1 //===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Peephole optimize the CFG.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "simplifycfg"
15 #include "llvm/Transforms/Utils/Local.h"
16 #include "llvm/Constants.h"
17 #include "llvm/Instructions.h"
18 #include "llvm/IntrinsicInst.h"
19 #include "llvm/Type.h"
20 #include "llvm/DerivedTypes.h"
21 #include "llvm/GlobalVariable.h"
22 #include "llvm/Analysis/InstructionSimplify.h"
23 #include "llvm/Target/TargetData.h"
24 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
25 #include "llvm/ADT/DenseMap.h"
26 #include "llvm/ADT/SmallVector.h"
27 #include "llvm/ADT/SmallPtrSet.h"
28 #include "llvm/ADT/Statistic.h"
29 #include "llvm/ADT/STLExtras.h"
30 #include "llvm/Support/CFG.h"
31 #include "llvm/Support/Debug.h"
32 #include "llvm/Support/raw_ostream.h"
38 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
41 class SimplifyCFGOpt {
42 const TargetData *const TD;
44 Value *isValueEqualityComparison(TerminatorInst *TI);
45 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
46 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases);
47 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
49 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI);
51 bool SimplifyReturn(ReturnInst *RI);
52 bool SimplifyUnwind(UnwindInst *UI);
53 bool SimplifyUnreachable(UnreachableInst *UI);
54 bool SimplifySwitch(SwitchInst *SI);
55 bool SimplifyIndirectBr(IndirectBrInst *IBI);
56 bool SimplifyUncondBranch(BranchInst *BI);
57 bool SimplifyCondBranch(BranchInst *BI);
60 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
61 bool run(BasicBlock *BB);
65 /// SafeToMergeTerminators - Return true if it is safe to merge these two
66 /// terminator instructions together.
68 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
69 if (SI1 == SI2) return false; // Can't merge with self!
71 // It is not safe to merge these two switch instructions if they have a common
72 // successor, and if that successor has a PHI node, and if *that* PHI node has
73 // conflicting incoming values from the two switch blocks.
74 BasicBlock *SI1BB = SI1->getParent();
75 BasicBlock *SI2BB = SI2->getParent();
76 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
78 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
79 if (SI1Succs.count(*I))
80 for (BasicBlock::iterator BBI = (*I)->begin();
81 isa<PHINode>(BBI); ++BBI) {
82 PHINode *PN = cast<PHINode>(BBI);
83 if (PN->getIncomingValueForBlock(SI1BB) !=
84 PN->getIncomingValueForBlock(SI2BB))
91 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
92 /// now be entries in it from the 'NewPred' block. The values that will be
93 /// flowing into the PHI nodes will be the same as those coming in from
94 /// ExistPred, an existing predecessor of Succ.
95 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
96 BasicBlock *ExistPred) {
97 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
98 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
99 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
102 for (BasicBlock::iterator I = Succ->begin();
103 (PN = dyn_cast<PHINode>(I)); ++I)
104 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
108 /// GetIfCondition - Given a basic block (BB) with two predecessors (and at
109 /// least one PHI node in it), check to see if the merge at this block is due
110 /// to an "if condition". If so, return the boolean condition that determines
111 /// which entry into BB will be taken. Also, return by references the block
112 /// that will be entered from if the condition is true, and the block that will
113 /// be entered if the condition is false.
116 static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
117 BasicBlock *&IfFalse) {
118 PHINode *SomePHI = cast<PHINode>(BB->begin());
119 assert(SomePHI->getNumIncomingValues() == 2 &&
120 "Function can only handle blocks with 2 predecessors!");
121 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
122 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
124 // We can only handle branches. Other control flow will be lowered to
125 // branches if possible anyway.
126 if (!isa<BranchInst>(Pred1->getTerminator()) ||
127 !isa<BranchInst>(Pred2->getTerminator()))
129 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
130 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
132 // Eliminate code duplication by ensuring that Pred1Br is conditional if
134 if (Pred2Br->isConditional()) {
135 // If both branches are conditional, we don't have an "if statement". In
136 // reality, we could transform this case, but since the condition will be
137 // required anyway, we stand no chance of eliminating it, so the xform is
138 // probably not profitable.
139 if (Pred1Br->isConditional())
142 std::swap(Pred1, Pred2);
143 std::swap(Pred1Br, Pred2Br);
146 if (Pred1Br->isConditional()) {
147 // If we found a conditional branch predecessor, make sure that it branches
148 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
149 if (Pred1Br->getSuccessor(0) == BB &&
150 Pred1Br->getSuccessor(1) == Pred2) {
153 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
154 Pred1Br->getSuccessor(1) == BB) {
158 // We know that one arm of the conditional goes to BB, so the other must
159 // go somewhere unrelated, and this must not be an "if statement".
163 // The only thing we have to watch out for here is to make sure that Pred2
164 // doesn't have incoming edges from other blocks. If it does, the condition
165 // doesn't dominate BB.
166 if (++pred_begin(Pred2) != pred_end(Pred2))
169 return Pred1Br->getCondition();
172 // Ok, if we got here, both predecessors end with an unconditional branch to
173 // BB. Don't panic! If both blocks only have a single (identical)
174 // predecessor, and THAT is a conditional branch, then we're all ok!
175 if (pred_begin(Pred1) == pred_end(Pred1) ||
176 ++pred_begin(Pred1) != pred_end(Pred1) ||
177 pred_begin(Pred2) == pred_end(Pred2) ||
178 ++pred_begin(Pred2) != pred_end(Pred2) ||
179 *pred_begin(Pred1) != *pred_begin(Pred2))
182 // Otherwise, if this is a conditional branch, then we can use it!
183 BasicBlock *CommonPred = *pred_begin(Pred1);
184 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
185 assert(BI->isConditional() && "Two successors but not conditional?");
186 if (BI->getSuccessor(0) == Pred1) {
193 return BI->getCondition();
198 /// DominatesMergePoint - If we have a merge point of an "if condition" as
199 /// accepted above, return true if the specified value dominates the block. We
200 /// don't handle the true generality of domination here, just a special case
201 /// which works well enough for us.
203 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
204 /// see if V (which must be an instruction) is cheap to compute and is
205 /// non-trapping. If both are true, the instruction is inserted into the set
206 /// and true is returned.
207 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
208 std::set<Instruction*> *AggressiveInsts) {
209 Instruction *I = dyn_cast<Instruction>(V);
211 // Non-instructions all dominate instructions, but not all constantexprs
212 // can be executed unconditionally.
213 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
218 BasicBlock *PBB = I->getParent();
220 // We don't want to allow weird loops that might have the "if condition" in
221 // the bottom of this block.
222 if (PBB == BB) return false;
224 // If this instruction is defined in a block that contains an unconditional
225 // branch to BB, then it must be in the 'conditional' part of the "if
227 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
228 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
229 if (!AggressiveInsts) return false;
230 // Okay, it looks like the instruction IS in the "condition". Check to
231 // see if it's a cheap instruction to unconditionally compute, and if it
232 // only uses stuff defined outside of the condition. If so, hoist it out.
233 if (!I->isSafeToSpeculativelyExecute())
236 switch (I->getOpcode()) {
237 default: return false; // Cannot hoist this out safely.
238 case Instruction::Load: {
239 // We have to check to make sure there are no instructions before the
240 // load in its basic block, as we are going to hoist the loop out to
242 BasicBlock::iterator IP = PBB->begin();
243 while (isa<DbgInfoIntrinsic>(IP))
245 if (IP != BasicBlock::iterator(I))
249 case Instruction::Add:
250 case Instruction::Sub:
251 case Instruction::And:
252 case Instruction::Or:
253 case Instruction::Xor:
254 case Instruction::Shl:
255 case Instruction::LShr:
256 case Instruction::AShr:
257 case Instruction::ICmp:
258 break; // These are all cheap and non-trapping instructions.
261 // Okay, we can only really hoist these out if their operands are not
262 // defined in the conditional region.
263 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
264 if (!DominatesMergePoint(*i, BB, 0))
266 // Okay, it's safe to do this! Remember this instruction.
267 AggressiveInsts->insert(I);
273 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
274 /// and PointerNullValue. Return NULL if value is not a constant int.
275 static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
276 // Normal constant int.
277 ConstantInt *CI = dyn_cast<ConstantInt>(V);
278 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
281 // This is some kind of pointer constant. Turn it into a pointer-sized
282 // ConstantInt if possible.
283 const IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
285 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
286 if (isa<ConstantPointerNull>(V))
287 return ConstantInt::get(PtrTy, 0);
289 // IntToPtr const int.
290 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
291 if (CE->getOpcode() == Instruction::IntToPtr)
292 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
293 // The constant is very likely to have the right type already.
294 if (CI->getType() == PtrTy)
297 return cast<ConstantInt>
298 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
303 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
304 /// collection of icmp eq/ne instructions that compare a value against a
305 /// constant, return the value being compared, and stick the constant into the
308 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
309 const TargetData *TD, bool isEQ) {
310 Instruction *I = dyn_cast<Instruction>(V);
311 if (I == 0) return 0;
313 // If this is an icmp against a constant, handle this as one of the cases.
