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/Debug.h"
32 #include "llvm/Support/raw_ostream.h"
38 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
41 class SimplifyCFGOpt {
42 const TargetData *const TD;
44 Value *isValueEqualityComparison(TerminatorInst *TI);
45 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
46 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases);
47 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
49 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI);
51 bool SimplifyReturn(ReturnInst *RI);
52 bool SimplifyUnwind(UnwindInst *UI);
53 bool SimplifyUnreachable(UnreachableInst *UI);
54 bool SimplifySwitch(SwitchInst *SI);
55 bool SimplifyIndirectBr(IndirectBrInst *IBI);
56 bool SimplifyUncondBranch(BranchInst *BI);
57 bool SimplifyCondBranch(BranchInst *BI);
60 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
61 bool run(BasicBlock *BB);
65 /// SafeToMergeTerminators - Return true if it is safe to merge these two
66 /// terminator instructions together.
68 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
69 if (SI1 == SI2) return false; // Can't merge with self!
71 // It is not safe to merge these two switch instructions if they have a common
72 // successor, and if that successor has a PHI node, and if *that* PHI node has
73 // conflicting incoming values from the two switch blocks.
74 BasicBlock *SI1BB = SI1->getParent();
75 BasicBlock *SI2BB = SI2->getParent();
76 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
78 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
79 if (SI1Succs.count(*I))
80 for (BasicBlock::iterator BBI = (*I)->begin();
81 isa<PHINode>(BBI); ++BBI) {
82 PHINode *PN = cast<PHINode>(BBI);
83 if (PN->getIncomingValueForBlock(SI1BB) !=
84 PN->getIncomingValueForBlock(SI2BB))
91 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
92 /// now be entries in it from the 'NewPred' block. The values that will be
93 /// flowing into the PHI nodes will be the same as those coming in from
94 /// ExistPred, an existing predecessor of Succ.
95 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
96 BasicBlock *ExistPred) {
97 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
100 for (BasicBlock::iterator I = Succ->begin();
101 (PN = dyn_cast<PHINode>(I)); ++I)
102 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
106 /// GetIfCondition - Given a basic block (BB) with two predecessors (and at
107 /// least one PHI node in it), check to see if the merge at this block is due
108 /// to an "if condition". If so, return the boolean condition that determines
109 /// which entry into BB will be taken. Also, return by references the block
110 /// that will be entered from if the condition is true, and the block that will
111 /// be entered if the condition is false.
113 /// This does no checking to see if the true/false blocks have large or unsavory
114 /// instructions in them.
115 static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
116 BasicBlock *&IfFalse) {
117 PHINode *SomePHI = cast<PHINode>(BB->begin());
118 assert(SomePHI->getNumIncomingValues() == 2 &&
119 "Function can only handle blocks with 2 predecessors!");
120 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
121 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
123 // We can only handle branches. Other control flow will be lowered to
124 // branches if possible anyway.
125 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
126 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
127 if (Pred1Br == 0 || Pred2Br == 0)
130 // Eliminate code duplication by ensuring that Pred1Br is conditional if
132 if (Pred2Br->isConditional()) {
133 // If both branches are conditional, we don't have an "if statement". In
134 // reality, we could transform this case, but since the condition will be
135 // required anyway, we stand no chance of eliminating it, so the xform is
136 // probably not profitable.
137 if (Pred1Br->isConditional())
140 std::swap(Pred1, Pred2);
141 std::swap(Pred1Br, Pred2Br);
144 if (Pred1Br->isConditional()) {
145 // The only thing we have to watch out for here is to make sure that Pred2
146 // doesn't have incoming edges from other blocks. If it does, the condition
147 // doesn't dominate BB.
148 if (Pred2->getSinglePredecessor() == 0)
151 // If we found a conditional branch predecessor, make sure that it branches
152 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
153 if (Pred1Br->getSuccessor(0) == BB &&
154 Pred1Br->getSuccessor(1) == Pred2) {
157 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
158 Pred1Br->getSuccessor(1) == BB) {
162 // We know that one arm of the conditional goes to BB, so the other must
163 // go somewhere unrelated, and this must not be an "if statement".
167 return Pred1Br->getCondition();
170 // Ok, if we got here, both predecessors end with an unconditional branch to
171 // BB. Don't panic! If both blocks only have a single (identical)
172 // predecessor, and THAT is a conditional branch, then we're all ok!
173 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
174 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
177 // Otherwise, if this is a conditional branch, then we can use it!
178 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
179 if (BI == 0) return 0;
181 assert(BI->isConditional() && "Two successors but not conditional?");
182 if (BI->getSuccessor(0) == Pred1) {
189 return BI->getCondition();
192 /// DominatesMergePoint - If we have a merge point of an "if condition" as
193 /// accepted above, return true if the specified value dominates the block. We
194 /// don't handle the true generality of domination here, just a special case
195 /// which works well enough for us.
197 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
198 /// see if V (which must be an instruction) is cheap to compute and is
199 /// non-trapping. If both are true, the instruction is inserted into the set
200 /// and true is returned.
201 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
202 SmallPtrSet<Instruction*, 4> *AggressiveInsts) {
203 Instruction *I = dyn_cast<Instruction>(V);
205 // Non-instructions all dominate instructions, but not all constantexprs
206 // can be executed unconditionally.
207 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
212 BasicBlock *PBB = I->getParent();
214 // We don't want to allow weird loops that might have the "if condition" in
215 // the bottom of this block.
216 if (PBB == BB) return false;
218 // If this instruction is defined in a block that contains an unconditional
219 // branch to BB, then it must be in the 'conditional' part of the "if
220 // statement". If not, it definitely dominates the region.
221 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
222 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB)
225 // If we aren't allowing aggressive promotion anymore, then don't consider
226 // instructions in the 'if region'.
227 if (AggressiveInsts == 0) return false;
229 // Okay, it looks like the instruction IS in the "condition". Check to
230 // see if it's a cheap instruction to unconditionally compute, and if it
231 // only uses stuff defined outside of the condition. If so, hoist it out.
232 if (!I->isSafeToSpeculativelyExecute())
235 switch (I->getOpcode()) {
236 default: return false; // Cannot hoist this out safely.
237 case Instruction::Load:
238 // We have to check to make sure there are no instructions before the
239 // load in its basic block, as we are going to hoist the load out to its
241 if (PBB->getFirstNonPHIOrDbg() != I)
244 case Instruction::Add:
245 case Instruction::Sub:
246 case Instruction::And:
247 case Instruction::Or:
248 case Instruction::Xor:
249 case Instruction::Shl:
250 case Instruction::LShr:
251 case Instruction::AShr:
252 case Instruction::ICmp:
253 break; // These are all cheap and non-trapping instructions.
256 // Okay, we can only really hoist these out if their operands are not
257 // defined in the conditional region.
258 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
259 if (!DominatesMergePoint(*i, BB, 0))
261 // Okay, it's safe to do this! Remember this instruction.
262 AggressiveInsts->insert(I);
266 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
267 /// and PointerNullValue. Return NULL if value is not a constant int.
268 static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
269 // Normal constant int.
270 ConstantInt *CI = dyn_cast<ConstantInt>(V);
271 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
274 // This is some kind of pointer constant. Turn it into a pointer-sized
275 // ConstantInt if possible.
