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 /// ValueEqualityComparisonCase - Represents a case of a switch.
60 struct ValueEqualityComparisonCase {
64 ValueEqualityComparisonCase(ConstantInt *Value, BasicBlock *Dest)
65 : Value(Value), Dest(Dest) {}
67 bool operator<(ValueEqualityComparisonCase RHS) const {
68 // Comparing pointers is ok as we only rely on the order for uniquing.
69 return Value < RHS.Value;
73 class SimplifyCFGOpt {
74 const TargetData *const TD;
76 Value *isValueEqualityComparison(TerminatorInst *TI);
77 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
78 std::vector<ValueEqualityComparisonCase> &Cases);
79 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
81 IRBuilder<> &Builder);
82 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
83 IRBuilder<> &Builder);
85 bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder);
86 bool SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder);
87 bool SimplifyUnreachable(UnreachableInst *UI);
88 bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
89 bool SimplifyIndirectBr(IndirectBrInst *IBI);
90 bool SimplifyUncondBranch(BranchInst *BI, IRBuilder <> &Builder);
91 bool SimplifyCondBranch(BranchInst *BI, IRBuilder <>&Builder);
94 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
95 bool run(BasicBlock *BB);
99 /// SafeToMergeTerminators - Return true if it is safe to merge these two
100 /// terminator instructions together.
102 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
103 if (SI1 == SI2) return false; // Can't merge with self!
105 // It is not safe to merge these two switch instructions if they have a common
106 // successor, and if that successor has a PHI node, and if *that* PHI node has
107 // conflicting incoming values from the two switch blocks.
108 BasicBlock *SI1BB = SI1->getParent();
109 BasicBlock *SI2BB = SI2->getParent();
110 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
112 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
113 if (SI1Succs.count(*I))
114 for (BasicBlock::iterator BBI = (*I)->begin();
115 isa<PHINode>(BBI); ++BBI) {
116 PHINode *PN = cast<PHINode>(BBI);
117 if (PN->getIncomingValueForBlock(SI1BB) !=
118 PN->getIncomingValueForBlock(SI2BB))
125 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
126 /// now be entries in it from the 'NewPred' block. The values that will be
127 /// flowing into the PHI nodes will be the same as those coming in from
128 /// ExistPred, an existing predecessor of Succ.
129 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
130 BasicBlock *ExistPred) {
131 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
134 for (BasicBlock::iterator I = Succ->begin();
135 (PN = dyn_cast<PHINode>(I)); ++I)
136 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
140 /// GetIfCondition - Given a basic block (BB) with two predecessors (and at
141 /// least one PHI node in it), check to see if the merge at this block is due
142 /// to an "if condition". If so, return the boolean condition that determines
143 /// which entry into BB will be taken. Also, return by references the block
144 /// that will be entered from if the condition is true, and the block that will
145 /// be entered if the condition is false.
147 /// This does no checking to see if the true/false blocks have large or unsavory
148 /// instructions in them.
149 static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
150 BasicBlock *&IfFalse) {
151 PHINode *SomePHI = cast<PHINode>(BB->begin());
152 assert(SomePHI->getNumIncomingValues() == 2 &&
153 "Function can only handle blocks with 2 predecessors!");
154 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
155 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
157 // We can only handle branches. Other control flow will be lowered to
158 // branches if possible anyway.
159 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
160 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
161 if (Pred1Br == 0 || Pred2Br == 0)
164 // Eliminate code duplication by ensuring that Pred1Br is conditional if
166 if (Pred2Br->isConditional()) {
167 // If both branches are conditional, we don't have an "if statement". In
168 // reality, we could transform this case, but since the condition will be
169 // required anyway, we stand no chance of eliminating it, so the xform is
170 // probably not profitable.
171 if (Pred1Br->isConditional())
174 std::swap(Pred1, Pred2);
175 std::swap(Pred1Br, Pred2Br);
178 if (Pred1Br->isConditional()) {
179 // The only thing we have to watch out for here is to make sure that Pred2
180 // doesn't have incoming edges from other blocks. If it does, the condition
181 // doesn't dominate BB.
182 if (Pred2->getSinglePredecessor() == 0)
185 // If we found a conditional branch predecessor, make sure that it branches
186 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
187 if (Pred1Br->getSuccessor(0) == BB &&
188 Pred1Br->getSuccessor(1) == Pred2) {
191 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
192 Pred1Br->getSuccessor(1) == BB) {
196 // We know that one arm of the conditional goes to BB, so the other must
197 // go somewhere unrelated, and this must not be an "if statement".
201 return Pred1Br->getCondition();
204 // Ok, if we got here, both predecessors end with an unconditional branch to
205 // BB. Don't panic! If both blocks only have a single (identical)
206 // predecessor, and THAT is a conditional branch, then we're all ok!
207 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
208 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
211 // Otherwise, if this is a conditional branch, then we can use it!
212 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
213 if (BI == 0) return 0;
215 assert(BI->isConditional() && "Two successors but not conditional?");
216 if (BI->getSuccessor(0) == Pred1) {
223 return BI->getCondition();
226 /// ComputeSpeculuationCost - Compute an abstract "cost" of speculating the
227 /// given instruction, which is assumed to be safe to speculate. 1 means
228 /// cheap, 2 means less cheap, and UINT_MAX means prohibitively expensive.
229 static unsigned ComputeSpeculationCost(const User *I) {
230 assert(isSafeToSpeculativelyExecute(I) &&
231 "Instruction is not safe to speculatively execute!");
232 switch (Operator::getOpcode(I)) {
234 // In doubt, be conservative.
236 case Instruction::GetElementPtr:
237 // GEPs are cheap if all indices are constant.
238 if (!cast<GEPOperator>(I)->hasAllConstantIndices())
241 case Instruction::Load:
242 case Instruction::Add:
243 case Instruction::Sub:
244 case Instruction::And:
245 case Instruction::Or:
246 case Instruction::Xor:
247 case Instruction::Shl:
248 case Instruction::LShr:
249 case Instruction::AShr:
250 case Instruction::ICmp:
251 case Instruction::Trunc:
252 case Instruction::ZExt:
253 case Instruction::SExt:
254 return 1; // These are all cheap.
256 case Instruction::Call:
257 case Instruction::Select:
262 /// DominatesMergePoint - If we have a merge point of an "if condition" as
263 /// accepted above, return true if the specified value dominates the block. We
264 /// don't handle the true generality of domination here, just a special case
265 /// which works well enough for us.
267 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
268 /// see if V (which must be an instruction) and its recursive operands
269 /// that do not dominate BB have a combined cost lower than CostRemaining and
270 /// are non-trapping. If both are true, the instruction is inserted into the
271 /// set and true is returned.
273 /// The cost for most non-trapping instructions is defined as 1 except for
274 /// Select whose cost is 2.
276 /// After this function returns, CostRemaining is decreased by the cost of
277 /// V plus its non-dominating operands. If that cost is greater than
278 /// CostRemaining, false is returned and CostRemaining is undefined.
279 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
280 SmallPtrSet<Instruction*, 4> *AggressiveInsts,
281 unsigned &CostRemaining) {
282 Instruction *I = dyn_cast<Instruction>(V);
284 // Non-instructions all dominate instructions, but not all constantexprs
285 // can be executed unconditionally.
286 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
291 BasicBlock *PBB = I->getParent();
293 // We don't want to allow weird loops that might have the "if condition" in
294 // the bottom of this block.
295 if (PBB == BB) return false;
297 // If this instruction is defined in a block that contains an unconditional
298 // branch to BB, then it must be in the 'conditional' part of the "if
299 // statement". If not, it definitely dominates the region.
300 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
301 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB)
304 // If we aren't allowing aggressive promotion anymore, then don't consider
305 // instructions in the 'if region'.
306 if (AggressiveInsts == 0) return false;
308 // If we have seen this instruction before, don't count it again.
309 if (AggressiveInsts->count(I)) return true;
311 // Okay, it looks like the instruction IS in the "condition". Check to
312 // see if it's a cheap instruction to unconditionally compute, and if it
313 // only uses stuff defined outside of the condition. If so, hoist it out.
314 if (!isSafeToSpeculativelyExecute(I))
317 unsigned Cost = ComputeSpeculationCost(I);
319 if (Cost > CostRemaining)
322 CostRemaining -= Cost;
324 // Okay, we can only really hoist these out if their operands do
325 // not take us over the cost threshold.
326 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
327 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining))
329 // Okay, it's safe to do this! Remember this instruction.
330 AggressiveInsts->insert(I);
334 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
335 /// and PointerNullValue. Return NULL if value is not a constant int.
336 static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
337 // Normal constant int.
338 ConstantInt *CI = dyn_cast<ConstantInt>(V);
339 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
342 // This is some kind of pointer constant. Turn it into a pointer-sized
343 // ConstantInt if possible.
344 IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
346 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
347 if (isa<ConstantPointerNull>(V))
348 return ConstantInt::get(PtrTy, 0);
350 // IntToPtr const int.
351 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
352 if (CE->getOpcode() == Instruction::IntToPtr)
353 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
354 // The constant is very likely to have the right type already.
355 if (CI->getType() == PtrTy)
358 return cast<ConstantInt>
359 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
364 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
365 /// collection of icmp eq/ne instructions that compare a value against a
366 /// constant, return the value being compared, and stick the constant into the
369 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
370 const TargetData *TD, bool isEQ, unsigned &UsedICmps) {
371 Instruction *I = dyn_cast<Instruction>(V);
372 if (I == 0) return 0;
374 // If this is an icmp against a constant, handle this as one of the cases.
375 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
376 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
377 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
380 return I->getOperand(0);
383 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
386 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
388 // If this is an and/!= check then we want to optimize "x ugt 2" into
391 Span = Span.inverse();
393 // If there are a ton of values, we don't want to make a ginormous switch.
394 if (Span.getSetSize().ugt(8) || Span.isEmptySet())
397 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
398 Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
400 return I->getOperand(0);
405 // Otherwise, we can only handle an | or &, depending on isEQ.
406 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
409 unsigned NumValsBeforeLHS = Vals.size();
410 unsigned UsedICmpsBeforeLHS = UsedICmps;
411 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
413 unsigned NumVals = Vals.size();
414 unsigned UsedICmpsBeforeRHS = UsedICmps;
415 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
419 Vals.resize(NumVals);
420 UsedICmps = UsedICmpsBeforeRHS;
423 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
424 // set it and return success.
425 if (Extra == 0 || Extra == I->getOperand(1)) {
426 Extra = I->getOperand(1);
430 Vals.resize(NumValsBeforeLHS);
431 UsedICmps = UsedICmpsBeforeLHS;
435 // If the LHS can't be folded in, but Extra is available and RHS can, try to
437 if (Extra == 0 || Extra == I->getOperand(0)) {
438 Value *OldExtra = Extra;
439 Extra = I->getOperand(0);
440 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
443 assert(Vals.size() == NumValsBeforeLHS);
450 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
451 Instruction *Cond = 0;
452 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
453 Cond = dyn_cast<Instruction>(SI->getCondition());
454 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
455 if (BI->isConditional())
456 Cond = dyn_cast<Instruction>(BI->getCondition());
457 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
458 Cond = dyn_cast<Instruction>(IBI->getAddress());
461 TI->eraseFromParent();
462 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
465 /// isValueEqualityComparison - Return true if the specified terminator checks
466 /// to see if a value is equal to constant integer value.