314 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
315 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE))
316 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
318 return I->getOperand(0);
323 // Otherwise, we can only handle an | or &, depending on isEQ.
324 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
327 unsigned NumValsBeforeLHS = Vals.size();
328 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
330 unsigned NumVals = Vals.size();
331 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
335 Vals.resize(NumVals);
338 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
339 // set it and return success.
340 if (Extra == 0 || Extra == I->getOperand(1)) {
341 Extra = I->getOperand(1);
345 Vals.resize(NumValsBeforeLHS);
349 // If the LHS can't be folded in, but Extra is available and RHS can, try to
351 if (Extra == 0 || Extra == I->getOperand(0)) {
352 Value *OldExtra = Extra;
353 Extra = I->getOperand(0);
354 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
357 assert(Vals.size() == NumValsBeforeLHS);
364 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
365 Instruction* Cond = 0;
366 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
367 Cond = dyn_cast<Instruction>(SI->getCondition());
368 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
369 if (BI->isConditional())
370 Cond = dyn_cast<Instruction>(BI->getCondition());
371 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
372 Cond = dyn_cast<Instruction>(IBI->getAddress());
375 TI->eraseFromParent();
376 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
379 /// isValueEqualityComparison - Return true if the specified terminator checks
380 /// to see if a value is equal to constant integer value.
381 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
383 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
384 // Do not permit merging of large switch instructions into their
385 // predecessors unless there is only one predecessor.
386 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
387 pred_end(SI->getParent())) <= 128)
388 CV = SI->getCondition();
389 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
390 if (BI->isConditional() && BI->getCondition()->hasOneUse())
391 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
392 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
393 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
394 GetConstantInt(ICI->getOperand(1), TD))
395 CV = ICI->getOperand(0);
397 // Unwrap any lossless ptrtoint cast.
398 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
399 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
400 CV = PTII->getOperand(0);
404 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
405 /// decode all of the 'cases' that it represents and return the 'default' block.
406 BasicBlock *SimplifyCFGOpt::
407 GetValueEqualityComparisonCases(TerminatorInst *TI,
408 std::vector<std::pair<ConstantInt*,
409 BasicBlock*> > &Cases) {
410 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
411 Cases.reserve(SI->getNumCases());
412 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
413 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
414 return SI->getDefaultDest();
417 BranchInst *BI = cast<BranchInst>(TI);
418 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
419 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD),
420 BI->getSuccessor(ICI->getPredicate() ==
421 ICmpInst::ICMP_NE)));
422 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
426 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
427 /// in the list that match the specified block.
428 static void EliminateBlockCases(BasicBlock *BB,
429 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
430 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
431 if (Cases[i].second == BB) {
432 Cases.erase(Cases.begin()+i);
437 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
440 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
441 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
442 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
444 // Make V1 be smaller than V2.
445 if (V1->size() > V2->size())
448 if (V1->size() == 0) return false;
449 if (V1->size() == 1) {
451 ConstantInt *TheVal = (*V1)[0].first;
452 for (unsigned i = 0, e = V2->size(); i != e; ++i)
453 if (TheVal == (*V2)[i].first)
457 // Otherwise, just sort both lists and compare element by element.
458 array_pod_sort(V1->begin(), V1->end());
459 array_pod_sort(V2->begin(), V2->end());
460 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
461 while (i1 != e1 && i2 != e2) {
462 if ((*V1)[i1].first == (*V2)[i2].first)
464 if ((*V1)[i1].first < (*V2)[i2].first)
472 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
473 /// terminator instruction and its block is known to only have a single
474 /// predecessor block, check to see if that predecessor is also a value
475 /// comparison with the same value, and if that comparison determines the
476 /// outcome of this comparison. If so, simplify TI. This does a very limited
477 /// form of jump threading.
478 bool SimplifyCFGOpt::
479 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
481 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
482 if (!PredVal) return false; // Not a value comparison in predecessor.
484 Value *ThisVal = isValueEqualityComparison(TI);
485 assert(ThisVal && "This isn't a value comparison!!");
486 if (ThisVal != PredVal) return false; // Different predicates.
488 // Find out information about when control will move from Pred to TI's block.
489 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
490 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
492 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
494 // Find information about how control leaves this block.
495 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
496 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
497 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
499 // If TI's block is the default block from Pred's comparison, potentially
500 // simplify TI based on this knowledge.
501 if (PredDef == TI->getParent()) {
502 // If we are here, we know that the value is none of those cases listed in
503 // PredCases. If there are any cases in ThisCases that are in PredCases, we
505 if (!ValuesOverlap(PredCases, ThisCases))
508 if (isa<BranchInst>(TI)) {
509 // Okay, one of the successors of this condbr is dead. Convert it to a
511 assert(ThisCases.size() == 1 && "Branch can only have one case!");
512 // Insert the new branch.
513 Instruction *NI = BranchInst::Create(ThisDef, TI);
516 // Remove PHI node entries for the dead edge.
517 ThisCases[0].second->removePredecessor(TI->getParent());
519 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
520 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
522 EraseTerminatorInstAndDCECond(TI);
526 SwitchInst *SI = cast<SwitchInst>(TI);
527 // Okay, TI has cases that are statically dead, prune them away.
528 SmallPtrSet<Constant*, 16> DeadCases;
529 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
530 DeadCases.insert(PredCases[i].first);
532 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
533 << "Through successor TI: " << *TI);
535 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
536 if (DeadCases.count(SI->getCaseValue(i))) {
537 SI->getSuccessor(i)->removePredecessor(TI->getParent());
541 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
545 // Otherwise, TI's block must correspond to some matched value. Find out
546 // which value (or set of values) this is.
547 ConstantInt *TIV = 0;
548 BasicBlock *TIBB = TI->getParent();
549 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
550 if (PredCases[i].second == TIBB) {
552 return false; // Cannot handle multiple values coming to this block.
553 TIV = PredCases[i].first;
555 assert(TIV && "No edge from pred to succ?");
557 // Okay, we found the one constant that our value can be if we get into TI's
558 // BB. Find out which successor will unconditionally be branched to.
559 BasicBlock *TheRealDest = 0;
560 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
561 if (ThisCases[i].first == TIV) {
562 TheRealDest = ThisCases[i].second;
566 // If not handled by any explicit cases, it is handled by the default case.
567 if (TheRealDest == 0) TheRealDest = ThisDef;
569 // Remove PHI node entries for dead edges.
570 BasicBlock *CheckEdge = TheRealDest;
571 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
572 if (*SI != CheckEdge)
573 (*SI)->removePredecessor(TIBB);
577 // Insert the new branch.
578 Instruction *NI = BranchInst::Create(TheRealDest, TI);
581 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
582 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
584 EraseTerminatorInstAndDCECond(TI);
589 /// ConstantIntOrdering - This class implements a stable ordering of constant
590 /// integers that does not depend on their address. This is important for
591 /// applications that sort ConstantInt's to ensure uniqueness.
592 struct ConstantIntOrdering {
593 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
594 return LHS->getValue().ult(RHS->getValue());
599 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
600 const ConstantInt *LHS = *(const ConstantInt**)P1;
601 const ConstantInt *RHS = *(const ConstantInt**)P2;
602 return LHS->getValue().ult(RHS->getValue()) ? 1 : -1;
605 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
606 /// equality comparison instruction (either a switch or a branch on "X == c").
607 /// See if any of the predecessors of the terminator block are value comparisons
608 /// on the same value. If so, and if safe to do so, fold them together.
609 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
610 BasicBlock *BB = TI->getParent();
611 Value *CV = isValueEqualityComparison(TI); // CondVal
612 assert(CV && "Not a comparison?");
613 bool Changed = false;
615 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
616 while (!Preds.empty()) {
617 BasicBlock *Pred = Preds.pop_back_val();
619 // See if the predecessor is a comparison with the same value.
620 TerminatorInst *PTI = Pred->getTerminator();
621 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
623 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
624 // Figure out which 'cases' to copy from SI to PSI.
625 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
626 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
628 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
629 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
631 // Based on whether the default edge from PTI goes to BB or not, fill in
632 // PredCases and PredDefault with the new switch cases we would like to
634 SmallVector<BasicBlock*, 8> NewSuccessors;
636 if (PredDefault == BB) {
637 // If this is the default destination from PTI, only the edges in TI
638 // that don't occur in PTI, or that branch to BB will be activated.
639 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
640 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
641 if (PredCases[i].second != BB)
642 PTIHandled.insert(PredCases[i].first);
644 // The default destination is BB, we don't need explicit targets.
645 std::swap(PredCases[i], PredCases.back());
646 PredCases.pop_back();
650 // Reconstruct the new switch statement we will be building.
