1 //===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Peephole optimize the CFG.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "simplifycfg"
15 #include "llvm/Transforms/Utils/Local.h"
16 #include "llvm/Constants.h"
17 #include "llvm/Instructions.h"
18 #include "llvm/IntrinsicInst.h"
19 #include "llvm/Type.h"
20 #include "llvm/DerivedTypes.h"
21 #include "llvm/GlobalVariable.h"
22 #include "llvm/Analysis/InstructionSimplify.h"
23 #include "llvm/Target/TargetData.h"
24 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
25 #include "llvm/ADT/DenseMap.h"
26 #include "llvm/ADT/SmallVector.h"
27 #include "llvm/ADT/SmallPtrSet.h"
28 #include "llvm/ADT/Statistic.h"
29 #include "llvm/ADT/STLExtras.h"
30 #include "llvm/Support/CFG.h"
31 #include "llvm/Support/CommandLine.h"
32 #include "llvm/Support/ConstantRange.h"
33 #include "llvm/Support/Debug.h"
34 #include "llvm/Support/raw_ostream.h"
41 DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false),
42 cl::desc("Duplicate return instructions into unconditional branches"));
44 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
47 class SimplifyCFGOpt {
48 const TargetData *const TD;
50 Value *isValueEqualityComparison(TerminatorInst *TI);
51 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
52 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases);
53 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
55 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI);
57 bool SimplifyReturn(ReturnInst *RI);
58 bool SimplifyUnwind(UnwindInst *UI);
59 bool SimplifyUnreachable(UnreachableInst *UI);
60 bool SimplifySwitch(SwitchInst *SI);
61 bool SimplifyIndirectBr(IndirectBrInst *IBI);
62 bool SimplifyUncondBranch(BranchInst *BI);
63 bool SimplifyCondBranch(BranchInst *BI);
66 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
67 bool run(BasicBlock *BB);
71 /// SafeToMergeTerminators - Return true if it is safe to merge these two
72 /// terminator instructions together.
74 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
75 if (SI1 == SI2) return false; // Can't merge with self!
77 // It is not safe to merge these two switch instructions if they have a common
78 // successor, and if that successor has a PHI node, and if *that* PHI node has
79 // conflicting incoming values from the two switch blocks.
80 BasicBlock *SI1BB = SI1->getParent();
81 BasicBlock *SI2BB = SI2->getParent();
82 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
84 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
85 if (SI1Succs.count(*I))
86 for (BasicBlock::iterator BBI = (*I)->begin();
87 isa<PHINode>(BBI); ++BBI) {
88 PHINode *PN = cast<PHINode>(BBI);
89 if (PN->getIncomingValueForBlock(SI1BB) !=
90 PN->getIncomingValueForBlock(SI2BB))
97 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
98 /// now be entries in it from the 'NewPred' block. The values that will be
99 /// flowing into the PHI nodes will be the same as those coming in from
100 /// ExistPred, an existing predecessor of Succ.
101 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
102 BasicBlock *ExistPred) {
103 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
106 for (BasicBlock::iterator I = Succ->begin();
107 (PN = dyn_cast<PHINode>(I)); ++I)
108 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
112 /// GetIfCondition - Given a basic block (BB) with two predecessors (and at
113 /// least one PHI node in it), check to see if the merge at this block is due
114 /// to an "if condition". If so, return the boolean condition that determines
115 /// which entry into BB will be taken. Also, return by references the block
116 /// that will be entered from if the condition is true, and the block that will
117 /// be entered if the condition is false.
119 /// This does no checking to see if the true/false blocks have large or unsavory
120 /// instructions in them.
121 static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
122 BasicBlock *&IfFalse) {
123 PHINode *SomePHI = cast<PHINode>(BB->begin());
124 assert(SomePHI->getNumIncomingValues() == 2 &&
125 "Function can only handle blocks with 2 predecessors!");
126 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
127 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
129 // We can only handle branches. Other control flow will be lowered to
130 // branches if possible anyway.
131 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
132 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
133 if (Pred1Br == 0 || Pred2Br == 0)
136 // Eliminate code duplication by ensuring that Pred1Br is conditional if
138 if (Pred2Br->isConditional()) {
139 // If both branches are conditional, we don't have an "if statement". In
140 // reality, we could transform this case, but since the condition will be
141 // required anyway, we stand no chance of eliminating it, so the xform is
142 // probably not profitable.
143 if (Pred1Br->isConditional())
146 std::swap(Pred1, Pred2);
147 std::swap(Pred1Br, Pred2Br);
150 if (Pred1Br->isConditional()) {
151 // The only thing we have to watch out for here is to make sure that Pred2
152 // doesn't have incoming edges from other blocks. If it does, the condition
153 // doesn't dominate BB.
154 if (Pred2->getSinglePredecessor() == 0)
157 // If we found a conditional branch predecessor, make sure that it branches
158 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
159 if (Pred1Br->getSuccessor(0) == BB &&
160 Pred1Br->getSuccessor(1) == Pred2) {
163 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
164 Pred1Br->getSuccessor(1) == BB) {
168 // We know that one arm of the conditional goes to BB, so the other must
169 // go somewhere unrelated, and this must not be an "if statement".
173 return Pred1Br->getCondition();
176 // Ok, if we got here, both predecessors end with an unconditional branch to
177 // BB. Don't panic! If both blocks only have a single (identical)
178 // predecessor, and THAT is a conditional branch, then we're all ok!
179 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
180 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
183 // Otherwise, if this is a conditional branch, then we can use it!
184 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
185 if (BI == 0) return 0;
187 assert(BI->isConditional() && "Two successors but not conditional?");
188 if (BI->getSuccessor(0) == Pred1) {
195 return BI->getCondition();
198 /// DominatesMergePoint - If we have a merge point of an "if condition" as
199 /// accepted above, return true if the specified value dominates the block. We
200 /// don't handle the true generality of domination here, just a special case
201 /// which works well enough for us.
203 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
204 /// see if V (which must be an instruction) is cheap to compute and is
205 /// non-trapping. If both are true, the instruction is inserted into the set
206 /// and true is returned.
207 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
208 SmallPtrSet<Instruction*, 4> *AggressiveInsts) {
209 Instruction *I = dyn_cast<Instruction>(V);
211 // Non-instructions all dominate instructions, but not all constantexprs
212 // can be executed unconditionally.
213 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
218 BasicBlock *PBB = I->getParent();
220 // We don't want to allow weird loops that might have the "if condition" in
221 // the bottom of this block.
222 if (PBB == BB) return false;
224 // If this instruction is defined in a block that contains an unconditional
225 // branch to BB, then it must be in the 'conditional' part of the "if
226 // statement". If not, it definitely dominates the region.
227 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
228 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB)
231 // If we aren't allowing aggressive promotion anymore, then don't consider
232 // instructions in the 'if region'.
233 if (AggressiveInsts == 0) return false;
235 // Okay, it looks like the instruction IS in the "condition". Check to
236 // see if it's a cheap instruction to unconditionally compute, and if it
237 // only uses stuff defined outside of the condition. If so, hoist it out.
238 if (!I->isSafeToSpeculativelyExecute())
241 switch (I->getOpcode()) {
242 default: return false; // Cannot hoist this out safely.
243 case Instruction::Load:
244 // We have to check to make sure there are no instructions before the
245 // load in its basic block, as we are going to hoist the load out to its
247 if (PBB->getFirstNonPHIOrDbg() != I)
250 case Instruction::GetElementPtr:
251 // GEPs are cheap if all indices are constant.
252 if (!cast<GetElementPtrInst>(I)->hasAllConstantIndices())
255 case Instruction::Add:
256 case Instruction::Sub:
257 case Instruction::And:
258 case Instruction::Or:
259 case Instruction::Xor:
260 case Instruction::Shl:
261 case Instruction::LShr:
262 case Instruction::AShr:
263 case Instruction::ICmp:
264 break; // These are all cheap and non-trapping instructions.
267 // Okay, we can only really hoist these out if their operands are not
268 // defined in the conditional region.
269 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
270 if (!DominatesMergePoint(*i, BB, 0))
272 // Okay, it's safe to do this! Remember this instruction.
273 AggressiveInsts->insert(I);
277 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
278 /// and PointerNullValue. Return NULL if value is not a constant int.
279 static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
280 // Normal constant int.
281 ConstantInt *CI = dyn_cast<ConstantInt>(V);
282 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
285 // This is some kind of pointer constant. Turn it into a pointer-sized
286 // ConstantInt if possible.
287 const IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
289 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
290 if (isa<ConstantPointerNull>(V))
291 return ConstantInt::get(PtrTy, 0);
293 // IntToPtr const int.
294 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
295 if (CE->getOpcode() == Instruction::IntToPtr)
296 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
297 // The constant is very likely to have the right type already.
298 if (CI->getType() == PtrTy)
301 return cast<ConstantInt>
302 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
307 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
308 /// collection of icmp eq/ne instructions that compare a value against a
309 /// constant, return the value being compared, and stick the constant into the
312 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
313 const TargetData *TD, bool isEQ, unsigned &UsedICmps) {
314 Instruction *I = dyn_cast<Instruction>(V);
315 if (I == 0) return 0;
317 // If this is an icmp against a constant, handle this as one of the cases.
318 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
319 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
320 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
323 return I->getOperand(0);
326 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
329 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
331 // If this is an and/!= check then we want to optimize "x ugt 2" into
334 Span = Span.inverse();
336 // If there are a ton of values, we don't want to make a ginormous switch.
