.resize(NumVals);
406 UsedICmps = UsedICmpsBeforeRHS;
409 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
410 // set it and return success.
411 if (Extra == 0 || Extra == I->getOperand(1)) {
412 Extra = I->getOperand(1);
416 Vals.resize(NumValsBeforeLHS);
417 UsedICmps = UsedICmpsBeforeLHS;
421 // If the LHS can't be folded in, but Extra is available and RHS can, try to
423 if (Extra == 0 || Extra == I->getOperand(0)) {
424 Value *OldExtra = Extra;
425 Extra = I->getOperand(0);
426 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
429 assert(Vals.size() == NumValsBeforeLHS);
436 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
437 Instruction *Cond = 0;
438 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
439 Cond = dyn_cast<Instruction>(SI->getCondition());
440 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
441 if (BI->isConditional())
442 Cond = dyn_cast<Instruction>(BI->getCondition());
443 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
444 Cond = dyn_cast<Instruction>(IBI->getAddress());
447 TI->eraseFromParent();
448 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
451 /// isValueEqualityComparison - Return true if the specified terminator checks
452 /// to see if a value is equal to constant integer value.
453 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
455 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
456 // Do not permit merging of large switch instructions into their
457 // predecessors unless there is only one predecessor.
458 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
459 pred_end(SI->getParent())) <= 128)
460 CV = SI->getCondition();
461 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
462 if (BI->isConditional() && BI->getCondition()->hasOneUse())
463 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
464 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
465 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
466 GetConstantInt(ICI->getOperand(1), TD))
467 CV = ICI->getOperand(0);
469 // Unwrap any lossless ptrtoint cast.
470 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
471 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
472 CV = PTII->getOperand(0);
476 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
477 /// decode all of the 'cases' that it represents and return the 'default' block.
478 BasicBlock *SimplifyCFGOpt::
479 GetValueEqualityComparisonCases(TerminatorInst *TI,
480 std::vector<std::pair<ConstantInt*,
481 BasicBlock*> > &Cases) {
482 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
483 Cases.reserve(SI->getNumCases());
484 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i)
485 Cases.push_back(std::make_pair(i.getCaseValue(),
486 i.getCaseSuccessor()));
487 return SI->getDefaultDest();
490 BranchInst *BI = cast<BranchInst>(TI);
491 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
492 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD),
493 BI->getSuccessor(ICI->getPredicate() ==
494 ICmpInst::ICMP_NE)));
495 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
499 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
500 /// in the list that match the specified block.
501 static void EliminateBlockCases(BasicBlock *BB,
502 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
503 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
504 if (Cases[i].second == BB) {
505 Cases.erase(Cases.begin()+i);
510 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
513 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
514 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
515 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
517 // Make V1 be smaller than V2.
518 if (V1->size() > V2->size())
521 if (V1->size() == 0) return false;
522 if (V1->size() == 1) {
524 ConstantInt *TheVal = (*V1)[0].first;
525 for (unsigned i = 0, e = V2->size(); i != e; ++i)
526 if (TheVal == (*V2)[i].first)
530 // Otherwise, just sort both lists and compare element by element.
531 array_pod_sort(V1->begin(), V1->end());
532 array_pod_sort(V2->begin(), V2->end());
533 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
534 while (i1 != e1 && i2 != e2) {
535 if ((*V1)[i1].first == (*V2)[i2].first)
537 if ((*V1)[i1].first < (*V2)[i2].first)
545 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
546 /// terminator instruction and its block is known to only have a single
547 /// predecessor block, check to see if that predecessor is also a value
548 /// comparison with the same value, and if that comparison determines the
549 /// outcome of this comparison. If so, simplify TI. This does a very limited
550 /// form of jump threading.
551 bool SimplifyCFGOpt::
552 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
554 IRBuilder<> &Builder) {
555 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
556 if (!PredVal) return false; // Not a value comparison in predecessor.
558 Value *ThisVal = isValueEqualityComparison(TI);
559 assert(ThisVal && "This isn't a value comparison!!");
560 if (ThisVal != PredVal) return false; // Different predicates.
562 // Find out information about when control will move from Pred to TI's block.
563 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
564 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
566 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
568 // Find information about how control leaves this block.
569 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
570 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
571 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
573 // If TI's block is the default block from Pred's comparison, potentially
574 // simplify TI based on this knowledge.
575 if (PredDef == TI->getParent()) {
576 // If we are here, we know that the value is none of those cases listed in
577 // PredCases. If there are any cases in ThisCases that are in PredCases, we
579 if (!ValuesOverlap(PredCases, ThisCases))
582 if (isa<BranchInst>(TI)) {
583 // Okay, one of the successors of this condbr is dead. Convert it to a
585 assert(ThisCases.size() == 1 && "Branch can only have one case!");
586 // Insert the new branch.
587 Instruction *NI = Builder.CreateBr(ThisDef);
590 // Remove PHI node entries for the dead edge.
591 ThisCases[0].second->removePredecessor(TI->getParent());
593 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
594 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
596 EraseTerminatorInstAndDCECond(TI);
600 SwitchInst *SI = cast<SwitchInst>(TI);
601 // Okay, TI has cases that are statically dead, prune them away.
602 SmallPtrSet<Constant*, 16> DeadCases;
603 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
604 DeadCases.insert(PredCases[i].first);
606 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
607 << "Through successor TI: " << *TI);
609 for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) {
611 if (DeadCases.count(i.getCaseValue())) {
612 i.getCaseSuccessor()->removePredecessor(TI->getParent());
617 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
621 // Otherwise, TI's block must correspond to some matched value. Find out
622 // which value (or set of values) this is.
623 ConstantInt *TIV = 0;
624 BasicBlock *TIBB = TI->getParent();
625 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
626 if (PredCases[i].second == TIBB) {
628 return false; // Cannot handle multiple values coming to this block.
629 TIV = PredCases[i].first;
631 assert(TIV && "No edge from pred to succ?");
633 // Okay, we found the one constant that our value can be if we get into TI's
634 // BB. Find out which successor will unconditionally be branched to.
635 BasicBlock *TheRealDest = 0;
636 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
637 if (ThisCases[i].first == TIV) {
638 TheRealDest = ThisCases[i].second;
642 // If not handled by any explicit cases, it is handled by the default case.
643 if (TheRealDest == 0) TheRealDest = ThisDef;
645 // Remove PHI node entries for dead edges.
646 BasicBlock *CheckEdge = TheRealDest;
647 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
648 if (*SI != CheckEdge)
649 (*SI)->removePredecessor(TIBB);
653 // Insert the new branch.
654 Instruction *NI = Builder.CreateBr(TheRealDest);
657 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
658 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
660 EraseTerminatorInstAndDCECond(TI);
665 /// ConstantIntOrdering - This class implements a stable ordering of constant
666 /// integers that does not depend on their address. This is important for
667 /// applications that sort ConstantInt's to ensure uniqueness.
668 struct ConstantIntOrdering {
669 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
670 return LHS->getValue().ult(RHS->getValue());
675 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
676 const ConstantInt *LHS = *(const ConstantInt**)P1;
677 const ConstantInt *RHS = *(const ConstantInt**)P2;
678 if (LHS->getValue().ult(RHS->getValue()))
680 if (LHS->getValue() == RHS->getValue())
685 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
686 /// equality comparison instruction (either a switch or a branch on "X == c").
687 /// See if any of the predecessors of the terminator block are value comparisons
688 /// on the same value. If so, and if safe to do so, fold them together.
689 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
690 IRBuilder<> &Builder) {
691 BasicBlock *BB = TI->getParent();
692 Value *CV = isValueEqualityComparison(TI); // CondVal
693 assert(CV && "Not a comparison?");
694 bool Changed = false;
696 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
697 while (!Preds.empty()) {
698 BasicBlock *Pred = Preds.pop_back_val();
700 // See if the predecessor is a comparison with the same value.
701 TerminatorInst *PTI = Pred->getTerminator();
702 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
704 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
705 // Figure out which 'cases' to copy from SI to PSI.
706 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
707 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
709 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
710 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
712 // Based on whether the default edge from PTI goes to BB or not, fill in
713 // PredCases and PredDefault with the new switch cases we would like to
715 SmallVector<BasicBlock*, 8> NewSuccessors;
717 if (PredDefault == BB) {
718 // If this is the default destination from PTI, only the edges in TI
719 // that don't occur in PTI, or that branch to BB will be activated.
720 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
721 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
722 if (PredCases[i].second != BB)
723 PTIHandled.insert(PredCases[i].first);
725 // The default destination is BB, we don't need explicit targets.
726 std::swap(PredCases[i], PredCases.back());
727 PredCases.pop_back();
731 // Reconstruct the new switch statement we will be building.
732 if (PredDefault != BBDefault) {
733 PredDefault->removePredecessor(Pred);
734 PredDefault = BBDefault;
735 NewSuccessors.push_back(BBDefault);
737 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
738 if (!PTIHandled.count(BBCases[i].first) &&
739 BBCases[i].second != BBDefault) {
740 PredCases.push_back(BBCases[i]);
741 NewSuccessors.push_back(BBCases[i].second);
745 // If this is not the default destination from PSI, only the edges
746 // in SI that occur in PSI with a destination of BB will be
748 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
749 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
750 if (PredCases[i].second == BB) {
751 PTIHandled.insert(PredCases[i].first);
752 std::swap(PredCases[i], PredCases.back());
753 PredCases.pop_back();
757 // Okay, now we know which constants were sent to BB from the
758 // predecessor. Figure out where they will all go now.
759 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
760 if (PTIHandled.count(BBCases[i].first)) {
761 // If this is one we are capable of getting...
762 PredCases.push_back(BBCases[i]);
763 NewSuccessors.push_back(BBCases[i].second);
764 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
767 // If there are any constants vectored to BB that TI doesn't handle,
768 // they must go to the default destination of TI.