651 if (PredDefault != BBDefault) {
652 PredDefault->removePredecessor(Pred);
653 PredDefault = BBDefault;
654 NewSuccessors.push_back(BBDefault);
656 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
657 if (!PTIHandled.count(BBCases[i].first) &&
658 BBCases[i].second != BBDefault) {
659 PredCases.push_back(BBCases[i]);
660 NewSuccessors.push_back(BBCases[i].second);
664 // If this is not the default destination from PSI, only the edges
665 // in SI that occur in PSI with a destination of BB will be
667 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
668 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
669 if (PredCases[i].second == BB) {
670 PTIHandled.insert(PredCases[i].first);
671 std::swap(PredCases[i], PredCases.back());
672 PredCases.pop_back();
676 // Okay, now we know which constants were sent to BB from the
677 // predecessor. Figure out where they will all go now.
678 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
679 if (PTIHandled.count(BBCases[i].first)) {
680 // If this is one we are capable of getting...
681 PredCases.push_back(BBCases[i]);
682 NewSuccessors.push_back(BBCases[i].second);
683 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
686 // If there are any constants vectored to BB that TI doesn't handle,
687 // they must go to the default destination of TI.
688 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
690 E = PTIHandled.end(); I != E; ++I) {
691 PredCases.push_back(std::make_pair(*I, BBDefault));
692 NewSuccessors.push_back(BBDefault);
696 // Okay, at this point, we know which new successor Pred will get. Make
697 // sure we update the number of entries in the PHI nodes for these
699 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
700 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
702 // Convert pointer to int before we switch.
703 if (CV->getType()->isPointerTy()) {
704 assert(TD && "Cannot switch on pointer without TargetData");
705 CV = new PtrToIntInst(CV, TD->getIntPtrType(CV->getContext()),
709 // Now that the successors are updated, create the new Switch instruction.
710 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
711 PredCases.size(), PTI);
712 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
713 NewSI->addCase(PredCases[i].first, PredCases[i].second);
715 EraseTerminatorInstAndDCECond(PTI);
717 // Okay, last check. If BB is still a successor of PSI, then we must
718 // have an infinite loop case. If so, add an infinitely looping block
719 // to handle the case to preserve the behavior of the code.
720 BasicBlock *InfLoopBlock = 0;
721 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
722 if (NewSI->getSuccessor(i) == BB) {
723 if (InfLoopBlock == 0) {
724 // Insert it at the end of the function, because it's either code,
725 // or it won't matter if it's hot. :)
726 InfLoopBlock = BasicBlock::Create(BB->getContext(),
727 "infloop", BB->getParent());
728 BranchInst::Create(InfLoopBlock, InfLoopBlock);
730 NewSI->setSuccessor(i, InfLoopBlock);
739 // isSafeToHoistInvoke - If we would need to insert a select that uses the
740 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
741 // would need to do this), we can't hoist the invoke, as there is nowhere
742 // to put the select in this case.
743 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
744 Instruction *I1, Instruction *I2) {
745 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
747 for (BasicBlock::iterator BBI = SI->begin();
748 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
749 Value *BB1V = PN->getIncomingValueForBlock(BB1);
750 Value *BB2V = PN->getIncomingValueForBlock(BB2);
751 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
759 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
760 /// BB2, hoist any common code in the two blocks up into the branch block. The
761 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
762 static bool HoistThenElseCodeToIf(BranchInst *BI) {
763 // This does very trivial matching, with limited scanning, to find identical
764 // instructions in the two blocks. In particular, we don't want to get into
765 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
766 // such, we currently just scan for obviously identical instructions in an
768 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
769 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
771 BasicBlock::iterator BB1_Itr = BB1->begin();
772 BasicBlock::iterator BB2_Itr = BB2->begin();
774 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
775 while (isa<DbgInfoIntrinsic>(I1))
777 while (isa<DbgInfoIntrinsic>(I2))
779 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
780 !I1->isIdenticalToWhenDefined(I2) ||
781 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
784 // If we get here, we can hoist at least one instruction.
785 BasicBlock *BIParent = BI->getParent();
788 // If we are hoisting the terminator instruction, don't move one (making a
789 // broken BB), instead clone it, and remove BI.
790 if (isa<TerminatorInst>(I1))
791 goto HoistTerminator;
793 // For a normal instruction, we just move one to right before the branch,
794 // then replace all uses of the other with the first. Finally, we remove
795 // the now redundant second instruction.
796 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
797 if (!I2->use_empty())
798 I2->replaceAllUsesWith(I1);
799 I1->intersectOptionalDataWith(I2);
800 I2->eraseFromParent();
803 while (isa<DbgInfoIntrinsic>(I1))
806 while (isa<DbgInfoIntrinsic>(I2))
808 } while (I1->getOpcode() == I2->getOpcode() &&
809 I1->isIdenticalToWhenDefined(I2));
814 // It may not be possible to hoist an invoke.
815 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
818 // Okay, it is safe to hoist the terminator.
819 Instruction *NT = I1->clone();
820 BIParent->getInstList().insert(BI, NT);
821 if (!NT->getType()->isVoidTy()) {
822 I1->replaceAllUsesWith(NT);
823 I2->replaceAllUsesWith(NT);
827 // Hoisting one of the terminators from our successor is a great thing.
828 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
829 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
830 // nodes, so we insert select instruction to compute the final result.
831 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
832 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
834 for (BasicBlock::iterator BBI = SI->begin();
835 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
836 Value *BB1V = PN->getIncomingValueForBlock(BB1);
837 Value *BB2V = PN->getIncomingValueForBlock(BB2);
838 if (BB1V == BB2V) continue;
840 // These values do not agree. Insert a select instruction before NT
841 // that determines the right value.
842 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
844 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
845 BB1V->getName()+"."+BB2V->getName(), NT);
846 // Make the PHI node use the select for all incoming values for BB1/BB2
847 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
848 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
849 PN->setIncomingValue(i, SI);
853 // Update any PHI nodes in our new successors.
854 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
855 AddPredecessorToBlock(*SI, BIParent, BB1);
857 EraseTerminatorInstAndDCECond(BI);
861 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
862 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
863 /// (for now, restricted to a single instruction that's side effect free) from
864 /// the BB1 into the branch block to speculatively execute it.
865 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
866 // Only speculatively execution a single instruction (not counting the
867 // terminator) for now.
868 Instruction *HInst = NULL;
869 Instruction *Term = BB1->getTerminator();
870 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
872 Instruction *I = BBI;
874 if (isa<DbgInfoIntrinsic>(I)) continue;
875 if (I == Term) break;
884 // Be conservative for now. FP select instruction can often be expensive.
885 Value *BrCond = BI->getCondition();
886 if (isa<FCmpInst>(BrCond))
889 // If BB1 is actually on the false edge of the conditional branch, remember
890 // to swap the select operands later.
892 if (BB1 != BI->getSuccessor(0)) {
893 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
900 // br i1 %t1, label %BB1, label %BB2
909 // %t3 = select i1 %t1, %t2, %t3
910 switch (HInst->getOpcode()) {
911 default: return false; // Not safe / profitable to hoist.
912 case Instruction::Add:
913 case Instruction::Sub:
914 // Not worth doing for vector ops.
915 if (HInst->getType()->isVectorTy())
918 case Instruction::And:
919 case Instruction::Or:
920 case Instruction::Xor:
921 case Instruction::Shl:
922 case Instruction::LShr:
923 case Instruction::AShr:
924 // Don't mess with vector operations.
925 if (HInst->getType()->isVectorTy())
927 break; // These are all cheap and non-trapping instructions.
930 // If the instruction is obviously dead, don't try to predicate it.
931 if (HInst->use_empty()) {
932 HInst->eraseFromParent();
936 // Can we speculatively execute the instruction? And what is the value
937 // if the condition is false? Consider the phi uses, if the incoming value
938 // from the "if" block are all the same V, then V is the value of the
939 // select if the condition is false.
940 BasicBlock *BIParent = BI->getParent();
941 SmallVector<PHINode*, 4> PHIUses;
942 Value *FalseV = NULL;
944 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
945 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
947 // Ignore any user that is not a PHI node in BB2. These can only occur in
948 // unreachable blocks, because they would not be dominated by the instr.
949 PHINode *PN = dyn_cast<PHINode>(*UI);
950 if (!PN || PN->getParent() != BB2)
952 PHIUses.push_back(PN);
954 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
957 else if (FalseV != PHIV)
958 return false; // Inconsistent value when condition is false.
961 assert(FalseV && "Must have at least one user, and it must be a PHI");
963 // Do not hoist the instruction if any of its operands are defined but not
964 // used in this BB. The transformation will prevent the operand from
965 // being sunk into the use block.
966 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
968 Instruction *OpI = dyn_cast<Instruction>(*i);
969 if (OpI && OpI->getParent() == BIParent &&
970 !OpI->isUsedInBasicBlock(BIParent))
974 // If we get here, we can hoist the instruction. Try to place it
975 // before the icmp instruction preceding the conditional branch.
976 BasicBlock::iterator InsertPos = BI;
977 if (InsertPos != BIParent->begin())
979 // Skip debug info between condition and branch.