337 if (Span.getSetSize().ugt(8) || Span.isEmptySet() ||
338 // We don't handle wrapped sets yet.
342 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
343 Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
345 return I->getOperand(0);
350 // Otherwise, we can only handle an | or &, depending on isEQ.
351 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
354 unsigned NumValsBeforeLHS = Vals.size();
355 unsigned UsedICmpsBeforeLHS = UsedICmps;
356 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
358 unsigned NumVals = Vals.size();
359 unsigned UsedICmpsBeforeRHS = UsedICmps;
360 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
364 Vals.resize(NumVals);
365 UsedICmps = UsedICmpsBeforeRHS;
368 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
369 // set it and return success.
370 if (Extra == 0 || Extra == I->getOperand(1)) {
371 Extra = I->getOperand(1);
375 Vals.resize(NumValsBeforeLHS);
376 UsedICmps = UsedICmpsBeforeLHS;
380 // If the LHS can't be folded in, but Extra is available and RHS can, try to
382 if (Extra == 0 || Extra == I->getOperand(0)) {
383 Value *OldExtra = Extra;
384 Extra = I->getOperand(0);
385 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
388 assert(Vals.size() == NumValsBeforeLHS);
395 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
396 Instruction* Cond = 0;
397 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
398 Cond = dyn_cast<Instruction>(SI->getCondition());
399 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
400 if (BI->isConditional())
401 Cond = dyn_cast<Instruction>(BI->getCondition());
402 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
403 Cond = dyn_cast<Instruction>(IBI->getAddress());
406 TI->eraseFromParent();
407 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
410 /// isValueEqualityComparison - Return true if the specified terminator checks
411 /// to see if a value is equal to constant integer value.
412 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
414 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
415 // Do not permit merging of large switch instructions into their
416 // predecessors unless there is only one predecessor.
417 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
418 pred_end(SI->getParent())) <= 128)
419 CV = SI->getCondition();
420 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
421 if (BI->isConditional() && BI->getCondition()->hasOneUse())
422 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
423 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
424 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
425 GetConstantInt(ICI->getOperand(1), TD))
426 CV = ICI->getOperand(0);
428 // Unwrap any lossless ptrtoint cast.
429 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
430 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
431 CV = PTII->getOperand(0);
435 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
436 /// decode all of the 'cases' that it represents and return the 'default' block.
437 BasicBlock *SimplifyCFGOpt::
438 GetValueEqualityComparisonCases(TerminatorInst *TI,
439 std::vector<std::pair<ConstantInt*,
440 BasicBlock*> > &Cases) {
441 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
442 Cases.reserve(SI->getNumCases());
443 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
444 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
445 return SI->getDefaultDest();
448 BranchInst *BI = cast<BranchInst>(TI);
449 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
450 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD),
451 BI->getSuccessor(ICI->getPredicate() ==
452 ICmpInst::ICMP_NE)));
453 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
457 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
458 /// in the list that match the specified block.
459 static void EliminateBlockCases(BasicBlock *BB,
460 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
461 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
462 if (Cases[i].second == BB) {
463 Cases.erase(Cases.begin()+i);
468 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
471 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
472 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
473 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
475 // Make V1 be smaller than V2.
476 if (V1->size() > V2->size())
479 if (V1->size() == 0) return false;
480 if (V1->size() == 1) {
482 ConstantInt *TheVal = (*V1)[0].first;
483 for (unsigned i = 0, e = V2->size(); i != e; ++i)
484 if (TheVal == (*V2)[i].first)
488 // Otherwise, just sort both lists and compare element by element.
489 array_pod_sort(V1->begin(), V1->end());
490 array_pod_sort(V2->begin(), V2->end());
491 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
492 while (i1 != e1 && i2 != e2) {
493 if ((*V1)[i1].first == (*V2)[i2].first)
495 if ((*V1)[i1].first < (*V2)[i2].first)
503 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
504 /// terminator instruction and its block is known to only have a single
505 /// predecessor block, check to see if that predecessor is also a value
506 /// comparison with the same value, and if that comparison determines the
507 /// outcome of this comparison. If so, simplify TI. This does a very limited
508 /// form of jump threading.
509 bool SimplifyCFGOpt::
510 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
512 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
513 if (!PredVal) return false; // Not a value comparison in predecessor.
515 Value *ThisVal = isValueEqualityComparison(TI);
516 assert(ThisVal && "This isn't a value comparison!!");
517 if (ThisVal != PredVal) return false; // Different predicates.
519 // Find out information about when control will move from Pred to TI's block.
520 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
521 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
523 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
525 // Find information about how control leaves this block.
526 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
527 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
528 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
530 // If TI's block is the default block from Pred's comparison, potentially
531 // simplify TI based on this knowledge.
532 if (PredDef == TI->getParent()) {
533 // If we are here, we know that the value is none of those cases listed in
534 // PredCases. If there are any cases in ThisCases that are in PredCases, we
536 if (!ValuesOverlap(PredCases, ThisCases))
539 if (isa<BranchInst>(TI)) {
540 // Okay, one of the successors of this condbr is dead. Convert it to a
542 assert(ThisCases.size() == 1 && "Branch can only have one case!");
543 // Insert the new branch.
544 Instruction *NI = BranchInst::Create(ThisDef, TI);
547 // Remove PHI node entries for the dead edge.
548 ThisCases[0].second->removePredecessor(TI->getParent());
550 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
551 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
553 EraseTerminatorInstAndDCECond(TI);
557 SwitchInst *SI = cast<SwitchInst>(TI);
558 // Okay, TI has cases that are statically dead, prune them away.
559 SmallPtrSet<Constant*, 16> DeadCases;
560 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
561 DeadCases.insert(PredCases[i].first);
563 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
564 << "Through successor TI: " << *TI);
566 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
567 if (DeadCases.count(SI->getCaseValue(i))) {
568 SI->getSuccessor(i)->removePredecessor(TI->getParent());
572 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
576 // Otherwise, TI's block must correspond to some matched value. Find out
577 // which value (or set of values) this is.
578 ConstantInt *TIV = 0;
579 BasicBlock *TIBB = TI->getParent();
580 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
581 if (PredCases[i].second == TIBB) {
583 return false; // Cannot handle multiple values coming to this block.
584 TIV = PredCases[i].first;
586 assert(TIV && "No edge from pred to succ?");
588 // Okay, we found the one constant that our value can be if we get into TI's
589 // BB. Find out which successor will unconditionally be branched to.
590 BasicBlock *TheRealDest = 0;
591 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
592 if (ThisCases[i].first == TIV) {
593 TheRealDest = ThisCases[i].second;
597 // If not handled by any explicit cases, it is handled by the default case.
598 if (TheRealDest == 0) TheRealDest = ThisDef;
600 // Remove PHI node entries for dead edges.
601 BasicBlock *CheckEdge = TheRealDest;
602 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
603 if (*SI != CheckEdge)
604 (*SI)->removePredecessor(TIBB);
608 // Insert the new branch.
609 Instruction *NI = BranchInst::Create(TheRealDest, TI);
612 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
613 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
615 EraseTerminatorInstAndDCECond(TI);
620 /// ConstantIntOrdering - This class implements a stable ordering of constant
621 /// integers that does not depend on their address. This is important for
622 /// applications that sort ConstantInt's to ensure uniqueness.
623 struct ConstantIntOrdering {
624 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
625 return LHS->getValue().ult(RHS->getValue());
630 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
631 const ConstantInt *LHS = *(const ConstantInt**)P1;
632 const ConstantInt *RHS = *(const ConstantInt**)P2;
633 if (LHS->getValue().ult(RHS->getValue()))
635 if (LHS->getValue() == RHS->getValue())
640 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
641 /// equality comparison instruction (either a switch or a branch on "X == c").
642 /// See if any of the predecessors of the terminator block are value comparisons
643 /// on the same value. If so, and if safe to do so, fold them together.
644 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
645 BasicBlock *BB = TI->getParent();
646 Value *CV = isValueEqualityComparison(TI); // CondVal
647 assert(CV && "Not a comparison?");
648 bool Changed = false;
650 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
651 while (!Preds.empty()) {
652 BasicBlock *Pred = Preds.pop_back_val();
654 // See if the predecessor is a comparison with the same value.
655 TerminatorInst *PTI = Pred->getTerminator();
656 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
658 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
659 // Figure out which 'cases' to copy from SI to PSI.
660 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
661 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
663 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
664 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
666 // Based on whether the default edge from PTI goes to BB or not, fill in
667 // PredCases and PredDefault with the new switch cases we would like to
669 SmallVector<BasicBlock*, 8> NewSuccessors;
671 if (PredDefault == BB) {
672 // If this is the default destination from PTI, only the edges in TI
673 // that don't occur in PTI, or that branch to BB will be activated.
674 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
675 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
676 if (PredCases[i].second != BB)
677 PTIHandled.insert(PredCases[i].first);
679 // The default destination is BB, we don't need explicit targets.
680 std::swap(PredCases[i], PredCases.back());
681 PredCases.pop_back();
685 // Reconstruct the new switch statement we will be building.