276 const IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
278 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
279 if (isa<ConstantPointerNull>(V))
280 return ConstantInt::get(PtrTy, 0);
282 // IntToPtr const int.
283 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
284 if (CE->getOpcode() == Instruction::IntToPtr)
285 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
286 // The constant is very likely to have the right type already.
287 if (CI->getType() == PtrTy)
290 return cast<ConstantInt>
291 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
296 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
297 /// collection of icmp eq/ne instructions that compare a value against a
298 /// constant, return the value being compared, and stick the constant into the
301 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
302 const TargetData *TD, bool isEQ) {
303 Instruction *I = dyn_cast<Instruction>(V);
304 if (I == 0) return 0;
306 // If this is an icmp against a constant, handle this as one of the cases.
307 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
308 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE))
309 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
311 return I->getOperand(0);
316 // Otherwise, we can only handle an | or &, depending on isEQ.
317 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
320 unsigned NumValsBeforeLHS = Vals.size();
321 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
323 unsigned NumVals = Vals.size();
324 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
328 Vals.resize(NumVals);
331 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
332 // set it and return success.
333 if (Extra == 0 || Extra == I->getOperand(1)) {
334 Extra = I->getOperand(1);
338 Vals.resize(NumValsBeforeLHS);
342 // If the LHS can't be folded in, but Extra is available and RHS can, try to
344 if (Extra == 0 || Extra == I->getOperand(0)) {
345 Value *OldExtra = Extra;
346 Extra = I->getOperand(0);
347 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
350 assert(Vals.size() == NumValsBeforeLHS);
357 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
358 Instruction* Cond = 0;
359 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
360 Cond = dyn_cast<Instruction>(SI->getCondition());
361 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
362 if (BI->isConditional())
363 Cond = dyn_cast<Instruction>(BI->getCondition());
364 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
365 Cond = dyn_cast<Instruction>(IBI->getAddress());
368 TI->eraseFromParent();
369 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
372 /// isValueEqualityComparison - Return true if the specified terminator checks
373 /// to see if a value is equal to constant integer value.
374 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
376 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
377 // Do not permit merging of large switch instructions into their
378 // predecessors unless there is only one predecessor.
379 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
380 pred_end(SI->getParent())) <= 128)
381 CV = SI->getCondition();
382 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
383 if (BI->isConditional() && BI->getCondition()->hasOneUse())
384 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
385 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
386 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
387 GetConstantInt(ICI->getOperand(1), TD))
388 CV = ICI->getOperand(0);
390 // Unwrap any lossless ptrtoint cast.
391 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
392 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
393 CV = PTII->getOperand(0);
397 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
398 /// decode all of the 'cases' that it represents and return the 'default' block.
399 BasicBlock *SimplifyCFGOpt::
400 GetValueEqualityComparisonCases(TerminatorInst *TI,
401 std::vector<std::pair<ConstantInt*,
402 BasicBlock*> > &Cases) {
403 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
404 Cases.reserve(SI->getNumCases());
405 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
406 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
407 return SI->getDefaultDest();
410 BranchInst *BI = cast<BranchInst>(TI);
411 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
412 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD),
413 BI->getSuccessor(ICI->getPredicate() ==
414 ICmpInst::ICMP_NE)));
415 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
419 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
420 /// in the list that match the specified block.
421 static void EliminateBlockCases(BasicBlock *BB,
422 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
423 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
424 if (Cases[i].second == BB) {
425 Cases.erase(Cases.begin()+i);
430 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
433 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
434 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
435 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
437 // Make V1 be smaller than V2.
438 if (V1->size() > V2->size())
441 if (V1->size() == 0) return false;
442 if (V1->size() == 1) {
444 ConstantInt *TheVal = (*V1)[0].first;
445 for (unsigned i = 0, e = V2->size(); i != e; ++i)
446 if (TheVal == (*V2)[i].first)
450 // Otherwise, just sort both lists and compare element by element.
451 array_pod_sort(V1->begin(), V1->end());
452 array_pod_sort(V2->begin(), V2->end());
453 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
454 while (i1 != e1 && i2 != e2) {
455 if ((*V1)[i1].first == (*V2)[i2].first)
457 if ((*V1)[i1].first < (*V2)[i2].first)
465 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
466 /// terminator instruction and its block is known to only have a single
467 /// predecessor block, check to see if that predecessor is also a value
468 /// comparison with the same value, and if that comparison determines the
469 /// outcome of this comparison. If so, simplify TI. This does a very limited
470 /// form of jump threading.
471 bool SimplifyCFGOpt::
472 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
474 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
475 if (!PredVal) return false; // Not a value comparison in predecessor.
477 Value *ThisVal = isValueEqualityComparison(TI);
478 assert(ThisVal && "This isn't a value comparison!!");
479 if (ThisVal != PredVal) return false; // Different predicates.
481 // Find out information about when control will move from Pred to TI's block.
482 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
483 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
485 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
487 // Find information about how control leaves this block.
488 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
489 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
490 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
492 // If TI's block is the default block from Pred's comparison, potentially
493 // simplify TI based on this knowledge.
494 if (PredDef == TI->getParent()) {
495 // If we are here, we know that the value is none of those cases listed in
496 // PredCases. If there are any cases in ThisCases that are in PredCases, we
498 if (!ValuesOverlap(PredCases, ThisCases))
501 if (isa<BranchInst>(TI)) {
502 // Okay, one of the successors of this condbr is dead. Convert it to a
504 assert(ThisCases.size() == 1 && "Branch can only have one case!");
505 // Insert the new branch.
506 Instruction *NI = BranchInst::Create(ThisDef, TI);
509 // Remove PHI node entries for the dead edge.
510 ThisCases[0].second->removePredecessor(TI->getParent());
512 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
513 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
515 EraseTerminatorInstAndDCECond(TI);
519 SwitchInst *SI = cast<SwitchInst>(TI);
520 // Okay, TI has cases that are statically dead, prune them away.
521 SmallPtrSet<Constant*, 16> DeadCases;
522 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
523 DeadCases.insert(PredCases[i].first);
525 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
526 << "Through successor TI: " << *TI);
528 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
529 if (DeadCases.count(SI->getCaseValue(i))) {
530 SI->getSuccessor(i)->removePredecessor(TI->getParent());
534 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
538 // Otherwise, TI's block must correspond to some matched value. Find out
539 // which value (or set of values) this is.
540 ConstantInt *TIV = 0;
541 BasicBlock *TIBB = TI->getParent();
542 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
543 if (PredCases[i].second == TIBB) {
545 return false; // Cannot handle multiple values coming to this block.
546 TIV = PredCases[i].first;
548 assert(TIV && "No edge from pred to succ?");
550 // Okay, we found the one constant that our value can be if we get into TI's
551 // BB. Find out which successor will unconditionally be branched to.
552 BasicBlock *TheRealDest = 0;
553 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
554 if (ThisCases[i].first == TIV) {
555 TheRealDest = ThisCases[i].second;
559 // If not handled by any explicit cases, it is handled by the default case.
560 if (TheRealDest == 0) TheRealDest = ThisDef;
562 // Remove PHI node entries for dead edges.
563 BasicBlock *CheckEdge = TheRealDest;
564 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
565 if (*SI != CheckEdge)
566 (*SI)->removePredecessor(TIBB);
570 // Insert the new branch.