980 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
982 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
983 SmallPtrSet<Instruction *, 4> BB1Insns;
984 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
985 BB1I != BB1E; ++BB1I)
986 BB1Insns.insert(BB1I);
987 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
989 Instruction *Use = cast<Instruction>(*UI);
990 if (!BB1Insns.count(Use)) continue;
992 // If BrCond uses the instruction that place it just before
993 // branch instruction.
999 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
1001 // Create a select whose true value is the speculatively executed value and
1002 // false value is the previously determined FalseV.
1005 SI = SelectInst::Create(BrCond, FalseV, HInst,
1006 FalseV->getName() + "." + HInst->getName(), BI);
1008 SI = SelectInst::Create(BrCond, HInst, FalseV,
1009 HInst->getName() + "." + FalseV->getName(), BI);
1011 // Make the PHI node use the select for all incoming values for "then" and
1013 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1014 PHINode *PN = PHIUses[i];
1015 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1016 if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent)
1017 PN->setIncomingValue(j, SI);
1024 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1025 /// across this block.
1026 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1027 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1030 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1031 if (isa<DbgInfoIntrinsic>(BBI))
1033 if (Size > 10) return false; // Don't clone large BB's.
1036 // We can only support instructions that do not define values that are
1037 // live outside of the current basic block.
1038 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1040 Instruction *U = cast<Instruction>(*UI);
1041 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1044 // Looks ok, continue checking.
1050 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1051 /// that is defined in the same block as the branch and if any PHI entries are
1052 /// constants, thread edges corresponding to that entry to be branches to their
1053 /// ultimate destination.
1054 static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
1055 BasicBlock *BB = BI->getParent();
1056 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1057 // NOTE: we currently cannot transform this case if the PHI node is used
1058 // outside of the block.
1059 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1062 // Degenerate case of a single entry PHI.
1063 if (PN->getNumIncomingValues() == 1) {
1064 FoldSingleEntryPHINodes(PN->getParent());
1068 // Now we know that this block has multiple preds and two succs.
1069 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1071 // Okay, this is a simple enough basic block. See if any phi values are
1073 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1074 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1075 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1077 // Okay, we now know that all edges from PredBB should be revectored to
1078 // branch to RealDest.
1079 BasicBlock *PredBB = PN->getIncomingBlock(i);
1080 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1082 if (RealDest == BB) continue; // Skip self loops.
1084 // The dest block might have PHI nodes, other predecessors and other
1085 // difficult cases. Instead of being smart about this, just insert a new
1086 // block that jumps to the destination block, effectively splitting
1087 // the edge we are about to create.
1088 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1089 RealDest->getName()+".critedge",
1090 RealDest->getParent(), RealDest);
1091 BranchInst::Create(RealDest, EdgeBB);
1093 for (BasicBlock::iterator BBI = RealDest->begin();
1094 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1095 Value *V = PN->getIncomingValueForBlock(BB);
1096 PN->addIncoming(V, EdgeBB);
1099 // BB may have instructions that are being threaded over. Clone these
1100 // instructions into EdgeBB. We know that there will be no uses of the
1101 // cloned instructions outside of EdgeBB.
1102 BasicBlock::iterator InsertPt = EdgeBB->begin();
1103 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1104 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1105 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1106 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1109 // Clone the instruction.
1110 Instruction *N = BBI->clone();
1111 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1113 // Update operands due to translation.
1114 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1116 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1117 if (PI != TranslateMap.end())
1121 // Check for trivial simplification.
1122 if (Value *V = SimplifyInstruction(N, TD)) {
1123 TranslateMap[BBI] = V;
1124 delete N; // Instruction folded away, don't need actual inst
1126 // Insert the new instruction into its new home.
1127 EdgeBB->getInstList().insert(InsertPt, N);
1128 if (!BBI->use_empty())
1129 TranslateMap[BBI] = N;
1133 // Loop over all of the edges from PredBB to BB, changing them to branch
1134 // to EdgeBB instead.
1135 TerminatorInst *PredBBTI = PredBB->getTerminator();
1136 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1137 if (PredBBTI->getSuccessor(i) == BB) {
1138 BB->removePredecessor(PredBB);
1139 PredBBTI->setSuccessor(i, EdgeBB);
1142 // Recurse, simplifying any other constants.
1143 return FoldCondBranchOnPHI(BI, TD) | true;
1149 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1150 /// PHI node, see if we can eliminate it.
1151 static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
1152 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1153 // statement", which has a very simple dominance structure. Basically, we
1154 // are trying to find the condition that is being branched on, which
1155 // subsequently causes this merge to happen. We really want control
1156 // dependence information for this check, but simplifycfg can't keep it up
1157 // to date, and this catches most of the cases we care about anyway.
1158 BasicBlock *BB = PN->getParent();
1159 BasicBlock *IfTrue, *IfFalse;
1160 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1161 if (!IfCond) return false;
1163 // Okay, we found that we can merge this two-entry phi node into a select.
1164 // Doing so would require us to fold *all* two entry phi nodes in this block.
1165 // At some point this becomes non-profitable (particularly if the target
1166 // doesn't support cmov's). Only do this transformation if there are two or
1167 // fewer PHI nodes in this block.
1168 unsigned NumPhis = 0;
1169 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1173 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1174 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1176 // Loop over the PHI's seeing if we can promote them all to select
1177 // instructions. While we are at it, keep track of the instructions
1178 // that need to be moved to the dominating block.
1179 std::set<Instruction*> AggressiveInsts;
1181 BasicBlock::iterator AfterPHIIt = BB->begin();
1182 while (isa<PHINode>(AfterPHIIt)) {
1183 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1184 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1185 if (PN->getIncomingValue(0) != PN)
1186 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1188 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1189 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1190 &AggressiveInsts) ||
1191 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1192 &AggressiveInsts)) {
1197 // If we all PHI nodes are promotable, check to make sure that all
1198 // instructions in the predecessor blocks can be promoted as well. If
1199 // not, we won't be able to get rid of the control flow, so it's not
1200 // worth promoting to select instructions.
1201 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1202 PN = cast<PHINode>(BB->begin());
1203 BasicBlock *Pred = PN->getIncomingBlock(0);
1204 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1206 DomBlock = *pred_begin(Pred);
1207 for (BasicBlock::iterator I = Pred->begin();
1208 !isa<TerminatorInst>(I); ++I)
1209 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1210 // This is not an aggressive instruction that we can promote.
1211 // Because of this, we won't be able to get rid of the control
1212 // flow, so the xform is not worth it.
1217 Pred = PN->getIncomingBlock(1);
1218 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1220 DomBlock = *pred_begin(Pred);
1221 for (BasicBlock::iterator I = Pred->begin();
1222 !isa<TerminatorInst>(I); ++I)
1223 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1224 // This is not an aggressive instruction that we can promote.
1225 // Because of this, we won't be able to get rid of the control
1226 // flow, so the xform is not worth it.
1231 // If we can still promote the PHI nodes after this gauntlet of tests,
1232 // do all of the PHI's now.
1234 // Move all 'aggressive' instructions, which are defined in the
1235 // conditional parts of the if's up to the dominating block.
1237 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1238 IfBlock1->getInstList(), IfBlock1->begin(),
1239 IfBlock1->getTerminator());
1241 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1242 IfBlock2->getInstList(), IfBlock2->begin(),
1243 IfBlock2->getTerminator());
1245 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1246 // Change the PHI node into a select instruction.
1247 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1248 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1251 if (Value *V = SimplifySelectInst(IfCond, TrueVal, FalseVal, TD))
1253 else if (TrueVal->getType()->isIntegerTy(1) && isa<ConstantInt>(TrueVal) &&
1254 cast<ConstantInt>(TrueVal)->isOne()) {
1255 if (Value *V = SimplifyOrInst(IfCond, FalseVal, TD))
1258 NV = BinaryOperator::CreateOr(IfCond, FalseVal, "", AfterPHIIt);
1260 NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1261 PN->replaceAllUsesWith(NV);
1263 PN->eraseFromParent();
1268 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1269 /// to two returning blocks, try to merge them together into one return,
1270 /// introducing a select if the return values disagree.
1271 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1272 assert(BI->isConditional() && "Must be a conditional branch");
1273 BasicBlock *TrueSucc = BI->getSuccessor(0);
1274 BasicBlock *FalseSucc = BI->getSuccessor(1);
1275 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1276 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1278 // Check to ensure both blocks are empty (just a return) or optionally empty
1279 // with PHI nodes. If there are other instructions, merging would cause extra
1280 // computation on one path or the other.
1281 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1283 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1286 // Okay, we found a branch that is going to two return nodes. If
1287 // there is no return value for this function, just change the
1288 // branch into a return.
1289 if (FalseRet->getNumOperands() == 0) {
1290 TrueSucc->removePredecessor(BI->getParent());
1291 FalseSucc->removePredecessor(BI->getParent());
1292 ReturnInst::Create(BI->getContext(), 0, BI);
1293 EraseTerminatorInstAndDCECond(BI);
1297 // Otherwise, figure out what the true and false return values are
1298 // so we can insert a new select instruction.
