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) and its recursive operands
205 /// that do not dominate BB have a combined cost lower than CostRemaining and
206 /// are non-trapping. If both are true, the instruction is inserted into the
207 /// set and true is returned.
209 /// The cost for most non-trapping instructions is defined as 1 except for
210 /// Select whose cost is 2.
212 /// After this function returns, CostRemaining is decreased by the cost of
213 /// V plus its non-dominating operands. If that cost is greater than
214 /// CostRemaining, false is returned and CostRemaining is undefined.
215 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
216 SmallPtrSet<Instruction*, 4> *AggressiveInsts,
217 unsigned &CostRemaining) {
218 Instruction *I = dyn_cast<Instruction>(V);
220 // Non-instructions all dominate instructions, but not all constantexprs
221 // can be executed unconditionally.
222 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
227 BasicBlock *PBB = I->getParent();
229 // We don't want to allow weird loops that might have the "if condition" in
230 // the bottom of this block.
231 if (PBB == BB) return false;
233 // If this instruction is defined in a block that contains an unconditional
234 // branch to BB, then it must be in the 'conditional' part of the "if
235 // statement". If not, it definitely dominates the region.
236 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
237 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB)
240 // If we aren't allowing aggressive promotion anymore, then don't consider
241 // instructions in the 'if region'.
242 if (AggressiveInsts == 0) return false;
244 // If we have seen this instruction before, don't count it again.
245 if (AggressiveInsts->count(I)) return true;
247 // Okay, it looks like the instruction IS in the "condition". Check to
248 // see if it's a cheap instruction to unconditionally compute, and if it
249 // only uses stuff defined outside of the condition. If so, hoist it out.
250 if (!I->isSafeToSpeculativelyExecute())
255 switch (I->getOpcode()) {
256 default: return false; // Cannot hoist this out safely.
257 case Instruction::Load:
258 // We have to check to make sure there are no instructions before the
259 // load in its basic block, as we are going to hoist the load out to its
261 if (PBB->getFirstNonPHIOrDbg() != I)
265 case Instruction::GetElementPtr:
266 // GEPs are cheap if all indices are constant.
267 if (!cast<GetElementPtrInst>(I)->hasAllConstantIndices())
271 case Instruction::Add:
272 case Instruction::Sub:
273 case Instruction::And:
274 case Instruction::Or:
275 case Instruction::Xor:
276 case Instruction::Shl:
277 case Instruction::LShr:
278 case Instruction::AShr:
279 case Instruction::ICmp:
280 case Instruction::Trunc:
281 case Instruction::ZExt:
282 case Instruction::SExt:
284 break; // These are all cheap and non-trapping instructions.
286 case Instruction::Select:
291 if (Cost > CostRemaining)
294 CostRemaining -= Cost;
296 // Okay, we can only really hoist these out if their operands do
297 // not take us over the cost threshold.
298 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
299 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining))
301 // Okay, it's safe to do this! Remember this instruction.
302 AggressiveInsts->insert(I);
306 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
307 /// and PointerNullValue. Return NULL if value is not a constant int.
308 static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
309 // Normal constant int.
310 ConstantInt *CI = dyn_cast<ConstantInt>(V);
311 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
314 // This is some kind of pointer constant. Turn it into a pointer-sized
315 // ConstantInt if possible.
316 const IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
318 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
319 if (isa<ConstantPointerNull>(V))
320 return ConstantInt::get(PtrTy, 0);
322 // IntToPtr const int.
323 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
324 if (CE->getOpcode() == Instruction::IntToPtr)
325 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
326 // The constant is very likely to have the right type already.
327 if (CI->getType() == PtrTy)
330 return cast<ConstantInt>
331 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
336 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
337 /// collection of icmp eq/ne instructions that compare a value against a
338 /// constant, return the value being compared, and stick the constant into the
341 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
342 const TargetData *TD, bool isEQ, unsigned &UsedICmps) {
343 Instruction *I = dyn_cast<Instruction>(V);
344 if (I == 0) return 0;
346 // If this is an icmp against a constant, handle this as one of the cases.
347 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
348 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
349 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
352 return I->getOperand(0);
355 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
358 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
360 // If this is an and/!= check then we want to optimize "x ugt 2" into
363 Span = Span.inverse();
365 // If there are a ton of values, we don't want to make a ginormous switch.
366 if (Span.getSetSize().ugt(8) || Span.isEmptySet() ||
367 // We don't handle wrapped sets yet.
371 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
372 Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
374 return I->getOperand(0);
379 // Otherwise, we can only handle an | or &, depending on isEQ.
380 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
383 unsigned NumValsBeforeLHS = Vals.size();
384 unsigned UsedICmpsBeforeLHS = UsedICmps;
385 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
387 unsigned NumVals = Vals.size();
388 unsigned UsedICmpsBeforeRHS = UsedICmps;
389 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
393 Vals.resize(NumVals);
394 UsedICmps = UsedICmpsBeforeRHS;
397 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
398 // set it and return success.
399 if (Extra == 0 || Extra == I->getOperand(1)) {
400 Extra = I->getOperand(1);
404 Vals.resize(NumValsBeforeLHS);
405 UsedICmps = UsedICmpsBeforeLHS;
409 // If the LHS can't be folded in, but Extra is available and RHS can, try to
411 if (Extra == 0 || Extra == I->getOperand(0)) {
412 Value *OldExtra = Extra;
413 Extra = I->getOperand(0);
414 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
417 assert(Vals.size() == NumValsBeforeLHS);
424 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
425 Instruction* Cond = 0;
426 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
427 Cond = dyn_cast<Instruction>(SI->getCondition());
428 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
429 if (BI->isConditional())
430 Cond = dyn_cast<Instruction>(BI->getCondition());
431 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
432 Cond = dyn_cast<Instruction>(IBI->getAddress());
435 TI->eraseFromParent();
436 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
439 /// isValueEqualityComparison - Return true if the specified terminator checks
440 /// to see if a value is equal to constant integer value.
441 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
443 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
444 // Do not permit merging of large switch instructions into their
445 // predecessors unless there is only one predecessor.
446 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
447 pred_end(SI->getParent())) <= 128)
448 CV = SI->getCondition();
449 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
450 if (BI->isConditional() && BI->getCondition()->hasOneUse())
451 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
452 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
453 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
454 GetConstantInt(ICI->getOperand(1), TD))
455 CV = ICI->getOperand(0);
457 // Unwrap any lossless ptrtoint cast.
458 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
459 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
460 CV = PTII->getOperand(0);
464 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
465 /// decode all of the 'cases' that it represents and return the 'default' block.
466 BasicBlock *SimplifyCFGOpt::
467 GetValueEqualityComparisonCases(TerminatorInst *TI,
468 std::vector<std::pair<ConstantInt*,
469 BasicBlock*> > &Cases) {
470 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
471 Cases.reserve(SI->getNumCases());
472 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
473 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
474 return SI->getDefaultDest();
477 BranchInst *BI = cast<BranchInst>(TI);
478 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
479 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD),
480 BI->getSuccessor(ICI->getPredicate() ==
481 ICmpInst::ICMP_NE)));
482 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
486 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
487 /// in the list that match the specified block.
488 static void EliminateBlockCases(BasicBlock *BB,
489 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
490 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
491 if (Cases[i].second == BB) {
492 Cases.erase(Cases.begin()+i);
497 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
500 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
501 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
502 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
504 // Make V1 be smaller than V2.
505 if (V1->size() > V2->size())
508 if (V1->size() == 0) return false;
509 if (V1->size() == 1) {
511 ConstantInt *TheVal = (*V1)[0].first;
512 for (unsigned i = 0, e = V2->size(); i != e; ++i)
513 if (TheVal == (*V2)[i].first)
517 // Otherwise, just sort both lists and compare element by element.
518 array_pod_sort(V1->begin(), V1->end());
519 array_pod_sort(V2->begin(), V2->end());
520 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
521 while (i1 != e1 && i2 != e2) {
522 if ((*V1)[i1].first == (*V2)[i2].first)
524 if ((*V1)[i1].first < (*V2)[i2].first)
532 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
533 /// terminator instruction and its block is known to only have a single
534 /// predecessor block, check to see if that predecessor is also a value
535 /// comparison with the same value, and if that comparison determines the
536 /// outcome of this comparison. If so, simplify TI. This does a very limited
537 /// form of jump threading.
538 bool SimplifyCFGOpt::
539 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
541 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
542 if (!PredVal) return false; // Not a value comparison in predecessor.
544 Value *ThisVal = isValueEqualityComparison(TI);
545 assert(ThisVal && "This isn't a value comparison!!");
546 if (ThisVal != PredVal) return false; // Different predicates.
548 // Find out information about when control will move from Pred to TI's block.
