1 //===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Peephole optimize the CFG.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "simplifycfg"
15 #include "llvm/Transforms/Utils/Local.h"
16 #include "llvm/Constants.h"
17 #include "llvm/DerivedTypes.h"
18 #include "llvm/GlobalVariable.h"
19 #include "llvm/Instructions.h"
20 #include "llvm/IntrinsicInst.h"
21 #include "llvm/Type.h"
22 #include "llvm/Analysis/InstructionSimplify.h"
23 #include "llvm/Analysis/ValueTracking.h"
24 #include "llvm/Target/TargetData.h"
25 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
26 #include "llvm/ADT/DenseMap.h"
27 #include "llvm/ADT/SmallVector.h"
28 #include "llvm/ADT/SmallPtrSet.h"
29 #include "llvm/ADT/Statistic.h"
30 #include "llvm/ADT/STLExtras.h"
31 #include "llvm/Support/CFG.h"
32 #include "llvm/Support/CommandLine.h"
33 #include "llvm/Support/ConstantRange.h"
34 #include "llvm/Support/Debug.h"
35 #include "llvm/Support/IRBuilder.h"
36 #include "llvm/Support/NoFolder.h"
37 #include "llvm/Support/raw_ostream.h"
43 static cl::opt<unsigned>
44 PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(1),
45 cl::desc("Control the amount of phi node folding to perform (default = 1)"));
48 DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false),
49 cl::desc("Duplicate return instructions into unconditional branches"));
51 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
54 class SimplifyCFGOpt {
55 const TargetData *const TD;
57 Value *isValueEqualityComparison(TerminatorInst *TI);
58 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
59 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases);
60 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
62 IRBuilder<> &Builder);
63 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
64 IRBuilder<> &Builder);
66 bool SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder);
67 bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder);
68 bool SimplifyUnwind(UnwindInst *UI, IRBuilder<> &Builder);
69 bool SimplifyUnreachable(UnreachableInst *UI);
70 bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
71 bool SimplifyIndirectBr(IndirectBrInst *IBI);
72 bool SimplifyUncondBranch(BranchInst *BI, IRBuilder <> &Builder);
73 bool SimplifyCondBranch(BranchInst *BI, IRBuilder <>&Builder);
76 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
77 bool run(BasicBlock *BB);
81 /// SafeToMergeTerminators - Return true if it is safe to merge these two
82 /// terminator instructions together.
84 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
85 if (SI1 == SI2) return false; // Can't merge with self!
87 // It is not safe to merge these two switch instructions if they have a common
88 // successor, and if that successor has a PHI node, and if *that* PHI node has
89 // conflicting incoming values from the two switch blocks.
90 BasicBlock *SI1BB = SI1->getParent();
91 BasicBlock *SI2BB = SI2->getParent();
92 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
94 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
95 if (SI1Succs.count(*I))
96 for (BasicBlock::iterator BBI = (*I)->begin();
97 isa<PHINode>(BBI); ++BBI) {
98 PHINode *PN = cast<PHINode>(BBI);
99 if (PN->getIncomingValueForBlock(SI1BB) !=
100 PN->getIncomingValueForBlock(SI2BB))
107 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
108 /// now be entries in it from the 'NewPred' block. The values that will be
109 /// flowing into the PHI nodes will be the same as those coming in from
110 /// ExistPred, an existing predecessor of Succ.
111 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
112 BasicBlock *ExistPred) {
113 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
116 for (BasicBlock::iterator I = Succ->begin();
117 (PN = dyn_cast<PHINode>(I)); ++I)
118 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
122 /// GetIfCondition - Given a basic block (BB) with two predecessors (and at
123 /// least one PHI node in it), check to see if the merge at this block is due
124 /// to an "if condition". If so, return the boolean condition that determines
125 /// which entry into BB will be taken. Also, return by references the block
126 /// that will be entered from if the condition is true, and the block that will
127 /// be entered if the condition is false.
129 /// This does no checking to see if the true/false blocks have large or unsavory
130 /// instructions in them.
131 static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
132 BasicBlock *&IfFalse) {
133 PHINode *SomePHI = cast<PHINode>(BB->begin());
134 assert(SomePHI->getNumIncomingValues() == 2 &&
135 "Function can only handle blocks with 2 predecessors!");
136 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
137 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
139 // We can only handle branches. Other control flow will be lowered to
140 // branches if possible anyway.
141 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
142 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
143 if (Pred1Br == 0 || Pred2Br == 0)
146 // Eliminate code duplication by ensuring that Pred1Br is conditional if
148 if (Pred2Br->isConditional()) {
149 // If both branches are conditional, we don't have an "if statement". In
150 // reality, we could transform this case, but since the condition will be
151 // required anyway, we stand no chance of eliminating it, so the xform is
152 // probably not profitable.
153 if (Pred1Br->isConditional())
156 std::swap(Pred1, Pred2);
157 std::swap(Pred1Br, Pred2Br);
160 if (Pred1Br->isConditional()) {
161 // The only thing we have to watch out for here is to make sure that Pred2
162 // doesn't have incoming edges from other blocks. If it does, the condition
163 // doesn't dominate BB.
164 if (Pred2->getSinglePredecessor() == 0)
167 // If we found a conditional branch predecessor, make sure that it branches
168 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
169 if (Pred1Br->getSuccessor(0) == BB &&
170 Pred1Br->getSuccessor(1) == Pred2) {
173 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
174 Pred1Br->getSuccessor(1) == BB) {
178 // We know that one arm of the conditional goes to BB, so the other must
179 // go somewhere unrelated, and this must not be an "if statement".
183 return Pred1Br->getCondition();
186 // Ok, if we got here, both predecessors end with an unconditional branch to
187 // BB. Don't panic! If both blocks only have a single (identical)
188 // predecessor, and THAT is a conditional branch, then we're all ok!
189 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
190 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
193 // Otherwise, if this is a conditional branch, then we can use it!
194 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
195 if (BI == 0) return 0;
197 assert(BI->isConditional() && "Two successors but not conditional?");
198 if (BI->getSuccessor(0) == Pred1) {
205 return BI->getCondition();
208 /// DominatesMergePoint - If we have a merge point of an "if condition" as
209 /// accepted above, return true if the specified value dominates the block. We
210 /// don't handle the true generality of domination here, just a special case
211 /// which works well enough for us.
213 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
214 /// see if V (which must be an instruction) and its recursive operands
215 /// that do not dominate BB have a combined cost lower than CostRemaining and
216 /// are non-trapping. If both are true, the instruction is inserted into the
217 /// set and true is returned.
219 /// The cost for most non-trapping instructions is defined as 1 except for
220 /// Select whose cost is 2.
222 /// After this function returns, CostRemaining is decreased by the cost of
223 /// V plus its non-dominating operands. If that cost is greater than
224 /// CostRemaining, false is returned and CostRemaining is undefined.
225 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
226 SmallPtrSet<Instruction*, 4> *AggressiveInsts,
227 unsigned &CostRemaining) {
228 Instruction *I = dyn_cast<Instruction>(V);
230 // Non-instructions all dominate instructions, but not all constantexprs
231 // can be executed unconditionally.
232 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
237 BasicBlock *PBB = I->getParent();
239 // We don't want to allow weird loops that might have the "if condition" in
240 // the bottom of this block.
241 if (PBB == BB) return false;
243 // If this instruction is defined in a block that contains an unconditional
244 // branch to BB, then it must be in the 'conditional' part of the "if
245 // statement". If not, it definitely dominates the region.
246 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
247 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB)
250 // If we aren't allowing aggressive promotion anymore, then don't consider
251 // instructions in the 'if region'.
252 if (AggressiveInsts == 0) return false;
254 // If we have seen this instruction before, don't count it again.
255 if (AggressiveInsts->count(I)) return true;
257 // Okay, it looks like the instruction IS in the "condition". Check to
258 // see if it's a cheap instruction to unconditionally compute, and if it
259 // only uses stuff defined outside of the condition. If so, hoist it out.
260 if (!isSafeToSpeculativelyExecute(I))
265 switch (I->getOpcode()) {
266 default: return false; // Cannot hoist this out safely.
267 case Instruction::Load:
268 // We have to check to make sure there are no instructions before the
269 // load in its basic block, as we are going to hoist the load out to its
271 if (PBB->getFirstNonPHIOrDbg() != I)
275 case Instruction::GetElementPtr:
276 // GEPs are cheap if all indices are constant.
277 if (!cast<GetElementPtrInst>(I)->hasAllConstantIndices())
281 case Instruction::Add:
282 case Instruction::Sub:
283 case Instruction::And:
284 case Instruction::Or:
285 case Instruction::Xor:
286 case Instruction::Shl:
287 case Instruction::LShr:
288 case Instruction::AShr:
289 case Instruction::ICmp:
290 case Instruction::Trunc:
291 case Instruction::ZExt:
292 case Instruction::SExt:
294 break; // These are all cheap and non-trapping instructions.
296 case Instruction::Call:
297 case Instruction::Select:
302 if (Cost > CostRemaining)
305 CostRemaining -= Cost;
307 // Okay, we can only really hoist these out if their operands do
308 // not take us over the cost threshold.
309 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
310 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining))
312 // Okay, it's safe to do this! Remember this instruction.
313 AggressiveInsts->insert(I);
317 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
318 /// and PointerNullValue. Return NULL if value is not a constant int.
319 static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
320 // Normal constant int.
321 ConstantInt *CI = dyn_cast<ConstantInt>(V);
322 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
325 // This is some kind of pointer constant. Turn it into a pointer-sized
326 // ConstantInt if possible.
327 IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
329 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
330 if (isa<ConstantPointerNull>(V))
331 return ConstantInt::get(PtrTy, 0);
333 // IntToPtr const int.
334 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
335 if (CE->getOpcode() == Instruction::IntToPtr)
336 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
337 // The constant is very likely to have the right type already.
338 if (CI->getType() == PtrTy)
341 return cast<ConstantInt>
342 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
347 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
348 /// collection of icmp eq/ne instructions that compare a value against a
349 /// constant, return the value being compared, and stick the constant into the
352 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
353 const TargetData *TD, bool isEQ, unsigned &UsedICmps) {
354 Instruction *I = dyn_cast<Instruction>(V);
355 if (I == 0) return 0;
357 // If this is an icmp against a constant, handle this as one of the cases.
358 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
359 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
360 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
363 return I->getOperand(0);
366 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
369 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
371 // If this is an and/!= check then we want to optimize "x ugt 2" into
374 Span = Span.inverse();
376 // If there are a ton of values, we don't want to make a ginormous switch.
377 if (Span.getSetSize().ugt(8) || Span.isEmptySet() ||
378 // We don't handle wrapped sets yet.
