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 while (isa<DbgInfoIntrinsic>(I1))
812 while (isa<DbgInfoIntrinsic>(I2))
814 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
815 !I1->isIdenticalToWhenDefined(I2) ||
816 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
819 // If we get here, we can hoist at least one instruction.
820 BasicBlock *BIParent = BI->getParent();
823 // If we are hoisting the terminator instruction, don't move one (making a
824 // broken BB), instead clone it, and remove BI.
825 if (isa<TerminatorInst>(I1))
826 goto HoistTerminator;
828 // For a normal instruction, we just move one to right before the branch,
829 // then replace all uses of the other with the first. Finally, we remove
830 // the now redundant second instruction.
831 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
832 if (!I2->use_empty())
833 I2->replaceAllUsesWith(I1);
834 I1->intersectOptionalDataWith(I2);
835 I2->eraseFromParent();
838 while (isa<DbgInfoIntrinsic>(I1))
841 while (isa<DbgInfoIntrinsic>(I2))
843 } while (I1->getOpcode() == I2->getOpcode() &&
844 I1->isIdenticalToWhenDefined(I2));
849 // It may not be possible to hoist an invoke.
850 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
853 // Okay, it is safe to hoist the terminator.
854 Instruction *NT = I1->clone();
855 BIParent->getInstList().insert(BI, NT);
856 if (!NT->getType()->isVoidTy()) {
857 I1->replaceAllUsesWith(NT);
858 I2->replaceAllUsesWith(NT);
862 // Hoisting one of the terminators from our successor is a great thing.
863 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
864 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
865 // nodes, so we insert select instruction to compute the final result.
866 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
867 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
869 for (BasicBlock::iterator BBI = SI->begin();
870 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
871 Value *BB1V = PN->getIncomingValueForBlock(BB1);
872 Value *BB2V = PN->getIncomingValueForBlock(BB2);
873 if (BB1V == BB2V) continue;
875 // These values do not agree. Insert a select instruction before NT
876 // that determines the right value.
877 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
879 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
880 BB1V->getName()+"."+BB2V->getName(), NT);
881 // Make the PHI node use the select for all incoming values for BB1/BB2
882 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
883 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
884 PN->setIncomingValue(i, SI);
888 // Update any PHI nodes in our new successors.
889 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
890 AddPredecessorToBlock(*SI, BIParent, BB1);
892 EraseTerminatorInstAndDCECond(BI);
896 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
897 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
898 /// (for now, restricted to a single instruction that's side effect free) from
899 /// the BB1 into the branch block to speculatively execute it.
900 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
901 // Only speculatively execution a single instruction (not counting the
902 // terminator) for now.
903 Instruction *HInst = NULL;
904 Instruction *Term = BB1->getTerminator();
905 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
907 Instruction *I = BBI;
909 if (isa<DbgInfoIntrinsic>(I)) continue;
910 if (I == Term) break;
919 // Be conservative for now. FP select instruction can often be expensive.
920 Value *BrCond = BI->getCondition();
921 if (isa<FCmpInst>(BrCond))
924 // If BB1 is actually on the false edge of the conditional branch, remember
925 // to swap the select operands later.
927 if (BB1 != BI->getSuccessor(0)) {
928 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
935 // br i1 %t1, label %BB1, label %BB2
944 // %t3 = select i1 %t1, %t2, %t3
945 switch (HInst->getOpcode()) {
946 default: return false; // Not safe / profitable to hoist.
947 case Instruction::Add:
948 case Instruction::Sub:
949 // Not worth doing for vector ops.
950 if (HInst->getType()->isVectorTy())
953 case Instruction::And:
954 case Instruction::Or:
955 case Instruction::Xor:
956 case Instruction::Shl:
957 case Instruction::LShr:
958 case Instruction::AShr:
959 // Don't mess with vector operations.
960 if (HInst->getType()->isVectorTy())
962 break; // These are all cheap and non-trapping instructions.
965 // If the instruction is obviously dead, don't try to predicate it.
966 if (HInst->use_empty()) {
967 HInst->eraseFromParent();
971 // Can we speculatively execute the instruction? And what is the value
972 // if the condition is false? Consider the phi uses, if the incoming value
973 // from the "if" block are all the same V, then V is the value of the
974 // select if the condition is false.
975 BasicBlock *BIParent = BI->getParent();
976 SmallVector<PHINode*, 4> PHIUses;
977 Value *FalseV = NULL;
979 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
980 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
982 // Ignore any user that is not a PHI node in BB2. These can only occur in
983 // unreachable blocks, because they would not be dominated by the instr.
984 PHINode *PN = dyn_cast<PHINode>(*UI);
985 if (!PN || PN->getParent() != BB2)
987 PHIUses.push_back(PN);
989 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
992 else if (FalseV != PHIV)
993 return false; // Inconsistent value when condition is false.
996 assert(FalseV && "Must have at least one user, and it must be a PHI");
998 // Do not hoist the instruction if any of its operands are defined but not
999 // used in this BB. The transformation will prevent the operand from
1000 // being sunk into the use block.
1001 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1003 Instruction *OpI = dyn_cast<Instruction>(*i);
1004 if (OpI && OpI->getParent() == BIParent &&
1005 !OpI->isUsedInBasicBlock(BIParent))
1009 // If we get here, we can hoist the instruction. Try to place it
1010 // before the icmp instruction preceding the conditional branch.
1011 BasicBlock::iterator InsertPos = BI;
1012 if (InsertPos != BIParent->begin())
1014 // Skip debug info between condition and branch.
1015 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
1017 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
1018 SmallPtrSet<Instruction *, 4> BB1Insns;
1019 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
1020 BB1I != BB1E; ++BB1I)
1021 BB1Insns.insert(BB1I);
1022 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
1024 Instruction *Use = cast<Instruction>(*UI);
1025 if (!BB1Insns.count(Use)) continue;
1027 // If BrCond uses the instruction that place it just before
1028 // branch instruction.
1034 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
1036 // Create a select whose true value is the speculatively executed value and
1037 // false value is the previously determined FalseV.
1040 SI = SelectInst::Create(BrCond, FalseV, HInst,
1041 FalseV->getName() + "." + HInst->getName(), BI);
1043 SI = SelectInst::Create(BrCond, HInst, FalseV,
1044 HInst->getName() + "." + FalseV->getName(), BI);
1046 // Make the PHI node use the select for all incoming values for "then" and
1048 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1049 PHINode *PN = PHIUses[i];
1050 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1051 if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent)
1052 PN->setIncomingValue(j, SI);
1059 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1060 /// across this block.
