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 case Instruction::Trunc:
265 case Instruction::ZExt:
266 case Instruction::SExt:
267 break; // These are all cheap and non-trapping instructions.
270 // Okay, we can only really hoist these out if their operands are not
271 // defined in the conditional region.
272 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
273 if (!DominatesMergePoint(*i, BB, 0))
275 // Okay, it's safe to do this! Remember this instruction.
276 AggressiveInsts->insert(I);
280 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
281 /// and PointerNullValue. Return NULL if value is not a constant int.
282 static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
283 // Normal constant int.
284 ConstantInt *CI = dyn_cast<ConstantInt>(V);
285 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
288 // This is some kind of pointer constant. Turn it into a pointer-sized
289 // ConstantInt if possible.
290 const IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
292 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
293 if (isa<ConstantPointerNull>(V))
294 return ConstantInt::get(PtrTy, 0);
296 // IntToPtr const int.
297 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
298 if (CE->getOpcode() == Instruction::IntToPtr)
299 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
300 // The constant is very likely to have the right type already.
301 if (CI->getType() == PtrTy)
304 return cast<ConstantInt>
305 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
310 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
311 /// collection of icmp eq/ne instructions that compare a value against a
312 /// constant, return the value being compared, and stick the constant into the
315 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
316 const TargetData *TD, bool isEQ, unsigned &UsedICmps) {
317 Instruction *I = dyn_cast<Instruction>(V);
318 if (I == 0) return 0;
320 // If this is an icmp against a constant, handle this as one of the cases.
321 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
322 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
323 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
326 return I->getOperand(0);
329 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
332 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
334 // If this is an and/!= check then we want to optimize "x ugt 2" into
337 Span = Span.inverse();
339 // If there are a ton of values, we don't want to make a ginormous switch.
340 if (Span.getSetSize().ugt(8) || Span.isEmptySet() ||
341 // We don't handle wrapped sets yet.
345 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
346 Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
348 return I->getOperand(0);
353 // Otherwise, we can only handle an | or &, depending on isEQ.
354 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
357 unsigned NumValsBeforeLHS = Vals.size();
358 unsigned UsedICmpsBeforeLHS = UsedICmps;
359 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
361 unsigned NumVals = Vals.size();
362 unsigned UsedICmpsBeforeRHS = UsedICmps;
363 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
367 Vals.resize(NumVals);
368 UsedICmps = UsedICmpsBeforeRHS;
371 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
372 // set it and return success.
373 if (Extra == 0 || Extra == I->getOperand(1)) {
374 Extra = I->getOperand(1);
378 Vals.resize(NumValsBeforeLHS);
379 UsedICmps = UsedICmpsBeforeLHS;
383 // If the LHS can't be folded in, but Extra is available and RHS can, try to
385 if (Extra == 0 || Extra == I->getOperand(0)) {
386 Value *OldExtra = Extra;
387 Extra = I->getOperand(0);
388 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
391 assert(Vals.size() == NumValsBeforeLHS);
398 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
399 Instruction* Cond = 0;
400 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
401 Cond = dyn_cast<Instruction>(SI->getCondition());
402 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
403 if (BI->isConditional())
404 Cond = dyn_cast<Instruction>(BI->getCondition());
405 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
406 Cond = dyn_cast<Instruction>(IBI->getAddress());
409 TI->eraseFromParent();
410 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
413 /// isValueEqualityComparison - Return true if the specified terminator checks
414 /// to see if a value is equal to constant integer value.
415 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
417 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
418 // Do not permit merging of large switch instructions into their
419 // predecessors unless there is only one predecessor.
420 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
421 pred_end(SI->getParent())) <= 128)
422 CV = SI->getCondition();
423 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
424 if (BI->isConditional() && BI->getCondition()->hasOneUse())
425 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
426 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
427 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
428 GetConstantInt(ICI->getOperand(1), TD))
429 CV = ICI->getOperand(0);
431 // Unwrap any lossless ptrtoint cast.
432 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
433 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
434 CV = PTII->getOperand(0);
438 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
439 /// decode all of the 'cases' that it represents and return the 'default' block.
440 BasicBlock *SimplifyCFGOpt::
441 GetValueEqualityComparisonCases(TerminatorInst *TI,
442 std::vector<std::pair<ConstantInt*,
443 BasicBlock*> > &Cases) {
444 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
445 Cases.reserve(SI->getNumCases());
446 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
447 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
448 return SI->getDefaultDest();
451 BranchInst *BI = cast<BranchInst>(TI);
452 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
453 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD),
454 BI->getSuccessor(ICI->getPredicate() ==
455 ICmpInst::ICMP_NE)));
456 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
460 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
461 /// in the list that match the specified block.
462 static void EliminateBlockCases(BasicBlock *BB,
463 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
464 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
465 if (Cases[i].second == BB) {
466 Cases.erase(Cases.begin()+i);
471 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
474 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
475 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
476 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
478 // Make V1 be smaller than V2.
479 if (V1->size() > V2->size())
482 if (V1->size() == 0) return false;
483 if (V1->size() == 1) {
485 ConstantInt *TheVal = (*V1)[0].first;
486 for (unsigned i = 0, e = V2->size(); i != e; ++i)
487 if (TheVal == (*V2)[i].first)
491 // Otherwise, just sort both lists and compare element by element.
492 array_pod_sort(V1->begin(), V1->end());
493 array_pod_sort(V2->begin(), V2->end());
494 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
495 while (i1 != e1 && i2 != e2) {
496 if ((*V1)[i1].first == (*V2)[i2].first)
498 if ((*V1)[i1].first < (*V2)[i2].first)
506 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
507 /// terminator instruction and its block is known to only have a single
508 /// predecessor block, check to see if that predecessor is also a value
509 /// comparison with the same value, and if that comparison determines the
510 /// outcome of this comparison. If so, simplify TI. This does a very limited
511 /// form of jump threading.
512 bool SimplifyCFGOpt::
513 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
515 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
516 if (!PredVal) return false; // Not a value comparison in predecessor.
518 Value *ThisVal = isValueEqualityComparison(TI);
519 assert(ThisVal && "This isn't a value comparison!!");
520 if (ThisVal != PredVal) return false; // Different predicates.
522 // Find out information about when control will move from Pred to TI's block.
523 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
524 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
526 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
528 // Find information about how control leaves this block.
529 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
530 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
531 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
533 // If TI's block is the default block from Pred's comparison, potentially
534 // simplify TI based on this knowledge.
535 if (PredDef == TI->getParent()) {
536 // If we are here, we know that the value is none of those cases listed in
537 // PredCases. If there are any cases in ThisCases that are in PredCases, we
539 if (!ValuesOverlap(PredCases, ThisCases))
542 if (isa<BranchInst>(TI)) {
543 // Okay, one of the successors of this condbr is dead. Convert it to a
545 assert(ThisCases.size() == 1 && "Branch can only have one case!");
546 // Insert the new branch.
547 Instruction *NI = BranchInst::Create(ThisDef, TI);
550 // Remove PHI node entries for the dead edge.
551 ThisCases[0].second->removePredecessor(TI->getParent());
553 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
554 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
556 EraseTerminatorInstAndDCECond(TI);
560 SwitchInst *SI = cast<SwitchInst>(TI);
561 // Okay, TI has cases that are statically dead, prune them away.
562 SmallPtrSet<Constant*, 16> DeadCases;
563 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
564 DeadCases.insert(PredCases[i].first);
566 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
567 << "Through successor TI: " << *TI);
569 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
570 if (DeadCases.count(SI->getCaseValue(i))) {
571 SI->getSuccessor(i)->removePredecessor(TI->getParent());
575 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
579 // Otherwise, TI's block must correspond to some matched value. Find out
580 // which value (or set of values) this is.
581 ConstantInt *TIV = 0;
582 BasicBlock *TIBB = TI->getParent();
583 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
584 if (PredCases[i].second == TIBB) {
586 return false; // Cannot handle multiple values coming to this block.
587 TIV = PredCases[i].first;
589 assert(TIV && "No edge from pred to succ?");
591 // Okay, we found the one constant that our value can be if we get into TI's
592 // BB. Find out which successor will unconditionally be branched to.
593 BasicBlock *TheRealDest = 0;
594 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
595 if (ThisCases[i].first == TIV) {
596 TheRealDest = ThisCases[i].second;
600 // If not handled by any explicit cases, it is handled by the default case.
601 if (TheRealDest == 0) TheRealDest = ThisDef;
603 // Remove PHI node entries for dead edges.