686 if (PredDefault != BBDefault) {
687 PredDefault->removePredecessor(Pred);
688 PredDefault = BBDefault;
689 NewSuccessors.push_back(BBDefault);
691 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
692 if (!PTIHandled.count(BBCases[i].first) &&
693 BBCases[i].second != BBDefault) {
694 PredCases.push_back(BBCases[i]);
695 NewSuccessors.push_back(BBCases[i].second);
699 // If this is not the default destination from PSI, only the edges
700 // in SI that occur in PSI with a destination of BB will be
702 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
703 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
704 if (PredCases[i].second == BB) {
705 PTIHandled.insert(PredCases[i].first);
706 std::swap(PredCases[i], PredCases.back());
707 PredCases.pop_back();
711 // Okay, now we know which constants were sent to BB from the
712 // predecessor. Figure out where they will all go now.
713 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
714 if (PTIHandled.count(BBCases[i].first)) {
715 // If this is one we are capable of getting...
716 PredCases.push_back(BBCases[i]);
717 NewSuccessors.push_back(BBCases[i].second);
718 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
721 // If there are any constants vectored to BB that TI doesn't handle,
722 // they must go to the default destination of TI.
723 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
725 E = PTIHandled.end(); I != E; ++I) {
726 PredCases.push_back(std::make_pair(*I, BBDefault));
727 NewSuccessors.push_back(BBDefault);
731 // Okay, at this point, we know which new successor Pred will get. Make
732 // sure we update the number of entries in the PHI nodes for these
734 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
735 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
737 // Convert pointer to int before we switch.
738 if (CV->getType()->isPointerTy()) {
739 assert(TD && "Cannot switch on pointer without TargetData");
740 CV = new PtrToIntInst(CV, TD->getIntPtrType(CV->getContext()),
744 // Now that the successors are updated, create the new Switch instruction.
745 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
746 PredCases.size(), PTI);
747 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
748 NewSI->addCase(PredCases[i].first, PredCases[i].second);
750 EraseTerminatorInstAndDCECond(PTI);
752 // Okay, last check. If BB is still a successor of PSI, then we must
753 // have an infinite loop case. If so, add an infinitely looping block
754 // to handle the case to preserve the behavior of the code.
755 BasicBlock *InfLoopBlock = 0;
756 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
757 if (NewSI->getSuccessor(i) == BB) {
758 if (InfLoopBlock == 0) {
759 // Insert it at the end of the function, because it's either code,
760 // or it won't matter if it's hot. :)
761 InfLoopBlock = BasicBlock::Create(BB->getContext(),
762 "infloop", BB->getParent());
763 BranchInst::Create(InfLoopBlock, InfLoopBlock);
765 NewSI->setSuccessor(i, InfLoopBlock);
774 // isSafeToHoistInvoke - If we would need to insert a select that uses the
775 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
776 // would need to do this), we can't hoist the invoke, as there is nowhere
777 // to put the select in this case.
778 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
779 Instruction *I1, Instruction *I2) {
780 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
782 for (BasicBlock::iterator BBI = SI->begin();
783 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
784 Value *BB1V = PN->getIncomingValueForBlock(BB1);
785 Value *BB2V = PN->getIncomingValueForBlock(BB2);
786 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
794 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
795 /// BB2, hoist any common code in the two blocks up into the branch block. The
796 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
797 static bool HoistThenElseCodeToIf(BranchInst *BI) {
798 // This does very trivial matching, with limited scanning, to find identical
799 // instructions in the two blocks. In particular, we don't want to get into
800 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
801 // such, we currently just scan for obviously identical instructions in an
803 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
804 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
806 BasicBlock::iterator BB1_Itr = BB1->begin();
807 BasicBlock::iterator BB2_Itr = BB2->begin();
809 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
810 // Skip debug info if it is not identical.
811 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
812 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
813 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
814 while (isa<DbgInfoIntrinsic>(I1))
816 while (isa<DbgInfoIntrinsic>(I2))
819 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
820 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
823 // If we get here, we can hoist at least one instruction.
824 BasicBlock *BIParent = BI->getParent();
827 // If we are hoisting the terminator instruction, don't move one (making a
828 // broken BB), instead clone it, and remove BI.
829 if (isa<TerminatorInst>(I1))
830 goto HoistTerminator;
832 // For a normal instruction, we just move one to right before the branch,
833 // then replace all uses of the other with the first. Finally, we remove
834 // the now redundant second instruction.
835 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
836 if (!I2->use_empty())
837 I2->replaceAllUsesWith(I1);
838 I1->intersectOptionalDataWith(I2);
839 I2->eraseFromParent();
843 // Skip debug info if it is not identical.
844 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
845 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
846 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
847 while (isa<DbgInfoIntrinsic>(I1))
849 while (isa<DbgInfoIntrinsic>(I2))
852 } while (I1->isIdenticalToWhenDefined(I2));
857 // It may not be possible to hoist an invoke.
858 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
861 // Okay, it is safe to hoist the terminator.
862 Instruction *NT = I1->clone();
863 BIParent->getInstList().insert(BI, NT);
864 if (!NT->getType()->isVoidTy()) {
865 I1->replaceAllUsesWith(NT);
866 I2->replaceAllUsesWith(NT);
870 // Hoisting one of the terminators from our successor is a great thing.
871 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
872 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
873 // nodes, so we insert select instruction to compute the final result.
874 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
875 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
877 for (BasicBlock::iterator BBI = SI->begin();
878 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
879 Value *BB1V = PN->getIncomingValueForBlock(BB1);
880 Value *BB2V = PN->getIncomingValueForBlock(BB2);
881 if (BB1V == BB2V) continue;
883 // These values do not agree. Insert a select instruction before NT
884 // that determines the right value.
885 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
887 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
888 BB1V->getName()+"."+BB2V->getName(), NT);
889 // Make the PHI node use the select for all incoming values for BB1/BB2
890 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
891 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
892 PN->setIncomingValue(i, SI);
896 // Update any PHI nodes in our new successors.
897 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
898 AddPredecessorToBlock(*SI, BIParent, BB1);
900 EraseTerminatorInstAndDCECond(BI);
904 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
905 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
906 /// (for now, restricted to a single instruction that's side effect free) from
907 /// the BB1 into the branch block to speculatively execute it.
908 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
909 // Only speculatively execution a single instruction (not counting the
910 // terminator) for now.
911 Instruction *HInst = NULL;
912 Instruction *Term = BB1->getTerminator();
913 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
915 Instruction *I = BBI;
917 if (isa<DbgInfoIntrinsic>(I)) continue;
918 if (I == Term) break;
927 // Be conservative for now. FP select instruction can often be expensive.
928 Value *BrCond = BI->getCondition();
929 if (isa<FCmpInst>(BrCond))
932 // If BB1 is actually on the false edge of the conditional branch, remember
933 // to swap the select operands later.
935 if (BB1 != BI->getSuccessor(0)) {
936 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
943 // br i1 %t1, label %BB1, label %BB2
952 // %t3 = select i1 %t1, %t2, %t3
953 switch (HInst->getOpcode()) {
954 default: return false; // Not safe / profitable to hoist.
955 case Instruction::Add:
956 case Instruction::Sub:
957 // Not worth doing for vector ops.
958 if (HInst->getType()->isVectorTy())
961 case Instruction::And:
962 case Instruction::Or:
963 case Instruction::Xor:
964 case Instruction::Shl:
965 case Instruction::LShr:
966 case Instruction::AShr:
967 // Don't mess with vector operations.
968 if (HInst->getType()->isVectorTy())
970 break; // These are all cheap and non-trapping instructions.
973 // If the instruction is obviously dead, don't try to predicate it.
974 if (HInst->use_empty()) {
975 HInst->eraseFromParent();
979 // Can we speculatively execute the instruction? And what is the value
980 // if the condition is false? Consider the phi uses, if the incoming value
981 // from the "if" block are all the same V, then V is the value of the
982 // select if the condition is false.
983 BasicBlock *BIParent = BI->getParent();
984 SmallVector<PHINode*, 4> PHIUses;
985 Value *FalseV = NULL;
987 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
988 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
990 // Ignore any user that is not a PHI node in BB2. These can only occur in
991 // unreachable blocks, because they would not be dominated by the instr.
992 PHINode *PN = dyn_cast<PHINode>(*UI);
993 if (!PN || PN->getParent() != BB2)
995 PHIUses.push_back(PN);
997 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1000 else if (FalseV != PHIV)
1001 return false; // Inconsistent value when condition is false.
1004 assert(FalseV && "Must have at least one user, and it must be a PHI");
1006 // Do not hoist the instruction if any of its operands are defined but not
1007 // used in this BB. The transformation will prevent the operand from
1008 // being sunk into the use block.
1009 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1011 Instruction *OpI = dyn_cast<Instruction>(*i);
1012 if (OpI && OpI->getParent() == BIParent &&
1013 !OpI->isUsedInBasicBlock(BIParent))
1017 // If we get here, we can hoist the instruction. Try to place it
1018 // before the icmp instruction preceding the conditional branch.
1019 BasicBlock::iterator InsertPos = BI;
1020 if (InsertPos != BIParent->begin())
1022 // Skip debug info between condition and branch.
1023 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
1025 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
1026 SmallPtrSet<Instruction *, 4> BB1Insns;
1027 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
1028 BB1I != BB1E; ++BB1I)
1029 BB1Insns.insert(BB1I);
1030 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
1032 Instruction *Use = cast<Instruction>(*UI);
1033 if (!BB1Insns.count(Use)) continue;
1035 // If BrCond uses the instruction that place it just before
1036 // branch instruction.