1061 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1062 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1065 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1066 if (isa<DbgInfoIntrinsic>(BBI))
1068 if (Size > 10) return false; // Don't clone large BB's.
1071 // We can only support instructions that do not define values that are
1072 // live outside of the current basic block.
1073 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1075 Instruction *U = cast<Instruction>(*UI);
1076 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1079 // Looks ok, continue checking.
1085 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1086 /// that is defined in the same block as the branch and if any PHI entries are
1087 /// constants, thread edges corresponding to that entry to be branches to their
1088 /// ultimate destination.
1089 static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
1090 BasicBlock *BB = BI->getParent();
1091 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1092 // NOTE: we currently cannot transform this case if the PHI node is used
1093 // outside of the block.
1094 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1097 // Degenerate case of a single entry PHI.
1098 if (PN->getNumIncomingValues() == 1) {
1099 FoldSingleEntryPHINodes(PN->getParent());
1103 // Now we know that this block has multiple preds and two succs.
1104 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1106 // Okay, this is a simple enough basic block. See if any phi values are
1108 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1109 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1110 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1112 // Okay, we now know that all edges from PredBB should be revectored to
1113 // branch to RealDest.
1114 BasicBlock *PredBB = PN->getIncomingBlock(i);
1115 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1117 if (RealDest == BB) continue; // Skip self loops.
1119 // The dest block might have PHI nodes, other predecessors and other
1120 // difficult cases. Instead of being smart about this, just insert a new
1121 // block that jumps to the destination block, effectively splitting
1122 // the edge we are about to create.
1123 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1124 RealDest->getName()+".critedge",
1125 RealDest->getParent(), RealDest);
1126 BranchInst::Create(RealDest, EdgeBB);
1128 // Update PHI nodes.
1129 AddPredecessorToBlock(RealDest, EdgeBB, BB);
1131 // BB may have instructions that are being threaded over. Clone these
1132 // instructions into EdgeBB. We know that there will be no uses of the
1133 // cloned instructions outside of EdgeBB.
1134 BasicBlock::iterator InsertPt = EdgeBB->begin();
1135 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1136 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1137 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1138 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1141 // Clone the instruction.
1142 Instruction *N = BBI->clone();
1143 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1145 // Update operands due to translation.
1146 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1148 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1149 if (PI != TranslateMap.end())
1153 // Check for trivial simplification.
1154 if (Value *V = SimplifyInstruction(N, TD)) {
1155 TranslateMap[BBI] = V;
1156 delete N; // Instruction folded away, don't need actual inst
1158 // Insert the new instruction into its new home.
1159 EdgeBB->getInstList().insert(InsertPt, N);
1160 if (!BBI->use_empty())
1161 TranslateMap[BBI] = N;
1165 // Loop over all of the edges from PredBB to BB, changing them to branch
1166 // to EdgeBB instead.
1167 TerminatorInst *PredBBTI = PredBB->getTerminator();
1168 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1169 if (PredBBTI->getSuccessor(i) == BB) {
1170 BB->removePredecessor(PredBB);
1171 PredBBTI->setSuccessor(i, EdgeBB);
1174 // Recurse, simplifying any other constants.
1175 return FoldCondBranchOnPHI(BI, TD) | true;
1181 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1182 /// PHI node, see if we can eliminate it.
1183 static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
1184 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1185 // statement", which has a very simple dominance structure. Basically, we
1186 // are trying to find the condition that is being branched on, which
1187 // subsequently causes this merge to happen. We really want control
1188 // dependence information for this check, but simplifycfg can't keep it up
1189 // to date, and this catches most of the cases we care about anyway.
1190 BasicBlock *BB = PN->getParent();
1191 BasicBlock *IfTrue, *IfFalse;
1192 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1194 // Don't bother if the branch will be constant folded trivially.
1195 isa<ConstantInt>(IfCond))
1198 // Okay, we found that we can merge this two-entry phi node into a select.
1199 // Doing so would require us to fold *all* two entry phi nodes in this block.
1200 // At some point this becomes non-profitable (particularly if the target
1201 // doesn't support cmov's). Only do this transformation if there are two or
1202 // fewer PHI nodes in this block.
1203 unsigned NumPhis = 0;
1204 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1208 // Loop over the PHI's seeing if we can promote them all to select
1209 // instructions. While we are at it, keep track of the instructions
1210 // that need to be moved to the dominating block.
1211 SmallPtrSet<Instruction*, 4> AggressiveInsts;
1213 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1214 PHINode *PN = cast<PHINode>(II++);
1215 if (Value *V = SimplifyInstruction(PN, TD)) {
1216 PN->replaceAllUsesWith(V);
1217 PN->eraseFromParent();
1221 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts) ||
1222 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts))
1226 // If we folded the the first phi, PN dangles at this point. Refresh it. If
1227 // we ran out of PHIs then we simplified them all.
1228 PN = dyn_cast<PHINode>(BB->begin());
1229 if (PN == 0) return true;
1231 // Don't fold i1 branches on PHIs which contain binary operators. These can
1232 // often be turned into switches and other things.
1233 if (PN->getType()->isIntegerTy(1) &&
1234 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1235 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1236 isa<BinaryOperator>(IfCond)))
1239 // If we all PHI nodes are promotable, check to make sure that all
1240 // instructions in the predecessor blocks can be promoted as well. If
1241 // not, we won't be able to get rid of the control flow, so it's not
1242 // worth promoting to select instructions.
1243 BasicBlock *DomBlock = 0;
1244 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1245 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1246 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1249 DomBlock = *pred_begin(IfBlock1);
1250 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1251 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1252 // This is not an aggressive instruction that we can promote.
1253 // Because of this, we won't be able to get rid of the control
1254 // flow, so the xform is not worth it.
1259 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1262 DomBlock = *pred_begin(IfBlock2);
1263 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1264 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1265 // This is not an aggressive instruction that we can promote.
1266 // Because of this, we won't be able to get rid of the control
1267 // flow, so the xform is not worth it.
1272 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1273 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1275 // If we can still promote the PHI nodes after this gauntlet of tests,
1276 // do all of the PHI's now.
1277 Instruction *InsertPt = DomBlock->getTerminator();
1279 // Move all 'aggressive' instructions, which are defined in the
1280 // conditional parts of the if's up to the dominating block.