769 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
771 E = PTIHandled.end(); I != E; ++I) {
772 PredCases.push_back(std::make_pair(*I, BBDefault));
773 NewSuccessors.push_back(BBDefault);
777 // Okay, at this point, we know which new successor Pred will get. Make
778 // sure we update the number of entries in the PHI nodes for these
780 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
781 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
783 Builder.SetInsertPoint(PTI);
784 // Convert pointer to int before we switch.
785 if (CV->getType()->isPointerTy()) {
786 assert(TD && "Cannot switch on pointer without TargetData");
787 CV = Builder.CreatePtrToInt(CV, TD->getIntPtrType(CV->getContext()),
791 // Now that the successors are updated, create the new Switch instruction.
792 SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault,
794 NewSI->setDebugLoc(PTI->getDebugLoc());
795 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
796 NewSI->addCase(PredCases[i].first, PredCases[i].second);
798 EraseTerminatorInstAndDCECond(PTI);
800 // Okay, last check. If BB is still a successor of PSI, then we must
801 // have an infinite loop case. If so, add an infinitely looping block
802 // to handle the case to preserve the behavior of the code.
803 BasicBlock *InfLoopBlock = 0;
804 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
805 if (NewSI->getSuccessor(i) == BB) {
806 if (InfLoopBlock == 0) {
807 // Insert it at the end of the function, because it's either code,
808 // or it won't matter if it's hot. :)
809 InfLoopBlock = BasicBlock::Create(BB->getContext(),
810 "infloop", BB->getParent());
811 BranchInst::Create(InfLoopBlock, InfLoopBlock);
813 NewSI->setSuccessor(i, InfLoopBlock);
822 // isSafeToHoistInvoke - If we would need to insert a select that uses the
823 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
824 // would need to do this), we can't hoist the invoke, as there is nowhere
825 // to put the select in this case.
826 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
827 Instruction *I1, Instruction *I2) {
828 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
830 for (BasicBlock::iterator BBI = SI->begin();
831 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
832 Value *BB1V = PN->getIncomingValueForBlock(BB1);
833 Value *BB2V = PN->getIncomingValueForBlock(BB2);
834 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
842 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
843 /// BB2, hoist any common code in the two blocks up into the branch block. The
844 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
845 static bool HoistThenElseCodeToIf(BranchInst *BI) {
846 // This does very trivial matching, with limited scanning, to find identical
847 // instructions in the two blocks. In particular, we don't want to get into
848 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
849 // such, we currently just scan for obviously identical instructions in an
851 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
852 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
854 BasicBlock::iterator BB1_Itr = BB1->begin();
855 BasicBlock::iterator BB2_Itr = BB2->begin();
857 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
858 // Skip debug info if it is not identical.
859 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
860 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
861 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
862 while (isa<DbgInfoIntrinsic>(I1))
864 while (isa<DbgInfoIntrinsic>(I2))
867 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
868 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
871 // If we get here, we can hoist at least one instruction.
872 BasicBlock *BIParent = BI->getParent();
875 // If we are hoisting the terminator instruction, don't move one (making a
876 // broken BB), instead clone it, and remove BI.
877 if (isa<TerminatorInst>(I1))
878 goto HoistTerminator;
880 // For a normal instruction, we just move one to right before the branch,
881 // then replace all uses of the other with the first. Finally, we remove
882 // the now redundant second instruction.
883 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
884 if (!I2->use_empty())
885 I2->replaceAllUsesWith(I1);
886 I1->intersectOptionalDataWith(I2);
887 I2->eraseFromParent();
891 // Skip debug info if it is not identical.
892 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
893 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
894 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
895 while (isa<DbgInfoIntrinsic>(I1))
897 while (isa<DbgInfoIntrinsic>(I2))
900 } while (I1->isIdenticalToWhenDefined(I2));
905 // It may not be possible to hoist an invoke.
906 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
909 // Okay, it is safe to hoist the terminator.
910 Instruction *NT = I1->clone();
911 BIParent->getInstList().insert(BI, NT);
912 if (!NT->getType()->isVoidTy()) {
913 I1->replaceAllUsesWith(NT);
914 I2->replaceAllUsesWith(NT);
918 IRBuilder<true, NoFolder> Builder(NT);
919 // Hoisting one of the terminators from our successor is a great thing.
920 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
921 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
922 // nodes, so we insert select instruction to compute the final result.
923 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
924 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
926 for (BasicBlock::iterator BBI = SI->begin();
927 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
928 Value *BB1V = PN->getIncomingValueForBlock(BB1);
929 Value *BB2V = PN->getIncomingValueForBlock(BB2);
930 if (BB1V == BB2V) continue;
932 // These values do not agree. Insert a select instruction before NT
933 // that determines the right value.
934 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
936 SI = cast<SelectInst>
937 (Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,
938 BB1V->getName()+"."+BB2V->getName()));
940 // Make the PHI node use the select for all incoming values for BB1/BB2
941 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
942 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
943 PN->setIncomingValue(i, SI);
947 // Update any PHI nodes in our new successors.
948 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
949 AddPredecessorToBlock(*SI, BIParent, BB1);
951 EraseTerminatorInstAndDCECond(BI);
955 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
956 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
957 /// (for now, restricted to a single instruction that's side effect free) from
958 /// the BB1 into the branch block to speculatively execute it.
963 /// br i1 %t1, label %BB1, label %BB2
972 /// %t3 = select i1 %t1, %t2, %t3
973 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
974 // Only speculatively execution a single instruction (not counting the
975 // terminator) for now.
976 Instruction *HInst = NULL;
977 Instruction *Term = BB1->getTerminator();
978 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
980 Instruction *I = BBI;
982 if (isa<DbgInfoIntrinsic>(I)) continue;
983 if (I == Term) break;
990 BasicBlock *BIParent = BI->getParent();
992 // Check the instruction to be hoisted, if there is one.
994 // Don't hoist the instruction if it's unsafe or expensive.
995 if (!isSafeToSpeculativelyExecute(HInst))
997 if (ComputeSpeculationCost(HInst) > PHINodeFoldingThreshold)
1000 // Do not hoist the instruction if any of its operands are defined but not
1001 // used in this BB. The transformation will prevent the operand from
1002 // being sunk into the use block.
1003 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1005 Instruction *OpI = dyn_cast<Instruction>(*i);
1006 if (OpI && OpI->getParent() == BIParent &&
1007 !OpI->mayHaveSideEffects() &&
1008 !OpI->isUsedInBasicBlock(BIParent))
1013 // Be conservative for now. FP select instruction can often be expensive.
1014 Value *BrCond = BI->getCondition();
1015 if (isa<FCmpInst>(BrCond))
1018 // If BB1 is actually on the false edge of the conditional branch, remember
1019 // to swap the select operands later.
1020 bool Invert = false;
1021 if (BB1 != BI->getSuccessor(0)) {
1022 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
1026 // Collect interesting PHIs, and scan for hazards.
1027 SmallSetVector<std::pair<Value *, Value *>, 4> PHIs;
1028 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
1029 for (BasicBlock::iterator I = BB2->begin();
1030 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1031 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1032 Value *BIParentV = PN->getIncomingValueForBlock(BIParent);
1034 // Skip PHIs which are trivial.
1035 if (BB1V == BIParentV)
1038 // Check for saftey.
1039 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BB1V)) {
1040 // An unfolded ConstantExpr could end up getting expanded into
1041 // Instructions. Don't speculate this and another instruction at
1045 if (!isSafeToSpeculativelyExecute(CE))
1047 if (ComputeSpeculationCost(CE) > PHINodeFoldingThreshold)
1051 // Ok, we may insert a select for this PHI.
1052 PHIs.insert(std::make_pair(BB1V, BIParentV));
1055 // If there are no PHIs to process, bail early. This helps ensure idempotence
1060 // If we get here, we can hoist the instruction and if-convert.
1061 DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *BB1 << "\n";);
1063 // Hoist the instruction.
1065 BIParent->getInstList().splice(BI, BB1->getInstList(), HInst);
1067 // Insert selects and rewrite the PHI operands.
1068 IRBuilder<true, NoFolder> Builder(BI);
1069 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
1070 Value *TrueV = PHIs[i].first;
1071 Value *FalseV = PHIs[i].second;
1073 // Create a select whose true value is the speculatively executed value and
1074 // false value is the previously determined FalseV.
1077 SI = cast<SelectInst>
1078 (Builder.CreateSelect(BrCond, FalseV, TrueV,
1079 FalseV->getName() + "." + TrueV->getName()));
1081 SI = cast<SelectInst>
1082 (Builder.CreateSelect(BrCond, TrueV, FalseV,
1083 TrueV->getName() + "." + FalseV->getName()));
1085 // Make the PHI node use the select for all incoming values for "then" and
1087 for (BasicBlock::iterator I = BB2->begin();
1088 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1089 unsigned BB1I = PN->getBasicBlockIndex(BB1);
1090 unsigned BIParentI = PN->getBasicBlockIndex(BIParent);
1091 Value *BB1V = PN->getIncomingValue(BB1I);
1092 Value *BIParentV = PN->getIncomingValue(BIParentI);
1093 if (TrueV == BB1V && FalseV == BIParentV) {
1094 PN->setIncomingValue(BB1I, SI);
1095 PN->setIncomingValue(BIParentI, SI);
1104 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1105 /// across this block.
1106 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1107 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1110 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1111 if (isa<DbgInfoIntrinsic>(BBI))
1113 if (Size > 10) return false; // Don't clone large BB's.
1116 // We can only support instructions that do not define values that are
1117 // live outside of the current basic block.
1118 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1120 Instruction *U = cast<Instruction>(*UI);
1121 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1124 // Looks ok, continue checking.
1130 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1131 /// that is defined in the same block as the branch and if any PHI entries are
1132 /// constants, thread edges corresponding to that entry to be branches to their
1133 /// ultimate destination.