571 Instruction *NI = BranchInst::Create(TheRealDest, TI);
574 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
575 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
577 EraseTerminatorInstAndDCECond(TI);
582 /// ConstantIntOrdering - This class implements a stable ordering of constant
583 /// integers that does not depend on their address. This is important for
584 /// applications that sort ConstantInt's to ensure uniqueness.
585 struct ConstantIntOrdering {
586 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
587 return LHS->getValue().ult(RHS->getValue());
592 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
593 const ConstantInt *LHS = *(const ConstantInt**)P1;
594 const ConstantInt *RHS = *(const ConstantInt**)P2;
595 if (LHS->getValue().ult(RHS->getValue()))
597 if (LHS->getValue() == RHS->getValue())
602 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
603 /// equality comparison instruction (either a switch or a branch on "X == c").
604 /// See if any of the predecessors of the terminator block are value comparisons
605 /// on the same value. If so, and if safe to do so, fold them together.
606 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
607 BasicBlock *BB = TI->getParent();
608 Value *CV = isValueEqualityComparison(TI); // CondVal
609 assert(CV && "Not a comparison?");
610 bool Changed = false;
612 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
613 while (!Preds.empty()) {
614 BasicBlock *Pred = Preds.pop_back_val();
616 // See if the predecessor is a comparison with the same value.
617 TerminatorInst *PTI = Pred->getTerminator();
618 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
620 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
621 // Figure out which 'cases' to copy from SI to PSI.
622 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
623 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
625 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
626 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
628 // Based on whether the default edge from PTI goes to BB or not, fill in
629 // PredCases and PredDefault with the new switch cases we would like to
631 SmallVector<BasicBlock*, 8> NewSuccessors;
633 if (PredDefault == BB) {
634 // If this is the default destination from PTI, only the edges in TI
635 // that don't occur in PTI, or that branch to BB will be activated.
636 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
637 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
638 if (PredCases[i].second != BB)
639 PTIHandled.insert(PredCases[i].first);
641 // The default destination is BB, we don't need explicit targets.
642 std::swap(PredCases[i], PredCases.back());
643 PredCases.pop_back();
647 // Reconstruct the new switch statement we will be building.
648 if (PredDefault != BBDefault) {
649 PredDefault->removePredecessor(Pred);
650 PredDefault = BBDefault;
651 NewSuccessors.push_back(BBDefault);
653 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
654 if (!PTIHandled.count(BBCases[i].first) &&
655 BBCases[i].second != BBDefault) {
656 PredCases.push_back(BBCases[i]);
657 NewSuccessors.push_back(BBCases[i].second);
661 // If this is not the default destination from PSI, only the edges
662 // in SI that occur in PSI with a destination of BB will be
664 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
665 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
666 if (PredCases[i].second == BB) {
667 PTIHandled.insert(PredCases[i].first);
668 std::swap(PredCases[i], PredCases.back());
669 PredCases.pop_back();
673 // Okay, now we know which constants were sent to BB from the
674 // predecessor. Figure out where they will all go now.
675 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
676 if (PTIHandled.count(BBCases[i].first)) {
677 // If this is one we are capable of getting...
678 PredCases.push_back(BBCases[i]);
679 NewSuccessors.push_back(BBCases[i].second);
680 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
683 // If there are any constants vectored to BB that TI doesn't handle,
684 // they must go to the default destination of TI.
685 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
687 E = PTIHandled.end(); I != E; ++I) {
688 PredCases.push_back(std::make_pair(*I, BBDefault));
689 NewSuccessors.push_back(BBDefault);
693 // Okay, at this point, we know which new successor Pred will get. Make
694 // sure we update the number of entries in the PHI nodes for these
696 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
697 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
699 // Convert pointer to int before we switch.
700 if (CV->getType()->isPointerTy()) {
701 assert(TD && "Cannot switch on pointer without TargetData");
702 CV = new PtrToIntInst(CV, TD->getIntPtrType(CV->getContext()),
706 // Now that the successors are updated, create the new Switch instruction.
707 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
708 PredCases.size(), PTI);
709 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
710 NewSI->addCase(PredCases[i].first, PredCases[i].second);
712 EraseTerminatorInstAndDCECond(PTI);
714 // Okay, last check. If BB is still a successor of PSI, then we must
715 // have an infinite loop case. If so, add an infinitely looping block
716 // to handle the case to preserve the behavior of the code.
717 BasicBlock *InfLoopBlock = 0;
718 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
719 if (NewSI->getSuccessor(i) == BB) {
720 if (InfLoopBlock == 0) {
721 // Insert it at the end of the function, because it's either code,
722 // or it won't matter if it's hot. :)
723 InfLoopBlock = BasicBlock::Create(BB->getContext(),
724 "infloop", BB->getParent());
725 BranchInst::Create(InfLoopBlock, InfLoopBlock);
727 NewSI->setSuccessor(i, InfLoopBlock);
736 // isSafeToHoistInvoke - If we would need to insert a select that uses the
737 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
738 // would need to do this), we can't hoist the invoke, as there is nowhere
739 // to put the select in this case.
740 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
741 Instruction *I1, Instruction *I2) {
742 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
744 for (BasicBlock::iterator BBI = SI->begin();
745 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
746 Value *BB1V = PN->getIncomingValueForBlock(BB1);
747 Value *BB2V = PN->getIncomingValueForBlock(BB2);
748 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
756 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
757 /// BB2, hoist any common code in the two blocks up into the branch block. The
758 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
759 static bool HoistThenElseCodeToIf(BranchInst *BI) {
760 // This does very trivial matching, with limited scanning, to find identical
761 // instructions in the two blocks. In particular, we don't want to get into
762 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
763 // such, we currently just scan for obviously identical instructions in an
765 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
766 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
768 BasicBlock::iterator BB1_Itr = BB1->begin();
769 BasicBlock::iterator BB2_Itr = BB2->begin();
771 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
772 while (isa<DbgInfoIntrinsic>(I1))
774 while (isa<DbgInfoIntrinsic>(I2))
776 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
777 !I1->isIdenticalToWhenDefined(I2) ||
778 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
781 // If we get here, we can hoist at least one instruction.
782 BasicBlock *BIParent = BI->getParent();
785 // If we are hoisting the terminator instruction, don't move one (making a
786 // broken BB), instead clone it, and remove BI.
787 if (isa<TerminatorInst>(I1))
788 goto HoistTerminator;
790 // For a normal instruction, we just move one to right before the branch,
791 // then replace all uses of the other with the first. Finally, we remove
792 // the now redundant second instruction.
793 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
794 if (!I2->use_empty())
795 I2->replaceAllUsesWith(I1);
796 I1->intersectOptionalDataWith(I2);
797 I2->eraseFromParent();
800 while (isa<DbgInfoIntrinsic>(I1))
803 while (isa<DbgInfoIntrinsic>(I2))
805 } while (I1->getOpcode() == I2->getOpcode() &&
806 I1->isIdenticalToWhenDefined(I2));
811 // It may not be possible to hoist an invoke.
812 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
815 // Okay, it is safe to hoist the terminator.
816 Instruction *NT = I1->clone();
817 BIParent->getInstList().insert(BI, NT);
818 if (!NT->getType()->isVoidTy()) {
819 I1->replaceAllUsesWith(NT);
820 I2->replaceAllUsesWith(NT);
824 // Hoisting one of the terminators from our successor is a great thing.