382 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
383 Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
385 return I->getOperand(0);
390 // Otherwise, we can only handle an | or &, depending on isEQ.
391 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
394 unsigned NumValsBeforeLHS = Vals.size();
395 unsigned UsedICmpsBeforeLHS = UsedICmps;
396 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
398 unsigned NumVals = Vals.size();
399 unsigned UsedICmpsBeforeRHS = UsedICmps;
400 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
404 Vals.resize(NumVals);
405 UsedICmps = UsedICmpsBeforeRHS;
408 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
409 // set it and return success.
410 if (Extra == 0 || Extra == I->getOperand(1)) {
411 Extra = I->getOperand(1);
415 Vals.resize(NumValsBeforeLHS);
416 UsedICmps = UsedICmpsBeforeLHS;
420 // If the LHS can't be folded in, but Extra is available and RHS can, try to
422 if (Extra == 0 || Extra == I->getOperand(0)) {
423 Value *OldExtra = Extra;
424 Extra = I->getOperand(0);
425 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
428 assert(Vals.size() == NumValsBeforeLHS);
435 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
436 Instruction *Cond = 0;
437 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
438 Cond = dyn_cast<Instruction>(SI->getCondition());
439 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
440 if (BI->isConditional())
441 Cond = dyn_cast<Instruction>(BI->getCondition());
442 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
443 Cond = dyn_cast<Instruction>(IBI->getAddress());
446 TI->eraseFromParent();
447 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
450 /// isValueEqualityComparison - Return true if the specified terminator checks
451 /// to see if a value is equal to constant integer value.
452 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
454 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
455 // Do not permit merging of large switch instructions into their
456 // predecessors unless there is only one predecessor.
457 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
458 pred_end(SI->getParent())) <= 128)
459 CV = SI->getCondition();
460 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
461 if (BI->isConditional() && BI->getCondition()->hasOneUse())
462 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
463 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
464 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
465 GetConstantInt(ICI->getOperand(1), TD))
466 CV = ICI->getOperand(0);
468 // Unwrap any lossless ptrtoint cast.
469 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
470 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
471 CV = PTII->getOperand(0);
475 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
476 /// decode all of the 'cases' that it represents and return the 'default' block.
477 BasicBlock *SimplifyCFGOpt::
478 GetValueEqualityComparisonCases(TerminatorInst *TI,
479 std::vector<std::pair<ConstantInt*,
480 BasicBlock*> > &Cases) {
481 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
482 Cases.reserve(SI->getNumCases());
483 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
484 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
485 return SI->getDefaultDest();
488 BranchInst *BI = cast<BranchInst>(TI);
489 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
490 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD),
491 BI->getSuccessor(ICI->getPredicate() ==
492 ICmpInst::ICMP_NE)));
493 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
497 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
498 /// in the list that match the specified block.
499 static void EliminateBlockCases(BasicBlock *BB,
500 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
501 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
502 if (Cases[i].second == BB) {
503 Cases.erase(Cases.begin()+i);
508 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
511 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
512 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
513 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
515 // Make V1 be smaller than V2.
516 if (V1->size() > V2->size())
519 if (V1->size() == 0) return false;
520 if (V1->size() == 1) {
522 ConstantInt *TheVal = (*V1)[0].first;
523 for (unsigned i = 0, e = V2->size(); i != e; ++i)
524 if (TheVal == (*V2)[i].first)
528 // Otherwise, just sort both lists and compare element by element.
529 array_pod_sort(V1->begin(), V1->end());
530 array_pod_sort(V2->begin(), V2->end());
531 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
532 while (i1 != e1 && i2 != e2) {
533 if ((*V1)[i1].first == (*V2)[i2].first)
535 if ((*V1)[i1].first < (*V2)[i2].first)
543 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
544 /// terminator instruction and its block is known to only have a single
545 /// predecessor block, check to see if that predecessor is also a value
546 /// comparison with the same value, and if that comparison determines the
547 /// outcome of this comparison. If so, simplify TI. This does a very limited
548 /// form of jump threading.
549 bool SimplifyCFGOpt::
550 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
552 IRBuilder<> &Builder) {
553 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
554 if (!PredVal) return false; // Not a value comparison in predecessor.
556 Value *ThisVal = isValueEqualityComparison(TI);
557 assert(ThisVal && "This isn't a value comparison!!");
558 if (ThisVal != PredVal) return false; // Different predicates.
560 // Find out information about when control will move from Pred to TI's block.
561 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
562 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
564 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
566 // Find information about how control leaves this block.
567 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
568 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
569 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
571 // If TI's block is the default block from Pred's comparison, potentially
572 // simplify TI based on this knowledge.
573 if (PredDef == TI->getParent()) {
574 // If we are here, we know that the value is none of those cases listed in
575 // PredCases. If there are any cases in ThisCases that are in PredCases, we
577 if (!ValuesOverlap(PredCases, ThisCases))
580 if (isa<BranchInst>(TI)) {
581 // Okay, one of the successors of this condbr is dead. Convert it to a
583 assert(ThisCases.size() == 1 && "Branch can only have one case!");
584 // Insert the new branch.
585 Instruction *NI = Builder.CreateBr(ThisDef);
588 // Remove PHI node entries for the dead edge.
589 ThisCases[0].second->removePredecessor(TI->getParent());
591 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
592 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
594 EraseTerminatorInstAndDCECond(TI);
598 SwitchInst *SI = cast<SwitchInst>(TI);
599 // Okay, TI has cases that are statically dead, prune them away.
600 SmallPtrSet<Constant*, 16> DeadCases;
601 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
602 DeadCases.insert(PredCases[i].first);
604 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
605 << "Through successor TI: " << *TI);
607 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
608 if (DeadCases.count(SI->getCaseValue(i))) {
609 SI->getSuccessor(i)->removePredecessor(TI->getParent());
613 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
617 // Otherwise, TI's block must correspond to some matched value. Find out
618 // which value (or set of values) this is.
619 ConstantInt *TIV = 0;
620 BasicBlock *TIBB = TI->getParent();
621 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
622 if (PredCases[i].second == TIBB) {
624 return false; // Cannot handle multiple values coming to this block.
625 TIV = PredCases[i].first;
627 assert(TIV && "No edge from pred to succ?");
629 // Okay, we found the one constant that our value can be if we get into TI's
630 // BB. Find out which successor will unconditionally be branched to.
631 BasicBlock *TheRealDest = 0;
632 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
633 if (ThisCases[i].first == TIV) {
634 TheRealDest = ThisCases[i].second;
638 // If not handled by any explicit cases, it is handled by the default case.
639 if (TheRealDest == 0) TheRealDest = ThisDef;
641 // Remove PHI node entries for dead edges.
642 BasicBlock *CheckEdge = TheRealDest;
643 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
644 if (*SI != CheckEdge)
645 (*SI)->removePredecessor(TIBB);
649 // Insert the new branch.
650 Instruction *NI = Builder.CreateBr(TheRealDest);
653 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
654 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
656 EraseTerminatorInstAndDCECond(TI);
661 /// ConstantIntOrdering - This class implements a stable ordering of constant
662 /// integers that does not depend on their address. This is important for
663 /// applications that sort ConstantInt's to ensure uniqueness.
664 struct ConstantIntOrdering {
665 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
666 return LHS->getValue().ult(RHS->getValue());
671 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
672 const ConstantInt *LHS = *(const ConstantInt**)P1;
673 const ConstantInt *RHS = *(const ConstantInt**)P2;
674 if (LHS->getValue().ult(RHS->getValue()))
676 if (LHS->getValue() == RHS->getValue())
681 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
682 /// equality comparison instruction (either a switch or a branch on "X == c").
683 /// See if any of the predecessors of the terminator block are value comparisons
684 /// on the same value. If so, and if safe to do so, fold them together.
685 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
686 IRBuilder<> &Builder) {
687 BasicBlock *BB = TI->getParent();
688 Value *CV = isValueEqualityComparison(TI); // CondVal
689 assert(CV && "Not a comparison?");
690 bool Changed = false;
692 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
693 while (!Preds.empty()) {
694 BasicBlock *Pred = Preds.pop_back_val();
696 // See if the predecessor is a comparison with the same value.
697 TerminatorInst *PTI = Pred->getTerminator();
698 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
700 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
701 // Figure out which 'cases' to copy from SI to PSI.
702 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
703 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
705 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
706 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
708 // Based on whether the default edge from PTI goes to BB or not, fill in
709 // PredCases and PredDefault with the new switch cases we would like to
711 SmallVector<BasicBlock*, 8> NewSuccessors;
713 if (PredDefault == BB) {
714 // If this is the default destination from PTI, only the edges in TI
715 // that don't occur in PTI, or that branch to BB will be activated.
716 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
717 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
718 if (PredCases[i].second != BB)
719 PTIHandled.insert(PredCases[i].first);
721 // The default destination is BB, we don't need explicit targets.
722 std::swap(PredCases[i], PredCases.back());
723 PredCases.pop_back();
727 // Reconstruct the new switch statement we will be building.
728 if (PredDefault != BBDefault) {
729 PredDefault->removePredecessor(Pred);
730 PredDefault = BBDefault;
731 NewSuccessors.push_back(BBDefault);
733 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
734 if (!PTIHandled.count(BBCases[i].first) &&
735 BBCases[i].second != BBDefault) {
736 PredCases.push_back(BBCases[i]);
737 NewSuccessors.push_back(BBCases[i].second);
741 // If this is not the default destination from PSI, only the edges
742 // in SI that occur in PSI with a destination of BB will be
744 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
745 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
746 if (PredCases[i].second == BB) {
747 PTIHandled.insert(PredCases[i].first);
748 std::swap(PredCases[i], PredCases.back());
749 PredCases.pop_back();
753 // Okay, now we know which constants were sent to BB from the
754 // predecessor. Figure out where they will all go now.
755 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
756 if (PTIHandled.count(BBCases[i].first)) {
757 // If this is one we are capable of getting...
758 PredCases.push_back(BBCases[i]);
759 NewSuccessors.push_back(BBCases[i].second);
760 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
763 // If there are any constants vectored to BB that TI doesn't handle,
764 // they must go to the default destination of TI.
765 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
767 E = PTIHandled.end(); I != E; ++I) {
768 PredCases.push_back(std::make_pair(*I, BBDefault));
769 NewSuccessors.push_back(BBDefault);
773 // Okay, at this point, we know which new successor Pred will get. Make
774 // sure we update the number of entries in the PHI nodes for these
776 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
777 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
779 Builder.SetInsertPoint(PTI);
780 // Convert pointer to int before we switch.
781 if (CV->getType()->isPointerTy()) {
782 assert(TD && "Cannot switch on pointer without TargetData");
783 CV = Builder.CreatePtrToInt(CV, TD->getIntPtrType(CV->getContext()),
787 // Now that the successors are updated, create the new Switch instruction.