549 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
550 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
552 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
554 // Find information about how control leaves this block.
555 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
556 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
557 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
559 // If TI's block is the default block from Pred's comparison, potentially
560 // simplify TI based on this knowledge.
561 if (PredDef == TI->getParent()) {
562 // If we are here, we know that the value is none of those cases listed in
563 // PredCases. If there are any cases in ThisCases that are in PredCases, we
565 if (!ValuesOverlap(PredCases, ThisCases))
568 if (isa<BranchInst>(TI)) {
569 // Okay, one of the successors of this condbr is dead. Convert it to a
571 assert(ThisCases.size() == 1 && "Branch can only have one case!");
572 // Insert the new branch.
573 Instruction *NI = BranchInst::Create(ThisDef, TI);
576 // Remove PHI node entries for the dead edge.
577 ThisCases[0].second->removePredecessor(TI->getParent());
579 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
580 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
582 EraseTerminatorInstAndDCECond(TI);
586 SwitchInst *SI = cast<SwitchInst>(TI);
587 // Okay, TI has cases that are statically dead, prune them away.
588 SmallPtrSet<Constant*, 16> DeadCases;
589 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
590 DeadCases.insert(PredCases[i].first);
592 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
593 << "Through successor TI: " << *TI);
595 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
596 if (DeadCases.count(SI->getCaseValue(i))) {
597 SI->getSuccessor(i)->removePredecessor(TI->getParent());
601 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
605 // Otherwise, TI's block must correspond to some matched value. Find out
606 // which value (or set of values) this is.
607 ConstantInt *TIV = 0;
608 BasicBlock *TIBB = TI->getParent();
609 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
610 if (PredCases[i].second == TIBB) {
612 return false; // Cannot handle multiple values coming to this block.
613 TIV = PredCases[i].first;
615 assert(TIV && "No edge from pred to succ?");
617 // Okay, we found the one constant that our value can be if we get into TI's
618 // BB. Find out which successor will unconditionally be branched to.
619 BasicBlock *TheRealDest = 0;
620 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
621 if (ThisCases[i].first == TIV) {
622 TheRealDest = ThisCases[i].second;
626 // If not handled by any explicit cases, it is handled by the default case.
627 if (TheRealDest == 0) TheRealDest = ThisDef;
629 // Remove PHI node entries for dead edges.
630 BasicBlock *CheckEdge = TheRealDest;
631 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
632 if (*SI != CheckEdge)
633 (*SI)->removePredecessor(TIBB);
637 // Insert the new branch.
638 Instruction *NI = BranchInst::Create(TheRealDest, TI);
641 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
642 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
644 EraseTerminatorInstAndDCECond(TI);
649 /// ConstantIntOrdering - This class implements a stable ordering of constant
650 /// integers that does not depend on their address. This is important for
651 /// applications that sort ConstantInt's to ensure uniqueness.
652 struct ConstantIntOrdering {
653 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
654 return LHS->getValue().ult(RHS->getValue());
659 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
660 const ConstantInt *LHS = *(const ConstantInt**)P1;
661 const ConstantInt *RHS = *(const ConstantInt**)P2;
662 if (LHS->getValue().ult(RHS->getValue()))
664 if (LHS->getValue() == RHS->getValue())
669 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
670 /// equality comparison instruction (either a switch or a branch on "X == c").
671 /// See if any of the predecessors of the terminator block are value comparisons
672 /// on the same value. If so, and if safe to do so, fold them together.
673 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
674 BasicBlock *BB = TI->getParent();
675 Value *CV = isValueEqualityComparison(TI); // CondVal
676 assert(CV && "Not a comparison?");
677 bool Changed = false;
679 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
680 while (!Preds.empty()) {
681 BasicBlock *Pred = Preds.pop_back_val();
683 // See if the predecessor is a comparison with the same value.
684 TerminatorInst *PTI = Pred->getTerminator();
685 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
687 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
688 // Figure out which 'cases' to copy from SI to PSI.
689 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
690 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
692 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
693 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
695 // Based on whether the default edge from PTI goes to BB or not, fill in
696 // PredCases and PredDefault with the new switch cases we would like to
698 SmallVector<BasicBlock*, 8> NewSuccessors;
700 if (PredDefault == BB) {
701 // If this is the default destination from PTI, only the edges in TI
702 // that don't occur in PTI, or that branch to BB will be activated.
703 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
704 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
705 if (PredCases[i].second != BB)
706 PTIHandled.insert(PredCases[i].first);
708 // The default destination is BB, we don't need explicit targets.
709 std::swap(PredCases[i], PredCases.back());
710 PredCases.pop_back();
714 // Reconstruct the new switch statement we will be building.
715 if (PredDefault != BBDefault) {
716 PredDefault->removePredecessor(Pred);
717 PredDefault = BBDefault;
718 NewSuccessors.push_back(BBDefault);
720 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
721 if (!PTIHandled.count(BBCases[i].first) &&
722 BBCases[i].second != BBDefault) {
723 PredCases.push_back(BBCases[i]);
724 NewSuccessors.push_back(BBCases[i].second);
728 // If this is not the default destination from PSI, only the edges
729 // in SI that occur in PSI with a destination of BB will be
731 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
732 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
733 if (PredCases[i].second == BB) {
734 PTIHandled.insert(PredCases[i].first);
735 std::swap(PredCases[i], PredCases.back());
736 PredCases.pop_back();
740 // Okay, now we know which constants were sent to BB from the
741 // predecessor. Figure out where they will all go now.
742 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
743 if (PTIHandled.count(BBCases[i].first)) {
744 // If this is one we are capable of getting...
745 PredCases.push_back(BBCases[i]);
746 NewSuccessors.push_back(BBCases[i].second);
747 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
750 // If there are any constants vectored to BB that TI doesn't handle,
751 // they must go to the default destination of TI.
752 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
754 E = PTIHandled.end(); I != E; ++I) {
755 PredCases.push_back(std::make_pair(*I, BBDefault));
756 NewSuccessors.push_back(BBDefault);
760 // Okay, at this point, we know which new successor Pred will get. Make
761 // sure we update the number of entries in the PHI nodes for these
763 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
764 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
766 // Convert pointer to int before we switch.
767 if (CV->getType()->isPointerTy()) {
768 assert(TD && "Cannot switch on pointer without TargetData");
769 CV = new PtrToIntInst(CV, TD->getIntPtrType(CV->getContext()),
773 // Now that the successors are updated, create the new Switch instruction.
774 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
775 PredCases.size(), PTI);
776 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
777 NewSI->addCase(PredCases[i].first, PredCases[i].second);
779 EraseTerminatorInstAndDCECond(PTI);
781 // Okay, last check. If BB is still a successor of PSI, then we must
782 // have an infinite loop case. If so, add an infinitely looping block
783 // to handle the case to preserve the behavior of the code.
784 BasicBlock *InfLoopBlock = 0;
785 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
786 if (NewSI->getSuccessor(i) == BB) {
787 if (InfLoopBlock == 0) {
788 // Insert it at the end of the function, because it's either code,
789 // or it won't matter if it's hot. :)
790 InfLoopBlock = BasicBlock::Create(BB->getContext(),
791 "infloop", BB->getParent());
792 BranchInst::Create(InfLoopBlock, InfLoopBlock);
794 NewSI->setSuccessor(i, InfLoopBlock);
803 // isSafeToHoistInvoke - If we would need to insert a select that uses the
804 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
805 // would need to do this), we can't hoist the invoke, as there is nowhere
806 // to put the select in this case.
807 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
808 Instruction *I1, Instruction *I2) {
809 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
811 for (BasicBlock::iterator BBI = SI->begin();
812 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
813 Value *BB1V = PN->getIncomingValueForBlock(BB1);
814 Value *BB2V = PN->getIncomingValueForBlock(BB2);
815 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
823 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
824 /// BB2, hoist any common code in the two blocks up into the branch block. The
825 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
826 static bool HoistThenElseCodeToIf(BranchInst *BI) {
827 // This does very trivial matching, with limited scanning, to find identical
828 // instructions in the two blocks. In particular, we don't want to get into
829 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
830 // such, we currently just scan for obviously identical instructions in an
832 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
833 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
835 BasicBlock::iterator BB1_Itr = BB1->begin();
836 BasicBlock::iterator BB2_Itr = BB2->begin();
838 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
839 // Skip debug info if it is not identical.
840 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
841 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
842 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
843 while (isa<DbgInfoIntrinsic>(I1))
845 while (isa<DbgInfoIntrinsic>(I2))
848 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
849 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
852 // If we get here, we can hoist at least one instruction.
853 BasicBlock *BIParent = BI->getParent();
856 // If we are hoisting the terminator instruction, don't move one (making a
857 // broken BB), instead clone it, and remove BI.
