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 this is an icmp against a constant, handle this as one of the cases.
305 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
306 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE))
307 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
309 return I->getOperand(0);
314 // Otherwise, we can only handle an | or &, depending on isEQ.
315 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
318 unsigned NumValsBeforeLHS = Vals.size();
319 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
321 unsigned NumVals = Vals.size();
322 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
327 Vals.resize(NumVals);
329 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
330 // set it and return success.
331 if (Extra == 0 || Extra == I->getOperand(1)) {
332 Extra = I->getOperand(1);
336 Vals.resize(NumValsBeforeLHS);
340 // If the LHS can't be folded in, but Extra is available and RHS can, try to
342 if (Extra == 0 || Extra == I->getOperand(0)) {
343 Extra = I->getOperand(0);
344 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
347 Vals.resize(NumValsBeforeLHS);
354 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
355 Instruction* Cond = 0;
356 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
357 Cond = dyn_cast<Instruction>(SI->getCondition());
358 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
359 if (BI->isConditional())
360 Cond = dyn_cast<Instruction>(BI->getCondition());
361 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
362 Cond = dyn_cast<Instruction>(IBI->getAddress());
365 TI->eraseFromParent();
366 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
369 /// isValueEqualityComparison - Return true if the specified terminator checks
370 /// to see if a value is equal to constant integer value.
371 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
373 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
374 // Do not permit merging of large switch instructions into their
375 // predecessors unless there is only one predecessor.
376 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
377 pred_end(SI->getParent())) <= 128)
378 CV = SI->getCondition();
379 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
380 if (BI->isConditional() && BI->getCondition()->hasOneUse())
381 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
382 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
383 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
384 GetConstantInt(ICI->getOperand(1), TD))
385 CV = ICI->getOperand(0);
387 // Unwrap any lossless ptrtoint cast.
388 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
389 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
390 CV = PTII->getOperand(0);
394 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
395 /// decode all of the 'cases' that it represents and return the 'default' block.
396 BasicBlock *SimplifyCFGOpt::
397 GetValueEqualityComparisonCases(TerminatorInst *TI,
398 std::vector<std::pair<ConstantInt*,
399 BasicBlock*> > &Cases) {
400 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
401 Cases.reserve(SI->getNumCases());
402 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
403 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
404 return SI->getDefaultDest();
407 BranchInst *BI = cast<BranchInst>(TI);
408 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
409 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD),
410 BI->getSuccessor(ICI->getPredicate() ==
411 ICmpInst::ICMP_NE)));
412 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
416 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
417 /// in the list that match the specified block.
418 static void EliminateBlockCases(BasicBlock *BB,
419 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
420 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
421 if (Cases[i].second == BB) {
422 Cases.erase(Cases.begin()+i);
427 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
430 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
431 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
432 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
434 // Make V1 be smaller than V2.
435 if (V1->size() > V2->size())
438 if (V1->size() == 0) return false;
439 if (V1->size() == 1) {
441 ConstantInt *TheVal = (*V1)[0].first;
442 for (unsigned i = 0, e = V2->size(); i != e; ++i)
443 if (TheVal == (*V2)[i].first)
447 // Otherwise, just sort both lists and compare element by element.
448 array_pod_sort(V1->begin(), V1->end());
449 array_pod_sort(V2->begin(), V2->end());
450 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
451 while (i1 != e1 && i2 != e2) {
452 if ((*V1)[i1].first == (*V2)[i2].first)
454 if ((*V1)[i1].first < (*V2)[i2].first)
462 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
463 /// terminator instruction and its block is known to only have a single
464 /// predecessor block, check to see if that predecessor is also a value
465 /// comparison with the same value, and if that comparison determines the
466 /// outcome of this comparison. If so, simplify TI. This does a very limited
467 /// form of jump threading.
468 bool SimplifyCFGOpt::
469 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
471 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
472 if (!PredVal) return false; // Not a value comparison in predecessor.
474 Value *ThisVal = isValueEqualityComparison(TI);
475 assert(ThisVal && "This isn't a value comparison!!");
476 if (ThisVal != PredVal) return false; // Different predicates.
478 // Find out information about when control will move from Pred to TI's block.
479 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
480 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
482 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
484 // Find information about how control leaves this block.
485 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
486 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
487 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
489 // If TI's block is the default block from Pred's comparison, potentially
490 // simplify TI based on this knowledge.
491 if (PredDef == TI->getParent()) {
492 // If we are here, we know that the value is none of those cases listed in
493 // PredCases. If there are any cases in ThisCases that are in PredCases, we
495 if (!ValuesOverlap(PredCases, ThisCases))
498 if (isa<BranchInst>(TI)) {
499 // Okay, one of the successors of this condbr is dead. Convert it to a
501 assert(ThisCases.size() == 1 && "Branch can only have one case!");
502 // Insert the new branch.
503 Instruction *NI = BranchInst::Create(ThisDef, TI);
506 // Remove PHI node entries for the dead edge.
507 ThisCases[0].second->removePredecessor(TI->getParent());
509 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
510 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
512 EraseTerminatorInstAndDCECond(TI);
516 SwitchInst *SI = cast<SwitchInst>(TI);
517 // Okay, TI has cases that are statically dead, prune them away.
518 SmallPtrSet<Constant*, 16> DeadCases;
519 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
520 DeadCases.insert(PredCases[i].first);
522 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
523 << "Through successor TI: " << *TI);
525 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
526 if (DeadCases.count(SI->getCaseValue(i))) {
527 SI->getSuccessor(i)->removePredecessor(TI->getParent());
531 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
535 // Otherwise, TI's block must correspond to some matched value. Find out
536 // which value (or set of values) this is.
537 ConstantInt *TIV = 0;
538 BasicBlock *TIBB = TI->getParent();
539 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
540 if (PredCases[i].second == TIBB) {
542 return false; // Cannot handle multiple values coming to this block.
543 TIV = PredCases[i].first;
545 assert(TIV && "No edge from pred to succ?");
547 // Okay, we found the one constant that our value can be if we get into TI's
548 // BB. Find out which successor will unconditionally be branched to.
549 BasicBlock *TheRealDest = 0;
550 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
551 if (ThisCases[i].first == TIV) {
552 TheRealDest = ThisCases[i].second;
556 // If not handled by any explicit cases, it is handled by the default case.
557 if (TheRealDest == 0) TheRealDest = ThisDef;
559 // Remove PHI node entries for dead edges.
560 BasicBlock *CheckEdge = TheRealDest;
561 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
562 if (*SI != CheckEdge)
563 (*SI)->removePredecessor(TIBB);
567 // Insert the new branch.
568 Instruction *NI = BranchInst::Create(TheRealDest, TI);
571 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
572 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
574 EraseTerminatorInstAndDCECond(TI);
579 /// ConstantIntOrdering - This class implements a stable ordering of constant
580 /// integers that does not depend on their address. This is important for
581 /// applications that sort ConstantInt's to ensure uniqueness.
582 struct ConstantIntOrdering {
583 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
584 return LHS->getValue().ult(RHS->getValue());
589 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
590 const ConstantInt *LHS = *(const ConstantInt**)P1;
591 const ConstantInt *RHS = *(const ConstantInt**)P2;
592 return LHS->getValue().ult(RHS->getValue());
595 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
596 /// equality comparison instruction (either a switch or a branch on "X == c").
597 /// See if any of the predecessors of the terminator block are value comparisons
598 /// on the same value. If so, and if safe to do so, fold them together.
599 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
600 BasicBlock *BB = TI->getParent();
601 Value *CV = isValueEqualityComparison(TI); // CondVal
602 assert(CV && "Not a comparison?");
603 bool Changed = false;
605 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
606 while (!Preds.empty()) {
607 BasicBlock *Pred = Preds.pop_back_val();
609 // See if the predecessor is a comparison with the same value.