1282 DomBlock->getInstList().splice(InsertPt,
1283 IfBlock1->getInstList(), IfBlock1->begin(),
1284 IfBlock1->getTerminator());
1286 DomBlock->getInstList().splice(InsertPt,
1287 IfBlock2->getInstList(), IfBlock2->begin(),
1288 IfBlock2->getTerminator());
1290 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1291 // Change the PHI node into a select instruction.
1292 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1293 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1295 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", InsertPt);
1296 PN->replaceAllUsesWith(NV);
1298 PN->eraseFromParent();
1301 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1302 // has been flattened. Change DomBlock to jump directly to our new block to
1303 // avoid other simplifycfg's kicking in on the diamond.
1304 TerminatorInst *OldTI = DomBlock->getTerminator();
1305 BranchInst::Create(BB, OldTI);
1306 OldTI->eraseFromParent();
1310 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1311 /// to two returning blocks, try to merge them together into one return,
1312 /// introducing a select if the return values disagree.
1313 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1314 assert(BI->isConditional() && "Must be a conditional branch");
1315 BasicBlock *TrueSucc = BI->getSuccessor(0);
1316 BasicBlock *FalseSucc = BI->getSuccessor(1);
1317 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1318 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1320 // Check to ensure both blocks are empty (just a return) or optionally empty
1321 // with PHI nodes. If there are other instructions, merging would cause extra
1322 // computation on one path or the other.
1323 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1325 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1328 // Okay, we found a branch that is going to two return nodes. If
1329 // there is no return value for this function, just change the
1330 // branch into a return.
1331 if (FalseRet->getNumOperands() == 0) {
1332 TrueSucc->removePredecessor(BI->getParent());
1333 FalseSucc->removePredecessor(BI->getParent());
1334 ReturnInst::Create(BI->getContext(), 0, BI);
1335 EraseTerminatorInstAndDCECond(BI);
1339 // Otherwise, figure out what the true and false return values are
1340 // so we can insert a new select instruction.
1341 Value *TrueValue = TrueRet->getReturnValue();
1342 Value *FalseValue = FalseRet->getReturnValue();
1344 // Unwrap any PHI nodes in the return blocks.
1345 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1346 if (TVPN->getParent() == TrueSucc)
1347 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1348 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1349 if (FVPN->getParent() == FalseSucc)
1350 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1352 // In order for this transformation to be safe, we must be able to
1353 // unconditionally execute both operands to the return. This is
1354 // normally the case, but we could have a potentially-trapping
1355 // constant expression that prevents this transformation from being
1357 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1360 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1364 // Okay, we collected all the mapped values and checked them for sanity, and
1365 // defined to really do this transformation. First, update the CFG.
1366 TrueSucc->removePredecessor(BI->getParent());
1367 FalseSucc->removePredecessor(BI->getParent());
1369 // Insert select instructions where needed.
1370 Value *BrCond = BI->getCondition();
1372 // Insert a select if the results differ.
1373 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1374 } else if (isa<UndefValue>(TrueValue)) {
1375 TrueValue = FalseValue;
1377 TrueValue = SelectInst::Create(BrCond, TrueValue,
1378 FalseValue, "retval", BI);
1382 Value *RI = !TrueValue ?
1383 ReturnInst::Create(BI->getContext(), BI) :
1384 ReturnInst::Create(BI->getContext(), TrueValue, BI);
1387 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1388 << "\n " << *BI << "NewRet = " << *RI
1389 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1391 EraseTerminatorInstAndDCECond(BI);
1396 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1397 /// and if a predecessor branches to us and one of our successors, fold the
1398 /// setcc into the predecessor and use logical operations to pick the right
1400 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1401 BasicBlock *BB = BI->getParent();
1402 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1403 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1404 Cond->getParent() != BB || !Cond->hasOneUse())
1407 // Only allow this if the condition is a simple instruction that can be
1408 // executed unconditionally. It must be in the same block as the branch, and
1409 // must be at the front of the block.
1410 BasicBlock::iterator FrontIt = BB->front();
1411 // Ignore dbg intrinsics.
1412 while (isa<DbgInfoIntrinsic>(FrontIt))
1415 // Allow a single instruction to be hoisted in addition to the compare
1416 // that feeds the branch. We later ensure that any values that _it_ uses
1417 // were also live in the predecessor, so that we don't unnecessarily create
1418 // register pressure or inhibit out-of-order execution.
1419 Instruction *BonusInst = 0;
1420 if (&*FrontIt != Cond &&
1421 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1422 FrontIt->isSafeToSpeculativelyExecute()) {
1423 BonusInst = &*FrontIt;
1427 // Only a single bonus inst is allowed.
1428 if (&*FrontIt != Cond)
1431 // Make sure the instruction after the condition is the cond branch.
1432 BasicBlock::iterator CondIt = Cond; ++CondIt;
1433 // Ingore dbg intrinsics.
1434 while(isa<DbgInfoIntrinsic>(CondIt))
1436 if (&*CondIt != BI) {
1437 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!");
1441 // Cond is known to be a compare or binary operator. Check to make sure that
1442 // neither operand is a potentially-trapping constant expression.
1443 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1446 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1451 // Finally, don't infinitely unroll conditional loops.
1452 BasicBlock *TrueDest = BI->getSuccessor(0);
1453 BasicBlock *FalseDest = BI->getSuccessor(1);
1454 if (TrueDest == BB || FalseDest == BB)
1457 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1458 BasicBlock *PredBlock = *PI;
1459 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1461 // Check that we have two conditional branches. If there is a PHI node in
1462 // the common successor, verify that the same value flows in from both
1464 if (PBI == 0 || PBI->isUnconditional() ||
1465 !SafeToMergeTerminators(BI, PBI))
1468 // Ensure that any values used in the bonus instruction are also used
1469 // by the terminator of the predecessor. This means that those values
1470 // must already have been resolved, so we won't be inhibiting the
1471 // out-of-order core by speculating them earlier.
1473 // Collect the values used by the bonus inst
1474 SmallPtrSet<Value*, 4> UsedValues;
1475 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1476 OE = BonusInst->op_end(); OI != OE; ++OI) {
1478 if (!isa<Constant>(V))
1479 UsedValues.insert(V);
1482 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1483 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1485 // Walk up to four levels back up the use-def chain of the predecessor's
1486 // terminator to see if all those values were used. The choice of four
1487 // levels is arbitrary, to provide a compile-time-cost bound.