858 if (isa<TerminatorInst>(I1))
859 goto HoistTerminator;
861 // For a normal instruction, we just move one to right before the branch,
862 // then replace all uses of the other with the first. Finally, we remove
863 // the now redundant second instruction.
864 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
865 if (!I2->use_empty())
866 I2->replaceAllUsesWith(I1);
867 I1->intersectOptionalDataWith(I2);
868 I2->eraseFromParent();
872 // Skip debug info if it is not identical.
873 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
874 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
875 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
876 while (isa<DbgInfoIntrinsic>(I1))
878 while (isa<DbgInfoIntrinsic>(I2))
881 } while (I1->isIdenticalToWhenDefined(I2));
886 // It may not be possible to hoist an invoke.
887 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
890 // Okay, it is safe to hoist the terminator.
891 Instruction *NT = I1->clone();
892 BIParent->getInstList().insert(BI, NT);
893 if (!NT->getType()->isVoidTy()) {
894 I1->replaceAllUsesWith(NT);
895 I2->replaceAllUsesWith(NT);
899 // Hoisting one of the terminators from our successor is a great thing.
900 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
901 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
902 // nodes, so we insert select instruction to compute the final result.
903 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
904 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
906 for (BasicBlock::iterator BBI = SI->begin();
907 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
908 Value *BB1V = PN->getIncomingValueForBlock(BB1);
909 Value *BB2V = PN->getIncomingValueForBlock(BB2);
910 if (BB1V == BB2V) continue;
912 // These values do not agree. Insert a select instruction before NT
913 // that determines the right value.
914 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
916 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
917 BB1V->getName()+"."+BB2V->getName(), NT);
918 // Make the PHI node use the select for all incoming values for BB1/BB2
919 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
920 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
921 PN->setIncomingValue(i, SI);
925 // Update any PHI nodes in our new successors.
926 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
927 AddPredecessorToBlock(*SI, BIParent, BB1);
929 EraseTerminatorInstAndDCECond(BI);
933 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
934 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
935 /// (for now, restricted to a single instruction that's side effect free) from
936 /// the BB1 into the branch block to speculatively execute it.
937 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
938 // Only speculatively execution a single instruction (not counting the
939 // terminator) for now.
940 Instruction *HInst = NULL;
941 Instruction *Term = BB1->getTerminator();
942 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
944 Instruction *I = BBI;
946 if (isa<DbgInfoIntrinsic>(I)) continue;
947 if (I == Term) break;
956 // Be conservative for now. FP select instruction can often be expensive.
957 Value *BrCond = BI->getCondition();
958 if (isa<FCmpInst>(BrCond))
961 // If BB1 is actually on the false edge of the conditional branch, remember
962 // to swap the select operands later.
964 if (BB1 != BI->getSuccessor(0)) {
965 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
972 // br i1 %t1, label %BB1, label %BB2
981 // %t3 = select i1 %t1, %t2, %t3
982 switch (HInst->getOpcode()) {
983 default: return false; // Not safe / profitable to hoist.
984 case Instruction::Add:
985 case Instruction::Sub:
986 // Not worth doing for vector ops.
987 if (HInst->getType()->isVectorTy())
990 case Instruction::And:
991 case Instruction::Or:
992 case Instruction::Xor:
993 case Instruction::Shl:
994 case Instruction::LShr:
995 case Instruction::AShr:
996 // Don't mess with vector operations.
997 if (HInst->getType()->isVectorTy())
999 break; // These are all cheap and non-trapping instructions.
1002 // If the instruction is obviously dead, don't try to predicate it.
1003 if (HInst->use_empty()) {
1004 HInst->eraseFromParent();
1008 // Can we speculatively execute the instruction? And what is the value
1009 // if the condition is false? Consider the phi uses, if the incoming value
1010 // from the "if" block are all the same V, then V is the value of the
1011 // select if the condition is false.
1012 BasicBlock *BIParent = BI->getParent();
1013 SmallVector<PHINode*, 4> PHIUses;
1014 Value *FalseV = NULL;
1016 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
1017 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
1019 // Ignore any user that is not a PHI node in BB2. These can only occur in
1020 // unreachable blocks, because they would not be dominated by the instr.
1021 PHINode *PN = dyn_cast<PHINode>(*UI);
1022 if (!PN || PN->getParent() != BB2)
1024 PHIUses.push_back(PN);
1026 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1029 else if (FalseV != PHIV)
1030 return false; // Inconsistent value when condition is false.
1033 assert(FalseV && "Must have at least one user, and it must be a PHI");
1035 // Do not hoist the instruction if any of its operands are defined but not
1036 // used in this BB. The transformation will prevent the operand from
1037 // being sunk into the use block.
1038 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1040 Instruction *OpI = dyn_cast<Instruction>(*i);
1041 if (OpI && OpI->getParent() == BIParent &&
1042 !OpI->isUsedInBasicBlock(BIParent))
1046 // If we get here, we can hoist the instruction. Try to place it
1047 // before the icmp instruction preceding the conditional branch.
1048 BasicBlock::iterator InsertPos = BI;
1049 if (InsertPos != BIParent->begin())
1051 // Skip debug info between condition and branch.
1052 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
1054 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
1055 SmallPtrSet<Instruction *, 4> BB1Insns;
1056 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
1057 BB1I != BB1E; ++BB1I)
1058 BB1Insns.insert(BB1I);
1059 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
1061 Instruction *Use = cast<Instruction>(*UI);
1062 if (!BB1Insns.count(Use)) continue;
1064 // If BrCond uses the instruction that place it just before
1065 // branch instruction.
1071 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
1073 // Create a select whose true value is the speculatively executed value and
1074 // false value is the previously determined FalseV.
1077 SI = SelectInst::Create(BrCond, FalseV, HInst,
1078 FalseV->getName() + "." + HInst->getName(), BI);
1080 SI = SelectInst::Create(BrCond, HInst, FalseV,
1081 HInst->getName() + "." + FalseV->getName(), BI);
1083 // Make the PHI node use the select for all incoming values for "then" and
1085 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1086 PHINode *PN = PHIUses[i];
1087 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1088 if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent)
1089 PN->setIncomingValue(j, SI);
1096 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1097 /// across this block.
1098 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1099 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1102 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1103 if (isa<DbgInfoIntrinsic>(BBI))
1105 if (Size > 10) return false; // Don't clone large BB's.
1108 // We can only support instructions that do not define values that are
1109 // live outside of the current basic block.
1110 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1112 Instruction *U = cast<Instruction>(*UI);
1113 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1116 // Looks ok, continue checking.
1122 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1123 /// that is defined in the same block as the branch and if any PHI entries are
1124 /// constants, thread edges corresponding to that entry to be branches to their
1125 /// ultimate destination.
1126 static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
1127 BasicBlock *BB = BI->getParent();
1128 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1129 // NOTE: we currently cannot transform this case if the PHI node is used
1130 // outside of the block.
1131 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1134 // Degenerate case of a single entry PHI.
1135 if (PN->getNumIncomingValues() == 1) {
1136 FoldSingleEntryPHINodes(PN->getParent());
1140 // Now we know that this block has multiple preds and two succs.
1141 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1143 // Okay, this is a simple enough basic block. See if any phi values are
1145 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1146 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1147 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1149 // Okay, we now know that all edges from PredBB should be revectored to
1150 // branch to RealDest.
1151 BasicBlock *PredBB = PN->getIncomingBlock(i);
1152 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1154 if (RealDest == BB) continue; // Skip self loops.
1156 // The dest block might have PHI nodes, other predecessors and other
1157 // difficult cases. Instead of being smart about this, just insert a new
1158 // block that jumps to the destination block, effectively splitting
1159 // the edge we are about to create.
1160 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1161 RealDest->getName()+".critedge",
1162 RealDest->getParent(), RealDest);
1163 BranchInst::Create(RealDest, EdgeBB);
1165 // Update PHI nodes.
1166 AddPredecessorToBlock(RealDest, EdgeBB, BB);
1168 // BB may have instructions that are being threaded over. Clone these
1169 // instructions into EdgeBB. We know that there will be no uses of the
1170 // cloned instructions outside of EdgeBB.
1171 BasicBlock::iterator InsertPt = EdgeBB->begin();
1172 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1173 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1174 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1175 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1178 // Clone the instruction.
1179 Instruction *N = BBI->clone();
1180 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1182 // Update operands due to translation.
1183 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1185 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1186 if (PI != TranslateMap.end())
1190 // Check for trivial simplification.
1191 if (Value *V = SimplifyInstruction(N, TD)) {
1192 TranslateMap[BBI] = V;
1193 delete N; // Instruction folded away, don't need actual inst
1195 // Insert the new instruction into its new home.