788 SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault,
790 NewSI->setDebugLoc(PTI->getDebugLoc());
791 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
792 NewSI->addCase(PredCases[i].first, PredCases[i].second);
794 EraseTerminatorInstAndDCECond(PTI);
796 // Okay, last check. If BB is still a successor of PSI, then we must
797 // have an infinite loop case. If so, add an infinitely looping block
798 // to handle the case to preserve the behavior of the code.
799 BasicBlock *InfLoopBlock = 0;
800 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
801 if (NewSI->getSuccessor(i) == BB) {
802 if (InfLoopBlock == 0) {
803 // Insert it at the end of the function, because it's either code,
804 // or it won't matter if it's hot. :)
805 InfLoopBlock = BasicBlock::Create(BB->getContext(),
806 "infloop", BB->getParent());
807 BranchInst::Create(InfLoopBlock, InfLoopBlock);
809 NewSI->setSuccessor(i, InfLoopBlock);
818 // isSafeToHoistInvoke - If we would need to insert a select that uses the
819 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
820 // would need to do this), we can't hoist the invoke, as there is nowhere
821 // to put the select in this case.
822 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
823 Instruction *I1, Instruction *I2) {
824 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
826 for (BasicBlock::iterator BBI = SI->begin();
827 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
828 Value *BB1V = PN->getIncomingValueForBlock(BB1);
829 Value *BB2V = PN->getIncomingValueForBlock(BB2);
830 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
838 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
839 /// BB2, hoist any common code in the two blocks up into the branch block. The
840 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
841 static bool HoistThenElseCodeToIf(BranchInst *BI) {
842 // This does very trivial matching, with limited scanning, to find identical
843 // instructions in the two blocks. In particular, we don't want to get into
844 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
845 // such, we currently just scan for obviously identical instructions in an
847 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
848 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
850 BasicBlock::iterator BB1_Itr = BB1->begin();
851 BasicBlock::iterator BB2_Itr = BB2->begin();
853 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
854 // Skip debug info if it is not identical.
855 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
856 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
857 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
858 while (isa<DbgInfoIntrinsic>(I1))
860 while (isa<DbgInfoIntrinsic>(I2))
863 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
864 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
867 // If we get here, we can hoist at least one instruction.
868 BasicBlock *BIParent = BI->getParent();
871 // If we are hoisting the terminator instruction, don't move one (making a
872 // broken BB), instead clone it, and remove BI.
873 if (isa<TerminatorInst>(I1))
874 goto HoistTerminator;
876 // For a normal instruction, we just move one to right before the branch,
877 // then replace all uses of the other with the first. Finally, we remove
878 // the now redundant second instruction.
879 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
880 if (!I2->use_empty())
881 I2->replaceAllUsesWith(I1);
882 I1->intersectOptionalDataWith(I2);
883 I2->eraseFromParent();
887 // Skip debug info if it is not identical.
888 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
889 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
890 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
891 while (isa<DbgInfoIntrinsic>(I1))
893 while (isa<DbgInfoIntrinsic>(I2))
896 } while (I1->isIdenticalToWhenDefined(I2));
901 // It may not be possible to hoist an invoke.
902 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
905 // Okay, it is safe to hoist the terminator.
906 Instruction *NT = I1->clone();
907 BIParent->getInstList().insert(BI, NT);
908 if (!NT->getType()->isVoidTy()) {
909 I1->replaceAllUsesWith(NT);
910 I2->replaceAllUsesWith(NT);
914 IRBuilder<true, NoFolder> Builder(NT);
915 // Hoisting one of the terminators from our successor is a great thing.
916 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
917 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
918 // nodes, so we insert select instruction to compute the final result.
919 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
920 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
922 for (BasicBlock::iterator BBI = SI->begin();
923 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
924 Value *BB1V = PN->getIncomingValueForBlock(BB1);
925 Value *BB2V = PN->getIncomingValueForBlock(BB2);
926 if (BB1V == BB2V) continue;
928 // These values do not agree. Insert a select instruction before NT
929 // that determines the right value.
930 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
932 SI = cast<SelectInst>
933 (Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,
934 BB1V->getName()+"."+BB2V->getName()));
936 // Make the PHI node use the select for all incoming values for BB1/BB2
937 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
938 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
939 PN->setIncomingValue(i, SI);
943 // Update any PHI nodes in our new successors.
944 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
945 AddPredecessorToBlock(*SI, BIParent, BB1);
947 EraseTerminatorInstAndDCECond(BI);
951 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
952 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
953 /// (for now, restricted to a single instruction that's side effect free) from
954 /// the BB1 into the branch block to speculatively execute it.
955 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
956 // Only speculatively execution a single instruction (not counting the
957 // terminator) for now.
958 Instruction *HInst = NULL;
959 Instruction *Term = BB1->getTerminator();
960 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
962 Instruction *I = BBI;
964 if (isa<DbgInfoIntrinsic>(I)) continue;
965 if (I == Term) break;
974 // Be conservative for now. FP select instruction can often be expensive.
975 Value *BrCond = BI->getCondition();
976 if (isa<FCmpInst>(BrCond))
979 // If BB1 is actually on the false edge of the conditional branch, remember
980 // to swap the select operands later.
982 if (BB1 != BI->getSuccessor(0)) {
983 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
990 // br i1 %t1, label %BB1, label %BB2
999 // %t3 = select i1 %t1, %t2, %t3
1000 switch (HInst->getOpcode()) {
1001 default: return false; // Not safe / profitable to hoist.
1002 case Instruction::Add:
1003 case Instruction::Sub:
1004 // Not worth doing for vector ops.
1005 if (HInst->getType()->isVectorTy())
1008 case Instruction::And:
1009 case Instruction::Or:
1010 case Instruction::Xor:
1011 case Instruction::Shl:
1012 case Instruction::LShr:
1013 case Instruction::AShr:
1014 // Don't mess with vector operations.
1015 if (HInst->getType()->isVectorTy())
1017 break; // These are all cheap and non-trapping instructions.
1020 // If the instruction is obviously dead, don't try to predicate it.
1021 if (HInst->use_empty()) {
1022 HInst->eraseFromParent();
1026 // Can we speculatively execute the instruction? And what is the value
1027 // if the condition is false? Consider the phi uses, if the incoming value
1028 // from the "if" block are all the same V, then V is the value of the
1029 // select if the condition is false.
1030 BasicBlock *BIParent = BI->getParent();
1031 SmallVector<PHINode*, 4> PHIUses;
1032 Value *FalseV = NULL;
1034 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
1035 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
1037 // Ignore any user that is not a PHI node in BB2. These can only occur in
1038 // unreachable blocks, because they would not be dominated by the instr.
1039 PHINode *PN = dyn_cast<PHINode>(*UI);
1040 if (!PN || PN->getParent() != BB2)
1042 PHIUses.push_back(PN);
1044 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1047 else if (FalseV != PHIV)
1048 return false; // Inconsistent value when condition is false.
1051 assert(FalseV && "Must have at least one user, and it must be a PHI");
1053 // Do not hoist the instruction if any of its operands are defined but not
1054 // used in this BB. The transformation will prevent the operand from
1055 // being sunk into the use block.
1056 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1058 Instruction *OpI = dyn_cast<Instruction>(*i);
1059 if (OpI && OpI->getParent() == BIParent &&
1060 !OpI->isUsedInBasicBlock(BIParent))
1064 // If we get here, we can hoist the instruction. Try to place it
1065 // before the icmp instruction preceding the conditional branch.
1066 BasicBlock::iterator InsertPos = BI;
1067 if (InsertPos != BIParent->begin())
1069 // Skip debug info between condition and branch.
1070 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
1072 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
1073 SmallPtrSet<Instruction *, 4> BB1Insns;
1074 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
1075 BB1I != BB1E; ++BB1I)
1076 BB1Insns.insert(BB1I);
1077 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
1079 Instruction *Use = cast<Instruction>(*UI);
1080 if (!BB1Insns.count(Use)) continue;
1082 // If BrCond uses the instruction that place it just before
1083 // branch instruction.
1089 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
1091 // Create a select whose true value is the speculatively executed value and
1092 // false value is the previously determined FalseV.
1093 IRBuilder<true, NoFolder> Builder(BI);
1096 SI = cast<SelectInst>
1097 (Builder.CreateSelect(BrCond, FalseV, HInst,
1098 FalseV->getName() + "." + HInst->getName()));
1100 SI = cast<SelectInst>
1101 (Builder.CreateSelect(BrCond, HInst, FalseV,
1102 HInst->getName() + "." + FalseV->getName()));
1104 // Make the PHI node use the select for all incoming values for "then" and
1106 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1107 PHINode *PN = PHIUses[i];
1108 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1109 if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent)
1110 PN->setIncomingValue(j, SI);
1117 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1118 /// across this block.
1119 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1120 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1123 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1124 if (isa<DbgInfoIntrinsic>(BBI))
1126 if (Size > 10) return false; // Don't clone large BB's.
1129 // We can only support instructions that do not define values that are
1130 // live outside of the current basic block.
1131 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1133 Instruction *U = cast<Instruction>(*UI);
1134 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1137 // Looks ok, continue checking.
1143 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1144 /// that is defined in the same block as the branch and if any PHI entries are
1145 /// constants, thread edges corresponding to that entry to be branches to their
1146 /// ultimate destination.
1147 static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
1148 BasicBlock *BB = BI->getParent();
1149 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1150 // NOTE: we currently cannot transform this case if the PHI node is used
1151 // outside of the block.
1152 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1155 // Degenerate case of a single entry PHI.
1156 if (PN->getNumIncomingValues() == 1) {
1157 FoldSingleEntryPHINodes(PN->getParent());
1161 // Now we know that this block has multiple preds and two succs.
1162 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1164 // Okay, this is a simple enough basic block. See if any phi values are
1166 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1167 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1168 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1170 // Okay, we now know that all edges from PredBB should be revectored to
1171 // branch to RealDest.
1172 BasicBlock *PredBB = PN->getIncomingBlock(i);
1173 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1175 if (RealDest == BB) continue; // Skip self loops.
1176 // Skip if the predecessor's terminator is an indirect branch.
1177 if (isa<IndirectBrInst>(PredBB->getTerminator())) continue;
1179 // The dest block might have PHI nodes, other predecessors and other
1180 // difficult cases. Instead of being smart about this, just insert a new
1181 // block that jumps to the destination block, effectively splitting
1182 // the edge we are about to create.
1183 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1184 RealDest->getName()+".critedge",
1185 RealDest->getParent(), RealDest);
1186 BranchInst::Create(RealDest, EdgeBB);
1188 // Update PHI nodes.