1488 while (!Worklist.empty()) {
1489 std::pair<Value*, unsigned> Pair = Worklist.back();
1490 Worklist.pop_back();
1492 if (Pair.second >= 4) continue;
1493 UsedValues.erase(Pair.first);
1494 if (UsedValues.empty()) break;
1496 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
1497 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1499 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1503 if (!UsedValues.empty()) return false;
1506 Instruction::BinaryOps Opc;
1507 bool InvertPredCond = false;
1509 if (PBI->getSuccessor(0) == TrueDest)
1510 Opc = Instruction::Or;
1511 else if (PBI->getSuccessor(1) == FalseDest)
1512 Opc = Instruction::And;
1513 else if (PBI->getSuccessor(0) == FalseDest)
1514 Opc = Instruction::And, InvertPredCond = true;
1515 else if (PBI->getSuccessor(1) == TrueDest)
1516 Opc = Instruction::Or, InvertPredCond = true;
1520 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1522 // If we need to invert the condition in the pred block to match, do so now.
1523 if (InvertPredCond) {
1524 Value *NewCond = PBI->getCondition();
1526 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
1527 CmpInst *CI = cast<CmpInst>(NewCond);
1528 CI->setPredicate(CI->getInversePredicate());
1530 NewCond = BinaryOperator::CreateNot(NewCond,
1531 PBI->getCondition()->getName()+".not", PBI);
1534 PBI->setCondition(NewCond);
1535 BasicBlock *OldTrue = PBI->getSuccessor(0);
1536 BasicBlock *OldFalse = PBI->getSuccessor(1);
1537 PBI->setSuccessor(0, OldFalse);
1538 PBI->setSuccessor(1, OldTrue);
1541 // If we have a bonus inst, clone it into the predecessor block.
1542 Instruction *NewBonus = 0;
1544 NewBonus = BonusInst->clone();
1545 PredBlock->getInstList().insert(PBI, NewBonus);
1546 NewBonus->takeName(BonusInst);
1547 BonusInst->setName(BonusInst->getName()+".old");
1550 // Clone Cond into the predecessor basic block, and or/and the
1551 // two conditions together.
1552 Instruction *New = Cond->clone();
1553 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1554 PredBlock->getInstList().insert(PBI, New);
1555 New->takeName(Cond);
1556 Cond->setName(New->getName()+".old");
1558 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1559 New, "or.cond", PBI);
1560 PBI->setCondition(NewCond);
1561 if (PBI->getSuccessor(0) == BB) {
1562 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1563 PBI->setSuccessor(0, TrueDest);
1565 if (PBI->getSuccessor(1) == BB) {
1566 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1567 PBI->setSuccessor(1, FalseDest);
1574 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1575 /// predecessor of another block, this function tries to simplify it. We know
1576 /// that PBI and BI are both conditional branches, and BI is in one of the
1577 /// successor blocks of PBI - PBI branches to BI.
1578 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1579 assert(PBI->isConditional() && BI->isConditional());
1580 BasicBlock *BB = BI->getParent();
1582 // If this block ends with a branch instruction, and if there is a
1583 // predecessor that ends on a branch of the same condition, make
1584 // this conditional branch redundant.
1585 if (PBI->getCondition() == BI->getCondition() &&
1586 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1587 // Okay, the outcome of this conditional branch is statically
1588 // knowable. If this block had a single pred, handle specially.
1589 if (BB->getSinglePredecessor()) {
1590 // Turn this into a branch on constant.
1591 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1592 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1594 return true; // Nuke the branch on constant.
1597 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1598 // in the constant and simplify the block result. Subsequent passes of
1599 // simplifycfg will thread the block.
1600 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1601 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1602 BI->getCondition()->getName() + ".pr",
1604 // Okay, we're going to insert the PHI node. Since PBI is not the only
1605 // predecessor, compute the PHI'd conditional value for all of the preds.
1606 // Any predecessor where the condition is not computable we keep symbolic.
1607 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1608 BasicBlock *P = *PI;
1609 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
1610 PBI != BI && PBI->isConditional() &&
1611 PBI->getCondition() == BI->getCondition() &&
1612 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1613 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1614 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1617 NewPN->addIncoming(BI->getCondition(), P);
1621 BI->setCondition(NewPN);
1626 // If this is a conditional branch in an empty block, and if any
1627 // predecessors is a conditional branch to one of our destinations,
1628 // fold the conditions into logical ops and one cond br.
1629 BasicBlock::iterator BBI = BB->begin();
1630 // Ignore dbg intrinsics.
1631 while (isa<DbgInfoIntrinsic>(BBI))
1637 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1642 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1644 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1645 PBIOp = 0, BIOp = 1;
1646 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1647 PBIOp = 1, BIOp = 0;
1648 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1653 // Check to make sure that the other destination of this branch
1654 // isn't BB itself. If so, this is an infinite loop that will
1655 // keep getting unwound.
1656 if (PBI->getSuccessor(PBIOp) == BB)
1659 // Do not perform this transformation if it would require
1660 // insertion of a large number of select instructions. For targets
1661 // without predication/cmovs, this is a big pessimization.
1662 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1664 unsigned NumPhis = 0;
1665 for (BasicBlock::iterator II = CommonDest->begin();
1666 isa<PHINode>(II); ++II, ++NumPhis)
1667 if (NumPhis > 2) // Disable this xform.
1670 // Finally, if everything is ok, fold the branches to logical ops.
1671 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1673 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
1674 << "AND: " << *BI->getParent());
1677 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1678 // branch in it, where one edge (OtherDest) goes back to itself but the other
1679 // exits. We don't *know* that the program avoids the infinite loop
1680 // (even though that seems likely). If we do this xform naively, we'll end up
1681 // recursively unpeeling the loop. Since we know that (after the xform is
1682 // done) that the block *is* infinite if reached, we just make it an obviously
1683 // infinite loop with no cond branch.
1684 if (OtherDest == BB) {
1685 // Insert it at the end of the function, because it's either code,
1686 // or it won't matter if it's hot. :)
1687 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1688 "infloop", BB->getParent());
1689 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1690 OtherDest = InfLoopBlock;
1693 DEBUG(dbgs() << *PBI->getParent()->getParent());
1695 // BI may have other predecessors. Because of this, we leave
1696 // it alone, but modify PBI.
1698 // Make sure we get to CommonDest on True&True directions.
1699 Value *PBICond = PBI->getCondition();
1701 PBICond = BinaryOperator::CreateNot(PBICond,
1702 PBICond->getName()+".not",
1704 Value *BICond = BI->getCondition();
1706 BICond = BinaryOperator::CreateNot(BICond,
1707 BICond->getName()+".not",
1709 // Merge the conditions.
