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/NoFolder.h"
41 #include "llvm/Support/raw_ostream.h"
47 static cl::opt<unsigned>
48 PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(1),
49 cl::desc("Control the amount of phi node folding to perform (default = 1)"));
52 DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false),
53 cl::desc("Duplicate return instructions into unconditional branches"));
55 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
58 class SimplifyCFGOpt {
59 const TargetData *const TD;
61 Value *isValueEqualityComparison(TerminatorInst *TI);
62 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
63 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases);
64 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
66 IRBuilder<> &Builder);
67 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
68 IRBuilder<> &Builder);
70 bool SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder);
71 bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder);
72 bool SimplifyUnwind(UnwindInst *UI, IRBuilder<> &Builder);
73 bool SimplifyUnreachable(UnreachableInst *UI);
74 bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
75 bool SimplifyIndirectBr(IndirectBrInst *IBI);
76 bool SimplifyUncondBranch(BranchInst *BI, IRBuilder <> &Builder);
77 bool SimplifyCondBranch(BranchInst *BI, IRBuilder <>&Builder);
80 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
81 bool run(BasicBlock *BB);
85 /// SafeToMergeTerminators - Return true if it is safe to merge these two
86 /// terminator instructions together.
88 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
89 if (SI1 == SI2) return false; // Can't merge with self!
91 // It is not safe to merge these two switch instructions if they have a common
92 // successor, and if that successor has a PHI node, and if *that* PHI node has
93 // conflicting incoming values from the two switch blocks.
94 BasicBlock *SI1BB = SI1->getParent();
95 BasicBlock *SI2BB = SI2->getParent();
96 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
98 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
99 if (SI1Succs.count(*I))
100 for (BasicBlock::iterator BBI = (*I)->begin();
101 isa<PHINode>(BBI); ++BBI) {
102 PHINode *PN = cast<PHINode>(BBI);
103 if (PN->getIncomingValueForBlock(SI1BB) !=
104 PN->getIncomingValueForBlock(SI2BB))
111 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
112 /// now be entries in it from the 'NewPred' block. The values that will be
113 /// flowing into the PHI nodes will be the same as those coming in from
114 /// ExistPred, an existing predecessor of Succ.
115 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
116 BasicBlock *ExistPred) {
117 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
120 for (BasicBlock::iterator I = Succ->begin();
121 (PN = dyn_cast<PHINode>(I)); ++I)
122 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
126 /// GetIfCondition - Given a basic block (BB) with two predecessors (and at
127 /// least one PHI node in it), check to see if the merge at this block is due
128 /// to an "if condition". If so, return the boolean condition that determines
129 /// which entry into BB will be taken. Also, return by references the block
130 /// that will be entered from if the condition is true, and the block that will
131 /// be entered if the condition is false.
133 /// This does no checking to see if the true/false blocks have large or unsavory
134 /// instructions in them.
135 static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
136 BasicBlock *&IfFalse) {
137 PHINode *SomePHI = cast<PHINode>(BB->begin());
138 assert(SomePHI->getNumIncomingValues() == 2 &&
139 "Function can only handle blocks with 2 predecessors!");
140 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
141 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
143 // We can only handle branches. Other control flow will be lowered to
144 // branches if possible anyway.
145 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
146 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
147 if (Pred1Br == 0 || Pred2Br == 0)
150 // Eliminate code duplication by ensuring that Pred1Br is conditional if
152 if (Pred2Br->isConditional()) {
153 // If both branches are conditional, we don't have an "if statement". In
154 // reality, we could transform this case, but since the condition will be
155 // required anyway, we stand no chance of eliminating it, so the xform is
156 // probably not profitable.
157 if (Pred1Br->isConditional())
160 std::swap(Pred1, Pred2);
161 std::swap(Pred1Br, Pred2Br);
164 if (Pred1Br->isConditional()) {
165 // The only thing we have to watch out for here is to make sure that Pred2
166 // doesn't have incoming edges from other blocks. If it does, the condition
167 // doesn't dominate BB.
168 if (Pred2->getSinglePredecessor() == 0)
171 // If we found a conditional branch predecessor, make sure that it branches
172 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
173 if (Pred1Br->getSuccessor(0) == BB &&
174 Pred1Br->getSuccessor(1) == Pred2) {
177 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
178 Pred1Br->getSuccessor(1) == BB) {
182 // We know that one arm of the conditional goes to BB, so the other must
183 // go somewhere unrelated, and this must not be an "if statement".
187 return Pred1Br->getCondition();
190 // Ok, if we got here, both predecessors end with an unconditional branch to
191 // BB. Don't panic! If both blocks only have a single (identical)
192 // predecessor, and THAT is a conditional branch, then we're all ok!
193 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
194 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
197 // Otherwise, if this is a conditional branch, then we can use it!
198 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
199 if (BI == 0) return 0;
201 assert(BI->isConditional() && "Two successors but not conditional?");
202 if (BI->getSuccessor(0) == Pred1) {
209 return BI->getCondition();
212 /// ComputeSpeculuationCost - Compute an abstract "cost" of speculating the
213 /// given instruction, which is assumed to be safe to speculate. 1 means
214 /// cheap, 2 means less cheap, and UINT_MAX means prohibitively expensive.
215 static unsigned ComputeSpeculationCost(const User *I) {
216 assert(isSafeToSpeculativelyExecute(I) &&
217 "Instruction is not safe to speculatively execute!");
218 switch (Operator::getOpcode(I)) {
220 // In doubt, be conservative.
222 case Instruction::GetElementPtr:
223 // GEPs are cheap if all indices are constant.
224 if (!cast<GEPOperator>(I)->hasAllConstantIndices())
227 case Instruction::Load:
228 case Instruction::Add:
229 case Instruction::Sub:
230 case Instruction::And:
231 case Instruction::Or:
232 case Instruction::Xor:
233 case Instruction::Shl:
234 case Instruction::LShr:
235 case Instruction::AShr:
236 case Instruction::ICmp:
237 case Instruction::Trunc:
238 case Instruction::ZExt:
239 case Instruction::SExt:
240 return 1; // These are all cheap.
242 case Instruction::Call:
243 case Instruction::Select:
248 /// DominatesMergePoint - If we have a merge point of an "if condition" as
249 /// accepted above, return true if the specified value dominates the block. We
250 /// don't handle the true generality of domination here, just a special case
251 /// which works well enough for us.
253 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
254 /// see if V (which must be an instruction) and its recursive operands
255 /// that do not dominate BB have a combined cost lower than CostRemaining and
256 /// are non-trapping. If both are true, the instruction is inserted into the
257 /// set and true is returned.
259 /// The cost for most non-trapping instructions is defined as 1 except for
260 /// Select whose cost is 2.
262 /// After this function returns, CostRemaining is decreased by the cost of
263 /// V plus its non-dominating operands. If that cost is greater than
264 /// CostRemaining, false is returned and CostRemaining is undefined.
265 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
266 SmallPtrSet<Instruction*, 4> *AggressiveInsts,
267 unsigned &CostRemaining) {
268 Instruction *I = dyn_cast<Instruction>(V);
270 // Non-instructions all dominate instructions, but not all constantexprs
271 // can be executed unconditionally.
272 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
277 BasicBlock *PBB = I->getParent();
279 // We don't want to allow weird loops that might have the "if condition" in
280 // the bottom of this block.
281 if (PBB == BB) return false;
283 // If this instruction is defined in a block that contains an unconditional
284 // branch to BB, then it must be in the 'conditional' part of the "if
285 // statement". If not, it definitely dominates the region.
286 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
287 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB)
290 // If we aren't allowing aggressive promotion anymore, then don't consider
291 // instructions in the 'if region'.
292 if (AggressiveInsts == 0) return false;
294 // If we have seen this instruction before, don't count it again.
295 if (AggressiveInsts->count(I)) return true;
297 // Okay, it looks like the instruction IS in the "condition". Check to
298 // see if it's a cheap instruction to unconditionally compute, and if it
299 // only uses stuff defined outside of the condition. If so, hoist it out.
300 if (!isSafeToSpeculativelyExecute(I))
303 unsigned Cost = ComputeSpeculationCost(I);
305 if (Cost > CostRemaining)
308 CostRemaining -= Cost;
310 // Okay, we can only really hoist these out if their operands do
311 // not take us over the cost threshold.
312 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
313 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining))
315 // Okay, it's safe to do this! Remember this instruction.
316 AggressiveInsts->insert(I);
320 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
321 /// and PointerNullValue. Return NULL if value is not a constant int.
322 static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
323 // Normal constant int.
324 ConstantInt *CI = dyn_cast<ConstantInt>(V);
325 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
328 // This is some kind of pointer constant. Turn it into a pointer-sized
329 // ConstantInt if possible.
330 IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
332 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
333 if (isa<ConstantPointerNull>(V))
334 return ConstantInt::get(PtrTy, 0);
336 // IntToPtr const int.
337 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
338 if (CE->getOpcode() == Instruction::IntToPtr)
339 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
340 // The constant is very likely to have the right type already.
341 if (CI->getType() == PtrTy)
344 return cast<ConstantInt>
345 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
350 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
351 /// collection of icmp eq/ne instructions that compare a value against a
352 /// constant, return the value being compared, and stick the constant into the
355 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
356 const TargetData *TD, bool isEQ, unsigned &UsedICmps) {
357 Instruction *I = dyn_cast<Instruction>(V);
358 if (I == 0) return 0;
360 // If this is an icmp against a constant, handle this as one of the cases.
361 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
362 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
363 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
366 return I->getOperand(0);
369 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
372 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
374 // If this is an and/!= check then we want to optimize "x ugt 2" into
377 Span = Span.inverse();
379 // If there are a ton of values, we don't want to make a ginormous switch.
380 if (Span.getSetSize().ugt(8) || Span.isEmptySet())
383 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
384 Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
386 return I->getOperand(0);
391 // Otherwise, we can only handle an | or &, depending on isEQ.
392 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
395 unsigned NumValsBeforeLHS = Vals.size();
396 unsigned UsedICmpsBeforeLHS = UsedICmps;
397 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
399 unsigned NumVals = Vals.size();
400 unsigned UsedICmpsBeforeRHS = UsedICmps;
401 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
405 Vals.resize(NumVals);
406 UsedICmps = UsedICmpsBeforeRHS;
409 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
410 // set it and return success.
411 if (Extra == 0 || Extra == I->getOperand(1)) {
412 Extra = I->getOperand(1);
416 Vals.resize(NumValsBeforeLHS);
417 UsedICmps = UsedICmpsBeforeLHS;
421 // If the LHS can't be folded in, but Extra is available and RHS can, try to
423 if (Extra == 0 || Extra == I->getOperand(0)) {
424 Value *OldExtra = Extra;
425 Extra = I->getOperand(0);
426 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
429 assert(Vals.size() == NumValsBeforeLHS);
436 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
437 Instruction *Cond = 0;
438 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
439 Cond = dyn_cast<Instruction>(SI->getCondition());
440 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
441 if (BI->isConditional())
442 Cond = dyn_cast<Instruction>(BI->getCondition());
443 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
444 Cond = dyn_cast<Instruction>(IBI->getAddress());
447 TI->eraseFromParent();
448 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
451 /// isValueEqualityComparison - Return true if the specified terminator checks
452 /// to see if a value is equal to constant integer value.
453 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
455 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
456 // Do not permit merging of large switch instructions into their
457 // predecessors unless there is only one predecessor.
