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/Support/CFG.h"
23 #include "llvm/Support/Debug.h"
24 #include "llvm/Support/raw_ostream.h"
25 #include "llvm/Analysis/ConstantFolding.h"
26 #include "llvm/Target/TargetData.h"
27 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
28 #include "llvm/ADT/DenseMap.h"
29 #include "llvm/ADT/SmallVector.h"
30 #include "llvm/ADT/SmallPtrSet.h"
31 #include "llvm/ADT/Statistic.h"
32 #include "llvm/ADT/STLExtras.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);
52 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
53 bool run(BasicBlock *BB);
57 /// SafeToMergeTerminators - Return true if it is safe to merge these two
58 /// terminator instructions together.
60 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
61 if (SI1 == SI2) return false; // Can't merge with self!
63 // It is not safe to merge these two switch instructions if they have a common
64 // successor, and if that successor has a PHI node, and if *that* PHI node has
65 // conflicting incoming values from the two switch blocks.
66 BasicBlock *SI1BB = SI1->getParent();
67 BasicBlock *SI2BB = SI2->getParent();
68 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
70 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
71 if (SI1Succs.count(*I))
72 for (BasicBlock::iterator BBI = (*I)->begin();
73 isa<PHINode>(BBI); ++BBI) {
74 PHINode *PN = cast<PHINode>(BBI);
75 if (PN->getIncomingValueForBlock(SI1BB) !=
76 PN->getIncomingValueForBlock(SI2BB))
83 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
84 /// now be entries in it from the 'NewPred' block. The values that will be
85 /// flowing into the PHI nodes will be the same as those coming in from
86 /// ExistPred, an existing predecessor of Succ.
87 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
88 BasicBlock *ExistPred) {
89 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
90 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
91 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
94 for (BasicBlock::iterator I = Succ->begin();
95 (PN = dyn_cast<PHINode>(I)); ++I)
96 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
100 /// GetIfCondition - Given a basic block (BB) with two predecessors (and
101 /// presumably PHI nodes in it), check to see if the merge at this block is due
102 /// to an "if condition". If so, return the boolean condition that determines
103 /// which entry into BB will be taken. Also, return by references the block
104 /// that will be entered from if the condition is true, and the block that will
105 /// be entered if the condition is false.
108 static Value *GetIfCondition(BasicBlock *BB,
109 BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
110 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
111 "Function can only handle blocks with 2 predecessors!");
112 BasicBlock *Pred1 = *pred_begin(BB);
113 BasicBlock *Pred2 = *++pred_begin(BB);
115 // We can only handle branches. Other control flow will be lowered to
116 // branches if possible anyway.
117 if (!isa<BranchInst>(Pred1->getTerminator()) ||
118 !isa<BranchInst>(Pred2->getTerminator()))
120 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
121 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
123 // Eliminate code duplication by ensuring that Pred1Br is conditional if
125 if (Pred2Br->isConditional()) {
126 // If both branches are conditional, we don't have an "if statement". In
127 // reality, we could transform this case, but since the condition will be
128 // required anyway, we stand no chance of eliminating it, so the xform is
129 // probably not profitable.
130 if (Pred1Br->isConditional())
133 std::swap(Pred1, Pred2);
134 std::swap(Pred1Br, Pred2Br);
137 if (Pred1Br->isConditional()) {
138 // If we found a conditional branch predecessor, make sure that it branches
139 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
140 if (Pred1Br->getSuccessor(0) == BB &&
141 Pred1Br->getSuccessor(1) == Pred2) {
144 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
145 Pred1Br->getSuccessor(1) == BB) {
149 // We know that one arm of the conditional goes to BB, so the other must
150 // go somewhere unrelated, and this must not be an "if statement".
154 // The only thing we have to watch out for here is to make sure that Pred2
155 // doesn't have incoming edges from other blocks. If it does, the condition
156 // doesn't dominate BB.
157 if (++pred_begin(Pred2) != pred_end(Pred2))
160 return Pred1Br->getCondition();
163 // Ok, if we got here, both predecessors end with an unconditional branch to
164 // BB. Don't panic! If both blocks only have a single (identical)
165 // predecessor, and THAT is a conditional branch, then we're all ok!
166 if (pred_begin(Pred1) == pred_end(Pred1) ||
167 ++pred_begin(Pred1) != pred_end(Pred1) ||
168 pred_begin(Pred2) == pred_end(Pred2) ||
169 ++pred_begin(Pred2) != pred_end(Pred2) ||
170 *pred_begin(Pred1) != *pred_begin(Pred2))
173 // Otherwise, if this is a conditional branch, then we can use it!
174 BasicBlock *CommonPred = *pred_begin(Pred1);
175 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
176 assert(BI->isConditional() && "Two successors but not conditional?");
177 if (BI->getSuccessor(0) == Pred1) {
184 return BI->getCondition();
189 /// DominatesMergePoint - If we have a merge point of an "if condition" as
190 /// accepted above, return true if the specified value dominates the block. We
191 /// don't handle the true generality of domination here, just a special case
192 /// which works well enough for us.
194 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
195 /// see if V (which must be an instruction) is cheap to compute and is
196 /// non-trapping. If both are true, the instruction is inserted into the set
197 /// and true is returned.
198 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
199 std::set<Instruction*> *AggressiveInsts) {
200 Instruction *I = dyn_cast<Instruction>(V);
202 // Non-instructions all dominate instructions, but not all constantexprs
203 // can be executed unconditionally.
204 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
209 BasicBlock *PBB = I->getParent();
211 // We don't want to allow weird loops that might have the "if condition" in
212 // the bottom of this block.
213 if (PBB == BB) return false;
215 // If this instruction is defined in a block that contains an unconditional
216 // branch to BB, then it must be in the 'conditional' part of the "if
218 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
219 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
220 if (!AggressiveInsts) return false;
221 // Okay, it looks like the instruction IS in the "condition". Check to
222 // see if it's a cheap instruction to unconditionally compute, and if it
223 // only uses stuff defined outside of the condition. If so, hoist it out.
224 if (!I->isSafeToSpeculativelyExecute())
227 switch (I->getOpcode()) {
228 default: return false; // Cannot hoist this out safely.
229 case Instruction::Load: {
230 // We have to check to make sure there are no instructions before the
231 // load in its basic block, as we are going to hoist the loop out to
233 BasicBlock::iterator IP = PBB->begin();
234 while (isa<DbgInfoIntrinsic>(IP))
236 if (IP != BasicBlock::iterator(I))
240 case Instruction::Add:
241 case Instruction::Sub:
242 case Instruction::And:
243 case Instruction::Or:
244 case Instruction::Xor:
245 case Instruction::Shl:
246 case Instruction::LShr:
247 case Instruction::AShr:
248 case Instruction::ICmp:
249 break; // These are all cheap and non-trapping instructions.
252 // Okay, we can only really hoist these out if their operands are not
253 // defined in the conditional region.
254 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
255 if (!DominatesMergePoint(*i, BB, 0))
257 // Okay, it's safe to do this! Remember this instruction.
258 AggressiveInsts->insert(I);
264 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
265 /// and PointerNullValue. Return NULL if value is not a constant int.
266 static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
267 // Normal constant int.
268 ConstantInt *CI = dyn_cast<ConstantInt>(V);
269 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
272 // This is some kind of pointer constant. Turn it into a pointer-sized
273 // ConstantInt if possible.
274 const IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
276 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
277 if (isa<ConstantPointerNull>(V))
278 return ConstantInt::get(PtrTy, 0);
280 // IntToPtr const int.
281 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
282 if (CE->getOpcode() == Instruction::IntToPtr)
283 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
284 // The constant is very likely to have the right type already.
285 if (CI->getType() == PtrTy)
288 return cast<ConstantInt>
289 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
294 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
295 /// collection of icmp eq/ne instructions that compare a value against a
296 /// constant, return the value being compared, and stick the constant into the
299 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
300 const TargetData *TD, bool isEQ) {
301 Instruction *I = dyn_cast<Instruction>(V);
302 if (I == 0) return 0;
304 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
305 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE))
306 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
308 return I->getOperand(0);
313 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
316 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
318 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
327 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
328 Instruction* Cond = 0;
329 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
330 Cond = dyn_cast<Instruction>(SI->getCondition());
331 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
332 if (BI->isConditional())
333 Cond = dyn_cast<Instruction>(BI->getCondition());
334 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
335 Cond = dyn_cast<Instruction>(IBI->getAddress());
338 TI->eraseFromParent();
339 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
342 /// isValueEqualityComparison - Return true if the specified terminator checks
343 /// to see if a value is equal to constant integer value.