610 TerminatorInst *PTI = Pred->getTerminator();
611 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
613 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
614 // Figure out which 'cases' to copy from SI to PSI.
615 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
616 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
618 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
619 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
621 // Based on whether the default edge from PTI goes to BB or not, fill in
622 // PredCases and PredDefault with the new switch cases we would like to
624 SmallVector<BasicBlock*, 8> NewSuccessors;
626 if (PredDefault == BB) {
627 // If this is the default destination from PTI, only the edges in TI
628 // that don't occur in PTI, or that branch to BB will be activated.
629 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
630 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
631 if (PredCases[i].second != BB)
632 PTIHandled.insert(PredCases[i].first);
634 // The default destination is BB, we don't need explicit targets.
635 std::swap(PredCases[i], PredCases.back());
636 PredCases.pop_back();
640 // Reconstruct the new switch statement we will be building.
641 if (PredDefault != BBDefault) {
642 PredDefault->removePredecessor(Pred);
643 PredDefault = BBDefault;
644 NewSuccessors.push_back(BBDefault);
646 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
647 if (!PTIHandled.count(BBCases[i].first) &&
648 BBCases[i].second != BBDefault) {
649 PredCases.push_back(BBCases[i]);
650 NewSuccessors.push_back(BBCases[i].second);
654 // If this is not the default destination from PSI, only the edges
655 // in SI that occur in PSI with a destination of BB will be
657 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
658 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
659 if (PredCases[i].second == BB) {
660 PTIHandled.insert(PredCases[i].first);
661 std::swap(PredCases[i], PredCases.back());
662 PredCases.pop_back();
666 // Okay, now we know which constants were sent to BB from the
667 // predecessor. Figure out where they will all go now.
668 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
669 if (PTIHandled.count(BBCases[i].first)) {
670 // If this is one we are capable of getting...
671 PredCases.push_back(BBCases[i]);
672 NewSuccessors.push_back(BBCases[i].second);
673 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
676 // If there are any constants vectored to BB that TI doesn't handle,
677 // they must go to the default destination of TI.
678 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
680 E = PTIHandled.end(); I != E; ++I) {
681 PredCases.push_back(std::make_pair(*I, BBDefault));
682 NewSuccessors.push_back(BBDefault);
686 // Okay, at this point, we know which new successor Pred will get. Make
687 // sure we update the number of entries in the PHI nodes for these
689 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
690 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
692 // Convert pointer to int before we switch.
693 if (CV->getType()->isPointerTy()) {
694 assert(TD && "Cannot switch on pointer without TargetData");
695 CV = new PtrToIntInst(CV, TD->getIntPtrType(CV->getContext()),
699 // Now that the successors are updated, create the new Switch instruction.
700 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
701 PredCases.size(), PTI);
702 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
703 NewSI->addCase(PredCases[i].first, PredCases[i].second);
705 EraseTerminatorInstAndDCECond(PTI);
707 // Okay, last check. If BB is still a successor of PSI, then we must
708 // have an infinite loop case. If so, add an infinitely looping block
709 // to handle the case to preserve the behavior of the code.
710 BasicBlock *InfLoopBlock = 0;
711 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
712 if (NewSI->getSuccessor(i) == BB) {
713 if (InfLoopBlock == 0) {
714 // Insert it at the end of the function, because it's either code,
715 // or it won't matter if it's hot. :)
716 InfLoopBlock = BasicBlock::Create(BB->getContext(),
717 "infloop", BB->getParent());
718 BranchInst::Create(InfLoopBlock, InfLoopBlock);
720 NewSI->setSuccessor(i, InfLoopBlock);
729 // isSafeToHoistInvoke - If we would need to insert a select that uses the
730 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
731 // would need to do this), we can't hoist the invoke, as there is nowhere
732 // to put the select in this case.
733 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
734 Instruction *I1, Instruction *I2) {
735 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
737 for (BasicBlock::iterator BBI = SI->begin();
738 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
739 Value *BB1V = PN->getIncomingValueForBlock(BB1);
740 Value *BB2V = PN->getIncomingValueForBlock(BB2);
741 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
749 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
750 /// BB2, hoist any common code in the two blocks up into the branch block. The
751 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
752 static bool HoistThenElseCodeToIf(BranchInst *BI) {
753 // This does very trivial matching, with limited scanning, to find identical
754 // instructions in the two blocks. In particular, we don't want to get into
755 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
756 // such, we currently just scan for obviously identical instructions in an
758 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
759 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
761 BasicBlock::iterator BB1_Itr = BB1->begin();
762 BasicBlock::iterator BB2_Itr = BB2->begin();
764 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
765 while (isa<DbgInfoIntrinsic>(I1))
767 while (isa<DbgInfoIntrinsic>(I2))
769 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
770 !I1->isIdenticalToWhenDefined(I2) ||
771 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
774 // If we get here, we can hoist at least one instruction.
775 BasicBlock *BIParent = BI->getParent();
778 // If we are hoisting the terminator instruction, don't move one (making a
779 // broken BB), instead clone it, and remove BI.
780 if (isa<TerminatorInst>(I1))
781 goto HoistTerminator;
783 // For a normal instruction, we just move one to right before the branch,
784 // then replace all uses of the other with the first. Finally, we remove
785 // the now redundant second instruction.
786 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
787 if (!I2->use_empty())
788 I2->replaceAllUsesWith(I1);
789 I1->intersectOptionalDataWith(I2);
790 BB2->getInstList().erase(I2);
793 while (isa<DbgInfoIntrinsic>(I1))
796 while (isa<DbgInfoIntrinsic>(I2))
798 } while (I1->getOpcode() == I2->getOpcode() &&
799 I1->isIdenticalToWhenDefined(I2));
804 // It may not be possible to hoist an invoke.
805 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
808 // Okay, it is safe to hoist the terminator.
809 Instruction *NT = I1->clone();
810 BIParent->getInstList().insert(BI, NT);
811 if (!NT->getType()->isVoidTy()) {
812 I1->replaceAllUsesWith(NT);
813 I2->replaceAllUsesWith(NT);
817 // Hoisting one of the terminators from our successor is a great thing.
818 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
819 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
820 // nodes, so we insert select instruction to compute the final result.
821 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
822 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
824 for (BasicBlock::iterator BBI = SI->begin();
825 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
826 Value *BB1V = PN->getIncomingValueForBlock(BB1);
827 Value *BB2V = PN->getIncomingValueForBlock(BB2);
828 if (BB1V == BB2V) continue;
830 // These values do not agree. Insert a select instruction before NT
831 // that determines the right value.
832 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
834 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
835 BB1V->getName()+"."+BB2V->getName(), NT);
836 // Make the PHI node use the select for all incoming values for BB1/BB2
837 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
838 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
839 PN->setIncomingValue(i, SI);
843 // Update any PHI nodes in our new successors.
844 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
845 AddPredecessorToBlock(*SI, BIParent, BB1);
847 EraseTerminatorInstAndDCECond(BI);
851 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
852 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
853 /// (for now, restricted to a single instruction that's side effect free) from
854 /// the BB1 into the branch block to speculatively execute it.
855 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
856 // Only speculatively execution a single instruction (not counting the
857 // terminator) for now.
858 Instruction *HInst = NULL;
859 Instruction *Term = BB1->getTerminator();
860 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
862 Instruction *I = BBI;
864 if (isa<DbgInfoIntrinsic>(I)) continue;
865 if (I == Term) break;
874 // Be conservative for now. FP select instruction can often be expensive.