825 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
826 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
827 // nodes, so we insert select instruction to compute the final result.
828 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
829 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
831 for (BasicBlock::iterator BBI = SI->begin();
832 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
833 Value *BB1V = PN->getIncomingValueForBlock(BB1);
834 Value *BB2V = PN->getIncomingValueForBlock(BB2);
835 if (BB1V == BB2V) continue;
837 // These values do not agree. Insert a select instruction before NT
838 // that determines the right value.
839 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
841 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
842 BB1V->getName()+"."+BB2V->getName(), NT);
843 // Make the PHI node use the select for all incoming values for BB1/BB2
844 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
845 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
846 PN->setIncomingValue(i, SI);
850 // Update any PHI nodes in our new successors.
851 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
852 AddPredecessorToBlock(*SI, BIParent, BB1);
854 EraseTerminatorInstAndDCECond(BI);
858 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
859 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
860 /// (for now, restricted to a single instruction that's side effect free) from
861 /// the BB1 into the branch block to speculatively execute it.
862 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
863 // Only speculatively execution a single instruction (not counting the
864 // terminator) for now.
865 Instruction *HInst = NULL;
866 Instruction *Term = BB1->getTerminator();
867 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
869 Instruction *I = BBI;
871 if (isa<DbgInfoIntrinsic>(I)) continue;
872 if (I == Term) break;
881 // Be conservative for now. FP select instruction can often be expensive.
882 Value *BrCond = BI->getCondition();
883 if (isa<FCmpInst>(BrCond))
886 // If BB1 is actually on the false edge of the conditional branch, remember
887 // to swap the select operands later.
889 if (BB1 != BI->getSuccessor(0)) {
890 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
897 // br i1 %t1, label %BB1, label %BB2
906 // %t3 = select i1 %t1, %t2, %t3
907 switch (HInst->getOpcode()) {
908 default: return false; // Not safe / profitable to hoist.
909 case Instruction::Add:
910 case Instruction::Sub:
911 // Not worth doing for vector ops.
912 if (HInst->getType()->isVectorTy())
915 case Instruction::And:
916 case Instruction::Or:
917 case Instruction::Xor:
918 case Instruction::Shl:
919 case Instruction::LShr:
920 case Instruction::AShr:
921 // Don't mess with vector operations.
922 if (HInst->getType()->isVectorTy())
924 break; // These are all cheap and non-trapping instructions.
927 // If the instruction is obviously dead, don't try to predicate it.
928 if (HInst->use_empty()) {
929 HInst->eraseFromParent();
933 // Can we speculatively execute the instruction? And what is the value
934 // if the condition is false? Consider the phi uses, if the incoming value
935 // from the "if" block are all the same V, then V is the value of the
936 // select if the condition is false.
937 BasicBlock *BIParent = BI->getParent();
938 SmallVector<PHINode*, 4> PHIUses;
939 Value *FalseV = NULL;
941 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
942 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
944 // Ignore any user that is not a PHI node in BB2. These can only occur in
945 // unreachable blocks, because they would not be dominated by the instr.
946 PHINode *PN = dyn_cast<PHINode>(*UI);
947 if (!PN || PN->getParent() != BB2)
949 PHIUses.push_back(PN);
951 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
954 else if (FalseV != PHIV)
955 return false; // Inconsistent value when condition is false.
958 assert(FalseV && "Must have at least one user, and it must be a PHI");
960 // Do not hoist the instruction if any of its operands are defined but not
961 // used in this BB. The transformation will prevent the operand from
962 // being sunk into the use block.
963 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
965 Instruction *OpI = dyn_cast<Instruction>(*i);
966 if (OpI && OpI->getParent() == BIParent &&
967 !OpI->isUsedInBasicBlock(BIParent))
971 // If we get here, we can hoist the instruction. Try to place it
972 // before the icmp instruction preceding the conditional branch.
973 BasicBlock::iterator InsertPos = BI;
974 if (InsertPos != BIParent->begin())
976 // Skip debug info between condition and branch.
977 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
979 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
980 SmallPtrSet<Instruction *, 4> BB1Insns;
981 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
982 BB1I != BB1E; ++BB1I)
983 BB1Insns.insert(BB1I);
984 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
986 Instruction *Use = cast<Instruction>(*UI);
987 if (!BB1Insns.count(Use)) continue;
989 // If BrCond uses the instruction that place it just before
990 // branch instruction.
996 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
998 // Create a select whose true value is the speculatively executed value and
999 // false value is the previously determined FalseV.
1002 SI = SelectInst::Create(BrCond, FalseV, HInst,
1003 FalseV->getName() + "." + HInst->getName(), BI);
1005 SI = SelectInst::Create(BrCond, HInst, FalseV,
1006 HInst->getName() + "." + FalseV->getName(), BI);
1008 // Make the PHI node use the select for all incoming values for "then" and
1010 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1011 PHINode *PN = PHIUses[i];
1012 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1013 if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent)
1014 PN->setIncomingValue(j, SI);
1021 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1022 /// across this block.
1023 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1024 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1027 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1028 if (isa<DbgInfoIntrinsic>(BBI))
1030 if (Size > 10) return false; // Don't clone large BB's.
1033 // We can only support instructions that do not define values that are
1034 // live outside of the current basic block.
1035 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1037 Instruction *U = cast<Instruction>(*UI);
1038 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1041 // Looks ok, continue checking.
1047 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1048 /// that is defined in the same block as the branch and if any PHI entries are
1049 /// constants, thread edges corresponding to that entry to be branches to their
1050 /// ultimate destination.
1051 static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
1052 BasicBlock *BB = BI->getParent();
1053 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1054 // NOTE: we currently cannot transform this case if the PHI node is used
1055 // outside of the block.
1056 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1059 // Degenerate case of a single entry PHI.
1060 if (PN->getNumIncomingValues() == 1) {
1061 FoldSingleEntryPHINodes(PN->getParent());
1065 // Now we know that this block has multiple preds and two succs.
1066 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1068 // Okay, this is a simple enough basic block. See if any phi values are
1070 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1071 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1072 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1074 // Okay, we now know that all edges from PredBB should be revectored to
1075 // branch to RealDest.
1076 BasicBlock *PredBB = PN->getIncomingBlock(i);
1077 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1079 if (RealDest == BB) continue; // Skip self loops.
1081 // The dest block might have PHI nodes, other predecessors and other
1082 // difficult cases. Instead of being smart about this, just insert a new
1083 // block that jumps to the destination block, effectively splitting
1084 // the edge we are about to create.
1085 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1086 RealDest->getName()+".critedge",
1087 RealDest->getParent(), RealDest);
1088 BranchInst::Create(RealDest, EdgeBB);
1090 // Update PHI nodes.
1091 AddPredecessorToBlock(RealDest, EdgeBB, BB);
1093 // BB may have instructions that are being threaded over. Clone these
1094 // instructions into EdgeBB. We know that there will be no uses of the
1095 // cloned instructions outside of EdgeBB.
1096 BasicBlock::iterator InsertPt = EdgeBB->begin();
1097 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1098 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1099 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1100 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1103 // Clone the instruction.
1104 Instruction *N = BBI->clone();
1105 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1107 // Update operands due to translation.
1108 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1110 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1111 if (PI != TranslateMap.end())
1115 // Check for trivial simplification.