344 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
346 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
347 // Do not permit merging of large switch instructions into their
348 // predecessors unless there is only one predecessor.
349 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
350 pred_end(SI->getParent())) <= 128)
351 CV = SI->getCondition();
352 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
353 if (BI->isConditional() && BI->getCondition()->hasOneUse())
354 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
355 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
356 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
357 GetConstantInt(ICI->getOperand(1), TD))
358 CV = ICI->getOperand(0);
360 // Unwrap any lossless ptrtoint cast.
361 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
362 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
363 CV = PTII->getOperand(0);
367 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
368 /// decode all of the 'cases' that it represents and return the 'default' block.
369 BasicBlock *SimplifyCFGOpt::
370 GetValueEqualityComparisonCases(TerminatorInst *TI,
371 std::vector<std::pair<ConstantInt*,
372 BasicBlock*> > &Cases) {
373 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
374 Cases.reserve(SI->getNumCases());
375 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
376 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
377 return SI->getDefaultDest();
380 BranchInst *BI = cast<BranchInst>(TI);
381 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
382 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD),
383 BI->getSuccessor(ICI->getPredicate() ==
384 ICmpInst::ICMP_NE)));
385 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
389 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
390 /// in the list that match the specified block.
391 static void EliminateBlockCases(BasicBlock *BB,
392 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
393 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
394 if (Cases[i].second == BB) {
395 Cases.erase(Cases.begin()+i);
400 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
403 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
404 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
405 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
407 // Make V1 be smaller than V2.
408 if (V1->size() > V2->size())
411 if (V1->size() == 0) return false;
412 if (V1->size() == 1) {
414 ConstantInt *TheVal = (*V1)[0].first;
415 for (unsigned i = 0, e = V2->size(); i != e; ++i)
416 if (TheVal == (*V2)[i].first)
420 // Otherwise, just sort both lists and compare element by element.
421 array_pod_sort(V1->begin(), V1->end());
422 array_pod_sort(V2->begin(), V2->end());
423 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
424 while (i1 != e1 && i2 != e2) {
425 if ((*V1)[i1].first == (*V2)[i2].first)
427 if ((*V1)[i1].first < (*V2)[i2].first)
435 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
436 /// terminator instruction and its block is known to only have a single
437 /// predecessor block, check to see if that predecessor is also a value
438 /// comparison with the same value, and if that comparison determines the
439 /// outcome of this comparison. If so, simplify TI. This does a very limited
440 /// form of jump threading.
441 bool SimplifyCFGOpt::
442 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
444 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
445 if (!PredVal) return false; // Not a value comparison in predecessor.
447 Value *ThisVal = isValueEqualityComparison(TI);
448 assert(ThisVal && "This isn't a value comparison!!");
449 if (ThisVal != PredVal) return false; // Different predicates.
451 // Find out information about when control will move from Pred to TI's block.
452 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
453 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
455 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
457 // Find information about how control leaves this block.
458 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
459 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
460 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
462 // If TI's block is the default block from Pred's comparison, potentially
463 // simplify TI based on this knowledge.
464 if (PredDef == TI->getParent()) {
465 // If we are here, we know that the value is none of those cases listed in
466 // PredCases. If there are any cases in ThisCases that are in PredCases, we
468 if (!ValuesOverlap(PredCases, ThisCases))
471 if (isa<BranchInst>(TI)) {
472 // Okay, one of the successors of this condbr is dead. Convert it to a
474 assert(ThisCases.size() == 1 && "Branch can only have one case!");
475 // Insert the new branch.
476 Instruction *NI = BranchInst::Create(ThisDef, TI);
479 // Remove PHI node entries for the dead edge.
480 ThisCases[0].second->removePredecessor(TI->getParent());
482 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
483 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
485 EraseTerminatorInstAndDCECond(TI);
489 SwitchInst *SI = cast<SwitchInst>(TI);
490 // Okay, TI has cases that are statically dead, prune them away.
491 SmallPtrSet<Constant*, 16> DeadCases;
492 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
493 DeadCases.insert(PredCases[i].first);
495 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
496 << "Through successor TI: " << *TI);
498 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
499 if (DeadCases.count(SI->getCaseValue(i))) {
500 SI->getSuccessor(i)->removePredecessor(TI->getParent());
504 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
508 // Otherwise, TI's block must correspond to some matched value. Find out
509 // which value (or set of values) this is.
510 ConstantInt *TIV = 0;
511 BasicBlock *TIBB = TI->getParent();
512 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
513 if (PredCases[i].second == TIBB) {
515 return false; // Cannot handle multiple values coming to this block.
516 TIV = PredCases[i].first;
518 assert(TIV && "No edge from pred to succ?");
520 // Okay, we found the one constant that our value can be if we get into TI's
521 // BB. Find out which successor will unconditionally be branched to.
522 BasicBlock *TheRealDest = 0;
523 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
524 if (ThisCases[i].first == TIV) {
525 TheRealDest = ThisCases[i].second;
529 // If not handled by any explicit cases, it is handled by the default case.
530 if (TheRealDest == 0) TheRealDest = ThisDef;
532 // Remove PHI node entries for dead edges.
533 BasicBlock *CheckEdge = TheRealDest;
534 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
535 if (*SI != CheckEdge)
536 (*SI)->removePredecessor(TIBB);
540 // Insert the new branch.
541 Instruction *NI = BranchInst::Create(TheRealDest, TI);
544 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
545 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
547 EraseTerminatorInstAndDCECond(TI);
552 /// ConstantIntOrdering - This class implements a stable ordering of constant
553 /// integers that does not depend on their address. This is important for
554 /// applications that sort ConstantInt's to ensure uniqueness.
555 struct ConstantIntOrdering {
556 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
557 return LHS->getValue().ult(RHS->getValue());
562 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
563 const ConstantInt *LHS = *(const ConstantInt**)P1;
564 const ConstantInt *RHS = *(const ConstantInt**)P2;
565 return LHS->getValue().ult(RHS->getValue());
568 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
569 /// equality comparison instruction (either a switch or a branch on "X == c").
570 /// See if any of the predecessors of the terminator block are value comparisons
571 /// on the same value. If so, and if safe to do so, fold them together.
572 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
573 BasicBlock *BB = TI->getParent();
574 Value *CV = isValueEqualityComparison(TI); // CondVal
575 assert(CV && "Not a comparison?");
576 bool Changed = false;
578 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
579 while (!Preds.empty()) {
580 BasicBlock *Pred = Preds.pop_back_val();
582 // See if the predecessor is a comparison with the same value.
583 TerminatorInst *PTI = Pred->getTerminator();
584 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
586 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
587 // Figure out which 'cases' to copy from SI to PSI.
588 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
589 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
591 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
592 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
594 // Based on whether the default edge from PTI goes to BB or not, fill in
595 // PredCases and PredDefault with the new switch cases we would like to
597 SmallVector<BasicBlock*, 8> NewSuccessors;
599 if (PredDefault == BB) {
600 // If this is the default destination from PTI, only the edges in TI
601 // that don't occur in PTI, or that branch to BB will be activated.
602 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
603 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
604 if (PredCases[i].second != BB)
605 PTIHandled.insert(PredCases[i].first);
607 // The default destination is BB, we don't need explicit targets.
608 std::swap(PredCases[i], PredCases.back());
609 PredCases.pop_back();
613 // Reconstruct the new switch statement we will be building.
614 if (PredDefault != BBDefault) {
615 PredDefault->removePredecessor(Pred);
616 PredDefault = BBDefault;
617 NewSuccessors.push_back(BBDefault);
619 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
620 if (!PTIHandled.count(BBCases[i].first) &&
621 BBCases[i].second != BBDefault) {
622 PredCases.push_back(BBCases[i]);
623 NewSuccessors.push_back(BBCases[i].second);
627 // If this is not the default destination from PSI, only the edges
628 // in SI that occur in PSI with a destination of BB will be
630 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
631 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
632 if (PredCases[i].second == BB) {
633 PTIHandled.insert(PredCases[i].first);
634 std::swap(PredCases[i], PredCases.back());
635 PredCases.pop_back();
639 // Okay, now we know which constants were sent to BB from the
640 // predecessor. Figure out where they will all go now.
641 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
642 if (PTIHandled.count(BBCases[i].first)) {
643 // If this is one we are capable of getting...