875 Value *BrCond = BI->getCondition();
876 if (isa<FCmpInst>(BrCond))
879 // If BB1 is actually on the false edge of the conditional branch, remember
880 // to swap the select operands later.
882 if (BB1 != BI->getSuccessor(0)) {
883 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
890 // br i1 %t1, label %BB1, label %BB2
899 // %t3 = select i1 %t1, %t2, %t3
900 switch (HInst->getOpcode()) {
901 default: return false; // Not safe / profitable to hoist.
902 case Instruction::Add:
903 case Instruction::Sub:
904 // Not worth doing for vector ops.
905 if (HInst->getType()->isVectorTy())
908 case Instruction::And:
909 case Instruction::Or:
910 case Instruction::Xor:
911 case Instruction::Shl:
912 case Instruction::LShr:
913 case Instruction::AShr:
914 // Don't mess with vector operations.
915 if (HInst->getType()->isVectorTy())
917 break; // These are all cheap and non-trapping instructions.
920 // If the instruction is obviously dead, don't try to predicate it.
921 if (HInst->use_empty()) {
922 HInst->eraseFromParent();
926 // Can we speculatively execute the instruction? And what is the value
927 // if the condition is false? Consider the phi uses, if the incoming value
928 // from the "if" block are all the same V, then V is the value of the
929 // select if the condition is false.
930 BasicBlock *BIParent = BI->getParent();
931 SmallVector<PHINode*, 4> PHIUses;
932 Value *FalseV = NULL;
934 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
935 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
937 // Ignore any user that is not a PHI node in BB2. These can only occur in
938 // unreachable blocks, because they would not be dominated by the instr.
939 PHINode *PN = dyn_cast<PHINode>(*UI);
940 if (!PN || PN->getParent() != BB2)
942 PHIUses.push_back(PN);
944 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
947 else if (FalseV != PHIV)
948 return false; // Inconsistent value when condition is false.
951 assert(FalseV && "Must have at least one user, and it must be a PHI");
953 // Do not hoist the instruction if any of its operands are defined but not
954 // used in this BB. The transformation will prevent the operand from
955 // being sunk into the use block.
956 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
958 Instruction *OpI = dyn_cast<Instruction>(*i);
959 if (OpI && OpI->getParent() == BIParent &&
960 !OpI->isUsedInBasicBlock(BIParent))
964 // If we get here, we can hoist the instruction. Try to place it
965 // before the icmp instruction preceding the conditional branch.
966 BasicBlock::iterator InsertPos = BI;
967 if (InsertPos != BIParent->begin())
969 // Skip debug info between condition and branch.
970 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
972 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
973 SmallPtrSet<Instruction *, 4> BB1Insns;
974 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
975 BB1I != BB1E; ++BB1I)
976 BB1Insns.insert(BB1I);
977 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
979 Instruction *Use = cast<Instruction>(*UI);
980 if (!BB1Insns.count(Use)) continue;
982 // If BrCond uses the instruction that place it just before
983 // branch instruction.
989 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
991 // Create a select whose true value is the speculatively executed value and
992 // false value is the previously determined FalseV.
995 SI = SelectInst::Create(BrCond, FalseV, HInst,
996 FalseV->getName() + "." + HInst->getName(), BI);
998 SI = SelectInst::Create(BrCond, HInst, FalseV,
999 HInst->getName() + "." + FalseV->getName(), BI);
1001 // Make the PHI node use the select for all incoming values for "then" and
1003 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1004 PHINode *PN = PHIUses[i];
1005 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1006 if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent)
1007 PN->setIncomingValue(j, SI);
1014 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1015 /// across this block.
1016 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1017 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1020 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1021 if (isa<DbgInfoIntrinsic>(BBI))
1023 if (Size > 10) return false; // Don't clone large BB's.
1026 // We can only support instructions that do not define values that are
1027 // live outside of the current basic block.
1028 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1030 Instruction *U = cast<Instruction>(*UI);
1031 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1034 // Looks ok, continue checking.
1040 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1041 /// that is defined in the same block as the branch and if any PHI entries are
1042 /// constants, thread edges corresponding to that entry to be branches to their
1043 /// ultimate destination.
1044 static bool FoldCondBranchOnPHI(BranchInst *BI) {
1045 BasicBlock *BB = BI->getParent();
1046 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1047 // NOTE: we currently cannot transform this case if the PHI node is used
1048 // outside of the block.
1049 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1052 // Degenerate case of a single entry PHI.
1053 if (PN->getNumIncomingValues() == 1) {
1054 FoldSingleEntryPHINodes(PN->getParent());
1058 // Now we know that this block has multiple preds and two succs.
1059 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1061 // Okay, this is a simple enough basic block. See if any phi values are
1063 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1064 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1065 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1067 // Okay, we now know that all edges from PredBB should be revectored to
1068 // branch to RealDest.
1069 BasicBlock *PredBB = PN->getIncomingBlock(i);
1070 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1072 if (RealDest == BB) continue; // Skip self loops.
1074 // The dest block might have PHI nodes, other predecessors and other
1075 // difficult cases. Instead of being smart about this, just insert a new
1076 // block that jumps to the destination block, effectively splitting
1077 // the edge we are about to create.
1078 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1079 RealDest->getName()+".critedge",
1080 RealDest->getParent(), RealDest);
1081 BranchInst::Create(RealDest, EdgeBB);
1083 for (BasicBlock::iterator BBI = RealDest->begin();
1084 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1085 Value *V = PN->getIncomingValueForBlock(BB);
1086 PN->addIncoming(V, EdgeBB);
1089 // BB may have instructions that are being threaded over. Clone these
1090 // instructions into EdgeBB. We know that there will be no uses of the
1091 // cloned instructions outside of EdgeBB.
1092 BasicBlock::iterator InsertPt = EdgeBB->begin();
1093 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1094 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1095 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1096 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1099 // Clone the instruction.
1100 Instruction *N = BBI->clone();
1101 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1103 // Update operands due to translation.
1104 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1106 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1107 if (PI != TranslateMap.end())
1111 // Check for trivial simplification.
1112 if (Constant *C = ConstantFoldInstruction(N)) {
1113 TranslateMap[BBI] = C;
1114 delete N; // Constant folded away, don't need actual inst
1116 // Insert the new instruction into its new home.
1117 EdgeBB->getInstList().insert(InsertPt, N);
1118 if (!BBI->use_empty())
1119 TranslateMap[BBI] = N;
1123 // Loop over all of the edges from PredBB to BB, changing them to branch
1124 // to EdgeBB instead.
1125 TerminatorInst *PredBBTI = PredBB->getTerminator();
1126 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1127 if (PredBBTI->getSuccessor(i) == BB) {
1128 BB->removePredecessor(PredBB);
1129 PredBBTI->setSuccessor(i, EdgeBB);
1132 // Recurse, simplifying any other constants.
1133 return FoldCondBranchOnPHI(BI) | true;
1139 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1140 /// PHI node, see if we can eliminate it.
1141 static bool FoldTwoEntryPHINode(PHINode *PN) {
1142 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1143 // statement", which has a very simple dominance structure. Basically, we
1144 // are trying to find the condition that is being branched on, which
1145 // subsequently causes this merge to happen. We really want control
1146 // dependence information for this check, but simplifycfg can't keep it up
1147 // to date, and this catches most of the cases we care about anyway.
1149 BasicBlock *BB = PN->getParent();
1150 BasicBlock *IfTrue, *IfFalse;
1151 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1152 if (!IfCond) return false;
1154 // Okay, we found that we can merge this two-entry phi node into a select.
1155 // Doing so would require us to fold *all* two entry phi nodes in this block.
1156 // At some point this becomes non-profitable (particularly if the target
1157 // doesn't support cmov's). Only do this transformation if there are two or
1158 // fewer PHI nodes in this block.