1116 if (Value *V = SimplifyInstruction(N, TD)) {
1117 TranslateMap[BBI] = V;
1118 delete N; // Instruction folded away, don't need actual inst
1120 // Insert the new instruction into its new home.
1121 EdgeBB->getInstList().insert(InsertPt, N);
1122 if (!BBI->use_empty())
1123 TranslateMap[BBI] = N;
1127 // Loop over all of the edges from PredBB to BB, changing them to branch
1128 // to EdgeBB instead.
1129 TerminatorInst *PredBBTI = PredBB->getTerminator();
1130 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1131 if (PredBBTI->getSuccessor(i) == BB) {
1132 BB->removePredecessor(PredBB);
1133 PredBBTI->setSuccessor(i, EdgeBB);
1136 // Recurse, simplifying any other constants.
1137 return FoldCondBranchOnPHI(BI, TD) | true;
1143 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1144 /// PHI node, see if we can eliminate it.
1145 static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
1146 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1147 // statement", which has a very simple dominance structure. Basically, we
1148 // are trying to find the condition that is being branched on, which
1149 // subsequently causes this merge to happen. We really want control
1150 // dependence information for this check, but simplifycfg can't keep it up
1151 // to date, and this catches most of the cases we care about anyway.
1152 BasicBlock *BB = PN->getParent();
1153 BasicBlock *IfTrue, *IfFalse;
1154 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1156 // Don't bother if the branch will be constant folded trivially.
1157 isa<ConstantInt>(IfCond))
1160 // Okay, we found that we can merge this two-entry phi node into a select.
1161 // Doing so would require us to fold *all* two entry phi nodes in this block.
1162 // At some point this becomes non-profitable (particularly if the target
1163 // doesn't support cmov's). Only do this transformation if there are two or
1164 // fewer PHI nodes in this block.
1165 unsigned NumPhis = 0;
1166 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1170 // Loop over the PHI's seeing if we can promote them all to select
1171 // instructions. While we are at it, keep track of the instructions
1172 // that need to be moved to the dominating block.
1173 SmallPtrSet<Instruction*, 4> AggressiveInsts;
1175 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1176 PHINode *PN = cast<PHINode>(II++);
1177 if (Value *V = SimplifyInstruction(PN, TD)) {
1178 PN->replaceAllUsesWith(V);
1179 PN->eraseFromParent();
1183 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts) ||
1184 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts))
1188 // If we folded the the first phi, PN dangles at this point. Refresh it. If
1189 // we ran out of PHIs then we simplified them all.
1190 PN = dyn_cast<PHINode>(BB->begin());
1191 if (PN == 0) return true;
1193 // Don't fold i1 branches on PHIs which contain binary operators. These can
1194 // often be turned into switches and other things.
1195 if (PN->getType()->isIntegerTy(1) &&
1196 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1197 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1198 isa<BinaryOperator>(IfCond)))
1201 // If we all PHI nodes are promotable, check to make sure that all
1202 // instructions in the predecessor blocks can be promoted as well. If
1203 // not, we won't be able to get rid of the control flow, so it's not
1204 // worth promoting to select instructions.
1205 BasicBlock *DomBlock = 0;
1206 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1207 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1208 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1211 DomBlock = *pred_begin(IfBlock1);
1212 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1213 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1214 // This is not an aggressive instruction that we can promote.
1215 // Because of this, we won't be able to get rid of the control
1216 // flow, so the xform is not worth it.
1221 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1224 DomBlock = *pred_begin(IfBlock2);
1225 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1226 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1227 // This is not an aggressive instruction that we can promote.
1228 // Because of this, we won't be able to get rid of the control
1229 // flow, so the xform is not worth it.
1234 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1235 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1237 // If we can still promote the PHI nodes after this gauntlet of tests,
1238 // do all of the PHI's now.
1239 Instruction *InsertPt = DomBlock->getTerminator();
1241 // Move all 'aggressive' instructions, which are defined in the
1242 // conditional parts of the if's up to the dominating block.
1244 DomBlock->getInstList().splice(InsertPt,
1245 IfBlock1->getInstList(), IfBlock1->begin(),
1246 IfBlock1->getTerminator());
1248 DomBlock->getInstList().splice(InsertPt,
1249 IfBlock2->getInstList(), IfBlock2->begin(),
1250 IfBlock2->getTerminator());
1252 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1253 // Change the PHI node into a select instruction.
1254 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1255 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1257 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", InsertPt);
1258 PN->replaceAllUsesWith(NV);
1260 PN->eraseFromParent();
1263 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1264 // has been flattened. Change DomBlock to jump directly to our new block to
1265 // avoid other simplifycfg's kicking in on the diamond.
1266 TerminatorInst *OldTI = DomBlock->getTerminator();
1267 BranchInst::Create(BB, OldTI);
1268 OldTI->eraseFromParent();
1272 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1273 /// to two returning blocks, try to merge them together into one return,
1274 /// introducing a select if the return values disagree.
1275 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1276 assert(BI->isConditional() && "Must be a conditional branch");
1277 BasicBlock *TrueSucc = BI->getSuccessor(0);
1278 BasicBlock *FalseSucc = BI->getSuccessor(1);
1279 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1280 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1282 // Check to ensure both blocks are empty (just a return) or optionally empty
1283 // with PHI nodes. If there are other instructions, merging would cause extra
1284 // computation on one path or the other.
1285 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1287 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1290 // Okay, we found a branch that is going to two return nodes. If
1291 // there is no return value for this function, just change the
1292 // branch into a return.
1293 if (FalseRet->getNumOperands() == 0) {
1294 TrueSucc->removePredecessor(BI->getParent());
1295 FalseSucc->removePredecessor(BI->getParent());
1296 ReturnInst::Create(BI->getContext(), 0, BI);
1297 EraseTerminatorInstAndDCECond(BI);
1301 // Otherwise, figure out what the true and false return values are
1302 // so we can insert a new select instruction.
1303 Value *TrueValue = TrueRet->getReturnValue();
1304 Value *FalseValue = FalseRet->getReturnValue();
1306 // Unwrap any PHI nodes in the return blocks.
1307 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1308 if (TVPN->getParent() == TrueSucc)
1309 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1310 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1311 if (FVPN->getParent() == FalseSucc)
1312 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1314 // In order for this transformation to be safe, we must be able to
1315 // unconditionally execute both operands to the return. This is
1316 // normally the case, but we could have a potentially-trapping
1317 // constant expression that prevents this transformation from being
1319 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1322 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1326 // Okay, we collected all the mapped values and checked them for sanity, and
1327 // defined to really do this transformation. First, update the CFG.
1328 TrueSucc->removePredecessor(BI->getParent());
1329 FalseSucc->removePredecessor(BI->getParent());
1331 // Insert select instructions where needed.
1332 Value *BrCond = BI->getCondition();
1334 // Insert a select if the results differ.