1134 static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
1135 BasicBlock *BB = BI->getParent();
1136 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1137 // NOTE: we currently cannot transform this case if the PHI node is used
1138 // outside of the block.
1139 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1142 // Degenerate case of a single entry PHI.
1143 if (PN->getNumIncomingValues() == 1) {
1144 FoldSingleEntryPHINodes(PN->getParent());
1148 // Now we know that this block has multiple preds and two succs.
1149 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1151 // Okay, this is a simple enough basic block. See if any phi values are
1153 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1154 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1155 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1157 // Okay, we now know that all edges from PredBB should be revectored to
1158 // branch to RealDest.
1159 BasicBlock *PredBB = PN->getIncomingBlock(i);
1160 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1162 if (RealDest == BB) continue; // Skip self loops.
1163 // Skip if the predecessor's terminator is an indirect branch.
1164 if (isa<IndirectBrInst>(PredBB->getTerminator())) continue;
1166 // The dest block might have PHI nodes, other predecessors and other
1167 // difficult cases. Instead of being smart about this, just insert a new
1168 // block that jumps to the destination block, effectively splitting
1169 // the edge we are about to create.
1170 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1171 RealDest->getName()+".critedge",
1172 RealDest->getParent(), RealDest);
1173 BranchInst::Create(RealDest, EdgeBB);
1175 // Update PHI nodes.
1176 AddPredecessorToBlock(RealDest, EdgeBB, BB);
1178 // BB may have instructions that are being threaded over. Clone these
1179 // instructions into EdgeBB. We know that there will be no uses of the
1180 // cloned instructions outside of EdgeBB.
1181 BasicBlock::iterator InsertPt = EdgeBB->begin();
1182 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1183 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1184 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1185 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1188 // Clone the instruction.
1189 Instruction *N = BBI->clone();
1190 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1192 // Update operands due to translation.
1193 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1195 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1196 if (PI != TranslateMap.end())
1200 // Check for trivial simplification.
1201 if (Value *V = SimplifyInstruction(N, TD)) {
1202 TranslateMap[BBI] = V;
1203 delete N; // Instruction folded away, don't need actual inst
1205 // Insert the new instruction into its new home.
1206 EdgeBB->getInstList().insert(InsertPt, N);
1207 if (!BBI->use_empty())
1208 TranslateMap[BBI] = N;
1212 // Loop over all of the edges from PredBB to BB, changing them to branch
1213 // to EdgeBB instead.
1214 TerminatorInst *PredBBTI = PredBB->getTerminator();
1215 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1216 if (PredBBTI->getSuccessor(i) == BB) {
1217 BB->removePredecessor(PredBB);
1218 PredBBTI->setSuccessor(i, EdgeBB);
1221 // Recurse, simplifying any other constants.
1222 return FoldCondBranchOnPHI(BI, TD) | true;
1228 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1229 /// PHI node, see if we can eliminate it.
1230 static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
1231 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1232 // statement", which has a very simple dominance structure. Basically, we
1233 // are trying to find the condition that is being branched on, which
1234 // subsequently causes this merge to happen. We really want control
1235 // dependence information for this check, but simplifycfg can't keep it up
1236 // to date, and this catches most of the cases we care about anyway.
1237 BasicBlock *BB = PN->getParent();
1238 BasicBlock *IfTrue, *IfFalse;
1239 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1241 // Don't bother if the branch will be constant folded trivially.
1242 isa<ConstantInt>(IfCond))
1245 // Okay, we found that we can merge this two-entry phi node into a select.
1246 // Doing so would require us to fold *all* two entry phi nodes in this block.
1247 // At some point this becomes non-profitable (particularly if the target
1248 // doesn't support cmov's). Only do this transformation if there are two or
1249 // fewer PHI nodes in this block.
1250 unsigned NumPhis = 0;
1251 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1255 // Loop over the PHI's seeing if we can promote them all to select
1256 // instructions. While we are at it, keep track of the instructions
1257 // that need to be moved to the dominating block.
1258 SmallPtrSet<Instruction*, 4> AggressiveInsts;
1259 unsigned MaxCostVal0 = PHINodeFoldingThreshold,
1260 MaxCostVal1 = PHINodeFoldingThreshold;
1262 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1263 PHINode *PN = cast<PHINode>(II++);
1264 if (Value *V = SimplifyInstruction(PN, TD)) {
1265 PN->replaceAllUsesWith(V);
1266 PN->eraseFromParent();
1270 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
1272 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
1277 // If we folded the the first phi, PN dangles at this point. Refresh it. If
1278 // we ran out of PHIs then we simplified them all.
1279 PN = dyn_cast<PHINode>(BB->begin());
1280 if (PN == 0) return true;
1282 // Don't fold i1 branches on PHIs which contain binary operators. These can
1283 // often be turned into switches and other things.
1284 if (PN->getType()->isIntegerTy(1) &&
1285 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1286 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1287 isa<BinaryOperator>(IfCond)))
1290 // If we all PHI nodes are promotable, check to make sure that all
1291 // instructions in the predecessor blocks can be promoted as well. If
1292 // not, we won't be able to get rid of the control flow, so it's not
1293 // worth promoting to select instructions.
1294 BasicBlock *DomBlock = 0;
1295 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1296 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1297 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1300 DomBlock = *pred_begin(IfBlock1);
1301 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1302 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1303 // This is not an aggressive instruction that we can promote.
1304 // Because of this, we won't be able to get rid of the control
1305 // flow, so the xform is not worth it.
1310 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1313 DomBlock = *pred_begin(IfBlock2);
1314 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1315 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1316 // This is not an aggressive instruction that we can promote.
1317 // Because of this, we won't be able to get rid of the control
1318 // flow, so the xform is not worth it.
1323 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1324 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1326 // If we can still promote the PHI nodes after this gauntlet of tests,
1327 // do all of the PHI's now.
1328 Instruction *InsertPt = DomBlock->getTerminator();
1329 IRBuilder<true, NoFolder> Builder(InsertPt);
1331 // Move all 'aggressive' instructions, which are defined in the
1332 // conditional parts of the if's up to the dominating block.
1334 DomBlock->getInstList().splice(InsertPt,
1335 IfBlock1->getInstList(), IfBlock1->begin(),
1336 IfBlock1->getTerminator());
1338 DomBlock->getInstList().splice(InsertPt,
1339 IfBlock2->getInstList(), IfBlock2->begin(),
1340 IfBlock2->getTerminator());
1342 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1343 // Change the PHI node into a select instruction.
1344 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1345 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1348 cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, ""));
1349 PN->replaceAllUsesWith(NV);
1351 PN->eraseFromParent();
1354 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1355 // has been flattened. Change DomBlock to jump directly to our new block to
1356 // avoid other simplifycfg's kicking in on the diamond.
1357 TerminatorInst *OldTI = DomBlock->getTerminator();
1358 Builder.SetInsertPoint(OldTI);
1359 Builder.CreateBr(BB);
1360 OldTI->eraseFromParent();
1364 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1365 /// to two returning blocks, try to merge them together into one return,
1366 /// introducing a select if the return values disagree.
1367 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
1368 IRBuilder<> &Builder) {
1369 assert(BI->isConditional() && "Must be a conditional branch");
1370 BasicBlock *TrueSucc = BI->getSuccessor(0);
1371 BasicBlock *FalseSucc = BI->getSuccessor(1);
1372 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1373 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1375 // Check to ensure both blocks are empty (just a return) or optionally empty
1376 // with PHI nodes. If there are other instructions, merging would cause extra
1377 // computation on one path or the other.
1378 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1380 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1383 Builder.SetInsertPoint(BI);
1384 // Okay, we found a branch that is going to two return nodes. If
1385 // there is no return value for this function, just change the
1386 // branch into a return.
1387 if (FalseRet->getNumOperands() == 0) {
1388 TrueSucc->removePredecessor(BI->getParent());
1389 FalseSucc->removePredecessor(BI->getParent());
1390 Builder.CreateRetVoid();
1391 EraseTerminatorInstAndDCECond(BI);
1395 // Otherwise, figure out what the true and false return values are
1396 // so we can insert a new select instruction.
1397 Value *TrueValue = TrueRet->getReturnValue();
1398 Value *FalseValue = FalseRet->getReturnValue();
1400 // Unwrap any PHI nodes in the return blocks.
1401 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1402 if (TVPN->getParent() == TrueSucc)
1403 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1404 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1405 if (FVPN->getParent() == FalseSucc)
1406 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1408 // In order for this transformation to be safe, we must be able to
1409 // unconditionally execute both operands to the return. This is
1410 // normally the case, but we could have a potentially-trapping
1411 // constant expression that prevents this transformation from being
1413 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1416 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1420 // Okay, we collected all the mapped values and checked them for sanity, and
1421 // defined to really do this transformation. First, update the CFG.
1422 TrueSucc->removePredecessor(BI->getParent());
1423 FalseSucc->removePredecessor(BI->getParent());
1425 // Insert select instructions where needed.
1426 Value *BrCond = BI->getCondition();
1428 // Insert a select if the results differ.