467 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
469 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
470 // Do not permit merging of large switch instructions into their
471 // predecessors unless there is only one predecessor.
472 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
473 pred_end(SI->getParent())) <= 128)
474 CV = SI->getCondition();
475 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
476 if (BI->isConditional() && BI->getCondition()->hasOneUse())
477 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
478 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
479 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
480 GetConstantInt(ICI->getOperand(1), TD))
481 CV = ICI->getOperand(0);
483 // Unwrap any lossless ptrtoint cast.
484 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
485 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
486 CV = PTII->getOperand(0);
490 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
491 /// decode all of the 'cases' that it represents and return the 'default' block.
492 BasicBlock *SimplifyCFGOpt::
493 GetValueEqualityComparisonCases(TerminatorInst *TI,
494 std::vector<ValueEqualityComparisonCase>
496 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
497 Cases.reserve(SI->getNumCases());
498 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i)
499 Cases.push_back(ValueEqualityComparisonCase(i.getCaseValue(),
500 i.getCaseSuccessor()));
501 return SI->getDefaultDest();
504 BranchInst *BI = cast<BranchInst>(TI);
505 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
506 BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE);
507 Cases.push_back(ValueEqualityComparisonCase(GetConstantInt(ICI->getOperand(1),
510 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
514 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
515 /// in the list that match the specified block.
516 static void EliminateBlockCases(BasicBlock *BB,
517 std::vector<ValueEqualityComparisonCase> &Cases) {
518 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
519 if (Cases[i].Dest == BB) {
520 Cases.erase(Cases.begin()+i);
525 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
528 ValuesOverlap(std::vector<ValueEqualityComparisonCase> &C1,
529 std::vector<ValueEqualityComparisonCase > &C2) {
530 std::vector<ValueEqualityComparisonCase> *V1 = &C1, *V2 = &C2;
532 // Make V1 be smaller than V2.
533 if (V1->size() > V2->size())
536 if (V1->size() == 0) return false;
537 if (V1->size() == 1) {
539 ConstantInt *TheVal = (*V1)[0].Value;
540 for (unsigned i = 0, e = V2->size(); i != e; ++i)
541 if (TheVal == (*V2)[i].Value)
545 // Otherwise, just sort both lists and compare element by element.
546 array_pod_sort(V1->begin(), V1->end());
547 array_pod_sort(V2->begin(), V2->end());
548 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
549 while (i1 != e1 && i2 != e2) {
550 if ((*V1)[i1].Value == (*V2)[i2].Value)
552 if ((*V1)[i1].Value < (*V2)[i2].Value)
560 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
561 /// terminator instruction and its block is known to only have a single
562 /// predecessor block, check to see if that predecessor is also a value
563 /// comparison with the same value, and if that comparison determines the
564 /// outcome of this comparison. If so, simplify TI. This does a very limited
565 /// form of jump threading.
566 bool SimplifyCFGOpt::
567 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
569 IRBuilder<> &Builder) {
570 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
571 if (!PredVal) return false; // Not a value comparison in predecessor.
573 Value *ThisVal = isValueEqualityComparison(TI);
574 assert(ThisVal && "This isn't a value comparison!!");
575 if (ThisVal != PredVal) return false; // Different predicates.
577 // Find out information about when control will move from Pred to TI's block.
578 std::vector<ValueEqualityComparisonCase> PredCases;
579 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
581 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
583 // Find information about how control leaves this block.
584 std::vector<ValueEqualityComparisonCase> ThisCases;
585 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
586 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
588 // If TI's block is the default block from Pred's comparison, potentially
589 // simplify TI based on this knowledge.
590 if (PredDef == TI->getParent()) {
591 // If we are here, we know that the value is none of those cases listed in
592 // PredCases. If there are any cases in ThisCases that are in PredCases, we
594 if (!ValuesOverlap(PredCases, ThisCases))
597 if (isa<BranchInst>(TI)) {
598 // Okay, one of the successors of this condbr is dead. Convert it to a
600 assert(ThisCases.size() == 1 && "Branch can only have one case!");
601 // Insert the new branch.
602 Instruction *NI = Builder.CreateBr(ThisDef);
605 // Remove PHI node entries for the dead edge.
606 ThisCases[0].Dest->removePredecessor(TI->getParent());
608 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
609 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
611 EraseTerminatorInstAndDCECond(TI);
615 SwitchInst *SI = cast<SwitchInst>(TI);
616 // Okay, TI has cases that are statically dead, prune them away.
617 SmallPtrSet<Constant*, 16> DeadCases;
618 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
619 DeadCases.insert(PredCases[i].Value);
621 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
622 << "Through successor TI: " << *TI);
624 for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) {
626 if (DeadCases.count(i.getCaseValue())) {
627 i.getCaseSuccessor()->removePredecessor(TI->getParent());
632 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
636 // Otherwise, TI's block must correspond to some matched value. Find out
637 // which value (or set of values) this is.
638 ConstantInt *TIV = 0;
639 BasicBlock *TIBB = TI->getParent();
640 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
641 if (PredCases[i].Dest == TIBB) {
643 return false; // Cannot handle multiple values coming to this block.
644 TIV = PredCases[i].Value;
646 assert(TIV && "No edge from pred to succ?");
648 // Okay, we found the one constant that our value can be if we get into TI's
649 // BB. Find out which successor will unconditionally be branched to.
650 BasicBlock *TheRealDest = 0;
651 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
652 if (ThisCases[i].Value == TIV) {
653 TheRealDest = ThisCases[i].Dest;
657 // If not handled by any explicit cases, it is handled by the default case.
658 if (TheRealDest == 0) TheRealDest = ThisDef;
660 // Remove PHI node entries for dead edges.
661 BasicBlock *CheckEdge = TheRealDest;
662 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
663 if (*SI != CheckEdge)
664 (*SI)->removePredecessor(TIBB);
668 // Insert the new branch.
669 Instruction *NI = Builder.CreateBr(TheRealDest);
672 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
673 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
675 EraseTerminatorInstAndDCECond(TI);
680 /// ConstantIntOrdering - This class implements a stable ordering of constant
681 /// integers that does not depend on their address. This is important for
682 /// applications that sort ConstantInt's to ensure uniqueness.
683 struct ConstantIntOrdering {
684 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
685 return LHS->getValue().ult(RHS->getValue());
690 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
691 const ConstantInt *LHS = *(const ConstantInt**)P1;
692 const ConstantInt *RHS = *(const ConstantInt**)P2;
693 if (LHS->getValue().ult(RHS->getValue()))
695 if (LHS->getValue() == RHS->getValue())
700 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
701 /// equality comparison instruction (either a switch or a branch on "X == c").
702 /// See if any of the predecessors of the terminator block are value comparisons
703 /// on the same value. If so, and if safe to do so, fold them together.
704 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
705 IRBuilder<> &Builder) {
706 BasicBlock *BB = TI->getParent();
707 Value *CV = isValueEqualityComparison(TI); // CondVal
708 assert(CV && "Not a comparison?");
709 bool Changed = false;
711 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
712 while (!Preds.empty()) {
713 BasicBlock *Pred = Preds.pop_back_val();
715 // See if the predecessor is a comparison with the same value.
716 TerminatorInst *PTI = Pred->getTerminator();
717 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
719 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
720 // Figure out which 'cases' to copy from SI to PSI.
721 std::vector<ValueEqualityComparisonCase> BBCases;
722 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
724 std::vector<ValueEqualityComparisonCase> PredCases;
725 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
727 // Based on whether the default edge from PTI goes to BB or not, fill in
728 // PredCases and PredDefault with the new switch cases we would like to
730 SmallVector<BasicBlock*, 8> NewSuccessors;
732 if (PredDefault == BB) {
733 // If this is the default destination from PTI, only the edges in TI
734 // that don't occur in PTI, or that branch to BB will be activated.
735 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
736 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
737 if (PredCases[i].Dest != BB)
738 PTIHandled.insert(PredCases[i].Value);
740 // The default destination is BB, we don't need explicit targets.
741 std::swap(PredCases[i], PredCases.back());
742 PredCases.pop_back();
746 // Reconstruct the new switch statement we will be building.
747 if (PredDefault != BBDefault) {
748 PredDefault->removePredecessor(Pred);
749 PredDefault = BBDefault;
750 NewSuccessors.push_back(BBDefault);
752 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
753 if (!PTIHandled.count(BBCases[i].Value) &&
754 BBCases[i].Dest != BBDefault) {
755 PredCases.push_back(BBCases[i]);
756 NewSuccessors.push_back(BBCases[i].Dest);
760 // If this is not the default destination from PSI, only the edges
761 // in SI that occur in PSI with a destination of BB will be
763 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
764 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
765 if (PredCases[i].Dest == BB) {
766 PTIHandled.insert(PredCases[i].Value);
767 std::swap(PredCases[i], PredCases.back());
768 PredCases.pop_back();
772 // Okay, now we know which constants were sent to BB from the
773 // predecessor. Figure out where they will all go now.
774 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
775 if (PTIHandled.count(BBCases[i].Value)) {
776 // If this is one we are capable of getting...
777 PredCases.push_back(BBCases[i]);
778 NewSuccessors.push_back(BBCases[i].Dest);
779 PTIHandled.erase(BBCases[i].Value);// This constant is taken care of
782 // If there are any constants vectored to BB that TI doesn't handle,
783 // they must go to the default destination of TI.
784 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
786 E = PTIHandled.end(); I != E; ++I) {
787 PredCases.push_back(ValueEqualityComparisonCase(*I, BBDefault));
788 NewSuccessors.push_back(BBDefault);
792 // Okay, at this point, we know which new successor Pred will get. Make
793 // sure we update the number of entries in the PHI nodes for these
795 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
796 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
798 Builder.SetInsertPoint(PTI);
799 // Convert pointer to int before we switch.
800 if (CV->getType()->isPointerTy()) {
801 assert(TD && "Cannot switch on pointer without TargetData");
802 CV = Builder.CreatePtrToInt(CV, TD->getIntPtrType(CV->getContext()),
806 // Now that the successors are updated, create the new Switch instruction.
807 SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault,
809 NewSI->setDebugLoc(PTI->getDebugLoc());
810 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
811 NewSI->addCase(PredCases[i].Value, PredCases[i].Dest);
813 EraseTerminatorInstAndDCECond(PTI);
815 // Okay, last check. If BB is still a successor of PSI, then we must
816 // have an infinite loop case. If so, add an infinitely looping block
817 // to handle the case to preserve the behavior of the code.
818 BasicBlock *InfLoopBlock = 0;
819 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
820 if (NewSI->getSuccessor(i) == BB) {
821 if (InfLoopBlock == 0) {
822 // Insert it at the end of the function, because it's either code,
823 // or it won't matter if it's hot. :)
824 InfLoopBlock = BasicBlock::Create(BB->getContext(),
825 "infloop", BB->getParent());
826 BranchInst::Create(InfLoopBlock, InfLoopBlock);
828 NewSI->setSuccessor(i, InfLoopBlock);
837 // isSafeToHoistInvoke - If we would need to insert a select that uses the
838 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
839 // would need to do this), we can't hoist the invoke, as there is nowhere
840 // to put the select in this case.