644 PredCases.push_back(BBCases[i]);
645 NewSuccessors.push_back(BBCases[i].second);
646 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
649 // If there are any constants vectored to BB that TI doesn't handle,
650 // they must go to the default destination of TI.
651 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
653 E = PTIHandled.end(); I != E; ++I) {
654 PredCases.push_back(std::make_pair(*I, BBDefault));
655 NewSuccessors.push_back(BBDefault);
659 // Okay, at this point, we know which new successor Pred will get. Make
660 // sure we update the number of entries in the PHI nodes for these
662 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
663 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
665 // Convert pointer to int before we switch.
666 if (CV->getType()->isPointerTy()) {
667 assert(TD && "Cannot switch on pointer without TargetData");
668 CV = new PtrToIntInst(CV, TD->getIntPtrType(CV->getContext()),
672 // Now that the successors are updated, create the new Switch instruction.
673 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
674 PredCases.size(), PTI);
675 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
676 NewSI->addCase(PredCases[i].first, PredCases[i].second);
678 EraseTerminatorInstAndDCECond(PTI);
680 // Okay, last check. If BB is still a successor of PSI, then we must
681 // have an infinite loop case. If so, add an infinitely looping block
682 // to handle the case to preserve the behavior of the code.
683 BasicBlock *InfLoopBlock = 0;
684 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
685 if (NewSI->getSuccessor(i) == BB) {
686 if (InfLoopBlock == 0) {
687 // Insert it at the end of the function, because it's either code,
688 // or it won't matter if it's hot. :)
689 InfLoopBlock = BasicBlock::Create(BB->getContext(),
690 "infloop", BB->getParent());
691 BranchInst::Create(InfLoopBlock, InfLoopBlock);
693 NewSI->setSuccessor(i, InfLoopBlock);
702 // isSafeToHoistInvoke - If we would need to insert a select that uses the
703 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
704 // would need to do this), we can't hoist the invoke, as there is nowhere
705 // to put the select in this case.
706 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
707 Instruction *I1, Instruction *I2) {
708 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
710 for (BasicBlock::iterator BBI = SI->begin();
711 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
712 Value *BB1V = PN->getIncomingValueForBlock(BB1);
713 Value *BB2V = PN->getIncomingValueForBlock(BB2);
714 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
722 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
723 /// BB2, hoist any common code in the two blocks up into the branch block. The
724 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
725 static bool HoistThenElseCodeToIf(BranchInst *BI) {
726 // This does very trivial matching, with limited scanning, to find identical
727 // instructions in the two blocks. In particular, we don't want to get into
728 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
729 // such, we currently just scan for obviously identical instructions in an
731 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
732 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
734 BasicBlock::iterator BB1_Itr = BB1->begin();
735 BasicBlock::iterator BB2_Itr = BB2->begin();
737 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
738 while (isa<DbgInfoIntrinsic>(I1))
740 while (isa<DbgInfoIntrinsic>(I2))
742 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
743 !I1->isIdenticalToWhenDefined(I2) ||
744 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
747 // If we get here, we can hoist at least one instruction.
748 BasicBlock *BIParent = BI->getParent();
751 // If we are hoisting the terminator instruction, don't move one (making a
752 // broken BB), instead clone it, and remove BI.
753 if (isa<TerminatorInst>(I1))
754 goto HoistTerminator;
756 // For a normal instruction, we just move one to right before the branch,
757 // then replace all uses of the other with the first. Finally, we remove
758 // the now redundant second instruction.
759 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
760 if (!I2->use_empty())
761 I2->replaceAllUsesWith(I1);
762 I1->intersectOptionalDataWith(I2);
763 BB2->getInstList().erase(I2);
766 while (isa<DbgInfoIntrinsic>(I1))
769 while (isa<DbgInfoIntrinsic>(I2))
771 } while (I1->getOpcode() == I2->getOpcode() &&
772 I1->isIdenticalToWhenDefined(I2));
777 // It may not be possible to hoist an invoke.
778 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
781 // Okay, it is safe to hoist the terminator.
782 Instruction *NT = I1->clone();
783 BIParent->getInstList().insert(BI, NT);
784 if (!NT->getType()->isVoidTy()) {
785 I1->replaceAllUsesWith(NT);
786 I2->replaceAllUsesWith(NT);
790 // Hoisting one of the terminators from our successor is a great thing.
791 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
792 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
793 // nodes, so we insert select instruction to compute the final result.
794 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
795 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
797 for (BasicBlock::iterator BBI = SI->begin();
798 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
799 Value *BB1V = PN->getIncomingValueForBlock(BB1);
800 Value *BB2V = PN->getIncomingValueForBlock(BB2);
801 if (BB1V == BB2V) continue;
803 // These values do not agree. Insert a select instruction before NT
804 // that determines the right value.
805 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
807 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
808 BB1V->getName()+"."+BB2V->getName(), NT);
809 // Make the PHI node use the select for all incoming values for BB1/BB2
810 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
811 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
812 PN->setIncomingValue(i, SI);
816 // Update any PHI nodes in our new successors.
817 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
818 AddPredecessorToBlock(*SI, BIParent, BB1);
820 EraseTerminatorInstAndDCECond(BI);
824 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
825 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
826 /// (for now, restricted to a single instruction that's side effect free) from
827 /// the BB1 into the branch block to speculatively execute it.
828 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
829 // Only speculatively execution a single instruction (not counting the
830 // terminator) for now.
831 Instruction *HInst = NULL;
832 Instruction *Term = BB1->getTerminator();
833 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
835 Instruction *I = BBI;
837 if (isa<DbgInfoIntrinsic>(I)) continue;
838 if (I == Term) break;
847 // Be conservative for now. FP select instruction can often be expensive.
848 Value *BrCond = BI->getCondition();
849 if (isa<FCmpInst>(BrCond))
852 // If BB1 is actually on the false edge of the conditional branch, remember
853 // to swap the select operands later.
855 if (BB1 != BI->getSuccessor(0)) {
856 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
863 // br i1 %t1, label %BB1, label %BB2
872 // %t3 = select i1 %t1, %t2, %t3
873 switch (HInst->getOpcode()) {
874 default: return false; // Not safe / profitable to hoist.
875 case Instruction::Add:
876 case Instruction::Sub:
877 // Not worth doing for vector ops.
878 if (HInst->getType()->isVectorTy())
881 case Instruction::And:
882 case Instruction::Or:
883 case Instruction::Xor:
884 case Instruction::Shl:
885 case Instruction::LShr:
886 case Instruction::AShr:
887 // Don't mess with vector operations.
888 if (HInst->getType()->isVectorTy())
890 break; // These are all cheap and non-trapping instructions.
893 // If the instruction is obviously dead, don't try to predicate it.
894 if (HInst->use_empty()) {
895 HInst->eraseFromParent();
899 // Can we speculatively execute the instruction? And what is the value
900 // if the condition is false? Consider the phi uses, if the incoming value
901 // from the "if" block are all the same V, then V is the value of the
902 // select if the condition is false.
903 BasicBlock *BIParent = BI->getParent();
904 SmallVector<PHINode*, 4> PHIUses;
905 Value *FalseV = NULL;
907 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
908 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
910 // Ignore any user that is not a PHI node in BB2. These can only occur in
911 // unreachable blocks, because they would not be dominated by the instr.
912 PHINode *PN = dyn_cast<PHINode>(*UI);
913 if (!PN || PN->getParent() != BB2)
915 PHIUses.push_back(PN);
917 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
920 else if (FalseV != PHIV)
921 return false; // Inconsistent value when condition is false.
924 assert(FalseV && "Must have at least one user, and it must be a PHI");
926 // Do not hoist the instruction if any of its operands are defined but not
927 // used in this BB. The transformation will prevent the operand from
928 // being sunk into the use block.
929 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
931 Instruction *OpI = dyn_cast<Instruction>(*i);
932 if (OpI && OpI->getParent() == BIParent &&
933 !OpI->isUsedInBasicBlock(BIParent))
937 // If we get here, we can hoist the instruction. Try to place it
938 // before the icmp instruction preceding the conditional branch.
939 BasicBlock::iterator InsertPos = BI;
940 if (InsertPos != BIParent->begin())
942 // Skip debug info between condition and branch.