1042 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
1044 // Create a select whose true value is the speculatively executed value and
1045 // false value is the previously determined FalseV.
1048 SI = SelectInst::Create(BrCond, FalseV, HInst,
1049 FalseV->getName() + "." + HInst->getName(), BI);
1051 SI = SelectInst::Create(BrCond, HInst, FalseV,
1052 HInst->getName() + "." + FalseV->getName(), BI);
1054 // Make the PHI node use the select for all incoming values for "then" and
1056 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1057 PHINode *PN = PHIUses[i];
1058 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1059 if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent)
1060 PN->setIncomingValue(j, SI);
1067 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1068 /// across this block.
1069 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1070 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1073 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1074 if (isa<DbgInfoIntrinsic>(BBI))
1076 if (Size > 10) return false; // Don't clone large BB's.
1079 // We can only support instructions that do not define values that are
1080 // live outside of the current basic block.
1081 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1083 Instruction *U = cast<Instruction>(*UI);
1084 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1087 // Looks ok, continue checking.
1093 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1094 /// that is defined in the same block as the branch and if any PHI entries are
1095 /// constants, thread edges corresponding to that entry to be branches to their
1096 /// ultimate destination.
1097 static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
1098 BasicBlock *BB = BI->getParent();
1099 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1100 // NOTE: we currently cannot transform this case if the PHI node is used
1101 // outside of the block.
1102 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1105 // Degenerate case of a single entry PHI.
1106 if (PN->getNumIncomingValues() == 1) {
1107 FoldSingleEntryPHINodes(PN->getParent());
1111 // Now we know that this block has multiple preds and two succs.
1112 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1114 // Okay, this is a simple enough basic block. See if any phi values are
1116 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1117 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1118 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1120 // Okay, we now know that all edges from PredBB should be revectored to
1121 // branch to RealDest.
1122 BasicBlock *PredBB = PN->getIncomingBlock(i);
1123 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1125 if (RealDest == BB) continue; // Skip self loops.
1127 // The dest block might have PHI nodes, other predecessors and other
1128 // difficult cases. Instead of being smart about this, just insert a new
1129 // block that jumps to the destination block, effectively splitting
1130 // the edge we are about to create.
1131 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1132 RealDest->getName()+".critedge",
1133 RealDest->getParent(), RealDest);
1134 BranchInst::Create(RealDest, EdgeBB);
1136 // Update PHI nodes.
1137 AddPredecessorToBlock(RealDest, EdgeBB, BB);
1139 // BB may have instructions that are being threaded over. Clone these
1140 // instructions into EdgeBB. We know that there will be no uses of the
1141 // cloned instructions outside of EdgeBB.
1142 BasicBlock::iterator InsertPt = EdgeBB->begin();
1143 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1144 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1145 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1146 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1149 // Clone the instruction.
1150 Instruction *N = BBI->clone();
1151 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1153 // Update operands due to translation.
1154 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1156 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1157 if (PI != TranslateMap.end())
1161 // Check for trivial simplification.
1162 if (Value *V = SimplifyInstruction(N, TD)) {
1163 TranslateMap[BBI] = V;
1164 delete N; // Instruction folded away, don't need actual inst
1166 // Insert the new instruction into its new home.
1167 EdgeBB->getInstList().insert(InsertPt, N);
1168 if (!BBI->use_empty())
1169 TranslateMap[BBI] = N;
1173 // Loop over all of the edges from PredBB to BB, changing them to branch
1174 // to EdgeBB instead.
1175 TerminatorInst *PredBBTI = PredBB->getTerminator();
1176 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1177 if (PredBBTI->getSuccessor(i) == BB) {
1178 BB->removePredecessor(PredBB);
1179 PredBBTI->setSuccessor(i, EdgeBB);
1182 // Recurse, simplifying any other constants.
1183 return FoldCondBranchOnPHI(BI, TD) | true;
1189 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1190 /// PHI node, see if we can eliminate it.
1191 static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
1192 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1193 // statement", which has a very simple dominance structure. Basically, we
1194 // are trying to find the condition that is being branched on, which
1195 // subsequently causes this merge to happen. We really want control
1196 // dependence information for this check, but simplifycfg can't keep it up
1197 // to date, and this catches most of the cases we care about anyway.
1198 BasicBlock *BB = PN->getParent();
1199 BasicBlock *IfTrue, *IfFalse;
1200 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1202 // Don't bother if the branch will be constant folded trivially.
1203 isa<ConstantInt>(IfCond))
1206 // Okay, we found that we can merge this two-entry phi node into a select.
1207 // Doing so would require us to fold *all* two entry phi nodes in this block.
1208 // At some point this becomes non-profitable (particularly if the target
1209 // doesn't support cmov's). Only do this transformation if there are two or
1210 // fewer PHI nodes in this block.
1211 unsigned NumPhis = 0;
1212 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1216 // Loop over the PHI's seeing if we can promote them all to select
1217 // instructions. While we are at it, keep track of the instructions
1218 // that need to be moved to the dominating block.
1219 SmallPtrSet<Instruction*, 4> AggressiveInsts;
1221 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1222 PHINode *PN = cast<PHINode>(II++);
1223 if (Value *V = SimplifyInstruction(PN, TD)) {
1224 PN->replaceAllUsesWith(V);
1225 PN->eraseFromParent();
1229 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts) ||
1230 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts))
1234 // If we folded the the first phi, PN dangles at this point. Refresh it. If
1235 // we ran out of PHIs then we simplified them all.
1236 PN = dyn_cast<PHINode>(BB->begin());
1237 if (PN == 0) return true;
1239 // Don't fold i1 branches on PHIs which contain binary operators. These can
1240 // often be turned into switches and other things.
1241 if (PN->getType()->isIntegerTy(1) &&
1242 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1243 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1244 isa<BinaryOperator>(IfCond)))
1247 // If we all PHI nodes are promotable, check to make sure that all
1248 // instructions in the predecessor blocks can be promoted as well. If
1249 // not, we won't be able to get rid of the control flow, so it's not
1250 // worth promoting to select instructions.
1251 BasicBlock *DomBlock = 0;
1252 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1253 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1254 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1257 DomBlock = *pred_begin(IfBlock1);
1258 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1259 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1260 // This is not an aggressive instruction that we can promote.
1261 // Because of this, we won't be able to get rid of the control
1262 // flow, so the xform is not worth it.
1267 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1270 DomBlock = *pred_begin(IfBlock2);
1271 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1272 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1273 // This is not an aggressive instruction that we can promote.
1274 // Because of this, we won't be able to get rid of the control
1275 // flow, so the xform is not worth it.
1280 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1281 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1283 // If we can still promote the PHI nodes after this gauntlet of tests,
1284 // do all of the PHI's now.
1285 Instruction *InsertPt = DomBlock->getTerminator();
1287 // Move all 'aggressive' instructions, which are defined in the
1288 // conditional parts of the if's up to the dominating block.
1290 DomBlock->getInstList().splice(InsertPt,
1291 IfBlock1->getInstList(), IfBlock1->begin(),
1292 IfBlock1->getTerminator());
1294 DomBlock->getInstList().splice(InsertPt,
1295 IfBlock2->getInstList(), IfBlock2->begin(),
1296 IfBlock2->getTerminator());
1298 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1299 // Change the PHI node into a select instruction.
1300 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1301 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1303 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", InsertPt);
1304 PN->replaceAllUsesWith(NV);
1306 PN->eraseFromParent();
1309 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1310 // has been flattened. Change DomBlock to jump directly to our new block to
1311 // avoid other simplifycfg's kicking in on the diamond.
1312 TerminatorInst *OldTI = DomBlock->getTerminator();
1313 BranchInst::Create(BB, OldTI);
1314 OldTI->eraseFromParent();
1318 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1319 /// to two returning blocks, try to merge them together into one return,
1320 /// introducing a select if the return values disagree.
1321 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1322 assert(BI->isConditional() && "Must be a conditional branch");
1323 BasicBlock *TrueSucc = BI->getSuccessor(0);
1324 BasicBlock *FalseSucc = BI->getSuccessor(1);
1325 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1326 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1328 // Check to ensure both blocks are empty (just a return) or optionally empty
1329 // with PHI nodes. If there are other instructions, merging would cause extra
1330 // computation on one path or the other.
1331 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1333 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1336 // Okay, we found a branch that is going to two return nodes. If
1337 // there is no return value for this function, just change the
1338 // branch into a return.
1339 if (FalseRet->getNumOperands() == 0) {
1340 TrueSucc->removePredecessor(BI->getParent());
1341 FalseSucc->removePredecessor(BI->getParent());
1342 ReturnInst::Create(BI->getContext(), 0, BI);
1343 EraseTerminatorInstAndDCECond(BI);
1347 // Otherwise, figure out what the true and false return values are
1348 // so we can insert a new select instruction.
1349 Value *TrueValue = TrueRet->getReturnValue();
1350 Value *FalseValue = FalseRet->getReturnValue();
1352 // Unwrap any PHI nodes in the return blocks.
1353 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1354 if (TVPN->getParent() == TrueSucc)
1355 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1356 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1357 if (FVPN->getParent() == FalseSucc)
1358 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1360 // In order for this transformation to be safe, we must be able to
1361 // unconditionally execute both operands to the return. This is
1362 // normally the case, but we could have a potentially-trapping
1363 // constant expression that prevents this transformation from being
1365 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1368 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1372 // Okay, we collected all the mapped values and checked them for sanity, and
1373 // defined to really do this transformation. First, update the CFG.