458 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
459 pred_end(SI->getParent())) <= 128)
460 CV = SI->getCondition();
461 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
462 if (BI->isConditional() && BI->getCondition()->hasOneUse())
463 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
464 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
465 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
466 GetConstantInt(ICI->getOperand(1), TD))
467 CV = ICI->getOperand(0);
469 // Unwrap any lossless ptrtoint cast.
470 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
471 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
472 CV = PTII->getOperand(0);
476 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
477 /// decode all of the 'cases' that it represents and return the 'default' block.
478 BasicBlock *SimplifyCFGOpt::
479 GetValueEqualityComparisonCases(TerminatorInst *TI,
480 std::vector<std::pair<ConstantInt*,
481 BasicBlock*> > &Cases) {
482 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
483 Cases.reserve(SI->getNumCases());
484 for (unsigned i = 0, e = SI->getNumCases(); i != e; ++i)
485 Cases.push_back(std::make_pair(SI->getCaseValue(i),
486 SI->getCaseSuccessor(i)));
487 return SI->getDefaultDest();
490 BranchInst *BI = cast<BranchInst>(TI);
491 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
492 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD),
493 BI->getSuccessor(ICI->getPredicate() ==
494 ICmpInst::ICMP_NE)));
495 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
499 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
500 /// in the list that match the specified block.
501 static void EliminateBlockCases(BasicBlock *BB,
502 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
503 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
504 if (Cases[i].second == BB) {
505 Cases.erase(Cases.begin()+i);
510 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
513 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
514 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
515 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
517 // Make V1 be smaller than V2.
518 if (V1->size() > V2->size())
521 if (V1->size() == 0) return false;
522 if (V1->size() == 1) {
524 ConstantInt *TheVal = (*V1)[0].first;
525 for (unsigned i = 0, e = V2->size(); i != e; ++i)
526 if (TheVal == (*V2)[i].first)
530 // Otherwise, just sort both lists and compare element by element.
531 array_pod_sort(V1->begin(), V1->end());
532 array_pod_sort(V2->begin(), V2->end());
533 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
534 while (i1 != e1 && i2 != e2) {
535 if ((*V1)[i1].first == (*V2)[i2].first)
537 if ((*V1)[i1].first < (*V2)[i2].first)
545 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
546 /// terminator instruction and its block is known to only have a single
547 /// predecessor block, check to see if that predecessor is also a value
548 /// comparison with the same value, and if that comparison determines the
549 /// outcome of this comparison. If so, simplify TI. This does a very limited
550 /// form of jump threading.
551 bool SimplifyCFGOpt::
552 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
554 IRBuilder<> &Builder) {
555 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
556 if (!PredVal) return false; // Not a value comparison in predecessor.
558 Value *ThisVal = isValueEqualityComparison(TI);
559 assert(ThisVal && "This isn't a value comparison!!");
560 if (ThisVal != PredVal) return false; // Different predicates.
562 // Find out information about when control will move from Pred to TI's block.
563 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
564 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
566 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
568 // Find information about how control leaves this block.
569 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
570 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
571 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
573 // If TI's block is the default block from Pred's comparison, potentially
574 // simplify TI based on this knowledge.
575 if (PredDef == TI->getParent()) {
576 // If we are here, we know that the value is none of those cases listed in
577 // PredCases. If there are any cases in ThisCases that are in PredCases, we
579 if (!ValuesOverlap(PredCases, ThisCases))
582 if (isa<BranchInst>(TI)) {
583 // Okay, one of the successors of this condbr is dead. Convert it to a
585 assert(ThisCases.size() == 1 && "Branch can only have one case!");
586 // Insert the new branch.
587 Instruction *NI = Builder.CreateBr(ThisDef);
590 // Remove PHI node entries for the dead edge.
591 ThisCases[0].second->removePredecessor(TI->getParent());
593 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
594 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
596 EraseTerminatorInstAndDCECond(TI);
600 SwitchInst *SI = cast<SwitchInst>(TI);
601 // Okay, TI has cases that are statically dead, prune them away.
602 SmallPtrSet<Constant*, 16> DeadCases;
603 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
604 DeadCases.insert(PredCases[i].first);
606 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
607 << "Through successor TI: " << *TI);
609 for (unsigned i = SI->getNumCases(); i != 0;) {
611 if (DeadCases.count(SI->getCaseValue(i))) {
612 SI->getCaseSuccessor(i)->removePredecessor(TI->getParent());
617 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
621 // Otherwise, TI's block must correspond to some matched value. Find out
622 // which value (or set of values) this is.
623 ConstantInt *TIV = 0;
624 BasicBlock *TIBB = TI->getParent();
625 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
626 if (PredCases[i].second == TIBB) {
628 return false; // Cannot handle multiple values coming to this block.
629 TIV = PredCases[i].first;
631 assert(TIV && "No edge from pred to succ?");
633 // Okay, we found the one constant that our value can be if we get into TI's
634 // BB. Find out which successor will unconditionally be branched to.
635 BasicBlock *TheRealDest = 0;
636 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
637 if (ThisCases[i].first == TIV) {
638 TheRealDest = ThisCases[i].second;
642 // If not handled by any explicit cases, it is handled by the default case.
643 if (TheRealDest == 0) TheRealDest = ThisDef;
645 // Remove PHI node entries for dead edges.
646 BasicBlock *CheckEdge = TheRealDest;
647 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
648 if (*SI != CheckEdge)
649 (*SI)->removePredecessor(TIBB);
653 // Insert the new branch.
654 Instruction *NI = Builder.CreateBr(TheRealDest);
657 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
658 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
660 EraseTerminatorInstAndDCECond(TI);
665 /// ConstantIntOrdering - This class implements a stable ordering of constant
666 /// integers that does not depend on their address. This is important for
667 /// applications that sort ConstantInt's to ensure uniqueness.
668 struct ConstantIntOrdering {
669 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
670 return LHS->getValue().ult(RHS->getValue());
675 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
676 const ConstantInt *LHS = *(const ConstantInt**)P1;
677 const ConstantInt *RHS = *(const ConstantInt**)P2;
678 if (LHS->getValue().ult(RHS->getValue()))
680 if (LHS->getValue() == RHS->getValue())
685 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
686 /// equality comparison instruction (either a switch or a branch on "X == c").
687 /// See if any of the predecessors of the terminator block are value comparisons
688 /// on the same value. If so, and if safe to do so, fold them together.
689 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
690 IRBuilder<> &Builder) {
691 BasicBlock *BB = TI->getParent();
692 Value *CV = isValueEqualityComparison(TI); // CondVal
693 assert(CV && "Not a comparison?");
694 bool Changed = false;
696 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
697 while (!Preds.empty()) {
698 BasicBlock *Pred = Preds.pop_back_val();
700 // See if the predecessor is a comparison with the same value.
701 TerminatorInst *PTI = Pred->getTerminator();
702 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
704 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
705 // Figure out which 'cases' to copy from SI to PSI.
706 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
707 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
709 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
710 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
712 // Based on whether the default edge from PTI goes to BB or not, fill in
713 // PredCases and PredDefault with the new switch cases we would like to
715 SmallVector<BasicBlock*, 8> NewSuccessors;
717 if (PredDefault == BB) {
718 // If this is the default destination from PTI, only the edges in TI
719 // that don't occur in PTI, or that branch to BB will be activated.
720 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
721 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
722 if (PredCases[i].second != BB)
723 PTIHandled.insert(PredCases[i].first);
725 // The default destination is BB, we don't need explicit targets.
726 std::swap(PredCases[i], PredCases.back());
727 PredCases.pop_back();
731 // Reconstruct the new switch statement we will be building.
732 if (PredDefault != BBDefault) {
733 PredDefault->removePredecessor(Pred);
734 PredDefault = BBDefault;
735 NewSuccessors.push_back(BBDefault);
737 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
738 if (!PTIHandled.count(BBCases[i].first) &&
739 BBCases[i].second != BBDefault) {
740 PredCases.push_back(BBCases[i]);
741 NewSuccessors.push_back(BBCases[i].second);
745 // If this is not the default destination from PSI, only the edges
746 // in SI that occur in PSI with a destination of BB will be
748 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
749 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
750 if (PredCases[i].second == BB) {
751 PTIHandled.insert(PredCases[i].first);
752 std::swap(PredCases[i], PredCases.back());
753 PredCases.pop_back();
757 // Okay, now we know which constants were sent to BB from the
758 // predecessor. Figure out where they will all go now.
759 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
760 if (PTIHandled.count(BBCases[i].first)) {
761 // If this is one we are capable of getting...
762 PredCases.push_back(BBCases[i]);
763 NewSuccessors.push_back(BBCases[i].second);
764 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
767 // If there are any constants vectored to BB that TI doesn't handle,
768 // they must go to the default destination of TI.
769 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
771 E = PTIHandled.end(); I != E; ++I) {
772 PredCases.push_back(std::make_pair(*I, BBDefault));
773 NewSuccessors.push_back(BBDefault);
777 // Okay, at this point, we know which new successor Pred will get. Make
778 // sure we update the number of entries in the PHI nodes for these
780 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
781 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
783 Builder.SetInsertPoint(PTI);
784 // Convert pointer to int before we switch.
785 if (CV->getType()->isPointerTy()) {
786 assert(TD && "Cannot switch on pointer without TargetData");
787 CV = Builder.CreatePtrToInt(CV, TD->getIntPtrType(CV->getContext()),
791 // Now that the successors are updated, create the new Switch instruction.
792 SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault,
794 NewSI->setDebugLoc(PTI->getDebugLoc());
795 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
796 NewSI->addCase(PredCases[i].first, PredCases[i].second);
798 EraseTerminatorInstAndDCECond(PTI);
800 // Okay, last check. If BB is still a successor of PSI, then we must
801 // have an infinite loop case. If so, add an infinitely looping block
802 // to handle the case to preserve the behavior of the code.
803 BasicBlock *InfLoopBlock = 0;
804 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
805 if (NewSI->getSuccessor(i) == BB) {
806 if (InfLoopBlock == 0) {
807 // Insert it at the end of the function, because it's either code,
808 // or it won't matter if it's hot. :)
809 InfLoopBlock = BasicBlock::Create(BB->getContext(),
810 "infloop", BB->getParent());
811 BranchInst::Create(InfLoopBlock, InfLoopBlock);
813 NewSI->setSuccessor(i, InfLoopBlock);
822 // isSafeToHoistInvoke - If we would need to insert a select that uses the
823 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
824 // would need to do this), we can't hoist the invoke, as there is nowhere
825 // to put the select in this case.
826 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
827 Instruction *I1, Instruction *I2) {
828 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
830 for (BasicBlock::iterator BBI = SI->begin();
831 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
832 Value *BB1V = PN->getIncomingValueForBlock(BB1);
833 Value *BB2V = PN->getIncomingValueForBlock(BB2);
834 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
842 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
843 /// BB2, hoist any common code in the two blocks up into the branch block. The
844 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
845 static bool HoistThenElseCodeToIf(BranchInst *BI) {
846 // This does very trivial matching, with limited scanning, to find identical
847 // instructions in the two blocks. In particular, we don't want to get into
848 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
849 // such, we currently just scan for obviously identical instructions in an
851 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
852 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
854 BasicBlock::iterator BB1_Itr = BB1->begin();
855 BasicBlock::iterator BB2_Itr = BB2->begin();
857 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
858 // Skip debug info if it is not identical.