1299 Value *TrueValue = TrueRet->getReturnValue();
1300 Value *FalseValue = FalseRet->getReturnValue();
1302 // Unwrap any PHI nodes in the return blocks.
1303 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1304 if (TVPN->getParent() == TrueSucc)
1305 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1306 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1307 if (FVPN->getParent() == FalseSucc)
1308 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1310 // In order for this transformation to be safe, we must be able to
1311 // unconditionally execute both operands to the return. This is
1312 // normally the case, but we could have a potentially-trapping
1313 // constant expression that prevents this transformation from being
1315 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1318 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1322 // Okay, we collected all the mapped values and checked them for sanity, and
1323 // defined to really do this transformation. First, update the CFG.
1324 TrueSucc->removePredecessor(BI->getParent());
1325 FalseSucc->removePredecessor(BI->getParent());
1327 // Insert select instructions where needed.
1328 Value *BrCond = BI->getCondition();
1330 // Insert a select if the results differ.
1331 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1332 } else if (isa<UndefValue>(TrueValue)) {
1333 TrueValue = FalseValue;
1335 TrueValue = SelectInst::Create(BrCond, TrueValue,
1336 FalseValue, "retval", BI);
1340 Value *RI = !TrueValue ?
1341 ReturnInst::Create(BI->getContext(), BI) :
1342 ReturnInst::Create(BI->getContext(), TrueValue, BI);
1345 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1346 << "\n " << *BI << "NewRet = " << *RI
1347 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1349 EraseTerminatorInstAndDCECond(BI);
1354 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1355 /// and if a predecessor branches to us and one of our successors, fold the
1356 /// setcc into the predecessor and use logical operations to pick the right
1358 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1359 BasicBlock *BB = BI->getParent();
1360 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1361 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1362 Cond->getParent() != BB || !Cond->hasOneUse())
1365 // Only allow this if the condition is a simple instruction that can be
1366 // executed unconditionally. It must be in the same block as the branch, and
1367 // must be at the front of the block.
1368 BasicBlock::iterator FrontIt = BB->front();
1369 // Ignore dbg intrinsics.
1370 while (isa<DbgInfoIntrinsic>(FrontIt))
1373 // Allow a single instruction to be hoisted in addition to the compare
1374 // that feeds the branch. We later ensure that any values that _it_ uses
1375 // were also live in the predecessor, so that we don't unnecessarily create
1376 // register pressure or inhibit out-of-order execution.
1377 Instruction *BonusInst = 0;
1378 if (&*FrontIt != Cond &&
1379 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1380 FrontIt->isSafeToSpeculativelyExecute()) {
1381 BonusInst = &*FrontIt;
1385 // Only a single bonus inst is allowed.
1386 if (&*FrontIt != Cond)
1389 // Make sure the instruction after the condition is the cond branch.
1390 BasicBlock::iterator CondIt = Cond; ++CondIt;
1391 // Ingore dbg intrinsics.
1392 while(isa<DbgInfoIntrinsic>(CondIt))
1394 if (&*CondIt != BI) {
1395 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!");
1399 // Cond is known to be a compare or binary operator. Check to make sure that
1400 // neither operand is a potentially-trapping constant expression.
1401 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1404 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1409 // Finally, don't infinitely unroll conditional loops.
1410 BasicBlock *TrueDest = BI->getSuccessor(0);
1411 BasicBlock *FalseDest = BI->getSuccessor(1);
1412 if (TrueDest == BB || FalseDest == BB)
1415 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1416 BasicBlock *PredBlock = *PI;
1417 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1419 // Check that we have two conditional branches. If there is a PHI node in
1420 // the common successor, verify that the same value flows in from both
1422 if (PBI == 0 || PBI->isUnconditional() ||
1423 !SafeToMergeTerminators(BI, PBI))
1426 // Ensure that any values used in the bonus instruction are also used
1427 // by the terminator of the predecessor. This means that those values
1428 // must already have been resolved, so we won't be inhibiting the
1429 // out-of-order core by speculating them earlier.
1431 // Collect the values used by the bonus inst
1432 SmallPtrSet<Value*, 4> UsedValues;
1433 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1434 OE = BonusInst->op_end(); OI != OE; ++OI) {
1436 if (!isa<Constant>(V))
1437 UsedValues.insert(V);
1440 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1441 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1443 // Walk up to four levels back up the use-def chain of the predecessor's
1444 // terminator to see if all those values were used. The choice of four
1445 // levels is arbitrary, to provide a compile-time-cost bound.
1446 while (!Worklist.empty()) {
1447 std::pair<Value*, unsigned> Pair = Worklist.back();
1448 Worklist.pop_back();
1450 if (Pair.second >= 4) continue;
1451 UsedValues.erase(Pair.first);
1452 if (UsedValues.empty()) break;
1454 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
1455 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1457 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1461 if (!UsedValues.empty()) return false;
1464 Instruction::BinaryOps Opc;
1465 bool InvertPredCond = false;
1467 if (PBI->getSuccessor(0) == TrueDest)
1468 Opc = Instruction::Or;
1469 else if (PBI->getSuccessor(1) == FalseDest)
1470 Opc = Instruction::And;
1471 else if (PBI->getSuccessor(0) == FalseDest)
1472 Opc = Instruction::And, InvertPredCond = true;
1473 else if (PBI->getSuccessor(1) == TrueDest)
1474 Opc = Instruction::Or, InvertPredCond = true;
1478 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1480 // If we need to invert the condition in the pred block to match, do so now.
1481 if (InvertPredCond) {
1482 Value *NewCond = PBI->getCondition();
1484 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
1485 CmpInst *CI = cast<CmpInst>(NewCond);
1486 CI->setPredicate(CI->getInversePredicate());
1488 NewCond = BinaryOperator::CreateNot(NewCond,
1489 PBI->getCondition()->getName()+".not", PBI);
1492 PBI->setCondition(NewCond);
1493 BasicBlock *OldTrue = PBI->getSuccessor(0);
1494 BasicBlock *OldFalse = PBI->getSuccessor(1);
1495 PBI->setSuccessor(0, OldFalse);
1496 PBI->setSuccessor(1, OldTrue);
1499 // If we have a bonus inst, clone it into the predecessor block.
1500 Instruction *NewBonus = 0;
1502 NewBonus = BonusInst->clone();
1503 PredBlock->getInstList().insert(PBI, NewBonus);
1504 NewBonus->takeName(BonusInst);
1505 BonusInst->setName(BonusInst->getName()+".old");
1508 // Clone Cond into the predecessor basic block, and or/and the
1509 // two conditions together.
1510 Instruction *New = Cond->clone();
1511 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1512 PredBlock->getInstList().insert(PBI, New);
1513 New->takeName(Cond);
1514 Cond->setName(New->getName()+".old");
1516 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1517 New, "or.cond", PBI);
1518 PBI->setCondition(NewCond);
1519 if (PBI->getSuccessor(0) == BB) {
1520 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1521 PBI->setSuccessor(0, TrueDest);
1523 if (PBI->getSuccessor(1) == BB) {
1524 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1525 PBI->setSuccessor(1, FalseDest);
1532 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1533 /// predecessor of another block, this function tries to simplify it. We know
1534 /// that PBI and BI are both conditional branches, and BI is in one of the
1535 /// successor blocks of PBI - PBI branches to BI.
1536 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1537 assert(PBI->isConditional() && BI->isConditional());
1538 BasicBlock *BB = BI->getParent();
1540 // If this block ends with a branch instruction, and if there is a
1541 // predecessor that ends on a branch of the same condition, make
1542 // this conditional branch redundant.
1543 if (PBI->getCondition() == BI->getCondition() &&
1544 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1545 // Okay, the outcome of this conditional branch is statically
1546 // knowable. If this block had a single pred, handle specially.
1547 if (BB->getSinglePredecessor()) {
1548 // Turn this into a branch on constant.
1549 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1550 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1552 return true; // Nuke the branch on constant.
1555 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1556 // in the constant and simplify the block result. Subsequent passes of
1557 // simplifycfg will thread the block.
1558 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1559 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1560 BI->getCondition()->getName() + ".pr",
1562 // Okay, we're going to insert the PHI node. Since PBI is not the only
1563 // predecessor, compute the PHI'd conditional value for all of the preds.
1564 // Any predecessor where the condition is not computable we keep symbolic.
1565 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1566 BasicBlock *P = *PI;
1567 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
1568 PBI != BI && PBI->isConditional() &&
1569 PBI->getCondition() == BI->getCondition() &&
1570 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1571 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1572 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1575 NewPN->addIncoming(BI->getCondition(), P);
1579 BI->setCondition(NewPN);
1584 // If this is a conditional branch in an empty block, and if any
1585 // predecessors is a conditional branch to one of our destinations,
1586 // fold the conditions into logical ops and one cond br.