1374 TrueSucc->removePredecessor(BI->getParent());
1375 FalseSucc->removePredecessor(BI->getParent());
1377 // Insert select instructions where needed.
1378 Value *BrCond = BI->getCondition();
1380 // Insert a select if the results differ.
1381 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1382 } else if (isa<UndefValue>(TrueValue)) {
1383 TrueValue = FalseValue;
1385 TrueValue = SelectInst::Create(BrCond, TrueValue,
1386 FalseValue, "retval", BI);
1390 Value *RI = !TrueValue ?
1391 ReturnInst::Create(BI->getContext(), BI) :
1392 ReturnInst::Create(BI->getContext(), TrueValue, BI);
1395 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1396 << "\n " << *BI << "NewRet = " << *RI
1397 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1399 EraseTerminatorInstAndDCECond(BI);
1404 /// FoldBranchToCommonDest - If this basic block is simple enough, and if a
1405 /// predecessor branches to us and one of our successors, fold the block into
1406 /// the predecessor and use logical operations to pick the right destination.
1407 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1408 BasicBlock *BB = BI->getParent();
1409 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1410 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1411 Cond->getParent() != BB || !Cond->hasOneUse())
1414 // Only allow this if the condition is a simple instruction that can be
1415 // executed unconditionally. It must be in the same block as the branch, and
1416 // must be at the front of the block.
1417 BasicBlock::iterator FrontIt = BB->front();
1419 // Ignore dbg intrinsics.
1420 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1422 // Allow a single instruction to be hoisted in addition to the compare
1423 // that feeds the branch. We later ensure that any values that _it_ uses
1424 // were also live in the predecessor, so that we don't unnecessarily create
1425 // register pressure or inhibit out-of-order execution.
1426 Instruction *BonusInst = 0;
1427 if (&*FrontIt != Cond &&
1428 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1429 FrontIt->isSafeToSpeculativelyExecute()) {
1430 BonusInst = &*FrontIt;
1433 // Ignore dbg intrinsics.
1434 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1437 // Only a single bonus inst is allowed.
1438 if (&*FrontIt != Cond)
1441 // Make sure the instruction after the condition is the cond branch.
1442 BasicBlock::iterator CondIt = Cond; ++CondIt;
1444 // Ingore dbg intrinsics.
1445 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
1450 // Cond is known to be a compare or binary operator. Check to make sure that
1451 // neither operand is a potentially-trapping constant expression.
1452 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1455 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1459 // Finally, don't infinitely unroll conditional loops.
1460 BasicBlock *TrueDest = BI->getSuccessor(0);
1461 BasicBlock *FalseDest = BI->getSuccessor(1);
1462 if (TrueDest == BB || FalseDest == BB)
1465 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1466 BasicBlock *PredBlock = *PI;
1467 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1469 // Check that we have two conditional branches. If there is a PHI node in
1470 // the common successor, verify that the same value flows in from both
1472 if (PBI == 0 || PBI->isUnconditional() || !SafeToMergeTerminators(BI, PBI))
1475 // Determine if the two branches share a common destination.
1476 Instruction::BinaryOps Opc;
1477 bool InvertPredCond = false;
1479 if (PBI->getSuccessor(0) == TrueDest)
1480 Opc = Instruction::Or;
1481 else if (PBI->getSuccessor(1) == FalseDest)
1482 Opc = Instruction::And;
1483 else if (PBI->getSuccessor(0) == FalseDest)
1484 Opc = Instruction::And, InvertPredCond = true;
1485 else if (PBI->getSuccessor(1) == TrueDest)
1486 Opc = Instruction::Or, InvertPredCond = true;
1490 // Ensure that any values used in the bonus instruction are also used
1491 // by the terminator of the predecessor. This means that those values
1492 // must already have been resolved, so we won't be inhibiting the
1493 // out-of-order core by speculating them earlier.
1495 // Collect the values used by the bonus inst
1496 SmallPtrSet<Value*, 4> UsedValues;
1497 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1498 OE = BonusInst->op_end(); OI != OE; ++OI) {
1500 if (!isa<Constant>(V))
1501 UsedValues.insert(V);
1504 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1505 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1507 // Walk up to four levels back up the use-def chain of the predecessor's
1508 // terminator to see if all those values were used. The choice of four
1509 // levels is arbitrary, to provide a compile-time-cost bound.
1510 while (!Worklist.empty()) {
1511 std::pair<Value*, unsigned> Pair = Worklist.back();
1512 Worklist.pop_back();
1514 if (Pair.second >= 4) continue;
1515 UsedValues.erase(Pair.first);
1516 if (UsedValues.empty()) break;
1518 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
1519 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1521 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1525 if (!UsedValues.empty()) return false;
1528 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1530 // If we need to invert the condition in the pred block to match, do so now.
1531 if (InvertPredCond) {
1532 Value *NewCond = PBI->getCondition();
1534 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
1535 CmpInst *CI = cast<CmpInst>(NewCond);
1536 CI->setPredicate(CI->getInversePredicate());
1538 NewCond = BinaryOperator::CreateNot(NewCond,
1539 PBI->getCondition()->getName()+".not", PBI);
1542 PBI->setCondition(NewCond);
1543 BasicBlock *OldTrue = PBI->getSuccessor(0);
1544 BasicBlock *OldFalse = PBI->getSuccessor(1);
1545 PBI->setSuccessor(0, OldFalse);
1546 PBI->setSuccessor(1, OldTrue);
1549 // If we have a bonus inst, clone it into the predecessor block.
1550 Instruction *NewBonus = 0;
1552 NewBonus = BonusInst->clone();
1553 PredBlock->getInstList().insert(PBI, NewBonus);
1554 NewBonus->takeName(BonusInst);
1555 BonusInst->setName(BonusInst->getName()+".old");
1558 // Clone Cond into the predecessor basic block, and or/and the
1559 // two conditions together.
1560 Instruction *New = Cond->clone();
1561 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1562 PredBlock->getInstList().insert(PBI, New);
1563 New->takeName(Cond);
1564 Cond->setName(New->getName()+".old");
1566 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1567 New, "or.cond", PBI);
1568 PBI->setCondition(NewCond);
1569 if (PBI->getSuccessor(0) == BB) {
1570 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1571 PBI->setSuccessor(0, TrueDest);
1573 if (PBI->getSuccessor(1) == BB) {
1574 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1575 PBI->setSuccessor(1, FalseDest);
1578 // Copy any debug value intrinsics into the end of PredBlock.
1579 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
1580 if (isa<DbgInfoIntrinsic>(*I))
1581 I->clone()->insertBefore(PBI);
1588 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1589 /// predecessor of another block, this function tries to simplify it. We know
1590 /// that PBI and BI are both conditional branches, and BI is in one of the
1591 /// successor blocks of PBI - PBI branches to BI.
1592 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1593 assert(PBI->isConditional() && BI->isConditional());
1594 BasicBlock *BB = BI->getParent();
1596 // If this block ends with a branch instruction, and if there is a
1597 // predecessor that ends on a branch of the same condition, make
1598 // this conditional branch redundant.
1599 if (PBI->getCondition() == BI->getCondition() &&
1600 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1601 // Okay, the outcome of this conditional branch is statically
1602 // knowable. If this block had a single pred, handle specially.
1603 if (BB->getSinglePredecessor()) {
1604 // Turn this into a branch on constant.
1605 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1606 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1608 return true; // Nuke the branch on constant.
1611 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1612 // in the constant and simplify the block result. Subsequent passes of
1613 // simplifycfg will thread the block.
1614 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1615 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
1616 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1617 std::distance(PB, PE),
1618 BI->getCondition()->getName() + ".pr",
1620 // Okay, we're going to insert the PHI node. Since PBI is not the only
1621 // predecessor, compute the PHI'd conditional value for all of the preds.
1622 // Any predecessor where the condition is not computable we keep symbolic.
1623 for (pred_iterator PI = PB; PI != PE; ++PI) {
1624 BasicBlock *P = *PI;
1625 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
1626 PBI != BI && PBI->isConditional() &&
1627 PBI->getCondition() == BI->getCondition() &&
1628 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1629 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1630 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1633 NewPN->addIncoming(BI->getCondition(), P);
1637 BI->setCondition(NewPN);
1642 // If this is a conditional branch in an empty block, and if any
1643 // predecessors is a conditional branch to one of our destinations,
1644 // fold the conditions into logical ops and one cond br.
1645 BasicBlock::iterator BBI = BB->begin();
1646 // Ignore dbg intrinsics.
1647 while (isa<DbgInfoIntrinsic>(BBI))
1653 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1658 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1660 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1661 PBIOp = 0, BIOp = 1;
1662 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1663 PBIOp = 1, BIOp = 0;
1664 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1669 // Check to make sure that the other destination of this branch
1670 // isn't BB itself. If so, this is an infinite loop that will
1671 // keep getting unwound.
1672 if (PBI->getSuccessor(PBIOp) == BB)
1675 // Do not perform this transformation if it would require
1676 // insertion of a large number of select instructions. For targets
1677 // without predication/cmovs, this is a big pessimization.
1678 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1680 unsigned NumPhis = 0;
1681 for (BasicBlock::iterator II = CommonDest->begin();
1682 isa<PHINode>(II); ++II, ++NumPhis)
1683 if (NumPhis > 2) // Disable this xform.