1159 unsigned NumPhis = 0;
1160 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1164 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1165 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1167 // Loop over the PHI's seeing if we can promote them all to select
1168 // instructions. While we are at it, keep track of the instructions
1169 // that need to be moved to the dominating block.
1170 std::set<Instruction*> AggressiveInsts;
1172 BasicBlock::iterator AfterPHIIt = BB->begin();
1173 while (isa<PHINode>(AfterPHIIt)) {
1174 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1175 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1176 if (PN->getIncomingValue(0) != PN)
1177 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1179 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1180 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1181 &AggressiveInsts) ||
1182 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1183 &AggressiveInsts)) {
1188 // If we all PHI nodes are promotable, check to make sure that all
1189 // instructions in the predecessor blocks can be promoted as well. If
1190 // not, we won't be able to get rid of the control flow, so it's not
1191 // worth promoting to select instructions.
1192 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1193 PN = cast<PHINode>(BB->begin());
1194 BasicBlock *Pred = PN->getIncomingBlock(0);
1195 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1197 DomBlock = *pred_begin(Pred);
1198 for (BasicBlock::iterator I = Pred->begin();
1199 !isa<TerminatorInst>(I); ++I)
1200 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1201 // This is not an aggressive instruction that we can promote.
1202 // Because of this, we won't be able to get rid of the control
1203 // flow, so the xform is not worth it.
1208 Pred = PN->getIncomingBlock(1);
1209 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1211 DomBlock = *pred_begin(Pred);
1212 for (BasicBlock::iterator I = Pred->begin();
1213 !isa<TerminatorInst>(I); ++I)
1214 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1215 // This is not an aggressive instruction that we can promote.
1216 // Because of this, we won't be able to get rid of the control
1217 // flow, so the xform is not worth it.
1222 // If we can still promote the PHI nodes after this gauntlet of tests,
1223 // do all of the PHI's now.
1225 // Move all 'aggressive' instructions, which are defined in the
1226 // conditional parts of the if's up to the dominating block.
1228 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1229 IfBlock1->getInstList(), IfBlock1->begin(),
1230 IfBlock1->getTerminator());
1232 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1233 IfBlock2->getInstList(), IfBlock2->begin(),
1234 IfBlock2->getTerminator());
1236 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1237 // Change the PHI node into a select instruction.
1238 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1239 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1241 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1242 PN->replaceAllUsesWith(NV);
1245 BB->getInstList().erase(PN);
1250 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1251 /// to two returning blocks, try to merge them together into one return,
1252 /// introducing a select if the return values disagree.
1253 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1254 assert(BI->isConditional() && "Must be a conditional branch");
1255 BasicBlock *TrueSucc = BI->getSuccessor(0);
1256 BasicBlock *FalseSucc = BI->getSuccessor(1);
1257 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1258 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1260 // Check to ensure both blocks are empty (just a return) or optionally empty
1261 // with PHI nodes. If there are other instructions, merging would cause extra
1262 // computation on one path or the other.
1263 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1265 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1268 // Okay, we found a branch that is going to two return nodes. If
1269 // there is no return value for this function, just change the
1270 // branch into a return.
1271 if (FalseRet->getNumOperands() == 0) {
1272 TrueSucc->removePredecessor(BI->getParent());
1273 FalseSucc->removePredecessor(BI->getParent());
1274 ReturnInst::Create(BI->getContext(), 0, BI);
1275 EraseTerminatorInstAndDCECond(BI);
1279 // Otherwise, figure out what the true and false return values are
1280 // so we can insert a new select instruction.
1281 Value *TrueValue = TrueRet->getReturnValue();
1282 Value *FalseValue = FalseRet->getReturnValue();
1284 // Unwrap any PHI nodes in the return blocks.
1285 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1286 if (TVPN->getParent() == TrueSucc)
1287 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1288 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1289 if (FVPN->getParent() == FalseSucc)
1290 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1292 // In order for this transformation to be safe, we must be able to
1293 // unconditionally execute both operands to the return. This is
1294 // normally the case, but we could have a potentially-trapping
1295 // constant expression that prevents this transformation from being
1297 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1300 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1304 // Okay, we collected all the mapped values and checked them for sanity, and
1305 // defined to really do this transformation. First, update the CFG.
1306 TrueSucc->removePredecessor(BI->getParent());
1307 FalseSucc->removePredecessor(BI->getParent());
1309 // Insert select instructions where needed.
1310 Value *BrCond = BI->getCondition();
1312 // Insert a select if the results differ.
1313 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1314 } else if (isa<UndefValue>(TrueValue)) {
1315 TrueValue = FalseValue;
1317 TrueValue = SelectInst::Create(BrCond, TrueValue,
1318 FalseValue, "retval", BI);
1322 Value *RI = !TrueValue ?
1323 ReturnInst::Create(BI->getContext(), BI) :
1324 ReturnInst::Create(BI->getContext(), TrueValue, BI);
1327 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1328 << "\n " << *BI << "NewRet = " << *RI
1329 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1331 EraseTerminatorInstAndDCECond(BI);
1336 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1337 /// and if a predecessor branches to us and one of our successors, fold the
1338 /// setcc into the predecessor and use logical operations to pick the right
1340 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1341 BasicBlock *BB = BI->getParent();
1342 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1343 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1344 Cond->getParent() != BB || !Cond->hasOneUse())
1347 // Only allow this if the condition is a simple instruction that can be
1348 // executed unconditionally. It must be in the same block as the branch, and
1349 // must be at the front of the block.
1350 BasicBlock::iterator FrontIt = BB->front();
1351 // Ignore dbg intrinsics.
1352 while(isa<DbgInfoIntrinsic>(FrontIt))
1355 // Allow a single instruction to be hoisted in addition to the compare
1356 // that feeds the branch. We later ensure that any values that _it_ uses
1357 // were also live in the predecessor, so that we don't unnecessarily create
1358 // register pressure or inhibit out-of-order execution.
1359 Instruction *BonusInst = 0;
1360 if (&*FrontIt != Cond &&
1361 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1362 FrontIt->isSafeToSpeculativelyExecute()) {
1363 BonusInst = &*FrontIt;
1367 // Only a single bonus inst is allowed.
1368 if (&*FrontIt != Cond)
1371 // Make sure the instruction after the condition is the cond branch.
1372 BasicBlock::iterator CondIt = Cond; ++CondIt;
1373 // Ingore dbg intrinsics.
1374 while(isa<DbgInfoIntrinsic>(CondIt))
1376 if (&*CondIt != BI) {
1377 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!");
1381 // Cond is known to be a compare or binary operator. Check to make sure that
1382 // neither operand is a potentially-trapping constant expression.
1383 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1386 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1391 // Finally, don't infinitely unroll conditional loops.
1392 BasicBlock *TrueDest = BI->getSuccessor(0);
1393 BasicBlock *FalseDest = BI->getSuccessor(1);
1394 if (TrueDest == BB || FalseDest == BB)
1397 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1398 BasicBlock *PredBlock = *PI;
1399 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1401 // Check that we have two conditional branches. If there is a PHI node in
1402 // the common successor, verify that the same value flows in from both
1404 if (PBI == 0 || PBI->isUnconditional() ||
1405 !SafeToMergeTerminators(BI, PBI))
1408 // Ensure that any values used in the bonus instruction are also used
1409 // by the terminator of the predecessor. This means that those values
1410 // must already have been resolved, so we won't be inhibiting the
1411 // out-of-order core by speculating them earlier.