1587 BasicBlock::iterator BBI = BB->begin();
1588 // Ignore dbg intrinsics.
1589 while (isa<DbgInfoIntrinsic>(BBI))
1595 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1600 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1602 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1603 PBIOp = 0, BIOp = 1;
1604 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1605 PBIOp = 1, BIOp = 0;
1606 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1611 // Check to make sure that the other destination of this branch
1612 // isn't BB itself. If so, this is an infinite loop that will
1613 // keep getting unwound.
1614 if (PBI->getSuccessor(PBIOp) == BB)
1617 // Do not perform this transformation if it would require
1618 // insertion of a large number of select instructions. For targets
1619 // without predication/cmovs, this is a big pessimization.
1620 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1622 unsigned NumPhis = 0;
1623 for (BasicBlock::iterator II = CommonDest->begin();
1624 isa<PHINode>(II); ++II, ++NumPhis)
1625 if (NumPhis > 2) // Disable this xform.
1628 // Finally, if everything is ok, fold the branches to logical ops.
1629 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1631 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
1632 << "AND: " << *BI->getParent());
1635 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1636 // branch in it, where one edge (OtherDest) goes back to itself but the other
1637 // exits. We don't *know* that the program avoids the infinite loop
1638 // (even though that seems likely). If we do this xform naively, we'll end up
1639 // recursively unpeeling the loop. Since we know that (after the xform is
1640 // done) that the block *is* infinite if reached, we just make it an obviously
1641 // infinite loop with no cond branch.
1642 if (OtherDest == BB) {
1643 // Insert it at the end of the function, because it's either code,
1644 // or it won't matter if it's hot. :)
1645 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1646 "infloop", BB->getParent());
1647 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1648 OtherDest = InfLoopBlock;
1651 DEBUG(dbgs() << *PBI->getParent()->getParent());
1653 // BI may have other predecessors. Because of this, we leave
1654 // it alone, but modify PBI.
1656 // Make sure we get to CommonDest on True&True directions.
1657 Value *PBICond = PBI->getCondition();
1659 PBICond = BinaryOperator::CreateNot(PBICond,
1660 PBICond->getName()+".not",
1662 Value *BICond = BI->getCondition();
1664 BICond = BinaryOperator::CreateNot(BICond,
1665 BICond->getName()+".not",
1667 // Merge the conditions.
1668 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1670 // Modify PBI to branch on the new condition to the new dests.
1671 PBI->setCondition(Cond);
1672 PBI->setSuccessor(0, CommonDest);
1673 PBI->setSuccessor(1, OtherDest);
1675 // OtherDest may have phi nodes. If so, add an entry from PBI's
1676 // block that are identical to the entries for BI's block.
1678 for (BasicBlock::iterator II = OtherDest->begin();
1679 (PN = dyn_cast<PHINode>(II)); ++II) {
1680 Value *V = PN->getIncomingValueForBlock(BB);
1681 PN->addIncoming(V, PBI->getParent());
1684 // We know that the CommonDest already had an edge from PBI to
1685 // it. If it has PHIs though, the PHIs may have different
1686 // entries for BB and PBI's BB. If so, insert a select to make
1688 for (BasicBlock::iterator II = CommonDest->begin();
1689 (PN = dyn_cast<PHINode>(II)); ++II) {
1690 Value *BIV = PN->getIncomingValueForBlock(BB);
1691 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1692 Value *PBIV = PN->getIncomingValue(PBBIdx);
1694 // Insert a select in PBI to pick the right value.
1695 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1696 PBIV->getName()+".mux", PBI);
1697 PN->setIncomingValue(PBBIdx, NV);
1701 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1702 DEBUG(dbgs() << *PBI->getParent()->getParent());
1704 // This basic block is probably dead. We know it has at least
1705 // one fewer predecessor.
1709 // SimplifyIndirectBrOnSelect - Replaces
1710 // (indirectbr (select cond, blockaddress(@fn, BlockA),
1711 // blockaddress(@fn, BlockB)))
1713 // (br cond, BlockA, BlockB).
1714 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
1715 // Check that both operands of the select are block addresses.
1716 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
1717 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
1721 // Extract the actual blocks.
1722 BasicBlock *TrueBB = TBA->getBasicBlock();
1723 BasicBlock *FalseBB = FBA->getBasicBlock();
1725 // Remove any superfluous successor edges from the CFG.
1726 // First, figure out which successors to preserve.
1727 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
1729 BasicBlock *KeepEdge1 = TrueBB;
1730 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
1732 // Then remove the rest.
1733 for (unsigned I = 0, E = IBI->getNumSuccessors(); I != E; ++I) {
1734 BasicBlock *Succ = IBI->getSuccessor(I);
1735 // Make sure only to keep exactly one copy of each edge.
1736 if (Succ == KeepEdge1)
1738 else if (Succ == KeepEdge2)
1741 Succ->removePredecessor(IBI->getParent());
1744 // Insert an appropriate new terminator.
1745 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
1746 if (TrueBB == FalseBB)
1747 // We were only looking for one successor, and it was present.
1748 // Create an unconditional branch to it.
1749 BranchInst::Create(TrueBB, IBI);
1751 // We found both of the successors we were looking for.
1752 // Create a conditional branch sharing the condition of the select.
1753 BranchInst::Create(TrueBB, FalseBB, SI->getCondition(), IBI);
1754 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
1755 // Neither of the selected blocks were successors, so this
1756 // indirectbr must be unreachable.
1757 new UnreachableInst(IBI->getContext(), IBI);
1759 // One of the selected values was a successor, but the other wasn't.
1760 // Insert an unconditional branch to the one that was found;
1761 // the edge to the one that wasn't must be unreachable.
1763 // Only TrueBB was found.
1764 BranchInst::Create(TrueBB, IBI);
1766 // Only FalseBB was found.
1767 BranchInst::Create(FalseBB, IBI);
1770 EraseTerminatorInstAndDCECond(IBI);
1774 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
1775 /// instruction (a seteq/setne with a constant) as the only instruction in a
1776 /// block that ends with an uncond branch. We are looking for a very specific
1777 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
1778 /// this case, we merge the first two "or's of icmp" into a switch, but then the
1779 /// default value goes to an uncond block with a seteq in it, we get something
1782 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
1784 /// %tmp = icmp eq i8 %A, 92
1787 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
1789 /// We prefer to split the edge to 'end' so that there is a true/false entry to
1790 /// the PHI, merging the third icmp into the switch.
1791 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
1792 const TargetData *TD) {
1793 BasicBlock *BB = ICI->getParent();
1794 // If the block has any PHIs in it or the icmp has multiple uses, it is too
1796 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
1798 Value *V = ICI->getOperand(0);
1799 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
1801 // The pattern we're looking for is where our only predecessor is a switch on
1802 // 'V' and this block is the default case for the switch. In this case we can
1803 // fold the compared value into the switch to simplify things.
1804 BasicBlock *Pred = BB->getSinglePredecessor();
1805 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
1807 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
1808 if (SI->getCondition() != V)
1811 // If BB is reachable on a non-default case, then we simply know the value of
1812 // V in this block. Substitute it and constant fold the icmp instruction
1814 if (SI->getDefaultDest() != BB) {
1815 ConstantInt *VVal = SI->findCaseDest(BB);
1816 assert(VVal && "Should have a unique destination value");
1817 ICI->setOperand(0, VVal);
1819 if (Value *V = SimplifyInstruction(ICI, TD)) {
1820 ICI->replaceAllUsesWith(V);
1821 ICI->eraseFromParent();
1823 // BB is now empty, so it is likely to simplify away.
1824 return SimplifyCFG(BB) | true;
1827 // Ok, the block is reachable from the default dest. If the constant we're
1828 // comparing exists in one of the other edges, then we can constant fold ICI
1830 if (SI->findCaseValue(Cst) != 0) {
1832 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1833 V = ConstantInt::getFalse(BB->getContext());
1835 V = ConstantInt::getTrue(BB->getContext());
1837 ICI->replaceAllUsesWith(V);
1838 ICI->eraseFromParent();
1839 // BB is now empty, so it is likely to simplify away.
1840 return SimplifyCFG(BB) | true;
1843 // The use of the icmp has to be in the 'end' block, by the only PHI node in
1845 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
1846 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
1847 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
1848 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
1851 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
1853 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
1854 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
1856 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1857 std::swap(DefaultCst, NewCst);
1859 // Replace ICI (which is used by the PHI for the default value) with true or
1860 // false depending on if it is EQ or NE.
1861 ICI->replaceAllUsesWith(DefaultCst);
1862 ICI->eraseFromParent();
1864 // Okay, the switch goes to this block on a default value. Add an edge from
1865 // the switch to the merge point on the compared value.
1866 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
1867 BB->getParent(), BB);
1868 SI->addCase(Cst, NewBB);
1870 // NewBB branches to the phi block, add the uncond branch and the phi entry.