943 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
945 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
946 SmallPtrSet<Instruction *, 4> BB1Insns;
947 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
948 BB1I != BB1E; ++BB1I)
949 BB1Insns.insert(BB1I);
950 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
952 Instruction *Use = cast<Instruction>(*UI);
953 if (!BB1Insns.count(Use)) continue;
955 // If BrCond uses the instruction that place it just before
956 // branch instruction.
962 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
964 // Create a select whose true value is the speculatively executed value and
965 // false value is the previously determined FalseV.
968 SI = SelectInst::Create(BrCond, FalseV, HInst,
969 FalseV->getName() + "." + HInst->getName(), BI);
971 SI = SelectInst::Create(BrCond, HInst, FalseV,
972 HInst->getName() + "." + FalseV->getName(), BI);
974 // Make the PHI node use the select for all incoming values for "then" and
976 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
977 PHINode *PN = PHIUses[i];
978 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
979 if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent)
980 PN->setIncomingValue(j, SI);
987 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
988 /// across this block.
989 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
990 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
993 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
994 if (isa<DbgInfoIntrinsic>(BBI))
996 if (Size > 10) return false; // Don't clone large BB's.
999 // We can only support instructions that do not define values that are
1000 // live outside of the current basic block.
1001 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1003 Instruction *U = cast<Instruction>(*UI);
1004 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1007 // Looks ok, continue checking.
1013 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1014 /// that is defined in the same block as the branch and if any PHI entries are
1015 /// constants, thread edges corresponding to that entry to be branches to their
1016 /// ultimate destination.
1017 static bool FoldCondBranchOnPHI(BranchInst *BI) {
1018 BasicBlock *BB = BI->getParent();
1019 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1020 // NOTE: we currently cannot transform this case if the PHI node is used
1021 // outside of the block.
1022 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1025 // Degenerate case of a single entry PHI.
1026 if (PN->getNumIncomingValues() == 1) {
1027 FoldSingleEntryPHINodes(PN->getParent());
1031 // Now we know that this block has multiple preds and two succs.
1032 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1034 // Okay, this is a simple enough basic block. See if any phi values are
1036 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1037 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1038 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1040 // Okay, we now know that all edges from PredBB should be revectored to
1041 // branch to RealDest.
1042 BasicBlock *PredBB = PN->getIncomingBlock(i);
1043 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1045 if (RealDest == BB) continue; // Skip self loops.
1047 // The dest block might have PHI nodes, other predecessors and other
1048 // difficult cases. Instead of being smart about this, just insert a new
1049 // block that jumps to the destination block, effectively splitting
1050 // the edge we are about to create.
1051 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1052 RealDest->getName()+".critedge",
1053 RealDest->getParent(), RealDest);
1054 BranchInst::Create(RealDest, EdgeBB);
1056 for (BasicBlock::iterator BBI = RealDest->begin();
1057 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1058 Value *V = PN->getIncomingValueForBlock(BB);
1059 PN->addIncoming(V, EdgeBB);
1062 // BB may have instructions that are being threaded over. Clone these
1063 // instructions into EdgeBB. We know that there will be no uses of the
1064 // cloned instructions outside of EdgeBB.
1065 BasicBlock::iterator InsertPt = EdgeBB->begin();
1066 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1067 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1068 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1069 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1072 // Clone the instruction.
1073 Instruction *N = BBI->clone();
1074 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1076 // Update operands due to translation.
1077 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1079 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1080 if (PI != TranslateMap.end())
1084 // Check for trivial simplification.
1085 if (Constant *C = ConstantFoldInstruction(N)) {
1086 TranslateMap[BBI] = C;
1087 delete N; // Constant folded away, don't need actual inst
1089 // Insert the new instruction into its new home.
1090 EdgeBB->getInstList().insert(InsertPt, N);
1091 if (!BBI->use_empty())
1092 TranslateMap[BBI] = N;
1096 // Loop over all of the edges from PredBB to BB, changing them to branch
1097 // to EdgeBB instead.
1098 TerminatorInst *PredBBTI = PredBB->getTerminator();
1099 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1100 if (PredBBTI->getSuccessor(i) == BB) {
1101 BB->removePredecessor(PredBB);
1102 PredBBTI->setSuccessor(i, EdgeBB);
1105 // Recurse, simplifying any other constants.
1106 return FoldCondBranchOnPHI(BI) | true;
1112 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1113 /// PHI node, see if we can eliminate it.
1114 static bool FoldTwoEntryPHINode(PHINode *PN) {
1115 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1116 // statement", which has a very simple dominance structure. Basically, we
1117 // are trying to find the condition that is being branched on, which
1118 // subsequently causes this merge to happen. We really want control
1119 // dependence information for this check, but simplifycfg can't keep it up
1120 // to date, and this catches most of the cases we care about anyway.
1122 BasicBlock *BB = PN->getParent();
1123 BasicBlock *IfTrue, *IfFalse;
1124 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1125 if (!IfCond) return false;
1127 // Okay, we found that we can merge this two-entry phi node into a select.
1128 // Doing so would require us to fold *all* two entry phi nodes in this block.
1129 // At some point this becomes non-profitable (particularly if the target
1130 // doesn't support cmov's). Only do this transformation if there are two or
1131 // fewer PHI nodes in this block.
1132 unsigned NumPhis = 0;
1133 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1137 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1138 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1140 // Loop over the PHI's seeing if we can promote them all to select
1141 // instructions. While we are at it, keep track of the instructions
1142 // that need to be moved to the dominating block.
1143 std::set<Instruction*> AggressiveInsts;
1145 BasicBlock::iterator AfterPHIIt = BB->begin();
1146 while (isa<PHINode>(AfterPHIIt)) {
1147 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1148 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1149 if (PN->getIncomingValue(0) != PN)
1150 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1152 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1153 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1154 &AggressiveInsts) ||
1155 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1156 &AggressiveInsts)) {
1161 // If we all PHI nodes are promotable, check to make sure that all
1162 // instructions in the predecessor blocks can be promoted as well. If
1163 // not, we won't be able to get rid of the control flow, so it's not
1164 // worth promoting to select instructions.
1165 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1166 PN = cast<PHINode>(BB->begin());
1167 BasicBlock *Pred = PN->getIncomingBlock(0);
1168 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1170 DomBlock = *pred_begin(Pred);
1171 for (BasicBlock::iterator I = Pred->begin();
1172 !isa<TerminatorInst>(I); ++I)
1173 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1174 // This is not an aggressive instruction that we can promote.
1175 // Because of this, we won't be able to get rid of the control
1176 // flow, so the xform is not worth it.
1181 Pred = PN->getIncomingBlock(1);
1182 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1184 DomBlock = *pred_begin(Pred);
1185 for (BasicBlock::iterator I = Pred->begin();
1186 !isa<TerminatorInst>(I); ++I)
1187 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1188 // This is not an aggressive instruction that we can promote.
1189 // Because of this, we won't be able to get rid of the control
1190 // flow, so the xform is not worth it.
1195 // If we can still promote the PHI nodes after this gauntlet of tests,
1196 // do all of the PHI's now.
1198 // Move all 'aggressive' instructions, which are defined in the
1199 // conditional parts of the if's up to the dominating block.
1201 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1202 IfBlock1->getInstList(), IfBlock1->begin(),
1203 IfBlock1->getTerminator());
1205 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1206 IfBlock2->getInstList(), IfBlock2->begin(),
1207 IfBlock2->getTerminator());
1209 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1210 // Change the PHI node into a select instruction.
1211 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1212 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1214 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1215 PN->replaceAllUsesWith(NV);
1218 BB->getInstList().erase(PN);
1223 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1224 /// to two returning blocks, try to merge them together into one return,
1225 /// introducing a select if the return values disagree.
1226 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1227 assert(BI->isConditional() && "Must be a conditional branch");
1228 BasicBlock *TrueSucc = BI->getSuccessor(0);
1229 BasicBlock *FalseSucc = BI->getSuccessor(1);
1230 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1231 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1233 // Check to ensure both blocks are empty (just a return) or optionally empty
1234 // with PHI nodes. If there are other instructions, merging would cause extra
1235 // computation on one path or the other.
1236 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1238 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1241 // Okay, we found a branch that is going to two return nodes. If
1242 // there is no return value for this function, just change the
1243 // branch into a return.
1244 if (FalseRet->getNumOperands() == 0) {
1245 TrueSucc->removePredecessor(BI->getParent());
1246 FalseSucc->removePredecessor(BI->getParent());
1247 ReturnInst::Create(BI->getContext(), 0, BI);
1248 EraseTerminatorInstAndDCECond(BI);
1252 // Otherwise, figure out what the true and false return values are
1253 // so we can insert a new select instruction.