1413 // Collect the values used by the bonus inst
1414 SmallPtrSet<Value*, 4> UsedValues;
1415 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1416 OE = BonusInst->op_end(); OI != OE; ++OI) {
1418 if (!isa<Constant>(V))
1419 UsedValues.insert(V);
1422 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1423 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1425 // Walk up to four levels back up the use-def chain of the predecessor's
1426 // terminator to see if all those values were used. The choice of four
1427 // levels is arbitrary, to provide a compile-time-cost bound.
1428 while (!Worklist.empty()) {
1429 std::pair<Value*, unsigned> Pair = Worklist.back();
1430 Worklist.pop_back();
1432 if (Pair.second >= 4) continue;
1433 UsedValues.erase(Pair.first);
1434 if (UsedValues.empty()) break;
1436 if (Instruction* I = dyn_cast<Instruction>(Pair.first)) {
1437 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1439 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1443 if (!UsedValues.empty()) return false;
1446 Instruction::BinaryOps Opc;
1447 bool InvertPredCond = false;
1449 if (PBI->getSuccessor(0) == TrueDest)
1450 Opc = Instruction::Or;
1451 else if (PBI->getSuccessor(1) == FalseDest)
1452 Opc = Instruction::And;
1453 else if (PBI->getSuccessor(0) == FalseDest)
1454 Opc = Instruction::And, InvertPredCond = true;
1455 else if (PBI->getSuccessor(1) == TrueDest)
1456 Opc = Instruction::Or, InvertPredCond = true;
1460 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1462 // If we need to invert the condition in the pred block to match, do so now.
1463 if (InvertPredCond) {
1465 BinaryOperator::CreateNot(PBI->getCondition(),
1466 PBI->getCondition()->getName()+".not", PBI);
1467 PBI->setCondition(NewCond);
1468 BasicBlock *OldTrue = PBI->getSuccessor(0);
1469 BasicBlock *OldFalse = PBI->getSuccessor(1);
1470 PBI->setSuccessor(0, OldFalse);
1471 PBI->setSuccessor(1, OldTrue);
1474 // If we have a bonus inst, clone it into the predecessor block.
1475 Instruction *NewBonus = 0;
1477 NewBonus = BonusInst->clone();
1478 PredBlock->getInstList().insert(PBI, NewBonus);
1479 NewBonus->takeName(BonusInst);
1480 BonusInst->setName(BonusInst->getName()+".old");
1483 // Clone Cond into the predecessor basic block, and or/and the
1484 // two conditions together.
1485 Instruction *New = Cond->clone();
1486 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1487 PredBlock->getInstList().insert(PBI, New);
1488 New->takeName(Cond);
1489 Cond->setName(New->getName()+".old");
1491 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1492 New, "or.cond", PBI);
1493 PBI->setCondition(NewCond);
1494 if (PBI->getSuccessor(0) == BB) {
1495 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1496 PBI->setSuccessor(0, TrueDest);
1498 if (PBI->getSuccessor(1) == BB) {
1499 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1500 PBI->setSuccessor(1, FalseDest);
1507 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1508 /// predecessor of another block, this function tries to simplify it. We know
1509 /// that PBI and BI are both conditional branches, and BI is in one of the
1510 /// successor blocks of PBI - PBI branches to BI.
1511 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1512 assert(PBI->isConditional() && BI->isConditional());
1513 BasicBlock *BB = BI->getParent();
1515 // If this block ends with a branch instruction, and if there is a
1516 // predecessor that ends on a branch of the same condition, make
1517 // this conditional branch redundant.
1518 if (PBI->getCondition() == BI->getCondition() &&
1519 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1520 // Okay, the outcome of this conditional branch is statically
1521 // knowable. If this block had a single pred, handle specially.
1522 if (BB->getSinglePredecessor()) {
1523 // Turn this into a branch on constant.
1524 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1525 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1527 return true; // Nuke the branch on constant.
1530 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1531 // in the constant and simplify the block result. Subsequent passes of
1532 // simplifycfg will thread the block.
1533 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1534 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1535 BI->getCondition()->getName() + ".pr",
1537 // Okay, we're going to insert the PHI node. Since PBI is not the only
1538 // predecessor, compute the PHI'd conditional value for all of the preds.
1539 // Any predecessor where the condition is not computable we keep symbolic.
1540 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1541 BasicBlock *P = *PI;
1542 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
1543 PBI != BI && PBI->isConditional() &&
1544 PBI->getCondition() == BI->getCondition() &&
1545 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1546 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1547 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1550 NewPN->addIncoming(BI->getCondition(), P);
1554 BI->setCondition(NewPN);
1559 // If this is a conditional branch in an empty block, and if any
1560 // predecessors is a conditional branch to one of our destinations,
1561 // fold the conditions into logical ops and one cond br.
1562 BasicBlock::iterator BBI = BB->begin();
1563 // Ignore dbg intrinsics.
1564 while (isa<DbgInfoIntrinsic>(BBI))
1570 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1575 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1577 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1578 PBIOp = 0, BIOp = 1;
1579 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1580 PBIOp = 1, BIOp = 0;
1581 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1586 // Check to make sure that the other destination of this branch
1587 // isn't BB itself. If so, this is an infinite loop that will
1588 // keep getting unwound.
1589 if (PBI->getSuccessor(PBIOp) == BB)
1592 // Do not perform this transformation if it would require
1593 // insertion of a large number of select instructions. For targets
1594 // without predication/cmovs, this is a big pessimization.
1595 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1597 unsigned NumPhis = 0;
1598 for (BasicBlock::iterator II = CommonDest->begin();
1599 isa<PHINode>(II); ++II, ++NumPhis)
1600 if (NumPhis > 2) // Disable this xform.
1603 // Finally, if everything is ok, fold the branches to logical ops.
1604 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1606 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
1607 << "AND: " << *BI->getParent());
1610 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1611 // branch in it, where one edge (OtherDest) goes back to itself but the other
1612 // exits. We don't *know* that the program avoids the infinite loop
1613 // (even though that seems likely). If we do this xform naively, we'll end up
1614 // recursively unpeeling the loop. Since we know that (after the xform is
1615 // done) that the block *is* infinite if reached, we just make it an obviously
1616 // infinite loop with no cond branch.
1617 if (OtherDest == BB) {
1618 // Insert it at the end of the function, because it's either code,
1619 // or it won't matter if it's hot. :)
1620 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1621 "infloop", BB->getParent());
1622 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1623 OtherDest = InfLoopBlock;
1626 DEBUG(dbgs() << *PBI->getParent()->getParent());
1628 // BI may have other predecessors. Because of this, we leave
1629 // it alone, but modify PBI.
1631 // Make sure we get to CommonDest on True&True directions.
1632 Value *PBICond = PBI->getCondition();
1634 PBICond = BinaryOperator::CreateNot(PBICond,
1635 PBICond->getName()+".not",
1637 Value *BICond = BI->getCondition();
1639 BICond = BinaryOperator::CreateNot(BICond,
1640 BICond->getName()+".not",
1642 // Merge the conditions.
1643 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1645 // Modify PBI to branch on the new condition to the new dests.
1646 PBI->setCondition(Cond);
1647 PBI->setSuccessor(0, CommonDest);
1648 PBI->setSuccessor(1, OtherDest);
1650 // OtherDest may have phi nodes. If so, add an entry from PBI's
1651 // block that are identical to the entries for BI's block.
1653 for (BasicBlock::iterator II = OtherDest->begin();
1654 (PN = dyn_cast<PHINode>(II)); ++II) {
1655 Value *V = PN->getIncomingValueForBlock(BB);
1656 PN->addIncoming(V, PBI->getParent());
1659 // We know that the CommonDest already had an edge from PBI to
1660 // it. If it has PHIs though, the PHIs may have different
1661 // entries for BB and PBI's BB. If so, insert a select to make
1663 for (BasicBlock::iterator II = CommonDest->begin();
1664 (PN = dyn_cast<PHINode>(II)); ++II) {
1665 Value *BIV = PN->getIncomingValueForBlock(BB);
1666 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1667 Value *PBIV = PN->getIncomingValue(PBBIdx);
1669 // Insert a select in PBI to pick the right value.