841 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
842 Instruction *I1, Instruction *I2) {
843 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
845 for (BasicBlock::iterator BBI = SI->begin();
846 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
847 Value *BB1V = PN->getIncomingValueForBlock(BB1);
848 Value *BB2V = PN->getIncomingValueForBlock(BB2);
849 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
857 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
858 /// BB2, hoist any common code in the two blocks up into the branch block. The
859 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
860 static bool HoistThenElseCodeToIf(BranchInst *BI) {
861 // This does very trivial matching, with limited scanning, to find identical
862 // instructions in the two blocks. In particular, we don't want to get into
863 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
864 // such, we currently just scan for obviously identical instructions in an
866 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
867 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
869 BasicBlock::iterator BB1_Itr = BB1->begin();
870 BasicBlock::iterator BB2_Itr = BB2->begin();
872 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
873 // Skip debug info if it is not identical.
874 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
875 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
876 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
877 while (isa<DbgInfoIntrinsic>(I1))
879 while (isa<DbgInfoIntrinsic>(I2))
882 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
883 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
886 // If we get here, we can hoist at least one instruction.
887 BasicBlock *BIParent = BI->getParent();
890 // If we are hoisting the terminator instruction, don't move one (making a
891 // broken BB), instead clone it, and remove BI.
892 if (isa<TerminatorInst>(I1))
893 goto HoistTerminator;
895 // For a normal instruction, we just move one to right before the branch,
896 // then replace all uses of the other with the first. Finally, we remove
897 // the now redundant second instruction.
898 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
899 if (!I2->use_empty())
900 I2->replaceAllUsesWith(I1);
901 I1->intersectOptionalDataWith(I2);
902 I2->eraseFromParent();
906 // Skip debug info if it is not identical.
907 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
908 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
909 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
910 while (isa<DbgInfoIntrinsic>(I1))
912 while (isa<DbgInfoIntrinsic>(I2))
915 } while (I1->isIdenticalToWhenDefined(I2));
920 // It may not be possible to hoist an invoke.
921 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
924 // Okay, it is safe to hoist the terminator.
925 Instruction *NT = I1->clone();
926 BIParent->getInstList().insert(BI, NT);
927 if (!NT->getType()->isVoidTy()) {
928 I1->replaceAllUsesWith(NT);
929 I2->replaceAllUsesWith(NT);
933 IRBuilder<true, NoFolder> Builder(NT);
934 // Hoisting one of the terminators from our successor is a great thing.
935 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
936 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
937 // nodes, so we insert select instruction to compute the final result.
938 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
939 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
941 for (BasicBlock::iterator BBI = SI->begin();
942 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
943 Value *BB1V = PN->getIncomingValueForBlock(BB1);
944 Value *BB2V = PN->getIncomingValueForBlock(BB2);
945 if (BB1V == BB2V) continue;
947 // These values do not agree. Insert a select instruction before NT
948 // that determines the right value.
949 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
951 SI = cast<SelectInst>
952 (Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,
953 BB1V->getName()+"."+BB2V->getName()));
955 // Make the PHI node use the select for all incoming values for BB1/BB2
956 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
957 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
958 PN->setIncomingValue(i, SI);
962 // Update any PHI nodes in our new successors.
963 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
964 AddPredecessorToBlock(*SI, BIParent, BB1);
966 EraseTerminatorInstAndDCECond(BI);
970 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
971 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
972 /// (for now, restricted to a single instruction that's side effect free) from
973 /// the BB1 into the branch block to speculatively execute it.
978 /// br i1 %t1, label %BB1, label %BB2
987 /// %t3 = select i1 %t1, %t2, %t3
988 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
989 // Only speculatively execution a single instruction (not counting the
990 // terminator) for now.
991 Instruction *HInst = NULL;
992 Instruction *Term = BB1->getTerminator();
993 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
995 Instruction *I = BBI;
997 if (isa<DbgInfoIntrinsic>(I)) continue;
998 if (I == Term) break;
1005 BasicBlock *BIParent = BI->getParent();
1007 // Check the instruction to be hoisted, if there is one.
1009 // Don't hoist the instruction if it's unsafe or expensive.
1010 if (!isSafeToSpeculativelyExecute(HInst))
1012 if (ComputeSpeculationCost(HInst) > PHINodeFoldingThreshold)
1015 // Do not hoist the instruction if any of its operands are defined but not
1016 // used in this BB. The transformation will prevent the operand from
1017 // being sunk into the use block.
1018 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1020 Instruction *OpI = dyn_cast<Instruction>(*i);
1021 if (OpI && OpI->getParent() == BIParent &&
1022 !OpI->mayHaveSideEffects() &&
1023 !OpI->isUsedInBasicBlock(BIParent))
1028 // Be conservative for now. FP select instruction can often be expensive.
1029 Value *BrCond = BI->getCondition();
1030 if (isa<FCmpInst>(BrCond))
1033 // If BB1 is actually on the false edge of the conditional branch, remember
1034 // to swap the select operands later.
1035 bool Invert = false;
1036 if (BB1 != BI->getSuccessor(0)) {
1037 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
1041 // Collect interesting PHIs, and scan for hazards.
1042 SmallSetVector<std::pair<Value *, Value *>, 4> PHIs;
1043 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
1044 for (BasicBlock::iterator I = BB2->begin();
1045 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1046 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1047 Value *BIParentV = PN->getIncomingValueForBlock(BIParent);
1049 // Skip PHIs which are trivial.
1050 if (BB1V == BIParentV)
1053 // Check for saftey.
1054 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BB1V)) {
1055 // An unfolded ConstantExpr could end up getting expanded into
1056 // Instructions. Don't speculate this and another instruction at
1060 if (!isSafeToSpeculativelyExecute(CE))
1062 if (ComputeSpeculationCost(CE) > PHINodeFoldingThreshold)
1066 // Ok, we may insert a select for this PHI.
1067 PHIs.insert(std::make_pair(BB1V, BIParentV));
1070 // If there are no PHIs to process, bail early. This helps ensure idempotence
1075 // If we get here, we can hoist the instruction and if-convert.
1076 DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *BB1 << "\n";);
1078 // Hoist the instruction.
1080 BIParent->getInstList().splice(BI, BB1->getInstList(), HInst);
1082 // Insert selects and rewrite the PHI operands.
1083 IRBuilder<true, NoFolder> Builder(BI);
1084 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
1085 Value *TrueV = PHIs[i].first;
1086 Value *FalseV = PHIs[i].second;
1088 // Create a select whose true value is the speculatively executed value and
1089 // false value is the previously determined FalseV.
1092 SI = cast<SelectInst>
1093 (Builder.CreateSelect(BrCond, FalseV, TrueV,
1094 FalseV->getName() + "." + TrueV->getName()));
1096 SI = cast<SelectInst>
1097 (Builder.CreateSelect(BrCond, TrueV, FalseV,
1098 TrueV->getName() + "." + FalseV->getName()));
1100 // Make the PHI node use the select for all incoming values for "then" and
1102 for (BasicBlock::iterator I = BB2->begin();
1103 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1104 unsigned BB1I = PN->getBasicBlockIndex(BB1);
1105 unsigned BIParentI = PN->getBasicBlockIndex(BIParent);
1106 Value *BB1V = PN->getIncomingValue(BB1I);
1107 Value *BIParentV = PN->getIncomingValue(BIParentI);
1108 if (TrueV == BB1V && FalseV == BIParentV) {
1109 PN->setIncomingValue(BB1I, SI);
1110 PN->setIncomingValue(BIParentI, SI);
1119 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1120 /// across this block.
1121 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1122 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1125 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1126 if (isa<DbgInfoIntrinsic>(BBI))
1128 if (Size > 10) return false; // Don't clone large BB's.
1131 // We can only support instructions that do not define values that are
1132 // live outside of the current basic block.
1133 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1135 Instruction *U = cast<Instruction>(*UI);
1136 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1139 // Looks ok, continue checking.
1145 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1146 /// that is defined in the same block as the branch and if any PHI entries are
1147 /// constants, thread edges corresponding to that entry to be branches to their
1148 /// ultimate destination.
1149 static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
1150 BasicBlock *BB = BI->getParent();
1151 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1152 // NOTE: we currently cannot transform this case if the PHI node is used
1153 // outside of the block.
1154 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1157 // Degenerate case of a single entry PHI.
1158 if (PN->getNumIncomingValues() == 1) {
1159 FoldSingleEntryPHINodes(PN->getParent());
1163 // Now we know that this block has multiple preds and two succs.
1164 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1166 // Okay, this is a simple enough basic block. See if any phi values are
1168 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1169 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1170 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1172 // Okay, we now know that all edges from PredBB should be revectored to
1173 // branch to RealDest.
1174 BasicBlock *PredBB = PN->getIncomingBlock(i);
1175 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1177 if (RealDest == BB) continue; // Skip self loops.
1178 // Skip if the predecessor's terminator is an indirect branch.
1179 if (isa<IndirectBrInst>(PredBB->getTerminator())) continue;
1181 // The dest block might have PHI nodes, other predecessors and other
1182 // difficult cases. Instead of being smart about this, just insert a new
1183 // block that jumps to the destination block, effectively splitting
1184 // the edge we are about to create.
1185 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1186 RealDest->getName()+".critedge",
1187 RealDest->getParent(), RealDest);
1188 BranchInst::Create(RealDest, EdgeBB);
1190 // Update PHI nodes.
1191 AddPredecessorToBlock(RealDest, EdgeBB, BB);
1193 // BB may have instructions that are being threaded over. Clone these
1194 // instructions into EdgeBB. We know that there will be no uses of the
1195 // cloned instructions outside of EdgeBB.
1196 BasicBlock::iterator InsertPt = EdgeBB->begin();
1197 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1198 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1199 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1200 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1203 // Clone the instruction.
1204 Instruction *N = BBI->clone();
1205 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1207 // Update operands due to translation.
1208 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1210 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1211 if (PI != TranslateMap.end())
1215 // Check for trivial simplification.
1216 if (Value *V = SimplifyInstruction(N, TD)) {
1217 TranslateMap[BBI] = V;
1218 delete N; // Instruction folded away, don't need actual inst
1220 // Insert the new instruction into its new home.
1221 EdgeBB->getInstList().insert(InsertPt, N);
1222 if (!BBI->use_empty())
1223 TranslateMap[BBI] = N;
1227 // Loop over all of the edges from PredBB to BB, changing them to branch
1228 // to EdgeBB instead.
1229 TerminatorInst *PredBBTI = PredBB->getTerminator();
1230 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1231 if (PredBBTI->getSuccessor(i) == BB) {
1232 BB->removePredecessor(PredBB);
1233 PredBBTI->setSuccessor(i, EdgeBB);
1236 // Recurse, simplifying any other constants.
1237 return FoldCondBranchOnPHI(BI, TD) | true;
1243 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1244 /// PHI node, see if we can eliminate it.