1254 Value *TrueValue = TrueRet->getReturnValue();
1255 Value *FalseValue = FalseRet->getReturnValue();
1257 // Unwrap any PHI nodes in the return blocks.
1258 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1259 if (TVPN->getParent() == TrueSucc)
1260 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1261 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1262 if (FVPN->getParent() == FalseSucc)
1263 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1265 // In order for this transformation to be safe, we must be able to
1266 // unconditionally execute both operands to the return. This is
1267 // normally the case, but we could have a potentially-trapping
1268 // constant expression that prevents this transformation from being
1270 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1273 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1277 // Okay, we collected all the mapped values and checked them for sanity, and
1278 // defined to really do this transformation. First, update the CFG.
1279 TrueSucc->removePredecessor(BI->getParent());
1280 FalseSucc->removePredecessor(BI->getParent());
1282 // Insert select instructions where needed.
1283 Value *BrCond = BI->getCondition();
1285 // Insert a select if the results differ.
1286 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1287 } else if (isa<UndefValue>(TrueValue)) {
1288 TrueValue = FalseValue;
1290 TrueValue = SelectInst::Create(BrCond, TrueValue,
1291 FalseValue, "retval", BI);
1295 Value *RI = !TrueValue ?
1296 ReturnInst::Create(BI->getContext(), BI) :
1297 ReturnInst::Create(BI->getContext(), TrueValue, BI);
1300 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1301 << "\n " << *BI << "NewRet = " << *RI
1302 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1304 EraseTerminatorInstAndDCECond(BI);
1309 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1310 /// and if a predecessor branches to us and one of our successors, fold the
1311 /// setcc into the predecessor and use logical operations to pick the right
1313 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1314 BasicBlock *BB = BI->getParent();
1315 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1316 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1317 Cond->getParent() != BB || !Cond->hasOneUse())
1320 // Only allow this if the condition is a simple instruction that can be
1321 // executed unconditionally. It must be in the same block as the branch, and
1322 // must be at the front of the block.
1323 BasicBlock::iterator FrontIt = BB->front();
1324 // Ignore dbg intrinsics.
1325 while(isa<DbgInfoIntrinsic>(FrontIt))
1328 // Allow a single instruction to be hoisted in addition to the compare
1329 // that feeds the branch. We later ensure that any values that _it_ uses
1330 // were also live in the predecessor, so that we don't unnecessarily create
1331 // register pressure or inhibit out-of-order execution.
1332 Instruction *BonusInst = 0;
1333 if (&*FrontIt != Cond &&
1334 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1335 FrontIt->isSafeToSpeculativelyExecute()) {
1336 BonusInst = &*FrontIt;
1340 // Only a single bonus inst is allowed.
1341 if (&*FrontIt != Cond)
1344 // Make sure the instruction after the condition is the cond branch.
1345 BasicBlock::iterator CondIt = Cond; ++CondIt;
1346 // Ingore dbg intrinsics.
1347 while(isa<DbgInfoIntrinsic>(CondIt))
1349 if (&*CondIt != BI) {
1350 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!");
1354 // Cond is known to be a compare or binary operator. Check to make sure that
1355 // neither operand is a potentially-trapping constant expression.
1356 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1359 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1364 // Finally, don't infinitely unroll conditional loops.
1365 BasicBlock *TrueDest = BI->getSuccessor(0);
1366 BasicBlock *FalseDest = BI->getSuccessor(1);
1367 if (TrueDest == BB || FalseDest == BB)
1370 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1371 BasicBlock *PredBlock = *PI;
1372 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1374 // Check that we have two conditional branches. If there is a PHI node in
1375 // the common successor, verify that the same value flows in from both
1377 if (PBI == 0 || PBI->isUnconditional() ||
1378 !SafeToMergeTerminators(BI, PBI))
1381 // Ensure that any values used in the bonus instruction are also used
1382 // by the terminator of the predecessor. This means that those values
1383 // must already have been resolved, so we won't be inhibiting the
1384 // out-of-order core by speculating them earlier.
1386 // Collect the values used by the bonus inst
1387 SmallPtrSet<Value*, 4> UsedValues;
1388 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1389 OE = BonusInst->op_end(); OI != OE; ++OI) {
1391 if (!isa<Constant>(V))
1392 UsedValues.insert(V);
1395 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1396 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1398 // Walk up to four levels back up the use-def chain of the predecessor's
1399 // terminator to see if all those values were used. The choice of four
1400 // levels is arbitrary, to provide a compile-time-cost bound.
1401 while (!Worklist.empty()) {
1402 std::pair<Value*, unsigned> Pair = Worklist.back();
1403 Worklist.pop_back();
1405 if (Pair.second >= 4) continue;
1406 UsedValues.erase(Pair.first);
1407 if (UsedValues.empty()) break;
1409 if (Instruction* I = dyn_cast<Instruction>(Pair.first)) {
1410 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1412 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1416 if (!UsedValues.empty()) return false;
1419 Instruction::BinaryOps Opc;
1420 bool InvertPredCond = false;
1422 if (PBI->getSuccessor(0) == TrueDest)
1423 Opc = Instruction::Or;
1424 else if (PBI->getSuccessor(1) == FalseDest)
1425 Opc = Instruction::And;
1426 else if (PBI->getSuccessor(0) == FalseDest)
1427 Opc = Instruction::And, InvertPredCond = true;
1428 else if (PBI->getSuccessor(1) == TrueDest)
1429 Opc = Instruction::Or, InvertPredCond = true;
1433 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1435 // If we need to invert the condition in the pred block to match, do so now.
1436 if (InvertPredCond) {
1438 BinaryOperator::CreateNot(PBI->getCondition(),
1439 PBI->getCondition()->getName()+".not", PBI);
1440 PBI->setCondition(NewCond);
1441 BasicBlock *OldTrue = PBI->getSuccessor(0);
1442 BasicBlock *OldFalse = PBI->getSuccessor(1);
1443 PBI->setSuccessor(0, OldFalse);
1444 PBI->setSuccessor(1, OldTrue);
1447 // If we have a bonus inst, clone it into the predecessor block.
1448 Instruction *NewBonus = 0;
1450 NewBonus = BonusInst->clone();
1451 PredBlock->getInstList().insert(PBI, NewBonus);
1452 NewBonus->takeName(BonusInst);
1453 BonusInst->setName(BonusInst->getName()+".old");
1456 // Clone Cond into the predecessor basic block, and or/and the
1457 // two conditions together.
1458 Instruction *New = Cond->clone();
1459 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1460 PredBlock->getInstList().insert(PBI, New);
1461 New->takeName(Cond);
1462 Cond->setName(New->getName()+".old");
1464 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1465 New, "or.cond", PBI);
1466 PBI->setCondition(NewCond);
1467 if (PBI->getSuccessor(0) == BB) {
1468 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1469 PBI->setSuccessor(0, TrueDest);
1471 if (PBI->getSuccessor(1) == BB) {
1472 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1473 PBI->setSuccessor(1, FalseDest);
1480 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1481 /// predecessor of another block, this function tries to simplify it. We know
1482 /// that PBI and BI are both conditional branches, and BI is in one of the
1483 /// successor blocks of PBI - PBI branches to BI.
1484 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1485 assert(PBI->isConditional() && BI->isConditional());
1486 BasicBlock *BB = BI->getParent();
1488 // If this block ends with a branch instruction, and if there is a
1489 // predecessor that ends on a branch of the same condition, make
1490 // this conditional branch redundant.
1491 if (PBI->getCondition() == BI->getCondition() &&
1492 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1493 // Okay, the outcome of this conditional branch is statically
1494 // knowable. If this block had a single pred, handle specially.
1495 if (BB->getSinglePredecessor()) {
1496 // Turn this into a branch on constant.
1497 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1498 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1500 return true; // Nuke the branch on constant.
1503 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1504 // in the constant and simplify the block result. Subsequent passes of
1505 // simplifycfg will thread the block.
1506 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1507 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1508 BI->getCondition()->getName() + ".pr",
1510 // Okay, we're going to insert the PHI node. Since PBI is not the only
1511 // predecessor, compute the PHI'd conditional value for all of the preds.
1512 // Any predecessor where the condition is not computable we keep symbolic.