1686 // Finally, if everything is ok, fold the branches to logical ops.
1687 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1689 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
1690 << "AND: " << *BI->getParent());
1693 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1694 // branch in it, where one edge (OtherDest) goes back to itself but the other
1695 // exits. We don't *know* that the program avoids the infinite loop
1696 // (even though that seems likely). If we do this xform naively, we'll end up
1697 // recursively unpeeling the loop. Since we know that (after the xform is
1698 // done) that the block *is* infinite if reached, we just make it an obviously
1699 // infinite loop with no cond branch.
1700 if (OtherDest == BB) {
1701 // Insert it at the end of the function, because it's either code,
1702 // or it won't matter if it's hot. :)
1703 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1704 "infloop", BB->getParent());
1705 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1706 OtherDest = InfLoopBlock;
1709 DEBUG(dbgs() << *PBI->getParent()->getParent());
1711 // BI may have other predecessors. Because of this, we leave
1712 // it alone, but modify PBI.
1714 // Make sure we get to CommonDest on True&True directions.
1715 Value *PBICond = PBI->getCondition();
1717 PBICond = BinaryOperator::CreateNot(PBICond,
1718 PBICond->getName()+".not",
1720 Value *BICond = BI->getCondition();
1722 BICond = BinaryOperator::CreateNot(BICond,
1723 BICond->getName()+".not",
1725 // Merge the conditions.
1726 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1728 // Modify PBI to branch on the new condition to the new dests.
1729 PBI->setCondition(Cond);
1730 PBI->setSuccessor(0, CommonDest);
1731 PBI->setSuccessor(1, OtherDest);
1733 // OtherDest may have phi nodes. If so, add an entry from PBI's
1734 // block that are identical to the entries for BI's block.
1735 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
1737 // We know that the CommonDest already had an edge from PBI to
1738 // it. If it has PHIs though, the PHIs may have different
1739 // entries for BB and PBI's BB. If so, insert a select to make
1742 for (BasicBlock::iterator II = CommonDest->begin();
1743 (PN = dyn_cast<PHINode>(II)); ++II) {
1744 Value *BIV = PN->getIncomingValueForBlock(BB);
1745 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1746 Value *PBIV = PN->getIncomingValue(PBBIdx);
1748 // Insert a select in PBI to pick the right value.
1749 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1750 PBIV->getName()+".mux", PBI);
1751 PN->setIncomingValue(PBBIdx, NV);
1755 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1756 DEBUG(dbgs() << *PBI->getParent()->getParent());
1758 // This basic block is probably dead. We know it has at least
1759 // one fewer predecessor.
1763 // SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
1764 // branch to TrueBB if Cond is true or to FalseBB if Cond is false.
1765 // Takes care of updating the successors and removing the old terminator.
1766 // Also makes sure not to introduce new successors by assuming that edges to
1767 // non-successor TrueBBs and FalseBBs aren't reachable.
1768 static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
1769 BasicBlock *TrueBB, BasicBlock *FalseBB){
1770 // Remove any superfluous successor edges from the CFG.
1771 // First, figure out which successors to preserve.
1772 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
1774 BasicBlock *KeepEdge1 = TrueBB;
1775 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
1777 // Then remove the rest.
1778 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
1779 BasicBlock *Succ = OldTerm->getSuccessor(I);
1780 // Make sure only to keep exactly one copy of each edge.
1781 if (Succ == KeepEdge1)
1783 else if (Succ == KeepEdge2)
1786 Succ->removePredecessor(OldTerm->getParent());
1789 // Insert an appropriate new terminator.
1790 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
1791 if (TrueBB == FalseBB)
1792 // We were only looking for one successor, and it was present.
1793 // Create an unconditional branch to it.
1794 BranchInst::Create(TrueBB, OldTerm);
1796 // We found both of the successors we were looking for.
1797 // Create a conditional branch sharing the condition of the select.
1798 BranchInst::Create(TrueBB, FalseBB, Cond, OldTerm);
1799 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
1800 // Neither of the selected blocks were successors, so this
1801 // terminator must be unreachable.
1802 new UnreachableInst(OldTerm->getContext(), OldTerm);
1804 // One of the selected values was a successor, but the other wasn't.
1805 // Insert an unconditional branch to the one that was found;
1806 // the edge to the one that wasn't must be unreachable.
1808 // Only TrueBB was found.
1809 BranchInst::Create(TrueBB, OldTerm);
1811 // Only FalseBB was found.
1812 BranchInst::Create(FalseBB, OldTerm);
1815 EraseTerminatorInstAndDCECond(OldTerm);
1819 // SimplifySwitchOnSelect - Replaces
1820 // (switch (select cond, X, Y)) on constant X, Y
1821 // with a branch - conditional if X and Y lead to distinct BBs,
1822 // unconditional otherwise.
1823 static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
1824 // Check for constant integer values in the select.
1825 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
1826 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
1827 if (!TrueVal || !FalseVal)
1830 // Find the relevant condition and destinations.
1831 Value *Condition = Select->getCondition();
1832 BasicBlock *TrueBB = SI->getSuccessor(SI->findCaseValue(TrueVal));
1833 BasicBlock *FalseBB = SI->getSuccessor(SI->findCaseValue(FalseVal));
1835 // Perform the actual simplification.
1836 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB);
1839 // SimplifyIndirectBrOnSelect - Replaces
1840 // (indirectbr (select cond, blockaddress(@fn, BlockA),
1841 // blockaddress(@fn, BlockB)))
1843 // (br cond, BlockA, BlockB).
1844 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
1845 // Check that both operands of the select are block addresses.
1846 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
1847 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
1851 // Extract the actual blocks.
1852 BasicBlock *TrueBB = TBA->getBasicBlock();
1853 BasicBlock *FalseBB = FBA->getBasicBlock();
1855 // Perform the actual simplification.
1856 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB);
1859 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
1860 /// instruction (a seteq/setne with a constant) as the only instruction in a
1861 /// block that ends with an uncond branch. We are looking for a very specific
1862 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
1863 /// this case, we merge the first two "or's of icmp" into a switch, but then the
1864 /// default value goes to an uncond block with a seteq in it, we get something
1867 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
1869 /// %tmp = icmp eq i8 %A, 92
1872 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
1874 /// We prefer to split the edge to 'end' so that there is a true/false entry to
1875 /// the PHI, merging the third icmp into the switch.
1876 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
1877 const TargetData *TD) {
1878 BasicBlock *BB = ICI->getParent();
1879 // If the block has any PHIs in it or the icmp has multiple uses, it is too
1881 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
1883 Value *V = ICI->getOperand(0);
1884 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
1886 // The pattern we're looking for is where our only predecessor is a switch on
1887 // 'V' and this block is the default case for the switch. In this case we can
1888 // fold the compared value into the switch to simplify things.
1889 BasicBlock *Pred = BB->getSinglePredecessor();
1890 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
1892 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
1893 if (SI->getCondition() != V)
1896 // If BB is reachable on a non-default case, then we simply know the value of
1897 // V in this block. Substitute it and constant fold the icmp instruction
1899 if (SI->getDefaultDest() != BB) {
1900 ConstantInt *VVal = SI->findCaseDest(BB);
1901 assert(VVal && "Should have a unique destination value");
1902 ICI->setOperand(0, VVal);
1904 if (Value *V = SimplifyInstruction(ICI, TD)) {
1905 ICI->replaceAllUsesWith(V);
1906 ICI->eraseFromParent();
1908 // BB is now empty, so it is likely to simplify away.
1909 return SimplifyCFG(BB) | true;
1912 // Ok, the block is reachable from the default dest. If the constant we're
1913 // comparing exists in one of the other edges, then we can constant fold ICI
1915 if (SI->findCaseValue(Cst) != 0) {
1917 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1918 V = ConstantInt::getFalse(BB->getContext());
1920 V = ConstantInt::getTrue(BB->getContext());
1922 ICI->replaceAllUsesWith(V);
1923 ICI->eraseFromParent();
1924 // BB is now empty, so it is likely to simplify away.
1925 return SimplifyCFG(BB) | true;
1928 // The use of the icmp has to be in the 'end' block, by the only PHI node in
1930 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
1931 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
1932 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
1933 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
1936 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
1938 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
1939 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
1941 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1942 std::swap(DefaultCst, NewCst);
1944 // Replace ICI (which is used by the PHI for the default value) with true or
1945 // false depending on if it is EQ or NE.
1946 ICI->replaceAllUsesWith(DefaultCst);
1947 ICI->eraseFromParent();
1949 // Okay, the switch goes to this block on a default value. Add an edge from
1950 // the switch to the merge point on the compared value.
1951 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
1952 BB->getParent(), BB);
1953 SI->addCase(Cst, NewBB);
1955 // NewBB branches to the phi block, add the uncond branch and the phi entry.
1956 BranchInst::Create(SuccBlock, NewBB);
1957 PHIUse->addIncoming(NewCst, NewBB);
1961 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
1962 /// Check to see if it is branching on an or/and chain of icmp instructions, and
1963 /// fold it into a switch instruction if so.
1964 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD) {
1965 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1966 if (Cond == 0) return false;
1969 // Change br (X == 0 | X == 1), T, F into a switch instruction.
1970 // If this is a bunch of seteq's or'd together, or if it's a bunch of
1971 // 'setne's and'ed together, collect them.