1429 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1430 } else if (isa<UndefValue>(TrueValue)) {
1431 TrueValue = FalseValue;
1433 TrueValue = Builder.CreateSelect(BrCond, TrueValue,
1434 FalseValue, "retval");
1438 Value *RI = !TrueValue ?
1439 Builder.CreateRetVoid() : Builder.CreateRet(TrueValue);
1443 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1444 << "\n " << *BI << "NewRet = " << *RI
1445 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1447 EraseTerminatorInstAndDCECond(BI);
1452 /// ExtractBranchMetadata - Given a conditional BranchInstruction, retrieve the
1453 /// probabilities of the branch taking each edge. Fills in the two APInt
1454 /// parameters and return true, or returns false if no or invalid metadata was
1456 static bool ExtractBranchMetadata(BranchInst *BI,
1457 APInt &ProbTrue, APInt &ProbFalse) {
1458 assert(BI->isConditional() &&
1459 "Looking for probabilities on unconditional branch?");
1460 MDNode *ProfileData = BI->getMetadata(LLVMContext::MD_prof);
1461 if (!ProfileData || ProfileData->getNumOperands() != 3) return false;
1462 ConstantInt *CITrue = dyn_cast<ConstantInt>(ProfileData->getOperand(1));
1463 ConstantInt *CIFalse = dyn_cast<ConstantInt>(ProfileData->getOperand(2));
1464 if (!CITrue || !CIFalse) return false;
1465 ProbTrue = CITrue->getValue();
1466 ProbFalse = CIFalse->getValue();
1467 assert(ProbTrue.getBitWidth() == 32 && ProbFalse.getBitWidth() == 32 &&
1468 "Branch probability metadata must be 32-bit integers");
1472 /// MultiplyAndLosePrecision - Multiplies A and B, then returns the result. In
1473 /// the event of overflow, logically-shifts all four inputs right until the
1475 static APInt MultiplyAndLosePrecision(APInt &A, APInt &B, APInt &C, APInt &D,
1476 unsigned &BitsLost) {
1478 bool Overflow = false;
1479 APInt Result = A.umul_ov(B, Overflow);
1481 APInt MaxB = APInt::getMaxValue(A.getBitWidth()).udiv(A);
1485 } while (B.ugt(MaxB));
1486 A = A.lshr(BitsLost);
1487 C = C.lshr(BitsLost);
1488 D = D.lshr(BitsLost);
1495 /// FoldBranchToCommonDest - If this basic block is simple enough, and if a
1496 /// predecessor branches to us and one of our successors, fold the block into
1497 /// the predecessor and use logical operations to pick the right destination.
1498 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1499 BasicBlock *BB = BI->getParent();
1501 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1502 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1503 Cond->getParent() != BB || !Cond->hasOneUse())
1506 // Only allow this if the condition is a simple instruction that can be
1507 // executed unconditionally. It must be in the same block as the branch, and
1508 // must be at the front of the block.
1509 BasicBlock::iterator FrontIt = BB->front();
1511 // Ignore dbg intrinsics.
1512 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1514 // Allow a single instruction to be hoisted in addition to the compare
1515 // that feeds the branch. We later ensure that any values that _it_ uses
1516 // were also live in the predecessor, so that we don't unnecessarily create
1517 // register pressure or inhibit out-of-order execution.
1518 Instruction *BonusInst = 0;
1519 if (&*FrontIt != Cond &&
1520 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1521 isSafeToSpeculativelyExecute(FrontIt)) {
1522 BonusInst = &*FrontIt;
1525 // Ignore dbg intrinsics.
1526 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1529 // Only a single bonus inst is allowed.
1530 if (&*FrontIt != Cond)
1533 // Make sure the instruction after the condition is the cond branch.
1534 BasicBlock::iterator CondIt = Cond; ++CondIt;
1536 // Ingore dbg intrinsics.
1537 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
1542 // Cond is known to be a compare or binary operator. Check to make sure that
1543 // neither operand is a potentially-trapping constant expression.
1544 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1547 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1551 // Finally, don't infinitely unroll conditional loops.
1552 BasicBlock *TrueDest = BI->getSuccessor(0);
1553 BasicBlock *FalseDest = BI->getSuccessor(1);
1554 if (TrueDest == BB || FalseDest == BB)
1557 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1558 BasicBlock *PredBlock = *PI;
1559 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1561 // Check that we have two conditional branches. If there is a PHI node in
1562 // the common successor, verify that the same value flows in from both
1564 if (PBI == 0 || PBI->isUnconditional() || !SafeToMergeTerminators(BI, PBI))
1567 // Determine if the two branches share a common destination.
1568 Instruction::BinaryOps Opc;
1569 bool InvertPredCond = false;
1571 if (PBI->getSuccessor(0) == TrueDest)
1572 Opc = Instruction::Or;
1573 else if (PBI->getSuccessor(1) == FalseDest)
1574 Opc = Instruction::And;
1575 else if (PBI->getSuccessor(0) == FalseDest)
1576 Opc = Instruction::And, InvertPredCond = true;
1577 else if (PBI->getSuccessor(1) == TrueDest)
1578 Opc = Instruction::Or, InvertPredCond = true;
1582 // Ensure that any values used in the bonus instruction are also used
1583 // by the terminator of the predecessor. This means that those values
1584 // must already have been resolved, so we won't be inhibiting the
1585 // out-of-order core by speculating them earlier.
1587 // Collect the values used by the bonus inst
1588 SmallPtrSet<Value*, 4> UsedValues;
1589 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1590 OE = BonusInst->op_end(); OI != OE; ++OI) {
1592 if (!isa<Constant>(V))
1593 UsedValues.insert(V);
1596 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1597 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1599 // Walk up to four levels back up the use-def chain of the predecessor's
1600 // terminator to see if all those values were used. The choice of four
1601 // levels is arbitrary, to provide a compile-time-cost bound.
1602 while (!Worklist.empty()) {
1603 std::pair<Value*, unsigned> Pair = Worklist.back();
1604 Worklist.pop_back();
1606 if (Pair.second >= 4) continue;
1607 UsedValues.erase(Pair.first);
1608 if (UsedValues.empty()) break;
1610 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
1611 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1613 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1617 if (!UsedValues.empty()) return false;
1620 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1621 IRBuilder<> Builder(PBI);
1623 // If we need to invert the condition in the pred block to match, do so now.
1624 if (InvertPredCond) {
1625 Value *NewCond = PBI->getCondition();
1627 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
1628 CmpInst *CI = cast<CmpInst>(NewCond);
1629 CI->setPredicate(CI->getInversePredicate());
1631 NewCond = Builder.CreateNot(NewCond,
1632 PBI->getCondition()->getName()+".not");
1635 PBI->setCondition(NewCond);
1636 PBI->swapSuccessors();
1639 // If we have a bonus inst, clone it into the predecessor block.
1640 Instruction *NewBonus = 0;
1642 NewBonus = BonusInst->clone();
1643 PredBlock->getInstList().insert(PBI, NewBonus);
1644 NewBonus->takeName(BonusInst);
1645 BonusInst->setName(BonusInst->getName()+".old");
1648 // Clone Cond into the predecessor basic block, and or/and the
1649 // two conditions together.
1650 Instruction *New = Cond->clone();
1651 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1652 PredBlock->getInstList().insert(PBI, New);
1653 New->takeName(Cond);
1654 Cond->setName(New->getName()+".old");
1656 Instruction *NewCond =
1657 cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(),
1659 PBI->setCondition(NewCond);
1660 if (PBI->getSuccessor(0) == BB) {
1661 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1662 PBI->setSuccessor(0, TrueDest);
1664 if (PBI->getSuccessor(1) == BB) {
1665 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1666 PBI->setSuccessor(1, FalseDest);
1669 // TODO: If BB is reachable from all paths through PredBlock, then we
1670 // could replace PBI's branch probabilities with BI's.
1672 // Merge probability data into PredBlock's branch.
1674 if (ExtractBranchMetadata(PBI, C, D) && ExtractBranchMetadata(BI, A, B)) {
1675 // Given IR which does:
1677 // br i1 %x, label %bbB, label %bbC
1679 // br i1 %y, label %bbD, label %bbC
1680 // Let's call the probability that we take the edge from %bbA to %bbB
1681 // 'a', from %bbA to %bbC, 'b', from %bbB to %bbD 'c' and from %bbB to
1682 // %bbC probability 'd'.
1684 // We transform the IR into:
1686 // br i1 %z, label %bbD, label %bbC
1687 // where the probability of going to %bbD is (a*c) and going to bbC is
1690 // Probabilities aren't stored as ratios directly. Using branch weights,
1692 // (a*c)% = A*C, (b+(a*d))% = A*D+B*C+B*D.
1694 // In the event of overflow, we want to drop the LSB of the input
1698 // Ignore overflow result on ProbTrue.
1699 APInt ProbTrue = MultiplyAndLosePrecision(A, C, B, D, BitsLost);
1701 APInt Tmp1 = MultiplyAndLosePrecision(B, D, A, C, BitsLost);
1703 ProbTrue = ProbTrue.lshr(BitsLost*2);
1706 APInt Tmp2 = MultiplyAndLosePrecision(A, D, C, B, BitsLost);
1708 ProbTrue = ProbTrue.lshr(BitsLost*2);
1709 Tmp1 = Tmp1.lshr(BitsLost*2);
1712 APInt Tmp3 = MultiplyAndLosePrecision(B, C, A, D, BitsLost);
1714 ProbTrue = ProbTrue.lshr(BitsLost*2);
1715 Tmp1 = Tmp1.lshr(BitsLost*2);
1716 Tmp2 = Tmp2.lshr(BitsLost*2);
1719 bool Overflow1 = false, Overflow2 = false;
1720 APInt Tmp4 = Tmp2.uadd_ov(Tmp3, Overflow1);
1721 APInt ProbFalse = Tmp4.uadd_ov(Tmp1, Overflow2);
1723 if (Overflow1 || Overflow2) {
1724 ProbTrue = ProbTrue.lshr(1);
1725 Tmp1 = Tmp1.lshr(1);
1726 Tmp2 = Tmp2.lshr(1);
1727 Tmp3 = Tmp3.lshr(1);
1729 ProbFalse = Tmp4 + Tmp1;
1732 // The sum of branch weights must fit in 32-bits.
1733 if (ProbTrue.isNegative() && ProbFalse.isNegative()) {
1734 ProbTrue = ProbTrue.lshr(1);
1735 ProbFalse = ProbFalse.lshr(1);
1738 if (ProbTrue != ProbFalse) {
1739 // Normalize the result.