1513 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1514 BasicBlock *P = *PI;
1515 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
1516 PBI != BI && PBI->isConditional() &&
1517 PBI->getCondition() == BI->getCondition() &&
1518 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1519 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1520 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1523 NewPN->addIncoming(BI->getCondition(), P);
1527 BI->setCondition(NewPN);
1532 // If this is a conditional branch in an empty block, and if any
1533 // predecessors is a conditional branch to one of our destinations,
1534 // fold the conditions into logical ops and one cond br.
1535 BasicBlock::iterator BBI = BB->begin();
1536 // Ignore dbg intrinsics.
1537 while (isa<DbgInfoIntrinsic>(BBI))
1543 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1548 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1550 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1551 PBIOp = 0, BIOp = 1;
1552 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1553 PBIOp = 1, BIOp = 0;
1554 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1559 // Check to make sure that the other destination of this branch
1560 // isn't BB itself. If so, this is an infinite loop that will
1561 // keep getting unwound.
1562 if (PBI->getSuccessor(PBIOp) == BB)
1565 // Do not perform this transformation if it would require
1566 // insertion of a large number of select instructions. For targets
1567 // without predication/cmovs, this is a big pessimization.
1568 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1570 unsigned NumPhis = 0;
1571 for (BasicBlock::iterator II = CommonDest->begin();
1572 isa<PHINode>(II); ++II, ++NumPhis)
1573 if (NumPhis > 2) // Disable this xform.
1576 // Finally, if everything is ok, fold the branches to logical ops.
1577 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1579 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
1580 << "AND: " << *BI->getParent());
1583 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1584 // branch in it, where one edge (OtherDest) goes back to itself but the other
1585 // exits. We don't *know* that the program avoids the infinite loop
1586 // (even though that seems likely). If we do this xform naively, we'll end up
1587 // recursively unpeeling the loop. Since we know that (after the xform is
1588 // done) that the block *is* infinite if reached, we just make it an obviously
1589 // infinite loop with no cond branch.
1590 if (OtherDest == BB) {
1591 // Insert it at the end of the function, because it's either code,
1592 // or it won't matter if it's hot. :)
1593 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1594 "infloop", BB->getParent());
1595 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1596 OtherDest = InfLoopBlock;
1599 DEBUG(dbgs() << *PBI->getParent()->getParent());
1601 // BI may have other predecessors. Because of this, we leave
1602 // it alone, but modify PBI.
1604 // Make sure we get to CommonDest on True&True directions.
1605 Value *PBICond = PBI->getCondition();
1607 PBICond = BinaryOperator::CreateNot(PBICond,
1608 PBICond->getName()+".not",
1610 Value *BICond = BI->getCondition();
1612 BICond = BinaryOperator::CreateNot(BICond,
1613 BICond->getName()+".not",
1615 // Merge the conditions.
1616 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1618 // Modify PBI to branch on the new condition to the new dests.
1619 PBI->setCondition(Cond);
1620 PBI->setSuccessor(0, CommonDest);
1621 PBI->setSuccessor(1, OtherDest);
1623 // OtherDest may have phi nodes. If so, add an entry from PBI's
1624 // block that are identical to the entries for BI's block.
1626 for (BasicBlock::iterator II = OtherDest->begin();
1627 (PN = dyn_cast<PHINode>(II)); ++II) {
1628 Value *V = PN->getIncomingValueForBlock(BB);
1629 PN->addIncoming(V, PBI->getParent());
1632 // We know that the CommonDest already had an edge from PBI to
1633 // it. If it has PHIs though, the PHIs may have different
1634 // entries for BB and PBI's BB. If so, insert a select to make
1636 for (BasicBlock::iterator II = CommonDest->begin();
1637 (PN = dyn_cast<PHINode>(II)); ++II) {
1638 Value *BIV = PN->getIncomingValueForBlock(BB);
1639 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1640 Value *PBIV = PN->getIncomingValue(PBBIdx);
1642 // Insert a select in PBI to pick the right value.
1643 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1644 PBIV->getName()+".mux", PBI);
1645 PN->setIncomingValue(PBBIdx, NV);
1649 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1650 DEBUG(dbgs() << *PBI->getParent()->getParent());
1652 // This basic block is probably dead. We know it has at least
1653 // one fewer predecessor.
1657 // SimplifyIndirectBrOnSelect - Replaces
1658 // (indirectbr (select cond, blockaddress(@fn, BlockA),
1659 // blockaddress(@fn, BlockB)))
1661 // (br cond, BlockA, BlockB).
1662 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
1663 // Check that both operands of the select are block addresses.
1664 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
1665 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
1669 // Extract the actual blocks.
1670 BasicBlock *TrueBB = TBA->getBasicBlock();
1671 BasicBlock *FalseBB = FBA->getBasicBlock();
1673 // Remove any superfluous successor edges from the CFG.
1674 // First, figure out which successors to preserve.
1675 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
1677 BasicBlock *KeepEdge1 = TrueBB;
1678 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
1680 // Then remove the rest.
1681 for (unsigned I = 0, E = IBI->getNumSuccessors(); I != E; ++I) {
1682 BasicBlock *Succ = IBI->getSuccessor(I);
1683 // Make sure only to keep exactly one copy of each edge.
1684 if (Succ == KeepEdge1)
1686 else if (Succ == KeepEdge2)
1689 Succ->removePredecessor(IBI->getParent());
1692 // Insert an appropriate new terminator.
1693 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
1694 if (TrueBB == FalseBB)
1695 // We were only looking for one successor, and it was present.
1696 // Create an unconditional branch to it.
1697 BranchInst::Create(TrueBB, IBI);
1699 // We found both of the successors we were looking for.
1700 // Create a conditional branch sharing the condition of the select.
1701 BranchInst::Create(TrueBB, FalseBB, SI->getCondition(), IBI);
1702 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
1703 // Neither of the selected blocks were successors, so this
1704 // indirectbr must be unreachable.
1705 new UnreachableInst(IBI->getContext(), IBI);
1707 // One of the selected values was a successor, but the other wasn't.
1708 // Insert an unconditional branch to the one that was found;
1709 // the edge to the one that wasn't must be unreachable.
1711 // Only TrueBB was found.
1712 BranchInst::Create(TrueBB, IBI);
1714 // Only FalseBB was found.
1715 BranchInst::Create(FalseBB, IBI);
1718 EraseTerminatorInstAndDCECond(IBI);
1722 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
1723 /// instruction (a seteq/setne with a constant) as the only instruction in a
1724 /// block that ends with an uncond branch. We are looking for a very specific
1725 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
1726 /// this case, we merge the first two "or's of icmp" into a switch, but then the
1727 /// default value goes to an uncond block with a seteq in it, we get something
1730 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
1732 /// %tmp = icmp eq i8 %A, 92
1735 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
1737 /// We prefer to split the edge to 'end' so that there is a true/false entry to
1738 /// the PHI, merging the third icmp into the switch.
1739 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI) {
1740 BasicBlock *BB = ICI->getParent();
1741 // If the block has any PHIs in it or the icmp has multiple uses, it is too
1743 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
1745 Value *V = ICI->getOperand(0);
1746 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
1748 // The pattern we're looking for is where our only predecessor is a switch on
1749 // 'V' and this block is the default case for the switch. In this case we can
1750 // fold the compared value into the switch to simplify things.
1751 BasicBlock *Pred = BB->getSinglePredecessor();
1752 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
1754 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
1755 if (SI->getCondition() != V)
1758 // If BB is reachable on a non-default case, then we simply know the value of
1759 // V in this block. Substitute it and constant fold the icmp instruction
1761 if (SI->getDefaultDest() != BB) {
1762 ConstantInt *VVal = SI->findCaseDest(BB);
1763 assert(VVal && "Should have a unique destination value");
1764 ICI->setOperand(0, VVal);
1766 if (Constant *C = ConstantFoldInstruction(ICI)) {
1767 ICI->replaceAllUsesWith(C);
1768 ICI->eraseFromParent();
1770 // BB is now empty, so it is likely to simplify away.
1771 return SimplifyCFG(BB) | true;
1774 // Ok, the block is reachable from the default dest. If the constant we're
1775 // comparing exists in one of the other edges, then we can constant fold ICI
1777 if (SI->findCaseValue(Cst) != 0) {
1779 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1780 V = ConstantInt::getFalse(BB->getContext());
1782 V = ConstantInt::getTrue(BB->getContext());
1784 ICI->replaceAllUsesWith(V);
1785 ICI->eraseFromParent();
1786 // BB is now empty, so it is likely to simplify away.