1196 EdgeBB->getInstList().insert(InsertPt, N);
1197 if (!BBI->use_empty())
1198 TranslateMap[BBI] = N;
1202 // Loop over all of the edges from PredBB to BB, changing them to branch
1203 // to EdgeBB instead.
1204 TerminatorInst *PredBBTI = PredBB->getTerminator();
1205 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1206 if (PredBBTI->getSuccessor(i) == BB) {
1207 BB->removePredecessor(PredBB);
1208 PredBBTI->setSuccessor(i, EdgeBB);
1211 // Recurse, simplifying any other constants.
1212 return FoldCondBranchOnPHI(BI, TD) | true;
1218 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1219 /// PHI node, see if we can eliminate it.
1220 static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
1221 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1222 // statement", which has a very simple dominance structure. Basically, we
1223 // are trying to find the condition that is being branched on, which
1224 // subsequently causes this merge to happen. We really want control
1225 // dependence information for this check, but simplifycfg can't keep it up
1226 // to date, and this catches most of the cases we care about anyway.
1227 BasicBlock *BB = PN->getParent();
1228 BasicBlock *IfTrue, *IfFalse;
1229 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1231 // Don't bother if the branch will be constant folded trivially.
1232 isa<ConstantInt>(IfCond))
1235 // Okay, we found that we can merge this two-entry phi node into a select.
1236 // Doing so would require us to fold *all* two entry phi nodes in this block.
1237 // At some point this becomes non-profitable (particularly if the target
1238 // doesn't support cmov's). Only do this transformation if there are two or
1239 // fewer PHI nodes in this block.
1240 unsigned NumPhis = 0;
1241 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1245 // Loop over the PHI's seeing if we can promote them all to select
1246 // instructions. While we are at it, keep track of the instructions
1247 // that need to be moved to the dominating block.
1248 SmallPtrSet<Instruction*, 4> AggressiveInsts;
1249 unsigned MaxCostVal0 = 1, MaxCostVal1 = 1;
1251 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1252 PHINode *PN = cast<PHINode>(II++);
1253 if (Value *V = SimplifyInstruction(PN, TD)) {
1254 PN->replaceAllUsesWith(V);
1255 PN->eraseFromParent();
1259 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
1261 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
1266 // If we folded the the first phi, PN dangles at this point. Refresh it. If
1267 // we ran out of PHIs then we simplified them all.
1268 PN = dyn_cast<PHINode>(BB->begin());
1269 if (PN == 0) return true;
1271 // Don't fold i1 branches on PHIs which contain binary operators. These can
1272 // often be turned into switches and other things.
1273 if (PN->getType()->isIntegerTy(1) &&
1274 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1275 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1276 isa<BinaryOperator>(IfCond)))
1279 // If we all PHI nodes are promotable, check to make sure that all
1280 // instructions in the predecessor blocks can be promoted as well. If
1281 // not, we won't be able to get rid of the control flow, so it's not
1282 // worth promoting to select instructions.
1283 BasicBlock *DomBlock = 0;
1284 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1285 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1286 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1289 DomBlock = *pred_begin(IfBlock1);
1290 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1291 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1292 // This is not an aggressive instruction that we can promote.
1293 // Because of this, we won't be able to get rid of the control
1294 // flow, so the xform is not worth it.
1299 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1302 DomBlock = *pred_begin(IfBlock2);
1303 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1304 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1305 // This is not an aggressive instruction that we can promote.
1306 // Because of this, we won't be able to get rid of the control
1307 // flow, so the xform is not worth it.
1312 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1313 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1315 // If we can still promote the PHI nodes after this gauntlet of tests,
1316 // do all of the PHI's now.
1317 Instruction *InsertPt = DomBlock->getTerminator();
1319 // Move all 'aggressive' instructions, which are defined in the
1320 // conditional parts of the if's up to the dominating block.
1322 DomBlock->getInstList().splice(InsertPt,
1323 IfBlock1->getInstList(), IfBlock1->begin(),
1324 IfBlock1->getTerminator());
1326 DomBlock->getInstList().splice(InsertPt,
1327 IfBlock2->getInstList(), IfBlock2->begin(),
1328 IfBlock2->getTerminator());
1330 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1331 // Change the PHI node into a select instruction.
1332 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1333 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1335 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", InsertPt);
1336 PN->replaceAllUsesWith(NV);
1338 PN->eraseFromParent();
1341 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1342 // has been flattened. Change DomBlock to jump directly to our new block to
1343 // avoid other simplifycfg's kicking in on the diamond.
1344 TerminatorInst *OldTI = DomBlock->getTerminator();
1345 BranchInst::Create(BB, OldTI);
1346 OldTI->eraseFromParent();
1350 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1351 /// to two returning blocks, try to merge them together into one return,
1352 /// introducing a select if the return values disagree.
1353 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1354 assert(BI->isConditional() && "Must be a conditional branch");
1355 BasicBlock *TrueSucc = BI->getSuccessor(0);
1356 BasicBlock *FalseSucc = BI->getSuccessor(1);
1357 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1358 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1360 // Check to ensure both blocks are empty (just a return) or optionally empty
1361 // with PHI nodes. If there are other instructions, merging would cause extra
1362 // computation on one path or the other.
1363 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1365 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1368 // Okay, we found a branch that is going to two return nodes. If
1369 // there is no return value for this function, just change the
1370 // branch into a return.
1371 if (FalseRet->getNumOperands() == 0) {
1372 TrueSucc->removePredecessor(BI->getParent());
1373 FalseSucc->removePredecessor(BI->getParent());
1374 ReturnInst::Create(BI->getContext(), 0, BI);
1375 EraseTerminatorInstAndDCECond(BI);
1379 // Otherwise, figure out what the true and false return values are
1380 // so we can insert a new select instruction.
1381 Value *TrueValue = TrueRet->getReturnValue();
1382 Value *FalseValue = FalseRet->getReturnValue();
1384 // Unwrap any PHI nodes in the return blocks.
1385 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1386 if (TVPN->getParent() == TrueSucc)
1387 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1388 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1389 if (FVPN->getParent() == FalseSucc)
1390 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1392 // In order for this transformation to be safe, we must be able to
1393 // unconditionally execute both operands to the return. This is
1394 // normally the case, but we could have a potentially-trapping
1395 // constant expression that prevents this transformation from being
1397 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1400 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1404 // Okay, we collected all the mapped values and checked them for sanity, and
1405 // defined to really do this transformation. First, update the CFG.
1406 TrueSucc->removePredecessor(BI->getParent());
1407 FalseSucc->removePredecessor(BI->getParent());
1409 // Insert select instructions where needed.
1410 Value *BrCond = BI->getCondition();
1412 // Insert a select if the results differ.
1413 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1414 } else if (isa<UndefValue>(TrueValue)) {
1415 TrueValue = FalseValue;
1417 TrueValue = SelectInst::Create(BrCond, TrueValue,
1418 FalseValue, "retval", BI);
1422 Value *RI = !TrueValue ?
1423 ReturnInst::Create(BI->getContext(), BI) :
1424 ReturnInst::Create(BI->getContext(), TrueValue, BI);
1427 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1428 << "\n " << *BI << "NewRet = " << *RI
1429 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1431 EraseTerminatorInstAndDCECond(BI);
1436 /// FoldBranchToCommonDest - If this basic block is simple enough, and if a
1437 /// predecessor branches to us and one of our successors, fold the block into
1438 /// the predecessor and use logical operations to pick the right destination.
1439 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1440 BasicBlock *BB = BI->getParent();
1441 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1442 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1443 Cond->getParent() != BB || !Cond->hasOneUse())
1446 // Only allow this if the condition is a simple instruction that can be
1447 // executed unconditionally. It must be in the same block as the branch, and
1448 // must be at the front of the block.
1449 BasicBlock::iterator FrontIt = BB->front();
1451 // Ignore dbg intrinsics.
1452 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1454 // Allow a single instruction to be hoisted in addition to the compare
1455 // that feeds the branch. We later ensure that any values that _it_ uses
1456 // were also live in the predecessor, so that we don't unnecessarily create
1457 // register pressure or inhibit out-of-order execution.
1458 Instruction *BonusInst = 0;
1459 if (&*FrontIt != Cond &&
1460 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1461 FrontIt->isSafeToSpeculativelyExecute()) {
1462 BonusInst = &*FrontIt;
1465 // Ignore dbg intrinsics.
1466 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1469 // Only a single bonus inst is allowed.
1470 if (&*FrontIt != Cond)
1473 // Make sure the instruction after the condition is the cond branch.
1474 BasicBlock::iterator CondIt = Cond; ++CondIt;
1476 // Ingore dbg intrinsics.
1477 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
1482 // Cond is known to be a compare or binary operator. Check to make sure that
1483 // neither operand is a potentially-trapping constant expression.
1484 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1487 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1491 // Finally, don't infinitely unroll conditional loops.