1973 std::vector<ConstantInt*> Values;
1974 bool TrueWhenEqual = true;
1975 Value *ExtraCase = 0;
1976 unsigned UsedICmps = 0;
1978 if (Cond->getOpcode() == Instruction::Or) {
1979 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
1981 } else if (Cond->getOpcode() == Instruction::And) {
1982 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
1984 TrueWhenEqual = false;
1987 // If we didn't have a multiply compared value, fail.
1988 if (CompVal == 0) return false;
1990 // Avoid turning single icmps into a switch.
1994 // There might be duplicate constants in the list, which the switch
1995 // instruction can't handle, remove them now.
1996 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
1997 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
1999 // If Extra was used, we require at least two switch values to do the
2000 // transformation. A switch with one value is just an cond branch.
2001 if (ExtraCase && Values.size() < 2) return false;
2003 // Figure out which block is which destination.
2004 BasicBlock *DefaultBB = BI->getSuccessor(1);
2005 BasicBlock *EdgeBB = BI->getSuccessor(0);
2006 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2008 BasicBlock *BB = BI->getParent();
2010 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
2011 << " cases into SWITCH. BB is:\n" << *BB);
2013 // If there are any extra values that couldn't be folded into the switch
2014 // then we evaluate them with an explicit branch first. Split the block
2015 // right before the condbr to handle it.
2017 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
2018 // Remove the uncond branch added to the old block.
2019 TerminatorInst *OldTI = BB->getTerminator();
2022 BranchInst::Create(EdgeBB, NewBB, ExtraCase, OldTI);
2024 BranchInst::Create(NewBB, EdgeBB, ExtraCase, OldTI);
2026 OldTI->eraseFromParent();
2028 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
2029 // for the edge we just added.
2030 AddPredecessorToBlock(EdgeBB, BB, NewBB);
2032 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
2033 << "\nEXTRABB = " << *BB);
2037 // Convert pointer to int before we switch.
2038 if (CompVal->getType()->isPointerTy()) {
2039 assert(TD && "Cannot switch on pointer without TargetData");
2040 CompVal = new PtrToIntInst(CompVal,
2041 TD->getIntPtrType(CompVal->getContext()),
2045 // Create the new switch instruction now.
2046 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB, Values.size(), BI);
2048 // Add all of the 'cases' to the switch instruction.
2049 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2050 New->addCase(Values[i], EdgeBB);
2052 // We added edges from PI to the EdgeBB. As such, if there were any
2053 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2054 // the number of edges added.
2055 for (BasicBlock::iterator BBI = EdgeBB->begin();
2056 isa<PHINode>(BBI); ++BBI) {
2057 PHINode *PN = cast<PHINode>(BBI);
2058 Value *InVal = PN->getIncomingValueForBlock(BB);
2059 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2060 PN->addIncoming(InVal, BB);
2063 // Erase the old branch instruction.
2064 EraseTerminatorInstAndDCECond(BI);
2066 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
2070 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI) {
2071 BasicBlock *BB = RI->getParent();
2072 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2074 // Find predecessors that end with branches.
2075 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2076 SmallVector<BranchInst*, 8> CondBranchPreds;
2077 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2078 BasicBlock *P = *PI;
2079 TerminatorInst *PTI = P->getTerminator();
2080 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2081 if (BI->isUnconditional())
2082 UncondBranchPreds.push_back(P);
2084 CondBranchPreds.push_back(BI);
2088 // If we found some, do the transformation!
2089 if (!UncondBranchPreds.empty() && DupRet) {
2090 while (!UncondBranchPreds.empty()) {
2091 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2092 DEBUG(dbgs() << "FOLDING: " << *BB
2093 << "INTO UNCOND BRANCH PRED: " << *Pred);
2094 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
2097 // If we eliminated all predecessors of the block, delete the block now.
2098 if (pred_begin(BB) == pred_end(BB))
2099 // We know there are no successors, so just nuke the block.
2100 BB->eraseFromParent();
2105 // Check out all of the conditional branches going to this return
2106 // instruction. If any of them just select between returns, change the
2107 // branch itself into a select/return pair.
2108 while (!CondBranchPreds.empty()) {
2109 BranchInst *BI = CondBranchPreds.pop_back_val();
2111 // Check to see if the non-BB successor is also a return block.
2112 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2113 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2114 SimplifyCondBranchToTwoReturns(BI))
2120 bool SimplifyCFGOpt::SimplifyUnwind(UnwindInst *UI) {
2121 // Check to see if the first instruction in this block is just an unwind.
2122 // If so, replace any invoke instructions which use this as an exception
2123 // destination with call instructions.
2124 BasicBlock *BB = UI->getParent();
2125 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2127 bool Changed = false;
2128 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2129 while (!Preds.empty()) {
2130 BasicBlock *Pred = Preds.back();
2131 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
2132 if (II && II->getUnwindDest() == BB) {
2133 // Insert a new branch instruction before the invoke, because this
2134 // is now a fall through.
2135 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2136 Pred->getInstList().remove(II); // Take out of symbol table
2138 // Insert the call now.
2139 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
2140 CallInst *CI = CallInst::Create(II->getCalledValue(),
2141 Args.begin(), Args.end(),
2143 CI->setCallingConv(II->getCallingConv());
2144 CI->setAttributes(II->getAttributes());
2145 // If the invoke produced a value, the Call now does instead.
2146 II->replaceAllUsesWith(CI);
2154 // If this block is now dead (and isn't the entry block), remove it.
2155 if (pred_begin(BB) == pred_end(BB) &&
2156 BB != &BB->getParent()->getEntryBlock()) {
2157 // We know there are no successors, so just nuke the block.
2158 BB->eraseFromParent();
2165 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2166 BasicBlock *BB = UI->getParent();
2168 bool Changed = false;
2170 // If there are any instructions immediately before the unreachable that can
2171 // be removed, do so.
2172 while (UI != BB->begin()) {
2173 BasicBlock::iterator BBI = UI;
2175 // Do not delete instructions that can have side effects, like calls
2176 // (which may never return) and volatile loads and stores.
2177 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2179 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
2180 if (SI->isVolatile())
2183 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
2184 if (LI->isVolatile())
2187 // Delete this instruction (any uses are guaranteed to be dead)
2188 if (!BBI->use_empty())
2189 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
2190 BBI->eraseFromParent();
2194 // If the unreachable instruction is the first in the block, take a gander
2195 // at all of the predecessors of this instruction, and simplify them.
2196 if (&BB->front() != UI) return Changed;
2198 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2199 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2200 TerminatorInst *TI = Preds[i]->getTerminator();
2202 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2203 if (BI->isUnconditional()) {
2204 if (BI->getSuccessor(0) == BB) {
2205 new UnreachableInst(TI->getContext(), TI);
2206 TI->eraseFromParent();
2210 if (BI->getSuccessor(0) == BB) {
2211 BranchInst::Create(BI->getSuccessor(1), BI);
2212 EraseTerminatorInstAndDCECond(BI);
2213 } else if (BI->getSuccessor(1) == BB) {
2214 BranchInst::Create(BI->getSuccessor(0), BI);
2215 EraseTerminatorInstAndDCECond(BI);
2219 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2220 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2221 if (SI->getSuccessor(i) == BB) {
2222 BB->removePredecessor(SI->getParent());
2227 // If the default value is unreachable, figure out the most popular
2228 // destination and make it the default.
2229 if (SI->getSuccessor(0) == BB) {
2230 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
2231 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
2232 std::pair<unsigned, unsigned>& entry =
2233 Popularity[SI->getSuccessor(i)];
2234 if (entry.first == 0) {
2242 // Find the most popular block.
2243 unsigned MaxPop = 0;
2244 unsigned MaxIndex = 0;
2245 BasicBlock *MaxBlock = 0;
2246 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
2247 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2248 if (I->second.first > MaxPop ||
2249 (I->second.first == MaxPop && MaxIndex > I->second.second)) {
2250 MaxPop = I->second.first;
2251 MaxIndex = I->second.second;
2252 MaxBlock = I->first;
2256 // Make this the new default, allowing us to delete any explicit
2258 SI->setSuccessor(0, MaxBlock);
2261 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2263 if (isa<PHINode>(MaxBlock->begin()))
2264 for (unsigned i = 0; i != MaxPop-1; ++i)
2265 MaxBlock->removePredecessor(SI->getParent());
2267 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2268 if (SI->getSuccessor(i) == MaxBlock) {
2274 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2275 if (II->getUnwindDest() == BB) {
2276 // Convert the invoke to a call instruction. This would be a good
2277 // place to note that the call does not throw though.
2278 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2279 II->removeFromParent(); // Take out of symbol table
2281 // Insert the call now...
2282 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2283 CallInst *CI = CallInst::Create(II->getCalledValue(),
2284 Args.begin(), Args.end(),
2286 CI->setCallingConv(II->getCallingConv());
2287 CI->setAttributes(II->getAttributes());
2288 // If the invoke produced a value, the call does now instead.
2289 II->replaceAllUsesWith(CI);
2296 // If this block is now dead, remove it.
2297 if (pred_begin(BB) == pred_end(BB) &&
2298 BB != &BB->getParent()->getEntryBlock()) {
2299 // We know there are no successors, so just nuke the block.
2300 BB->eraseFromParent();
2307 /// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
2308 /// integer range comparison into a sub, an icmp and a branch.
2309 static bool TurnSwitchRangeIntoICmp(SwitchInst *SI) {
2310 assert(SI->getNumCases() > 2 && "Degenerate switch?");
2312 // Make sure all cases point to the same destination and gather the values.