1740 APInt GCD = APIntOps::GreatestCommonDivisor(ProbTrue, ProbFalse);
1741 ProbTrue = ProbTrue.udiv(GCD);
1742 ProbFalse = ProbFalse.udiv(GCD);
1744 MDBuilder MDB(BI->getContext());
1745 MDNode *N = MDB.createBranchWeights(ProbTrue.getZExtValue(),
1746 ProbFalse.getZExtValue());
1747 PBI->setMetadata(LLVMContext::MD_prof, N);
1749 PBI->setMetadata(LLVMContext::MD_prof, NULL);
1752 PBI->setMetadata(LLVMContext::MD_prof, NULL);
1755 // Copy any debug value intrinsics into the end of PredBlock.
1756 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
1757 if (isa<DbgInfoIntrinsic>(*I))
1758 I->clone()->insertBefore(PBI);
1765 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1766 /// predecessor of another block, this function tries to simplify it. We know
1767 /// that PBI and BI are both conditional branches, and BI is in one of the
1768 /// successor blocks of PBI - PBI branches to BI.
1769 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1770 assert(PBI->isConditional() && BI->isConditional());
1771 BasicBlock *BB = BI->getParent();
1773 // If this block ends with a branch instruction, and if there is a
1774 // predecessor that ends on a branch of the same condition, make
1775 // this conditional branch redundant.
1776 if (PBI->getCondition() == BI->getCondition() &&
1777 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1778 // Okay, the outcome of this conditional branch is statically
1779 // knowable. If this block had a single pred, handle specially.
1780 if (BB->getSinglePredecessor()) {
1781 // Turn this into a branch on constant.
1782 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1783 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1785 return true; // Nuke the branch on constant.
1788 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1789 // in the constant and simplify the block result. Subsequent passes of
1790 // simplifycfg will thread the block.
1791 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1792 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
1793 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1794 std::distance(PB, PE),
1795 BI->getCondition()->getName() + ".pr",
1797 // Okay, we're going to insert the PHI node. Since PBI is not the only
1798 // predecessor, compute the PHI'd conditional value for all of the preds.
1799 // Any predecessor where the condition is not computable we keep symbolic.
1800 for (pred_iterator PI = PB; PI != PE; ++PI) {
1801 BasicBlock *P = *PI;
1802 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
1803 PBI != BI && PBI->isConditional() &&
1804 PBI->getCondition() == BI->getCondition() &&
1805 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1806 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1807 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1810 NewPN->addIncoming(BI->getCondition(), P);
1814 BI->setCondition(NewPN);
1819 // If this is a conditional branch in an empty block, and if any
1820 // predecessors is a conditional branch to one of our destinations,
1821 // fold the conditions into logical ops and one cond br.
1822 BasicBlock::iterator BBI = BB->begin();
1823 // Ignore dbg intrinsics.
1824 while (isa<DbgInfoIntrinsic>(BBI))
1830 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1835 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1837 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1838 PBIOp = 0, BIOp = 1;
1839 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1840 PBIOp = 1, BIOp = 0;
1841 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1846 // Check to make sure that the other destination of this branch
1847 // isn't BB itself. If so, this is an infinite loop that will
1848 // keep getting unwound.
1849 if (PBI->getSuccessor(PBIOp) == BB)
1852 // Do not perform this transformation if it would require
1853 // insertion of a large number of select instructions. For targets
1854 // without predication/cmovs, this is a big pessimization.
1855 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1857 unsigned NumPhis = 0;
1858 for (BasicBlock::iterator II = CommonDest->begin();
1859 isa<PHINode>(II); ++II, ++NumPhis)
1860 if (NumPhis > 2) // Disable this xform.
1863 // Finally, if everything is ok, fold the branches to logical ops.
1864 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1866 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
1867 << "AND: " << *BI->getParent());
1870 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1871 // branch in it, where one edge (OtherDest) goes back to itself but the other
1872 // exits. We don't *know* that the program avoids the infinite loop
1873 // (even though that seems likely). If we do this xform naively, we'll end up
1874 // recursively unpeeling the loop. Since we know that (after the xform is
1875 // done) that the block *is* infinite if reached, we just make it an obviously
1876 // infinite loop with no cond branch.
1877 if (OtherDest == BB) {
1878 // Insert it at the end of the function, because it's either code,
1879 // or it won't matter if it's hot. :)
1880 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1881 "infloop", BB->getParent());
1882 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1883 OtherDest = InfLoopBlock;
1886 DEBUG(dbgs() << *PBI->getParent()->getParent());
1888 // BI may have other predecessors. Because of this, we leave
1889 // it alone, but modify PBI.
1891 // Make sure we get to CommonDest on True&True directions.
1892 Value *PBICond = PBI->getCondition();
1893 IRBuilder<true, NoFolder> Builder(PBI);
1895 PBICond = Builder.CreateNot(PBICond, PBICond->getName()+".not");
1897 Value *BICond = BI->getCondition();
1899 BICond = Builder.CreateNot(BICond, BICond->getName()+".not");
1901 // Merge the conditions.
1902 Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge");
1904 // Modify PBI to branch on the new condition to the new dests.
1905 PBI->setCondition(Cond);
1906 PBI->setSuccessor(0, CommonDest);
1907 PBI->setSuccessor(1, OtherDest);
1909 // OtherDest may have phi nodes. If so, add an entry from PBI's
1910 // block that are identical to the entries for BI's block.
1911 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
1913 // We know that the CommonDest already had an edge from PBI to
1914 // it. If it has PHIs though, the PHIs may have different
1915 // entries for BB and PBI's BB. If so, insert a select to make
1918 for (BasicBlock::iterator II = CommonDest->begin();
1919 (PN = dyn_cast<PHINode>(II)); ++II) {
1920 Value *BIV = PN->getIncomingValueForBlock(BB);
1921 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1922 Value *PBIV = PN->getIncomingValue(PBBIdx);
1924 // Insert a select in PBI to pick the right value.
1925 Value *NV = cast<SelectInst>
1926 (Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName()+".mux"));
1927 PN->setIncomingValue(PBBIdx, NV);
1931 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1932 DEBUG(dbgs() << *PBI->getParent()->getParent());
1934 // This basic block is probably dead. We know it has at least
1935 // one fewer predecessor.
1939 // SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
1940 // branch to TrueBB if Cond is true or to FalseBB if Cond is false.
1941 // Takes care of updating the successors and removing the old terminator.
1942 // Also makes sure not to introduce new successors by assuming that edges to
1943 // non-successor TrueBBs and FalseBBs aren't reachable.
1944 static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
1945 BasicBlock *TrueBB, BasicBlock *FalseBB){
1946 // Remove any superfluous successor edges from the CFG.
1947 // First, figure out which successors to preserve.
1948 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
1950 BasicBlock *KeepEdge1 = TrueBB;
1951 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
1953 // Then remove the rest.
1954 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
1955 BasicBlock *Succ = OldTerm->getSuccessor(I);
1956 // Make sure only to keep exactly one copy of each edge.
1957 if (Succ == KeepEdge1)
1959 else if (Succ == KeepEdge2)
1962 Succ->removePredecessor(OldTerm->getParent());
1965 IRBuilder<> Builder(OldTerm);
1966 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
1968 // Insert an appropriate new terminator.
1969 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
1970 if (TrueBB == FalseBB)
1971 // We were only looking for one successor, and it was present.
1972 // Create an unconditional branch to it.
1973 Builder.CreateBr(TrueBB);
1975 // We found both of the successors we were looking for.
1976 // Create a conditional branch sharing the condition of the select.
1977 Builder.CreateCondBr(Cond, TrueBB, FalseBB);
1978 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
1979 // Neither of the selected blocks were successors, so this
1980 // terminator must be unreachable.
1981 new UnreachableInst(OldTerm->getContext(), OldTerm);
1983 // One of the selected values was a successor, but the other wasn't.
1984 // Insert an unconditional branch to the one that was found;
1985 // the edge to the one that wasn't must be unreachable.
1987 // Only TrueBB was found.
1988 Builder.CreateBr(TrueBB);
1990 // Only FalseBB was found.
1991 Builder.CreateBr(FalseBB);
1994 EraseTerminatorInstAndDCECond(OldTerm);
1998 // SimplifySwitchOnSelect - Replaces
1999 // (switch (select cond, X, Y)) on constant X, Y
2000 // with a branch - conditional if X and Y lead to distinct BBs,
2001 // unconditional otherwise.
2002 static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
2003 // Check for constant integer values in the select.
2004 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
2005 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
2006 if (!TrueVal || !FalseVal)
2009 // Find the relevant condition and destinations.
2010 Value *Condition = Select->getCondition();
2011 BasicBlock *TrueBB = SI->findCaseValue(TrueVal).getCaseSuccessor();
2012 BasicBlock *FalseBB = SI->findCaseValue(FalseVal).getCaseSuccessor();
2014 // Perform the actual simplification.
2015 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB);
2018 // SimplifyIndirectBrOnSelect - Replaces
2019 // (indirectbr (select cond, blockaddress(@fn, BlockA),
2020 // blockaddress(@fn, BlockB)))
2022 // (br cond, BlockA, BlockB).
2023 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
2024 // Check that both operands of the select are block addresses.
2025 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
2026 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
2030 // Extract the actual blocks.
2031 BasicBlock *TrueBB = TBA->getBasicBlock();
2032 BasicBlock *FalseBB = FBA->getBasicBlock();
2034 // Perform the actual simplification.
2035 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB);
2038 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
2039 /// instruction (a seteq/setne with a constant) as the only instruction in a
2040 /// block that ends with an uncond branch. We are looking for a very specific
2041 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
2042 /// this case, we merge the first two "or's of icmp" into a switch, but then the
2043 /// default value goes to an uncond block with a seteq in it, we get something
2046 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
2048 /// %tmp = icmp eq i8 %A, 92
2051 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
2053 /// We prefer to split the edge to 'end' so that there is a true/false entry to
2054 /// the PHI, merging the third icmp into the switch.