604 BasicBlock *CheckEdge = TheRealDest;
605 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
606 if (*SI != CheckEdge)
607 (*SI)->removePredecessor(TIBB);
611 // Insert the new branch.
612 Instruction *NI = BranchInst::Create(TheRealDest, TI);
615 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
616 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
618 EraseTerminatorInstAndDCECond(TI);
623 /// ConstantIntOrdering - This class implements a stable ordering of constant
624 /// integers that does not depend on their address. This is important for
625 /// applications that sort ConstantInt's to ensure uniqueness.
626 struct ConstantIntOrdering {
627 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
628 return LHS->getValue().ult(RHS->getValue());
633 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
634 const ConstantInt *LHS = *(const ConstantInt**)P1;
635 const ConstantInt *RHS = *(const ConstantInt**)P2;
636 if (LHS->getValue().ult(RHS->getValue()))
638 if (LHS->getValue() == RHS->getValue())
643 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
644 /// equality comparison instruction (either a switch or a branch on "X == c").
645 /// See if any of the predecessors of the terminator block are value comparisons
646 /// on the same value. If so, and if safe to do so, fold them together.
647 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
648 BasicBlock *BB = TI->getParent();
649 Value *CV = isValueEqualityComparison(TI); // CondVal
650 assert(CV && "Not a comparison?");
651 bool Changed = false;
653 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
654 while (!Preds.empty()) {
655 BasicBlock *Pred = Preds.pop_back_val();
657 // See if the predecessor is a comparison with the same value.
658 TerminatorInst *PTI = Pred->getTerminator();
659 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
661 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
662 // Figure out which 'cases' to copy from SI to PSI.
663 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
664 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
666 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
667 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
669 // Based on whether the default edge from PTI goes to BB or not, fill in
670 // PredCases and PredDefault with the new switch cases we would like to
672 SmallVector<BasicBlock*, 8> NewSuccessors;
674 if (PredDefault == BB) {
675 // If this is the default destination from PTI, only the edges in TI
676 // that don't occur in PTI, or that branch to BB will be activated.
677 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
678 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
679 if (PredCases[i].second != BB)
680 PTIHandled.insert(PredCases[i].first);
682 // The default destination is BB, we don't need explicit targets.
683 std::swap(PredCases[i], PredCases.back());
684 PredCases.pop_back();
688 // Reconstruct the new switch statement we will be building.
689 if (PredDefault != BBDefault) {
690 PredDefault->removePredecessor(Pred);
691 PredDefault = BBDefault;
692 NewSuccessors.push_back(BBDefault);
694 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
695 if (!PTIHandled.count(BBCases[i].first) &&
696 BBCases[i].second != BBDefault) {
697 PredCases.push_back(BBCases[i]);
698 NewSuccessors.push_back(BBCases[i].second);
702 // If this is not the default destination from PSI, only the edges
703 // in SI that occur in PSI with a destination of BB will be
705 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
706 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
707 if (PredCases[i].second == BB) {
708 PTIHandled.insert(PredCases[i].first);
709 std::swap(PredCases[i], PredCases.back());
710 PredCases.pop_back();
714 // Okay, now we know which constants were sent to BB from the
715 // predecessor. Figure out where they will all go now.
716 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
717 if (PTIHandled.count(BBCases[i].first)) {
718 // If this is one we are capable of getting...
719 PredCases.push_back(BBCases[i]);
720 NewSuccessors.push_back(BBCases[i].second);
721 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
724 // If there are any constants vectored to BB that TI doesn't handle,
725 // they must go to the default destination of TI.
726 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
728 E = PTIHandled.end(); I != E; ++I) {
729 PredCases.push_back(std::make_pair(*I, BBDefault));
730 NewSuccessors.push_back(BBDefault);
734 // Okay, at this point, we know which new successor Pred will get. Make
735 // sure we update the number of entries in the PHI nodes for these
737 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
738 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
740 // Convert pointer to int before we switch.
741 if (CV->getType()->isPointerTy()) {
742 assert(TD && "Cannot switch on pointer without TargetData");
743 CV = new PtrToIntInst(CV, TD->getIntPtrType(CV->getContext()),
747 // Now that the successors are updated, create the new Switch instruction.
748 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
749 PredCases.size(), PTI);
750 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
751 NewSI->addCase(PredCases[i].first, PredCases[i].second);
753 EraseTerminatorInstAndDCECond(PTI);
755 // Okay, last check. If BB is still a successor of PSI, then we must
756 // have an infinite loop case. If so, add an infinitely looping block
757 // to handle the case to preserve the behavior of the code.
758 BasicBlock *InfLoopBlock = 0;
759 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
760 if (NewSI->getSuccessor(i) == BB) {
761 if (InfLoopBlock == 0) {
762 // Insert it at the end of the function, because it's either code,
763 // or it won't matter if it's hot. :)
764 InfLoopBlock = BasicBlock::Create(BB->getContext(),
765 "infloop", BB->getParent());
766 BranchInst::Create(InfLoopBlock, InfLoopBlock);
768 NewSI->setSuccessor(i, InfLoopBlock);
777 // isSafeToHoistInvoke - If we would need to insert a select that uses the
778 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
779 // would need to do this), we can't hoist the invoke, as there is nowhere
780 // to put the select in this case.
781 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
782 Instruction *I1, Instruction *I2) {
783 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
785 for (BasicBlock::iterator BBI = SI->begin();
786 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
787 Value *BB1V = PN->getIncomingValueForBlock(BB1);
788 Value *BB2V = PN->getIncomingValueForBlock(BB2);
789 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
797 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
798 /// BB2, hoist any common code in the two blocks up into the branch block. The
799 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
800 static bool HoistThenElseCodeToIf(BranchInst *BI) {
801 // This does very trivial matching, with limited scanning, to find identical
802 // instructions in the two blocks. In particular, we don't want to get into
803 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
804 // such, we currently just scan for obviously identical instructions in an
806 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
807 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
809 BasicBlock::iterator BB1_Itr = BB1->begin();
810 BasicBlock::iterator BB2_Itr = BB2->begin();
812 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
813 // Skip debug info if it is not identical.
814 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
815 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
816 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
817 while (isa<DbgInfoIntrinsic>(I1))
819 while (isa<DbgInfoIntrinsic>(I2))
822 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
823 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
826 // If we get here, we can hoist at least one instruction.
827 BasicBlock *BIParent = BI->getParent();
830 // If we are hoisting the terminator instruction, don't move one (making a
831 // broken BB), instead clone it, and remove BI.
832 if (isa<TerminatorInst>(I1))
833 goto HoistTerminator;
835 // For a normal instruction, we just move one to right before the branch,
836 // then replace all uses of the other with the first. Finally, we remove
837 // the now redundant second instruction.
838 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
839 if (!I2->use_empty())
840 I2->replaceAllUsesWith(I1);
841 I1->intersectOptionalDataWith(I2);
842 I2->eraseFromParent();
846 // Skip debug info if it is not identical.
847 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
848 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
849 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
850 while (isa<DbgInfoIntrinsic>(I1))
852 while (isa<DbgInfoIntrinsic>(I2))
855 } while (I1->isIdenticalToWhenDefined(I2));
860 // It may not be possible to hoist an invoke.
861 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
864 // Okay, it is safe to hoist the terminator.
865 Instruction *NT = I1->clone();
866 BIParent->getInstList().insert(BI, NT);
867 if (!NT->getType()->isVoidTy()) {
868 I1->replaceAllUsesWith(NT);
869 I2->replaceAllUsesWith(NT);
873 // Hoisting one of the terminators from our successor is a great thing.
874 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
875 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
876 // nodes, so we insert select instruction to compute the final result.
877 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
878 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
880 for (BasicBlock::iterator BBI = SI->begin();
881 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
882 Value *BB1V = PN->getIncomingValueForBlock(BB1);
883 Value *BB2V = PN->getIncomingValueForBlock(BB2);
884 if (BB1V == BB2V) continue;
886 // These values do not agree. Insert a select instruction before NT
887 // that determines the right value.
888 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
890 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
891 BB1V->getName()+"."+BB2V->getName(), NT);
892 // Make the PHI node use the select for all incoming values for BB1/BB2
893 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
894 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
895 PN->setIncomingValue(i, SI);
899 // Update any PHI nodes in our new successors.