1189 AddPredecessorToBlock(RealDest, EdgeBB, BB);
1191 // BB may have instructions that are being threaded over. Clone these
1192 // instructions into EdgeBB. We know that there will be no uses of the
1193 // cloned instructions outside of EdgeBB.
1194 BasicBlock::iterator InsertPt = EdgeBB->begin();
1195 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1196 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1197 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1198 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1201 // Clone the instruction.
1202 Instruction *N = BBI->clone();
1203 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1205 // Update operands due to translation.
1206 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1208 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1209 if (PI != TranslateMap.end())
1213 // Check for trivial simplification.
1214 if (Value *V = SimplifyInstruction(N, TD)) {
1215 TranslateMap[BBI] = V;
1216 delete N; // Instruction folded away, don't need actual inst
1218 // Insert the new instruction into its new home.
1219 EdgeBB->getInstList().insert(InsertPt, N);
1220 if (!BBI->use_empty())
1221 TranslateMap[BBI] = N;
1225 // Loop over all of the edges from PredBB to BB, changing them to branch
1226 // to EdgeBB instead.
1227 TerminatorInst *PredBBTI = PredBB->getTerminator();
1228 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1229 if (PredBBTI->getSuccessor(i) == BB) {
1230 BB->removePredecessor(PredBB);
1231 PredBBTI->setSuccessor(i, EdgeBB);
1234 // Recurse, simplifying any other constants.
1235 return FoldCondBranchOnPHI(BI, TD) | true;
1241 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1242 /// PHI node, see if we can eliminate it.
1243 static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
1244 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1245 // statement", which has a very simple dominance structure. Basically, we
1246 // are trying to find the condition that is being branched on, which
1247 // subsequently causes this merge to happen. We really want control
1248 // dependence information for this check, but simplifycfg can't keep it up
1249 // to date, and this catches most of the cases we care about anyway.
1250 BasicBlock *BB = PN->getParent();
1251 BasicBlock *IfTrue, *IfFalse;
1252 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1254 // Don't bother if the branch will be constant folded trivially.
1255 isa<ConstantInt>(IfCond))
1258 // Okay, we found that we can merge this two-entry phi node into a select.
1259 // Doing so would require us to fold *all* two entry phi nodes in this block.
1260 // At some point this becomes non-profitable (particularly if the target
1261 // doesn't support cmov's). Only do this transformation if there are two or
1262 // fewer PHI nodes in this block.
1263 unsigned NumPhis = 0;
1264 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1268 // Loop over the PHI's seeing if we can promote them all to select
1269 // instructions. While we are at it, keep track of the instructions
1270 // that need to be moved to the dominating block.
1271 SmallPtrSet<Instruction*, 4> AggressiveInsts;
1272 unsigned MaxCostVal0 = PHINodeFoldingThreshold,
1273 MaxCostVal1 = PHINodeFoldingThreshold;
1275 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1276 PHINode *PN = cast<PHINode>(II++);
1277 if (Value *V = SimplifyInstruction(PN, TD)) {
1278 PN->replaceAllUsesWith(V);
1279 PN->eraseFromParent();
1283 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
1285 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
1290 // If we folded the the first phi, PN dangles at this point. Refresh it. If
1291 // we ran out of PHIs then we simplified them all.
1292 PN = dyn_cast<PHINode>(BB->begin());
1293 if (PN == 0) return true;
1295 // Don't fold i1 branches on PHIs which contain binary operators. These can
1296 // often be turned into switches and other things.
1297 if (PN->getType()->isIntegerTy(1) &&
1298 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1299 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1300 isa<BinaryOperator>(IfCond)))
1303 // If we all PHI nodes are promotable, check to make sure that all
1304 // instructions in the predecessor blocks can be promoted as well. If
1305 // not, we won't be able to get rid of the control flow, so it's not
1306 // worth promoting to select instructions.
1307 BasicBlock *DomBlock = 0;
1308 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1309 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1310 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1313 DomBlock = *pred_begin(IfBlock1);
1314 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1315 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1316 // This is not an aggressive instruction that we can promote.
1317 // Because of this, we won't be able to get rid of the control
1318 // flow, so the xform is not worth it.
1323 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1326 DomBlock = *pred_begin(IfBlock2);
1327 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1328 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1329 // This is not an aggressive instruction that we can promote.
1330 // Because of this, we won't be able to get rid of the control
1331 // flow, so the xform is not worth it.
1336 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1337 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1339 // If we can still promote the PHI nodes after this gauntlet of tests,
1340 // do all of the PHI's now.
1341 Instruction *InsertPt = DomBlock->getTerminator();
1342 IRBuilder<true, NoFolder> Builder(InsertPt);
1344 // Move all 'aggressive' instructions, which are defined in the
1345 // conditional parts of the if's up to the dominating block.
1347 DomBlock->getInstList().splice(InsertPt,
1348 IfBlock1->getInstList(), IfBlock1->begin(),
1349 IfBlock1->getTerminator());
1351 DomBlock->getInstList().splice(InsertPt,
1352 IfBlock2->getInstList(), IfBlock2->begin(),
1353 IfBlock2->getTerminator());
1355 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1356 // Change the PHI node into a select instruction.
1357 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1358 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1361 cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, ""));
1362 PN->replaceAllUsesWith(NV);
1364 PN->eraseFromParent();
1367 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1368 // has been flattened. Change DomBlock to jump directly to our new block to
1369 // avoid other simplifycfg's kicking in on the diamond.
1370 TerminatorInst *OldTI = DomBlock->getTerminator();
1371 Builder.SetInsertPoint(OldTI);
1372 Builder.CreateBr(BB);
1373 OldTI->eraseFromParent();
1377 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1378 /// to two returning blocks, try to merge them together into one return,
1379 /// introducing a select if the return values disagree.
1380 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
1381 IRBuilder<> &Builder) {
1382 assert(BI->isConditional() && "Must be a conditional branch");
1383 BasicBlock *TrueSucc = BI->getSuccessor(0);
1384 BasicBlock *FalseSucc = BI->getSuccessor(1);
1385 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1386 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1388 // Check to ensure both blocks are empty (just a return) or optionally empty
1389 // with PHI nodes. If there are other instructions, merging would cause extra
1390 // computation on one path or the other.
1391 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1393 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1396 Builder.SetInsertPoint(BI);
1397 // Okay, we found a branch that is going to two return nodes. If
1398 // there is no return value for this function, just change the
1399 // branch into a return.
1400 if (FalseRet->getNumOperands() == 0) {
1401 TrueSucc->removePredecessor(BI->getParent());
1402 FalseSucc->removePredecessor(BI->getParent());
1403 Builder.CreateRetVoid();
1404 EraseTerminatorInstAndDCECond(BI);
1408 // Otherwise, figure out what the true and false return values are
1409 // so we can insert a new select instruction.
1410 Value *TrueValue = TrueRet->getReturnValue();
1411 Value *FalseValue = FalseRet->getReturnValue();
1413 // Unwrap any PHI nodes in the return blocks.
1414 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1415 if (TVPN->getParent() == TrueSucc)
1416 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1417 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1418 if (FVPN->getParent() == FalseSucc)
1419 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1421 // In order for this transformation to be safe, we must be able to
1422 // unconditionally execute both operands to the return. This is
1423 // normally the case, but we could have a potentially-trapping
1424 // constant expression that prevents this transformation from being
1426 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1429 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1433 // Okay, we collected all the mapped values and checked them for sanity, and
1434 // defined to really do this transformation. First, update the CFG.
1435 TrueSucc->removePredecessor(BI->getParent());
1436 FalseSucc->removePredecessor(BI->getParent());
1438 // Insert select instructions where needed.
1439 Value *BrCond = BI->getCondition();
1441 // Insert a select if the results differ.
1442 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1443 } else if (isa<UndefValue>(TrueValue)) {
1444 TrueValue = FalseValue;
1446 TrueValue = Builder.CreateSelect(BrCond, TrueValue,
1447 FalseValue, "retval");
1451 Value *RI = !TrueValue ?
1452 Builder.CreateRetVoid() : Builder.CreateRet(TrueValue);
1456 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1457 << "\n " << *BI << "NewRet = " << *RI
1458 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1460 EraseTerminatorInstAndDCECond(BI);
1465 /// FoldBranchToCommonDest - If this basic block is simple enough, and if a
1466 /// predecessor branches to us and one of our successors, fold the block into
1467 /// the predecessor and use logical operations to pick the right destination.
1468 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1469 BasicBlock *BB = BI->getParent();
1471 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1472 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1473 Cond->getParent() != BB || !Cond->hasOneUse())
1476 // Only allow this if the condition is a simple instruction that can be
1477 // executed unconditionally. It must be in the same block as the branch, and
1478 // must be at the front of the block.
1479 BasicBlock::iterator FrontIt = BB->front();
1481 // Ignore dbg intrinsics.
1482 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1484 // Allow a single instruction to be hoisted in addition to the compare
1485 // that feeds the branch. We later ensure that any values that _it_ uses
1486 // were also live in the predecessor, so that we don't unnecessarily create
1487 // register pressure or inhibit out-of-order execution.
1488 Instruction *BonusInst = 0;
1489 if (&*FrontIt != Cond &&
1490 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1491 isSafeToSpeculativelyExecute(FrontIt)) {
1492 BonusInst = &*FrontIt;
1495 // Ignore dbg intrinsics.
1496 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1499 // Only a single bonus inst is allowed.
1500 if (&*FrontIt != Cond)
1503 // Make sure the instruction after the condition is the cond branch.
1504 BasicBlock::iterator CondIt = Cond; ++CondIt;
1506 // Ingore dbg intrinsics.
1507 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
1512 // Cond is known to be a compare or binary operator. Check to make sure that
1513 // neither operand is a potentially-trapping constant expression.
1514 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1517 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1521 // Finally, don't infinitely unroll conditional loops.
1522 BasicBlock *TrueDest = BI->getSuccessor(0);
1523 BasicBlock *FalseDest = BI->getSuccessor(1);
1524 if (TrueDest == BB || FalseDest == BB)
1527 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1528 BasicBlock *PredBlock = *PI;
1529 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1531 // Check that we have two conditional branches. If there is a PHI node in
1532 // the common successor, verify that the same value flows in from both
1534 if (PBI == 0 || PBI->isUnconditional() || !SafeToMergeTerminators(BI, PBI))
1537 // Determine if the two branches share a common destination.
1538 Instruction::BinaryOps Opc;
1539 bool InvertPredCond = false;
1541 if (PBI->getSuccessor(0) == TrueDest)
1542 Opc = Instruction::Or;
1543 else if (PBI->getSuccessor(1) == FalseDest)
1544 Opc = Instruction::And;
1545 else if (PBI->getSuccessor(0) == FalseDest)
1546 Opc = Instruction::And, InvertPredCond = true;
1547 else if (PBI->getSuccessor(1) == TrueDest)
1548 Opc = Instruction::Or, InvertPredCond = true;
1552 // Ensure that any values used in the bonus instruction are also used
1553 // by the terminator of the predecessor. This means that those values
1554 // must already have been resolved, so we won't be inhibiting the
1555 // out-of-order core by speculating them earlier.