1710 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1712 // Modify PBI to branch on the new condition to the new dests.
1713 PBI->setCondition(Cond);
1714 PBI->setSuccessor(0, CommonDest);
1715 PBI->setSuccessor(1, OtherDest);
1717 // OtherDest may have phi nodes. If so, add an entry from PBI's
1718 // block that are identical to the entries for BI's block.
1719 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
1721 // We know that the CommonDest already had an edge from PBI to
1722 // it. If it has PHIs though, the PHIs may have different
1723 // entries for BB and PBI's BB. If so, insert a select to make
1726 for (BasicBlock::iterator II = CommonDest->begin();
1727 (PN = dyn_cast<PHINode>(II)); ++II) {
1728 Value *BIV = PN->getIncomingValueForBlock(BB);
1729 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1730 Value *PBIV = PN->getIncomingValue(PBBIdx);
1732 // Insert a select in PBI to pick the right value.
1733 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1734 PBIV->getName()+".mux", PBI);
1735 PN->setIncomingValue(PBBIdx, NV);
1739 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1740 DEBUG(dbgs() << *PBI->getParent()->getParent());
1742 // This basic block is probably dead. We know it has at least
1743 // one fewer predecessor.
1747 // SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
1748 // branch to TrueBB if Cond is true or to FalseBB if Cond is false.
1749 // Takes care of updating the successors and removing the old terminator.
1750 // Also makes sure not to introduce new successors by assuming that edges to
1751 // non-successor TrueBBs and FalseBBs aren't reachable.
1752 static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
1753 BasicBlock *TrueBB, BasicBlock *FalseBB){
1754 // Remove any superfluous successor edges from the CFG.
1755 // First, figure out which successors to preserve.
1756 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
1758 BasicBlock *KeepEdge1 = TrueBB;
1759 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
1761 // Then remove the rest.
1762 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
1763 BasicBlock *Succ = OldTerm->getSuccessor(I);
1764 // Make sure only to keep exactly one copy of each edge.
1765 if (Succ == KeepEdge1)
1767 else if (Succ == KeepEdge2)
1770 Succ->removePredecessor(OldTerm->getParent());
1773 // Insert an appropriate new terminator.
1774 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
1775 if (TrueBB == FalseBB)
1776 // We were only looking for one successor, and it was present.
1777 // Create an unconditional branch to it.
1778 BranchInst::Create(TrueBB, OldTerm);
1780 // We found both of the successors we were looking for.
1781 // Create a conditional branch sharing the condition of the select.
1782 BranchInst::Create(TrueBB, FalseBB, Cond, OldTerm);
1783 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
1784 // Neither of the selected blocks were successors, so this
1785 // terminator must be unreachable.
1786 new UnreachableInst(OldTerm->getContext(), OldTerm);
1788 // One of the selected values was a successor, but the other wasn't.
1789 // Insert an unconditional branch to the one that was found;
1790 // the edge to the one that wasn't must be unreachable.
1792 // Only TrueBB was found.
1793 BranchInst::Create(TrueBB, OldTerm);
1795 // Only FalseBB was found.
1796 BranchInst::Create(FalseBB, OldTerm);
1799 EraseTerminatorInstAndDCECond(OldTerm);
1803 // SimplifyIndirectBrOnSelect - Replaces
1804 // (indirectbr (select cond, blockaddress(@fn, BlockA),
1805 // blockaddress(@fn, BlockB)))
1807 // (br cond, BlockA, BlockB).
1808 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
1809 // Check that both operands of the select are block addresses.
1810 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
1811 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
1815 // Extract the actual blocks.
1816 BasicBlock *TrueBB = TBA->getBasicBlock();
1817 BasicBlock *FalseBB = FBA->getBasicBlock();
1819 // Perform the actual simplification.
1820 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB);
1823 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
1824 /// instruction (a seteq/setne with a constant) as the only instruction in a
1825 /// block that ends with an uncond branch. We are looking for a very specific
1826 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
1827 /// this case, we merge the first two "or's of icmp" into a switch, but then the
1828 /// default value goes to an uncond block with a seteq in it, we get something
1831 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
1833 /// %tmp = icmp eq i8 %A, 92
1836 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
1838 /// We prefer to split the edge to 'end' so that there is a true/false entry to
1839 /// the PHI, merging the third icmp into the switch.
1840 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
1841 const TargetData *TD) {
1842 BasicBlock *BB = ICI->getParent();
1843 // If the block has any PHIs in it or the icmp has multiple uses, it is too
1845 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
1847 Value *V = ICI->getOperand(0);
1848 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
1850 // The pattern we're looking for is where our only predecessor is a switch on
1851 // 'V' and this block is the default case for the switch. In this case we can
1852 // fold the compared value into the switch to simplify things.
1853 BasicBlock *Pred = BB->getSinglePredecessor();
1854 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
1856 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
1857 if (SI->getCondition() != V)
1860 // If BB is reachable on a non-default case, then we simply know the value of
1861 // V in this block. Substitute it and constant fold the icmp instruction
1863 if (SI->getDefaultDest() != BB) {
1864 ConstantInt *VVal = SI->findCaseDest(BB);
1865 assert(VVal && "Should have a unique destination value");
1866 ICI->setOperand(0, VVal);
1868 if (Value *V = SimplifyInstruction(ICI, TD)) {
1869 ICI->replaceAllUsesWith(V);
1870 ICI->eraseFromParent();
1872 // BB is now empty, so it is likely to simplify away.
1873 return SimplifyCFG(BB) | true;
1876 // Ok, the block is reachable from the default dest. If the constant we're
1877 // comparing exists in one of the other edges, then we can constant fold ICI
1879 if (SI->findCaseValue(Cst) != 0) {
1881 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1882 V = ConstantInt::getFalse(BB->getContext());
1884 V = ConstantInt::getTrue(BB->getContext());
1886 ICI->replaceAllUsesWith(V);
1887 ICI->eraseFromParent();
1888 // BB is now empty, so it is likely to simplify away.
1889 return SimplifyCFG(BB) | true;
1892 // The use of the icmp has to be in the 'end' block, by the only PHI node in
1894 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
1895 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
1896 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
1897 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
1900 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
1902 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
1903 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
1905 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1906 std::swap(DefaultCst, NewCst);
1908 // Replace ICI (which is used by the PHI for the default value) with true or
1909 // false depending on if it is EQ or NE.