900 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
901 AddPredecessorToBlock(*SI, BIParent, BB1);
903 EraseTerminatorInstAndDCECond(BI);
907 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
908 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
909 /// (for now, restricted to a single instruction that's side effect free) from
910 /// the BB1 into the branch block to speculatively execute it.
911 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
912 // Only speculatively execution a single instruction (not counting the
913 // terminator) for now.
914 Instruction *HInst = NULL;
915 Instruction *Term = BB1->getTerminator();
916 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
918 Instruction *I = BBI;
920 if (isa<DbgInfoIntrinsic>(I)) continue;
921 if (I == Term) break;
930 // Be conservative for now. FP select instruction can often be expensive.
931 Value *BrCond = BI->getCondition();
932 if (isa<FCmpInst>(BrCond))
935 // If BB1 is actually on the false edge of the conditional branch, remember
936 // to swap the select operands later.
938 if (BB1 != BI->getSuccessor(0)) {
939 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
946 // br i1 %t1, label %BB1, label %BB2
955 // %t3 = select i1 %t1, %t2, %t3
956 switch (HInst->getOpcode()) {
957 default: return false; // Not safe / profitable to hoist.
958 case Instruction::Add:
959 case Instruction::Sub:
960 // Not worth doing for vector ops.
961 if (HInst->getType()->isVectorTy())
964 case Instruction::And:
965 case Instruction::Or:
966 case Instruction::Xor:
967 case Instruction::Shl:
968 case Instruction::LShr:
969 case Instruction::AShr:
970 // Don't mess with vector operations.
971 if (HInst->getType()->isVectorTy())
973 break; // These are all cheap and non-trapping instructions.
976 // If the instruction is obviously dead, don't try to predicate it.
977 if (HInst->use_empty()) {
978 HInst->eraseFromParent();
982 // Can we speculatively execute the instruction? And what is the value
983 // if the condition is false? Consider the phi uses, if the incoming value
984 // from the "if" block are all the same V, then V is the value of the
985 // select if the condition is false.
986 BasicBlock *BIParent = BI->getParent();
987 SmallVector<PHINode*, 4> PHIUses;
988 Value *FalseV = NULL;
990 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
991 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
993 // Ignore any user that is not a PHI node in BB2. These can only occur in
994 // unreachable blocks, because they would not be dominated by the instr.
995 PHINode *PN = dyn_cast<PHINode>(*UI);
996 if (!PN || PN->getParent() != BB2)
998 PHIUses.push_back(PN);
1000 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1003 else if (FalseV != PHIV)
1004 return false; // Inconsistent value when condition is false.
1007 assert(FalseV && "Must have at least one user, and it must be a PHI");
1009 // Do not hoist the instruction if any of its operands are defined but not
1010 // used in this BB. The transformation will prevent the operand from
1011 // being sunk into the use block.
1012 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1014 Instruction *OpI = dyn_cast<Instruction>(*i);
1015 if (OpI && OpI->getParent() == BIParent &&
1016 !OpI->isUsedInBasicBlock(BIParent))
1020 // If we get here, we can hoist the instruction. Try to place it
1021 // before the icmp instruction preceding the conditional branch.
1022 BasicBlock::iterator InsertPos = BI;
1023 if (InsertPos != BIParent->begin())
1025 // Skip debug info between condition and branch.
1026 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
1028 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
1029 SmallPtrSet<Instruction *, 4> BB1Insns;
1030 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
1031 BB1I != BB1E; ++BB1I)
1032 BB1Insns.insert(BB1I);
1033 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
1035 Instruction *Use = cast<Instruction>(*UI);
1036 if (!BB1Insns.count(Use)) continue;
1038 // If BrCond uses the instruction that place it just before
1039 // branch instruction.
1045 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
1047 // Create a select whose true value is the speculatively executed value and
1048 // false value is the previously determined FalseV.
1051 SI = SelectInst::Create(BrCond, FalseV, HInst,
1052 FalseV->getName() + "." + HInst->getName(), BI);
1054 SI = SelectInst::Create(BrCond, HInst, FalseV,
1055 HInst->getName() + "." + FalseV->getName(), BI);
1057 // Make the PHI node use the select for all incoming values for "then" and
1059 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1060 PHINode *PN = PHIUses[i];
1061 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1062 if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent)
1063 PN->setIncomingValue(j, SI);
1070 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1071 /// across this block.
1072 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1073 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1076 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1077 if (isa<DbgInfoIntrinsic>(BBI))
1079 if (Size > 10) return false; // Don't clone large BB's.
1082 // We can only support instructions that do not define values that are
1083 // live outside of the current basic block.
1084 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1086 Instruction *U = cast<Instruction>(*UI);
1087 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1090 // Looks ok, continue checking.
1096 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1097 /// that is defined in the same block as the branch and if any PHI entries are
1098 /// constants, thread edges corresponding to that entry to be branches to their
1099 /// ultimate destination.
1100 static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
1101 BasicBlock *BB = BI->getParent();
1102 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1103 // NOTE: we currently cannot transform this case if the PHI node is used
1104 // outside of the block.
1105 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1108 // Degenerate case of a single entry PHI.
1109 if (PN->getNumIncomingValues() == 1) {
1110 FoldSingleEntryPHINodes(PN->getParent());
1114 // Now we know that this block has multiple preds and two succs.
1115 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1117 // Okay, this is a simple enough basic block. See if any phi values are
1119 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1120 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1121 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1123 // Okay, we now know that all edges from PredBB should be revectored to
1124 // branch to RealDest.
1125 BasicBlock *PredBB = PN->getIncomingBlock(i);
1126 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1128 if (RealDest == BB) continue; // Skip self loops.
1130 // The dest block might have PHI nodes, other predecessors and other
1131 // difficult cases. Instead of being smart about this, just insert a new
1132 // block that jumps to the destination block, effectively splitting
1133 // the edge we are about to create.
1134 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1135 RealDest->getName()+".critedge",
1136 RealDest->getParent(), RealDest);
1137 BranchInst::Create(RealDest, EdgeBB);
1139 // Update PHI nodes.
1140 AddPredecessorToBlock(RealDest, EdgeBB, BB);
1142 // BB may have instructions that are being threaded over. Clone these
1143 // instructions into EdgeBB. We know that there will be no uses of the
1144 // cloned instructions outside of EdgeBB.
1145 BasicBlock::iterator InsertPt = EdgeBB->begin();
1146 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1147 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1148 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1149 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1152 // Clone the instruction.
1153 Instruction *N = BBI->clone();
1154 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1156 // Update operands due to translation.
1157 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1159 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1160 if (PI != TranslateMap.end())
1164 // Check for trivial simplification.
1165 if (Value *V = SimplifyInstruction(N, TD)) {
1166 TranslateMap[BBI] = V;
1167 delete N; // Instruction folded away, don't need actual inst
1169 // Insert the new instruction into its new home.
1170 EdgeBB->getInstList().insert(InsertPt, N);
1171 if (!BBI->use_empty())
1172 TranslateMap[BBI] = N;
1176 // Loop over all of the edges from PredBB to BB, changing them to branch
1177 // to EdgeBB instead.
1178 TerminatorInst *PredBBTI = PredBB->getTerminator();
1179 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1180 if (PredBBTI->getSuccessor(i) == BB) {
1181 BB->removePredecessor(PredBB);
1182 PredBBTI->setSuccessor(i, EdgeBB);
1185 // Recurse, simplifying any other constants.
1186 return FoldCondBranchOnPHI(BI, TD) | true;
1192 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1193 /// PHI node, see if we can eliminate it.
1194 static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
1195 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1196 // statement", which has a very simple dominance structure. Basically, we
1197 // are trying to find the condition that is being branched on, which
1198 // subsequently causes this merge to happen. We really want control
1199 // dependence information for this check, but simplifycfg can't keep it up
1200 // to date, and this catches most of the cases we care about anyway.
1201 BasicBlock *BB = PN->getParent();
1202 BasicBlock *IfTrue, *IfFalse;
1203 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1205 // Don't bother if the branch will be constant folded trivially.
1206 isa<ConstantInt>(IfCond))
1209 // Okay, we found that we can merge this two-entry phi node into a select.
1210 // Doing so would require us to fold *all* two entry phi nodes in this block.
1211 // At some point this becomes non-profitable (particularly if the target
1212 // doesn't support cmov's). Only do this transformation if there are two or
1213 // fewer PHI nodes in this block.
1214 unsigned NumPhis = 0;
1215 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1219 // Loop over the PHI's seeing if we can promote them all to select
1220 // instructions. While we are at it, keep track of the instructions
1221 // that need to be moved to the dominating block.