859 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
860 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
861 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
862 while (isa<DbgInfoIntrinsic>(I1))
864 while (isa<DbgInfoIntrinsic>(I2))
867 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
868 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
871 // If we get here, we can hoist at least one instruction.
872 BasicBlock *BIParent = BI->getParent();
875 // If we are hoisting the terminator instruction, don't move one (making a
876 // broken BB), instead clone it, and remove BI.
877 if (isa<TerminatorInst>(I1))
878 goto HoistTerminator;
880 // For a normal instruction, we just move one to right before the branch,
881 // then replace all uses of the other with the first. Finally, we remove
882 // the now redundant second instruction.
883 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
884 if (!I2->use_empty())
885 I2->replaceAllUsesWith(I1);
886 I1->intersectOptionalDataWith(I2);
887 I2->eraseFromParent();
891 // Skip debug info if it is not identical.
892 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
893 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
894 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
895 while (isa<DbgInfoIntrinsic>(I1))
897 while (isa<DbgInfoIntrinsic>(I2))
900 } while (I1->isIdenticalToWhenDefined(I2));
905 // It may not be possible to hoist an invoke.
906 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
909 // Okay, it is safe to hoist the terminator.
910 Instruction *NT = I1->clone();
911 BIParent->getInstList().insert(BI, NT);
912 if (!NT->getType()->isVoidTy()) {
913 I1->replaceAllUsesWith(NT);
914 I2->replaceAllUsesWith(NT);
918 IRBuilder<true, NoFolder> Builder(NT);
919 // Hoisting one of the terminators from our successor is a great thing.
920 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
921 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
922 // nodes, so we insert select instruction to compute the final result.
923 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
924 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
926 for (BasicBlock::iterator BBI = SI->begin();
927 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
928 Value *BB1V = PN->getIncomingValueForBlock(BB1);
929 Value *BB2V = PN->getIncomingValueForBlock(BB2);
930 if (BB1V == BB2V) continue;
932 // These values do not agree. Insert a select instruction before NT
933 // that determines the right value.
934 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
936 SI = cast<SelectInst>
937 (Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,
938 BB1V->getName()+"."+BB2V->getName()));
940 // Make the PHI node use the select for all incoming values for BB1/BB2
941 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
942 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
943 PN->setIncomingValue(i, SI);
947 // Update any PHI nodes in our new successors.
948 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
949 AddPredecessorToBlock(*SI, BIParent, BB1);
951 EraseTerminatorInstAndDCECond(BI);
955 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
956 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
957 /// (for now, restricted to a single instruction that's side effect free) from
958 /// the BB1 into the branch block to speculatively execute it.
963 /// br i1 %t1, label %BB1, label %BB2
972 /// %t3 = select i1 %t1, %t2, %t3
973 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
974 // Only speculatively execution a single instruction (not counting the
975 // terminator) for now.
976 Instruction *HInst = NULL;
977 Instruction *Term = BB1->getTerminator();
978 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
980 Instruction *I = BBI;
982 if (isa<DbgInfoIntrinsic>(I)) continue;
983 if (I == Term) break;
990 BasicBlock *BIParent = BI->getParent();
992 // Check the instruction to be hoisted, if there is one.
994 // Don't hoist the instruction if it's unsafe or expensive.
995 if (!isSafeToSpeculativelyExecute(HInst))
997 if (ComputeSpeculationCost(HInst) > PHINodeFoldingThreshold)
1000 // Do not hoist the instruction if any of its operands are defined but not
1001 // used in this BB. The transformation will prevent the operand from
1002 // being sunk into the use block.
1003 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1005 Instruction *OpI = dyn_cast<Instruction>(*i);
1006 if (OpI && OpI->getParent() == BIParent &&
1007 !OpI->mayHaveSideEffects() &&
1008 !OpI->isUsedInBasicBlock(BIParent))
1013 // Be conservative for now. FP select instruction can often be expensive.
1014 Value *BrCond = BI->getCondition();
1015 if (isa<FCmpInst>(BrCond))
1018 // If BB1 is actually on the false edge of the conditional branch, remember
1019 // to swap the select operands later.
1020 bool Invert = false;
1021 if (BB1 != BI->getSuccessor(0)) {
1022 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
1026 // Collect interesting PHIs, and scan for hazards.
1027 SmallSetVector<std::pair<Value *, Value *>, 4> PHIs;
1028 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
1029 for (BasicBlock::iterator I = BB2->begin();
1030 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1031 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1032 Value *BIParentV = PN->getIncomingValueForBlock(BIParent);
1034 // Skip PHIs which are trivial.
1035 if (BB1V == BIParentV)
1038 // Check for saftey.
1039 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BB1V)) {
1040 // An unfolded ConstantExpr could end up getting expanded into
1041 // Instructions. Don't speculate this and another instruction at
1045 if (!isSafeToSpeculativelyExecute(CE))
1047 if (ComputeSpeculationCost(CE) > PHINodeFoldingThreshold)
1051 // Ok, we may insert a select for this PHI.
1052 PHIs.insert(std::make_pair(BB1V, BIParentV));
1055 // If there are no PHIs to process, bail early. This helps ensure idempotence
1060 // If we get here, we can hoist the instruction and if-convert.
1061 DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *BB1 << "\n";);
1063 // Hoist the instruction.
1065 BIParent->getInstList().splice(BI, BB1->getInstList(), HInst);
1067 // Insert selects and rewrite the PHI operands.
1068 IRBuilder<true, NoFolder> Builder(BI);
1069 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
1070 Value *TrueV = PHIs[i].first;
1071 Value *FalseV = PHIs[i].second;
1073 // Create a select whose true value is the speculatively executed value and
1074 // false value is the previously determined FalseV.
1077 SI = cast<SelectInst>
1078 (Builder.CreateSelect(BrCond, FalseV, TrueV,
1079 FalseV->getName() + "." + TrueV->getName()));
1081 SI = cast<SelectInst>
1082 (Builder.CreateSelect(BrCond, TrueV, FalseV,
1083 TrueV->getName() + "." + FalseV->getName()));
1085 // Make the PHI node use the select for all incoming values for "then" and
1087 for (BasicBlock::iterator I = BB2->begin();
1088 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1089 unsigned BB1I = PN->getBasicBlockIndex(BB1);
1090 unsigned BIParentI = PN->getBasicBlockIndex(BIParent);
1091 Value *BB1V = PN->getIncomingValue(BB1I);
1092 Value *BIParentV = PN->getIncomingValue(BIParentI);
1093 if (TrueV == BB1V && FalseV == BIParentV) {
1094 PN->setIncomingValue(BB1I, SI);
1095 PN->setIncomingValue(BIParentI, SI);
1104 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1105 /// across this block.
1106 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1107 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1110 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1111 if (isa<DbgInfoIntrinsic>(BBI))
1113 if (Size > 10) return false; // Don't clone large BB's.
1116 // We can only support instructions that do not define values that are
1117 // live outside of the current basic block.
1118 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1120 Instruction *U = cast<Instruction>(*UI);
1121 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1124 // Looks ok, continue checking.
1130 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1131 /// that is defined in the same block as the branch and if any PHI entries are
1132 /// constants, thread edges corresponding to that entry to be branches to their
1133 /// ultimate destination.
1134 static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
1135 BasicBlock *BB = BI->getParent();
1136 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1137 // NOTE: we currently cannot transform this case if the PHI node is used
1138 // outside of the block.
1139 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1142 // Degenerate case of a single entry PHI.
1143 if (PN->getNumIncomingValues() == 1) {
1144 FoldSingleEntryPHINodes(PN->getParent());
1148 // Now we know that this block has multiple preds and two succs.
1149 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1151 // Okay, this is a simple enough basic block. See if any phi values are
1153 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1154 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1155 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1157 // Okay, we now know that all edges from PredBB should be revectored to
1158 // branch to RealDest.
1159 BasicBlock *PredBB = PN->getIncomingBlock(i);
1160 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1162 if (RealDest == BB) continue; // Skip self loops.
1163 // Skip if the predecessor's terminator is an indirect branch.
1164 if (isa<IndirectBrInst>(PredBB->getTerminator())) continue;
1166 // The dest block might have PHI nodes, other predecessors and other
1167 // difficult cases. Instead of being smart about this, just insert a new
1168 // block that jumps to the destination block, effectively splitting
1169 // the edge we are about to create.
1170 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1171 RealDest->getName()+".critedge",
1172 RealDest->getParent(), RealDest);
1173 BranchInst::Create(RealDest, EdgeBB);
1175 // Update PHI nodes.
1176 AddPredecessorToBlock(RealDest, EdgeBB, BB);
1178 // BB may have instructions that are being threaded over. Clone these
1179 // instructions into EdgeBB. We know that there will be no uses of the
1180 // cloned instructions outside of EdgeBB.
1181 BasicBlock::iterator InsertPt = EdgeBB->begin();
1182 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1183 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1184 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1185 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1188 // Clone the instruction.
1189 Instruction *N = BBI->clone();
1190 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1192 // Update operands due to translation.
1193 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1195 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1196 if (PI != TranslateMap.end())
1200 // Check for trivial simplification.
1201 if (Value *V = SimplifyInstruction(N, TD)) {
1202 TranslateMap[BBI] = V;
1203 delete N; // Instruction folded away, don't need actual inst
1205 // Insert the new instruction into its new home.
1206 EdgeBB->getInstList().insert(InsertPt, N);
1207 if (!BBI->use_empty())
1208 TranslateMap[BBI] = N;
1212 // Loop over all of the edges from PredBB to BB, changing them to branch
1213 // to EdgeBB instead.
1214 TerminatorInst *PredBBTI = PredBB->getTerminator();
1215 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1216 if (PredBBTI->getSuccessor(i) == BB) {
1217 BB->removePredecessor(PredBB);
1218 PredBBTI->setSuccessor(i, EdgeBB);
1221 // Recurse, simplifying any other constants.
1222 return FoldCondBranchOnPHI(BI, TD) | true;
1228 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1229 /// PHI node, see if we can eliminate it.
1230 static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
1231 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1232 // statement", which has a very simple dominance structure. Basically, we
1233 // are trying to find the condition that is being branched on, which
1234 // subsequently causes this merge to happen. We really want control
1235 // dependence information for this check, but simplifycfg can't keep it up
1236 // to date, and this catches most of the cases we care about anyway.
1237 BasicBlock *BB = PN->getParent();
1238 BasicBlock *IfTrue, *IfFalse;
1239 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1241 // Don't bother if the branch will be constant folded trivially.
1242 isa<ConstantInt>(IfCond))
1245 // Okay, we found that we can merge this two-entry phi node into a select.
1246 // Doing so would require us to fold *all* two entry phi nodes in this block.
1247 // At some point this becomes non-profitable (particularly if the target
1248 // doesn't support cmov's). Only do this transformation if there are two or
1249 // fewer PHI nodes in this block.
1250 unsigned NumPhis = 0;
1251 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1255 // Loop over the PHI's seeing if we can promote them all to select
1256 // instructions. While we are at it, keep track of the instructions
1257 // that need to be moved to the dominating block.
1258 SmallPtrSet<Instruction*, 4> AggressiveInsts;
1259 unsigned MaxCostVal0 = PHINodeFoldingThreshold,
1260 MaxCostVal1 = PHINodeFoldingThreshold;
1262 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1263 PHINode *PN = cast<PHINode>(II++);
1264 if (Value *V = SimplifyInstruction(PN, TD)) {
1265 PN->replaceAllUsesWith(V);
1266 PN->eraseFromParent();
1270 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
1272 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
1277 // If we folded the the first phi, PN dangles at this point. Refresh it. If
1278 // we ran out of PHIs then we simplified them all.