1871 BranchInst::Create(SuccBlock, NewBB);
1872 PHIUse->addIncoming(NewCst, NewBB);
1876 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
1877 /// Check to see if it is branching on an or/and chain of icmp instructions, and
1878 /// fold it into a switch instruction if so.
1879 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD) {
1880 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1881 if (Cond == 0) return false;
1884 // Change br (X == 0 | X == 1), T, F into a switch instruction.
1885 // If this is a bunch of seteq's or'd together, or if it's a bunch of
1886 // 'setne's and'ed together, collect them.
1888 std::vector<ConstantInt*> Values;
1889 bool TrueWhenEqual = true;
1890 Value *ExtraCase = 0;
1892 if (Cond->getOpcode() == Instruction::Or) {
1893 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true);
1894 } else if (Cond->getOpcode() == Instruction::And) {
1895 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false);
1896 TrueWhenEqual = false;
1899 // If we didn't have a multiply compared value, fail.
1900 if (CompVal == 0) return false;
1902 // There might be duplicate constants in the list, which the switch
1903 // instruction can't handle, remove them now.
1904 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
1905 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
1907 // If Extra was used, we require at least two switch values to do the
1908 // transformation. A switch with one value is just an cond branch.
1909 if (ExtraCase && Values.size() < 2) return false;
1911 // Figure out which block is which destination.
1912 BasicBlock *DefaultBB = BI->getSuccessor(1);
1913 BasicBlock *EdgeBB = BI->getSuccessor(0);
1914 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
1916 BasicBlock *BB = BI->getParent();
1918 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
1919 << " cases into SWITCH. BB is:\n" << *BB);
1921 // If there are any extra values that couldn't be folded into the switch
1922 // then we evaluate them with an explicit branch first. Split the block
1923 // right before the condbr to handle it.
1925 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
1926 // Remove the uncond branch added to the old block.
1927 TerminatorInst *OldTI = BB->getTerminator();
1930 BranchInst::Create(EdgeBB, NewBB, ExtraCase, OldTI);
1932 BranchInst::Create(NewBB, EdgeBB, ExtraCase, OldTI);
1934 OldTI->eraseFromParent();
1936 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
1937 // for the edge we just added.
1938 for (BasicBlock::iterator I = EdgeBB->begin(); isa<PHINode>(I); ++I) {
1939 PHINode *PN = cast<PHINode>(I);
1940 PN->addIncoming(PN->getIncomingValueForBlock(NewBB), BB);
1943 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
1944 << "\nEXTRABB = " << *BB);
1948 // Convert pointer to int before we switch.
1949 if (CompVal->getType()->isPointerTy()) {
1950 assert(TD && "Cannot switch on pointer without TargetData");
1951 CompVal = new PtrToIntInst(CompVal,
1952 TD->getIntPtrType(CompVal->getContext()),
1956 // Create the new switch instruction now.
1957 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB, Values.size(), BI);
1959 // Add all of the 'cases' to the switch instruction.
1960 for (unsigned i = 0, e = Values.size(); i != e; ++i)
1961 New->addCase(Values[i], EdgeBB);
1963 // We added edges from PI to the EdgeBB. As such, if there were any
1964 // PHI nodes in EdgeBB, they need entries to be added corresponding to
1965 // the number of edges added.
1966 for (BasicBlock::iterator BBI = EdgeBB->begin();
1967 isa<PHINode>(BBI); ++BBI) {
1968 PHINode *PN = cast<PHINode>(BBI);
1969 Value *InVal = PN->getIncomingValueForBlock(BB);
1970 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
1971 PN->addIncoming(InVal, BB);
1974 // Erase the old branch instruction.
1975 EraseTerminatorInstAndDCECond(BI);
1977 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
1981 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI) {
1982 BasicBlock *BB = RI->getParent();
1983 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
1985 // Find predecessors that end with branches.
1986 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1987 SmallVector<BranchInst*, 8> CondBranchPreds;
1988 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1989 BasicBlock *P = *PI;
1990 TerminatorInst *PTI = P->getTerminator();
1991 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1992 if (BI->isUnconditional())
1993 UncondBranchPreds.push_back(P);
1995 CondBranchPreds.push_back(BI);
1999 // If we found some, do the transformation!
2000 if (!UncondBranchPreds.empty()) {
2001 while (!UncondBranchPreds.empty()) {
2002 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2003 DEBUG(dbgs() << "FOLDING: " << *BB
2004 << "INTO UNCOND BRANCH PRED: " << *Pred);
2005 Instruction *UncondBranch = Pred->getTerminator();
2006 // Clone the return and add it to the end of the predecessor.
2007 Instruction *NewRet = RI->clone();
2008 Pred->getInstList().push_back(NewRet);
2010 // If the return instruction returns a value, and if the value was a
2011 // PHI node in "BB", propagate the right value into the return.
2012 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
2014 if (PHINode *PN = dyn_cast<PHINode>(*i))
2015 if (PN->getParent() == BB)
2016 *i = PN->getIncomingValueForBlock(Pred);
2018 // Update any PHI nodes in the returning block to realize that we no
2019 // longer branch to them.
2020 BB->removePredecessor(Pred);
2021 UncondBranch->eraseFromParent();
2024 // If we eliminated all predecessors of the block, delete the block now.
2025 if (pred_begin(BB) == pred_end(BB))
2026 // We know there are no successors, so just nuke the block.
2027 BB->eraseFromParent();
2032 // Check out all of the conditional branches going to this return
2033 // instruction. If any of them just select between returns, change the
2034 // branch itself into a select/return pair.
2035 while (!CondBranchPreds.empty()) {
2036 BranchInst *BI = CondBranchPreds.pop_back_val();
2038 // Check to see if the non-BB successor is also a return block.
2039 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2040 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2041 SimplifyCondBranchToTwoReturns(BI))
2047 bool SimplifyCFGOpt::SimplifyUnwind(UnwindInst *UI) {
2048 // Check to see if the first instruction in this block is just an unwind.
2049 // If so, replace any invoke instructions which use this as an exception
2050 // destination with call instructions.
2051 BasicBlock *BB = UI->getParent();
2052 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2054 bool Changed = false;
2055 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2056 while (!Preds.empty()) {
2057 BasicBlock *Pred = Preds.back();
2058 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
2059 if (II && II->getUnwindDest() == BB) {
2060 // Insert a new branch instruction before the invoke, because this
2061 // is now a fall through.
2062 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2063 Pred->getInstList().remove(II); // Take out of symbol table
2065 // Insert the call now.
2066 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
2067 CallInst *CI = CallInst::Create(II->getCalledValue(),
2068 Args.begin(), Args.end(),
2070 CI->setCallingConv(II->getCallingConv());
2071 CI->setAttributes(II->getAttributes());
2072 // If the invoke produced a value, the Call now does instead.
2073 II->replaceAllUsesWith(CI);
2081 // If this block is now dead (and isn't the entry block), remove it.
2082 if (pred_begin(BB) == pred_end(BB) &&
2083 BB != &BB->getParent()->getEntryBlock()) {
2084 // We know there are no successors, so just nuke the block.
2085 BB->eraseFromParent();
2092 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2093 BasicBlock *BB = UI->getParent();
2095 bool Changed = false;
2097 // If there are any instructions immediately before the unreachable that can
2098 // be removed, do so.
2099 while (UI != BB->begin()) {
2100 BasicBlock::iterator BBI = UI;
2102 // Do not delete instructions that can have side effects, like calls
2103 // (which may never return) and volatile loads and stores.
2104 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2106 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
2107 if (SI->isVolatile())
2110 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
2111 if (LI->isVolatile())
2114 // Delete this instruction
2115 BBI->eraseFromParent();
2119 // If the unreachable instruction is the first in the block, take a gander
2120 // at all of the predecessors of this instruction, and simplify them.
2121 if (&BB->front() != UI) return Changed;
2123 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2124 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2125 TerminatorInst *TI = Preds[i]->getTerminator();
2127 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2128 if (BI->isUnconditional()) {
2129 if (BI->getSuccessor(0) == BB) {
2130 new UnreachableInst(TI->getContext(), TI);
2131 TI->eraseFromParent();
2135 if (BI->getSuccessor(0) == BB) {
2136 BranchInst::Create(BI->getSuccessor(1), BI);
2137 EraseTerminatorInstAndDCECond(BI);
2138 } else if (BI->getSuccessor(1) == BB) {
2139 BranchInst::Create(BI->getSuccessor(0), BI);
2140 EraseTerminatorInstAndDCECond(BI);
2144 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2145 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2146 if (SI->getSuccessor(i) == BB) {
2147 BB->removePredecessor(SI->getParent());
2152 // If the default value is unreachable, figure out the most popular
2153 // destination and make it the default.
2154 if (SI->getSuccessor(0) == BB) {
2155 std::map<BasicBlock*, unsigned> Popularity;
2156 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2157 Popularity[SI->getSuccessor(i)]++;
2159 // Find the most popular block.