2055 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
2056 const TargetData *TD,
2057 IRBuilder<> &Builder) {
2058 BasicBlock *BB = ICI->getParent();
2060 // If the block has any PHIs in it or the icmp has multiple uses, it is too
2062 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
2064 Value *V = ICI->getOperand(0);
2065 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
2067 // The pattern we're looking for is where our only predecessor is a switch on
2068 // 'V' and this block is the default case for the switch. In this case we can
2069 // fold the compared value into the switch to simplify things.
2070 BasicBlock *Pred = BB->getSinglePredecessor();
2071 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
2073 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
2074 if (SI->getCondition() != V)
2077 // If BB is reachable on a non-default case, then we simply know the value of
2078 // V in this block. Substitute it and constant fold the icmp instruction
2080 if (SI->getDefaultDest() != BB) {
2081 ConstantInt *VVal = SI->findCaseDest(BB);
2082 assert(VVal && "Should have a unique destination value");
2083 ICI->setOperand(0, VVal);
2085 if (Value *V = SimplifyInstruction(ICI, TD)) {
2086 ICI->replaceAllUsesWith(V);
2087 ICI->eraseFromParent();
2089 // BB is now empty, so it is likely to simplify away.
2090 return SimplifyCFG(BB) | true;
2093 // Ok, the block is reachable from the default dest. If the constant we're
2094 // comparing exists in one of the other edges, then we can constant fold ICI
2096 if (SI->findCaseValue(Cst) != SI->case_default()) {
2098 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2099 V = ConstantInt::getFalse(BB->getContext());
2101 V = ConstantInt::getTrue(BB->getContext());
2103 ICI->replaceAllUsesWith(V);
2104 ICI->eraseFromParent();
2105 // BB is now empty, so it is likely to simplify away.
2106 return SimplifyCFG(BB) | true;
2109 // The use of the icmp has to be in the 'end' block, by the only PHI node in
2111 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
2112 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
2113 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
2114 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
2117 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
2119 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
2120 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
2122 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2123 std::swap(DefaultCst, NewCst);
2125 // Replace ICI (which is used by the PHI for the default value) with true or
2126 // false depending on if it is EQ or NE.
2127 ICI->replaceAllUsesWith(DefaultCst);
2128 ICI->eraseFromParent();
2130 // Okay, the switch goes to this block on a default value. Add an edge from
2131 // the switch to the merge point on the compared value.
2132 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
2133 BB->getParent(), BB);
2134 SI->addCase(Cst, NewBB);
2136 // NewBB branches to the phi block, add the uncond branch and the phi entry.
2137 Builder.SetInsertPoint(NewBB);
2138 Builder.SetCurrentDebugLocation(SI->getDebugLoc());
2139 Builder.CreateBr(SuccBlock);
2140 PHIUse->addIncoming(NewCst, NewBB);
2144 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
2145 /// Check to see if it is branching on an or/and chain of icmp instructions, and
2146 /// fold it into a switch instruction if so.
2147 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD,
2148 IRBuilder<> &Builder) {
2149 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
2150 if (Cond == 0) return false;
2153 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2154 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2155 // 'setne's and'ed together, collect them.
2157 std::vector<ConstantInt*> Values;
2158 bool TrueWhenEqual = true;
2159 Value *ExtraCase = 0;
2160 unsigned UsedICmps = 0;
2162 if (Cond->getOpcode() == Instruction::Or) {
2163 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
2165 } else if (Cond->getOpcode() == Instruction::And) {
2166 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
2168 TrueWhenEqual = false;
2171 // If we didn't have a multiply compared value, fail.
2172 if (CompVal == 0) return false;
2174 // Avoid turning single icmps into a switch.
2178 // There might be duplicate constants in the list, which the switch
2179 // instruction can't handle, remove them now.
2180 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
2181 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2183 // If Extra was used, we require at least two switch values to do the
2184 // transformation. A switch with one value is just an cond branch.
2185 if (ExtraCase && Values.size() < 2) return false;
2187 // Figure out which block is which destination.
2188 BasicBlock *DefaultBB = BI->getSuccessor(1);
2189 BasicBlock *EdgeBB = BI->getSuccessor(0);
2190 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2192 BasicBlock *BB = BI->getParent();
2194 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
2195 << " cases into SWITCH. BB is:\n" << *BB);
2197 // If there are any extra values that couldn't be folded into the switch
2198 // then we evaluate them with an explicit branch first. Split the block
2199 // right before the condbr to handle it.
2201 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
2202 // Remove the uncond branch added to the old block.
2203 TerminatorInst *OldTI = BB->getTerminator();
2204 Builder.SetInsertPoint(OldTI);
2207 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
2209 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
2211 OldTI->eraseFromParent();
2213 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
2214 // for the edge we just added.
2215 AddPredecessorToBlock(EdgeBB, BB, NewBB);
2217 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
2218 << "\nEXTRABB = " << *BB);
2222 Builder.SetInsertPoint(BI);
2223 // Convert pointer to int before we switch.
2224 if (CompVal->getType()->isPointerTy()) {
2225 assert(TD && "Cannot switch on pointer without TargetData");
2226 CompVal = Builder.CreatePtrToInt(CompVal,
2227 TD->getIntPtrType(CompVal->getContext()),
2231 // Create the new switch instruction now.
2232 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
2234 // Add all of the 'cases' to the switch instruction.
2235 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2236 New->addCase(Values[i], EdgeBB);
2238 // We added edges from PI to the EdgeBB. As such, if there were any
2239 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2240 // the number of edges added.
2241 for (BasicBlock::iterator BBI = EdgeBB->begin();
2242 isa<PHINode>(BBI); ++BBI) {
2243 PHINode *PN = cast<PHINode>(BBI);
2244 Value *InVal = PN->getIncomingValueForBlock(BB);
2245 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2246 PN->addIncoming(InVal, BB);
2249 // Erase the old branch instruction.
2250 EraseTerminatorInstAndDCECond(BI);
2252 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
2256 bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
2257 // If this is a trivial landing pad that just continues unwinding the caught
2258 // exception then zap the landing pad, turning its invokes into calls.
2259 BasicBlock *BB = RI->getParent();
2260 LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI());
2261 if (RI->getValue() != LPInst)
2262 // Not a landing pad, or the resume is not unwinding the exception that
2263 // caused control to branch here.
2266 // Check that there are no other instructions except for debug intrinsics.
2267 BasicBlock::iterator I = LPInst, E = RI;
2269 if (!isa<DbgInfoIntrinsic>(I))
2272 // Turn all invokes that unwind here into calls and delete the basic block.
2273 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
2274 InvokeInst *II = cast<InvokeInst>((*PI++)->getTerminator());
2275 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
2276 // Insert a call instruction before the invoke.
2277 CallInst *Call = CallInst::Create(II->getCalledValue(), Args, "", II);
2279 Call->setCallingConv(II->getCallingConv());
2280 Call->setAttributes(II->getAttributes());
2281 Call->setDebugLoc(II->getDebugLoc());
2283 // Anything that used the value produced by the invoke instruction now uses
2284 // the value produced by the call instruction. Note that we do this even
2285 // for void functions and calls with no uses so that the callgraph edge is
2287 II->replaceAllUsesWith(Call);
2288 BB->removePredecessor(II->getParent());
2290 // Insert a branch to the normal destination right before the invoke.
2291 BranchInst::Create(II->getNormalDest(), II);
2293 // Finally, delete the invoke instruction!
2294 II->eraseFromParent();
2297 // The landingpad is now unreachable. Zap it.
2298 BB->eraseFromParent();
2302 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
2303 BasicBlock *BB = RI->getParent();
2304 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2306 // Find predecessors that end with branches.
2307 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2308 SmallVector<BranchInst*, 8> CondBranchPreds;
2309 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2310 BasicBlock *P = *PI;
2311 TerminatorInst *PTI = P->getTerminator();
2312 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2313 if (BI->isUnconditional())
2314 UncondBranchPreds.push_back(P);
2316 CondBranchPreds.push_back(BI);
2320 // If we found some, do the transformation!
2321 if (!UncondBranchPreds.empty() && DupRet) {
2322 while (!UncondBranchPreds.empty()) {
2323 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2324 DEBUG(dbgs() << "FOLDING: " << *BB
2325 << "INTO UNCOND BRANCH PRED: " << *Pred);
2326 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
2329 // If we eliminated all predecessors of the block, delete the block now.
2330 if (pred_begin(BB) == pred_end(BB))
2331 // We know there are no successors, so just nuke the block.
2332 BB->eraseFromParent();
2337 // Check out all of the conditional branches going to this return
2338 // instruction. If any of them just select between returns, change the
2339 // branch itself into a select/return pair.
2340 while (!CondBranchPreds.empty()) {
2341 BranchInst *BI = CondBranchPreds.pop_back_val();
2343 // Check to see if the non-BB successor is also a return block.
2344 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2345 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2346 SimplifyCondBranchToTwoReturns(BI, Builder))
2352 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2353 BasicBlock *BB = UI->getParent();
2355 bool Changed = false;
2357 // If there are any instructions immediately before the unreachable that can
2358 // be removed, do so.
2359 while (UI != BB->begin()) {
2360 BasicBlock::iterator BBI = UI;
2362 // Do not delete instructions that can have side effects which might cause
2363 // the unreachable to not be reachable; specifically, calls and volatile
2364 // operations may have this effect.
2365 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2367 if (BBI->mayHaveSideEffects()) {
2368 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
2369 if (SI->isVolatile())
2371 } else if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
2372 if (LI->isVolatile())
2374 } else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(BBI)) {
2375 if (RMWI->isVolatile())
2377 } else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) {
2378 if (CXI->isVolatile())
2380 } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) &&
2381 !isa<LandingPadInst>(BBI)) {
2384 // Note that deleting LandingPad's here is in fact okay, although it
2385 // involves a bit of subtle reasoning. If this inst is a LandingPad,
2386 // all the predecessors of this block will be the unwind edges of Invokes,
2387 // and we can therefore guarantee this block will be erased.