2313 SmallVector<ConstantInt *, 16> Cases;
2314 Cases.push_back(SI->getCaseValue(1));
2315 for (unsigned I = 2, E = SI->getNumCases(); I != E; ++I) {
2316 if (SI->getSuccessor(I-1) != SI->getSuccessor(I))
2318 Cases.push_back(SI->getCaseValue(I));
2320 assert(Cases.size() == SI->getNumCases()-1 && "Not all cases gathered");
2322 // Sort the case values, then check if they form a range we can transform.
2323 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
2324 for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
2325 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
2329 Constant *Offset = ConstantExpr::getNeg(Cases.back());
2330 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases()-1);
2332 Value *Sub = SI->getCondition();
2333 if (!Offset->isNullValue())
2334 Sub = BinaryOperator::CreateAdd(Sub, Offset, Sub->getName()+".off", SI);
2335 Value *Cmp = new ICmpInst(SI, ICmpInst::ICMP_ULT, Sub, NumCases, "switch");
2336 BranchInst::Create(SI->getSuccessor(1), SI->getDefaultDest(), Cmp, SI);
2338 // Prune obsolete incoming values off the successor's PHI nodes.
2339 for (BasicBlock::iterator BBI = SI->getSuccessor(1)->begin();
2340 isa<PHINode>(BBI); ++BBI) {
2341 for (unsigned I = 0, E = SI->getNumCases()-2; I != E; ++I)
2342 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
2344 SI->eraseFromParent();
2349 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI) {
2350 // If this switch is too complex to want to look at, ignore it.
2351 if (!isValueEqualityComparison(SI))
2354 BasicBlock *BB = SI->getParent();
2356 // If we only have one predecessor, and if it is a branch on this value,
2357 // see if that predecessor totally determines the outcome of this switch.
2358 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2359 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
2360 return SimplifyCFG(BB) | true;
2362 Value *Cond = SI->getCondition();
2363 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
2364 if (SimplifySwitchOnSelect(SI, Select))
2365 return SimplifyCFG(BB) | true;
2367 // If the block only contains the switch, see if we can fold the block
2368 // away into any preds.
2369 BasicBlock::iterator BBI = BB->begin();
2370 // Ignore dbg intrinsics.
2371 while (isa<DbgInfoIntrinsic>(BBI))
2374 if (FoldValueComparisonIntoPredecessors(SI))
2375 return SimplifyCFG(BB) | true;
2377 // Try to transform the switch into an icmp and a branch.
2378 if (TurnSwitchRangeIntoICmp(SI))
2379 return SimplifyCFG(BB) | true;
2384 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
2385 BasicBlock *BB = IBI->getParent();
2386 bool Changed = false;
2388 // Eliminate redundant destinations.
2389 SmallPtrSet<Value *, 8> Succs;
2390 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2391 BasicBlock *Dest = IBI->getDestination(i);
2392 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2393 Dest->removePredecessor(BB);
2394 IBI->removeDestination(i);
2400 if (IBI->getNumDestinations() == 0) {
2401 // If the indirectbr has no successors, change it to unreachable.
2402 new UnreachableInst(IBI->getContext(), IBI);
2403 EraseTerminatorInstAndDCECond(IBI);
2407 if (IBI->getNumDestinations() == 1) {
2408 // If the indirectbr has one successor, change it to a direct branch.
2409 BranchInst::Create(IBI->getDestination(0), IBI);
2410 EraseTerminatorInstAndDCECond(IBI);
2414 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2415 if (SimplifyIndirectBrOnSelect(IBI, SI))
2416 return SimplifyCFG(BB) | true;
2421 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI) {
2422 BasicBlock *BB = BI->getParent();
2424 // If the Terminator is the only non-phi instruction, simplify the block.
2425 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg();
2426 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
2427 TryToSimplifyUncondBranchFromEmptyBlock(BB))
2430 // If the only instruction in the block is a seteq/setne comparison
2431 // against a constant, try to simplify the block.
2432 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
2433 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
2434 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
2436 if (I->isTerminator() && TryToSimplifyUncondBranchWithICmpInIt(ICI, TD))
2444 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI) {
2445 BasicBlock *BB = BI->getParent();
2447 // Conditional branch
2448 if (isValueEqualityComparison(BI)) {
2449 // If we only have one predecessor, and if it is a branch on this value,
2450 // see if that predecessor totally determines the outcome of this
2452 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2453 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
2454 return SimplifyCFG(BB) | true;
2456 // This block must be empty, except for the setcond inst, if it exists.
2457 // Ignore dbg intrinsics.
2458 BasicBlock::iterator I = BB->begin();
2459 // Ignore dbg intrinsics.
2460 while (isa<DbgInfoIntrinsic>(I))
2463 if (FoldValueComparisonIntoPredecessors(BI))
2464 return SimplifyCFG(BB) | true;
2465 } else if (&*I == cast<Instruction>(BI->getCondition())){
2467 // Ignore dbg intrinsics.
2468 while (isa<DbgInfoIntrinsic>(I))
2470 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI))
2471 return SimplifyCFG(BB) | true;
2475 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
2476 if (SimplifyBranchOnICmpChain(BI, TD))
2479 // We have a conditional branch to two blocks that are only reachable
2480 // from BI. We know that the condbr dominates the two blocks, so see if
2481 // there is any identical code in the "then" and "else" blocks. If so, we
2482 // can hoist it up to the branching block.
2483 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
2484 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2485 if (HoistThenElseCodeToIf(BI))
2486 return SimplifyCFG(BB) | true;
2488 // If Successor #1 has multiple preds, we may be able to conditionally
2489 // execute Successor #0 if it branches to successor #1.
2490 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
2491 if (Succ0TI->getNumSuccessors() == 1 &&
2492 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
2493 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
2494 return SimplifyCFG(BB) | true;
2496 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2497 // If Successor #0 has multiple preds, we may be able to conditionally
2498 // execute Successor #1 if it branches to successor #0.
2499 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
2500 if (Succ1TI->getNumSuccessors() == 1 &&
2501 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
2502 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
2503 return SimplifyCFG(BB) | true;
2506 // If this is a branch on a phi node in the current block, thread control
2507 // through this block if any PHI node entries are constants.
2508 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
2509 if (PN->getParent() == BI->getParent())
2510 if (FoldCondBranchOnPHI(BI, TD))
2511 return SimplifyCFG(BB) | true;
2513 // If this basic block is ONLY a setcc and a branch, and if a predecessor
2514 // branches to us and one of our successors, fold the setcc into the
2515 // predecessor and use logical operations to pick the right destination.
2516 if (FoldBranchToCommonDest(BI))
2517 return SimplifyCFG(BB) | true;
2519 // Scan predecessor blocks for conditional branches.
2520 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2521 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2522 if (PBI != BI && PBI->isConditional())
2523 if (SimplifyCondBranchToCondBranch(PBI, BI))
2524 return SimplifyCFG(BB) | true;
2529 bool SimplifyCFGOpt::run(BasicBlock *BB) {
2530 bool Changed = false;
2532 assert(BB && BB->getParent() && "Block not embedded in function!");
2533 assert(BB->getTerminator() && "Degenerate basic block encountered!");
2535 // Remove basic blocks that have no predecessors (except the entry block)...
2536 // or that just have themself as a predecessor. These are unreachable.
2537 if ((pred_begin(BB) == pred_end(BB) &&
2538 BB != &BB->getParent()->getEntryBlock()) ||
2539 BB->getSinglePredecessor() == BB) {
2540 DEBUG(dbgs() << "Removing BB: \n" << *BB);
2541 DeleteDeadBlock(BB);
2545 // Check to see if we can constant propagate this terminator instruction
2547 Changed |= ConstantFoldTerminator(BB);
2549 // Check for and eliminate duplicate PHI nodes in this block.
2550 Changed |= EliminateDuplicatePHINodes(BB);
2552 // Merge basic blocks into their predecessor if there is only one distinct
2553 // pred, and if there is only one distinct successor of the predecessor, and
2554 // if there are no PHI nodes.
2556 if (MergeBlockIntoPredecessor(BB))
2559 // If there is a trivial two-entry PHI node in this basic block, and we can
2560 // eliminate it, do so now.
2561 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
2562 if (PN->getNumIncomingValues() == 2)
2563 Changed |= FoldTwoEntryPHINode(PN, TD);
2565 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
2566 if (BI->isUnconditional()) {
2567 if (SimplifyUncondBranch(BI)) return true;
2569 if (SimplifyCondBranch(BI)) return true;
2571 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
2572 if (SimplifyReturn(RI)) return true;
2573 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
2574 if (SimplifySwitch(SI)) return true;
2575 } else if (UnreachableInst *UI =
2576 dyn_cast<UnreachableInst>(BB->getTerminator())) {
2577 if (SimplifyUnreachable(UI)) return true;
2578 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
2579 if (SimplifyUnwind(UI)) return true;
2580 } else if (IndirectBrInst *IBI =
2581 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
2582 if (SimplifyIndirectBr(IBI)) return true;
2588 /// SimplifyCFG - This function is used to do simplification of a CFG. For
2589 /// example, it adjusts branches to branches to eliminate the extra hop, it
2590 /// eliminates unreachable basic blocks, and does other "peephole" optimization
2591 /// of the CFG. It returns true if a modification was made.
2593 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
2594 return SimplifyCFGOpt(TD).run(BB);