1335 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1336 } else if (isa<UndefValue>(TrueValue)) {
1337 TrueValue = FalseValue;
1339 TrueValue = SelectInst::Create(BrCond, TrueValue,
1340 FalseValue, "retval", BI);
1344 Value *RI = !TrueValue ?
1345 ReturnInst::Create(BI->getContext(), BI) :
1346 ReturnInst::Create(BI->getContext(), TrueValue, BI);
1349 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1350 << "\n " << *BI << "NewRet = " << *RI
1351 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1353 EraseTerminatorInstAndDCECond(BI);
1358 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1359 /// and if a predecessor branches to us and one of our successors, fold the
1360 /// setcc into the predecessor and use logical operations to pick the right
1362 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1363 BasicBlock *BB = BI->getParent();
1364 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1365 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1366 Cond->getParent() != BB || !Cond->hasOneUse())
1369 // Only allow this if the condition is a simple instruction that can be
1370 // executed unconditionally. It must be in the same block as the branch, and
1371 // must be at the front of the block.
1372 BasicBlock::iterator FrontIt = BB->front();
1373 // Ignore dbg intrinsics.
1374 while (isa<DbgInfoIntrinsic>(FrontIt))
1377 // Allow a single instruction to be hoisted in addition to the compare
1378 // that feeds the branch. We later ensure that any values that _it_ uses
1379 // were also live in the predecessor, so that we don't unnecessarily create
1380 // register pressure or inhibit out-of-order execution.
1381 Instruction *BonusInst = 0;
1382 if (&*FrontIt != Cond &&
1383 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1384 FrontIt->isSafeToSpeculativelyExecute()) {
1385 BonusInst = &*FrontIt;
1389 // Only a single bonus inst is allowed.
1390 if (&*FrontIt != Cond)
1393 // Make sure the instruction after the condition is the cond branch.
1394 BasicBlock::iterator CondIt = Cond; ++CondIt;
1395 // Ingore dbg intrinsics.
1396 while(isa<DbgInfoIntrinsic>(CondIt))
1398 if (&*CondIt != BI) {
1399 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!");
1403 // Cond is known to be a compare or binary operator. Check to make sure that
1404 // neither operand is a potentially-trapping constant expression.
1405 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1408 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1413 // Finally, don't infinitely unroll conditional loops.
1414 BasicBlock *TrueDest = BI->getSuccessor(0);
1415 BasicBlock *FalseDest = BI->getSuccessor(1);
1416 if (TrueDest == BB || FalseDest == BB)
1419 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1420 BasicBlock *PredBlock = *PI;
1421 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1423 // Check that we have two conditional branches. If there is a PHI node in
1424 // the common successor, verify that the same value flows in from both
1426 if (PBI == 0 || PBI->isUnconditional() ||
1427 !SafeToMergeTerminators(BI, PBI))
1430 // Ensure that any values used in the bonus instruction are also used
1431 // by the terminator of the predecessor. This means that those values
1432 // must already have been resolved, so we won't be inhibiting the
1433 // out-of-order core by speculating them earlier.
1435 // Collect the values used by the bonus inst
1436 SmallPtrSet<Value*, 4> UsedValues;
1437 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1438 OE = BonusInst->op_end(); OI != OE; ++OI) {
1440 if (!isa<Constant>(V))
1441 UsedValues.insert(V);
1444 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1445 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1447 // Walk up to four levels back up the use-def chain of the predecessor's
1448 // terminator to see if all those values were used. The choice of four
1449 // levels is arbitrary, to provide a compile-time-cost bound.
1450 while (!Worklist.empty()) {
1451 std::pair<Value*, unsigned> Pair = Worklist.back();
1452 Worklist.pop_back();
1454 if (Pair.second >= 4) continue;
1455 UsedValues.erase(Pair.first);
1456 if (UsedValues.empty()) break;
1458 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
1459 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1461 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1465 if (!UsedValues.empty()) return false;
1468 Instruction::BinaryOps Opc;
1469 bool InvertPredCond = false;
1471 if (PBI->getSuccessor(0) == TrueDest)
1472 Opc = Instruction::Or;
1473 else if (PBI->getSuccessor(1) == FalseDest)
1474 Opc = Instruction::And;
1475 else if (PBI->getSuccessor(0) == FalseDest)
1476 Opc = Instruction::And, InvertPredCond = true;
1477 else if (PBI->getSuccessor(1) == TrueDest)
1478 Opc = Instruction::Or, InvertPredCond = true;
1482 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1484 // If we need to invert the condition in the pred block to match, do so now.
1485 if (InvertPredCond) {
1486 Value *NewCond = PBI->getCondition();
1488 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
1489 CmpInst *CI = cast<CmpInst>(NewCond);
1490 CI->setPredicate(CI->getInversePredicate());
1492 NewCond = BinaryOperator::CreateNot(NewCond,
1493 PBI->getCondition()->getName()+".not", PBI);
1496 PBI->setCondition(NewCond);
1497 BasicBlock *OldTrue = PBI->getSuccessor(0);
1498 BasicBlock *OldFalse = PBI->getSuccessor(1);
1499 PBI->setSuccessor(0, OldFalse);
1500 PBI->setSuccessor(1, OldTrue);
1503 // If we have a bonus inst, clone it into the predecessor block.
1504 Instruction *NewBonus = 0;
1506 NewBonus = BonusInst->clone();
1507 PredBlock->getInstList().insert(PBI, NewBonus);
1508 NewBonus->takeName(BonusInst);
1509 BonusInst->setName(BonusInst->getName()+".old");
1512 // Clone Cond into the predecessor basic block, and or/and the
1513 // two conditions together.
1514 Instruction *New = Cond->clone();
1515 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1516 PredBlock->getInstList().insert(PBI, New);
1517 New->takeName(Cond);
1518 Cond->setName(New->getName()+".old");
1520 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1521 New, "or.cond", PBI);
1522 PBI->setCondition(NewCond);
1523 if (PBI->getSuccessor(0) == BB) {
1524 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1525 PBI->setSuccessor(0, TrueDest);
1527 if (PBI->getSuccessor(1) == BB) {
1528 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1529 PBI->setSuccessor(1, FalseDest);
1536 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1537 /// predecessor of another block, this function tries to simplify it. We know
1538 /// that PBI and BI are both conditional branches, and BI is in one of the
1539 /// successor blocks of PBI - PBI branches to BI.
1540 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1541 assert(PBI->isConditional() && BI->isConditional());
1542 BasicBlock *BB = BI->getParent();
1544 // If this block ends with a branch instruction, and if there is a
1545 // predecessor that ends on a branch of the same condition, make
1546 // this conditional branch redundant.
1547 if (PBI->getCondition() == BI->getCondition() &&
1548 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1549 // Okay, the outcome of this conditional branch is statically
1550 // knowable. If this block had a single pred, handle specially.
1551 if (BB->getSinglePredecessor()) {
1552 // Turn this into a branch on constant.
1553 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1554 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1556 return true; // Nuke the branch on constant.
1559 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1560 // in the constant and simplify the block result. Subsequent passes of
1561 // simplifycfg will thread the block.
1562 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1563 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1564 BI->getCondition()->getName() + ".pr",
1566 // Okay, we're going to insert the PHI node. Since PBI is not the only
1567 // predecessor, compute the PHI'd conditional value for all of the preds.
1568 // Any predecessor where the condition is not computable we keep symbolic.
1569 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1570 BasicBlock *P = *PI;
1571 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
1572 PBI != BI && PBI->isConditional() &&
1573 PBI->getCondition() == BI->getCondition() &&
1574 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1575 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1576 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1579 NewPN->addIncoming(BI->getCondition(), P);
1583 BI->setCondition(NewPN);
1588 // If this is a conditional branch in an empty block, and if any
1589 // predecessors is a conditional branch to one of our destinations,
1590 // fold the conditions into logical ops and one cond br.