2390 // Delete this instruction (any uses are guaranteed to be dead)
2391 if (!BBI->use_empty())
2392 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
2393 BBI->eraseFromParent();
2397 // If the unreachable instruction is the first in the block, take a gander
2398 // at all of the predecessors of this instruction, and simplify them.
2399 if (&BB->front() != UI) return Changed;
2401 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2402 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2403 TerminatorInst *TI = Preds[i]->getTerminator();
2404 IRBuilder<> Builder(TI);
2405 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2406 if (BI->isUnconditional()) {
2407 if (BI->getSuccessor(0) == BB) {
2408 new UnreachableInst(TI->getContext(), TI);
2409 TI->eraseFromParent();
2413 if (BI->getSuccessor(0) == BB) {
2414 Builder.CreateBr(BI->getSuccessor(1));
2415 EraseTerminatorInstAndDCECond(BI);
2416 } else if (BI->getSuccessor(1) == BB) {
2417 Builder.CreateBr(BI->getSuccessor(0));
2418 EraseTerminatorInstAndDCECond(BI);
2422 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2423 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2425 if (i.getCaseSuccessor() == BB) {
2426 BB->removePredecessor(SI->getParent());
2431 // If the default value is unreachable, figure out the most popular
2432 // destination and make it the default.
2433 if (SI->getDefaultDest() == BB) {
2434 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
2435 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2437 std::pair<unsigned, unsigned> &entry =
2438 Popularity[i.getCaseSuccessor()];
2439 if (entry.first == 0) {
2441 entry.second = i.getCaseIndex();
2447 // Find the most popular block.
2448 unsigned MaxPop = 0;
2449 unsigned MaxIndex = 0;
2450 BasicBlock *MaxBlock = 0;
2451 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
2452 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2453 if (I->second.first > MaxPop ||
2454 (I->second.first == MaxPop && MaxIndex > I->second.second)) {
2455 MaxPop = I->second.first;
2456 MaxIndex = I->second.second;
2457 MaxBlock = I->first;
2461 // Make this the new default, allowing us to delete any explicit
2463 SI->setDefaultDest(MaxBlock);
2466 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2468 if (isa<PHINode>(MaxBlock->begin()))
2469 for (unsigned i = 0; i != MaxPop-1; ++i)
2470 MaxBlock->removePredecessor(SI->getParent());
2472 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2474 if (i.getCaseSuccessor() == MaxBlock) {
2480 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2481 if (II->getUnwindDest() == BB) {
2482 // Convert the invoke to a call instruction. This would be a good
2483 // place to note that the call does not throw though.
2484 BranchInst *BI = Builder.CreateBr(II->getNormalDest());
2485 II->removeFromParent(); // Take out of symbol table
2487 // Insert the call now...
2488 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2489 Builder.SetInsertPoint(BI);
2490 CallInst *CI = Builder.CreateCall(II->getCalledValue(),
2491 Args, II->getName());
2492 CI->setCallingConv(II->getCallingConv());
2493 CI->setAttributes(II->getAttributes());
2494 // If the invoke produced a value, the call does now instead.
2495 II->replaceAllUsesWith(CI);
2502 // If this block is now dead, remove it.
2503 if (pred_begin(BB) == pred_end(BB) &&
2504 BB != &BB->getParent()->getEntryBlock()) {
2505 // We know there are no successors, so just nuke the block.
2506 BB->eraseFromParent();
2513 /// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
2514 /// integer range comparison into a sub, an icmp and a branch.
2515 static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
2516 assert(SI->getNumCases() > 1 && "Degenerate switch?");
2518 // Make sure all cases point to the same destination and gather the values.
2519 SmallVector<ConstantInt *, 16> Cases;
2520 SwitchInst::CaseIt I = SI->case_begin();
2521 Cases.push_back(I.getCaseValue());
2522 SwitchInst::CaseIt PrevI = I++;
2523 for (SwitchInst::CaseIt E = SI->case_end(); I != E; PrevI = I++) {
2524 if (PrevI.getCaseSuccessor() != I.getCaseSuccessor())
2526 Cases.push_back(I.getCaseValue());
2528 assert(Cases.size() == SI->getNumCases() && "Not all cases gathered");
2530 // Sort the case values, then check if they form a range we can transform.
2531 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
2532 for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
2533 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
2537 Constant *Offset = ConstantExpr::getNeg(Cases.back());
2538 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases());
2540 Value *Sub = SI->getCondition();
2541 if (!Offset->isNullValue())
2542 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off");
2543 Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
2544 Builder.CreateCondBr(
2545 Cmp, SI->case_begin().getCaseSuccessor(), SI->getDefaultDest());
2547 // Prune obsolete incoming values off the successor's PHI nodes.
2548 for (BasicBlock::iterator BBI = SI->case_begin().getCaseSuccessor()->begin();
2549 isa<PHINode>(BBI); ++BBI) {
2550 for (unsigned I = 0, E = SI->getNumCases()-1; I != E; ++I)
2551 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
2553 SI->eraseFromParent();
2558 /// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch
2559 /// and use it to remove dead cases.
2560 static bool EliminateDeadSwitchCases(SwitchInst *SI) {
2561 Value *Cond = SI->getCondition();
2562 unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth();
2563 APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
2564 ComputeMaskedBits(Cond, KnownZero, KnownOne);
2566 // Gather dead cases.
2567 SmallVector<ConstantInt*, 8> DeadCases;
2568 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
2569 if ((I.getCaseValue()->getValue() & KnownZero) != 0 ||
2570 (I.getCaseValue()->getValue() & KnownOne) != KnownOne) {
2571 DeadCases.push_back(I.getCaseValue());
2572 DEBUG(dbgs() << "SimplifyCFG: switch case '"
2573 << I.getCaseValue() << "' is dead.\n");
2577 // Remove dead cases from the switch.
2578 for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) {
2579 SwitchInst::CaseIt Case = SI->findCaseValue(DeadCases[I]);
2580 assert(Case != SI->case_default() &&
2581 "Case was not found. Probably mistake in DeadCases forming.");
2582 // Prune unused values from PHI nodes.
2583 Case.getCaseSuccessor()->removePredecessor(SI->getParent());
2584 SI->removeCase(Case);
2587 return !DeadCases.empty();
2590 /// FindPHIForConditionForwarding - If BB would be eligible for simplification
2591 /// by TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated
2592 /// by an unconditional branch), look at the phi node for BB in the successor
2593 /// block and see if the incoming value is equal to CaseValue. If so, return
2594 /// the phi node, and set PhiIndex to BB's index in the phi node.
2595 static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
2598 if (BB->getFirstNonPHIOrDbg() != BB->getTerminator())
2599 return NULL; // BB must be empty to be a candidate for simplification.
2600 if (!BB->getSinglePredecessor())
2601 return NULL; // BB must be dominated by the switch.
2603 BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
2604 if (!Branch || !Branch->isUnconditional())
2605 return NULL; // Terminator must be unconditional branch.
2607 BasicBlock *Succ = Branch->getSuccessor(0);
2609 BasicBlock::iterator I = Succ->begin();
2610 while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
2611 int Idx = PHI->getBasicBlockIndex(BB);
2612 assert(Idx >= 0 && "PHI has no entry for predecessor?");
2614 Value *InValue = PHI->getIncomingValue(Idx);
2615 if (InValue != CaseValue) continue;
2624 /// ForwardSwitchConditionToPHI - Try to forward the condition of a switch
2625 /// instruction to a phi node dominated by the switch, if that would mean that
2626 /// some of the destination blocks of the switch can be folded away.
2627 /// Returns true if a change is made.
2628 static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
2629 typedef DenseMap<PHINode*, SmallVector<int,4> > ForwardingNodesMap;
2630 ForwardingNodesMap ForwardingNodes;
2632 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
2633 ConstantInt *CaseValue = I.getCaseValue();
2634 BasicBlock *CaseDest = I.getCaseSuccessor();
2637 PHINode *PHI = FindPHIForConditionForwarding(CaseValue, CaseDest,
2641 ForwardingNodes[PHI].push_back(PhiIndex);
2644 bool Changed = false;
2646 for (ForwardingNodesMap::iterator I = ForwardingNodes.begin(),
2647 E = ForwardingNodes.end(); I != E; ++I) {
2648 PHINode *Phi = I->first;
2649 SmallVector<int,4> &Indexes = I->second;
2651 if (Indexes.size() < 2) continue;
2653 for (size_t I = 0, E = Indexes.size(); I != E; ++I)
2654 Phi->setIncomingValue(Indexes[I], SI->getCondition());
2661 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
2662 // If this switch is too complex to want to look at, ignore it.
2663 if (!isValueEqualityComparison(SI))
2666 BasicBlock *BB = SI->getParent();
2668 // If we only have one predecessor, and if it is a branch on this value,
2669 // see if that predecessor totally determines the outcome of this switch.
2670 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2671 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
2672 return SimplifyCFG(BB) | true;
2674 Value *Cond = SI->getCondition();
2675 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
2676 if (SimplifySwitchOnSelect(SI, Select))
2677 return SimplifyCFG(BB) | true;
2679 // If the block only contains the switch, see if we can fold the block
2680 // away into any preds.
2681 BasicBlock::iterator BBI = BB->begin();
2682 // Ignore dbg intrinsics.
2683 while (isa<DbgInfoIntrinsic>(BBI))
2686 if (FoldValueComparisonIntoPredecessors(SI, Builder))
2687 return SimplifyCFG(BB) | true;
2689 // Try to transform the switch into an icmp and a branch.
2690 if (TurnSwitchRangeIntoICmp(SI, Builder))
2691 return SimplifyCFG(BB) | true;
2693 // Remove unreachable cases.