1222 SmallPtrSet<Instruction*, 4> AggressiveInsts;
1224 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1225 PHINode *PN = cast<PHINode>(II++);
1226 if (Value *V = SimplifyInstruction(PN, TD)) {
1227 PN->replaceAllUsesWith(V);
1228 PN->eraseFromParent();
1232 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts) ||
1233 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts))
1237 // If we folded the the first phi, PN dangles at this point. Refresh it. If
1238 // we ran out of PHIs then we simplified them all.
1239 PN = dyn_cast<PHINode>(BB->begin());
1240 if (PN == 0) return true;
1242 // Don't fold i1 branches on PHIs which contain binary operators. These can
1243 // often be turned into switches and other things.
1244 if (PN->getType()->isIntegerTy(1) &&
1245 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1246 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1247 isa<BinaryOperator>(IfCond)))
1250 // If we all PHI nodes are promotable, check to make sure that all
1251 // instructions in the predecessor blocks can be promoted as well. If
1252 // not, we won't be able to get rid of the control flow, so it's not
1253 // worth promoting to select instructions.
1254 BasicBlock *DomBlock = 0;
1255 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1256 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1257 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1260 DomBlock = *pred_begin(IfBlock1);
1261 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1262 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1263 // This is not an aggressive instruction that we can promote.
1264 // Because of this, we won't be able to get rid of the control
1265 // flow, so the xform is not worth it.
1270 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1273 DomBlock = *pred_begin(IfBlock2);
1274 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1275 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1276 // This is not an aggressive instruction that we can promote.
1277 // Because of this, we won't be able to get rid of the control
1278 // flow, so the xform is not worth it.
1283 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1284 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1286 // If we can still promote the PHI nodes after this gauntlet of tests,
1287 // do all of the PHI's now.
1288 Instruction *InsertPt = DomBlock->getTerminator();
1290 // Move all 'aggressive' instructions, which are defined in the
1291 // conditional parts of the if's up to the dominating block.
1293 DomBlock->getInstList().splice(InsertPt,
1294 IfBlock1->getInstList(), IfBlock1->begin(),
1295 IfBlock1->getTerminator());
1297 DomBlock->getInstList().splice(InsertPt,
1298 IfBlock2->getInstList(), IfBlock2->begin(),
1299 IfBlock2->getTerminator());
1301 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1302 // Change the PHI node into a select instruction.
1303 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1304 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1306 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", InsertPt);
1307 PN->replaceAllUsesWith(NV);
1309 PN->eraseFromParent();
1312 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1313 // has been flattened. Change DomBlock to jump directly to our new block to
1314 // avoid other simplifycfg's kicking in on the diamond.
1315 TerminatorInst *OldTI = DomBlock->getTerminator();
1316 BranchInst::Create(BB, OldTI);
1317 OldTI->eraseFromParent();
1321 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1322 /// to two returning blocks, try to merge them together into one return,
1323 /// introducing a select if the return values disagree.
1324 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1325 assert(BI->isConditional() && "Must be a conditional branch");
1326 BasicBlock *TrueSucc = BI->getSuccessor(0);
1327 BasicBlock *FalseSucc = BI->getSuccessor(1);
1328 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1329 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1331 // Check to ensure both blocks are empty (just a return) or optionally empty
1332 // with PHI nodes. If there are other instructions, merging would cause extra
1333 // computation on one path or the other.
1334 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1336 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1339 // Okay, we found a branch that is going to two return nodes. If
1340 // there is no return value for this function, just change the
1341 // branch into a return.
1342 if (FalseRet->getNumOperands() == 0) {
1343 TrueSucc->removePredecessor(BI->getParent());
1344 FalseSucc->removePredecessor(BI->getParent());
1345 ReturnInst::Create(BI->getContext(), 0, BI);
1346 EraseTerminatorInstAndDCECond(BI);
1350 // Otherwise, figure out what the true and false return values are
1351 // so we can insert a new select instruction.
1352 Value *TrueValue = TrueRet->getReturnValue();
1353 Value *FalseValue = FalseRet->getReturnValue();
1355 // Unwrap any PHI nodes in the return blocks.
1356 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1357 if (TVPN->getParent() == TrueSucc)
1358 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1359 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1360 if (FVPN->getParent() == FalseSucc)
1361 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1363 // In order for this transformation to be safe, we must be able to
1364 // unconditionally execute both operands to the return. This is
1365 // normally the case, but we could have a potentially-trapping
1366 // constant expression that prevents this transformation from being
1368 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1371 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1375 // Okay, we collected all the mapped values and checked them for sanity, and
1376 // defined to really do this transformation. First, update the CFG.
1377 TrueSucc->removePredecessor(BI->getParent());
1378 FalseSucc->removePredecessor(BI->getParent());
1380 // Insert select instructions where needed.
1381 Value *BrCond = BI->getCondition();
1383 // Insert a select if the results differ.
1384 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1385 } else if (isa<UndefValue>(TrueValue)) {
1386 TrueValue = FalseValue;
1388 TrueValue = SelectInst::Create(BrCond, TrueValue,
1389 FalseValue, "retval", BI);
1393 Value *RI = !TrueValue ?
1394 ReturnInst::Create(BI->getContext(), BI) :
1395 ReturnInst::Create(BI->getContext(), TrueValue, BI);
1398 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1399 << "\n " << *BI << "NewRet = " << *RI
1400 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1402 EraseTerminatorInstAndDCECond(BI);
1407 /// FoldBranchToCommonDest - If this basic block is simple enough, and if a
1408 /// predecessor branches to us and one of our successors, fold the block into
1409 /// the predecessor and use logical operations to pick the right destination.
1410 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1411 BasicBlock *BB = BI->getParent();
1412 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1413 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1414 Cond->getParent() != BB || !Cond->hasOneUse())
1417 // Only allow this if the condition is a simple instruction that can be
1418 // executed unconditionally. It must be in the same block as the branch, and
1419 // must be at the front of the block.
1420 BasicBlock::iterator FrontIt = BB->front();
1422 // Ignore dbg intrinsics.
1423 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1425 // Allow a single instruction to be hoisted in addition to the compare
1426 // that feeds the branch. We later ensure that any values that _it_ uses
1427 // were also live in the predecessor, so that we don't unnecessarily create
1428 // register pressure or inhibit out-of-order execution.
1429 Instruction *BonusInst = 0;
1430 if (&*FrontIt != Cond &&
1431 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1432 FrontIt->isSafeToSpeculativelyExecute()) {
1433 BonusInst = &*FrontIt;
1436 // Ignore dbg intrinsics.
1437 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1440 // Only a single bonus inst is allowed.
1441 if (&*FrontIt != Cond)
1444 // Make sure the instruction after the condition is the cond branch.
1445 BasicBlock::iterator CondIt = Cond; ++CondIt;
1447 // Ingore dbg intrinsics.
1448 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
1453 // Cond is known to be a compare or binary operator. Check to make sure that
1454 // neither operand is a potentially-trapping constant expression.
1455 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1458 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1462 // Finally, don't infinitely unroll conditional loops.
1463 BasicBlock *TrueDest = BI->getSuccessor(0);
1464 BasicBlock *FalseDest = BI->getSuccessor(1);
1465 if (TrueDest == BB || FalseDest == BB)
1468 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1469 BasicBlock *PredBlock = *PI;
1470 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1472 // Check that we have two conditional branches. If there is a PHI node in
1473 // the common successor, verify that the same value flows in from both
1475 if (PBI == 0 || PBI->isUnconditional() || !SafeToMergeTerminators(BI, PBI))
1478 // Determine if the two branches share a common destination.
1479 Instruction::BinaryOps Opc;
1480 bool InvertPredCond = false;
1482 if (PBI->getSuccessor(0) == TrueDest)
1483 Opc = Instruction::Or;
1484 else if (PBI->getSuccessor(1) == FalseDest)
1485 Opc = Instruction::And;
1486 else if (PBI->getSuccessor(0) == FalseDest)
1487 Opc = Instruction::And, InvertPredCond = true;
1488 else if (PBI->getSuccessor(1) == TrueDest)
1489 Opc = Instruction::Or, InvertPredCond = true;
1493 // Ensure that any values used in the bonus instruction are also used
1494 // by the terminator of the predecessor. This means that those values
1495 // must already have been resolved, so we won't be inhibiting the
1496 // out-of-order core by speculating them earlier.