1787 return SimplifyCFG(BB) | true;
1790 // The use of the icmp has to be in the 'end' block, by the only PHI node in
1792 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
1793 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
1794 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
1795 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
1798 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
1800 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
1801 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
1803 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1804 std::swap(DefaultCst, NewCst);
1806 // Replace ICI (which is used by the PHI for the default value) with true or
1807 // false depending on if it is EQ or NE.
1808 ICI->replaceAllUsesWith(DefaultCst);
1809 ICI->eraseFromParent();
1811 // Okay, the switch goes to this block on a default value. Add an edge from
1812 // the switch to the merge point on the compared value.
1813 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
1814 BB->getParent(), BB);
1815 SI->addCase(Cst, NewBB);
1817 // NewBB branches to the phi block, add the uncond branch and the phi entry.
1818 BranchInst::Create(SuccBlock, NewBB);
1819 PHIUse->addIncoming(NewCst, NewBB);
1823 bool SimplifyCFGOpt::run(BasicBlock *BB) {
1824 bool Changed = false;
1825 Function *Fn = BB->getParent();
1827 assert(BB && Fn && "Block not embedded in function!");
1828 assert(BB->getTerminator() && "Degenerate basic block encountered!");
1830 // Remove basic blocks that have no predecessors (except the entry block)...
1831 // or that just have themself as a predecessor. These are unreachable.
1832 if ((pred_begin(BB) == pred_end(BB) && BB != &Fn->getEntryBlock()) ||
1833 BB->getSinglePredecessor() == BB) {
1834 DEBUG(dbgs() << "Removing BB: \n" << *BB);
1835 DeleteDeadBlock(BB);
1839 // Check to see if we can constant propagate this terminator instruction
1841 Changed |= ConstantFoldTerminator(BB);
1843 // Check for and eliminate duplicate PHI nodes in this block.
1844 Changed |= EliminateDuplicatePHINodes(BB);
1846 // If there is a trivial two-entry PHI node in this basic block, and we can
1847 // eliminate it, do so now.
1848 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1849 if (PN->getNumIncomingValues() == 2)
1850 Changed |= FoldTwoEntryPHINode(PN);
1852 // If this is a returning block with only PHI nodes in it, fold the return
1853 // instruction into any unconditional branch predecessors.
1855 // If any predecessor is a conditional branch that just selects among
1856 // different return values, fold the replace the branch/return with a select
1858 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1859 if (BB->getFirstNonPHIOrDbg()->isTerminator()) {
1860 // Find predecessors that end with branches.
1861 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1862 SmallVector<BranchInst*, 8> CondBranchPreds;
1863 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1864 BasicBlock *P = *PI;
1865 TerminatorInst *PTI = P->getTerminator();
1866 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1867 if (BI->isUnconditional())
1868 UncondBranchPreds.push_back(P);
1870 CondBranchPreds.push_back(BI);
1874 // If we found some, do the transformation!
1875 if (!UncondBranchPreds.empty()) {
1876 while (!UncondBranchPreds.empty()) {
1877 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
1878 DEBUG(dbgs() << "FOLDING: " << *BB
1879 << "INTO UNCOND BRANCH PRED: " << *Pred);
1880 Instruction *UncondBranch = Pred->getTerminator();
1881 // Clone the return and add it to the end of the predecessor.
1882 Instruction *NewRet = RI->clone();
1883 Pred->getInstList().push_back(NewRet);
1885 // If the return instruction returns a value, and if the value was a
1886 // PHI node in "BB", propagate the right value into the return.
1887 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
1889 if (PHINode *PN = dyn_cast<PHINode>(*i))
1890 if (PN->getParent() == BB)
1891 *i = PN->getIncomingValueForBlock(Pred);
1893 // Update any PHI nodes in the returning block to realize that we no
1894 // longer branch to them.
1895 BB->removePredecessor(Pred);
1896 Pred->getInstList().erase(UncondBranch);
1899 // If we eliminated all predecessors of the block, delete the block now.
1900 if (pred_begin(BB) == pred_end(BB))
1901 // We know there are no successors, so just nuke the block.
1902 Fn->getBasicBlockList().erase(BB);
1907 // Check out all of the conditional branches going to this return
1908 // instruction. If any of them just select between returns, change the
1909 // branch itself into a select/return pair.
1910 while (!CondBranchPreds.empty()) {
1911 BranchInst *BI = CondBranchPreds.pop_back_val();
1913 // Check to see if the non-BB successor is also a return block.
1914 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
1915 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
1916 SimplifyCondBranchToTwoReturns(BI))
1920 } else if (isa<UnwindInst>(BB->begin())) {
1921 // Check to see if the first instruction in this block is just an unwind.
1922 // If so, replace any invoke instructions which use this as an exception
1923 // destination with call instructions.
1925 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1926 while (!Preds.empty()) {
1927 BasicBlock *Pred = Preds.back();
1928 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
1929 if (II && II->getUnwindDest() == BB) {
1930 // Insert a new branch instruction before the invoke, because this
1931 // is now a fall through.
1932 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1933 Pred->getInstList().remove(II); // Take out of symbol table
1935 // Insert the call now.
1936 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
1937 CallInst *CI = CallInst::Create(II->getCalledValue(),
1938 Args.begin(), Args.end(),
1940 CI->setCallingConv(II->getCallingConv());
1941 CI->setAttributes(II->getAttributes());
1942 // If the invoke produced a value, the Call now does instead.
1943 II->replaceAllUsesWith(CI);
1951 // If this block is now dead (and isn't the entry block), remove it.
1952 if (pred_begin(BB) == pred_end(BB) && BB != &Fn->getEntryBlock()) {
1953 // We know there are no successors, so just nuke the block.
1954 Fn->getBasicBlockList().erase(BB);
1958 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1959 if (isValueEqualityComparison(SI)) {
1960 // If we only have one predecessor, and if it is a branch on this value,
1961 // see if that predecessor totally determines the outcome of this switch.
1962 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1963 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
1964 return SimplifyCFG(BB) || 1;
1966 // If the block only contains the switch, see if we can fold the block
1967 // away into any preds.
1968 BasicBlock::iterator BBI = BB->begin();
1969 // Ignore dbg intrinsics.
1970 while (isa<DbgInfoIntrinsic>(BBI))
1973 if (FoldValueComparisonIntoPredecessors(SI))
1974 return SimplifyCFG(BB) || 1;
1976 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1977 if (BI->isUnconditional()) {
1978 // If the Terminator is the only non-phi instruction, simplify the block.
1979 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg();
1980 if (I->isTerminator() && BB != &Fn->getEntryBlock() &&
1981 TryToSimplifyUncondBranchFromEmptyBlock(BB))
1984 // If the only instruction in the block is a seteq/setne comparison
1985 // against a constant, try to simplify the block.
1986 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
1987 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
1988 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
1990 if (I->isTerminator() &&
1991 TryToSimplifyUncondBranchWithICmpInIt(ICI))
1995 } else { // Conditional branch
1996 if (isValueEqualityComparison(BI)) {
1997 // If we only have one predecessor, and if it is a branch on this value,
1998 // see if that predecessor totally determines the outcome of this
2000 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2001 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
2002 return SimplifyCFG(BB) | true;
2004 // This block must be empty, except for the setcond inst, if it exists.
2005 // Ignore dbg intrinsics.
2006 BasicBlock::iterator I = BB->begin();
2007 // Ignore dbg intrinsics.
2008 while (isa<DbgInfoIntrinsic>(I))
2011 if (FoldValueComparisonIntoPredecessors(BI))
2012 return SimplifyCFG(BB) | true;
2013 } else if (&*I == cast<Instruction>(BI->getCondition())){
2015 // Ignore dbg intrinsics.
2016 while (isa<DbgInfoIntrinsic>(I))
2018 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI))
2019 return SimplifyCFG(BB) | true;
2023 // If this is a branch on a phi node in the current block, thread control
2024 // through this block if any PHI node entries are constants.
2025 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
2026 if (PN->getParent() == BI->getParent())
2027 if (FoldCondBranchOnPHI(BI))
2028 return SimplifyCFG(BB) | true;
2030 // If this basic block is ONLY a setcc and a branch, and if a predecessor
2031 // branches to us and one of our successors, fold the setcc into the
2032 // predecessor and use logical operations to pick the right destination.
2033 if (FoldBranchToCommonDest(BI))
2034 return SimplifyCFG(BB) | true;
2037 // Scan predecessor blocks for conditional branches.