1492 BasicBlock *TrueDest = BI->getSuccessor(0);
1493 BasicBlock *FalseDest = BI->getSuccessor(1);
1494 if (TrueDest == BB || FalseDest == BB)
1497 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1498 BasicBlock *PredBlock = *PI;
1499 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1501 // Check that we have two conditional branches. If there is a PHI node in
1502 // the common successor, verify that the same value flows in from both
1504 if (PBI == 0 || PBI->isUnconditional() || !SafeToMergeTerminators(BI, PBI))
1507 // Determine if the two branches share a common destination.
1508 Instruction::BinaryOps Opc;
1509 bool InvertPredCond = false;
1511 if (PBI->getSuccessor(0) == TrueDest)
1512 Opc = Instruction::Or;
1513 else if (PBI->getSuccessor(1) == FalseDest)
1514 Opc = Instruction::And;
1515 else if (PBI->getSuccessor(0) == FalseDest)
1516 Opc = Instruction::And, InvertPredCond = true;
1517 else if (PBI->getSuccessor(1) == TrueDest)
1518 Opc = Instruction::Or, InvertPredCond = true;
1522 // Ensure that any values used in the bonus instruction are also used
1523 // by the terminator of the predecessor. This means that those values
1524 // must already have been resolved, so we won't be inhibiting the
1525 // out-of-order core by speculating them earlier.
1527 // Collect the values used by the bonus inst
1528 SmallPtrSet<Value*, 4> UsedValues;
1529 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1530 OE = BonusInst->op_end(); OI != OE; ++OI) {
1532 if (!isa<Constant>(V))
1533 UsedValues.insert(V);
1536 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1537 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1539 // Walk up to four levels back up the use-def chain of the predecessor's
1540 // terminator to see if all those values were used. The choice of four
1541 // levels is arbitrary, to provide a compile-time-cost bound.
1542 while (!Worklist.empty()) {
1543 std::pair<Value*, unsigned> Pair = Worklist.back();
1544 Worklist.pop_back();
1546 if (Pair.second >= 4) continue;
1547 UsedValues.erase(Pair.first);
1548 if (UsedValues.empty()) break;
1550 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
1551 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1553 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1557 if (!UsedValues.empty()) return false;
1560 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1562 // If we need to invert the condition in the pred block to match, do so now.
1563 if (InvertPredCond) {
1564 Value *NewCond = PBI->getCondition();
1566 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
1567 CmpInst *CI = cast<CmpInst>(NewCond);
1568 CI->setPredicate(CI->getInversePredicate());
1570 NewCond = BinaryOperator::CreateNot(NewCond,
1571 PBI->getCondition()->getName()+".not", PBI);
1574 PBI->setCondition(NewCond);
1575 BasicBlock *OldTrue = PBI->getSuccessor(0);
1576 BasicBlock *OldFalse = PBI->getSuccessor(1);
1577 PBI->setSuccessor(0, OldFalse);
1578 PBI->setSuccessor(1, OldTrue);
1581 // If we have a bonus inst, clone it into the predecessor block.
1582 Instruction *NewBonus = 0;
1584 NewBonus = BonusInst->clone();
1585 PredBlock->getInstList().insert(PBI, NewBonus);
1586 NewBonus->takeName(BonusInst);
1587 BonusInst->setName(BonusInst->getName()+".old");
1590 // Clone Cond into the predecessor basic block, and or/and the
1591 // two conditions together.
1592 Instruction *New = Cond->clone();
1593 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1594 PredBlock->getInstList().insert(PBI, New);
1595 New->takeName(Cond);
1596 Cond->setName(New->getName()+".old");
1598 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1599 New, "or.cond", PBI);
1600 PBI->setCondition(NewCond);
1601 if (PBI->getSuccessor(0) == BB) {
1602 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1603 PBI->setSuccessor(0, TrueDest);
1605 if (PBI->getSuccessor(1) == BB) {
1606 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1607 PBI->setSuccessor(1, FalseDest);
1610 // Copy any debug value intrinsics into the end of PredBlock.
1611 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
1612 if (isa<DbgInfoIntrinsic>(*I))
1613 I->clone()->insertBefore(PBI);
1620 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1621 /// predecessor of another block, this function tries to simplify it. We know
1622 /// that PBI and BI are both conditional branches, and BI is in one of the
1623 /// successor blocks of PBI - PBI branches to BI.
1624 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1625 assert(PBI->isConditional() && BI->isConditional());
1626 BasicBlock *BB = BI->getParent();
1628 // If this block ends with a branch instruction, and if there is a
1629 // predecessor that ends on a branch of the same condition, make
1630 // this conditional branch redundant.
1631 if (PBI->getCondition() == BI->getCondition() &&
1632 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1633 // Okay, the outcome of this conditional branch is statically
1634 // knowable. If this block had a single pred, handle specially.
1635 if (BB->getSinglePredecessor()) {
1636 // Turn this into a branch on constant.
1637 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1638 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1640 return true; // Nuke the branch on constant.
1643 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1644 // in the constant and simplify the block result. Subsequent passes of
1645 // simplifycfg will thread the block.
1646 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1647 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
1648 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1649 std::distance(PB, PE),
1650 BI->getCondition()->getName() + ".pr",
1652 // Okay, we're going to insert the PHI node. Since PBI is not the only
1653 // predecessor, compute the PHI'd conditional value for all of the preds.
1654 // Any predecessor where the condition is not computable we keep symbolic.
1655 for (pred_iterator PI = PB; PI != PE; ++PI) {
1656 BasicBlock *P = *PI;
1657 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
1658 PBI != BI && PBI->isConditional() &&
1659 PBI->getCondition() == BI->getCondition() &&
1660 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1661 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1662 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1665 NewPN->addIncoming(BI->getCondition(), P);
1669 BI->setCondition(NewPN);
1674 // If this is a conditional branch in an empty block, and if any
1675 // predecessors is a conditional branch to one of our destinations,
1676 // fold the conditions into logical ops and one cond br.
1677 BasicBlock::iterator BBI = BB->begin();
1678 // Ignore dbg intrinsics.
1679 while (isa<DbgInfoIntrinsic>(BBI))
1685 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1690 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1692 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1693 PBIOp = 0, BIOp = 1;
1694 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1695 PBIOp = 1, BIOp = 0;
1696 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1701 // Check to make sure that the other destination of this branch
1702 // isn't BB itself. If so, this is an infinite loop that will
1703 // keep getting unwound.
1704 if (PBI->getSuccessor(PBIOp) == BB)
1707 // Do not perform this transformation if it would require
1708 // insertion of a large number of select instructions. For targets
1709 // without predication/cmovs, this is a big pessimization.
1710 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1712 unsigned NumPhis = 0;
1713 for (BasicBlock::iterator II = CommonDest->begin();
1714 isa<PHINode>(II); ++II, ++NumPhis)
1715 if (NumPhis > 2) // Disable this xform.
1718 // Finally, if everything is ok, fold the branches to logical ops.
1719 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1721 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
1722 << "AND: " << *BI->getParent());
1725 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1726 // branch in it, where one edge (OtherDest) goes back to itself but the other
1727 // exits. We don't *know* that the program avoids the infinite loop
1728 // (even though that seems likely). If we do this xform naively, we'll end up
1729 // recursively unpeeling the loop. Since we know that (after the xform is
1730 // done) that the block *is* infinite if reached, we just make it an obviously
1731 // infinite loop with no cond branch.
1732 if (OtherDest == BB) {
1733 // Insert it at the end of the function, because it's either code,
1734 // or it won't matter if it's hot. :)
1735 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1736 "infloop", BB->getParent());
1737 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1738 OtherDest = InfLoopBlock;
1741 DEBUG(dbgs() << *PBI->getParent()->getParent());
1743 // BI may have other predecessors. Because of this, we leave
1744 // it alone, but modify PBI.
1746 // Make sure we get to CommonDest on True&True directions.
1747 Value *PBICond = PBI->getCondition();
1749 PBICond = BinaryOperator::CreateNot(PBICond,
1750 PBICond->getName()+".not",
1752 Value *BICond = BI->getCondition();
1754 BICond = BinaryOperator::CreateNot(BICond,
1755 BICond->getName()+".not",
1757 // Merge the conditions.
1758 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1760 // Modify PBI to branch on the new condition to the new dests.
1761 PBI->setCondition(Cond);
1762 PBI->setSuccessor(0, CommonDest);
1763 PBI->setSuccessor(1, OtherDest);
1765 // OtherDest may have phi nodes. If so, add an entry from PBI's
1766 // block that are identical to the entries for BI's block.