1498 // Collect the values used by the bonus inst
1499 SmallPtrSet<Value*, 4> UsedValues;
1500 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1501 OE = BonusInst->op_end(); OI != OE; ++OI) {
1503 if (!isa<Constant>(V))
1504 UsedValues.insert(V);
1507 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1508 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1510 // Walk up to four levels back up the use-def chain of the predecessor's
1511 // terminator to see if all those values were used. The choice of four
1512 // levels is arbitrary, to provide a compile-time-cost bound.
1513 while (!Worklist.empty()) {
1514 std::pair<Value*, unsigned> Pair = Worklist.back();
1515 Worklist.pop_back();
1517 if (Pair.second >= 4) continue;
1518 UsedValues.erase(Pair.first);
1519 if (UsedValues.empty()) break;
1521 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
1522 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1524 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1528 if (!UsedValues.empty()) return false;
1531 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1533 // If we need to invert the condition in the pred block to match, do so now.
1534 if (InvertPredCond) {
1535 Value *NewCond = PBI->getCondition();
1537 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
1538 CmpInst *CI = cast<CmpInst>(NewCond);
1539 CI->setPredicate(CI->getInversePredicate());
1541 NewCond = BinaryOperator::CreateNot(NewCond,
1542 PBI->getCondition()->getName()+".not", PBI);
1545 PBI->setCondition(NewCond);
1546 BasicBlock *OldTrue = PBI->getSuccessor(0);
1547 BasicBlock *OldFalse = PBI->getSuccessor(1);
1548 PBI->setSuccessor(0, OldFalse);
1549 PBI->setSuccessor(1, OldTrue);
1552 // If we have a bonus inst, clone it into the predecessor block.
1553 Instruction *NewBonus = 0;
1555 NewBonus = BonusInst->clone();
1556 PredBlock->getInstList().insert(PBI, NewBonus);
1557 NewBonus->takeName(BonusInst);
1558 BonusInst->setName(BonusInst->getName()+".old");
1561 // Clone Cond into the predecessor basic block, and or/and the
1562 // two conditions together.
1563 Instruction *New = Cond->clone();
1564 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1565 PredBlock->getInstList().insert(PBI, New);
1566 New->takeName(Cond);
1567 Cond->setName(New->getName()+".old");
1569 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1570 New, "or.cond", PBI);
1571 PBI->setCondition(NewCond);
1572 if (PBI->getSuccessor(0) == BB) {
1573 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1574 PBI->setSuccessor(0, TrueDest);
1576 if (PBI->getSuccessor(1) == BB) {
1577 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1578 PBI->setSuccessor(1, FalseDest);
1581 // Copy any debug value intrinsics into the end of PredBlock.
1582 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
1583 if (isa<DbgInfoIntrinsic>(*I))
1584 I->clone()->insertBefore(PBI);
1591 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1592 /// predecessor of another block, this function tries to simplify it. We know
1593 /// that PBI and BI are both conditional branches, and BI is in one of the
1594 /// successor blocks of PBI - PBI branches to BI.
1595 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1596 assert(PBI->isConditional() && BI->isConditional());
1597 BasicBlock *BB = BI->getParent();
1599 // If this block ends with a branch instruction, and if there is a
1600 // predecessor that ends on a branch of the same condition, make
1601 // this conditional branch redundant.
1602 if (PBI->getCondition() == BI->getCondition() &&
1603 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1604 // Okay, the outcome of this conditional branch is statically
1605 // knowable. If this block had a single pred, handle specially.
1606 if (BB->getSinglePredecessor()) {
1607 // Turn this into a branch on constant.
1608 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1609 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1611 return true; // Nuke the branch on constant.
1614 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1615 // in the constant and simplify the block result. Subsequent passes of
1616 // simplifycfg will thread the block.
1617 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1618 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
1619 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1620 std::distance(PB, PE),
1621 BI->getCondition()->getName() + ".pr",
1623 // Okay, we're going to insert the PHI node. Since PBI is not the only
1624 // predecessor, compute the PHI'd conditional value for all of the preds.
1625 // Any predecessor where the condition is not computable we keep symbolic.
1626 for (pred_iterator PI = PB; PI != PE; ++PI) {
1627 BasicBlock *P = *PI;
1628 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
1629 PBI != BI && PBI->isConditional() &&
1630 PBI->getCondition() == BI->getCondition() &&
1631 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1632 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1633 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1636 NewPN->addIncoming(BI->getCondition(), P);
1640 BI->setCondition(NewPN);
1645 // If this is a conditional branch in an empty block, and if any
1646 // predecessors is a conditional branch to one of our destinations,
1647 // fold the conditions into logical ops and one cond br.
1648 BasicBlock::iterator BBI = BB->begin();
1649 // Ignore dbg intrinsics.
1650 while (isa<DbgInfoIntrinsic>(BBI))
1656 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1661 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1663 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1664 PBIOp = 0, BIOp = 1;
1665 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1666 PBIOp = 1, BIOp = 0;
1667 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1672 // Check to make sure that the other destination of this branch
1673 // isn't BB itself. If so, this is an infinite loop that will
1674 // keep getting unwound.
1675 if (PBI->getSuccessor(PBIOp) == BB)
1678 // Do not perform this transformation if it would require
1679 // insertion of a large number of select instructions. For targets
1680 // without predication/cmovs, this is a big pessimization.
1681 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1683 unsigned NumPhis = 0;
1684 for (BasicBlock::iterator II = CommonDest->begin();
1685 isa<PHINode>(II); ++II, ++NumPhis)
1686 if (NumPhis > 2) // Disable this xform.
1689 // Finally, if everything is ok, fold the branches to logical ops.
1690 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1692 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
1693 << "AND: " << *BI->getParent());
1696 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1697 // branch in it, where one edge (OtherDest) goes back to itself but the other
1698 // exits. We don't *know* that the program avoids the infinite loop
1699 // (even though that seems likely). If we do this xform naively, we'll end up
1700 // recursively unpeeling the loop. Since we know that (after the xform is
1701 // done) that the block *is* infinite if reached, we just make it an obviously
1702 // infinite loop with no cond branch.
1703 if (OtherDest == BB) {
1704 // Insert it at the end of the function, because it's either code,
1705 // or it won't matter if it's hot. :)
1706 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1707 "infloop", BB->getParent());
1708 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1709 OtherDest = InfLoopBlock;
1712 DEBUG(dbgs() << *PBI->getParent()->getParent());
1714 // BI may have other predecessors. Because of this, we leave
1715 // it alone, but modify PBI.
1717 // Make sure we get to CommonDest on True&True directions.
1718 Value *PBICond = PBI->getCondition();
1720 PBICond = BinaryOperator::CreateNot(PBICond,
1721 PBICond->getName()+".not",
1723 Value *BICond = BI->getCondition();
1725 BICond = BinaryOperator::CreateNot(BICond,
1726 BICond->getName()+".not",
1728 // Merge the conditions.
1729 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1731 // Modify PBI to branch on the new condition to the new dests.
1732 PBI->setCondition(Cond);
1733 PBI->setSuccessor(0, CommonDest);
1734 PBI->setSuccessor(1, OtherDest);
1736 // OtherDest may have phi nodes. If so, add an entry from PBI's
1737 // block that are identical to the entries for BI's block.
1738 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
1740 // We know that the CommonDest already had an edge from PBI to
1741 // it. If it has PHIs though, the PHIs may have different
1742 // entries for BB and PBI's BB. If so, insert a select to make
1745 for (BasicBlock::iterator II = CommonDest->begin();
1746 (PN = dyn_cast<PHINode>(II)); ++II) {
1747 Value *BIV = PN->getIncomingValueForBlock(BB);
1748 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1749 Value *PBIV = PN->getIncomingValue(PBBIdx);
1751 // Insert a select in PBI to pick the right value.
1752 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1753 PBIV->getName()+".mux", PBI);
1754 PN->setIncomingValue(PBBIdx, NV);
1758 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1759 DEBUG(dbgs() << *PBI->getParent()->getParent());
1761 // This basic block is probably dead. We know it has at least
1762 // one fewer predecessor.
1766 // SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
1767 // branch to TrueBB if Cond is true or to FalseBB if Cond is false.
1768 // Takes care of updating the successors and removing the old terminator.
1769 // Also makes sure not to introduce new successors by assuming that edges to
1770 // non-successor TrueBBs and FalseBBs aren't reachable.
1771 static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
1772 BasicBlock *TrueBB, BasicBlock *FalseBB){
1773 // Remove any superfluous successor edges from the CFG.