1670 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1671 PBIV->getName()+".mux", PBI);
1672 PN->setIncomingValue(PBBIdx, NV);
1676 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1677 DEBUG(dbgs() << *PBI->getParent()->getParent());
1679 // This basic block is probably dead. We know it has at least
1680 // one fewer predecessor.
1684 // SimplifyIndirectBrOnSelect - Replaces
1685 // (indirectbr (select cond, blockaddress(@fn, BlockA),
1686 // blockaddress(@fn, BlockB)))
1688 // (br cond, BlockA, BlockB).
1689 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
1690 // Check that both operands of the select are block addresses.
1691 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
1692 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
1696 // Extract the actual blocks.
1697 BasicBlock *TrueBB = TBA->getBasicBlock();
1698 BasicBlock *FalseBB = FBA->getBasicBlock();
1700 // Remove any superfluous successor edges from the CFG.
1701 // First, figure out which successors to preserve.
1702 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
1704 BasicBlock *KeepEdge1 = TrueBB;
1705 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
1707 // Then remove the rest.
1708 for (unsigned I = 0, E = IBI->getNumSuccessors(); I != E; ++I) {
1709 BasicBlock *Succ = IBI->getSuccessor(I);
1710 // Make sure only to keep exactly one copy of each edge.
1711 if (Succ == KeepEdge1)
1713 else if (Succ == KeepEdge2)
1716 Succ->removePredecessor(IBI->getParent());
1719 // Insert an appropriate new terminator.
1720 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
1721 if (TrueBB == FalseBB)
1722 // We were only looking for one successor, and it was present.
1723 // Create an unconditional branch to it.
1724 BranchInst::Create(TrueBB, IBI);
1726 // We found both of the successors we were looking for.
1727 // Create a conditional branch sharing the condition of the select.
1728 BranchInst::Create(TrueBB, FalseBB, SI->getCondition(), IBI);
1729 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
1730 // Neither of the selected blocks were successors, so this
1731 // indirectbr must be unreachable.
1732 new UnreachableInst(IBI->getContext(), IBI);
1734 // One of the selected values was a successor, but the other wasn't.
1735 // Insert an unconditional branch to the one that was found;
1736 // the edge to the one that wasn't must be unreachable.
1738 // Only TrueBB was found.
1739 BranchInst::Create(TrueBB, IBI);
1741 // Only FalseBB was found.
1742 BranchInst::Create(FalseBB, IBI);
1745 EraseTerminatorInstAndDCECond(IBI);
1749 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
1750 /// instruction (a seteq/setne with a constant) as the only instruction in a
1751 /// block that ends with an uncond branch. We are looking for a very specific
1752 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
1753 /// this case, we merge the first two "or's of icmp" into a switch, but then the
1754 /// default value goes to an uncond block with a seteq in it, we get something
1757 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
1759 /// %tmp = icmp eq i8 %A, 92
1762 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
1764 /// We prefer to split the edge to 'end' so that there is a true/false entry to
1765 /// the PHI, merging the third icmp into the switch.
1766 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI) {
1767 BasicBlock *BB = ICI->getParent();
1768 // If the block has any PHIs in it or the icmp has multiple uses, it is too
1770 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
1772 Value *V = ICI->getOperand(0);
1773 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
1775 // The pattern we're looking for is where our only predecessor is a switch on
1776 // 'V' and this block is the default case for the switch. In this case we can
1777 // fold the compared value into the switch to simplify things.
1778 BasicBlock *Pred = BB->getSinglePredecessor();
1779 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
1781 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
1782 if (SI->getCondition() != V)
1785 // If BB is reachable on a non-default case, then we simply know the value of
1786 // V in this block. Substitute it and constant fold the icmp instruction
1788 if (SI->getDefaultDest() != BB) {
1789 ConstantInt *VVal = SI->findCaseDest(BB);
1790 assert(VVal && "Should have a unique destination value");
1791 ICI->setOperand(0, VVal);
1793 if (Constant *C = ConstantFoldInstruction(ICI)) {
1794 ICI->replaceAllUsesWith(C);
1795 ICI->eraseFromParent();
1797 // BB is now empty, so it is likely to simplify away.
1798 return SimplifyCFG(BB) | true;
1801 // Ok, the block is reachable from the default dest. If the constant we're
1802 // comparing exists in one of the other edges, then we can constant fold ICI
1804 if (SI->findCaseValue(Cst) != 0) {
1806 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1807 V = ConstantInt::getFalse(BB->getContext());
1809 V = ConstantInt::getTrue(BB->getContext());
1811 ICI->replaceAllUsesWith(V);
1812 ICI->eraseFromParent();
1813 // BB is now empty, so it is likely to simplify away.
1814 return SimplifyCFG(BB) | true;
1817 // The use of the icmp has to be in the 'end' block, by the only PHI node in
1819 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
1820 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
1821 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
1822 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
1825 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
1827 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
1828 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
1830 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1831 std::swap(DefaultCst, NewCst);
1833 // Replace ICI (which is used by the PHI for the default value) with true or
1834 // false depending on if it is EQ or NE.
1835 ICI->replaceAllUsesWith(DefaultCst);
1836 ICI->eraseFromParent();
1838 // Okay, the switch goes to this block on a default value. Add an edge from
1839 // the switch to the merge point on the compared value.
1840 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
1841 BB->getParent(), BB);
1842 SI->addCase(Cst, NewBB);
1844 // NewBB branches to the phi block, add the uncond branch and the phi entry.
1845 BranchInst::Create(SuccBlock, NewBB);
1846 PHIUse->addIncoming(NewCst, NewBB);
1850 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
1851 /// Check to see if it is branching on an or/and chain of icmp instructions, and
1852 /// fold it into a switch instruction if so.
1853 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD) {
1854 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1855 if (Cond == 0) return false;
1858 // Change br (X == 0 | X == 1), T, F into a switch instruction.
1859 // If this is a bunch of seteq's or'd together, or if it's a bunch of
1860 // 'setne's and'ed together, collect them.
1862 std::vector<ConstantInt*> Values;
1863 bool TrueWhenEqual = true;
1864 Value *ExtraCase = 0;
1866 if (Cond->getOpcode() == Instruction::Or) {
1867 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true);
1868 } else if (Cond->getOpcode() == Instruction::And) {
1869 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false);
1870 TrueWhenEqual = false;
1873 // If we didn't have a multiply compared value, fail.
1874 if (CompVal == 0) return false;
1876 // There might be duplicate constants in the list, which the switch
1877 // instruction can't handle, remove them now.
1878 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
1879 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
1881 // If Extra was used, we require at least two switch values to do the
1882 // transformation. A switch with one value is just an cond branch.
1883 if (ExtraCase && Values.size() < 2) return false;
1885 // Figure out which block is which destination.
1886 BasicBlock *DefaultBB = BI->getSuccessor(1);
1887 BasicBlock *EdgeBB = BI->getSuccessor(0);
1888 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
1890 BasicBlock *BB = BI->getParent();
1892 // If there are any extra values that couldn't be folded into the switch
1893 // then we evaluate them with an explicit branch first. Split the block
1894 // right before the condbr to handle it.
1896 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
1897 // Remove the uncond branch added to the old block.
1898 TerminatorInst *OldTI = BB->getTerminator();
1900 BranchInst::Create(EdgeBB, NewBB, ExtraCase, OldTI);
1901 OldTI->eraseFromParent();
1905 // Convert pointer to int before we switch.