1279 PN = dyn_cast<PHINode>(BB->begin());
1280 if (PN == 0) return true;
1282 // Don't fold i1 branches on PHIs which contain binary operators. These can
1283 // often be turned into switches and other things.
1284 if (PN->getType()->isIntegerTy(1) &&
1285 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1286 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1287 isa<BinaryOperator>(IfCond)))
1290 // If we all PHI nodes are promotable, check to make sure that all
1291 // instructions in the predecessor blocks can be promoted as well. If
1292 // not, we won't be able to get rid of the control flow, so it's not
1293 // worth promoting to select instructions.
1294 BasicBlock *DomBlock = 0;
1295 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1296 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1297 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1300 DomBlock = *pred_begin(IfBlock1);
1301 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1302 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1303 // This is not an aggressive instruction that we can promote.
1304 // Because of this, we won't be able to get rid of the control
1305 // flow, so the xform is not worth it.
1310 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1313 DomBlock = *pred_begin(IfBlock2);
1314 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1315 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1316 // This is not an aggressive instruction that we can promote.
1317 // Because of this, we won't be able to get rid of the control
1318 // flow, so the xform is not worth it.
1323 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1324 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1326 // If we can still promote the PHI nodes after this gauntlet of tests,
1327 // do all of the PHI's now.
1328 Instruction *InsertPt = DomBlock->getTerminator();
1329 IRBuilder<true, NoFolder> Builder(InsertPt);
1331 // Move all 'aggressive' instructions, which are defined in the
1332 // conditional parts of the if's up to the dominating block.
1334 DomBlock->getInstList().splice(InsertPt,
1335 IfBlock1->getInstList(), IfBlock1->begin(),
1336 IfBlock1->getTerminator());
1338 DomBlock->getInstList().splice(InsertPt,
1339 IfBlock2->getInstList(), IfBlock2->begin(),
1340 IfBlock2->getTerminator());
1342 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1343 // Change the PHI node into a select instruction.
1344 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1345 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1348 cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, ""));
1349 PN->replaceAllUsesWith(NV);
1351 PN->eraseFromParent();
1354 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1355 // has been flattened. Change DomBlock to jump directly to our new block to
1356 // avoid other simplifycfg's kicking in on the diamond.
1357 TerminatorInst *OldTI = DomBlock->getTerminator();
1358 Builder.SetInsertPoint(OldTI);
1359 Builder.CreateBr(BB);
1360 OldTI->eraseFromParent();
1364 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1365 /// to two returning blocks, try to merge them together into one return,
1366 /// introducing a select if the return values disagree.
1367 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
1368 IRBuilder<> &Builder) {
1369 assert(BI->isConditional() && "Must be a conditional branch");
1370 BasicBlock *TrueSucc = BI->getSuccessor(0);
1371 BasicBlock *FalseSucc = BI->getSuccessor(1);
1372 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1373 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1375 // Check to ensure both blocks are empty (just a return) or optionally empty
1376 // with PHI nodes. If there are other instructions, merging would cause extra
1377 // computation on one path or the other.
1378 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1380 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1383 Builder.SetInsertPoint(BI);
1384 // Okay, we found a branch that is going to two return nodes. If
1385 // there is no return value for this function, just change the
1386 // branch into a return.
1387 if (FalseRet->getNumOperands() == 0) {
1388 TrueSucc->removePredecessor(BI->getParent());
1389 FalseSucc->removePredecessor(BI->getParent());
1390 Builder.CreateRetVoid();
1391 EraseTerminatorInstAndDCECond(BI);
1395 // Otherwise, figure out what the true and false return values are
1396 // so we can insert a new select instruction.
1397 Value *TrueValue = TrueRet->getReturnValue();
1398 Value *FalseValue = FalseRet->getReturnValue();
1400 // Unwrap any PHI nodes in the return blocks.
1401 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1402 if (TVPN->getParent() == TrueSucc)
1403 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1404 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1405 if (FVPN->getParent() == FalseSucc)
1406 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1408 // In order for this transformation to be safe, we must be able to
1409 // unconditionally execute both operands to the return. This is
1410 // normally the case, but we could have a potentially-trapping
1411 // constant expression that prevents this transformation from being
1413 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1416 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1420 // Okay, we collected all the mapped values and checked them for sanity, and
1421 // defined to really do this transformation. First, update the CFG.
1422 TrueSucc->removePredecessor(BI->getParent());
1423 FalseSucc->removePredecessor(BI->getParent());
1425 // Insert select instructions where needed.
1426 Value *BrCond = BI->getCondition();
1428 // Insert a select if the results differ.
1429 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1430 } else if (isa<UndefValue>(TrueValue)) {
1431 TrueValue = FalseValue;
1433 TrueValue = Builder.CreateSelect(BrCond, TrueValue,
1434 FalseValue, "retval");
1438 Value *RI = !TrueValue ?
1439 Builder.CreateRetVoid() : Builder.CreateRet(TrueValue);
1443 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1444 << "\n " << *BI << "NewRet = " << *RI
1445 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1447 EraseTerminatorInstAndDCECond(BI);
1452 /// ExtractBranchMetadata - Given a conditional BranchInstruction, retrieve the
1453 /// probabilities of the branch taking each edge. Fills in the two APInt
1454 /// parameters and return true, or returns false if no or invalid metadata was
1456 static bool ExtractBranchMetadata(BranchInst *BI,
1457 APInt &ProbTrue, APInt &ProbFalse) {
1458 assert(BI->isConditional() &&
1459 "Looking for probabilities on unconditional branch?");
1460 MDNode *ProfileData = BI->getMetadata(LLVMContext::MD_prof);
1461 if (!ProfileData || ProfileData->getNumOperands() != 3) return false;
1462 ConstantInt *CITrue = dyn_cast<ConstantInt>(ProfileData->getOperand(1));
1463 ConstantInt *CIFalse = dyn_cast<ConstantInt>(ProfileData->getOperand(2));
1464 if (!CITrue || !CIFalse) return false;
1465 ProbTrue = CITrue->getValue();
1466 ProbFalse = CIFalse->getValue();
1467 assert(ProbTrue.getBitWidth() == 32 && ProbFalse.getBitWidth() == 32 &&
1468 "Branch probability metadata must be 32-bit integers");
1472 /// MultiplyAndLosePrecision - Multiplies A and B, then returns the result. In
1473 /// the event of overflow, logically-shifts all four inputs right until the
1475 static APInt MultiplyAndLosePrecision(APInt &A, APInt &B, APInt &C, APInt &D,
1476 unsigned &BitsLost) {
1478 bool Overflow = false;
1479 APInt Result = A.umul_ov(B, Overflow);
1481 APInt MaxB = APInt::getMaxValue(A.getBitWidth()).udiv(A);
1485 } while (B.ugt(MaxB));
1486 A = A.lshr(BitsLost);
1487 C = C.lshr(BitsLost);
1488 D = D.lshr(BitsLost);
1495 /// FoldBranchToCommonDest - If this basic block is simple enough, and if a
1496 /// predecessor branches to us and one of our successors, fold the block into
1497 /// the predecessor and use logical operations to pick the right destination.
1498 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1499 BasicBlock *BB = BI->getParent();
1501 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1502 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1503 Cond->getParent() != BB || !Cond->hasOneUse())
1506 // Only allow this if the condition is a simple instruction that can be
1507 // executed unconditionally. It must be in the same block as the branch, and
1508 // must be at the front of the block.
1509 BasicBlock::iterator FrontIt = BB->front();
1511 // Ignore dbg intrinsics.
1512 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1514 // Allow a single instruction to be hoisted in addition to the compare
1515 // that feeds the branch. We later ensure that any values that _it_ uses
1516 // were also live in the predecessor, so that we don't unnecessarily create
1517 // register pressure or inhibit out-of-order execution.
1518 Instruction *BonusInst = 0;
1519 if (&*FrontIt != Cond &&
1520 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1521 isSafeToSpeculativelyExecute(FrontIt)) {
1522 BonusInst = &*FrontIt;
1525 // Ignore dbg intrinsics.
1526 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1529 // Only a single bonus inst is allowed.
1530 if (&*FrontIt != Cond)
1533 // Make sure the instruction after the condition is the cond branch.
1534 BasicBlock::iterator CondIt = Cond; ++CondIt;
1536 // Ingore dbg intrinsics.
1537 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
1542 // Cond is known to be a compare or binary operator. Check to make sure that
1543 // neither operand is a potentially-trapping constant expression.
1544 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1547 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1551 // Finally, don't infinitely unroll conditional loops.
1552 BasicBlock *TrueDest = BI->getSuccessor(0);
1553 BasicBlock *FalseDest = BI->getSuccessor(1);
1554 if (TrueDest == BB || FalseDest == BB)
1557 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1558 BasicBlock *PredBlock = *PI;
1559 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1561 // Check that we have two conditional branches. If there is a PHI node in
1562 // the common successor, verify that the same value flows in from both
1564 if (PBI == 0 || PBI->isUnconditional() || !SafeToMergeTerminators(BI, PBI))
1567 // Determine if the two branches share a common destination.
1568 Instruction::BinaryOps Opc;
1569 bool InvertPredCond = false;
1571 if (PBI->getSuccessor(0) == TrueDest)
1572 Opc = Instruction::Or;
1573 else if (PBI->getSuccessor(1) == FalseDest)
1574 Opc = Instruction::And;
1575 else if (PBI->getSuccessor(0) == FalseDest)
1576 Opc = Instruction::And, InvertPredCond = true;
1577 else if (PBI->getSuccessor(1) == TrueDest)
1578 Opc = Instruction::Or, InvertPredCond = true;
1582 // Ensure that any values used in the bonus instruction are also used
1583 // by the terminator of the predecessor. This means that those values
1584 // must already have been resolved, so we won't be inhibiting the
1585 // out-of-order core by speculating them earlier.
1587 // Collect the values used by the bonus inst
1588 SmallPtrSet<Value*, 4> UsedValues;
1589 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1590 OE = BonusInst->op_end(); OI != OE; ++OI) {
1592 if (!isa<Constant>(V))
1593 UsedValues.insert(V);
1596 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1597 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1599 // Walk up to four levels back up the use-def chain of the predecessor's
1600 // terminator to see if all those values were used. The choice of four
1601 // levels is arbitrary, to provide a compile-time-cost bound.
1602 while (!Worklist.empty()) {
1603 std::pair<Value*, unsigned> Pair = Worklist.back();
1604 Worklist.pop_back();
1606 if (Pair.second >= 4) continue;
1607 UsedValues.erase(Pair.first);
1608 if (UsedValues.empty()) break;
1610 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
1611 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1613 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1617 if (!UsedValues.empty()) return false;
1620 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1621 IRBuilder<> Builder(PBI);
1623 // If we need to invert the condition in the pred block to match, do so now.
1624 if (InvertPredCond) {
1625 Value *NewCond = PBI->getCondition();
1627 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
1628 CmpInst *CI = cast<CmpInst>(NewCond);
1629 CI->setPredicate(CI->getInversePredicate());
1631 NewCond = Builder.CreateNot(NewCond,
1632 PBI->getCondition()->getName()+".not");
1635 PBI->setCondition(NewCond);
1636 PBI->swapSuccessors();
1639 // If we have a bonus inst, clone it into the predecessor block.