1774 // First, figure out which successors to preserve.
1775 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
1777 BasicBlock *KeepEdge1 = TrueBB;
1778 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
1780 // Then remove the rest.
1781 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
1782 BasicBlock *Succ = OldTerm->getSuccessor(I);
1783 // Make sure only to keep exactly one copy of each edge.
1784 if (Succ == KeepEdge1)
1786 else if (Succ == KeepEdge2)
1789 Succ->removePredecessor(OldTerm->getParent());
1792 // Insert an appropriate new terminator.
1793 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
1794 if (TrueBB == FalseBB)
1795 // We were only looking for one successor, and it was present.
1796 // Create an unconditional branch to it.
1797 BranchInst::Create(TrueBB, OldTerm);
1799 // We found both of the successors we were looking for.
1800 // Create a conditional branch sharing the condition of the select.
1801 BranchInst::Create(TrueBB, FalseBB, Cond, OldTerm);
1802 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
1803 // Neither of the selected blocks were successors, so this
1804 // terminator must be unreachable.
1805 new UnreachableInst(OldTerm->getContext(), OldTerm);
1807 // One of the selected values was a successor, but the other wasn't.
1808 // Insert an unconditional branch to the one that was found;
1809 // the edge to the one that wasn't must be unreachable.
1811 // Only TrueBB was found.
1812 BranchInst::Create(TrueBB, OldTerm);
1814 // Only FalseBB was found.
1815 BranchInst::Create(FalseBB, OldTerm);
1818 EraseTerminatorInstAndDCECond(OldTerm);
1822 // SimplifySwitchOnSelect - Replaces
1823 // (switch (select cond, X, Y)) on constant X, Y
1824 // with a branch - conditional if X and Y lead to distinct BBs,
1825 // unconditional otherwise.
1826 static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
1827 // Check for constant integer values in the select.
1828 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
1829 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
1830 if (!TrueVal || !FalseVal)
1833 // Find the relevant condition and destinations.
1834 Value *Condition = Select->getCondition();
1835 BasicBlock *TrueBB = SI->getSuccessor(SI->findCaseValue(TrueVal));
1836 BasicBlock *FalseBB = SI->getSuccessor(SI->findCaseValue(FalseVal));
1838 // Perform the actual simplification.
1839 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB);
1842 // SimplifyIndirectBrOnSelect - Replaces
1843 // (indirectbr (select cond, blockaddress(@fn, BlockA),
1844 // blockaddress(@fn, BlockB)))
1846 // (br cond, BlockA, BlockB).
1847 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
1848 // Check that both operands of the select are block addresses.
1849 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
1850 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
1854 // Extract the actual blocks.
1855 BasicBlock *TrueBB = TBA->getBasicBlock();
1856 BasicBlock *FalseBB = FBA->getBasicBlock();
1858 // Perform the actual simplification.
1859 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB);
1862 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
1863 /// instruction (a seteq/setne with a constant) as the only instruction in a
1864 /// block that ends with an uncond branch. We are looking for a very specific
1865 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
1866 /// this case, we merge the first two "or's of icmp" into a switch, but then the
1867 /// default value goes to an uncond block with a seteq in it, we get something
1870 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
1872 /// %tmp = icmp eq i8 %A, 92
1875 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
1877 /// We prefer to split the edge to 'end' so that there is a true/false entry to
1878 /// the PHI, merging the third icmp into the switch.
1879 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
1880 const TargetData *TD) {
1881 BasicBlock *BB = ICI->getParent();
1882 // If the block has any PHIs in it or the icmp has multiple uses, it is too
1884 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
1886 Value *V = ICI->getOperand(0);
1887 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
1889 // The pattern we're looking for is where our only predecessor is a switch on
1890 // 'V' and this block is the default case for the switch. In this case we can
1891 // fold the compared value into the switch to simplify things.
1892 BasicBlock *Pred = BB->getSinglePredecessor();
1893 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
1895 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
1896 if (SI->getCondition() != V)
1899 // If BB is reachable on a non-default case, then we simply know the value of
1900 // V in this block. Substitute it and constant fold the icmp instruction
1902 if (SI->getDefaultDest() != BB) {
1903 ConstantInt *VVal = SI->findCaseDest(BB);
1904 assert(VVal && "Should have a unique destination value");
1905 ICI->setOperand(0, VVal);
1907 if (Value *V = SimplifyInstruction(ICI, TD)) {
1908 ICI->replaceAllUsesWith(V);
1909 ICI->eraseFromParent();
1911 // BB is now empty, so it is likely to simplify away.
1912 return SimplifyCFG(BB) | true;
1915 // Ok, the block is reachable from the default dest. If the constant we're
1916 // comparing exists in one of the other edges, then we can constant fold ICI
1918 if (SI->findCaseValue(Cst) != 0) {
1920 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1921 V = ConstantInt::getFalse(BB->getContext());
1923 V = ConstantInt::getTrue(BB->getContext());
1925 ICI->replaceAllUsesWith(V);
1926 ICI->eraseFromParent();
1927 // BB is now empty, so it is likely to simplify away.
1928 return SimplifyCFG(BB) | true;
1931 // The use of the icmp has to be in the 'end' block, by the only PHI node in
1933 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
1934 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
1935 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
1936 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
1939 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
1941 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
1942 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
1944 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1945 std::swap(DefaultCst, NewCst);
1947 // Replace ICI (which is used by the PHI for the default value) with true or
1948 // false depending on if it is EQ or NE.
1949 ICI->replaceAllUsesWith(DefaultCst);
1950 ICI->eraseFromParent();
1952 // Okay, the switch goes to this block on a default value. Add an edge from
1953 // the switch to the merge point on the compared value.
1954 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
1955 BB->getParent(), BB);
1956 SI->addCase(Cst, NewBB);
1958 // NewBB branches to the phi block, add the uncond branch and the phi entry.
1959 BranchInst::Create(SuccBlock, NewBB);
1960 PHIUse->addIncoming(NewCst, NewBB);
1964 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
1965 /// Check to see if it is branching on an or/and chain of icmp instructions, and
1966 /// fold it into a switch instruction if so.
1967 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD) {
1968 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1969 if (Cond == 0) return false;
1972 // Change br (X == 0 | X == 1), T, F into a switch instruction.
1973 // If this is a bunch of seteq's or'd together, or if it's a bunch of
1974 // 'setne's and'ed together, collect them.
1976 std::vector<ConstantInt*> Values;
1977 bool TrueWhenEqual = true;
1978 Value *ExtraCase = 0;
1979 unsigned UsedICmps = 0;
1981 if (Cond->getOpcode() == Instruction::Or) {
1982 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
1984 } else if (Cond->getOpcode() == Instruction::And) {
1985 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
1987 TrueWhenEqual = false;
1990 // If we didn't have a multiply compared value, fail.
1991 if (CompVal == 0) return false;
1993 // Avoid turning single icmps into a switch.
1997 // There might be duplicate constants in the list, which the switch
1998 // instruction can't handle, remove them now.
1999 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
2000 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2002 // If Extra was used, we require at least two switch values to do the
2003 // transformation. A switch with one value is just an cond branch.
2004 if (ExtraCase && Values.size() < 2) return false;
2006 // Figure out which block is which destination.
2007 BasicBlock *DefaultBB = BI->getSuccessor(1);
2008 BasicBlock *EdgeBB = BI->getSuccessor(0);
2009 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2011 BasicBlock *BB = BI->getParent();
2013 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
2014 << " cases into SWITCH. BB is:\n" << *BB);
2016 // If there are any extra values that couldn't be folded into the switch
2017 // then we evaluate them with an explicit branch first. Split the block
2018 // right before the condbr to handle it.
2020 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
2021 // Remove the uncond branch added to the old block.
2022 TerminatorInst *OldTI = BB->getTerminator();
2025 BranchInst::Create(EdgeBB, NewBB, ExtraCase, OldTI);
2027 BranchInst::Create(NewBB, EdgeBB, ExtraCase, OldTI);
2029 OldTI->eraseFromParent();
2031 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
2032 // for the edge we just added.
2033 AddPredecessorToBlock(EdgeBB, BB, NewBB);
2035 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
2036 << "\nEXTRABB = " << *BB);
2040 // Convert pointer to int before we switch.
2041 if (CompVal->getType()->isPointerTy()) {
2042 assert(TD && "Cannot switch on pointer without TargetData");
2043 CompVal = new PtrToIntInst(CompVal,
2044 TD->getIntPtrType(CompVal->getContext()),
2048 // Create the new switch instruction now.