1906 if (CompVal->getType()->isPointerTy()) {
1907 assert(TD && "Cannot switch on pointer without TargetData");
1908 CompVal = new PtrToIntInst(CompVal,
1909 TD->getIntPtrType(CompVal->getContext()),
1913 // Create the new switch instruction now.
1915 SwitchInst::Create(CompVal, DefaultBB, Values.size(), BI);
1917 // Add all of the 'cases' to the switch instruction.
1918 for (unsigned i = 0, e = Values.size(); i != e; ++i)
1919 New->addCase(Values[i], EdgeBB);
1921 // We added edges from PI to the EdgeBB. As such, if there were any
1922 // PHI nodes in EdgeBB, they need entries to be added corresponding to
1923 // the number of edges added.
1924 for (BasicBlock::iterator BBI = EdgeBB->begin();
1925 isa<PHINode>(BBI); ++BBI) {
1926 PHINode *PN = cast<PHINode>(BBI);
1927 Value *InVal = PN->getIncomingValueForBlock(BB);
1928 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
1929 PN->addIncoming(InVal, BB);
1932 // Erase the old branch instruction.
1933 EraseTerminatorInstAndDCECond(BI);
1937 bool SimplifyCFGOpt::run(BasicBlock *BB) {
1938 bool Changed = false;
1939 Function *Fn = BB->getParent();
1941 assert(BB && Fn && "Block not embedded in function!");
1942 assert(BB->getTerminator() && "Degenerate basic block encountered!");
1944 // Remove basic blocks that have no predecessors (except the entry block)...
1945 // or that just have themself as a predecessor. These are unreachable.
1946 if ((pred_begin(BB) == pred_end(BB) && BB != &Fn->getEntryBlock()) ||
1947 BB->getSinglePredecessor() == BB) {
1948 DEBUG(dbgs() << "Removing BB: \n" << *BB);
1949 DeleteDeadBlock(BB);
1953 // Check to see if we can constant propagate this terminator instruction
1955 Changed |= ConstantFoldTerminator(BB);
1957 // Check for and eliminate duplicate PHI nodes in this block.
1958 Changed |= EliminateDuplicatePHINodes(BB);
1960 // If there is a trivial two-entry PHI node in this basic block, and we can
1961 // eliminate it, do so now.
1962 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1963 if (PN->getNumIncomingValues() == 2)
1964 Changed |= FoldTwoEntryPHINode(PN);
1966 // If this is a returning block with only PHI nodes in it, fold the return
1967 // instruction into any unconditional branch predecessors.
1969 // If any predecessor is a conditional branch that just selects among
1970 // different return values, fold the replace the branch/return with a select
1972 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1973 if (BB->getFirstNonPHIOrDbg()->isTerminator()) {
1974 // Find predecessors that end with branches.
1975 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1976 SmallVector<BranchInst*, 8> CondBranchPreds;
1977 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1978 BasicBlock *P = *PI;
1979 TerminatorInst *PTI = P->getTerminator();
1980 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1981 if (BI->isUnconditional())
1982 UncondBranchPreds.push_back(P);
1984 CondBranchPreds.push_back(BI);
1988 // If we found some, do the transformation!
1989 if (!UncondBranchPreds.empty()) {
1990 while (!UncondBranchPreds.empty()) {
1991 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
1992 DEBUG(dbgs() << "FOLDING: " << *BB
1993 << "INTO UNCOND BRANCH PRED: " << *Pred);
1994 Instruction *UncondBranch = Pred->getTerminator();
1995 // Clone the return and add it to the end of the predecessor.
1996 Instruction *NewRet = RI->clone();
1997 Pred->getInstList().push_back(NewRet);
1999 // If the return instruction returns a value, and if the value was a
2000 // PHI node in "BB", propagate the right value into the return.
2001 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
2003 if (PHINode *PN = dyn_cast<PHINode>(*i))
2004 if (PN->getParent() == BB)
2005 *i = PN->getIncomingValueForBlock(Pred);
2007 // Update any PHI nodes in the returning block to realize that we no
2008 // longer branch to them.
2009 BB->removePredecessor(Pred);
2010 Pred->getInstList().erase(UncondBranch);
2013 // If we eliminated all predecessors of the block, delete the block now.
2014 if (pred_begin(BB) == pred_end(BB))
2015 // We know there are no successors, so just nuke the block.
2016 Fn->getBasicBlockList().erase(BB);
2021 // Check out all of the conditional branches going to this return
2022 // instruction. If any of them just select between returns, change the
2023 // branch itself into a select/return pair.
2024 while (!CondBranchPreds.empty()) {
2025 BranchInst *BI = CondBranchPreds.pop_back_val();
2027 // Check to see if the non-BB successor is also a return block.
2028 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2029 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2030 SimplifyCondBranchToTwoReturns(BI))
2034 } else if (isa<UnwindInst>(BB->begin())) {
2035 // Check to see if the first instruction in this block is just an unwind.
2036 // If so, replace any invoke instructions which use this as an exception
2037 // destination with call instructions.
2039 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2040 while (!Preds.empty()) {
2041 BasicBlock *Pred = Preds.back();
2042 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
2043 if (II && II->getUnwindDest() == BB) {
2044 // Insert a new branch instruction before the invoke, because this
2045 // is now a fall through.
2046 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2047 Pred->getInstList().remove(II); // Take out of symbol table
2049 // Insert the call now.
2050 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
2051 CallInst *CI = CallInst::Create(II->getCalledValue(),
2052 Args.begin(), Args.end(),
2054 CI->setCallingConv(II->getCallingConv());
2055 CI->setAttributes(II->getAttributes());
2056 // If the invoke produced a value, the Call now does instead.
2057 II->replaceAllUsesWith(CI);
2065 // If this block is now dead (and isn't the entry block), remove it.
2066 if (pred_begin(BB) == pred_end(BB) && BB != &Fn->getEntryBlock()) {
2067 // We know there are no successors, so just nuke the block.
2068 Fn->getBasicBlockList().erase(BB);
2072 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
2073 if (isValueEqualityComparison(SI)) {
2074 // If we only have one predecessor, and if it is a branch on this value,
2075 // see if that predecessor totally determines the outcome of this switch.
2076 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2077 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
2078 return SimplifyCFG(BB) || 1;
2080 // If the block only contains the switch, see if we can fold the block
2081 // away into any preds.
2082 BasicBlock::iterator BBI = BB->begin();
2083 // Ignore dbg intrinsics.
2084 while (isa<DbgInfoIntrinsic>(BBI))
2087 if (FoldValueComparisonIntoPredecessors(SI))
2088 return SimplifyCFG(BB) || 1;
2090 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
2091 if (BI->isUnconditional()) {
2092 // If the Terminator is the only non-phi instruction, simplify the block.
2093 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg();
2094 if (I->isTerminator() && BB != &Fn->getEntryBlock() &&
2095 TryToSimplifyUncondBranchFromEmptyBlock(BB))
2098 // If the only instruction in the block is a seteq/setne comparison
2099 // against a constant, try to simplify the block.
2100 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
2101 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
2102 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
2104 if (I->isTerminator() &&
2105 TryToSimplifyUncondBranchWithICmpInIt(ICI))
2109 } else { // Conditional branch
2110 if (isValueEqualityComparison(BI)) {
2111 // If we only have one predecessor, and if it is a branch on this value,
2112 // see if that predecessor totally determines the outcome of this
2114 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2115 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
2116 return SimplifyCFG(BB) | true;
2118 // This block must be empty, except for the setcond inst, if it exists.
2119 // Ignore dbg intrinsics.
2120 BasicBlock::iterator I = BB->begin();
2121 // Ignore dbg intrinsics.