1245 static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
1246 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1247 // statement", which has a very simple dominance structure. Basically, we
1248 // are trying to find the condition that is being branched on, which
1249 // subsequently causes this merge to happen. We really want control
1250 // dependence information for this check, but simplifycfg can't keep it up
1251 // to date, and this catches most of the cases we care about anyway.
1252 BasicBlock *BB = PN->getParent();
1253 BasicBlock *IfTrue, *IfFalse;
1254 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1256 // Don't bother if the branch will be constant folded trivially.
1257 isa<ConstantInt>(IfCond))
1260 // Okay, we found that we can merge this two-entry phi node into a select.
1261 // Doing so would require us to fold *all* two entry phi nodes in this block.
1262 // At some point this becomes non-profitable (particularly if the target
1263 // doesn't support cmov's). Only do this transformation if there are two or
1264 // fewer PHI nodes in this block.
1265 unsigned NumPhis = 0;
1266 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1270 // Loop over the PHI's seeing if we can promote them all to select
1271 // instructions. While we are at it, keep track of the instructions
1272 // that need to be moved to the dominating block.
1273 SmallPtrSet<Instruction*, 4> AggressiveInsts;
1274 unsigned MaxCostVal0 = PHINodeFoldingThreshold,
1275 MaxCostVal1 = PHINodeFoldingThreshold;
1277 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1278 PHINode *PN = cast<PHINode>(II++);
1279 if (Value *V = SimplifyInstruction(PN, TD)) {
1280 PN->replaceAllUsesWith(V);
1281 PN->eraseFromParent();
1285 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
1287 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
1292 // If we folded the the first phi, PN dangles at this point. Refresh it. If
1293 // we ran out of PHIs then we simplified them all.
1294 PN = dyn_cast<PHINode>(BB->begin());
1295 if (PN == 0) return true;
1297 // Don't fold i1 branches on PHIs which contain binary operators. These can
1298 // often be turned into switches and other things.
1299 if (PN->getType()->isIntegerTy(1) &&
1300 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1301 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1302 isa<BinaryOperator>(IfCond)))
1305 // If we all PHI nodes are promotable, check to make sure that all
1306 // instructions in the predecessor blocks can be promoted as well. If
1307 // not, we won't be able to get rid of the control flow, so it's not
1308 // worth promoting to select instructions.
1309 BasicBlock *DomBlock = 0;
1310 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1311 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1312 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1315 DomBlock = *pred_begin(IfBlock1);
1316 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1317 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1318 // This is not an aggressive instruction that we can promote.
1319 // Because of this, we won't be able to get rid of the control
1320 // flow, so the xform is not worth it.
1325 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1328 DomBlock = *pred_begin(IfBlock2);
1329 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1330 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1331 // This is not an aggressive instruction that we can promote.
1332 // Because of this, we won't be able to get rid of the control
1333 // flow, so the xform is not worth it.
1338 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1339 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1341 // If we can still promote the PHI nodes after this gauntlet of tests,
1342 // do all of the PHI's now.
1343 Instruction *InsertPt = DomBlock->getTerminator();
1344 IRBuilder<true, NoFolder> Builder(InsertPt);
1346 // Move all 'aggressive' instructions, which are defined in the
1347 // conditional parts of the if's up to the dominating block.
1349 DomBlock->getInstList().splice(InsertPt,
1350 IfBlock1->getInstList(), IfBlock1->begin(),
1351 IfBlock1->getTerminator());
1353 DomBlock->getInstList().splice(InsertPt,
1354 IfBlock2->getInstList(), IfBlock2->begin(),
1355 IfBlock2->getTerminator());
1357 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1358 // Change the PHI node into a select instruction.
1359 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1360 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1363 cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, ""));
1364 PN->replaceAllUsesWith(NV);
1366 PN->eraseFromParent();
1369 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1370 // has been flattened. Change DomBlock to jump directly to our new block to
1371 // avoid other simplifycfg's kicking in on the diamond.
1372 TerminatorInst *OldTI = DomBlock->getTerminator();
1373 Builder.SetInsertPoint(OldTI);
1374 Builder.CreateBr(BB);
1375 OldTI->eraseFromParent();
1379 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1380 /// to two returning blocks, try to merge them together into one return,
1381 /// introducing a select if the return values disagree.
1382 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
1383 IRBuilder<> &Builder) {
1384 assert(BI->isConditional() && "Must be a conditional branch");
1385 BasicBlock *TrueSucc = BI->getSuccessor(0);
1386 BasicBlock *FalseSucc = BI->getSuccessor(1);
1387 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1388 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1390 // Check to ensure both blocks are empty (just a return) or optionally empty
1391 // with PHI nodes. If there are other instructions, merging would cause extra
1392 // computation on one path or the other.
1393 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1395 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1398 Builder.SetInsertPoint(BI);
1399 // Okay, we found a branch that is going to two return nodes. If
1400 // there is no return value for this function, just change the
1401 // branch into a return.
1402 if (FalseRet->getNumOperands() == 0) {
1403 TrueSucc->removePredecessor(BI->getParent());
1404 FalseSucc->removePredecessor(BI->getParent());
1405 Builder.CreateRetVoid();
1406 EraseTerminatorInstAndDCECond(BI);
1410 // Otherwise, figure out what the true and false return values are
1411 // so we can insert a new select instruction.
1412 Value *TrueValue = TrueRet->getReturnValue();
1413 Value *FalseValue = FalseRet->getReturnValue();
1415 // Unwrap any PHI nodes in the return blocks.
1416 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1417 if (TVPN->getParent() == TrueSucc)
1418 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1419 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1420 if (FVPN->getParent() == FalseSucc)
1421 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1423 // In order for this transformation to be safe, we must be able to
1424 // unconditionally execute both operands to the return. This is
1425 // normally the case, but we could have a potentially-trapping
1426 // constant expression that prevents this transformation from being
1428 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1431 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1435 // Okay, we collected all the mapped values and checked them for sanity, and
1436 // defined to really do this transformation. First, update the CFG.
1437 TrueSucc->removePredecessor(BI->getParent());
1438 FalseSucc->removePredecessor(BI->getParent());
1440 // Insert select instructions where needed.
1441 Value *BrCond = BI->getCondition();
1443 // Insert a select if the results differ.
1444 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1445 } else if (isa<UndefValue>(TrueValue)) {
1446 TrueValue = FalseValue;
1448 TrueValue = Builder.CreateSelect(BrCond, TrueValue,
1449 FalseValue, "retval");
1453 Value *RI = !TrueValue ?
1454 Builder.CreateRetVoid() : Builder.CreateRet(TrueValue);
1458 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1459 << "\n " << *BI << "NewRet = " << *RI
1460 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1462 EraseTerminatorInstAndDCECond(BI);
1467 /// ExtractBranchMetadata - Given a conditional BranchInstruction, retrieve the
1468 /// probabilities of the branch taking each edge. Fills in the two APInt
1469 /// parameters and return true, or returns false if no or invalid metadata was
1471 static bool ExtractBranchMetadata(BranchInst *BI,
1472 APInt &ProbTrue, APInt &ProbFalse) {
1473 assert(BI->isConditional() &&
1474 "Looking for probabilities on unconditional branch?");
1475 MDNode *ProfileData = BI->getMetadata(LLVMContext::MD_prof);
1476 if (!ProfileData || ProfileData->getNumOperands() != 3) return false;
1477 ConstantInt *CITrue = dyn_cast<ConstantInt>(ProfileData->getOperand(1));
1478 ConstantInt *CIFalse = dyn_cast<ConstantInt>(ProfileData->getOperand(2));
1479 if (!CITrue || !CIFalse) return false;
1480 ProbTrue = CITrue->getValue();
1481 ProbFalse = CIFalse->getValue();
1482 assert(ProbTrue.getBitWidth() == 32 && ProbFalse.getBitWidth() == 32 &&
1483 "Branch probability metadata must be 32-bit integers");
1487 /// MultiplyAndLosePrecision - Multiplies A and B, then returns the result. In
1488 /// the event of overflow, logically-shifts all four inputs right until the
1490 static APInt MultiplyAndLosePrecision(APInt &A, APInt &B, APInt &C, APInt &D,
1491 unsigned &BitsLost) {
1493 bool Overflow = false;
1494 APInt Result = A.umul_ov(B, Overflow);
1496 APInt MaxB = APInt::getMaxValue(A.getBitWidth()).udiv(A);
1500 } while (B.ugt(MaxB));
1501 A = A.lshr(BitsLost);
1502 C = C.lshr(BitsLost);
1503 D = D.lshr(BitsLost);
1510 /// FoldBranchToCommonDest - If this basic block is simple enough, and if a
1511 /// predecessor branches to us and one of our successors, fold the block into
1512 /// the predecessor and use logical operations to pick the right destination.
1513 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1514 BasicBlock *BB = BI->getParent();
1516 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1517 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1518 Cond->getParent() != BB || !Cond->hasOneUse())
1521 // Only allow this if the condition is a simple instruction that can be
1522 // executed unconditionally. It must be in the same block as the branch, and
1523 // must be at the front of the block.
1524 BasicBlock::iterator FrontIt = BB->front();
1526 // Ignore dbg intrinsics.
1527 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1529 // Allow a single instruction to be hoisted in addition to the compare
1530 // that feeds the branch. We later ensure that any values that _it_ uses
1531 // were also live in the predecessor, so that we don't unnecessarily create
1532 // register pressure or inhibit out-of-order execution.
1533 Instruction *BonusInst = 0;
1534 if (&*FrontIt != Cond &&
1535 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1536 isSafeToSpeculativelyExecute(FrontIt)) {
1537 BonusInst = &*FrontIt;
1540 // Ignore dbg intrinsics.
1541 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1544 // Only a single bonus inst is allowed.
1545 if (&*FrontIt != Cond)
1548 // Make sure the instruction after the condition is the cond branch.
1549 BasicBlock::iterator CondIt = Cond; ++CondIt;
1551 // Ingore dbg intrinsics.
1552 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
1557 // Cond is known to be a compare or binary operator. Check to make sure that
1558 // neither operand is a potentially-trapping constant expression.
1559 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1562 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1566 // Finally, don't infinitely unroll conditional loops.
1567 BasicBlock *TrueDest = BI->getSuccessor(0);
1568 BasicBlock *FalseDest = BI->getSuccessor(1);
1569 if (TrueDest == BB || FalseDest == BB)
1572 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1573 BasicBlock *PredBlock = *PI;
1574 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1576 // Check that we have two conditional branches. If there is a PHI node in
1577 // the common successor, verify that the same value flows in from both
1579 if (PBI == 0 || PBI->isUnconditional() || !SafeToMergeTerminators(BI, PBI))
1582 // Determine if the two branches share a common destination.
1583 Instruction::BinaryOps Opc;
1584 bool InvertPredCond = false;
1586 if (PBI->getSuccessor(0) == TrueDest)
1587 Opc = Instruction::Or;
1588 else if (PBI->getSuccessor(1) == FalseDest)
1589 Opc = Instruction::And;
1590 else if (PBI->getSuccessor(0) == FalseDest)
1591 Opc = Instruction::And, InvertPredCond = true;
1592 else if (PBI->getSuccessor(1) == TrueDest)
1593 Opc = Instruction::Or, InvertPredCond = true;
1597 // Ensure that any values used in the bonus instruction are also used
1598 // by the terminator of the predecessor. This means that those values
1599 // must already have been resolved, so we won't be inhibiting the
1600 // out-of-order core by speculating them earlier.