1640 Instruction *NewBonus = 0;
1642 NewBonus = BonusInst->clone();
1643 PredBlock->getInstList().insert(PBI, NewBonus);
1644 NewBonus->takeName(BonusInst);
1645 BonusInst->setName(BonusInst->getName()+".old");
1648 // Clone Cond into the predecessor basic block, and or/and the
1649 // two conditions together.
1650 Instruction *New = Cond->clone();
1651 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1652 PredBlock->getInstList().insert(PBI, New);
1653 New->takeName(Cond);
1654 Cond->setName(New->getName()+".old");
1656 Instruction *NewCond =
1657 cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(),
1659 PBI->setCondition(NewCond);
1660 if (PBI->getSuccessor(0) == BB) {
1661 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1662 PBI->setSuccessor(0, TrueDest);
1664 if (PBI->getSuccessor(1) == BB) {
1665 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1666 PBI->setSuccessor(1, FalseDest);
1669 // TODO: If BB is reachable from all paths through PredBlock, then we
1670 // could replace PBI's branch probabilities with BI's.
1672 // Merge probability data into PredBlock's branch.
1674 if (ExtractBranchMetadata(PBI, C, D) && ExtractBranchMetadata(BI, A, B)) {
1675 // Given IR which does:
1677 // br i1 %x, label %bbB, label %bbC
1679 // br i1 %y, label %bbD, label %bbC
1680 // Let's call the probability that we take the edge from %bbA to %bbB
1681 // 'a', from %bbA to %bbC, 'b', from %bbB to %bbD 'c' and from %bbB to
1682 // %bbC probability 'd'.
1684 // We transform the IR into:
1686 // br i1 %z, label %bbD, label %bbC
1687 // where the probability of going to %bbD is (a*c) and going to bbC is
1690 // Probabilities aren't stored as ratios directly. Using branch weights,
1692 // (a*c)% = A*C, (b+(a*d))% = A*D+B*C+B*D.
1694 // In the event of overflow, we want to drop the LSB of the input
1698 // Ignore overflow result on ProbTrue.
1699 APInt ProbTrue = MultiplyAndLosePrecision(A, C, B, D, BitsLost);
1701 APInt Tmp1 = MultiplyAndLosePrecision(B, D, A, C, BitsLost);
1703 ProbTrue = ProbTrue.lshr(BitsLost*2);
1706 APInt Tmp2 = MultiplyAndLosePrecision(A, D, C, B, BitsLost);
1708 ProbTrue = ProbTrue.lshr(BitsLost*2);
1709 Tmp1 = Tmp1.lshr(BitsLost*2);
1712 APInt Tmp3 = MultiplyAndLosePrecision(B, C, A, D, BitsLost);
1714 ProbTrue = ProbTrue.lshr(BitsLost*2);
1715 Tmp1 = Tmp1.lshr(BitsLost*2);
1716 Tmp2 = Tmp2.lshr(BitsLost*2);
1719 bool Overflow1 = false, Overflow2 = false;
1720 APInt Tmp4 = Tmp2.uadd_ov(Tmp3, Overflow1);
1721 APInt ProbFalse = Tmp4.uadd_ov(Tmp1, Overflow2);
1723 if (Overflow1 || Overflow2) {
1724 ProbTrue = ProbTrue.lshr(1);
1725 Tmp1 = Tmp1.lshr(1);
1726 Tmp2 = Tmp2.lshr(1);
1727 Tmp3 = Tmp3.lshr(1);
1729 ProbFalse = Tmp4 + Tmp1;
1732 // The sum of branch weights must fit in 32-bits.
1733 if (ProbTrue.isNegative() && ProbFalse.isNegative()) {
1734 ProbTrue = ProbTrue.lshr(1);
1735 ProbFalse = ProbFalse.lshr(1);
1738 if (ProbTrue != ProbFalse) {
1739 // Normalize the result.
1740 APInt GCD = APIntOps::GreatestCommonDivisor(ProbTrue, ProbFalse);
1741 ProbTrue = ProbTrue.udiv(GCD);
1742 ProbFalse = ProbFalse.udiv(GCD);
1744 LLVMContext &Context = BI->getContext();
1746 Ops[0] = BI->getMetadata(LLVMContext::MD_prof)->getOperand(0);
1747 Ops[1] = ConstantInt::get(Context, ProbTrue);
1748 Ops[2] = ConstantInt::get(Context, ProbFalse);
1749 PBI->setMetadata(LLVMContext::MD_prof, MDNode::get(Context, Ops));
1751 PBI->setMetadata(LLVMContext::MD_prof, NULL);
1754 PBI->setMetadata(LLVMContext::MD_prof, NULL);
1757 // Copy any debug value intrinsics into the end of PredBlock.
1758 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
1759 if (isa<DbgInfoIntrinsic>(*I))
1760 I->clone()->insertBefore(PBI);
1767 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1768 /// predecessor of another block, this function tries to simplify it. We know
1769 /// that PBI and BI are both conditional branches, and BI is in one of the
1770 /// successor blocks of PBI - PBI branches to BI.
1771 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1772 assert(PBI->isConditional() && BI->isConditional());
1773 BasicBlock *BB = BI->getParent();
1775 // If this block ends with a branch instruction, and if there is a
1776 // predecessor that ends on a branch of the same condition, make
1777 // this conditional branch redundant.
1778 if (PBI->getCondition() == BI->getCondition() &&
1779 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1780 // Okay, the outcome of this conditional branch is statically
1781 // knowable. If this block had a single pred, handle specially.
1782 if (BB->getSinglePredecessor()) {
1783 // Turn this into a branch on constant.
1784 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1785 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1787 return true; // Nuke the branch on constant.
1790 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1791 // in the constant and simplify the block result. Subsequent passes of
1792 // simplifycfg will thread the block.
1793 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1794 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
1795 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1796 std::distance(PB, PE),
1797 BI->getCondition()->getName() + ".pr",
1799 // Okay, we're going to insert the PHI node. Since PBI is not the only
1800 // predecessor, compute the PHI'd conditional value for all of the preds.
1801 // Any predecessor where the condition is not computable we keep symbolic.
1802 for (pred_iterator PI = PB; PI != PE; ++PI) {
1803 BasicBlock *P = *PI;
1804 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
1805 PBI != BI && PBI->isConditional() &&
1806 PBI->getCondition() == BI->getCondition() &&
1807 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1808 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1809 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1812 NewPN->addIncoming(BI->getCondition(), P);
1816 BI->setCondition(NewPN);
1821 // If this is a conditional branch in an empty block, and if any
1822 // predecessors is a conditional branch to one of our destinations,
1823 // fold the conditions into logical ops and one cond br.
1824 BasicBlock::iterator BBI = BB->begin();
1825 // Ignore dbg intrinsics.
1826 while (isa<DbgInfoIntrinsic>(BBI))
1832 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1837 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1839 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1840 PBIOp = 0, BIOp = 1;
1841 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1842 PBIOp = 1, BIOp = 0;
1843 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1848 // Check to make sure that the other destination of this branch
1849 // isn't BB itself. If so, this is an infinite loop that will
1850 // keep getting unwound.
1851 if (PBI->getSuccessor(PBIOp) == BB)
1854 // Do not perform this transformation if it would require
1855 // insertion of a large number of select instructions. For targets
1856 // without predication/cmovs, this is a big pessimization.
1857 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1859 unsigned NumPhis = 0;
1860 for (BasicBlock::iterator II = CommonDest->begin();
1861 isa<PHINode>(II); ++II, ++NumPhis)
1862 if (NumPhis > 2) // Disable this xform.
1865 // Finally, if everything is ok, fold the branches to logical ops.
1866 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1868 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
1869 << "AND: " << *BI->getParent());
1872 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1873 // branch in it, where one edge (OtherDest) goes back to itself but the other
1874 // exits. We don't *know* that the program avoids the infinite loop
1875 // (even though that seems likely). If we do this xform naively, we'll end up
1876 // recursively unpeeling the loop. Since we know that (after the xform is
1877 // done) that the block *is* infinite if reached, we just make it an obviously
1878 // infinite loop with no cond branch.
1879 if (OtherDest == BB) {
1880 // Insert it at the end of the function, because it's either code,
1881 // or it won't matter if it's hot. :)
1882 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1883 "infloop", BB->getParent());
1884 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1885 OtherDest = InfLoopBlock;
1888 DEBUG(dbgs() << *PBI->getParent()->getParent());
1890 // BI may have other predecessors. Because of this, we leave
1891 // it alone, but modify PBI.
1893 // Make sure we get to CommonDest on True&True directions.
1894 Value *PBICond = PBI->getCondition();
1895 IRBuilder<true, NoFolder> Builder(PBI);
1897 PBICond = Builder.CreateNot(PBICond, PBICond->getName()+".not");
1899 Value *BICond = BI->getCondition();
1901 BICond = Builder.CreateNot(BICond, BICond->getName()+".not");
1903 // Merge the conditions.
1904 Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge");
1906 // Modify PBI to branch on the new condition to the new dests.
1907 PBI->setCondition(Cond);
1908 PBI->setSuccessor(0, CommonDest);
1909 PBI->setSuccessor(1, OtherDest);
1911 // OtherDest may have phi nodes. If so, add an entry from PBI's
1912 // block that are identical to the entries for BI's block.
1913 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
1915 // We know that the CommonDest already had an edge from PBI to
1916 // it. If it has PHIs though, the PHIs may have different
1917 // entries for BB and PBI's BB. If so, insert a select to make
1920 for (BasicBlock::iterator II = CommonDest->begin();
1921 (PN = dyn_cast<PHINode>(II)); ++II) {
1922 Value *BIV = PN->getIncomingValueForBlock(BB);
1923 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1924 Value *PBIV = PN->getIncomingValue(PBBIdx);
1926 // Insert a select in PBI to pick the right value.
1927 Value *NV = cast<SelectInst>
1928 (Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName()+".mux"));
1929 PN->setIncomingValue(PBBIdx, NV);
1933 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1934 DEBUG(dbgs() << *PBI->getParent()->getParent());
1936 // This basic block is probably dead. We know it has at least
1937 // one fewer predecessor.
1941 // SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
1942 // branch to TrueBB if Cond is true or to FalseBB if Cond is false.
1943 // Takes care of updating the successors and removing the old terminator.
1944 // Also makes sure not to introduce new successors by assuming that edges to
1945 // non-successor TrueBBs and FalseBBs aren't reachable.
1946 static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
1947 BasicBlock *TrueBB, BasicBlock *FalseBB){
1948 // Remove any superfluous successor edges from the CFG.
1949 // First, figure out which successors to preserve.
1950 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
1952 BasicBlock *KeepEdge1 = TrueBB;
1953 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
1955 // Then remove the rest.
1956 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
1957 BasicBlock *Succ = OldTerm->getSuccessor(I);
1958 // Make sure only to keep exactly one copy of each edge.
1959 if (Succ == KeepEdge1)
1961 else if (Succ == KeepEdge2)
1964 Succ->removePredecessor(OldTerm->getParent());
1967 IRBuilder<> Builder(OldTerm);
1968 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
1970 // Insert an appropriate new terminator.
1971 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
1972 if (TrueBB == FalseBB)
1973 // We were only looking for one successor, and it was present.