2049 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB, Values.size(), BI);
2051 // Add all of the 'cases' to the switch instruction.
2052 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2053 New->addCase(Values[i], EdgeBB);
2055 // We added edges from PI to the EdgeBB. As such, if there were any
2056 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2057 // the number of edges added.
2058 for (BasicBlock::iterator BBI = EdgeBB->begin();
2059 isa<PHINode>(BBI); ++BBI) {
2060 PHINode *PN = cast<PHINode>(BBI);
2061 Value *InVal = PN->getIncomingValueForBlock(BB);
2062 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2063 PN->addIncoming(InVal, BB);
2066 // Erase the old branch instruction.
2067 EraseTerminatorInstAndDCECond(BI);
2069 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
2073 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI) {
2074 BasicBlock *BB = RI->getParent();
2075 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2077 // Find predecessors that end with branches.
2078 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2079 SmallVector<BranchInst*, 8> CondBranchPreds;
2080 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2081 BasicBlock *P = *PI;
2082 TerminatorInst *PTI = P->getTerminator();
2083 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2084 if (BI->isUnconditional())
2085 UncondBranchPreds.push_back(P);
2087 CondBranchPreds.push_back(BI);
2091 // If we found some, do the transformation!
2092 if (!UncondBranchPreds.empty() && DupRet) {
2093 while (!UncondBranchPreds.empty()) {
2094 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2095 DEBUG(dbgs() << "FOLDING: " << *BB
2096 << "INTO UNCOND BRANCH PRED: " << *Pred);
2097 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
2100 // If we eliminated all predecessors of the block, delete the block now.
2101 if (pred_begin(BB) == pred_end(BB))
2102 // We know there are no successors, so just nuke the block.
2103 BB->eraseFromParent();
2108 // Check out all of the conditional branches going to this return
2109 // instruction. If any of them just select between returns, change the
2110 // branch itself into a select/return pair.
2111 while (!CondBranchPreds.empty()) {
2112 BranchInst *BI = CondBranchPreds.pop_back_val();
2114 // Check to see if the non-BB successor is also a return block.
2115 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2116 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2117 SimplifyCondBranchToTwoReturns(BI))
2123 bool SimplifyCFGOpt::SimplifyUnwind(UnwindInst *UI) {
2124 // Check to see if the first instruction in this block is just an unwind.
2125 // If so, replace any invoke instructions which use this as an exception
2126 // destination with call instructions.
2127 BasicBlock *BB = UI->getParent();
2128 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2130 bool Changed = false;
2131 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2132 while (!Preds.empty()) {
2133 BasicBlock *Pred = Preds.back();
2134 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
2135 if (II && II->getUnwindDest() == BB) {
2136 // Insert a new branch instruction before the invoke, because this
2137 // is now a fall through.
2138 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2139 Pred->getInstList().remove(II); // Take out of symbol table
2141 // Insert the call now.
2142 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
2143 CallInst *CI = CallInst::Create(II->getCalledValue(),
2144 Args.begin(), Args.end(),
2146 CI->setCallingConv(II->getCallingConv());
2147 CI->setAttributes(II->getAttributes());
2148 // If the invoke produced a value, the Call now does instead.
2149 II->replaceAllUsesWith(CI);
2157 // If this block is now dead (and isn't the entry block), remove it.
2158 if (pred_begin(BB) == pred_end(BB) &&
2159 BB != &BB->getParent()->getEntryBlock()) {
2160 // We know there are no successors, so just nuke the block.
2161 BB->eraseFromParent();
2168 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2169 BasicBlock *BB = UI->getParent();
2171 bool Changed = false;
2173 // If there are any instructions immediately before the unreachable that can
2174 // be removed, do so.
2175 while (UI != BB->begin()) {
2176 BasicBlock::iterator BBI = UI;
2178 // Do not delete instructions that can have side effects, like calls
2179 // (which may never return) and volatile loads and stores.
2180 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2182 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
2183 if (SI->isVolatile())
2186 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
2187 if (LI->isVolatile())
2190 // Delete this instruction (any uses are guaranteed to be dead)
2191 if (!BBI->use_empty())
2192 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
2193 BBI->eraseFromParent();
2197 // If the unreachable instruction is the first in the block, take a gander
2198 // at all of the predecessors of this instruction, and simplify them.
2199 if (&BB->front() != UI) return Changed;
2201 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2202 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2203 TerminatorInst *TI = Preds[i]->getTerminator();
2205 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2206 if (BI->isUnconditional()) {
2207 if (BI->getSuccessor(0) == BB) {
2208 new UnreachableInst(TI->getContext(), TI);
2209 TI->eraseFromParent();
2213 if (BI->getSuccessor(0) == BB) {
2214 BranchInst::Create(BI->getSuccessor(1), BI);
2215 EraseTerminatorInstAndDCECond(BI);
2216 } else if (BI->getSuccessor(1) == BB) {
2217 BranchInst::Create(BI->getSuccessor(0), BI);
2218 EraseTerminatorInstAndDCECond(BI);
2222 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2223 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2224 if (SI->getSuccessor(i) == BB) {
2225 BB->removePredecessor(SI->getParent());
2230 // If the default value is unreachable, figure out the most popular
2231 // destination and make it the default.
2232 if (SI->getSuccessor(0) == BB) {
2233 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
2234 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
2235 std::pair<unsigned, unsigned>& entry =
2236 Popularity[SI->getSuccessor(i)];
2237 if (entry.first == 0) {
2245 // Find the most popular block.
2246 unsigned MaxPop = 0;
2247 unsigned MaxIndex = 0;
2248 BasicBlock *MaxBlock = 0;
2249 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
2250 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2251 if (I->second.first > MaxPop ||
2252 (I->second.first == MaxPop && MaxIndex > I->second.second)) {
2253 MaxPop = I->second.first;
2254 MaxIndex = I->second.second;
2255 MaxBlock = I->first;
2259 // Make this the new default, allowing us to delete any explicit
2261 SI->setSuccessor(0, MaxBlock);
2264 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2266 if (isa<PHINode>(MaxBlock->begin()))
2267 for (unsigned i = 0; i != MaxPop-1; ++i)
2268 MaxBlock->removePredecessor(SI->getParent());
2270 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2271 if (SI->getSuccessor(i) == MaxBlock) {
2277 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2278 if (II->getUnwindDest() == BB) {
2279 // Convert the invoke to a call instruction. This would be a good
2280 // place to note that the call does not throw though.
2281 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2282 II->removeFromParent(); // Take out of symbol table
2284 // Insert the call now...
2285 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2286 CallInst *CI = CallInst::Create(II->getCalledValue(),
2287 Args.begin(), Args.end(),
2289 CI->setCallingConv(II->getCallingConv());
2290 CI->setAttributes(II->getAttributes());
2291 // If the invoke produced a value, the call does now instead.
2292 II->replaceAllUsesWith(CI);
2299 // If this block is now dead, remove it.
2300 if (pred_begin(BB) == pred_end(BB) &&
2301 BB != &BB->getParent()->getEntryBlock()) {
2302 // We know there are no successors, so just nuke the block.
2303 BB->eraseFromParent();
2310 /// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
2311 /// integer range comparison into a sub, an icmp and a branch.
2312 static bool TurnSwitchRangeIntoICmp(SwitchInst *SI) {
2313 assert(SI->getNumCases() > 2 && "Degenerate switch?");
2315 // Make sure all cases point to the same destination and gather the values.
2316 SmallVector<ConstantInt *, 16> Cases;
2317 Cases.push_back(SI->getCaseValue(1));
2318 for (unsigned I = 2, E = SI->getNumCases(); I != E; ++I) {
2319 if (SI->getSuccessor(I-1) != SI->getSuccessor(I))
2321 Cases.push_back(SI->getCaseValue(I));
2323 assert(Cases.size() == SI->getNumCases()-1 && "Not all cases gathered");
2325 // Sort the case values, then check if they form a range we can transform.
2326 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
2327 for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
2328 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
2332 Constant *Offset = ConstantExpr::getNeg(Cases.back());
2333 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases()-1);
2335 Value *Sub = SI->getCondition();
2336 if (!Offset->isNullValue())
2337 Sub = BinaryOperator::CreateAdd(Sub, Offset, Sub->getName()+".off", SI);
2338 Value *Cmp = new ICmpInst(SI, ICmpInst::ICMP_ULT, Sub, NumCases, "switch");
2339 BranchInst::Create(SI->getSuccessor(1), SI->getDefaultDest(), Cmp, SI);
2341 // Prune obsolete incoming values off the successor's PHI nodes.