1767 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
1769 // We know that the CommonDest already had an edge from PBI to
1770 // it. If it has PHIs though, the PHIs may have different
1771 // entries for BB and PBI's BB. If so, insert a select to make
1774 for (BasicBlock::iterator II = CommonDest->begin();
1775 (PN = dyn_cast<PHINode>(II)); ++II) {
1776 Value *BIV = PN->getIncomingValueForBlock(BB);
1777 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1778 Value *PBIV = PN->getIncomingValue(PBBIdx);
1780 // Insert a select in PBI to pick the right value.
1781 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1782 PBIV->getName()+".mux", PBI);
1783 PN->setIncomingValue(PBBIdx, NV);
1787 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1788 DEBUG(dbgs() << *PBI->getParent()->getParent());
1790 // This basic block is probably dead. We know it has at least
1791 // one fewer predecessor.
1795 // SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
1796 // branch to TrueBB if Cond is true or to FalseBB if Cond is false.
1797 // Takes care of updating the successors and removing the old terminator.
1798 // Also makes sure not to introduce new successors by assuming that edges to
1799 // non-successor TrueBBs and FalseBBs aren't reachable.
1800 static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
1801 BasicBlock *TrueBB, BasicBlock *FalseBB){
1802 // Remove any superfluous successor edges from the CFG.
1803 // First, figure out which successors to preserve.
1804 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
1806 BasicBlock *KeepEdge1 = TrueBB;
1807 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
1809 // Then remove the rest.
1810 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
1811 BasicBlock *Succ = OldTerm->getSuccessor(I);
1812 // Make sure only to keep exactly one copy of each edge.
1813 if (Succ == KeepEdge1)
1815 else if (Succ == KeepEdge2)
1818 Succ->removePredecessor(OldTerm->getParent());
1821 // Insert an appropriate new terminator.
1822 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
1823 if (TrueBB == FalseBB)
1824 // We were only looking for one successor, and it was present.
1825 // Create an unconditional branch to it.
1826 BranchInst::Create(TrueBB, OldTerm);
1828 // We found both of the successors we were looking for.
1829 // Create a conditional branch sharing the condition of the select.
1830 BranchInst::Create(TrueBB, FalseBB, Cond, OldTerm);
1831 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
1832 // Neither of the selected blocks were successors, so this
1833 // terminator must be unreachable.
1834 new UnreachableInst(OldTerm->getContext(), OldTerm);
1836 // One of the selected values was a successor, but the other wasn't.
1837 // Insert an unconditional branch to the one that was found;
1838 // the edge to the one that wasn't must be unreachable.
1840 // Only TrueBB was found.
1841 BranchInst::Create(TrueBB, OldTerm);
1843 // Only FalseBB was found.
1844 BranchInst::Create(FalseBB, OldTerm);
1847 EraseTerminatorInstAndDCECond(OldTerm);
1851 // SimplifySwitchOnSelect - Replaces
1852 // (switch (select cond, X, Y)) on constant X, Y
1853 // with a branch - conditional if X and Y lead to distinct BBs,
1854 // unconditional otherwise.
1855 static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
1856 // Check for constant integer values in the select.
1857 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
1858 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
1859 if (!TrueVal || !FalseVal)
1862 // Find the relevant condition and destinations.
1863 Value *Condition = Select->getCondition();
1864 BasicBlock *TrueBB = SI->getSuccessor(SI->findCaseValue(TrueVal));
1865 BasicBlock *FalseBB = SI->getSuccessor(SI->findCaseValue(FalseVal));
1867 // Perform the actual simplification.
1868 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB);
1871 // SimplifyIndirectBrOnSelect - Replaces
1872 // (indirectbr (select cond, blockaddress(@fn, BlockA),
1873 // blockaddress(@fn, BlockB)))
1875 // (br cond, BlockA, BlockB).
1876 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
1877 // Check that both operands of the select are block addresses.
1878 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
1879 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
1883 // Extract the actual blocks.
1884 BasicBlock *TrueBB = TBA->getBasicBlock();
1885 BasicBlock *FalseBB = FBA->getBasicBlock();
1887 // Perform the actual simplification.
1888 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB);
1891 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
1892 /// instruction (a seteq/setne with a constant) as the only instruction in a
1893 /// block that ends with an uncond branch. We are looking for a very specific
1894 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
1895 /// this case, we merge the first two "or's of icmp" into a switch, but then the
1896 /// default value goes to an uncond block with a seteq in it, we get something
1899 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
1901 /// %tmp = icmp eq i8 %A, 92
1904 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
1906 /// We prefer to split the edge to 'end' so that there is a true/false entry to
1907 /// the PHI, merging the third icmp into the switch.
1908 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
1909 const TargetData *TD) {
1910 BasicBlock *BB = ICI->getParent();
1911 // If the block has any PHIs in it or the icmp has multiple uses, it is too
1913 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
1915 Value *V = ICI->getOperand(0);
1916 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
1918 // The pattern we're looking for is where our only predecessor is a switch on
1919 // 'V' and this block is the default case for the switch. In this case we can
1920 // fold the compared value into the switch to simplify things.
1921 BasicBlock *Pred = BB->getSinglePredecessor();
1922 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
1924 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
1925 if (SI->getCondition() != V)
1928 // If BB is reachable on a non-default case, then we simply know the value of
1929 // V in this block. Substitute it and constant fold the icmp instruction
1931 if (SI->getDefaultDest() != BB) {
1932 ConstantInt *VVal = SI->findCaseDest(BB);
1933 assert(VVal && "Should have a unique destination value");
1934 ICI->setOperand(0, VVal);
1936 if (Value *V = SimplifyInstruction(ICI, TD)) {
1937 ICI->replaceAllUsesWith(V);
1938 ICI->eraseFromParent();
1940 // BB is now empty, so it is likely to simplify away.
1941 return SimplifyCFG(BB) | true;
1944 // Ok, the block is reachable from the default dest. If the constant we're
1945 // comparing exists in one of the other edges, then we can constant fold ICI
1947 if (SI->findCaseValue(Cst) != 0) {
1949 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1950 V = ConstantInt::getFalse(BB->getContext());
1952 V = ConstantInt::getTrue(BB->getContext());
1954 ICI->replaceAllUsesWith(V);
1955 ICI->eraseFromParent();
1956 // BB is now empty, so it is likely to simplify away.
1957 return SimplifyCFG(BB) | true;
1960 // The use of the icmp has to be in the 'end' block, by the only PHI node in
1962 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
1963 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
1964 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
1965 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
1968 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
1970 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
1971 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
1973 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1974 std::swap(DefaultCst, NewCst);
1976 // Replace ICI (which is used by the PHI for the default value) with true or
1977 // false depending on if it is EQ or NE.
1978 ICI->replaceAllUsesWith(DefaultCst);
1979 ICI->eraseFromParent();
1981 // Okay, the switch goes to this block on a default value. Add an edge from
1982 // the switch to the merge point on the compared value.
1983 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
1984 BB->getParent(), BB);
1985 SI->addCase(Cst, NewBB);
1987 // NewBB branches to the phi block, add the uncond branch and the phi entry.
1988 BranchInst::Create(SuccBlock, NewBB);
1989 PHIUse->addIncoming(NewCst, NewBB);
1993 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
1994 /// Check to see if it is branching on an or/and chain of icmp instructions, and
1995 /// fold it into a switch instruction if so.
1996 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD) {
1997 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1998 if (Cond == 0) return false;
2001 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2002 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2003 // 'setne's and'ed together, collect them.
2005 std::vector<ConstantInt*> Values;
2006 bool TrueWhenEqual = true;
2007 Value *ExtraCase = 0;
2008 unsigned UsedICmps = 0;
2010 if (Cond->getOpcode() == Instruction::Or) {
2011 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
2013 } else if (Cond->getOpcode() == Instruction::And) {
2014 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
2016 TrueWhenEqual = false;
2019 // If we didn't have a multiply compared value, fail.
2020 if (CompVal == 0) return false;
2022 // Avoid turning single icmps into a switch.
2026 // There might be duplicate constants in the list, which the switch
2027 // instruction can't handle, remove them now.
2028 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
2029 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2031 // If Extra was used, we require at least two switch values to do the
2032 // transformation. A switch with one value is just an cond branch.
2033 if (ExtraCase && Values.size() < 2) return false;
2035 // Figure out which block is which destination.
2036 BasicBlock *DefaultBB = BI->getSuccessor(1);
2037 BasicBlock *EdgeBB = BI->getSuccessor(0);
2038 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2040 BasicBlock *BB = BI->getParent();
2042 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
2043 << " cases into SWITCH. BB is:\n" << *BB);
2045 // If there are any extra values that couldn't be folded into the switch
2046 // then we evaluate them with an explicit branch first. Split the block
2047 // right before the condbr to handle it.
2049 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
2050 // Remove the uncond branch added to the old block.