1602 // Collect the values used by the bonus inst
1603 SmallPtrSet<Value*, 4> UsedValues;
1604 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1605 OE = BonusInst->op_end(); OI != OE; ++OI) {
1607 if (!isa<Constant>(V))
1608 UsedValues.insert(V);
1611 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1612 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1614 // Walk up to four levels back up the use-def chain of the predecessor's
1615 // terminator to see if all those values were used. The choice of four
1616 // levels is arbitrary, to provide a compile-time-cost bound.
1617 while (!Worklist.empty()) {
1618 std::pair<Value*, unsigned> Pair = Worklist.back();
1619 Worklist.pop_back();
1621 if (Pair.second >= 4) continue;
1622 UsedValues.erase(Pair.first);
1623 if (UsedValues.empty()) break;
1625 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
1626 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1628 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1632 if (!UsedValues.empty()) return false;
1635 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1636 IRBuilder<> Builder(PBI);
1638 // If we need to invert the condition in the pred block to match, do so now.
1639 if (InvertPredCond) {
1640 Value *NewCond = PBI->getCondition();
1642 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
1643 CmpInst *CI = cast<CmpInst>(NewCond);
1644 CI->setPredicate(CI->getInversePredicate());
1646 NewCond = Builder.CreateNot(NewCond,
1647 PBI->getCondition()->getName()+".not");
1650 PBI->setCondition(NewCond);
1651 PBI->swapSuccessors();
1654 // If we have a bonus inst, clone it into the predecessor block.
1655 Instruction *NewBonus = 0;
1657 NewBonus = BonusInst->clone();
1658 PredBlock->getInstList().insert(PBI, NewBonus);
1659 NewBonus->takeName(BonusInst);
1660 BonusInst->setName(BonusInst->getName()+".old");
1663 // Clone Cond into the predecessor basic block, and or/and the
1664 // two conditions together.
1665 Instruction *New = Cond->clone();
1666 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1667 PredBlock->getInstList().insert(PBI, New);
1668 New->takeName(Cond);
1669 Cond->setName(New->getName()+".old");
1671 Instruction *NewCond =
1672 cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(),
1674 PBI->setCondition(NewCond);
1675 if (PBI->getSuccessor(0) == BB) {
1676 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1677 PBI->setSuccessor(0, TrueDest);
1679 if (PBI->getSuccessor(1) == BB) {
1680 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1681 PBI->setSuccessor(1, FalseDest);
1684 // TODO: If BB is reachable from all paths through PredBlock, then we
1685 // could replace PBI's branch probabilities with BI's.
1687 // Merge probability data into PredBlock's branch.
1689 if (ExtractBranchMetadata(PBI, C, D) && ExtractBranchMetadata(BI, A, B)) {
1690 // Given IR which does:
1692 // br i1 %x, label %bbB, label %bbC
1694 // br i1 %y, label %bbD, label %bbC
1695 // Let's call the probability that we take the edge from %bbA to %bbB
1696 // 'a', from %bbA to %bbC, 'b', from %bbB to %bbD 'c' and from %bbB to
1697 // %bbC probability 'd'.
1699 // We transform the IR into:
1701 // br i1 %z, label %bbD, label %bbC
1702 // where the probability of going to %bbD is (a*c) and going to bbC is
1705 // Probabilities aren't stored as ratios directly. Using branch weights,
1707 // (a*c)% = A*C, (b+(a*d))% = A*D+B*C+B*D.
1709 // In the event of overflow, we want to drop the LSB of the input
1713 // Ignore overflow result on ProbTrue.
1714 APInt ProbTrue = MultiplyAndLosePrecision(A, C, B, D, BitsLost);
1716 APInt Tmp1 = MultiplyAndLosePrecision(B, D, A, C, BitsLost);
1718 ProbTrue = ProbTrue.lshr(BitsLost*2);
1721 APInt Tmp2 = MultiplyAndLosePrecision(A, D, C, B, BitsLost);
1723 ProbTrue = ProbTrue.lshr(BitsLost*2);
1724 Tmp1 = Tmp1.lshr(BitsLost*2);
1727 APInt Tmp3 = MultiplyAndLosePrecision(B, C, A, D, BitsLost);
1729 ProbTrue = ProbTrue.lshr(BitsLost*2);
1730 Tmp1 = Tmp1.lshr(BitsLost*2);
1731 Tmp2 = Tmp2.lshr(BitsLost*2);
1734 bool Overflow1 = false, Overflow2 = false;
1735 APInt Tmp4 = Tmp2.uadd_ov(Tmp3, Overflow1);
1736 APInt ProbFalse = Tmp4.uadd_ov(Tmp1, Overflow2);
1738 if (Overflow1 || Overflow2) {
1739 ProbTrue = ProbTrue.lshr(1);
1740 Tmp1 = Tmp1.lshr(1);
1741 Tmp2 = Tmp2.lshr(1);
1742 Tmp3 = Tmp3.lshr(1);
1744 ProbFalse = Tmp4 + Tmp1;
1747 // The sum of branch weights must fit in 32-bits.
1748 if (ProbTrue.isNegative() && ProbFalse.isNegative()) {
1749 ProbTrue = ProbTrue.lshr(1);
1750 ProbFalse = ProbFalse.lshr(1);
1753 if (ProbTrue != ProbFalse) {
1754 // Normalize the result.
1755 APInt GCD = APIntOps::GreatestCommonDivisor(ProbTrue, ProbFalse);
1756 ProbTrue = ProbTrue.udiv(GCD);
1757 ProbFalse = ProbFalse.udiv(GCD);
1759 MDBuilder MDB(BI->getContext());
1760 MDNode *N = MDB.createBranchWeights(ProbTrue.getZExtValue(),
1761 ProbFalse.getZExtValue());
1762 PBI->setMetadata(LLVMContext::MD_prof, N);
1764 PBI->setMetadata(LLVMContext::MD_prof, NULL);
1767 PBI->setMetadata(LLVMContext::MD_prof, NULL);
1770 // Copy any debug value intrinsics into the end of PredBlock.
1771 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
1772 if (isa<DbgInfoIntrinsic>(*I))
1773 I->clone()->insertBefore(PBI);
1780 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1781 /// predecessor of another block, this function tries to simplify it. We know
1782 /// that PBI and BI are both conditional branches, and BI is in one of the
1783 /// successor blocks of PBI - PBI branches to BI.
1784 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1785 assert(PBI->isConditional() && BI->isConditional());
1786 BasicBlock *BB = BI->getParent();
1788 // If this block ends with a branch instruction, and if there is a
1789 // predecessor that ends on a branch of the same condition, make
1790 // this conditional branch redundant.
1791 if (PBI->getCondition() == BI->getCondition() &&
1792 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1793 // Okay, the outcome of this conditional branch is statically
1794 // knowable. If this block had a single pred, handle specially.
1795 if (BB->getSinglePredecessor()) {
1796 // Turn this into a branch on constant.
1797 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1798 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1800 return true; // Nuke the branch on constant.
1803 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1804 // in the constant and simplify the block result. Subsequent passes of
1805 // simplifycfg will thread the block.
1806 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1807 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
1808 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1809 std::distance(PB, PE),
1810 BI->getCondition()->getName() + ".pr",
1812 // Okay, we're going to insert the PHI node. Since PBI is not the only
1813 // predecessor, compute the PHI'd conditional value for all of the preds.
1814 // Any predecessor where the condition is not computable we keep symbolic.
1815 for (pred_iterator PI = PB; PI != PE; ++PI) {
1816 BasicBlock *P = *PI;
1817 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
1818 PBI != BI && PBI->isConditional() &&
1819 PBI->getCondition() == BI->getCondition() &&
1820 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1821 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1822 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1825 NewPN->addIncoming(BI->getCondition(), P);
1829 BI->setCondition(NewPN);
1834 // If this is a conditional branch in an empty block, and if any
1835 // predecessors is a conditional branch to one of our destinations,
1836 // fold the conditions into logical ops and one cond br.
1837 BasicBlock::iterator BBI = BB->begin();
1838 // Ignore dbg intrinsics.
1839 while (isa<DbgInfoIntrinsic>(BBI))
1845 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1850 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1852 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1853 PBIOp = 0, BIOp = 1;
1854 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1855 PBIOp = 1, BIOp = 0;
1856 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1861 // Check to make sure that the other destination of this branch
1862 // isn't BB itself. If so, this is an infinite loop that will
1863 // keep getting unwound.
1864 if (PBI->getSuccessor(PBIOp) == BB)
1867 // Do not perform this transformation if it would require
1868 // insertion of a large number of select instructions. For targets
1869 // without predication/cmovs, this is a big pessimization.
1870 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1872 unsigned NumPhis = 0;
1873 for (BasicBlock::iterator II = CommonDest->begin();
1874 isa<PHINode>(II); ++II, ++NumPhis)
1875 if (NumPhis > 2) // Disable this xform.
1878 // Finally, if everything is ok, fold the branches to logical ops.
1879 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1881 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
1882 << "AND: " << *BI->getParent());
1885 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1886 // branch in it, where one edge (OtherDest) goes back to itself but the other
1887 // exits. We don't *know* that the program avoids the infinite loop
1888 // (even though that seems likely). If we do this xform naively, we'll end up
1889 // recursively unpeeling the loop. Since we know that (after the xform is
1890 // done) that the block *is* infinite if reached, we just make it an obviously
1891 // infinite loop with no cond branch.
1892 if (OtherDest == BB) {
1893 // Insert it at the end of the function, because it's either code,
1894 // or it won't matter if it's hot. :)
1895 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1896 "infloop", BB->getParent());
1897 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1898 OtherDest = InfLoopBlock;
1901 DEBUG(dbgs() << *PBI->getParent()->getParent());
1903 // BI may have other predecessors. Because of this, we leave
1904 // it alone, but modify PBI.
1906 // Make sure we get to CommonDest on True&True directions.
1907 Value *PBICond = PBI->getCondition();
1908 IRBuilder<true, NoFolder> Builder(PBI);
1910 PBICond = Builder.CreateNot(PBICond, PBICond->getName()+".not");
1912 Value *BICond = BI->getCondition();
1914 BICond = Builder.CreateNot(BICond, BICond->getName()+".not");
1916 // Merge the conditions.
1917 Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge");
1919 // Modify PBI to branch on the new condition to the new dests.
1920 PBI->setCondition(Cond);
1921 PBI->setSuccessor(0, CommonDest);
1922 PBI->setSuccessor(1, OtherDest);
1924 // OtherDest may have phi nodes. If so, add an entry from PBI's
1925 // block that are identical to the entries for BI's block.
1926 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
1928 // We know that the CommonDest already had an edge from PBI to
1929 // it. If it has PHIs though, the PHIs may have different
1930 // entries for BB and PBI's BB. If so, insert a select to make
1933 for (BasicBlock::iterator II = CommonDest->begin();
1934 (PN = dyn_cast<PHINode>(II)); ++II) {
1935 Value *BIV = PN->getIncomingValueForBlock(BB);
1936 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1937 Value *PBIV = PN->getIncomingValue(PBBIdx);
1939 // Insert a select in PBI to pick the right value.