1910 ICI->replaceAllUsesWith(DefaultCst);
1911 ICI->eraseFromParent();
1913 // Okay, the switch goes to this block on a default value. Add an edge from
1914 // the switch to the merge point on the compared value.
1915 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
1916 BB->getParent(), BB);
1917 SI->addCase(Cst, NewBB);
1919 // NewBB branches to the phi block, add the uncond branch and the phi entry.
1920 BranchInst::Create(SuccBlock, NewBB);
1921 PHIUse->addIncoming(NewCst, NewBB);
1925 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
1926 /// Check to see if it is branching on an or/and chain of icmp instructions, and
1927 /// fold it into a switch instruction if so.
1928 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD) {
1929 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1930 if (Cond == 0) return false;
1933 // Change br (X == 0 | X == 1), T, F into a switch instruction.
1934 // If this is a bunch of seteq's or'd together, or if it's a bunch of
1935 // 'setne's and'ed together, collect them.
1937 std::vector<ConstantInt*> Values;
1938 bool TrueWhenEqual = true;
1939 Value *ExtraCase = 0;
1940 unsigned UsedICmps = 0;
1942 if (Cond->getOpcode() == Instruction::Or) {
1943 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
1945 } else if (Cond->getOpcode() == Instruction::And) {
1946 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
1948 TrueWhenEqual = false;
1951 // If we didn't have a multiply compared value, fail.
1952 if (CompVal == 0) return false;
1954 // Avoid turning single icmps into a switch.
1958 // There might be duplicate constants in the list, which the switch
1959 // instruction can't handle, remove them now.
1960 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
1961 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
1963 // If Extra was used, we require at least two switch values to do the
1964 // transformation. A switch with one value is just an cond branch.
1965 if (ExtraCase && Values.size() < 2) return false;
1967 // Figure out which block is which destination.
1968 BasicBlock *DefaultBB = BI->getSuccessor(1);
1969 BasicBlock *EdgeBB = BI->getSuccessor(0);
1970 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
1972 BasicBlock *BB = BI->getParent();
1974 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
1975 << " cases into SWITCH. BB is:\n" << *BB);
1977 // If there are any extra values that couldn't be folded into the switch
1978 // then we evaluate them with an explicit branch first. Split the block
1979 // right before the condbr to handle it.
1981 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
1982 // Remove the uncond branch added to the old block.
1983 TerminatorInst *OldTI = BB->getTerminator();
1986 BranchInst::Create(EdgeBB, NewBB, ExtraCase, OldTI);
1988 BranchInst::Create(NewBB, EdgeBB, ExtraCase, OldTI);
1990 OldTI->eraseFromParent();
1992 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
1993 // for the edge we just added.
1994 AddPredecessorToBlock(EdgeBB, BB, NewBB);
1996 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
1997 << "\nEXTRABB = " << *BB);
2001 // Convert pointer to int before we switch.
2002 if (CompVal->getType()->isPointerTy()) {
2003 assert(TD && "Cannot switch on pointer without TargetData");
2004 CompVal = new PtrToIntInst(CompVal,
2005 TD->getIntPtrType(CompVal->getContext()),
2009 // Create the new switch instruction now.
2010 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB, Values.size(), BI);
2012 // Add all of the 'cases' to the switch instruction.
2013 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2014 New->addCase(Values[i], EdgeBB);
2016 // We added edges from PI to the EdgeBB. As such, if there were any
2017 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2018 // the number of edges added.
2019 for (BasicBlock::iterator BBI = EdgeBB->begin();
2020 isa<PHINode>(BBI); ++BBI) {
2021 PHINode *PN = cast<PHINode>(BBI);
2022 Value *InVal = PN->getIncomingValueForBlock(BB);
2023 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2024 PN->addIncoming(InVal, BB);
2027 // Erase the old branch instruction.
2028 EraseTerminatorInstAndDCECond(BI);
2030 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
2034 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI) {
2035 BasicBlock *BB = RI->getParent();
2036 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2038 // Find predecessors that end with branches.
2039 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2040 SmallVector<BranchInst*, 8> CondBranchPreds;
2041 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2042 BasicBlock *P = *PI;
2043 TerminatorInst *PTI = P->getTerminator();
2044 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2045 if (BI->isUnconditional())
2046 UncondBranchPreds.push_back(P);
2048 CondBranchPreds.push_back(BI);
2052 // If we found some, do the transformation!
2053 if (!UncondBranchPreds.empty() && DupRet) {
2054 while (!UncondBranchPreds.empty()) {
2055 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2056 DEBUG(dbgs() << "FOLDING: " << *BB
2057 << "INTO UNCOND BRANCH PRED: " << *Pred);
2058 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
2061 // If we eliminated all predecessors of the block, delete the block now.
2062 if (pred_begin(BB) == pred_end(BB))
2063 // We know there are no successors, so just nuke the block.
2064 BB->eraseFromParent();
2069 // Check out all of the conditional branches going to this return
2070 // instruction. If any of them just select between returns, change the
2071 // branch itself into a select/return pair.
2072 while (!CondBranchPreds.empty()) {
2073 BranchInst *BI = CondBranchPreds.pop_back_val();
2075 // Check to see if the non-BB successor is also a return block.
2076 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2077 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2078 SimplifyCondBranchToTwoReturns(BI))
2084 bool SimplifyCFGOpt::SimplifyUnwind(UnwindInst *UI) {
2085 // Check to see if the first instruction in this block is just an unwind.
2086 // If so, replace any invoke instructions which use this as an exception
2087 // destination with call instructions.
2088 BasicBlock *BB = UI->getParent();
2089 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2091 bool Changed = false;
2092 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2093 while (!Preds.empty()) {
2094 BasicBlock *Pred = Preds.back();
2095 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
2096 if (II && II->getUnwindDest() == BB) {
2097 // Insert a new branch instruction before the invoke, because this
2098 // is now a fall through.
2099 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2100 Pred->getInstList().remove(II); // Take out of symbol table
2102 // Insert the call now.
2103 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
2104 CallInst *CI = CallInst::Create(II->getCalledValue(),
2105 Args.begin(), Args.end(),
2107 CI->setCallingConv(II->getCallingConv());
2108 CI->setAttributes(II->getAttributes());
2109 // If the invoke produced a value, the Call now does instead.
2110 II->replaceAllUsesWith(CI);
2118 // If this block is now dead (and isn't the entry block), remove it.
2119 if (pred_begin(BB) == pred_end(BB) &&
2120 BB != &BB->getParent()->getEntryBlock()) {
2121 // We know there are no successors, so just nuke the block.