1557 // Collect the values used by the bonus inst
1558 SmallPtrSet<Value*, 4> UsedValues;
1559 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1560 OE = BonusInst->op_end(); OI != OE; ++OI) {
1562 if (!isa<Constant>(V))
1563 UsedValues.insert(V);
1566 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1567 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1569 // Walk up to four levels back up the use-def chain of the predecessor's
1570 // terminator to see if all those values were used. The choice of four
1571 // levels is arbitrary, to provide a compile-time-cost bound.
1572 while (!Worklist.empty()) {
1573 std::pair<Value*, unsigned> Pair = Worklist.back();
1574 Worklist.pop_back();
1576 if (Pair.second >= 4) continue;
1577 UsedValues.erase(Pair.first);
1578 if (UsedValues.empty()) break;
1580 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
1581 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1583 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1587 if (!UsedValues.empty()) return false;
1590 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1591 IRBuilder<> Builder(PBI);
1593 // If we need to invert the condition in the pred block to match, do so now.
1594 if (InvertPredCond) {
1595 Value *NewCond = PBI->getCondition();
1597 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
1598 CmpInst *CI = cast<CmpInst>(NewCond);
1599 CI->setPredicate(CI->getInversePredicate());
1601 NewCond = Builder.CreateNot(NewCond,
1602 PBI->getCondition()->getName()+".not");
1605 PBI->setCondition(NewCond);
1606 PBI->swapSuccessors();
1609 // If we have a bonus inst, clone it into the predecessor block.
1610 Instruction *NewBonus = 0;
1612 NewBonus = BonusInst->clone();
1613 PredBlock->getInstList().insert(PBI, NewBonus);
1614 NewBonus->takeName(BonusInst);
1615 BonusInst->setName(BonusInst->getName()+".old");
1618 // Clone Cond into the predecessor basic block, and or/and the
1619 // two conditions together.
1620 Instruction *New = Cond->clone();
1621 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1622 PredBlock->getInstList().insert(PBI, New);
1623 New->takeName(Cond);
1624 Cond->setName(New->getName()+".old");
1626 Instruction *NewCond =
1627 cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(),
1629 PBI->setCondition(NewCond);
1630 if (PBI->getSuccessor(0) == BB) {
1631 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1632 PBI->setSuccessor(0, TrueDest);
1634 if (PBI->getSuccessor(1) == BB) {
1635 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1636 PBI->setSuccessor(1, FalseDest);
1639 // Copy any debug value intrinsics into the end of PredBlock.
1640 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
1641 if (isa<DbgInfoIntrinsic>(*I))
1642 I->clone()->insertBefore(PBI);
1649 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1650 /// predecessor of another block, this function tries to simplify it. We know
1651 /// that PBI and BI are both conditional branches, and BI is in one of the
1652 /// successor blocks of PBI - PBI branches to BI.
1653 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1654 assert(PBI->isConditional() && BI->isConditional());
1655 BasicBlock *BB = BI->getParent();
1657 // If this block ends with a branch instruction, and if there is a
1658 // predecessor that ends on a branch of the same condition, make
1659 // this conditional branch redundant.
1660 if (PBI->getCondition() == BI->getCondition() &&
1661 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1662 // Okay, the outcome of this conditional branch is statically
1663 // knowable. If this block had a single pred, handle specially.
1664 if (BB->getSinglePredecessor()) {
1665 // Turn this into a branch on constant.
1666 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1667 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1669 return true; // Nuke the branch on constant.
1672 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1673 // in the constant and simplify the block result. Subsequent passes of
1674 // simplifycfg will thread the block.
1675 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1676 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
1677 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1678 std::distance(PB, PE),
1679 BI->getCondition()->getName() + ".pr",
1681 // Okay, we're going to insert the PHI node. Since PBI is not the only
1682 // predecessor, compute the PHI'd conditional value for all of the preds.
1683 // Any predecessor where the condition is not computable we keep symbolic.
1684 for (pred_iterator PI = PB; PI != PE; ++PI) {
1685 BasicBlock *P = *PI;
1686 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
1687 PBI != BI && PBI->isConditional() &&
1688 PBI->getCondition() == BI->getCondition() &&
1689 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1690 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1691 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1694 NewPN->addIncoming(BI->getCondition(), P);
1698 BI->setCondition(NewPN);
1703 // If this is a conditional branch in an empty block, and if any
1704 // predecessors is a conditional branch to one of our destinations,
1705 // fold the conditions into logical ops and one cond br.
1706 BasicBlock::iterator BBI = BB->begin();
1707 // Ignore dbg intrinsics.
1708 while (isa<DbgInfoIntrinsic>(BBI))
1714 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1719 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1721 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1722 PBIOp = 0, BIOp = 1;
1723 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1724 PBIOp = 1, BIOp = 0;
1725 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1730 // Check to make sure that the other destination of this branch
1731 // isn't BB itself. If so, this is an infinite loop that will
1732 // keep getting unwound.
1733 if (PBI->getSuccessor(PBIOp) == BB)
1736 // Do not perform this transformation if it would require
1737 // insertion of a large number of select instructions. For targets
1738 // without predication/cmovs, this is a big pessimization.
1739 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1741 unsigned NumPhis = 0;
1742 for (BasicBlock::iterator II = CommonDest->begin();
1743 isa<PHINode>(II); ++II, ++NumPhis)
1744 if (NumPhis > 2) // Disable this xform.
1747 // Finally, if everything is ok, fold the branches to logical ops.
1748 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1750 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
1751 << "AND: " << *BI->getParent());
1754 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1755 // branch in it, where one edge (OtherDest) goes back to itself but the other
1756 // exits. We don't *know* that the program avoids the infinite loop
1757 // (even though that seems likely). If we do this xform naively, we'll end up
1758 // recursively unpeeling the loop. Since we know that (after the xform is
1759 // done) that the block *is* infinite if reached, we just make it an obviously
1760 // infinite loop with no cond branch.
1761 if (OtherDest == BB) {
1762 // Insert it at the end of the function, because it's either code,
1763 // or it won't matter if it's hot. :)
1764 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1765 "infloop", BB->getParent());
1766 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1767 OtherDest = InfLoopBlock;
1770 DEBUG(dbgs() << *PBI->getParent()->getParent());
1772 // BI may have other predecessors. Because of this, we leave
1773 // it alone, but modify PBI.
1775 // Make sure we get to CommonDest on True&True directions.
1776 Value *PBICond = PBI->getCondition();
1777 IRBuilder<true, NoFolder> Builder(PBI);
1779 PBICond = Builder.CreateNot(PBICond, PBICond->getName()+".not");
1781 Value *BICond = BI->getCondition();
1783 BICond = Builder.CreateNot(BICond, BICond->getName()+".not");
1785 // Merge the conditions.
1786 Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge");
1788 // Modify PBI to branch on the new condition to the new dests.
1789 PBI->setCondition(Cond);
1790 PBI->setSuccessor(0, CommonDest);
1791 PBI->setSuccessor(1, OtherDest);
1793 // OtherDest may have phi nodes. If so, add an entry from PBI's
1794 // block that are identical to the entries for BI's block.
1795 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
1797 // We know that the CommonDest already had an edge from PBI to
1798 // it. If it has PHIs though, the PHIs may have different
1799 // entries for BB and PBI's BB. If so, insert a select to make
1802 for (BasicBlock::iterator II = CommonDest->begin();
1803 (PN = dyn_cast<PHINode>(II)); ++II) {
1804 Value *BIV = PN->getIncomingValueForBlock(BB);
1805 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1806 Value *PBIV = PN->getIncomingValue(PBBIdx);
1808 // Insert a select in PBI to pick the right value.
1809 Value *NV = cast<SelectInst>
1810 (Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName()+".mux"));
1811 PN->setIncomingValue(PBBIdx, NV);
1815 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1816 DEBUG(dbgs() << *PBI->getParent()->getParent());
1818 // This basic block is probably dead. We know it has at least
1819 // one fewer predecessor.
1823 // SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
1824 // branch to TrueBB if Cond is true or to FalseBB if Cond is false.
1825 // Takes care of updating the successors and removing the old terminator.
1826 // Also makes sure not to introduce new successors by assuming that edges to
1827 // non-successor TrueBBs and FalseBBs aren't reachable.
1828 static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
1829 BasicBlock *TrueBB, BasicBlock *FalseBB){
1830 // Remove any superfluous successor edges from the CFG.
1831 // First, figure out which successors to preserve.
1832 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
1834 BasicBlock *KeepEdge1 = TrueBB;
1835 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
1837 // Then remove the rest.
1838 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
1839 BasicBlock *Succ = OldTerm->getSuccessor(I);
1840 // Make sure only to keep exactly one copy of each edge.
1841 if (Succ == KeepEdge1)
1843 else if (Succ == KeepEdge2)
1846 Succ->removePredecessor(OldTerm->getParent());
1849 IRBuilder<> Builder(OldTerm);
1850 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
1852 // Insert an appropriate new terminator.
1853 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
1854 if (TrueBB == FalseBB)
1855 // We were only looking for one successor, and it was present.
1856 // Create an unconditional branch to it.
1857 Builder.CreateBr(TrueBB);
1859 // We found both of the successors we were looking for.
1860 // Create a conditional branch sharing the condition of the select.
1861 Builder.CreateCondBr(Cond, TrueBB, FalseBB);
1862 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
1863 // Neither of the selected blocks were successors, so this
1864 // terminator must be unreachable.
1865 new UnreachableInst(OldTerm->getContext(), OldTerm);
1867 // One of the selected values was a successor, but the other wasn't.
1868 // Insert an unconditional branch to the one that was found;
1869 // the edge to the one that wasn't must be unreachable.
1871 // Only TrueBB was found.
1872 Builder.CreateBr(TrueBB);
1874 // Only FalseBB was found.
1875 Builder.CreateBr(FalseBB);
1878 EraseTerminatorInstAndDCECond(OldTerm);
1882 // SimplifySwitchOnSelect - Replaces
1883 // (switch (select cond, X, Y)) on constant X, Y
1884 // with a branch - conditional if X and Y lead to distinct BBs,
1885 // unconditional otherwise.
1886 static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
1887 // Check for constant integer values in the select.
1888 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
1889 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
1890 if (!TrueVal || !FalseVal)
1893 // Find the relevant condition and destinations.