1974 // Create an unconditional branch to it.
1975 Builder.CreateBr(TrueBB);
1977 // We found both of the successors we were looking for.
1978 // Create a conditional branch sharing the condition of the select.
1979 Builder.CreateCondBr(Cond, TrueBB, FalseBB);
1980 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
1981 // Neither of the selected blocks were successors, so this
1982 // terminator must be unreachable.
1983 new UnreachableInst(OldTerm->getContext(), OldTerm);
1985 // One of the selected values was a successor, but the other wasn't.
1986 // Insert an unconditional branch to the one that was found;
1987 // the edge to the one that wasn't must be unreachable.
1989 // Only TrueBB was found.
1990 Builder.CreateBr(TrueBB);
1992 // Only FalseBB was found.
1993 Builder.CreateBr(FalseBB);
1996 EraseTerminatorInstAndDCECond(OldTerm);
2000 // SimplifySwitchOnSelect - Replaces
2001 // (switch (select cond, X, Y)) on constant X, Y
2002 // with a branch - conditional if X and Y lead to distinct BBs,
2003 // unconditional otherwise.
2004 static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
2005 // Check for constant integer values in the select.
2006 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
2007 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
2008 if (!TrueVal || !FalseVal)
2011 // Find the relevant condition and destinations.
2012 Value *Condition = Select->getCondition();
2013 unsigned TrueCase = SI->findCaseValue(TrueVal);
2014 unsigned FalseCase = SI->findCaseValue(FalseVal);
2015 BasicBlock *TrueBB = SI->getSuccessor(SI->resolveSuccessorIndex(TrueCase));
2016 BasicBlock *FalseBB = SI->getSuccessor(SI->resolveSuccessorIndex(FalseCase));
2018 // Perform the actual simplification.
2019 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB);
2022 // SimplifyIndirectBrOnSelect - Replaces
2023 // (indirectbr (select cond, blockaddress(@fn, BlockA),
2024 // blockaddress(@fn, BlockB)))
2026 // (br cond, BlockA, BlockB).
2027 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
2028 // Check that both operands of the select are block addresses.
2029 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
2030 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
2034 // Extract the actual blocks.
2035 BasicBlock *TrueBB = TBA->getBasicBlock();
2036 BasicBlock *FalseBB = FBA->getBasicBlock();
2038 // Perform the actual simplification.
2039 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB);
2042 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
2043 /// instruction (a seteq/setne with a constant) as the only instruction in a
2044 /// block that ends with an uncond branch. We are looking for a very specific
2045 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
2046 /// this case, we merge the first two "or's of icmp" into a switch, but then the
2047 /// default value goes to an uncond block with a seteq in it, we get something
2050 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
2052 /// %tmp = icmp eq i8 %A, 92
2055 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
2057 /// We prefer to split the edge to 'end' so that there is a true/false entry to
2058 /// the PHI, merging the third icmp into the switch.
2059 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
2060 const TargetData *TD,
2061 IRBuilder<> &Builder) {
2062 BasicBlock *BB = ICI->getParent();
2064 // If the block has any PHIs in it or the icmp has multiple uses, it is too
2066 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
2068 Value *V = ICI->getOperand(0);
2069 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
2071 // The pattern we're looking for is where our only predecessor is a switch on
2072 // 'V' and this block is the default case for the switch. In this case we can
2073 // fold the compared value into the switch to simplify things.
2074 BasicBlock *Pred = BB->getSinglePredecessor();
2075 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
2077 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
2078 if (SI->getCondition() != V)
2081 // If BB is reachable on a non-default case, then we simply know the value of
2082 // V in this block. Substitute it and constant fold the icmp instruction
2084 if (SI->getDefaultDest() != BB) {
2085 ConstantInt *VVal = SI->findCaseDest(BB);
2086 assert(VVal && "Should have a unique destination value");
2087 ICI->setOperand(0, VVal);
2089 if (Value *V = SimplifyInstruction(ICI, TD)) {
2090 ICI->replaceAllUsesWith(V);
2091 ICI->eraseFromParent();
2093 // BB is now empty, so it is likely to simplify away.
2094 return SimplifyCFG(BB) | true;
2097 // Ok, the block is reachable from the default dest. If the constant we're
2098 // comparing exists in one of the other edges, then we can constant fold ICI
2100 if (SI->findCaseValue(Cst) != SwitchInst::ErrorIndex) {
2102 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2103 V = ConstantInt::getFalse(BB->getContext());
2105 V = ConstantInt::getTrue(BB->getContext());
2107 ICI->replaceAllUsesWith(V);
2108 ICI->eraseFromParent();
2109 // BB is now empty, so it is likely to simplify away.
2110 return SimplifyCFG(BB) | true;
2113 // The use of the icmp has to be in the 'end' block, by the only PHI node in
2115 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
2116 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
2117 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
2118 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
2121 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
2123 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
2124 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
2126 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2127 std::swap(DefaultCst, NewCst);
2129 // Replace ICI (which is used by the PHI for the default value) with true or
2130 // false depending on if it is EQ or NE.
2131 ICI->replaceAllUsesWith(DefaultCst);
2132 ICI->eraseFromParent();
2134 // Okay, the switch goes to this block on a default value. Add an edge from
2135 // the switch to the merge point on the compared value.
2136 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
2137 BB->getParent(), BB);
2138 SI->addCase(Cst, NewBB);
2140 // NewBB branches to the phi block, add the uncond branch and the phi entry.
2141 Builder.SetInsertPoint(NewBB);
2142 Builder.SetCurrentDebugLocation(SI->getDebugLoc());
2143 Builder.CreateBr(SuccBlock);
2144 PHIUse->addIncoming(NewCst, NewBB);
2148 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
2149 /// Check to see if it is branching on an or/and chain of icmp instructions, and
2150 /// fold it into a switch instruction if so.
2151 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD,
2152 IRBuilder<> &Builder) {
2153 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
2154 if (Cond == 0) return false;
2157 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2158 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2159 // 'setne's and'ed together, collect them.
2161 std::vector<ConstantInt*> Values;
2162 bool TrueWhenEqual = true;
2163 Value *ExtraCase = 0;
2164 unsigned UsedICmps = 0;
2166 if (Cond->getOpcode() == Instruction::Or) {
2167 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
2169 } else if (Cond->getOpcode() == Instruction::And) {
2170 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
2172 TrueWhenEqual = false;
2175 // If we didn't have a multiply compared value, fail.
2176 if (CompVal == 0) return false;
2178 // Avoid turning single icmps into a switch.
2182 // There might be duplicate constants in the list, which the switch
2183 // instruction can't handle, remove them now.
2184 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
2185 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2187 // If Extra was used, we require at least two switch values to do the
2188 // transformation. A switch with one value is just an cond branch.
2189 if (ExtraCase && Values.size() < 2) return false;
2191 // Figure out which block is which destination.
2192 BasicBlock *DefaultBB = BI->getSuccessor(1);
2193 BasicBlock *EdgeBB = BI->getSuccessor(0);
2194 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2196 BasicBlock *BB = BI->getParent();
2198 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
2199 << " cases into SWITCH. BB is:\n" << *BB);
2201 // If there are any extra values that couldn't be folded into the switch
2202 // then we evaluate them with an explicit branch first. Split the block
2203 // right before the condbr to handle it.
2205 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
2206 // Remove the uncond branch added to the old block.
2207 TerminatorInst *OldTI = BB->getTerminator();
2208 Builder.SetInsertPoint(OldTI);
2211 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
2213 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
2215 OldTI->eraseFromParent();
2217 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
2218 // for the edge we just added.
2219 AddPredecessorToBlock(EdgeBB, BB, NewBB);
2221 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
2222 << "\nEXTRABB = " << *BB);
2226 Builder.SetInsertPoint(BI);
2227 // Convert pointer to int before we switch.
2228 if (CompVal->getType()->isPointerTy()) {
2229 assert(TD && "Cannot switch on pointer without TargetData");
2230 CompVal = Builder.CreatePtrToInt(CompVal,
2231 TD->getIntPtrType(CompVal->getContext()),
2235 // Create the new switch instruction now.
2236 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
2238 // Add all of the 'cases' to the switch instruction.
2239 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2240 New->addCase(Values[i], EdgeBB);
2242 // We added edges from PI to the EdgeBB. As such, if there were any
2243 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2244 // the number of edges added.
2245 for (BasicBlock::iterator BBI = EdgeBB->begin();
2246 isa<PHINode>(BBI); ++BBI) {
2247 PHINode *PN = cast<PHINode>(BBI);
2248 Value *InVal = PN->getIncomingValueForBlock(BB);
2249 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2250 PN->addIncoming(InVal, BB);
2253 // Erase the old branch instruction.
2254 EraseTerminatorInstAndDCECond(BI);
2256 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
2260 bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
2261 // If this is a trivial landing pad that just continues unwinding the caught
2262 // exception then zap the landing pad, turning its invokes into calls.
2263 BasicBlock *BB = RI->getParent();
2264 LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI());
2265 if (RI->getValue() != LPInst)
2266 // Not a landing pad, or the resume is not unwinding the exception that
2267 // caused control to branch here.
2270 // Check that there are no other instructions except for debug intrinsics.
2271 BasicBlock::iterator I = LPInst, E = RI;
2273 if (!isa<DbgInfoIntrinsic>(I))
2276 // Turn all invokes that unwind here into calls and delete the basic block.
2277 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
2278 InvokeInst *II = cast<InvokeInst>((*PI++)->getTerminator());
2279 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
2280 // Insert a call instruction before the invoke.
2281 CallInst *Call = CallInst::Create(II->getCalledValue(), Args, "", II);
2283 Call->setCallingConv(II->getCallingConv());
2284 Call->setAttributes(II->getAttributes());
2285 Call->setDebugLoc(II->getDebugLoc());
2287 // Anything that used the value produced by the invoke instruction now uses
2288 // the value produced by the call instruction. Note that we do this even
2289 // for void functions and calls with no uses so that the callgraph edge is
2291 II->replaceAllUsesWith(Call);
2292 BB->removePredecessor(II->getParent());
2294 // Insert a branch to the normal destination right before the invoke.
2295 BranchInst::Create(II->getNormalDest(), II);
2297 // Finally, delete the invoke instruction!
2298 II->eraseFromParent();
2301 // The landingpad is now unreachable. Zap it.
2302 BB->eraseFromParent();
2306 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
2307 BasicBlock *BB = RI->getParent();
2308 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2310 // Find predecessors that end with branches.
2311 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2312 SmallVector<BranchInst*, 8> CondBranchPreds;
2313 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2314 BasicBlock *P = *PI;
2315 TerminatorInst *PTI = P->getTerminator();
2316 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2317 if (BI->isUnconditional())
2318 UncondBranchPreds.push_back(P);
2320 CondBranchPreds.push_back(BI);
2324 // If we found some, do the transformation!
2325 if (!UncondBranchPreds.empty() && DupRet) {
2326 while (!UncondBranchPreds.empty()) {
2327 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2328 DEBUG(dbgs() << "FOLDING: " << *BB
2329 << "INTO UNCOND BRANCH PRED: " << *Pred);
2330 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
2333 // If we eliminated all predecessors of the block, delete the block now.
2334 if (pred_begin(BB) == pred_end(BB))
2335 // We know there are no successors, so just nuke the block.
2336 BB->eraseFromParent();
2341 // Check out all of the conditional branches going to this return
2342 // instruction. If any of them just select between returns, change the
2343 // branch itself into a select/return pair.