2122 BB->eraseFromParent();
2129 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2130 BasicBlock *BB = UI->getParent();
2132 bool Changed = false;
2134 // If there are any instructions immediately before the unreachable that can
2135 // be removed, do so.
2136 while (UI != BB->begin()) {
2137 BasicBlock::iterator BBI = UI;
2139 // Do not delete instructions that can have side effects, like calls
2140 // (which may never return) and volatile loads and stores.
2141 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2143 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
2144 if (SI->isVolatile())
2147 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
2148 if (LI->isVolatile())
2151 // Delete this instruction
2152 BBI->eraseFromParent();
2156 // If the unreachable instruction is the first in the block, take a gander
2157 // at all of the predecessors of this instruction, and simplify them.
2158 if (&BB->front() != UI) return Changed;
2160 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2161 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2162 TerminatorInst *TI = Preds[i]->getTerminator();
2164 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2165 if (BI->isUnconditional()) {
2166 if (BI->getSuccessor(0) == BB) {
2167 new UnreachableInst(TI->getContext(), TI);
2168 TI->eraseFromParent();
2172 if (BI->getSuccessor(0) == BB) {
2173 BranchInst::Create(BI->getSuccessor(1), BI);
2174 EraseTerminatorInstAndDCECond(BI);
2175 } else if (BI->getSuccessor(1) == BB) {
2176 BranchInst::Create(BI->getSuccessor(0), BI);
2177 EraseTerminatorInstAndDCECond(BI);
2181 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2182 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2183 if (SI->getSuccessor(i) == BB) {
2184 BB->removePredecessor(SI->getParent());
2189 // If the default value is unreachable, figure out the most popular
2190 // destination and make it the default.
2191 if (SI->getSuccessor(0) == BB) {
2192 std::map<BasicBlock*, unsigned> Popularity;
2193 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2194 Popularity[SI->getSuccessor(i)]++;
2196 // Find the most popular block.
2197 unsigned MaxPop = 0;
2198 BasicBlock *MaxBlock = 0;
2199 for (std::map<BasicBlock*, unsigned>::iterator
2200 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2201 if (I->second > MaxPop) {
2203 MaxBlock = I->first;
2207 // Make this the new default, allowing us to delete any explicit
2209 SI->setSuccessor(0, MaxBlock);
2212 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2214 if (isa<PHINode>(MaxBlock->begin()))
2215 for (unsigned i = 0; i != MaxPop-1; ++i)
2216 MaxBlock->removePredecessor(SI->getParent());
2218 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2219 if (SI->getSuccessor(i) == MaxBlock) {
2225 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2226 if (II->getUnwindDest() == BB) {
2227 // Convert the invoke to a call instruction. This would be a good
2228 // place to note that the call does not throw though.
2229 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2230 II->removeFromParent(); // Take out of symbol table
2232 // Insert the call now...
2233 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2234 CallInst *CI = CallInst::Create(II->getCalledValue(),
2235 Args.begin(), Args.end(),
2237 CI->setCallingConv(II->getCallingConv());
2238 CI->setAttributes(II->getAttributes());
2239 // If the invoke produced a value, the call does now instead.
2240 II->replaceAllUsesWith(CI);
2247 // If this block is now dead, remove it.
2248 if (pred_begin(BB) == pred_end(BB) &&
2249 BB != &BB->getParent()->getEntryBlock()) {
2250 // We know there are no successors, so just nuke the block.
2251 BB->eraseFromParent();
2258 /// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
2259 /// integer range comparison into a sub, an icmp and a branch.
2260 static bool TurnSwitchRangeIntoICmp(SwitchInst *SI) {
2261 assert(SI->getNumCases() > 2 && "Degenerate switch?");
2263 // Make sure all cases point to the same destination and gather the values.
2264 SmallVector<ConstantInt *, 16> Cases;
2265 Cases.push_back(SI->getCaseValue(1));
2266 for (unsigned I = 2, E = SI->getNumCases(); I != E; ++I) {
2267 if (SI->getSuccessor(I-1) != SI->getSuccessor(I))
2269 Cases.push_back(SI->getCaseValue(I));
2271 assert(Cases.size() == SI->getNumCases()-1 && "Not all cases gathered");
2273 // Sort the case values, then check if they form a range we can transform.
2274 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
2275 for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
2276 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
2280 Constant *Offset = ConstantExpr::getNeg(Cases.back());
2281 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases()-1);
2283 Value *Sub = SI->getCondition();
2284 if (!Offset->isNullValue())
2285 Sub = BinaryOperator::CreateAdd(Sub, Offset, Sub->getName()+".off", SI);
2286 Value *Cmp = new ICmpInst(SI, ICmpInst::ICMP_ULT, Sub, NumCases, "switch");
2287 BranchInst::Create(SI->getSuccessor(1), SI->getDefaultDest(), Cmp, SI);
2289 // Prune obsolete incoming values off the successor's PHI nodes.
2290 for (BasicBlock::iterator BBI = SI->getSuccessor(1)->begin();
2291 isa<PHINode>(BBI); ++BBI) {
2292 for (unsigned I = 0, E = SI->getNumCases()-2; I != E; ++I)
2293 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
2295 SI->eraseFromParent();
2300 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI) {
2301 // If this switch is too complex to want to look at, ignore it.
2302 if (!isValueEqualityComparison(SI))
2305 BasicBlock *BB = SI->getParent();
2307 // If we only have one predecessor, and if it is a branch on this value,
2308 // see if that predecessor totally determines the outcome of this switch.
2309 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2310 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
2311 return SimplifyCFG(BB) | true;
2313 // If the block only contains the switch, see if we can fold the block
2314 // away into any preds.
2315 BasicBlock::iterator BBI = BB->begin();
2316 // Ignore dbg intrinsics.
2317 while (isa<DbgInfoIntrinsic>(BBI))
2320 if (FoldValueComparisonIntoPredecessors(SI))
2321 return SimplifyCFG(BB) | true;
2323 // Try to transform the switch into an icmp and a branch.
2324 if (TurnSwitchRangeIntoICmp(SI))
2325 return SimplifyCFG(BB) | true;
2330 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
2331 BasicBlock *BB = IBI->getParent();
2332 bool Changed = false;
2334 // Eliminate redundant destinations.
2335 SmallPtrSet<Value *, 8> Succs;
2336 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2337 BasicBlock *Dest = IBI->getDestination(i);
2338 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2339 Dest->removePredecessor(BB);
2340 IBI->removeDestination(i);
2346 if (IBI->getNumDestinations() == 0) {
2347 // If the indirectbr has no successors, change it to unreachable.