1894 Value *Condition = Select->getCondition();
1895 BasicBlock *TrueBB = SI->getSuccessor(SI->findCaseValue(TrueVal));
1896 BasicBlock *FalseBB = SI->getSuccessor(SI->findCaseValue(FalseVal));
1898 // Perform the actual simplification.
1899 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB);
1902 // SimplifyIndirectBrOnSelect - Replaces
1903 // (indirectbr (select cond, blockaddress(@fn, BlockA),
1904 // blockaddress(@fn, BlockB)))
1906 // (br cond, BlockA, BlockB).
1907 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
1908 // Check that both operands of the select are block addresses.
1909 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
1910 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
1914 // Extract the actual blocks.
1915 BasicBlock *TrueBB = TBA->getBasicBlock();
1916 BasicBlock *FalseBB = FBA->getBasicBlock();
1918 // Perform the actual simplification.
1919 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB);
1922 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
1923 /// instruction (a seteq/setne with a constant) as the only instruction in a
1924 /// block that ends with an uncond branch. We are looking for a very specific
1925 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
1926 /// this case, we merge the first two "or's of icmp" into a switch, but then the
1927 /// default value goes to an uncond block with a seteq in it, we get something
1930 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
1932 /// %tmp = icmp eq i8 %A, 92
1935 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
1937 /// We prefer to split the edge to 'end' so that there is a true/false entry to
1938 /// the PHI, merging the third icmp into the switch.
1939 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
1940 const TargetData *TD,
1941 IRBuilder<> &Builder) {
1942 BasicBlock *BB = ICI->getParent();
1944 // If the block has any PHIs in it or the icmp has multiple uses, it is too
1946 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
1948 Value *V = ICI->getOperand(0);
1949 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
1951 // The pattern we're looking for is where our only predecessor is a switch on
1952 // 'V' and this block is the default case for the switch. In this case we can
1953 // fold the compared value into the switch to simplify things.
1954 BasicBlock *Pred = BB->getSinglePredecessor();
1955 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
1957 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
1958 if (SI->getCondition() != V)
1961 // If BB is reachable on a non-default case, then we simply know the value of
1962 // V in this block. Substitute it and constant fold the icmp instruction
1964 if (SI->getDefaultDest() != BB) {
1965 ConstantInt *VVal = SI->findCaseDest(BB);
1966 assert(VVal && "Should have a unique destination value");
1967 ICI->setOperand(0, VVal);
1969 if (Value *V = SimplifyInstruction(ICI, TD)) {
1970 ICI->replaceAllUsesWith(V);
1971 ICI->eraseFromParent();
1973 // BB is now empty, so it is likely to simplify away.
1974 return SimplifyCFG(BB) | true;
1977 // Ok, the block is reachable from the default dest. If the constant we're
1978 // comparing exists in one of the other edges, then we can constant fold ICI
1980 if (SI->findCaseValue(Cst) != 0) {
1982 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1983 V = ConstantInt::getFalse(BB->getContext());
1985 V = ConstantInt::getTrue(BB->getContext());
1987 ICI->replaceAllUsesWith(V);
1988 ICI->eraseFromParent();
1989 // BB is now empty, so it is likely to simplify away.
1990 return SimplifyCFG(BB) | true;
1993 // The use of the icmp has to be in the 'end' block, by the only PHI node in
1995 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
1996 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
1997 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
1998 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
2001 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
2003 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
2004 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
2006 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2007 std::swap(DefaultCst, NewCst);
2009 // Replace ICI (which is used by the PHI for the default value) with true or
2010 // false depending on if it is EQ or NE.
2011 ICI->replaceAllUsesWith(DefaultCst);
2012 ICI->eraseFromParent();
2014 // Okay, the switch goes to this block on a default value. Add an edge from
2015 // the switch to the merge point on the compared value.
2016 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
2017 BB->getParent(), BB);
2018 SI->addCase(Cst, NewBB);
2020 // NewBB branches to the phi block, add the uncond branch and the phi entry.
2021 Builder.SetInsertPoint(NewBB);
2022 Builder.SetCurrentDebugLocation(SI->getDebugLoc());
2023 Builder.CreateBr(SuccBlock);
2024 PHIUse->addIncoming(NewCst, NewBB);
2028 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
2029 /// Check to see if it is branching on an or/and chain of icmp instructions, and
2030 /// fold it into a switch instruction if so.
2031 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD,
2032 IRBuilder<> &Builder) {
2033 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
2034 if (Cond == 0) return false;
2037 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2038 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2039 // 'setne's and'ed together, collect them.
2041 std::vector<ConstantInt*> Values;
2042 bool TrueWhenEqual = true;
2043 Value *ExtraCase = 0;
2044 unsigned UsedICmps = 0;
2046 if (Cond->getOpcode() == Instruction::Or) {
2047 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
2049 } else if (Cond->getOpcode() == Instruction::And) {
2050 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
2052 TrueWhenEqual = false;
2055 // If we didn't have a multiply compared value, fail.
2056 if (CompVal == 0) return false;
2058 // Avoid turning single icmps into a switch.
2062 // There might be duplicate constants in the list, which the switch
2063 // instruction can't handle, remove them now.
2064 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
2065 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2067 // If Extra was used, we require at least two switch values to do the
2068 // transformation. A switch with one value is just an cond branch.
2069 if (ExtraCase && Values.size() < 2) return false;
2071 // Figure out which block is which destination.
2072 BasicBlock *DefaultBB = BI->getSuccessor(1);
2073 BasicBlock *EdgeBB = BI->getSuccessor(0);
2074 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2076 BasicBlock *BB = BI->getParent();
2078 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
2079 << " cases into SWITCH. BB is:\n" << *BB);
2081 // If there are any extra values that couldn't be folded into the switch
2082 // then we evaluate them with an explicit branch first. Split the block
2083 // right before the condbr to handle it.
2085 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
2086 // Remove the uncond branch added to the old block.
2087 TerminatorInst *OldTI = BB->getTerminator();
2088 Builder.SetInsertPoint(OldTI);
2091 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
2093 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
2095 OldTI->eraseFromParent();
2097 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
2098 // for the edge we just added.
2099 AddPredecessorToBlock(EdgeBB, BB, NewBB);
2101 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
2102 << "\nEXTRABB = " << *BB);
2106 Builder.SetInsertPoint(BI);
2107 // Convert pointer to int before we switch.
2108 if (CompVal->getType()->isPointerTy()) {
2109 assert(TD && "Cannot switch on pointer without TargetData");
2110 CompVal = Builder.CreatePtrToInt(CompVal,
2111 TD->getIntPtrType(CompVal->getContext()),
2115 // Create the new switch instruction now.
2116 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
2118 // Add all of the 'cases' to the switch instruction.
2119 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2120 New->addCase(Values[i], EdgeBB);
2122 // We added edges from PI to the EdgeBB. As such, if there were any
2123 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2124 // the number of edges added.
2125 for (BasicBlock::iterator BBI = EdgeBB->begin();
2126 isa<PHINode>(BBI); ++BBI) {
2127 PHINode *PN = cast<PHINode>(BBI);
2128 Value *InVal = PN->getIncomingValueForBlock(BB);
2129 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2130 PN->addIncoming(InVal, BB);
2133 // Erase the old branch instruction.
2134 EraseTerminatorInstAndDCECond(BI);
2136 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
2140 bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
2141 // If this is a trivial landing pad that just continues unwinding the caught
2142 // exception then zap the landing pad, turning its invokes into calls.
2143 BasicBlock *BB = RI->getParent();
2144 LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI());
2145 if (RI->getValue() != LPInst)
2146 // Not a landing pad, or the resume is not unwinding the exception that
2147 // caused control to branch here.
2150 // Check that there are no other instructions except for debug intrinsics.
2151 BasicBlock::iterator I = LPInst, E = RI;
2153 if (!isa<DbgInfoIntrinsic>(I))
2156 // Turn all invokes that unwind here into calls and delete the basic block.
2157 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
2158 InvokeInst *II = cast<InvokeInst>((*PI++)->getTerminator());
2159 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
2160 // Insert a call instruction before the invoke.
2161 CallInst *Call = CallInst::Create(II->getCalledValue(), Args, "", II);
2163 Call->setCallingConv(II->getCallingConv());
2164 Call->setAttributes(II->getAttributes());
2165 Call->setDebugLoc(II->getDebugLoc());
2167 // Anything that used the value produced by the invoke instruction now uses
2168 // the value produced by the call instruction. Note that we do this even
2169 // for void functions and calls with no uses so that the callgraph edge is
2171 II->replaceAllUsesWith(Call);
2172 BB->removePredecessor(II->getParent());
2174 // Insert a branch to the normal destination right before the invoke.
2175 BranchInst::Create(II->getNormalDest(), II);
2177 // Finally, delete the invoke instruction!
2178 II->eraseFromParent();
2181 // The landingpad is now unreachable. Zap it.
2182 BB->eraseFromParent();
2186 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
2187 BasicBlock *BB = RI->getParent();
2188 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2190 // Find predecessors that end with branches.
2191 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2192 SmallVector<BranchInst*, 8> CondBranchPreds;
2193 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2194 BasicBlock *P = *PI;
2195 TerminatorInst *PTI = P->getTerminator();
2196 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2197 if (BI->isUnconditional())
2198 UncondBranchPreds.push_back(P);
2200 CondBranchPreds.push_back(BI);
2204 // If we found some, do the transformation!
2205 if (!UncondBranchPreds.empty() && DupRet) {
2206 while (!UncondBranchPreds.empty()) {
2207 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2208 DEBUG(dbgs() << "FOLDING: " << *BB
2209 << "INTO UNCOND BRANCH PRED: " << *Pred);
2210 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
2213 // If we eliminated all predecessors of the block, delete the block now.
2214 if (pred_begin(BB) == pred_end(BB))
2215 // We know there are no successors, so just nuke the block.
2216 BB->eraseFromParent();
2221 // Check out all of the conditional branches going to this return
2222 // instruction. If any of them just select between returns, change the
2223 // branch itself into a select/return pair.
2224 while (!CondBranchPreds.empty()) {
2225 BranchInst *BI = CondBranchPreds.pop_back_val();
2227 // Check to see if the non-BB successor is also a return block.
2228 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2229 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2230 SimplifyCondBranchToTwoReturns(BI, Builder))
2236 bool SimplifyCFGOpt::SimplifyUnwind(UnwindInst *UI, IRBuilder<> &Builder) {
2237 // Check to see if the first instruction in this block is just an unwind.
2238 // If so, replace any invoke instructions which use this as an exception
2239 // destination with call instructions.
2240 BasicBlock *BB = UI->getParent();
2241 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2243 bool Changed = false;
2244 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2245 while (!Preds.empty()) {
2246 BasicBlock *Pred = Preds.back();
2247 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
2248 if (II && II->getUnwindDest() == BB) {
2249 // Insert a new branch instruction before the invoke, because this
2250 // is now a fall through.