1940 Value *NV = cast<SelectInst>
1941 (Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName()+".mux"));
1942 PN->setIncomingValue(PBBIdx, NV);
1946 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1947 DEBUG(dbgs() << *PBI->getParent()->getParent());
1949 // This basic block is probably dead. We know it has at least
1950 // one fewer predecessor.
1954 // SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
1955 // branch to TrueBB if Cond is true or to FalseBB if Cond is false.
1956 // Takes care of updating the successors and removing the old terminator.
1957 // Also makes sure not to introduce new successors by assuming that edges to
1958 // non-successor TrueBBs and FalseBBs aren't reachable.
1959 static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
1960 BasicBlock *TrueBB, BasicBlock *FalseBB){
1961 // Remove any superfluous successor edges from the CFG.
1962 // First, figure out which successors to preserve.
1963 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
1965 BasicBlock *KeepEdge1 = TrueBB;
1966 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
1968 // Then remove the rest.
1969 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
1970 BasicBlock *Succ = OldTerm->getSuccessor(I);
1971 // Make sure only to keep exactly one copy of each edge.
1972 if (Succ == KeepEdge1)
1974 else if (Succ == KeepEdge2)
1977 Succ->removePredecessor(OldTerm->getParent());
1980 IRBuilder<> Builder(OldTerm);
1981 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
1983 // Insert an appropriate new terminator.
1984 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
1985 if (TrueBB == FalseBB)
1986 // We were only looking for one successor, and it was present.
1987 // Create an unconditional branch to it.
1988 Builder.CreateBr(TrueBB);
1990 // We found both of the successors we were looking for.
1991 // Create a conditional branch sharing the condition of the select.
1992 Builder.CreateCondBr(Cond, TrueBB, FalseBB);
1993 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
1994 // Neither of the selected blocks were successors, so this
1995 // terminator must be unreachable.
1996 new UnreachableInst(OldTerm->getContext(), OldTerm);
1998 // One of the selected values was a successor, but the other wasn't.
1999 // Insert an unconditional branch to the one that was found;
2000 // the edge to the one that wasn't must be unreachable.
2002 // Only TrueBB was found.
2003 Builder.CreateBr(TrueBB);
2005 // Only FalseBB was found.
2006 Builder.CreateBr(FalseBB);
2009 EraseTerminatorInstAndDCECond(OldTerm);
2013 // SimplifySwitchOnSelect - Replaces
2014 // (switch (select cond, X, Y)) on constant X, Y
2015 // with a branch - conditional if X and Y lead to distinct BBs,
2016 // unconditional otherwise.
2017 static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
2018 // Check for constant integer values in the select.
2019 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
2020 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
2021 if (!TrueVal || !FalseVal)
2024 // Find the relevant condition and destinations.
2025 Value *Condition = Select->getCondition();
2026 BasicBlock *TrueBB = SI->findCaseValue(TrueVal).getCaseSuccessor();
2027 BasicBlock *FalseBB = SI->findCaseValue(FalseVal).getCaseSuccessor();
2029 // Perform the actual simplification.
2030 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB);
2033 // SimplifyIndirectBrOnSelect - Replaces
2034 // (indirectbr (select cond, blockaddress(@fn, BlockA),
2035 // blockaddress(@fn, BlockB)))
2037 // (br cond, BlockA, BlockB).
2038 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
2039 // Check that both operands of the select are block addresses.
2040 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
2041 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
2045 // Extract the actual blocks.
2046 BasicBlock *TrueBB = TBA->getBasicBlock();
2047 BasicBlock *FalseBB = FBA->getBasicBlock();
2049 // Perform the actual simplification.
2050 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB);
2053 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
2054 /// instruction (a seteq/setne with a constant) as the only instruction in a
2055 /// block that ends with an uncond branch. We are looking for a very specific
2056 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
2057 /// this case, we merge the first two "or's of icmp" into a switch, but then the
2058 /// default value goes to an uncond block with a seteq in it, we get something
2061 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
2063 /// %tmp = icmp eq i8 %A, 92
2066 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
2068 /// We prefer to split the edge to 'end' so that there is a true/false entry to
2069 /// the PHI, merging the third icmp into the switch.
2070 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
2071 const TargetData *TD,
2072 IRBuilder<> &Builder) {
2073 BasicBlock *BB = ICI->getParent();
2075 // If the block has any PHIs in it or the icmp has multiple uses, it is too
2077 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
2079 Value *V = ICI->getOperand(0);
2080 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
2082 // The pattern we're looking for is where our only predecessor is a switch on
2083 // 'V' and this block is the default case for the switch. In this case we can
2084 // fold the compared value into the switch to simplify things.
2085 BasicBlock *Pred = BB->getSinglePredecessor();
2086 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
2088 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
2089 if (SI->getCondition() != V)
2092 // If BB is reachable on a non-default case, then we simply know the value of
2093 // V in this block. Substitute it and constant fold the icmp instruction
2095 if (SI->getDefaultDest() != BB) {
2096 ConstantInt *VVal = SI->findCaseDest(BB);
2097 assert(VVal && "Should have a unique destination value");
2098 ICI->setOperand(0, VVal);
2100 if (Value *V = SimplifyInstruction(ICI, TD)) {
2101 ICI->replaceAllUsesWith(V);
2102 ICI->eraseFromParent();
2104 // BB is now empty, so it is likely to simplify away.
2105 return SimplifyCFG(BB) | true;
2108 // Ok, the block is reachable from the default dest. If the constant we're
2109 // comparing exists in one of the other edges, then we can constant fold ICI
2111 if (SI->findCaseValue(Cst) != SI->case_default()) {
2113 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2114 V = ConstantInt::getFalse(BB->getContext());
2116 V = ConstantInt::getTrue(BB->getContext());
2118 ICI->replaceAllUsesWith(V);
2119 ICI->eraseFromParent();
2120 // BB is now empty, so it is likely to simplify away.
2121 return SimplifyCFG(BB) | true;
2124 // The use of the icmp has to be in the 'end' block, by the only PHI node in
2126 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
2127 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
2128 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
2129 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
2132 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
2134 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
2135 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
2137 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2138 std::swap(DefaultCst, NewCst);
2140 // Replace ICI (which is used by the PHI for the default value) with true or
2141 // false depending on if it is EQ or NE.
2142 ICI->replaceAllUsesWith(DefaultCst);
2143 ICI->eraseFromParent();
2145 // Okay, the switch goes to this block on a default value. Add an edge from
2146 // the switch to the merge point on the compared value.
2147 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
2148 BB->getParent(), BB);
2149 SI->addCase(Cst, NewBB);
2151 // NewBB branches to the phi block, add the uncond branch and the phi entry.
2152 Builder.SetInsertPoint(NewBB);
2153 Builder.SetCurrentDebugLocation(SI->getDebugLoc());
2154 Builder.CreateBr(SuccBlock);
2155 PHIUse->addIncoming(NewCst, NewBB);
2159 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
2160 /// Check to see if it is branching on an or/and chain of icmp instructions, and
2161 /// fold it into a switch instruction if so.
2162 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD,
2163 IRBuilder<> &Builder) {
2164 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
2165 if (Cond == 0) return false;
2168 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2169 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2170 // 'setne's and'ed together, collect them.
2172 std::vector<ConstantInt*> Values;
2173 bool TrueWhenEqual = true;
2174 Value *ExtraCase = 0;
2175 unsigned UsedICmps = 0;
2177 if (Cond->getOpcode() == Instruction::Or) {
2178 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
2180 } else if (Cond->getOpcode() == Instruction::And) {
2181 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
2183 TrueWhenEqual = false;
2186 // If we didn't have a multiply compared value, fail.
2187 if (CompVal == 0) return false;
2189 // Avoid turning single icmps into a switch.
2193 // There might be duplicate constants in the list, which the switch
2194 // instruction can't handle, remove them now.
2195 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
2196 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2198 // If Extra was used, we require at least two switch values to do the
2199 // transformation. A switch with one value is just an cond branch.
2200 if (ExtraCase && Values.size() < 2) return false;
2202 // Figure out which block is which destination.
2203 BasicBlock *DefaultBB = BI->getSuccessor(1);
2204 BasicBlock *EdgeBB = BI->getSuccessor(0);
2205 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2207 BasicBlock *BB = BI->getParent();
2209 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
2210 << " cases into SWITCH. BB is:\n" << *BB);
2212 // If there are any extra values that couldn't be folded into the switch
2213 // then we evaluate them with an explicit branch first. Split the block
2214 // right before the condbr to handle it.
2216 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
2217 // Remove the uncond branch added to the old block.
2218 TerminatorInst *OldTI = BB->getTerminator();
2219 Builder.SetInsertPoint(OldTI);
2222 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
2224 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
2226 OldTI->eraseFromParent();
2228 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
2229 // for the edge we just added.
2230 AddPredecessorToBlock(EdgeBB, BB, NewBB);
2232 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
2233 << "\nEXTRABB = " << *BB);
2237 Builder.SetInsertPoint(BI);
2238 // Convert pointer to int before we switch.
2239 if (CompVal->getType()->isPointerTy()) {
2240 assert(TD && "Cannot switch on pointer without TargetData");
2241 CompVal = Builder.CreatePtrToInt(CompVal,
2242 TD->getIntPtrType(CompVal->getContext()),
2246 // Create the new switch instruction now.
2247 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
2249 // Add all of the 'cases' to the switch instruction.
2250 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2251 New->addCase(Values[i], EdgeBB);
2253 // We added edges from PI to the EdgeBB. As such, if there were any
2254 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2255 // the number of edges added.
2256 for (BasicBlock::iterator BBI = EdgeBB->begin();
2257 isa<PHINode>(BBI); ++BBI) {
2258 PHINode *PN = cast<PHINode>(BBI);
2259 Value *InVal = PN->getIncomingValueForBlock(BB);
2260 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2261 PN->addIncoming(InVal, BB);
2264 // Erase the old branch instruction.
2265 EraseTerminatorInstAndDCECond(BI);
2267 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
2271 bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
2272 // If this is a trivial landing pad that just continues unwinding the caught
2273 // exception then zap the landing pad, turning its invokes into calls.
2274 BasicBlock *BB = RI->getParent();
2275 LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI());
2276 if (RI->getValue() != LPInst)
2277 // Not a landing pad, or the resume is not unwinding the exception that
2278 // caused control to branch here.
2281 // Check that there are no other instructions except for debug intrinsics.
2282 BasicBlock::iterator I = LPInst, E = RI;
2284 if (!isa<DbgInfoIntrinsic>(I))
2287 // Turn all invokes that unwind here into calls and delete the basic block.
2288 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
2289 InvokeInst *II = cast<InvokeInst>((*PI++)->getTerminator());
2290 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
2291 // Insert a call instruction before the invoke.
2292 CallInst *Call = CallInst::Create(II->getCalledValue(), Args, "", II);
2294 Call->setCallingConv(II->getCallingConv());
2295 Call->setAttributes(II->getAttributes());
2296 Call->setDebugLoc(II->getDebugLoc());
2298 // Anything that used the value produced by the invoke instruction now uses
2299 // the value produced by the call instruction. Note that we do this even
2300 // for void functions and calls with no uses so that the callgraph edge is
2302 II->replaceAllUsesWith(Call);
2303 BB->removePredecessor(II->getParent());
2305 // Insert a branch to the normal destination right before the invoke.