1591 BasicBlock::iterator BBI = BB->begin();
1592 // Ignore dbg intrinsics.
1593 while (isa<DbgInfoIntrinsic>(BBI))
1599 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1604 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1606 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1607 PBIOp = 0, BIOp = 1;
1608 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1609 PBIOp = 1, BIOp = 0;
1610 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1615 // Check to make sure that the other destination of this branch
1616 // isn't BB itself. If so, this is an infinite loop that will
1617 // keep getting unwound.
1618 if (PBI->getSuccessor(PBIOp) == BB)
1621 // Do not perform this transformation if it would require
1622 // insertion of a large number of select instructions. For targets
1623 // without predication/cmovs, this is a big pessimization.
1624 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1626 unsigned NumPhis = 0;
1627 for (BasicBlock::iterator II = CommonDest->begin();
1628 isa<PHINode>(II); ++II, ++NumPhis)
1629 if (NumPhis > 2) // Disable this xform.
1632 // Finally, if everything is ok, fold the branches to logical ops.
1633 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1635 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
1636 << "AND: " << *BI->getParent());
1639 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1640 // branch in it, where one edge (OtherDest) goes back to itself but the other
1641 // exits. We don't *know* that the program avoids the infinite loop
1642 // (even though that seems likely). If we do this xform naively, we'll end up
1643 // recursively unpeeling the loop. Since we know that (after the xform is
1644 // done) that the block *is* infinite if reached, we just make it an obviously
1645 // infinite loop with no cond branch.
1646 if (OtherDest == BB) {
1647 // Insert it at the end of the function, because it's either code,
1648 // or it won't matter if it's hot. :)
1649 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1650 "infloop", BB->getParent());
1651 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1652 OtherDest = InfLoopBlock;
1655 DEBUG(dbgs() << *PBI->getParent()->getParent());
1657 // BI may have other predecessors. Because of this, we leave
1658 // it alone, but modify PBI.
1660 // Make sure we get to CommonDest on True&True directions.
1661 Value *PBICond = PBI->getCondition();
1663 PBICond = BinaryOperator::CreateNot(PBICond,
1664 PBICond->getName()+".not",
1666 Value *BICond = BI->getCondition();
1668 BICond = BinaryOperator::CreateNot(BICond,
1669 BICond->getName()+".not",
1671 // Merge the conditions.
1672 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1674 // Modify PBI to branch on the new condition to the new dests.
1675 PBI->setCondition(Cond);
1676 PBI->setSuccessor(0, CommonDest);
1677 PBI->setSuccessor(1, OtherDest);
1679 // OtherDest may have phi nodes. If so, add an entry from PBI's
1680 // block that are identical to the entries for BI's block.
1681 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
1683 // We know that the CommonDest already had an edge from PBI to
1684 // it. If it has PHIs though, the PHIs may have different
1685 // entries for BB and PBI's BB. If so, insert a select to make
1688 for (BasicBlock::iterator II = CommonDest->begin();
1689 (PN = dyn_cast<PHINode>(II)); ++II) {
1690 Value *BIV = PN->getIncomingValueForBlock(BB);
1691 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1692 Value *PBIV = PN->getIncomingValue(PBBIdx);
1694 // Insert a select in PBI to pick the right value.
1695 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1696 PBIV->getName()+".mux", PBI);
1697 PN->setIncomingValue(PBBIdx, NV);
1701 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1702 DEBUG(dbgs() << *PBI->getParent()->getParent());
1704 // This basic block is probably dead. We know it has at least
1705 // one fewer predecessor.
1709 // SimplifyIndirectBrOnSelect - Replaces
1710 // (indirectbr (select cond, blockaddress(@fn, BlockA),
1711 // blockaddress(@fn, BlockB)))
1713 // (br cond, BlockA, BlockB).
1714 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
1715 // Check that both operands of the select are block addresses.
1716 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
1717 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
1721 // Extract the actual blocks.
1722 BasicBlock *TrueBB = TBA->getBasicBlock();
1723 BasicBlock *FalseBB = FBA->getBasicBlock();
1725 // Remove any superfluous successor edges from the CFG.
1726 // First, figure out which successors to preserve.
1727 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
1729 BasicBlock *KeepEdge1 = TrueBB;
1730 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
1732 // Then remove the rest.
1733 for (unsigned I = 0, E = IBI->getNumSuccessors(); I != E; ++I) {
1734 BasicBlock *Succ = IBI->getSuccessor(I);
1735 // Make sure only to keep exactly one copy of each edge.
1736 if (Succ == KeepEdge1)
1738 else if (Succ == KeepEdge2)
1741 Succ->removePredecessor(IBI->getParent());
1744 // Insert an appropriate new terminator.
1745 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
1746 if (TrueBB == FalseBB)
1747 // We were only looking for one successor, and it was present.
1748 // Create an unconditional branch to it.
1749 BranchInst::Create(TrueBB, IBI);
1751 // We found both of the successors we were looking for.
1752 // Create a conditional branch sharing the condition of the select.
1753 BranchInst::Create(TrueBB, FalseBB, SI->getCondition(), IBI);
1754 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
1755 // Neither of the selected blocks were successors, so this
1756 // indirectbr must be unreachable.
1757 new UnreachableInst(IBI->getContext(), IBI);
1759 // One of the selected values was a successor, but the other wasn't.
1760 // Insert an unconditional branch to the one that was found;
1761 // the edge to the one that wasn't must be unreachable.
1763 // Only TrueBB was found.
1764 BranchInst::Create(TrueBB, IBI);
1766 // Only FalseBB was found.
1767 BranchInst::Create(FalseBB, IBI);
1770 EraseTerminatorInstAndDCECond(IBI);
1774 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
1775 /// instruction (a seteq/setne with a constant) as the only instruction in a
1776 /// block that ends with an uncond branch. We are looking for a very specific
1777 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
1778 /// this case, we merge the first two "or's of icmp" into a switch, but then the
1779 /// default value goes to an uncond block with a seteq in it, we get something
1782 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
1784 /// %tmp = icmp eq i8 %A, 92
1787 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
1789 /// We prefer to split the edge to 'end' so that there is a true/false entry to
1790 /// the PHI, merging the third icmp into the switch.
1791 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
1792 const TargetData *TD) {
1793 BasicBlock *BB = ICI->getParent();
1794 // If the block has any PHIs in it or the icmp has multiple uses, it is too
1796 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
1798 Value *V = ICI->getOperand(0);
1799 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
1801 // The pattern we're looking for is where our only predecessor is a switch on
1802 // 'V' and this block is the default case for the switch. In this case we can
1803 // fold the compared value into the switch to simplify things.
1804 BasicBlock *Pred = BB->getSinglePredecessor();
1805 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
1807 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
1808 if (SI->getCondition() != V)
1811 // If BB is reachable on a non-default case, then we simply know the value of
1812 // V in this block. Substitute it and constant fold the icmp instruction
1814 if (SI->getDefaultDest() != BB) {
1815 ConstantInt *VVal = SI->findCaseDest(BB);
1816 assert(VVal && "Should have a unique destination value");
1817 ICI->setOperand(0, VVal);
1819 if (Value *V = SimplifyInstruction(ICI, TD)) {
1820 ICI->replaceAllUsesWith(V);
1821 ICI->eraseFromParent();
1823 // BB is now empty, so it is likely to simplify away.