2038 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2039 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2040 if (PBI != BI && PBI->isConditional())
2041 if (SimplifyCondBranchToCondBranch(PBI, BI))
2042 return SimplifyCFG(BB) | true;
2045 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2046 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2047 // 'setne's and'ed together, collect them.
2049 std::vector<ConstantInt*> Values;
2050 bool TrueWhenEqual = true;
2051 Value *ExtraCase = 0;
2053 if (Instruction *Cond = dyn_cast<Instruction>(BI->getCondition())) {
2054 if (Cond->getOpcode() == Instruction::Or) {
2055 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true);
2056 } else if (Cond->getOpcode() == Instruction::And) {
2057 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false);
2058 TrueWhenEqual = false;
2063 // There might be duplicate constants in the list, which the switch
2064 // instruction can't handle, remove them now.
2065 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
2066 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2068 // Figure out which block is which destination.
2069 BasicBlock *DefaultBB = BI->getSuccessor(1);
2070 BasicBlock *EdgeBB = BI->getSuccessor(0);
2071 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2073 // Convert pointer to int before we switch.
2074 if (CompVal->getType()->isPointerTy()) {
2075 assert(TD && "Cannot switch on pointer without TargetData");
2076 CompVal = new PtrToIntInst(CompVal,
2077 TD->getIntPtrType(CompVal->getContext()),
2081 // Create the new switch instruction now.
2082 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
2085 // Add all of the 'cases' to the switch instruction.
2086 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2087 New->addCase(Values[i], EdgeBB);
2089 // We added edges from PI to the EdgeBB. As such, if there were any
2090 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2091 // the number of edges added.
2092 for (BasicBlock::iterator BBI = EdgeBB->begin();
2093 isa<PHINode>(BBI); ++BBI) {
2094 PHINode *PN = cast<PHINode>(BBI);
2095 Value *InVal = PN->getIncomingValueForBlock(BB);
2096 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2097 PN->addIncoming(InVal, BB);
2100 // Erase the old branch instruction.
2101 EraseTerminatorInstAndDCECond(BI);
2105 } else if (isa<UnreachableInst>(BB->getTerminator())) {
2106 // If there are any instructions immediately before the unreachable that can
2107 // be removed, do so.
2108 Instruction *Unreachable = BB->getTerminator();
2109 while (Unreachable != BB->begin()) {
2110 BasicBlock::iterator BBI = Unreachable;
2112 // Do not delete instructions that can have side effects, like calls
2113 // (which may never return) and volatile loads and stores.
2114 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2116 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
2117 if (SI->isVolatile())
2120 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
2121 if (LI->isVolatile())
2124 // Delete this instruction
2125 BB->getInstList().erase(BBI);
2129 // If the unreachable instruction is the first in the block, take a gander
2130 // at all of the predecessors of this instruction, and simplify them.
2131 if (&BB->front() == Unreachable) {
2132 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2133 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2134 TerminatorInst *TI = Preds[i]->getTerminator();
2136 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2137 if (BI->isUnconditional()) {
2138 if (BI->getSuccessor(0) == BB) {
2139 new UnreachableInst(TI->getContext(), TI);
2140 TI->eraseFromParent();
2144 if (BI->getSuccessor(0) == BB) {
2145 BranchInst::Create(BI->getSuccessor(1), BI);
2146 EraseTerminatorInstAndDCECond(BI);
2147 } else if (BI->getSuccessor(1) == BB) {
2148 BranchInst::Create(BI->getSuccessor(0), BI);
2149 EraseTerminatorInstAndDCECond(BI);
2153 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2154 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2155 if (SI->getSuccessor(i) == BB) {
2156 BB->removePredecessor(SI->getParent());
2161 // If the default value is unreachable, figure out the most popular
2162 // destination and make it the default.
2163 if (SI->getSuccessor(0) == BB) {
2164 std::map<BasicBlock*, unsigned> Popularity;
2165 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2166 Popularity[SI->getSuccessor(i)]++;
2168 // Find the most popular block.
2169 unsigned MaxPop = 0;
2170 BasicBlock *MaxBlock = 0;
2171 for (std::map<BasicBlock*, unsigned>::iterator
2172 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2173 if (I->second > MaxPop) {
2175 MaxBlock = I->first;
2179 // Make this the new default, allowing us to delete any explicit
2181 SI->setSuccessor(0, MaxBlock);
2184 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2186 if (isa<PHINode>(MaxBlock->begin()))
2187 for (unsigned i = 0; i != MaxPop-1; ++i)
2188 MaxBlock->removePredecessor(SI->getParent());
2190 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2191 if (SI->getSuccessor(i) == MaxBlock) {
2197 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2198 if (II->getUnwindDest() == BB) {
2199 // Convert the invoke to a call instruction. This would be a good
2200 // place to note that the call does not throw though.
2201 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2202 II->removeFromParent(); // Take out of symbol table
2204 // Insert the call now...
2205 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2206 CallInst *CI = CallInst::Create(II->getCalledValue(),
2207 Args.begin(), Args.end(),
2209 CI->setCallingConv(II->getCallingConv());
2210 CI->setAttributes(II->getAttributes());
2211 // If the invoke produced a value, the call does now instead.
2212 II->replaceAllUsesWith(CI);
2219 // If this block is now dead, remove it.
2220 if (pred_begin(BB) == pred_end(BB) && BB != &Fn->getEntryBlock()) {
2221 // We know there are no successors, so just nuke the block.
2222 Fn->getBasicBlockList().erase(BB);
2226 } else if (IndirectBrInst *IBI =
2227 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
2228 // Eliminate redundant destinations.
2229 SmallPtrSet<Value *, 8> Succs;
2230 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2231 BasicBlock *Dest = IBI->getDestination(i);
2232 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2233 Dest->removePredecessor(BB);
2234 IBI->removeDestination(i);
2240 if (IBI->getNumDestinations() == 0) {
2241 // If the indirectbr has no successors, change it to unreachable.
2242 new UnreachableInst(IBI->getContext(), IBI);
2243 EraseTerminatorInstAndDCECond(IBI);
2245 } else if (IBI->getNumDestinations() == 1) {
2246 // If the indirectbr has one successor, change it to a direct branch.
2247 BranchInst::Create(IBI->getDestination(0), IBI);
2248 EraseTerminatorInstAndDCECond(IBI);
2250 } else if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2251 if (SimplifyIndirectBrOnSelect(IBI, SI))
2252 return SimplifyCFG(BB) | true;
2256 // Merge basic blocks into their predecessor if there is only one distinct
2257 // pred, and if there is only one distinct successor of the predecessor, and
2258 // if there are no PHI nodes.
2260 if (MergeBlockIntoPredecessor(BB))
2263 // Otherwise, if this block only has a single predecessor, and if that block
2264 // is a conditional branch, see if we can hoist any code from this block up
2265 // into our predecessor.
2266 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
2267 BasicBlock *OnlyPred = 0;
2268 for (; PI != PE; ++PI) { // Search all predecessors, see if they are all same
2271 else if (*PI != OnlyPred) {
2272 OnlyPred = 0; // There are multiple different predecessors...
2278 BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator());
2279 if (BI && BI->isConditional()) {
2280 // Get the other block.
2281 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
2282 PI = pred_begin(OtherBB);
2285 if (PI == pred_end(OtherBB)) {
2286 // We have a conditional branch to two blocks that are only reachable
2287 // from the condbr. We know that the condbr dominates the two blocks,
2288 // so see if there is any identical code in the "then" and "else"
2289 // blocks. If so, we can hoist it up to the branching block.
2290 Changed |= HoistThenElseCodeToIf(BI);
2292 BasicBlock* OnlySucc = NULL;
2293 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
2297 else if (*SI != OnlySucc) {
2298 OnlySucc = 0; // There are multiple distinct successors!
2303 if (OnlySucc == OtherBB) {
2304 // If BB's only successor is the other successor of the predecessor,
2305 // i.e. a triangle, see if we can hoist any code from this block up
2306 // to the "if" block.
2307 Changed |= SpeculativelyExecuteBB(BI, BB);
2316 /// SimplifyCFG - This function is used to do simplification of a CFG. For
2317 /// example, it adjusts branches to branches to eliminate the extra hop, it
2318 /// eliminates unreachable basic blocks, and does other "peephole" optimization
2319 /// of the CFG. It returns true if a modification was made.
2321 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
2322 return SimplifyCFGOpt(TD).run(BB);