2122 while (isa<DbgInfoIntrinsic>(I))
2125 if (FoldValueComparisonIntoPredecessors(BI))
2126 return SimplifyCFG(BB) | true;
2127 } else if (&*I == cast<Instruction>(BI->getCondition())){
2129 // Ignore dbg intrinsics.
2130 while (isa<DbgInfoIntrinsic>(I))
2132 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI))
2133 return SimplifyCFG(BB) | true;
2137 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
2138 if (SimplifyBranchOnICmpChain(BI, TD))
2141 // If this is a branch on a phi node in the current block, thread control
2142 // through this block if any PHI node entries are constants.
2143 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
2144 if (PN->getParent() == BI->getParent())
2145 if (FoldCondBranchOnPHI(BI))
2146 return SimplifyCFG(BB) | true;
2148 // If this basic block is ONLY a setcc and a branch, and if a predecessor
2149 // branches to us and one of our successors, fold the setcc into the
2150 // predecessor and use logical operations to pick the right destination.
2151 if (FoldBranchToCommonDest(BI))
2152 return SimplifyCFG(BB) | true;
2154 // Scan predecessor blocks for conditional branches.
2155 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2156 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2157 if (PBI != BI && PBI->isConditional())
2158 if (SimplifyCondBranchToCondBranch(PBI, BI))
2159 return SimplifyCFG(BB) | true;
2161 } else if (isa<UnreachableInst>(BB->getTerminator())) {
2162 // If there are any instructions immediately before the unreachable that can
2163 // be removed, do so.
2164 Instruction *Unreachable = BB->getTerminator();
2165 while (Unreachable != BB->begin()) {
2166 BasicBlock::iterator BBI = Unreachable;
2168 // Do not delete instructions that can have side effects, like calls
2169 // (which may never return) and volatile loads and stores.
2170 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2172 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
2173 if (SI->isVolatile())
2176 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
2177 if (LI->isVolatile())
2180 // Delete this instruction
2181 BB->getInstList().erase(BBI);
2185 // If the unreachable instruction is the first in the block, take a gander
2186 // at all of the predecessors of this instruction, and simplify them.
2187 if (&BB->front() == Unreachable) {
2188 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2189 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2190 TerminatorInst *TI = Preds[i]->getTerminator();
2192 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2193 if (BI->isUnconditional()) {
2194 if (BI->getSuccessor(0) == BB) {
2195 new UnreachableInst(TI->getContext(), TI);
2196 TI->eraseFromParent();
2200 if (BI->getSuccessor(0) == BB) {
2201 BranchInst::Create(BI->getSuccessor(1), BI);
2202 EraseTerminatorInstAndDCECond(BI);
2203 } else if (BI->getSuccessor(1) == BB) {
2204 BranchInst::Create(BI->getSuccessor(0), BI);
2205 EraseTerminatorInstAndDCECond(BI);
2209 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2210 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2211 if (SI->getSuccessor(i) == BB) {
2212 BB->removePredecessor(SI->getParent());
2217 // If the default value is unreachable, figure out the most popular
2218 // destination and make it the default.
2219 if (SI->getSuccessor(0) == BB) {
2220 std::map<BasicBlock*, unsigned> Popularity;
2221 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2222 Popularity[SI->getSuccessor(i)]++;
2224 // Find the most popular block.
2225 unsigned MaxPop = 0;
2226 BasicBlock *MaxBlock = 0;
2227 for (std::map<BasicBlock*, unsigned>::iterator
2228 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2229 if (I->second > MaxPop) {
2231 MaxBlock = I->first;
2235 // Make this the new default, allowing us to delete any explicit
2237 SI->setSuccessor(0, MaxBlock);
2240 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2242 if (isa<PHINode>(MaxBlock->begin()))
2243 for (unsigned i = 0; i != MaxPop-1; ++i)
2244 MaxBlock->removePredecessor(SI->getParent());
2246 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2247 if (SI->getSuccessor(i) == MaxBlock) {
2253 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2254 if (II->getUnwindDest() == BB) {
2255 // Convert the invoke to a call instruction. This would be a good
2256 // place to note that the call does not throw though.
2257 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2258 II->removeFromParent(); // Take out of symbol table
2260 // Insert the call now...
2261 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2262 CallInst *CI = CallInst::Create(II->getCalledValue(),
2263 Args.begin(), Args.end(),
2265 CI->setCallingConv(II->getCallingConv());
2266 CI->setAttributes(II->getAttributes());
2267 // If the invoke produced a value, the call does now instead.
2268 II->replaceAllUsesWith(CI);
2275 // If this block is now dead, remove it.
2276 if (pred_begin(BB) == pred_end(BB) && BB != &Fn->getEntryBlock()) {
2277 // We know there are no successors, so just nuke the block.
2278 Fn->getBasicBlockList().erase(BB);
2282 } else if (IndirectBrInst *IBI =
2283 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
2284 // Eliminate redundant destinations.
2285 SmallPtrSet<Value *, 8> Succs;
2286 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2287 BasicBlock *Dest = IBI->getDestination(i);
2288 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2289 Dest->removePredecessor(BB);
2290 IBI->removeDestination(i);
2296 if (IBI->getNumDestinations() == 0) {
2297 // If the indirectbr has no successors, change it to unreachable.
2298 new UnreachableInst(IBI->getContext(), IBI);
2299 EraseTerminatorInstAndDCECond(IBI);
2301 } else if (IBI->getNumDestinations() == 1) {
2302 // If the indirectbr has one successor, change it to a direct branch.
2303 BranchInst::Create(IBI->getDestination(0), IBI);
2304 EraseTerminatorInstAndDCECond(IBI);
2306 } else if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2307 if (SimplifyIndirectBrOnSelect(IBI, SI))
2308 return SimplifyCFG(BB) | true;
2312 // Merge basic blocks into their predecessor if there is only one distinct
2313 // pred, and if there is only one distinct successor of the predecessor, and
2314 // if there are no PHI nodes.
2316 if (MergeBlockIntoPredecessor(BB))
2319 // Otherwise, if this block only has a single predecessor, and if that block
2320 // is a conditional branch, see if we can hoist any code from this block up
2321 // into our predecessor.
2322 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
2323 BasicBlock *OnlyPred = 0;
2324 for (; PI != PE; ++PI) { // Search all predecessors, see if they are all same
2327 else if (*PI != OnlyPred) {
2328 OnlyPred = 0; // There are multiple different predecessors...
2334 BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator());
2335 if (BI && BI->isConditional()) {
2336 // Get the other block.
2337 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
2338 PI = pred_begin(OtherBB);
2341 if (PI == pred_end(OtherBB)) {
2342 // We have a conditional branch to two blocks that are only reachable
2343 // from the condbr. We know that the condbr dominates the two blocks,
2344 // so see if there is any identical code in the "then" and "else"
2345 // blocks. If so, we can hoist it up to the branching block.
2346 Changed |= HoistThenElseCodeToIf(BI);
2348 BasicBlock* OnlySucc = NULL;
2349 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
2353 else if (*SI != OnlySucc) {
2354 OnlySucc = 0; // There are multiple distinct successors!
2359 if (OnlySucc == OtherBB) {
2360 // If BB's only successor is the other successor of the predecessor,
2361 // i.e. a triangle, see if we can hoist any code from this block up
2362 // to the "if" block.
2363 Changed |= SpeculativelyExecuteBB(BI, BB);
2372 /// SimplifyCFG - This function is used to do simplification of a CFG. For
2373 /// example, it adjusts branches to branches to eliminate the extra hop, it
2374 /// eliminates unreachable basic blocks, and does other "peephole" optimization
2375 /// of the CFG. It returns true if a modification was made.
2377 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
2378 return SimplifyCFGOpt(TD).run(BB);