2251 Builder.SetInsertPoint(II);
2252 BranchInst *BI = Builder.CreateBr(II->getNormalDest());
2253 Pred->getInstList().remove(II); // Take out of symbol table
2255 // Insert the call now.
2256 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
2257 Builder.SetInsertPoint(BI);
2258 CallInst *CI = Builder.CreateCall(II->getCalledValue(),
2259 Args, II->getName());
2260 CI->setCallingConv(II->getCallingConv());
2261 CI->setAttributes(II->getAttributes());
2262 // If the invoke produced a value, the Call now does instead.
2263 II->replaceAllUsesWith(CI);
2271 // If this block is now dead (and isn't the entry block), remove it.
2272 if (pred_begin(BB) == pred_end(BB) &&
2273 BB != &BB->getParent()->getEntryBlock()) {
2274 // We know there are no successors, so just nuke the block.
2275 BB->eraseFromParent();
2282 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2283 BasicBlock *BB = UI->getParent();
2285 bool Changed = false;
2287 // If there are any instructions immediately before the unreachable that can
2288 // be removed, do so.
2289 while (UI != BB->begin()) {
2290 BasicBlock::iterator BBI = UI;
2292 // Do not delete instructions that can have side effects which might cause
2293 // the unreachable to not be reachable; specifically, calls and volatile
2294 // operations may have this effect.
2295 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2297 if (BBI->mayHaveSideEffects()) {
2298 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
2299 if (SI->isVolatile())
2301 } else if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
2302 if (LI->isVolatile())
2304 } else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(BBI)) {
2305 if (RMWI->isVolatile())
2307 } else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) {
2308 if (CXI->isVolatile())
2310 } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) &&
2311 !isa<LandingPadInst>(BBI)) {
2314 // Note that deleting LandingPad's here is in fact okay, although it
2315 // involves a bit of subtle reasoning. If this inst is a LandingPad,
2316 // all the predecessors of this block will be the unwind edges of Invokes,
2317 // and we can therefore guarantee this block will be erased.
2320 // Delete this instruction (any uses are guaranteed to be dead)
2321 if (!BBI->use_empty())
2322 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
2323 BBI->eraseFromParent();
2327 // If the unreachable instruction is the first in the block, take a gander
2328 // at all of the predecessors of this instruction, and simplify them.
2329 if (&BB->front() != UI) return Changed;
2331 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2332 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2333 TerminatorInst *TI = Preds[i]->getTerminator();
2334 IRBuilder<> Builder(TI);
2335 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2336 if (BI->isUnconditional()) {
2337 if (BI->getSuccessor(0) == BB) {
2338 new UnreachableInst(TI->getContext(), TI);
2339 TI->eraseFromParent();
2343 if (BI->getSuccessor(0) == BB) {
2344 Builder.CreateBr(BI->getSuccessor(1));
2345 EraseTerminatorInstAndDCECond(BI);
2346 } else if (BI->getSuccessor(1) == BB) {
2347 Builder.CreateBr(BI->getSuccessor(0));
2348 EraseTerminatorInstAndDCECond(BI);
2352 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2353 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2354 if (SI->getSuccessor(i) == BB) {
2355 BB->removePredecessor(SI->getParent());
2360 // If the default value is unreachable, figure out the most popular
2361 // destination and make it the default.
2362 if (SI->getSuccessor(0) == BB) {
2363 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
2364 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
2365 std::pair<unsigned, unsigned> &entry =
2366 Popularity[SI->getSuccessor(i)];
2367 if (entry.first == 0) {
2375 // Find the most popular block.
2376 unsigned MaxPop = 0;
2377 unsigned MaxIndex = 0;
2378 BasicBlock *MaxBlock = 0;
2379 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
2380 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2381 if (I->second.first > MaxPop ||
2382 (I->second.first == MaxPop && MaxIndex > I->second.second)) {
2383 MaxPop = I->second.first;
2384 MaxIndex = I->second.second;
2385 MaxBlock = I->first;
2389 // Make this the new default, allowing us to delete any explicit
2391 SI->setSuccessor(0, MaxBlock);
2394 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2396 if (isa<PHINode>(MaxBlock->begin()))
2397 for (unsigned i = 0; i != MaxPop-1; ++i)
2398 MaxBlock->removePredecessor(SI->getParent());
2400 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2401 if (SI->getSuccessor(i) == MaxBlock) {
2407 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2408 if (II->getUnwindDest() == BB) {
2409 // Convert the invoke to a call instruction. This would be a good
2410 // place to note that the call does not throw though.
2411 BranchInst *BI = Builder.CreateBr(II->getNormalDest());
2412 II->removeFromParent(); // Take out of symbol table
2414 // Insert the call now...
2415 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2416 Builder.SetInsertPoint(BI);
2417 CallInst *CI = Builder.CreateCall(II->getCalledValue(),
2418 Args, II->getName());
2419 CI->setCallingConv(II->getCallingConv());
2420 CI->setAttributes(II->getAttributes());
2421 // If the invoke produced a value, the call does now instead.
2422 II->replaceAllUsesWith(CI);
2429 // If this block is now dead, remove it.
2430 if (pred_begin(BB) == pred_end(BB) &&
2431 BB != &BB->getParent()->getEntryBlock()) {
2432 // We know there are no successors, so just nuke the block.
2433 BB->eraseFromParent();
2440 /// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
2441 /// integer range comparison into a sub, an icmp and a branch.
2442 static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
2443 assert(SI->getNumCases() > 2 && "Degenerate switch?");
2445 // Make sure all cases point to the same destination and gather the values.
2446 SmallVector<ConstantInt *, 16> Cases;
2447 Cases.push_back(SI->getCaseValue(1));
2448 for (unsigned I = 2, E = SI->getNumCases(); I != E; ++I) {
2449 if (SI->getSuccessor(I-1) != SI->getSuccessor(I))
2451 Cases.push_back(SI->getCaseValue(I));
2453 assert(Cases.size() == SI->getNumCases()-1 && "Not all cases gathered");
2455 // Sort the case values, then check if they form a range we can transform.
2456 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
2457 for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
2458 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
2462 Constant *Offset = ConstantExpr::getNeg(Cases.back());
2463 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases()-1);
2465 Value *Sub = SI->getCondition();
2466 if (!Offset->isNullValue())
2467 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off");
2468 Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
2469 Builder.CreateCondBr(Cmp, SI->getSuccessor(1), SI->getDefaultDest());
2471 // Prune obsolete incoming values off the successor's PHI nodes.
2472 for (BasicBlock::iterator BBI = SI->getSuccessor(1)->begin();
2473 isa<PHINode>(BBI); ++BBI) {
2474 for (unsigned I = 0, E = SI->getNumCases()-2; I != E; ++I)
2475 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
2477 SI->eraseFromParent();
2482 /// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch
2483 /// and use it to remove dead cases.
2484 static bool EliminateDeadSwitchCases(SwitchInst *SI) {
2485 Value *Cond = SI->getCondition();
2486 unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth();
2487 APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
2488 ComputeMaskedBits(Cond, APInt::getAllOnesValue(Bits), KnownZero, KnownOne);
2490 // Gather dead cases.
2491 SmallVector<ConstantInt*, 8> DeadCases;
2492 for (unsigned I = 1, E = SI->getNumCases(); I != E; ++I) {
2493 if ((SI->getCaseValue(I)->getValue() & KnownZero) != 0 ||
2494 (SI->getCaseValue(I)->getValue() & KnownOne) != KnownOne) {
2495 DeadCases.push_back(SI->getCaseValue(I));
2496 DEBUG(dbgs() << "SimplifyCFG: switch case '"
2497 << SI->getCaseValue(I)->getValue() << "' is dead.\n");
2501 // Remove dead cases from the switch.
2502 for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) {
2503 unsigned Case = SI->findCaseValue(DeadCases[I]);
2504 // Prune unused values from PHI nodes.
2505 SI->getSuccessor(Case)->removePredecessor(SI->getParent());
2506 SI->removeCase(Case);
2509 return !DeadCases.empty();
2512 /// FindPHIForConditionForwarding - If BB would be eligible for simplification
2513 /// by TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated
2514 /// by an unconditional branch), look at the phi node for BB in the successor
2515 /// block and see if the incoming value is equal to CaseValue. If so, return
2516 /// the phi node, and set PhiIndex to BB's index in the phi node.
2517 static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
2520 if (BB->getFirstNonPHIOrDbg() != BB->getTerminator())
2521 return NULL; // BB must be empty to be a candidate for simplification.
2522 if (!BB->getSinglePredecessor())
2523 return NULL; // BB must be dominated by the switch.
2525 BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
2526 if (!Branch || !Branch->isUnconditional())
2527 return NULL; // Terminator must be unconditional branch.
2529 BasicBlock *Succ = Branch->getSuccessor(0);
2531 BasicBlock::iterator I = Succ->begin();
2532 while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
2533 int Idx = PHI->getBasicBlockIndex(BB);
2534 assert(Idx >= 0 && "PHI has no entry for predecessor?");
2536 Value *InValue = PHI->getIncomingValue(Idx);
2537 if (InValue != CaseValue) continue;
2546 /// ForwardSwitchConditionToPHI - Try to forward the condition of a switch
2547 /// instruction to a phi node dominated by the switch, if that would mean that
2548 /// some of the destination blocks of the switch can be folded away.
2549 /// Returns true if a change is made.
2550 static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
2551 typedef DenseMap<PHINode*, SmallVector<int,4> > ForwardingNodesMap;
2552 ForwardingNodesMap ForwardingNodes;
2554 for (unsigned I = 1; I < SI->getNumCases(); ++I) { // 0 is the default case.
2555 ConstantInt *CaseValue = SI->getCaseValue(I);
2556 BasicBlock *CaseDest = SI->getSuccessor(I);
2559 PHINode *PHI = FindPHIForConditionForwarding(CaseValue, CaseDest,
2563 ForwardingNodes[PHI].push_back(PhiIndex);
2566 bool Changed = false;
2568 for (ForwardingNodesMap::iterator I = ForwardingNodes.begin(),
2569 E = ForwardingNodes.end(); I != E; ++I) {
2570 PHINode *Phi = I->first;
2571 SmallVector<int,4> &Indexes = I->second;
2573 if (Indexes.size() < 2) continue;
2575 for (size_t I = 0, E = Indexes.size(); I != E; ++I)
2576 Phi->setIncomingValue(Indexes[I], SI->getCondition());
2583 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
2584 // If this switch is too complex to want to look at, ignore it.
2585 if (!isValueEqualityComparison(SI))
2588 BasicBlock *BB = SI->getParent();
2590 // If we only have one predecessor, and if it is a branch on this value,
2591 // see if that predecessor totally determines the outcome of this switch.