2348 new UnreachableInst(IBI->getContext(), IBI);
2349 EraseTerminatorInstAndDCECond(IBI);
2353 if (IBI->getNumDestinations() == 1) {
2354 // If the indirectbr has one successor, change it to a direct branch.
2355 BranchInst::Create(IBI->getDestination(0), IBI);
2356 EraseTerminatorInstAndDCECond(IBI);
2360 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2361 if (SimplifyIndirectBrOnSelect(IBI, SI))
2362 return SimplifyCFG(BB) | true;
2367 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI) {
2368 BasicBlock *BB = BI->getParent();
2370 // If the Terminator is the only non-phi instruction, simplify the block.
2371 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg();
2372 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
2373 TryToSimplifyUncondBranchFromEmptyBlock(BB))
2376 // If the only instruction in the block is a seteq/setne comparison
2377 // against a constant, try to simplify the block.
2378 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
2379 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
2380 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
2382 if (I->isTerminator() && TryToSimplifyUncondBranchWithICmpInIt(ICI, TD))
2390 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI) {
2391 BasicBlock *BB = BI->getParent();
2393 // Conditional branch
2394 if (isValueEqualityComparison(BI)) {
2395 // If we only have one predecessor, and if it is a branch on this value,
2396 // see if that predecessor totally determines the outcome of this
2398 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2399 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
2400 return SimplifyCFG(BB) | true;
2402 // This block must be empty, except for the setcond inst, if it exists.
2403 // Ignore dbg intrinsics.
2404 BasicBlock::iterator I = BB->begin();
2405 // Ignore dbg intrinsics.
2406 while (isa<DbgInfoIntrinsic>(I))
2409 if (FoldValueComparisonIntoPredecessors(BI))
2410 return SimplifyCFG(BB) | true;
2411 } else if (&*I == cast<Instruction>(BI->getCondition())){
2413 // Ignore dbg intrinsics.
2414 while (isa<DbgInfoIntrinsic>(I))
2416 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI))
2417 return SimplifyCFG(BB) | true;
2421 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
2422 if (SimplifyBranchOnICmpChain(BI, TD))
2425 // We have a conditional branch to two blocks that are only reachable
2426 // from BI. We know that the condbr dominates the two blocks, so see if
2427 // there is any identical code in the "then" and "else" blocks. If so, we
2428 // can hoist it up to the branching block.
2429 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
2430 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2431 if (HoistThenElseCodeToIf(BI))
2432 return SimplifyCFG(BB) | true;
2434 // If Successor #1 has multiple preds, we may be able to conditionally
2435 // execute Successor #0 if it branches to successor #1.
2436 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
2437 if (Succ0TI->getNumSuccessors() == 1 &&
2438 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
2439 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
2440 return SimplifyCFG(BB) | true;
2442 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2443 // If Successor #0 has multiple preds, we may be able to conditionally
2444 // execute Successor #1 if it branches to successor #0.
2445 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
2446 if (Succ1TI->getNumSuccessors() == 1 &&
2447 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
2448 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
2449 return SimplifyCFG(BB) | true;
2452 // If this is a branch on a phi node in the current block, thread control
2453 // through this block if any PHI node entries are constants.
2454 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
2455 if (PN->getParent() == BI->getParent())
2456 if (FoldCondBranchOnPHI(BI, TD))
2457 return SimplifyCFG(BB) | true;
2459 // If this basic block is ONLY a setcc and a branch, and if a predecessor
2460 // branches to us and one of our successors, fold the setcc into the
2461 // predecessor and use logical operations to pick the right destination.
2462 if (FoldBranchToCommonDest(BI))
2463 return SimplifyCFG(BB) | true;
2465 // Scan predecessor blocks for conditional branches.
2466 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2467 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2468 if (PBI != BI && PBI->isConditional())
2469 if (SimplifyCondBranchToCondBranch(PBI, BI))
2470 return SimplifyCFG(BB) | true;
2475 bool SimplifyCFGOpt::run(BasicBlock *BB) {
2476 bool Changed = false;
2478 assert(BB && BB->getParent() && "Block not embedded in function!");
2479 assert(BB->getTerminator() && "Degenerate basic block encountered!");
2481 // Remove basic blocks that have no predecessors (except the entry block)...
2482 // or that just have themself as a predecessor. These are unreachable.
2483 if ((pred_begin(BB) == pred_end(BB) &&
2484 BB != &BB->getParent()->getEntryBlock()) ||
2485 BB->getSinglePredecessor() == BB) {
2486 DEBUG(dbgs() << "Removing BB: \n" << *BB);
2487 DeleteDeadBlock(BB);
2491 // Check to see if we can constant propagate this terminator instruction
2493 Changed |= ConstantFoldTerminator(BB);
2495 // Check for and eliminate duplicate PHI nodes in this block.
2496 Changed |= EliminateDuplicatePHINodes(BB);
2498 // Merge basic blocks into their predecessor if there is only one distinct
2499 // pred, and if there is only one distinct successor of the predecessor, and
2500 // if there are no PHI nodes.
2502 if (MergeBlockIntoPredecessor(BB))
2505 // If there is a trivial two-entry PHI node in this basic block, and we can
2506 // eliminate it, do so now.
2507 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
2508 if (PN->getNumIncomingValues() == 2)
2509 Changed |= FoldTwoEntryPHINode(PN, TD);
2511 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
2512 if (BI->isUnconditional()) {
2513 if (SimplifyUncondBranch(BI)) return true;
2515 if (SimplifyCondBranch(BI)) return true;
2517 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
2518 if (SimplifyReturn(RI)) return true;
2519 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
2520 if (SimplifySwitch(SI)) return true;
2521 } else if (UnreachableInst *UI =
2522 dyn_cast<UnreachableInst>(BB->getTerminator())) {
2523 if (SimplifyUnreachable(UI)) return true;
2524 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
2525 if (SimplifyUnwind(UI)) return true;
2526 } else if (IndirectBrInst *IBI =
2527 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
2528 if (SimplifyIndirectBr(IBI)) return true;
2534 /// SimplifyCFG - This function is used to do simplification of a CFG. For
2535 /// example, it adjusts branches to branches to eliminate the extra hop, it
2536 /// eliminates unreachable basic blocks, and does other "peephole" optimization
2537 /// of the CFG. It returns true if a modification was made.
2539 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
2540 return SimplifyCFGOpt(TD).run(BB);