2344 while (!CondBranchPreds.empty()) {
2345 BranchInst *BI = CondBranchPreds.pop_back_val();
2347 // Check to see if the non-BB successor is also a return block.
2348 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2349 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2350 SimplifyCondBranchToTwoReturns(BI, Builder))
2356 bool SimplifyCFGOpt::SimplifyUnwind(UnwindInst *UI, IRBuilder<> &Builder) {
2357 // Check to see if the first instruction in this block is just an unwind.
2358 // If so, replace any invoke instructions which use this as an exception
2359 // destination with call instructions.
2360 BasicBlock *BB = UI->getParent();
2361 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2363 bool Changed = false;
2364 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2365 while (!Preds.empty()) {
2366 BasicBlock *Pred = Preds.back();
2367 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
2368 if (II && II->getUnwindDest() == BB) {
2369 // Insert a new branch instruction before the invoke, because this
2370 // is now a fall through.
2371 Builder.SetInsertPoint(II);
2372 BranchInst *BI = Builder.CreateBr(II->getNormalDest());
2373 Pred->getInstList().remove(II); // Take out of symbol table
2375 // Insert the call now.
2376 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
2377 Builder.SetInsertPoint(BI);
2378 CallInst *CI = Builder.CreateCall(II->getCalledValue(),
2379 Args, II->getName());
2380 CI->setCallingConv(II->getCallingConv());
2381 CI->setAttributes(II->getAttributes());
2382 // If the invoke produced a value, the Call now does instead.
2383 II->replaceAllUsesWith(CI);
2391 // If this block is now dead (and isn't the entry block), remove it.
2392 if (pred_begin(BB) == pred_end(BB) &&
2393 BB != &BB->getParent()->getEntryBlock()) {
2394 // We know there are no successors, so just nuke the block.
2395 BB->eraseFromParent();
2402 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2403 BasicBlock *BB = UI->getParent();
2405 bool Changed = false;
2407 // If there are any instructions immediately before the unreachable that can
2408 // be removed, do so.
2409 while (UI != BB->begin()) {
2410 BasicBlock::iterator BBI = UI;
2412 // Do not delete instructions that can have side effects which might cause
2413 // the unreachable to not be reachable; specifically, calls and volatile
2414 // operations may have this effect.
2415 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2417 if (BBI->mayHaveSideEffects()) {
2418 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
2419 if (SI->isVolatile())
2421 } else if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
2422 if (LI->isVolatile())
2424 } else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(BBI)) {
2425 if (RMWI->isVolatile())
2427 } else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) {
2428 if (CXI->isVolatile())
2430 } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) &&
2431 !isa<LandingPadInst>(BBI)) {
2434 // Note that deleting LandingPad's here is in fact okay, although it
2435 // involves a bit of subtle reasoning. If this inst is a LandingPad,
2436 // all the predecessors of this block will be the unwind edges of Invokes,
2437 // and we can therefore guarantee this block will be erased.
2440 // Delete this instruction (any uses are guaranteed to be dead)
2441 if (!BBI->use_empty())
2442 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
2443 BBI->eraseFromParent();
2447 // If the unreachable instruction is the first in the block, take a gander
2448 // at all of the predecessors of this instruction, and simplify them.
2449 if (&BB->front() != UI) return Changed;
2451 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2452 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2453 TerminatorInst *TI = Preds[i]->getTerminator();
2454 IRBuilder<> Builder(TI);
2455 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2456 if (BI->isUnconditional()) {
2457 if (BI->getSuccessor(0) == BB) {
2458 new UnreachableInst(TI->getContext(), TI);
2459 TI->eraseFromParent();
2463 if (BI->getSuccessor(0) == BB) {
2464 Builder.CreateBr(BI->getSuccessor(1));
2465 EraseTerminatorInstAndDCECond(BI);
2466 } else if (BI->getSuccessor(1) == BB) {
2467 Builder.CreateBr(BI->getSuccessor(0));
2468 EraseTerminatorInstAndDCECond(BI);
2472 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2473 for (unsigned i = 0, e = SI->getNumCases(); i != e; ++i)
2474 if (SI->getCaseSuccessor(i) == BB) {
2475 BB->removePredecessor(SI->getParent());
2480 // If the default value is unreachable, figure out the most popular
2481 // destination and make it the default.
2482 if (SI->getDefaultDest() == BB) {
2483 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
2484 for (unsigned i = 0, e = SI->getNumCases(); i != e; ++i) {
2485 std::pair<unsigned, unsigned> &entry =
2486 Popularity[SI->getCaseSuccessor(i)];
2487 if (entry.first == 0) {
2495 // Find the most popular block.
2496 unsigned MaxPop = 0;
2497 unsigned MaxIndex = 0;
2498 BasicBlock *MaxBlock = 0;
2499 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
2500 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2501 if (I->second.first > MaxPop ||
2502 (I->second.first == MaxPop && MaxIndex > I->second.second)) {
2503 MaxPop = I->second.first;
2504 MaxIndex = I->second.second;
2505 MaxBlock = I->first;
2509 // Make this the new default, allowing us to delete any explicit
2511 SI->setDefaultDest(MaxBlock);
2514 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2516 if (isa<PHINode>(MaxBlock->begin()))
2517 for (unsigned i = 0; i != MaxPop-1; ++i)
2518 MaxBlock->removePredecessor(SI->getParent());
2520 for (unsigned i = 0, e = SI->getNumCases(); i != e; ++i)
2521 if (SI->getCaseSuccessor(i) == MaxBlock) {
2527 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2528 if (II->getUnwindDest() == BB) {
2529 // Convert the invoke to a call instruction. This would be a good
2530 // place to note that the call does not throw though.
2531 BranchInst *BI = Builder.CreateBr(II->getNormalDest());
2532 II->removeFromParent(); // Take out of symbol table
2534 // Insert the call now...
2535 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2536 Builder.SetInsertPoint(BI);
2537 CallInst *CI = Builder.CreateCall(II->getCalledValue(),
2538 Args, II->getName());
2539 CI->setCallingConv(II->getCallingConv());
2540 CI->setAttributes(II->getAttributes());
2541 // If the invoke produced a value, the call does now instead.
2542 II->replaceAllUsesWith(CI);
2549 // If this block is now dead, remove it.
2550 if (pred_begin(BB) == pred_end(BB) &&
2551 BB != &BB->getParent()->getEntryBlock()) {
2552 // We know there are no successors, so just nuke the block.
2553 BB->eraseFromParent();
2560 /// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
2561 /// integer range comparison into a sub, an icmp and a branch.
2562 static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
2563 assert(SI->getNumCases() > 1 && "Degenerate switch?");
2565 // Make sure all cases point to the same destination and gather the values.
2566 SmallVector<ConstantInt *, 16> Cases;
2567 Cases.push_back(SI->getCaseValue(0));
2568 for (unsigned I = 1, E = SI->getNumCases(); I != E; ++I) {
2569 if (SI->getCaseSuccessor(I-1) != SI->getCaseSuccessor(I))
2571 Cases.push_back(SI->getCaseValue(I));
2573 assert(Cases.size() == SI->getNumCases() && "Not all cases gathered");
2575 // Sort the case values, then check if they form a range we can transform.
2576 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
2577 for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
2578 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
2582 Constant *Offset = ConstantExpr::getNeg(Cases.back());
2583 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases());
2585 Value *Sub = SI->getCondition();
2586 if (!Offset->isNullValue())
2587 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off");
2588 Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
2589 Builder.CreateCondBr(Cmp, SI->getCaseSuccessor(0), SI->getDefaultDest());
2591 // Prune obsolete incoming values off the successor's PHI nodes.
2592 for (BasicBlock::iterator BBI = SI->getCaseSuccessor(0)->begin();
2593 isa<PHINode>(BBI); ++BBI) {
2594 for (unsigned I = 0, E = SI->getNumCases()-1; I != E; ++I)
2595 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
2597 SI->eraseFromParent();
2602 /// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch
2603 /// and use it to remove dead cases.
2604 static bool EliminateDeadSwitchCases(SwitchInst *SI) {
2605 Value *Cond = SI->getCondition();
2606 unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth();
2607 APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
2608 ComputeMaskedBits(Cond, APInt::getAllOnesValue(Bits), KnownZero, KnownOne);
2610 // Gather dead cases.
2611 SmallVector<ConstantInt*, 8> DeadCases;
2612 for (unsigned I = 0, E = SI->getNumCases(); I != E; ++I) {
2613 if ((SI->getCaseValue(I)->getValue() & KnownZero) != 0 ||
2614 (SI->getCaseValue(I)->getValue() & KnownOne) != KnownOne) {
2615 DeadCases.push_back(SI->getCaseValue(I));
2616 DEBUG(dbgs() << "SimplifyCFG: switch case '"
2617 << SI->getCaseValue(I)->getValue() << "' is dead.\n");
2621 // Remove dead cases from the switch.
2622 for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) {
2623 unsigned Case = SI->findCaseValue(DeadCases[I]);
2624 assert(Case != SwitchInst::ErrorIndex &&
2625 "Case was not found. Probably mistake in DeadCases forming.");
2626 // Prune unused values from PHI nodes.
2627 SI->getCaseSuccessor(Case)->removePredecessor(SI->getParent());
2628 SI->removeCase(Case);
2631 return !DeadCases.empty();
2634 /// FindPHIForConditionForwarding - If BB would be eligible for simplification
2635 /// by TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated
2636 /// by an unconditional branch), look at the phi node for BB in the successor
2637 /// block and see if the incoming value is equal to CaseValue. If so, return
2638 /// the phi node, and set PhiIndex to BB's index in the phi node.
2639 static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
2642 if (BB->getFirstNonPHIOrDbg() != BB->getTerminator())
2643 return NULL; // BB must be empty to be a candidate for simplification.
2644 if (!BB->getSinglePredecessor())
2645 return NULL; // BB must be dominated by the switch.
2647 BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
2648 if (!Branch || !Branch->isUnconditional())
2649 return NULL; // Terminator must be unconditional branch.
2651 BasicBlock *Succ = Branch->getSuccessor(0);
2653 BasicBlock::iterator I = Succ->begin();
2654 while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
2655 int Idx = PHI->getBasicBlockIndex(BB);
2656 assert(Idx >= 0 && "PHI has no entry for predecessor?");
2658 Value *InValue = PHI->getIncomingValue(Idx);
2659 if (InValue != CaseValue) continue;
2668 /// ForwardSwitchConditionToPHI - Try to forward the condition of a switch
2669 /// instruction to a phi node dominated by the switch, if that would mean that
2670 /// some of the destination blocks of the switch can be folded away.
2671 /// Returns true if a change is made.
2672 static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
2673 typedef DenseMap<PHINode*, SmallVector<int,4> > ForwardingNodesMap;
2674 ForwardingNodesMap ForwardingNodes;
2676 for (unsigned I = 0; I < SI->getNumCases(); ++I) { // 0 is the default case.