2694 if (EliminateDeadSwitchCases(SI))
2695 return SimplifyCFG(BB) | true;
2697 if (ForwardSwitchConditionToPHI(SI))
2698 return SimplifyCFG(BB) | true;
2703 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
2704 BasicBlock *BB = IBI->getParent();
2705 bool Changed = false;
2707 // Eliminate redundant destinations.
2708 SmallPtrSet<Value *, 8> Succs;
2709 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2710 BasicBlock *Dest = IBI->getDestination(i);
2711 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2712 Dest->removePredecessor(BB);
2713 IBI->removeDestination(i);
2719 if (IBI->getNumDestinations() == 0) {
2720 // If the indirectbr has no successors, change it to unreachable.
2721 new UnreachableInst(IBI->getContext(), IBI);
2722 EraseTerminatorInstAndDCECond(IBI);
2726 if (IBI->getNumDestinations() == 1) {
2727 // If the indirectbr has one successor, change it to a direct branch.
2728 BranchInst::Create(IBI->getDestination(0), IBI);
2729 EraseTerminatorInstAndDCECond(IBI);
2733 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2734 if (SimplifyIndirectBrOnSelect(IBI, SI))
2735 return SimplifyCFG(BB) | true;
2740 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
2741 BasicBlock *BB = BI->getParent();
2743 // If the Terminator is the only non-phi instruction, simplify the block.
2744 BasicBlock::iterator I = BB->getFirstNonPHIOrDbgOrLifetime();
2745 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
2746 TryToSimplifyUncondBranchFromEmptyBlock(BB))
2749 // If the only instruction in the block is a seteq/setne comparison
2750 // against a constant, try to simplify the block.
2751 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
2752 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
2753 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
2755 if (I->isTerminator() &&
2756 TryToSimplifyUncondBranchWithICmpInIt(ICI, TD, Builder))
2764 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
2765 BasicBlock *BB = BI->getParent();
2767 // Conditional branch
2768 if (isValueEqualityComparison(BI)) {
2769 // If we only have one predecessor, and if it is a branch on this value,
2770 // see if that predecessor totally determines the outcome of this
2772 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2773 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
2774 return SimplifyCFG(BB) | true;
2776 // This block must be empty, except for the setcond inst, if it exists.
2777 // Ignore dbg intrinsics.
2778 BasicBlock::iterator I = BB->begin();
2779 // Ignore dbg intrinsics.
2780 while (isa<DbgInfoIntrinsic>(I))
2783 if (FoldValueComparisonIntoPredecessors(BI, Builder))
2784 return SimplifyCFG(BB) | true;
2785 } else if (&*I == cast<Instruction>(BI->getCondition())){
2787 // Ignore dbg intrinsics.
2788 while (isa<DbgInfoIntrinsic>(I))
2790 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
2791 return SimplifyCFG(BB) | true;
2795 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
2796 if (SimplifyBranchOnICmpChain(BI, TD, Builder))
2799 // If this basic block is ONLY a compare and a branch, and if a predecessor
2800 // branches to us and one of our successors, fold the comparison into the
2801 // predecessor and use logical operations to pick the right destination.
2802 if (FoldBranchToCommonDest(BI))
2803 return SimplifyCFG(BB) | true;
2805 // We have a conditional branch to two blocks that are only reachable
2806 // from BI. We know that the condbr dominates the two blocks, so see if
2807 // there is any identical code in the "then" and "else" blocks. If so, we
2808 // can hoist it up to the branching block.
2809 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
2810 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2811 if (HoistThenElseCodeToIf(BI))
2812 return SimplifyCFG(BB) | true;
2814 // If Successor #1 has multiple preds, we may be able to conditionally
2815 // execute Successor #0 if it branches to successor #1.
2816 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
2817 if (Succ0TI->getNumSuccessors() == 1 &&
2818 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
2819 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
2820 return SimplifyCFG(BB) | true;
2822 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2823 // If Successor #0 has multiple preds, we may be able to conditionally
2824 // execute Successor #1 if it branches to successor #0.
2825 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
2826 if (Succ1TI->getNumSuccessors() == 1 &&
2827 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
2828 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
2829 return SimplifyCFG(BB) | true;
2832 // If this is a branch on a phi node in the current block, thread control
2833 // through this block if any PHI node entries are constants.
2834 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
2835 if (PN->getParent() == BI->getParent())
2836 if (FoldCondBranchOnPHI(BI, TD))
2837 return SimplifyCFG(BB) | true;
2839 // Scan predecessor blocks for conditional branches.
2840 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2841 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2842 if (PBI != BI && PBI->isConditional())
2843 if (SimplifyCondBranchToCondBranch(PBI, BI))
2844 return SimplifyCFG(BB) | true;
2849 /// Check if passing a value to an instruction will cause undefined behavior.
2850 static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
2851 Constant *C = dyn_cast<Constant>(V);
2855 if (!I->hasOneUse()) // Only look at single-use instructions, for compile time
2858 if (C->isNullValue()) {
2859 Instruction *Use = I->use_back();
2861 // Now make sure that there are no instructions in between that can alter
2862 // control flow (eg. calls)
2863 for (BasicBlock::iterator i = ++BasicBlock::iterator(I); &*i != Use; ++i)
2864 if (i == I->getParent()->end() || i->mayHaveSideEffects())
2867 // Look through GEPs. A load from a GEP derived from NULL is still undefined
2868 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))
2869 if (GEP->getPointerOperand() == I)
2870 return passingValueIsAlwaysUndefined(V, GEP);
2872 // Look through bitcasts.
2873 if (BitCastInst *BC = dyn_cast<BitCastInst>(Use))
2874 return passingValueIsAlwaysUndefined(V, BC);
2876 // Load from null is undefined.
2877 if (LoadInst *LI = dyn_cast<LoadInst>(Use))
2878 return LI->getPointerAddressSpace() == 0;
2880 // Store to null is undefined.
2881 if (StoreInst *SI = dyn_cast<StoreInst>(Use))
2882 return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I;
2887 /// If BB has an incoming value that will always trigger undefined behavior
2888 /// (eg. null pointer dereference), remove the branch leading here.
2889 static bool removeUndefIntroducingPredecessor(BasicBlock *BB) {
2890 for (BasicBlock::iterator i = BB->begin();
2891 PHINode *PHI = dyn_cast<PHINode>(i); ++i)
2892 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
2893 if (passingValueIsAlwaysUndefined(PHI->getIncomingValue(i), PHI)) {
2894 TerminatorInst *T = PHI->getIncomingBlock(i)->getTerminator();
2895 IRBuilder<> Builder(T);
2896 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
2897 BB->removePredecessor(PHI->getIncomingBlock(i));
2898 // Turn uncoditional branches into unreachables and remove the dead
2899 // destination from conditional branches.
2900 if (BI->isUnconditional())
2901 Builder.CreateUnreachable();
2903 Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1) :
2904 BI->getSuccessor(0));
2905 BI->eraseFromParent();
2908 // TODO: SwitchInst.
2914 bool SimplifyCFGOpt::run(BasicBlock *BB) {
2915 bool Changed = false;
2917 assert(BB && BB->getParent() && "Block not embedded in function!");
2918 assert(BB->getTerminator() && "Degenerate basic block encountered!");
2920 // Remove basic blocks that have no predecessors (except the entry block)...
2921 // or that just have themself as a predecessor. These are unreachable.
2922 if ((pred_begin(BB) == pred_end(BB) &&
2923 BB != &BB->getParent()->getEntryBlock()) ||
2924 BB->getSinglePredecessor() == BB) {
2925 DEBUG(dbgs() << "Removing BB: \n" << *BB);
2926 DeleteDeadBlock(BB);
2930 // Check to see if we can constant propagate this terminator instruction
2932 Changed |= ConstantFoldTerminator(BB, true);
2934 // Check for and eliminate duplicate PHI nodes in this block.
2935 Changed |= EliminateDuplicatePHINodes(BB);
2937 // Check for and remove branches that will always cause undefined behavior.
2938 Changed |= removeUndefIntroducingPredecessor(BB);
2940 // Merge basic blocks into their predecessor if there is only one distinct
2941 // pred, and if there is only one distinct successor of the predecessor, and
2942 // if there are no PHI nodes.
2944 if (MergeBlockIntoPredecessor(BB))
2947 IRBuilder<> Builder(BB);
2949 // If there is a trivial two-entry PHI node in this basic block, and we can
2950 // eliminate it, do so now.
2951 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
2952 if (PN->getNumIncomingValues() == 2)
2953 Changed |= FoldTwoEntryPHINode(PN, TD);
2955 Builder.SetInsertPoint(BB->getTerminator());
2956 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
2957 if (BI->isUnconditional()) {
2958 if (SimplifyUncondBranch(BI, Builder)) return true;
2960 if (SimplifyCondBranch(BI, Builder)) return true;
2962 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
2963 if (SimplifyReturn(RI, Builder)) return true;
2964 } else if (ResumeInst *RI = dyn_cast<ResumeInst>(BB->getTerminator())) {
2965 if (SimplifyResume(RI, Builder)) return true;
2966 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
2967 if (SimplifySwitch(SI, Builder)) return true;
2968 } else if (UnreachableInst *UI =
2969 dyn_cast<UnreachableInst>(BB->getTerminator())) {
2970 if (SimplifyUnreachable(UI)) return true;
2971 } else if (IndirectBrInst *IBI =
2972 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
2973 if (SimplifyIndirectBr(IBI)) return true;
2979 /// SimplifyCFG - This function is used to do simplification of a CFG. For
2980 /// example, it adjusts branches to branches to eliminate the extra hop, it
2981 /// eliminates unreachable basic blocks, and does other "peephole" optimization
2982 /// of the CFG. It returns true if a modification was made.
2984 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
2985 return SimplifyCFGOpt(TD).run(BB);