2306 BranchInst::Create(II->getNormalDest(), II);
2308 // Finally, delete the invoke instruction!
2309 II->eraseFromParent();
2312 // The landingpad is now unreachable. Zap it.
2313 BB->eraseFromParent();
2317 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
2318 BasicBlock *BB = RI->getParent();
2319 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2321 // Find predecessors that end with branches.
2322 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2323 SmallVector<BranchInst*, 8> CondBranchPreds;
2324 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2325 BasicBlock *P = *PI;
2326 TerminatorInst *PTI = P->getTerminator();
2327 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2328 if (BI->isUnconditional())
2329 UncondBranchPreds.push_back(P);
2331 CondBranchPreds.push_back(BI);
2335 // If we found some, do the transformation!
2336 if (!UncondBranchPreds.empty() && DupRet) {
2337 while (!UncondBranchPreds.empty()) {
2338 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2339 DEBUG(dbgs() << "FOLDING: " << *BB
2340 << "INTO UNCOND BRANCH PRED: " << *Pred);
2341 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
2344 // If we eliminated all predecessors of the block, delete the block now.
2345 if (pred_begin(BB) == pred_end(BB))
2346 // We know there are no successors, so just nuke the block.
2347 BB->eraseFromParent();
2352 // Check out all of the conditional branches going to this return
2353 // instruction. If any of them just select between returns, change the
2354 // branch itself into a select/return pair.
2355 while (!CondBranchPreds.empty()) {
2356 BranchInst *BI = CondBranchPreds.pop_back_val();
2358 // Check to see if the non-BB successor is also a return block.
2359 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2360 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2361 SimplifyCondBranchToTwoReturns(BI, Builder))
2367 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2368 BasicBlock *BB = UI->getParent();
2370 bool Changed = false;
2372 // If there are any instructions immediately before the unreachable that can
2373 // be removed, do so.
2374 while (UI != BB->begin()) {
2375 BasicBlock::iterator BBI = UI;
2377 // Do not delete instructions that can have side effects which might cause
2378 // the unreachable to not be reachable; specifically, calls and volatile
2379 // operations may have this effect.
2380 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2382 if (BBI->mayHaveSideEffects()) {
2383 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
2384 if (SI->isVolatile())
2386 } else if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
2387 if (LI->isVolatile())
2389 } else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(BBI)) {
2390 if (RMWI->isVolatile())
2392 } else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) {
2393 if (CXI->isVolatile())
2395 } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) &&
2396 !isa<LandingPadInst>(BBI)) {
2399 // Note that deleting LandingPad's here is in fact okay, although it
2400 // involves a bit of subtle reasoning. If this inst is a LandingPad,
2401 // all the predecessors of this block will be the unwind edges of Invokes,
2402 // and we can therefore guarantee this block will be erased.
2405 // Delete this instruction (any uses are guaranteed to be dead)
2406 if (!BBI->use_empty())
2407 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
2408 BBI->eraseFromParent();
2412 // If the unreachable instruction is the first in the block, take a gander
2413 // at all of the predecessors of this instruction, and simplify them.
2414 if (&BB->front() != UI) return Changed;
2416 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2417 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2418 TerminatorInst *TI = Preds[i]->getTerminator();
2419 IRBuilder<> Builder(TI);
2420 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2421 if (BI->isUnconditional()) {
2422 if (BI->getSuccessor(0) == BB) {
2423 new UnreachableInst(TI->getContext(), TI);
2424 TI->eraseFromParent();
2428 if (BI->getSuccessor(0) == BB) {
2429 Builder.CreateBr(BI->getSuccessor(1));
2430 EraseTerminatorInstAndDCECond(BI);
2431 } else if (BI->getSuccessor(1) == BB) {
2432 Builder.CreateBr(BI->getSuccessor(0));
2433 EraseTerminatorInstAndDCECond(BI);
2437 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2438 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2440 if (i.getCaseSuccessor() == BB) {
2441 BB->removePredecessor(SI->getParent());
2446 // If the default value is unreachable, figure out the most popular
2447 // destination and make it the default.
2448 if (SI->getDefaultDest() == BB) {
2449 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
2450 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2452 std::pair<unsigned, unsigned> &entry =
2453 Popularity[i.getCaseSuccessor()];
2454 if (entry.first == 0) {
2456 entry.second = i.getCaseIndex();
2462 // Find the most popular block.
2463 unsigned MaxPop = 0;
2464 unsigned MaxIndex = 0;
2465 BasicBlock *MaxBlock = 0;
2466 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
2467 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2468 if (I->second.first > MaxPop ||
2469 (I->second.first == MaxPop && MaxIndex > I->second.second)) {
2470 MaxPop = I->second.first;
2471 MaxIndex = I->second.second;
2472 MaxBlock = I->first;
2476 // Make this the new default, allowing us to delete any explicit
2478 SI->setDefaultDest(MaxBlock);
2481 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2483 if (isa<PHINode>(MaxBlock->begin()))
2484 for (unsigned i = 0; i != MaxPop-1; ++i)
2485 MaxBlock->removePredecessor(SI->getParent());
2487 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2489 if (i.getCaseSuccessor() == MaxBlock) {
2495 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2496 if (II->getUnwindDest() == BB) {
2497 // Convert the invoke to a call instruction. This would be a good
2498 // place to note that the call does not throw though.
2499 BranchInst *BI = Builder.CreateBr(II->getNormalDest());
2500 II->removeFromParent(); // Take out of symbol table
2502 // Insert the call now...
2503 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2504 Builder.SetInsertPoint(BI);
2505 CallInst *CI = Builder.CreateCall(II->getCalledValue(),
2506 Args, II->getName());
2507 CI->setCallingConv(II->getCallingConv());
2508 CI->setAttributes(II->getAttributes());
2509 // If the invoke produced a value, the call does now instead.
2510 II->replaceAllUsesWith(CI);
2517 // If this block is now dead, remove it.
2518 if (pred_begin(BB) == pred_end(BB) &&
2519 BB != &BB->getParent()->getEntryBlock()) {
2520 // We know there are no successors, so just nuke the block.
2521 BB->eraseFromParent();
2528 /// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
2529 /// integer range comparison into a sub, an icmp and a branch.
2530 static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
2531 assert(SI->getNumCases() > 1 && "Degenerate switch?");
2533 // Make sure all cases point to the same destination and gather the values.
2534 SmallVector<ConstantInt *, 16> Cases;
2535 SwitchInst::CaseIt I = SI->case_begin();
2536 Cases.push_back(I.getCaseValue());
2537 SwitchInst::CaseIt PrevI = I++;
2538 for (SwitchInst::CaseIt E = SI->case_end(); I != E; PrevI = I++) {
2539 if (PrevI.getCaseSuccessor() != I.getCaseSuccessor())
2541 Cases.push_back(I.getCaseValue());
2543 assert(Cases.size() == SI->getNumCases() && "Not all cases gathered");
2545 // Sort the case values, then check if they form a range we can transform.
2546 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
2547 for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
2548 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
2552 Constant *Offset = ConstantExpr::getNeg(Cases.back());
2553 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases());
2555 Value *Sub = SI->getCondition();
2556 if (!Offset->isNullValue())
2557 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off");
2558 Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
2559 Builder.CreateCondBr(
2560 Cmp, SI->case_begin().getCaseSuccessor(), SI->getDefaultDest());
2562 // Prune obsolete incoming values off the successor's PHI nodes.
2563 for (BasicBlock::iterator BBI = SI->case_begin().getCaseSuccessor()->begin();
2564 isa<PHINode>(BBI); ++BBI) {
2565 for (unsigned I = 0, E = SI->getNumCases()-1; I != E; ++I)
2566 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
2568 SI->eraseFromParent();
2573 /// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch
2574 /// and use it to remove dead cases.
2575 static bool EliminateDeadSwitchCases(SwitchInst *SI) {
2576 Value *Cond = SI->getCondition();
2577 unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth();
2578 APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
2579 ComputeMaskedBits(Cond, KnownZero, KnownOne);
2581 // Gather dead cases.
2582 SmallVector<ConstantInt*, 8> DeadCases;
2583 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
2584 if ((I.getCaseValue()->getValue() & KnownZero) != 0 ||
2585 (I.getCaseValue()->getValue() & KnownOne) != KnownOne) {
2586 DeadCases.push_back(I.getCaseValue());
2587 DEBUG(dbgs() << "SimplifyCFG: switch case '"
2588 << I.getCaseValue() << "' is dead.\n");
2592 // Remove dead cases from the switch.
2593 for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) {
2594 SwitchInst::CaseIt Case = SI->findCaseValue(DeadCases[I]);
2595 assert(Case != SI->case_default() &&
2596 "Case was not found. Probably mistake in DeadCases forming.");
2597 // Prune unused values from PHI nodes.
2598 Case.getCaseSuccessor()->removePredecessor(SI->getParent());
2599 SI->removeCase(Case);
2602 return !DeadCases.empty();
2605 /// FindPHIForConditionForwarding - If BB would be eligible for simplification
2606 /// by TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated
2607 /// by an unconditional branch), look at the phi node for BB in the successor
2608 /// block and see if the incoming value is equal to CaseValue. If so, return
2609 /// the phi node, and set PhiIndex to BB's index in the phi node.
2610 static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
2613 if (BB->getFirstNonPHIOrDbg() != BB->getTerminator())
2614 return NULL; // BB must be empty to be a candidate for simplification.
2615 if (!BB->getSinglePredecessor())
2616 return NULL; // BB must be dominated by the switch.
2618 BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
2619 if (!Branch || !Branch->isUnconditional())
2620 return NULL; // Terminator must be unconditional branch.
2622 BasicBlock *Succ = Branch->getSuccessor(0);
2624 BasicBlock::iterator I = Succ->begin();
2625 while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
2626 int Idx = PHI->getBasicBlockIndex(BB);
2627 assert(Idx >= 0 && "PHI has no entry for predecessor?");
2629 Value *InValue = PHI->getIncomingValue(Idx);
2630 if (InValue != CaseValue) continue;
2639 /// ForwardSwitchConditionToPHI - Try to forward the condition of a switch
2640 /// instruction to a phi node dominated by the switch, if that would mean that
2641 /// some of the destination blocks of the switch can be folded away.
2642 /// Returns true if a change is made.
2643 static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
2644 typedef DenseMap<PHINode*, SmallVector<int,4> > ForwardingNodesMap;
2645 ForwardingNodesMap ForwardingNodes;
2647 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
2648 ConstantInt *CaseValue = I.getCaseValue();
2649 BasicBlock *CaseDest = I.getCaseSuccessor();
2652 PHINode *PHI = FindPHIForConditionForwarding(CaseValue, CaseDest,
2656 ForwardingNodes[PHI].push_back(PhiIndex);
2659 bool Changed = false;
2661 for (ForwardingNodesMap::iterator I = ForwardingNodes.begin(),
2662 E = ForwardingNodes.end(); I != E; ++I) {
2663 PHINode *Phi = I->first;
2664 SmallVector<int,4> &Indexes = I->second;
2666 if (Indexes.size() < 2) continue;
2668 for (size_t I = 0, E = Indexes.size(); I != E; ++I)
2669 Phi->setIncomingValue(Indexes[I], SI->getCondition());
2676 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
2677 // If this switch is too complex to want to look at, ignore it.