2342 for (BasicBlock::iterator BBI = SI->getSuccessor(1)->begin();
2343 isa<PHINode>(BBI); ++BBI) {
2344 for (unsigned I = 0, E = SI->getNumCases()-2; I != E; ++I)
2345 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
2347 SI->eraseFromParent();
2352 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI) {
2353 // If this switch is too complex to want to look at, ignore it.
2354 if (!isValueEqualityComparison(SI))
2357 BasicBlock *BB = SI->getParent();
2359 // If we only have one predecessor, and if it is a branch on this value,
2360 // see if that predecessor totally determines the outcome of this switch.
2361 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2362 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
2363 return SimplifyCFG(BB) | true;
2365 Value *Cond = SI->getCondition();
2366 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
2367 if (SimplifySwitchOnSelect(SI, Select))
2368 return SimplifyCFG(BB) | true;
2370 // If the block only contains the switch, see if we can fold the block
2371 // away into any preds.
2372 BasicBlock::iterator BBI = BB->begin();
2373 // Ignore dbg intrinsics.
2374 while (isa<DbgInfoIntrinsic>(BBI))
2377 if (FoldValueComparisonIntoPredecessors(SI))
2378 return SimplifyCFG(BB) | true;
2380 // Try to transform the switch into an icmp and a branch.
2381 if (TurnSwitchRangeIntoICmp(SI))
2382 return SimplifyCFG(BB) | true;
2387 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
2388 BasicBlock *BB = IBI->getParent();
2389 bool Changed = false;
2391 // Eliminate redundant destinations.
2392 SmallPtrSet<Value *, 8> Succs;
2393 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2394 BasicBlock *Dest = IBI->getDestination(i);
2395 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2396 Dest->removePredecessor(BB);
2397 IBI->removeDestination(i);
2403 if (IBI->getNumDestinations() == 0) {
2404 // If the indirectbr has no successors, change it to unreachable.
2405 new UnreachableInst(IBI->getContext(), IBI);
2406 EraseTerminatorInstAndDCECond(IBI);
2410 if (IBI->getNumDestinations() == 1) {
2411 // If the indirectbr has one successor, change it to a direct branch.
2412 BranchInst::Create(IBI->getDestination(0), IBI);
2413 EraseTerminatorInstAndDCECond(IBI);
2417 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2418 if (SimplifyIndirectBrOnSelect(IBI, SI))
2419 return SimplifyCFG(BB) | true;
2424 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI) {
2425 BasicBlock *BB = BI->getParent();
2427 // If the Terminator is the only non-phi instruction, simplify the block.
2428 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg();
2429 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
2430 TryToSimplifyUncondBranchFromEmptyBlock(BB))
2433 // If the only instruction in the block is a seteq/setne comparison
2434 // against a constant, try to simplify the block.
2435 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
2436 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
2437 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
2439 if (I->isTerminator() && TryToSimplifyUncondBranchWithICmpInIt(ICI, TD))
2447 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI) {
2448 BasicBlock *BB = BI->getParent();
2450 // Conditional branch
2451 if (isValueEqualityComparison(BI)) {
2452 // If we only have one predecessor, and if it is a branch on this value,
2453 // see if that predecessor totally determines the outcome of this
2455 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2456 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
2457 return SimplifyCFG(BB) | true;
2459 // This block must be empty, except for the setcond inst, if it exists.
2460 // Ignore dbg intrinsics.
2461 BasicBlock::iterator I = BB->begin();
2462 // Ignore dbg intrinsics.
2463 while (isa<DbgInfoIntrinsic>(I))
2466 if (FoldValueComparisonIntoPredecessors(BI))
2467 return SimplifyCFG(BB) | true;
2468 } else if (&*I == cast<Instruction>(BI->getCondition())){
2470 // Ignore dbg intrinsics.
2471 while (isa<DbgInfoIntrinsic>(I))
2473 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI))
2474 return SimplifyCFG(BB) | true;
2478 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
2479 if (SimplifyBranchOnICmpChain(BI, TD))
2482 // We have a conditional branch to two blocks that are only reachable
2483 // from BI. We know that the condbr dominates the two blocks, so see if
2484 // there is any identical code in the "then" and "else" blocks. If so, we
2485 // can hoist it up to the branching block.
2486 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
2487 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2488 if (HoistThenElseCodeToIf(BI))
2489 return SimplifyCFG(BB) | true;
2491 // If Successor #1 has multiple preds, we may be able to conditionally
2492 // execute Successor #0 if it branches to successor #1.
2493 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
2494 if (Succ0TI->getNumSuccessors() == 1 &&
2495 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
2496 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
2497 return SimplifyCFG(BB) | true;
2499 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2500 // If Successor #0 has multiple preds, we may be able to conditionally
2501 // execute Successor #1 if it branches to successor #0.
2502 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
2503 if (Succ1TI->getNumSuccessors() == 1 &&
2504 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
2505 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
2506 return SimplifyCFG(BB) | true;
2509 // If this is a branch on a phi node in the current block, thread control
2510 // through this block if any PHI node entries are constants.
2511 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
2512 if (PN->getParent() == BI->getParent())
2513 if (FoldCondBranchOnPHI(BI, TD))
2514 return SimplifyCFG(BB) | true;
2516 // If this basic block is ONLY a setcc and a branch, and if a predecessor
2517 // branches to us and one of our successors, fold the setcc into the
2518 // predecessor and use logical operations to pick the right destination.
2519 if (FoldBranchToCommonDest(BI))
2520 return SimplifyCFG(BB) | true;
2522 // Scan predecessor blocks for conditional branches.
2523 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2524 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2525 if (PBI != BI && PBI->isConditional())
2526 if (SimplifyCondBranchToCondBranch(PBI, BI))
2527 return SimplifyCFG(BB) | true;
2532 bool SimplifyCFGOpt::run(BasicBlock *BB) {
2533 bool Changed = false;
2535 assert(BB && BB->getParent() && "Block not embedded in function!");
2536 assert(BB->getTerminator() && "Degenerate basic block encountered!");
2538 // Remove basic blocks that have no predecessors (except the entry block)...
2539 // or that just have themself as a predecessor. These are unreachable.
2540 if ((pred_begin(BB) == pred_end(BB) &&
2541 BB != &BB->getParent()->getEntryBlock()) ||
2542 BB->getSinglePredecessor() == BB) {
2543 DEBUG(dbgs() << "Removing BB: \n" << *BB);
2544 DeleteDeadBlock(BB);
2548 // Check to see if we can constant propagate this terminator instruction
2550 Changed |= ConstantFoldTerminator(BB);
2552 // Check for and eliminate duplicate PHI nodes in this block.
2553 Changed |= EliminateDuplicatePHINodes(BB);
2555 // Merge basic blocks into their predecessor if there is only one distinct
2556 // pred, and if there is only one distinct successor of the predecessor, and
2557 // if there are no PHI nodes.
2559 if (MergeBlockIntoPredecessor(BB))
2562 // If there is a trivial two-entry PHI node in this basic block, and we can
2563 // eliminate it, do so now.
2564 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
2565 if (PN->getNumIncomingValues() == 2)
2566 Changed |= FoldTwoEntryPHINode(PN, TD);
2568 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
2569 if (BI->isUnconditional()) {
2570 if (SimplifyUncondBranch(BI)) return true;
2572 if (SimplifyCondBranch(BI)) return true;
2574 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
2575 if (SimplifyReturn(RI)) return true;
2576 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
2577 if (SimplifySwitch(SI)) return true;
2578 } else if (UnreachableInst *UI =
2579 dyn_cast<UnreachableInst>(BB->getTerminator())) {
2580 if (SimplifyUnreachable(UI)) return true;
2581 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
2582 if (SimplifyUnwind(UI)) return true;
2583 } else if (IndirectBrInst *IBI =
2584 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
2585 if (SimplifyIndirectBr(IBI)) return true;
2591 /// SimplifyCFG - This function is used to do simplification of a CFG. For
2592 /// example, it adjusts branches to branches to eliminate the extra hop, it
2593 /// eliminates unreachable basic blocks, and does other "peephole" optimization
2594 /// of the CFG. It returns true if a modification was made.
2596 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
2597 return SimplifyCFGOpt(TD).run(BB);