2592 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2593 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
2594 return SimplifyCFG(BB) | true;
2596 Value *Cond = SI->getCondition();
2597 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
2598 if (SimplifySwitchOnSelect(SI, Select))
2599 return SimplifyCFG(BB) | true;
2601 // If the block only contains the switch, see if we can fold the block
2602 // away into any preds.
2603 BasicBlock::iterator BBI = BB->begin();
2604 // Ignore dbg intrinsics.
2605 while (isa<DbgInfoIntrinsic>(BBI))
2608 if (FoldValueComparisonIntoPredecessors(SI, Builder))
2609 return SimplifyCFG(BB) | true;
2611 // Try to transform the switch into an icmp and a branch.
2612 if (TurnSwitchRangeIntoICmp(SI, Builder))
2613 return SimplifyCFG(BB) | true;
2615 // Remove unreachable cases.
2616 if (EliminateDeadSwitchCases(SI))
2617 return SimplifyCFG(BB) | true;
2619 if (ForwardSwitchConditionToPHI(SI))
2620 return SimplifyCFG(BB) | true;
2625 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
2626 BasicBlock *BB = IBI->getParent();
2627 bool Changed = false;
2629 // Eliminate redundant destinations.
2630 SmallPtrSet<Value *, 8> Succs;
2631 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2632 BasicBlock *Dest = IBI->getDestination(i);
2633 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2634 Dest->removePredecessor(BB);
2635 IBI->removeDestination(i);
2641 if (IBI->getNumDestinations() == 0) {
2642 // If the indirectbr has no successors, change it to unreachable.
2643 new UnreachableInst(IBI->getContext(), IBI);
2644 EraseTerminatorInstAndDCECond(IBI);
2648 if (IBI->getNumDestinations() == 1) {
2649 // If the indirectbr has one successor, change it to a direct branch.
2650 BranchInst::Create(IBI->getDestination(0), IBI);
2651 EraseTerminatorInstAndDCECond(IBI);
2655 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2656 if (SimplifyIndirectBrOnSelect(IBI, SI))
2657 return SimplifyCFG(BB) | true;
2662 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
2663 BasicBlock *BB = BI->getParent();
2665 // If the Terminator is the only non-phi instruction, simplify the block.
2666 BasicBlock::iterator I = BB->getFirstNonPHIOrDbgOrLifetime();
2667 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
2668 TryToSimplifyUncondBranchFromEmptyBlock(BB))
2671 // If the only instruction in the block is a seteq/setne comparison
2672 // against a constant, try to simplify the block.
2673 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
2674 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
2675 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
2677 if (I->isTerminator() &&
2678 TryToSimplifyUncondBranchWithICmpInIt(ICI, TD, Builder))
2686 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
2687 BasicBlock *BB = BI->getParent();
2689 // Conditional branch
2690 if (isValueEqualityComparison(BI)) {
2691 // If we only have one predecessor, and if it is a branch on this value,
2692 // see if that predecessor totally determines the outcome of this
2694 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2695 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
2696 return SimplifyCFG(BB) | true;
2698 // This block must be empty, except for the setcond inst, if it exists.
2699 // Ignore dbg intrinsics.
2700 BasicBlock::iterator I = BB->begin();
2701 // Ignore dbg intrinsics.
2702 while (isa<DbgInfoIntrinsic>(I))
2705 if (FoldValueComparisonIntoPredecessors(BI, Builder))
2706 return SimplifyCFG(BB) | true;
2707 } else if (&*I == cast<Instruction>(BI->getCondition())){
2709 // Ignore dbg intrinsics.
2710 while (isa<DbgInfoIntrinsic>(I))
2712 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
2713 return SimplifyCFG(BB) | true;
2717 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
2718 if (SimplifyBranchOnICmpChain(BI, TD, Builder))
2721 // We have a conditional branch to two blocks that are only reachable
2722 // from BI. We know that the condbr dominates the two blocks, so see if
2723 // there is any identical code in the "then" and "else" blocks. If so, we
2724 // can hoist it up to the branching block.
2725 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
2726 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2727 if (HoistThenElseCodeToIf(BI))
2728 return SimplifyCFG(BB) | true;
2730 // If Successor #1 has multiple preds, we may be able to conditionally
2731 // execute Successor #0 if it branches to successor #1.
2732 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
2733 if (Succ0TI->getNumSuccessors() == 1 &&
2734 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
2735 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
2736 return SimplifyCFG(BB) | true;
2738 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2739 // If Successor #0 has multiple preds, we may be able to conditionally
2740 // execute Successor #1 if it branches to successor #0.
2741 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
2742 if (Succ1TI->getNumSuccessors() == 1 &&
2743 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
2744 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
2745 return SimplifyCFG(BB) | true;
2748 // If this is a branch on a phi node in the current block, thread control
2749 // through this block if any PHI node entries are constants.
2750 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
2751 if (PN->getParent() == BI->getParent())
2752 if (FoldCondBranchOnPHI(BI, TD))
2753 return SimplifyCFG(BB) | true;
2755 // If this basic block is ONLY a compare and a branch, and if a predecessor
2756 // branches to us and one of our successors, fold the comparison into the
2757 // predecessor and use logical operations to pick the right destination.
2758 if (FoldBranchToCommonDest(BI))
2759 return SimplifyCFG(BB) | true;
2761 // Scan predecessor blocks for conditional branches.
2762 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2763 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2764 if (PBI != BI && PBI->isConditional())
2765 if (SimplifyCondBranchToCondBranch(PBI, BI))
2766 return SimplifyCFG(BB) | true;
2771 /// Check if passing a value to an instruction will cause undefined behavior.
2772 static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
2773 Constant *C = dyn_cast<Constant>(V);
2777 if (!I->hasOneUse()) // Only look at single-use instructions, for compile time
2780 if (C->isNullValue()) {
2781 Instruction *Use = I->use_back();
2783 // Now make sure that there are no instructions in between that can alter
2784 // control flow (eg. calls)
2785 for (BasicBlock::iterator i = ++BasicBlock::iterator(I); &*i != Use; ++i)
2786 if (i == I->getParent()->end() || i->mayHaveSideEffects())
2789 // Look through GEPs. A load from a GEP derived from NULL is still undefined
2790 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))
2791 if (GEP->getPointerOperand() == I)
2792 return passingValueIsAlwaysUndefined(V, GEP);
2794 // Look through bitcasts.
2795 if (BitCastInst *BC = dyn_cast<BitCastInst>(Use))
2796 return passingValueIsAlwaysUndefined(V, BC);
2798 // Load from null is undefined.
2799 if (LoadInst *LI = dyn_cast<LoadInst>(Use))
2800 return LI->getPointerAddressSpace() == 0;
2802 // Store to null is undefined.
2803 if (StoreInst *SI = dyn_cast<StoreInst>(Use))
2804 return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I;
2809 /// If BB has an incoming value that will always trigger undefined behavior
2810 /// (eg. null pointer dereference), remove the branch leading here.
2811 static bool removeUndefIntroducingPredecessor(BasicBlock *BB) {
2812 for (BasicBlock::iterator i = BB->begin();
2813 PHINode *PHI = dyn_cast<PHINode>(i); ++i)
2814 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
2815 if (passingValueIsAlwaysUndefined(PHI->getIncomingValue(i), PHI)) {
2816 TerminatorInst *T = PHI->getIncomingBlock(i)->getTerminator();
2817 IRBuilder<> Builder(T);
2818 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
2819 BB->removePredecessor(PHI->getIncomingBlock(i));
2820 // Turn uncoditional branches into unreachables and remove the dead
2821 // destination from conditional branches.
2822 if (BI->isUnconditional())
2823 Builder.CreateUnreachable();
2825 Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1) :
2826 BI->getSuccessor(0));
2827 BI->eraseFromParent();
2830 // TODO: SwitchInst.
2836 bool SimplifyCFGOpt::run(BasicBlock *BB) {
2837 bool Changed = false;
2839 assert(BB && BB->getParent() && "Block not embedded in function!");
2840 assert(BB->getTerminator() && "Degenerate basic block encountered!");
2842 // Remove basic blocks that have no predecessors (except the entry block)...
2843 // or that just have themself as a predecessor. These are unreachable.
2844 if ((pred_begin(BB) == pred_end(BB) &&
2845 BB != &BB->getParent()->getEntryBlock()) ||
2846 BB->getSinglePredecessor() == BB) {
2847 DEBUG(dbgs() << "Removing BB: \n" << *BB);
2848 DeleteDeadBlock(BB);
2852 // Check to see if we can constant propagate this terminator instruction
2854 Changed |= ConstantFoldTerminator(BB, true);
2856 // Check for and eliminate duplicate PHI nodes in this block.
2857 Changed |= EliminateDuplicatePHINodes(BB);
2859 // Check for and remove branches that will always cause undefined behavior.
2860 Changed |= removeUndefIntroducingPredecessor(BB);
2862 // Merge basic blocks into their predecessor if there is only one distinct
2863 // pred, and if there is only one distinct successor of the predecessor, and
2864 // if there are no PHI nodes.
2866 if (MergeBlockIntoPredecessor(BB))
2869 IRBuilder<> Builder(BB);
2871 // If there is a trivial two-entry PHI node in this basic block, and we can
2872 // eliminate it, do so now.
2873 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
2874 if (PN->getNumIncomingValues() == 2)
2875 Changed |= FoldTwoEntryPHINode(PN, TD);
2877 Builder.SetInsertPoint(BB->getTerminator());
2878 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
2879 if (BI->isUnconditional()) {
2880 if (SimplifyUncondBranch(BI, Builder)) return true;
2882 if (SimplifyCondBranch(BI, Builder)) return true;
2884 } else if (ResumeInst *RI = dyn_cast<ResumeInst>(BB->getTerminator())) {
2885 if (SimplifyResume(RI, Builder)) return true;
2886 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
2887 if (SimplifyReturn(RI, Builder)) return true;
2888 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
2889 if (SimplifySwitch(SI, Builder)) return true;
2890 } else if (UnreachableInst *UI =
2891 dyn_cast<UnreachableInst>(BB->getTerminator())) {
2892 if (SimplifyUnreachable(UI)) return true;
2893 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
2894 if (SimplifyUnwind(UI, Builder)) return true;
2895 } else if (IndirectBrInst *IBI =
2896 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
2897 if (SimplifyIndirectBr(IBI)) return true;
2903 /// SimplifyCFG - This function is used to do simplification of a CFG. For
2904 /// example, it adjusts branches to branches to eliminate the extra hop, it
2905 /// eliminates unreachable basic blocks, and does other "peephole" optimization
2906 /// of the CFG. It returns true if a modification was made.
2908 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
2909 return SimplifyCFGOpt(TD).run(BB);