2678 if (!isValueEqualityComparison(SI))
2681 BasicBlock *BB = SI->getParent();
2683 // If we only have one predecessor, and if it is a branch on this value,
2684 // see if that predecessor totally determines the outcome of this switch.
2685 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2686 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
2687 return SimplifyCFG(BB) | true;
2689 Value *Cond = SI->getCondition();
2690 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
2691 if (SimplifySwitchOnSelect(SI, Select))
2692 return SimplifyCFG(BB) | true;
2694 // If the block only contains the switch, see if we can fold the block
2695 // away into any preds.
2696 BasicBlock::iterator BBI = BB->begin();
2697 // Ignore dbg intrinsics.
2698 while (isa<DbgInfoIntrinsic>(BBI))
2701 if (FoldValueComparisonIntoPredecessors(SI, Builder))
2702 return SimplifyCFG(BB) | true;
2704 // Try to transform the switch into an icmp and a branch.
2705 if (TurnSwitchRangeIntoICmp(SI, Builder))
2706 return SimplifyCFG(BB) | true;
2708 // Remove unreachable cases.
2709 if (EliminateDeadSwitchCases(SI))
2710 return SimplifyCFG(BB) | true;
2712 if (ForwardSwitchConditionToPHI(SI))
2713 return SimplifyCFG(BB) | true;
2718 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
2719 BasicBlock *BB = IBI->getParent();
2720 bool Changed = false;
2722 // Eliminate redundant destinations.
2723 SmallPtrSet<Value *, 8> Succs;
2724 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2725 BasicBlock *Dest = IBI->getDestination(i);
2726 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2727 Dest->removePredecessor(BB);
2728 IBI->removeDestination(i);
2734 if (IBI->getNumDestinations() == 0) {
2735 // If the indirectbr has no successors, change it to unreachable.
2736 new UnreachableInst(IBI->getContext(), IBI);
2737 EraseTerminatorInstAndDCECond(IBI);
2741 if (IBI->getNumDestinations() == 1) {
2742 // If the indirectbr has one successor, change it to a direct branch.
2743 BranchInst::Create(IBI->getDestination(0), IBI);
2744 EraseTerminatorInstAndDCECond(IBI);
2748 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2749 if (SimplifyIndirectBrOnSelect(IBI, SI))
2750 return SimplifyCFG(BB) | true;
2755 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
2756 BasicBlock *BB = BI->getParent();
2758 // If the Terminator is the only non-phi instruction, simplify the block.
2759 BasicBlock::iterator I = BB->getFirstNonPHIOrDbgOrLifetime();
2760 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
2761 TryToSimplifyUncondBranchFromEmptyBlock(BB))
2764 // If the only instruction in the block is a seteq/setne comparison
2765 // against a constant, try to simplify the block.
2766 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
2767 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
2768 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
2770 if (I->isTerminator() &&
2771 TryToSimplifyUncondBranchWithICmpInIt(ICI, TD, Builder))
2779 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
2780 BasicBlock *BB = BI->getParent();
2782 // Conditional branch
2783 if (isValueEqualityComparison(BI)) {
2784 // If we only have one predecessor, and if it is a branch on this value,
2785 // see if that predecessor totally determines the outcome of this
2787 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2788 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
2789 return SimplifyCFG(BB) | true;
2791 // This block must be empty, except for the setcond inst, if it exists.
2792 // Ignore dbg intrinsics.
2793 BasicBlock::iterator I = BB->begin();
2794 // Ignore dbg intrinsics.
2795 while (isa<DbgInfoIntrinsic>(I))
2798 if (FoldValueComparisonIntoPredecessors(BI, Builder))
2799 return SimplifyCFG(BB) | true;
2800 } else if (&*I == cast<Instruction>(BI->getCondition())){
2802 // Ignore dbg intrinsics.
2803 while (isa<DbgInfoIntrinsic>(I))
2805 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
2806 return SimplifyCFG(BB) | true;
2810 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
2811 if (SimplifyBranchOnICmpChain(BI, TD, Builder))
2814 // If this basic block is ONLY a compare and a branch, and if a predecessor
2815 // branches to us and one of our successors, fold the comparison into the
2816 // predecessor and use logical operations to pick the right destination.
2817 if (FoldBranchToCommonDest(BI))
2818 return SimplifyCFG(BB) | true;
2820 // We have a conditional branch to two blocks that are only reachable
2821 // from BI. We know that the condbr dominates the two blocks, so see if
2822 // there is any identical code in the "then" and "else" blocks. If so, we
2823 // can hoist it up to the branching block.
2824 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
2825 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2826 if (HoistThenElseCodeToIf(BI))
2827 return SimplifyCFG(BB) | true;
2829 // If Successor #1 has multiple preds, we may be able to conditionally
2830 // execute Successor #0 if it branches to successor #1.
2831 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
2832 if (Succ0TI->getNumSuccessors() == 1 &&
2833 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
2834 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
2835 return SimplifyCFG(BB) | true;
2837 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2838 // If Successor #0 has multiple preds, we may be able to conditionally
2839 // execute Successor #1 if it branches to successor #0.
2840 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
2841 if (Succ1TI->getNumSuccessors() == 1 &&
2842 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
2843 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
2844 return SimplifyCFG(BB) | true;
2847 // If this is a branch on a phi node in the current block, thread control
2848 // through this block if any PHI node entries are constants.
2849 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
2850 if (PN->getParent() == BI->getParent())
2851 if (FoldCondBranchOnPHI(BI, TD))
2852 return SimplifyCFG(BB) | true;
2854 // Scan predecessor blocks for conditional branches.
2855 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2856 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2857 if (PBI != BI && PBI->isConditional())
2858 if (SimplifyCondBranchToCondBranch(PBI, BI))
2859 return SimplifyCFG(BB) | true;
2864 /// Check if passing a value to an instruction will cause undefined behavior.
2865 static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
2866 Constant *C = dyn_cast<Constant>(V);
2870 if (!I->hasOneUse()) // Only look at single-use instructions, for compile time
2873 if (C->isNullValue()) {
2874 Instruction *Use = I->use_back();
2876 // Now make sure that there are no instructions in between that can alter
2877 // control flow (eg. calls)
2878 for (BasicBlock::iterator i = ++BasicBlock::iterator(I); &*i != Use; ++i)
2879 if (i == I->getParent()->end() || i->mayHaveSideEffects())
2882 // Look through GEPs. A load from a GEP derived from NULL is still undefined
2883 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))
2884 if (GEP->getPointerOperand() == I)
2885 return passingValueIsAlwaysUndefined(V, GEP);
2887 // Look through bitcasts.
2888 if (BitCastInst *BC = dyn_cast<BitCastInst>(Use))
2889 return passingValueIsAlwaysUndefined(V, BC);
2891 // Load from null is undefined.
2892 if (LoadInst *LI = dyn_cast<LoadInst>(Use))
2893 return LI->getPointerAddressSpace() == 0;
2895 // Store to null is undefined.
2896 if (StoreInst *SI = dyn_cast<StoreInst>(Use))
2897 return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I;
2902 /// If BB has an incoming value that will always trigger undefined behavior
2903 /// (eg. null pointer dereference), remove the branch leading here.
2904 static bool removeUndefIntroducingPredecessor(BasicBlock *BB) {
2905 for (BasicBlock::iterator i = BB->begin();
2906 PHINode *PHI = dyn_cast<PHINode>(i); ++i)
2907 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
2908 if (passingValueIsAlwaysUndefined(PHI->getIncomingValue(i), PHI)) {
2909 TerminatorInst *T = PHI->getIncomingBlock(i)->getTerminator();
2910 IRBuilder<> Builder(T);
2911 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
2912 BB->removePredecessor(PHI->getIncomingBlock(i));
2913 // Turn uncoditional branches into unreachables and remove the dead
2914 // destination from conditional branches.
2915 if (BI->isUnconditional())
2916 Builder.CreateUnreachable();
2918 Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1) :
2919 BI->getSuccessor(0));
2920 BI->eraseFromParent();
2923 // TODO: SwitchInst.
2929 bool SimplifyCFGOpt::run(BasicBlock *BB) {
2930 bool Changed = false;
2932 assert(BB && BB->getParent() && "Block not embedded in function!");
2933 assert(BB->getTerminator() && "Degenerate basic block encountered!");
2935 // Remove basic blocks that have no predecessors (except the entry block)...
2936 // or that just have themself as a predecessor. These are unreachable.
2937 if ((pred_begin(BB) == pred_end(BB) &&
2938 BB != &BB->getParent()->getEntryBlock()) ||
2939 BB->getSinglePredecessor() == BB) {
2940 DEBUG(dbgs() << "Removing BB: \n" << *BB);
2941 DeleteDeadBlock(BB);
2945 // Check to see if we can constant propagate this terminator instruction
2947 Changed |= ConstantFoldTerminator(BB, true);
2949 // Check for and eliminate duplicate PHI nodes in this block.
2950 Changed |= EliminateDuplicatePHINodes(BB);
2952 // Check for and remove branches that will always cause undefined behavior.
2953 Changed |= removeUndefIntroducingPredecessor(BB);
2955 // Merge basic blocks into their predecessor if there is only one distinct
2956 // pred, and if there is only one distinct successor of the predecessor, and
2957 // if there are no PHI nodes.
2959 if (MergeBlockIntoPredecessor(BB))
2962 IRBuilder<> Builder(BB);
2964 // If there is a trivial two-entry PHI node in this basic block, and we can
2965 // eliminate it, do so now.
2966 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
2967 if (PN->getNumIncomingValues() == 2)
2968 Changed |= FoldTwoEntryPHINode(PN, TD);
2970 Builder.SetInsertPoint(BB->getTerminator());
2971 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
2972 if (BI->isUnconditional()) {
2973 if (SimplifyUncondBranch(BI, Builder)) return true;
2975 if (SimplifyCondBranch(BI, Builder)) return true;
2977 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
2978 if (SimplifyReturn(RI, Builder)) return true;
2979 } else if (ResumeInst *RI = dyn_cast<ResumeInst>(BB->getTerminator())) {
2980 if (SimplifyResume(RI, Builder)) return true;
2981 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
2982 if (SimplifySwitch(SI, Builder)) return true;
2983 } else if (UnreachableInst *UI =
2984 dyn_cast<UnreachableInst>(BB->getTerminator())) {
2985 if (SimplifyUnreachable(UI)) return true;
2986 } else if (IndirectBrInst *IBI =
2987 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
2988 if (SimplifyIndirectBr(IBI)) return true;
2994 /// SimplifyCFG - This function is used to do simplification of a CFG. For
2995 /// example, it adjusts branches to branches to eliminate the extra hop, it
2996 /// eliminates unreachable basic blocks, and does other "peephole" optimization
2997 /// of the CFG. It returns true if a modification was made.
2999 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
3000 return SimplifyCFGOpt(TD).run(BB);