2051 TerminatorInst *OldTI = BB->getTerminator();
2054 BranchInst::Create(EdgeBB, NewBB, ExtraCase, OldTI);
2056 BranchInst::Create(NewBB, EdgeBB, ExtraCase, OldTI);
2058 OldTI->eraseFromParent();
2060 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
2061 // for the edge we just added.
2062 AddPredecessorToBlock(EdgeBB, BB, NewBB);
2064 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
2065 << "\nEXTRABB = " << *BB);
2069 // Convert pointer to int before we switch.
2070 if (CompVal->getType()->isPointerTy()) {
2071 assert(TD && "Cannot switch on pointer without TargetData");
2072 CompVal = new PtrToIntInst(CompVal,
2073 TD->getIntPtrType(CompVal->getContext()),
2077 // Create the new switch instruction now.
2078 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB, Values.size(), BI);
2080 // Add all of the 'cases' to the switch instruction.
2081 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2082 New->addCase(Values[i], EdgeBB);
2084 // We added edges from PI to the EdgeBB. As such, if there were any
2085 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2086 // the number of edges added.
2087 for (BasicBlock::iterator BBI = EdgeBB->begin();
2088 isa<PHINode>(BBI); ++BBI) {
2089 PHINode *PN = cast<PHINode>(BBI);
2090 Value *InVal = PN->getIncomingValueForBlock(BB);
2091 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2092 PN->addIncoming(InVal, BB);
2095 // Erase the old branch instruction.
2096 EraseTerminatorInstAndDCECond(BI);
2098 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
2102 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI) {
2103 BasicBlock *BB = RI->getParent();
2104 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2106 // Find predecessors that end with branches.
2107 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2108 SmallVector<BranchInst*, 8> CondBranchPreds;
2109 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2110 BasicBlock *P = *PI;
2111 TerminatorInst *PTI = P->getTerminator();
2112 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2113 if (BI->isUnconditional())
2114 UncondBranchPreds.push_back(P);
2116 CondBranchPreds.push_back(BI);
2120 // If we found some, do the transformation!
2121 if (!UncondBranchPreds.empty() && DupRet) {
2122 while (!UncondBranchPreds.empty()) {
2123 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2124 DEBUG(dbgs() << "FOLDING: " << *BB
2125 << "INTO UNCOND BRANCH PRED: " << *Pred);
2126 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
2129 // If we eliminated all predecessors of the block, delete the block now.
2130 if (pred_begin(BB) == pred_end(BB))
2131 // We know there are no successors, so just nuke the block.
2132 BB->eraseFromParent();
2137 // Check out all of the conditional branches going to this return
2138 // instruction. If any of them just select between returns, change the
2139 // branch itself into a select/return pair.
2140 while (!CondBranchPreds.empty()) {
2141 BranchInst *BI = CondBranchPreds.pop_back_val();
2143 // Check to see if the non-BB successor is also a return block.
2144 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2145 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2146 SimplifyCondBranchToTwoReturns(BI))
2152 bool SimplifyCFGOpt::SimplifyUnwind(UnwindInst *UI) {
2153 // Check to see if the first instruction in this block is just an unwind.
2154 // If so, replace any invoke instructions which use this as an exception
2155 // destination with call instructions.
2156 BasicBlock *BB = UI->getParent();
2157 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2159 bool Changed = false;
2160 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2161 while (!Preds.empty()) {
2162 BasicBlock *Pred = Preds.back();
2163 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
2164 if (II && II->getUnwindDest() == BB) {
2165 // Insert a new branch instruction before the invoke, because this
2166 // is now a fall through.
2167 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2168 Pred->getInstList().remove(II); // Take out of symbol table
2170 // Insert the call now.
2171 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
2172 CallInst *CI = CallInst::Create(II->getCalledValue(),
2173 Args.begin(), Args.end(),
2175 CI->setCallingConv(II->getCallingConv());
2176 CI->setAttributes(II->getAttributes());
2177 // If the invoke produced a value, the Call now does instead.
2178 II->replaceAllUsesWith(CI);
2186 // If this block is now dead (and isn't the entry block), remove it.
2187 if (pred_begin(BB) == pred_end(BB) &&
2188 BB != &BB->getParent()->getEntryBlock()) {
2189 // We know there are no successors, so just nuke the block.
2190 BB->eraseFromParent();
2197 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2198 BasicBlock *BB = UI->getParent();
2200 bool Changed = false;
2202 // If there are any instructions immediately before the unreachable that can
2203 // be removed, do so.
2204 while (UI != BB->begin()) {
2205 BasicBlock::iterator BBI = UI;
2207 // Do not delete instructions that can have side effects, like calls
2208 // (which may never return) and volatile loads and stores.
2209 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2211 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
2212 if (SI->isVolatile())
2215 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
2216 if (LI->isVolatile())
2219 // Delete this instruction (any uses are guaranteed to be dead)
2220 if (!BBI->use_empty())
2221 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
2222 BBI->eraseFromParent();
2226 // If the unreachable instruction is the first in the block, take a gander
2227 // at all of the predecessors of this instruction, and simplify them.
2228 if (&BB->front() != UI) return Changed;
2230 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2231 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2232 TerminatorInst *TI = Preds[i]->getTerminator();
2234 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2235 if (BI->isUnconditional()) {
2236 if (BI->getSuccessor(0) == BB) {
2237 new UnreachableInst(TI->getContext(), TI);
2238 TI->eraseFromParent();
2242 if (BI->getSuccessor(0) == BB) {
2243 BranchInst::Create(BI->getSuccessor(1), BI);
2244 EraseTerminatorInstAndDCECond(BI);
2245 } else if (BI->getSuccessor(1) == BB) {
2246 BranchInst::Create(BI->getSuccessor(0), BI);
2247 EraseTerminatorInstAndDCECond(BI);
2251 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2252 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2253 if (SI->getSuccessor(i) == BB) {
2254 BB->removePredecessor(SI->getParent());
2259 // If the default value is unreachable, figure out the most popular
2260 // destination and make it the default.
2261 if (SI->getSuccessor(0) == BB) {
2262 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
2263 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
2264 std::pair<unsigned, unsigned>& entry =
2265 Popularity[SI->getSuccessor(i)];
2266 if (entry.first == 0) {
2274 // Find the most popular block.
2275 unsigned MaxPop = 0;
2276 unsigned MaxIndex = 0;
2277 BasicBlock *MaxBlock = 0;
2278 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
2279 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2280 if (I->second.first > MaxPop ||
2281 (I->second.first == MaxPop && MaxIndex > I->second.second)) {
2282 MaxPop = I->second.first;
2283 MaxIndex = I->second.second;
2284 MaxBlock = I->first;
2288 // Make this the new default, allowing us to delete any explicit
2290 SI->setSuccessor(0, MaxBlock);
2293 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2295 if (isa<PHINode>(MaxBlock->begin()))
2296 for (unsigned i = 0; i != MaxPop-1; ++i)
2297 MaxBlock->removePredecessor(SI->getParent());
2299 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2300 if (SI->getSuccessor(i) == MaxBlock) {
2306 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2307 if (II->getUnwindDest() == BB) {
2308 // Convert the invoke to a call instruction. This would be a good
2309 // place to note that the call does not throw though.
2310 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2311 II->removeFromParent(); // Take out of symbol table
2313 // Insert the call now...
2314 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2315 CallInst *CI = CallInst::Create(II->getCalledValue(),
2316 Args.begin(), Args.end(),
2318 CI->setCallingConv(II->getCallingConv());
2319 CI->setAttributes(II->getAttributes());
2320 // If the invoke produced a value, the call does now instead.
2321 II->replaceAllUsesWith(CI);
2328 // If this block is now dead, remove it.
2329 if (pred_begin(BB) == pred_end(BB) &&
2330 BB != &BB->getParent()->getEntryBlock()) {
2331 // We know there are no successors, so just nuke the block.
2332 BB->eraseFromParent();
2339 /// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
2340 /// integer range comparison into a sub, an icmp and a branch.
2341 static bool TurnSwitchRangeIntoICmp(SwitchInst *SI) {
2342 assert(SI->getNumCases() > 2 && "Degenerate switch?");
2344 // Make sure all cases point to the same destination and gather the values.
2345 SmallVector<ConstantInt *, 16> Cases;
2346 Cases.push_back(SI->getCaseValue(1));
2347 for (unsigned I = 2, E = SI->getNumCases(); I != E; ++I) {
2348 if (SI->getSuccessor(I-1) != SI->getSuccessor(I))
2350 Cases.push_back(SI->getCaseValue(I));
2352 assert(Cases.size() == SI->getNumCases()-1 && "Not all cases gathered");
2354 // Sort the case values, then check if they form a range we can transform.