2677 ConstantInt *CaseValue = SI->getCaseValue(I);
2678 BasicBlock *CaseDest = SI->getCaseSuccessor(I);
2681 PHINode *PHI = FindPHIForConditionForwarding(CaseValue, CaseDest,
2685 ForwardingNodes[PHI].push_back(PhiIndex);
2688 bool Changed = false;
2690 for (ForwardingNodesMap::iterator I = ForwardingNodes.begin(),
2691 E = ForwardingNodes.end(); I != E; ++I) {
2692 PHINode *Phi = I->first;
2693 SmallVector<int,4> &Indexes = I->second;
2695 if (Indexes.size() < 2) continue;
2697 for (size_t I = 0, E = Indexes.size(); I != E; ++I)
2698 Phi->setIncomingValue(Indexes[I], SI->getCondition());
2705 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
2706 // If this switch is too complex to want to look at, ignore it.
2707 if (!isValueEqualityComparison(SI))
2710 BasicBlock *BB = SI->getParent();
2712 // If we only have one predecessor, and if it is a branch on this value,
2713 // see if that predecessor totally determines the outcome of this switch.
2714 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2715 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
2716 return SimplifyCFG(BB) | true;
2718 Value *Cond = SI->getCondition();
2719 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
2720 if (SimplifySwitchOnSelect(SI, Select))
2721 return SimplifyCFG(BB) | true;
2723 // If the block only contains the switch, see if we can fold the block
2724 // away into any preds.
2725 BasicBlock::iterator BBI = BB->begin();
2726 // Ignore dbg intrinsics.
2727 while (isa<DbgInfoIntrinsic>(BBI))
2730 if (FoldValueComparisonIntoPredecessors(SI, Builder))
2731 return SimplifyCFG(BB) | true;
2733 // Try to transform the switch into an icmp and a branch.
2734 if (TurnSwitchRangeIntoICmp(SI, Builder))
2735 return SimplifyCFG(BB) | true;
2737 // Remove unreachable cases.
2738 if (EliminateDeadSwitchCases(SI))
2739 return SimplifyCFG(BB) | true;
2741 if (ForwardSwitchConditionToPHI(SI))
2742 return SimplifyCFG(BB) | true;
2747 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
2748 BasicBlock *BB = IBI->getParent();
2749 bool Changed = false;
2751 // Eliminate redundant destinations.
2752 SmallPtrSet<Value *, 8> Succs;
2753 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2754 BasicBlock *Dest = IBI->getDestination(i);
2755 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2756 Dest->removePredecessor(BB);
2757 IBI->removeDestination(i);
2763 if (IBI->getNumDestinations() == 0) {
2764 // If the indirectbr has no successors, change it to unreachable.
2765 new UnreachableInst(IBI->getContext(), IBI);
2766 EraseTerminatorInstAndDCECond(IBI);
2770 if (IBI->getNumDestinations() == 1) {
2771 // If the indirectbr has one successor, change it to a direct branch.
2772 BranchInst::Create(IBI->getDestination(0), IBI);
2773 EraseTerminatorInstAndDCECond(IBI);
2777 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2778 if (SimplifyIndirectBrOnSelect(IBI, SI))
2779 return SimplifyCFG(BB) | true;
2784 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
2785 BasicBlock *BB = BI->getParent();
2787 // If the Terminator is the only non-phi instruction, simplify the block.
2788 BasicBlock::iterator I = BB->getFirstNonPHIOrDbgOrLifetime();
2789 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
2790 TryToSimplifyUncondBranchFromEmptyBlock(BB))
2793 // If the only instruction in the block is a seteq/setne comparison
2794 // against a constant, try to simplify the block.
2795 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
2796 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
2797 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
2799 if (I->isTerminator() &&
2800 TryToSimplifyUncondBranchWithICmpInIt(ICI, TD, Builder))
2808 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
2809 BasicBlock *BB = BI->getParent();
2811 // Conditional branch
2812 if (isValueEqualityComparison(BI)) {
2813 // If we only have one predecessor, and if it is a branch on this value,
2814 // see if that predecessor totally determines the outcome of this
2816 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2817 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
2818 return SimplifyCFG(BB) | true;
2820 // This block must be empty, except for the setcond inst, if it exists.
2821 // Ignore dbg intrinsics.
2822 BasicBlock::iterator I = BB->begin();
2823 // Ignore dbg intrinsics.
2824 while (isa<DbgInfoIntrinsic>(I))
2827 if (FoldValueComparisonIntoPredecessors(BI, Builder))
2828 return SimplifyCFG(BB) | true;
2829 } else if (&*I == cast<Instruction>(BI->getCondition())){
2831 // Ignore dbg intrinsics.
2832 while (isa<DbgInfoIntrinsic>(I))
2834 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
2835 return SimplifyCFG(BB) | true;
2839 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
2840 if (SimplifyBranchOnICmpChain(BI, TD, Builder))
2843 // If this basic block is ONLY a compare and a branch, and if a predecessor
2844 // branches to us and one of our successors, fold the comparison into the
2845 // predecessor and use logical operations to pick the right destination.
2846 if (FoldBranchToCommonDest(BI))
2847 return SimplifyCFG(BB) | true;
2849 // We have a conditional branch to two blocks that are only reachable
2850 // from BI. We know that the condbr dominates the two blocks, so see if
2851 // there is any identical code in the "then" and "else" blocks. If so, we
2852 // can hoist it up to the branching block.
2853 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
2854 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2855 if (HoistThenElseCodeToIf(BI))
2856 return SimplifyCFG(BB) | true;
2858 // If Successor #1 has multiple preds, we may be able to conditionally
2859 // execute Successor #0 if it branches to successor #1.
2860 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
2861 if (Succ0TI->getNumSuccessors() == 1 &&
2862 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
2863 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
2864 return SimplifyCFG(BB) | true;
2866 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2867 // If Successor #0 has multiple preds, we may be able to conditionally
2868 // execute Successor #1 if it branches to successor #0.
2869 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
2870 if (Succ1TI->getNumSuccessors() == 1 &&
2871 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
2872 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
2873 return SimplifyCFG(BB) | true;
2876 // If this is a branch on a phi node in the current block, thread control
2877 // through this block if any PHI node entries are constants.
2878 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
2879 if (PN->getParent() == BI->getParent())
2880 if (FoldCondBranchOnPHI(BI, TD))
2881 return SimplifyCFG(BB) | true;
2883 // Scan predecessor blocks for conditional branches.
2884 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2885 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2886 if (PBI != BI && PBI->isConditional())
2887 if (SimplifyCondBranchToCondBranch(PBI, BI))
2888 return SimplifyCFG(BB) | true;
2893 /// Check if passing a value to an instruction will cause undefined behavior.
2894 static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
2895 Constant *C = dyn_cast<Constant>(V);
2899 if (!I->hasOneUse()) // Only look at single-use instructions, for compile time
2902 if (C->isNullValue()) {
2903 Instruction *Use = I->use_back();
2905 // Now make sure that there are no instructions in between that can alter
2906 // control flow (eg. calls)
2907 for (BasicBlock::iterator i = ++BasicBlock::iterator(I); &*i != Use; ++i)
2908 if (i == I->getParent()->end() || i->mayHaveSideEffects())
2911 // Look through GEPs. A load from a GEP derived from NULL is still undefined
2912 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))
2913 if (GEP->getPointerOperand() == I)
2914 return passingValueIsAlwaysUndefined(V, GEP);
2916 // Look through bitcasts.
2917 if (BitCastInst *BC = dyn_cast<BitCastInst>(Use))
2918 return passingValueIsAlwaysUndefined(V, BC);
2920 // Load from null is undefined.
2921 if (LoadInst *LI = dyn_cast<LoadInst>(Use))
2922 return LI->getPointerAddressSpace() == 0;
2924 // Store to null is undefined.
2925 if (StoreInst *SI = dyn_cast<StoreInst>(Use))
2926 return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I;
2931 /// If BB has an incoming value that will always trigger undefined behavior
2932 /// (eg. null pointer dereference), remove the branch leading here.
2933 static bool removeUndefIntroducingPredecessor(BasicBlock *BB) {
2934 for (BasicBlock::iterator i = BB->begin();
2935 PHINode *PHI = dyn_cast<PHINode>(i); ++i)
2936 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
2937 if (passingValueIsAlwaysUndefined(PHI->getIncomingValue(i), PHI)) {
2938 TerminatorInst *T = PHI->getIncomingBlock(i)->getTerminator();
2939 IRBuilder<> Builder(T);
2940 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
2941 BB->removePredecessor(PHI->getIncomingBlock(i));
2942 // Turn uncoditional branches into unreachables and remove the dead
2943 // destination from conditional branches.
2944 if (BI->isUnconditional())
2945 Builder.CreateUnreachable();
2947 Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1) :
2948 BI->getSuccessor(0));
2949 BI->eraseFromParent();
2952 // TODO: SwitchInst.
2958 bool SimplifyCFGOpt::run(BasicBlock *BB) {
2959 bool Changed = false;
2961 assert(BB && BB->getParent() && "Block not embedded in function!");
2962 assert(BB->getTerminator() && "Degenerate basic block encountered!");
2964 // Remove basic blocks that have no predecessors (except the entry block)...
2965 // or that just have themself as a predecessor. These are unreachable.
2966 if ((pred_begin(BB) == pred_end(BB) &&
2967 BB != &BB->getParent()->getEntryBlock()) ||
2968 BB->getSinglePredecessor() == BB) {
2969 DEBUG(dbgs() << "Removing BB: \n" << *BB);
2970 DeleteDeadBlock(BB);
2974 // Check to see if we can constant propagate this terminator instruction
2976 Changed |= ConstantFoldTerminator(BB, true);
2978 // Check for and eliminate duplicate PHI nodes in this block.
2979 Changed |= EliminateDuplicatePHINodes(BB);
2981 // Check for and remove branches that will always cause undefined behavior.
2982 Changed |= removeUndefIntroducingPredecessor(BB);
2984 // Merge basic blocks into their predecessor if there is only one distinct
2985 // pred, and if there is only one distinct successor of the predecessor, and
2986 // if there are no PHI nodes.
2988 if (MergeBlockIntoPredecessor(BB))
2991 IRBuilder<> Builder(BB);
2993 // If there is a trivial two-entry PHI node in this basic block, and we can
2994 // eliminate it, do so now.
2995 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
2996 if (PN->getNumIncomingValues() == 2)
2997 Changed |= FoldTwoEntryPHINode(PN, TD);
2999 Builder.SetInsertPoint(BB->getTerminator());
3000 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
3001 if (BI->isUnconditional()) {
3002 if (SimplifyUncondBranch(BI, Builder)) return true;
3004 if (SimplifyCondBranch(BI, Builder)) return true;
3006 } else if (ResumeInst *RI = dyn_cast<ResumeInst>(BB->getTerminator())) {
3007 if (SimplifyResume(RI, Builder)) return true;
3008 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
3009 if (SimplifyReturn(RI, Builder)) return true;
3010 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
3011 if (SimplifySwitch(SI, Builder)) return true;
3012 } else if (UnreachableInst *UI =
3013 dyn_cast<UnreachableInst>(BB->getTerminator())) {
3014 if (SimplifyUnreachable(UI)) return true;
3015 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
3016 if (SimplifyUnwind(UI, Builder)) return true;
3017 } else if (IndirectBrInst *IBI =
3018 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
3019 if (SimplifyIndirectBr(IBI)) return true;
3025 /// SimplifyCFG - This function is used to do simplification of a CFG. For
3026 /// example, it adjusts branches to branches to eliminate the extra hop, it
3027 /// eliminates unreachable basic blocks, and does other "peephole" optimization
3028 /// of the CFG. It returns true if a modification was made.
3030 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
3031 return SimplifyCFGOpt(TD).run(BB);