2160 unsigned MaxPop = 0;
2161 BasicBlock *MaxBlock = 0;
2162 for (std::map<BasicBlock*, unsigned>::iterator
2163 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2164 if (I->second > MaxPop) {
2166 MaxBlock = I->first;
2170 // Make this the new default, allowing us to delete any explicit
2172 SI->setSuccessor(0, MaxBlock);
2175 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2177 if (isa<PHINode>(MaxBlock->begin()))
2178 for (unsigned i = 0; i != MaxPop-1; ++i)
2179 MaxBlock->removePredecessor(SI->getParent());
2181 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2182 if (SI->getSuccessor(i) == MaxBlock) {
2188 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2189 if (II->getUnwindDest() == BB) {
2190 // Convert the invoke to a call instruction. This would be a good
2191 // place to note that the call does not throw though.
2192 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2193 II->removeFromParent(); // Take out of symbol table
2195 // Insert the call now...
2196 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2197 CallInst *CI = CallInst::Create(II->getCalledValue(),
2198 Args.begin(), Args.end(),
2200 CI->setCallingConv(II->getCallingConv());
2201 CI->setAttributes(II->getAttributes());
2202 // If the invoke produced a value, the call does now instead.
2203 II->replaceAllUsesWith(CI);
2210 // If this block is now dead, remove it.
2211 if (pred_begin(BB) == pred_end(BB) &&
2212 BB != &BB->getParent()->getEntryBlock()) {
2213 // We know there are no successors, so just nuke the block.
2214 BB->eraseFromParent();
2222 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI) {
2223 // If this switch is too complex to want to look at, ignore it.
2224 if (!isValueEqualityComparison(SI))
2227 BasicBlock *BB = SI->getParent();
2229 // If we only have one predecessor, and if it is a branch on this value,
2230 // see if that predecessor totally determines the outcome of this switch.
2231 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2232 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
2233 return SimplifyCFG(BB) | true;
2235 // If the block only contains the switch, see if we can fold the block
2236 // away into any preds.
2237 BasicBlock::iterator BBI = BB->begin();
2238 // Ignore dbg intrinsics.
2239 while (isa<DbgInfoIntrinsic>(BBI))
2242 if (FoldValueComparisonIntoPredecessors(SI))
2243 return SimplifyCFG(BB) | true;
2248 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
2249 BasicBlock *BB = IBI->getParent();
2250 bool Changed = false;
2252 // Eliminate redundant destinations.
2253 SmallPtrSet<Value *, 8> Succs;
2254 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2255 BasicBlock *Dest = IBI->getDestination(i);
2256 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2257 Dest->removePredecessor(BB);
2258 IBI->removeDestination(i);
2264 if (IBI->getNumDestinations() == 0) {
2265 // If the indirectbr has no successors, change it to unreachable.
2266 new UnreachableInst(IBI->getContext(), IBI);
2267 EraseTerminatorInstAndDCECond(IBI);
2271 if (IBI->getNumDestinations() == 1) {
2272 // If the indirectbr has one successor, change it to a direct branch.
2273 BranchInst::Create(IBI->getDestination(0), IBI);
2274 EraseTerminatorInstAndDCECond(IBI);
2278 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2279 if (SimplifyIndirectBrOnSelect(IBI, SI))
2280 return SimplifyCFG(BB) | true;
2285 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI) {
2286 BasicBlock *BB = BI->getParent();
2288 // If the Terminator is the only non-phi instruction, simplify the block.
2289 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg();
2290 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
2291 TryToSimplifyUncondBranchFromEmptyBlock(BB))
2294 // If the only instruction in the block is a seteq/setne comparison
2295 // against a constant, try to simplify the block.
2296 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
2297 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
2298 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
2300 if (I->isTerminator() && TryToSimplifyUncondBranchWithICmpInIt(ICI, TD))
2308 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI) {
2309 BasicBlock *BB = BI->getParent();
2311 // Conditional branch
2312 if (isValueEqualityComparison(BI)) {
2313 // If we only have one predecessor, and if it is a branch on this value,
2314 // see if that predecessor totally determines the outcome of this
2316 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2317 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
2318 return SimplifyCFG(BB) | true;
2320 // This block must be empty, except for the setcond inst, if it exists.
2321 // Ignore dbg intrinsics.
2322 BasicBlock::iterator I = BB->begin();
2323 // Ignore dbg intrinsics.
2324 while (isa<DbgInfoIntrinsic>(I))
2327 if (FoldValueComparisonIntoPredecessors(BI))
2328 return SimplifyCFG(BB) | true;
2329 } else if (&*I == cast<Instruction>(BI->getCondition())){
2331 // Ignore dbg intrinsics.
2332 while (isa<DbgInfoIntrinsic>(I))
2334 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI))
2335 return SimplifyCFG(BB) | true;
2339 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
2340 if (SimplifyBranchOnICmpChain(BI, TD))
2343 // We have a conditional branch to two blocks that are only reachable
2344 // from BI. We know that the condbr dominates the two blocks, so see if
2345 // there is any identical code in the "then" and "else" blocks. If so, we
2346 // can hoist it up to the branching block.
2347 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
2348 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2349 if (HoistThenElseCodeToIf(BI))
2350 return SimplifyCFG(BB) | true;
2352 // If Successor #1 has multiple preds, we may be able to conditionally
2353 // execute Successor #0 if it branches to successor #1.
2354 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
2355 if (Succ0TI->getNumSuccessors() == 1 &&
2356 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
2357 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
2358 return SimplifyCFG(BB) | true;
2360 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2361 // If Successor #0 has multiple preds, we may be able to conditionally
2362 // execute Successor #1 if it branches to successor #0.
2363 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
2364 if (Succ1TI->getNumSuccessors() == 1 &&
2365 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
2366 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
2367 return SimplifyCFG(BB) | true;
2370 // If this is a branch on a phi node in the current block, thread control
2371 // through this block if any PHI node entries are constants.
2372 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
2373 if (PN->getParent() == BI->getParent())
2374 if (FoldCondBranchOnPHI(BI, TD))
2375 return SimplifyCFG(BB) | true;
2377 // If this basic block is ONLY a setcc and a branch, and if a predecessor
2378 // branches to us and one of our successors, fold the setcc into the
2379 // predecessor and use logical operations to pick the right destination.
2380 if (FoldBranchToCommonDest(BI))
2381 return SimplifyCFG(BB) | true;
2383 // Scan predecessor blocks for conditional branches.
2384 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2385 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2386 if (PBI != BI && PBI->isConditional())
2387 if (SimplifyCondBranchToCondBranch(PBI, BI))
2388 return SimplifyCFG(BB) | true;
2393 bool SimplifyCFGOpt::run(BasicBlock *BB) {
2394 bool Changed = false;
2396 assert(BB && BB->getParent() && "Block not embedded in function!");
2397 assert(BB->getTerminator() && "Degenerate basic block encountered!");
2399 // Remove basic blocks that have no predecessors (except the entry block)...
2400 // or that just have themself as a predecessor. These are unreachable.
2401 if ((pred_begin(BB) == pred_end(BB) &&
2402 BB != &BB->getParent()->getEntryBlock()) ||
2403 BB->getSinglePredecessor() == BB) {
2404 DEBUG(dbgs() << "Removing BB: \n" << *BB);
2405 DeleteDeadBlock(BB);
2409 // Check to see if we can constant propagate this terminator instruction
2411 Changed |= ConstantFoldTerminator(BB);
2413 // Check for and eliminate duplicate PHI nodes in this block.
2414 Changed |= EliminateDuplicatePHINodes(BB);
2416 // Merge basic blocks into their predecessor if there is only one distinct
2417 // pred, and if there is only one distinct successor of the predecessor, and
2418 // if there are no PHI nodes.
2420 if (MergeBlockIntoPredecessor(BB))
2423 // If there is a trivial two-entry PHI node in this basic block, and we can
2424 // eliminate it, do so now.
2425 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
2426 if (PN->getNumIncomingValues() == 2)
2427 Changed |= FoldTwoEntryPHINode(PN, TD);
2429 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
2430 if (BI->isUnconditional()) {
2431 if (SimplifyUncondBranch(BI)) return true;
2433 if (SimplifyCondBranch(BI)) return true;
2435 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
2436 if (SimplifyReturn(RI)) return true;
2437 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
2438 if (SimplifySwitch(SI)) return true;
2439 } else if (UnreachableInst *UI =
2440 dyn_cast<UnreachableInst>(BB->getTerminator())) {
2441 if (SimplifyUnreachable(UI)) return true;
2442 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
2443 if (SimplifyUnwind(UI)) return true;
2444 } else if (IndirectBrInst *IBI =
2445 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
2446 if (SimplifyIndirectBr(IBI)) return true;
2452 /// SimplifyCFG - This function is used to do simplification of a CFG. For
2453 /// example, it adjusts branches to branches to eliminate the extra hop, it
2454 /// eliminates unreachable basic blocks, and does other "peephole" optimization
2455 /// of the CFG. It returns true if a modification was made.
2457 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
2458 return SimplifyCFGOpt(TD).run(BB);