2355 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
2356 for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
2357 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
2361 Constant *Offset = ConstantExpr::getNeg(Cases.back());
2362 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases()-1);
2364 Value *Sub = SI->getCondition();
2365 if (!Offset->isNullValue())
2366 Sub = BinaryOperator::CreateAdd(Sub, Offset, Sub->getName()+".off", SI);
2367 Value *Cmp = new ICmpInst(SI, ICmpInst::ICMP_ULT, Sub, NumCases, "switch");
2368 BranchInst::Create(SI->getSuccessor(1), SI->getDefaultDest(), Cmp, SI);
2370 // Prune obsolete incoming values off the successor's PHI nodes.
2371 for (BasicBlock::iterator BBI = SI->getSuccessor(1)->begin();
2372 isa<PHINode>(BBI); ++BBI) {
2373 for (unsigned I = 0, E = SI->getNumCases()-2; I != E; ++I)
2374 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
2376 SI->eraseFromParent();
2381 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI) {
2382 // If this switch is too complex to want to look at, ignore it.
2383 if (!isValueEqualityComparison(SI))
2386 BasicBlock *BB = SI->getParent();
2388 // If we only have one predecessor, and if it is a branch on this value,
2389 // see if that predecessor totally determines the outcome of this switch.
2390 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2391 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
2392 return SimplifyCFG(BB) | true;
2394 Value *Cond = SI->getCondition();
2395 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
2396 if (SimplifySwitchOnSelect(SI, Select))
2397 return SimplifyCFG(BB) | true;
2399 // If the block only contains the switch, see if we can fold the block
2400 // away into any preds.
2401 BasicBlock::iterator BBI = BB->begin();
2402 // Ignore dbg intrinsics.
2403 while (isa<DbgInfoIntrinsic>(BBI))
2406 if (FoldValueComparisonIntoPredecessors(SI))
2407 return SimplifyCFG(BB) | true;
2409 // Try to transform the switch into an icmp and a branch.
2410 if (TurnSwitchRangeIntoICmp(SI))
2411 return SimplifyCFG(BB) | true;
2416 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
2417 BasicBlock *BB = IBI->getParent();
2418 bool Changed = false;
2420 // Eliminate redundant destinations.
2421 SmallPtrSet<Value *, 8> Succs;
2422 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2423 BasicBlock *Dest = IBI->getDestination(i);
2424 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2425 Dest->removePredecessor(BB);
2426 IBI->removeDestination(i);
2432 if (IBI->getNumDestinations() == 0) {
2433 // If the indirectbr has no successors, change it to unreachable.
2434 new UnreachableInst(IBI->getContext(), IBI);
2435 EraseTerminatorInstAndDCECond(IBI);
2439 if (IBI->getNumDestinations() == 1) {
2440 // If the indirectbr has one successor, change it to a direct branch.
2441 BranchInst::Create(IBI->getDestination(0), IBI);
2442 EraseTerminatorInstAndDCECond(IBI);
2446 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2447 if (SimplifyIndirectBrOnSelect(IBI, SI))
2448 return SimplifyCFG(BB) | true;
2453 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI) {
2454 BasicBlock *BB = BI->getParent();
2456 // If the Terminator is the only non-phi instruction, simplify the block.
2457 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg();
2458 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
2459 TryToSimplifyUncondBranchFromEmptyBlock(BB))
2462 // If the only instruction in the block is a seteq/setne comparison
2463 // against a constant, try to simplify the block.
2464 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
2465 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
2466 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
2468 if (I->isTerminator() && TryToSimplifyUncondBranchWithICmpInIt(ICI, TD))
2476 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI) {
2477 BasicBlock *BB = BI->getParent();
2479 // Conditional branch
2480 if (isValueEqualityComparison(BI)) {
2481 // If we only have one predecessor, and if it is a branch on this value,
2482 // see if that predecessor totally determines the outcome of this
2484 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2485 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
2486 return SimplifyCFG(BB) | true;
2488 // This block must be empty, except for the setcond inst, if it exists.
2489 // Ignore dbg intrinsics.
2490 BasicBlock::iterator I = BB->begin();
2491 // Ignore dbg intrinsics.
2492 while (isa<DbgInfoIntrinsic>(I))
2495 if (FoldValueComparisonIntoPredecessors(BI))
2496 return SimplifyCFG(BB) | true;
2497 } else if (&*I == cast<Instruction>(BI->getCondition())){
2499 // Ignore dbg intrinsics.
2500 while (isa<DbgInfoIntrinsic>(I))
2502 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI))
2503 return SimplifyCFG(BB) | true;
2507 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
2508 if (SimplifyBranchOnICmpChain(BI, TD))
2511 // We have a conditional branch to two blocks that are only reachable
2512 // from BI. We know that the condbr dominates the two blocks, so see if
2513 // there is any identical code in the "then" and "else" blocks. If so, we
2514 // can hoist it up to the branching block.
2515 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
2516 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2517 if (HoistThenElseCodeToIf(BI))
2518 return SimplifyCFG(BB) | true;
2520 // If Successor #1 has multiple preds, we may be able to conditionally
2521 // execute Successor #0 if it branches to successor #1.
2522 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
2523 if (Succ0TI->getNumSuccessors() == 1 &&
2524 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
2525 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
2526 return SimplifyCFG(BB) | true;
2528 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2529 // If Successor #0 has multiple preds, we may be able to conditionally
2530 // execute Successor #1 if it branches to successor #0.
2531 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
2532 if (Succ1TI->getNumSuccessors() == 1 &&
2533 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
2534 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
2535 return SimplifyCFG(BB) | true;
2538 // If this is a branch on a phi node in the current block, thread control
2539 // through this block if any PHI node entries are constants.
2540 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
2541 if (PN->getParent() == BI->getParent())
2542 if (FoldCondBranchOnPHI(BI, TD))
2543 return SimplifyCFG(BB) | true;
2545 // If this basic block is ONLY a setcc and a branch, and if a predecessor
2546 // branches to us and one of our successors, fold the setcc into the
2547 // predecessor and use logical operations to pick the right destination.
2548 if (FoldBranchToCommonDest(BI))
2549 return SimplifyCFG(BB) | true;
2551 // Scan predecessor blocks for conditional branches.
2552 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2553 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2554 if (PBI != BI && PBI->isConditional())
2555 if (SimplifyCondBranchToCondBranch(PBI, BI))
2556 return SimplifyCFG(BB) | true;
2561 bool SimplifyCFGOpt::run(BasicBlock *BB) {
2562 bool Changed = false;
2564 assert(BB && BB->getParent() && "Block not embedded in function!");
2565 assert(BB->getTerminator() && "Degenerate basic block encountered!");
2567 // Remove basic blocks that have no predecessors (except the entry block)...
2568 // or that just have themself as a predecessor. These are unreachable.
2569 if ((pred_begin(BB) == pred_end(BB) &&
2570 BB != &BB->getParent()->getEntryBlock()) ||
2571 BB->getSinglePredecessor() == BB) {
2572 DEBUG(dbgs() << "Removing BB: \n" << *BB);
2573 DeleteDeadBlock(BB);
2577 // Check to see if we can constant propagate this terminator instruction
2579 Changed |= ConstantFoldTerminator(BB);
2581 // Check for and eliminate duplicate PHI nodes in this block.
2582 Changed |= EliminateDuplicatePHINodes(BB);
2584 // Merge basic blocks into their predecessor if there is only one distinct
2585 // pred, and if there is only one distinct successor of the predecessor, and
2586 // if there are no PHI nodes.
2588 if (MergeBlockIntoPredecessor(BB))
2591 // If there is a trivial two-entry PHI node in this basic block, and we can
2592 // eliminate it, do so now.
2593 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
2594 if (PN->getNumIncomingValues() == 2)
2595 Changed |= FoldTwoEntryPHINode(PN, TD);
2597 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
2598 if (BI->isUnconditional()) {
2599 if (SimplifyUncondBranch(BI)) return true;
2601 if (SimplifyCondBranch(BI)) return true;
2603 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
2604 if (SimplifyReturn(RI)) return true;
2605 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
2606 if (SimplifySwitch(SI)) return true;
2607 } else if (UnreachableInst *UI =
2608 dyn_cast<UnreachableInst>(BB->getTerminator())) {
2609 if (SimplifyUnreachable(UI)) return true;
2610 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
2611 if (SimplifyUnwind(UI)) return true;
2612 } else if (IndirectBrInst *IBI =
2613 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
2614 if (SimplifyIndirectBr(IBI)) return true;
2620 /// SimplifyCFG - This function is used to do simplification of a CFG. For
2621 /// example, it adjusts branches to branches to eliminate the extra hop, it
2622 /// eliminates unreachable basic blocks, and does other "peephole" optimization
2623 /// of the CFG. It returns true if a modification was made.
2625 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
2626 return SimplifyCFGOpt(TD).run(BB);