1824 return SimplifyCFG(BB) | true;
1827 // Ok, the block is reachable from the default dest. If the constant we're
1828 // comparing exists in one of the other edges, then we can constant fold ICI
1830 if (SI->findCaseValue(Cst) != 0) {
1832 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1833 V = ConstantInt::getFalse(BB->getContext());
1835 V = ConstantInt::getTrue(BB->getContext());
1837 ICI->replaceAllUsesWith(V);
1838 ICI->eraseFromParent();
1839 // BB is now empty, so it is likely to simplify away.
1840 return SimplifyCFG(BB) | true;
1843 // The use of the icmp has to be in the 'end' block, by the only PHI node in
1845 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
1846 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
1847 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
1848 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
1851 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
1853 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
1854 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
1856 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1857 std::swap(DefaultCst, NewCst);
1859 // Replace ICI (which is used by the PHI for the default value) with true or
1860 // false depending on if it is EQ or NE.
1861 ICI->replaceAllUsesWith(DefaultCst);
1862 ICI->eraseFromParent();
1864 // Okay, the switch goes to this block on a default value. Add an edge from
1865 // the switch to the merge point on the compared value.
1866 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
1867 BB->getParent(), BB);
1868 SI->addCase(Cst, NewBB);
1870 // NewBB branches to the phi block, add the uncond branch and the phi entry.
1871 BranchInst::Create(SuccBlock, NewBB);
1872 PHIUse->addIncoming(NewCst, NewBB);
1876 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
1877 /// Check to see if it is branching on an or/and chain of icmp instructions, and
1878 /// fold it into a switch instruction if so.
1879 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD) {
1880 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1881 if (Cond == 0) return false;
1884 // Change br (X == 0 | X == 1), T, F into a switch instruction.
1885 // If this is a bunch of seteq's or'd together, or if it's a bunch of
1886 // 'setne's and'ed together, collect them.
1888 std::vector<ConstantInt*> Values;
1889 bool TrueWhenEqual = true;
1890 Value *ExtraCase = 0;
1892 if (Cond->getOpcode() == Instruction::Or) {
1893 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true);
1894 } else if (Cond->getOpcode() == Instruction::And) {
1895 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false);
1896 TrueWhenEqual = false;
1899 // If we didn't have a multiply compared value, fail.
1900 if (CompVal == 0) return false;
1902 // There might be duplicate constants in the list, which the switch
1903 // instruction can't handle, remove them now.
1904 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
1905 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
1907 // If Extra was used, we require at least two switch values to do the
1908 // transformation. A switch with one value is just an cond branch.
1909 if (ExtraCase && Values.size() < 2) return false;
1911 // Figure out which block is which destination.
1912 BasicBlock *DefaultBB = BI->getSuccessor(1);
1913 BasicBlock *EdgeBB = BI->getSuccessor(0);
1914 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
1916 BasicBlock *BB = BI->getParent();
1918 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
1919 << " cases into SWITCH. BB is:\n" << *BB);
1921 // If there are any extra values that couldn't be folded into the switch
1922 // then we evaluate them with an explicit branch first. Split the block
1923 // right before the condbr to handle it.
1925 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
1926 // Remove the uncond branch added to the old block.
1927 TerminatorInst *OldTI = BB->getTerminator();
1930 BranchInst::Create(EdgeBB, NewBB, ExtraCase, OldTI);
1932 BranchInst::Create(NewBB, EdgeBB, ExtraCase, OldTI);
1934 OldTI->eraseFromParent();
1936 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
1937 // for the edge we just added.
1938 AddPredecessorToBlock(EdgeBB, BB, NewBB);
1940 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
1941 << "\nEXTRABB = " << *BB);
1945 // Convert pointer to int before we switch.
1946 if (CompVal->getType()->isPointerTy()) {
1947 assert(TD && "Cannot switch on pointer without TargetData");
1948 CompVal = new PtrToIntInst(CompVal,
1949 TD->getIntPtrType(CompVal->getContext()),
1953 // Create the new switch instruction now.
1954 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB, Values.size(), BI);
1956 // Add all of the 'cases' to the switch instruction.
1957 for (unsigned i = 0, e = Values.size(); i != e; ++i)
1958 New->addCase(Values[i], EdgeBB);
1960 // We added edges from PI to the EdgeBB. As such, if there were any
1961 // PHI nodes in EdgeBB, they need entries to be added corresponding to
1962 // the number of edges added.
1963 for (BasicBlock::iterator BBI = EdgeBB->begin();
1964 isa<PHINode>(BBI); ++BBI) {
1965 PHINode *PN = cast<PHINode>(BBI);
1966 Value *InVal = PN->getIncomingValueForBlock(BB);
1967 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
1968 PN->addIncoming(InVal, BB);
1971 // Erase the old branch instruction.
1972 EraseTerminatorInstAndDCECond(BI);
1974 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
1978 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI) {
1979 BasicBlock *BB = RI->getParent();
1980 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
1982 // Find predecessors that end with branches.
1983 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1984 SmallVector<BranchInst*, 8> CondBranchPreds;
1985 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1986 BasicBlock *P = *PI;
1987 TerminatorInst *PTI = P->getTerminator();
1988 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1989 if (BI->isUnconditional())
1990 UncondBranchPreds.push_back(P);
1992 CondBranchPreds.push_back(BI);
1996 // If we found some, do the transformation!
1997 if (!UncondBranchPreds.empty()) {
1998 while (!UncondBranchPreds.empty()) {
1999 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2000 DEBUG(dbgs() << "FOLDING: " << *BB
2001 << "INTO UNCOND BRANCH PRED: " << *Pred);
2002 Instruction *UncondBranch = Pred->getTerminator();
2003 // Clone the return and add it to the end of the predecessor.
2004 Instruction *NewRet = RI->clone();
2005 Pred->getInstList().push_back(NewRet);
2007 // If the return instruction returns a value, and if the value was a
2008 // PHI node in "BB", propagate the right value into the return.
2009 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
2011 if (PHINode *PN = dyn_cast<PHINode>(*i))
2012 if (PN->getParent() == BB)
2013 *i = PN->getIncomingValueForBlock(Pred);
2015 // Update any PHI nodes in the returning block to realize that we no
2016 // longer branch to them.
2017 BB->removePredecessor(Pred);
2018 UncondBranch->eraseFromParent();
2021 // If we eliminated all predecessors of the block, delete the block now.
2022 if (pred_begin(BB) == pred_end(BB))
2023 // We know there are no successors, so just nuke the block.
2024 BB->eraseFromParent();
2029 // Check out all of the conditional branches going to this return
2030 // instruction. If any of them just select between returns, change the
2031 // branch itself into a select/return pair.
2032 while (!CondBranchPreds.empty()) {
2033 BranchInst *BI = CondBranchPreds.pop_back_val();
2035 // Check to see if the non-BB successor is also a return block.
2036 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2037 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2038 SimplifyCondBranchToTwoReturns(BI))
2044 bool SimplifyCFGOpt::SimplifyUnwind(UnwindInst *UI) {
2045 // Check to see if the first instruction in this block is just an unwind.
2046 // If so, replace any invoke instructions which use this as an exception
2047 // destination with call instructions.
2048 BasicBlock *BB = UI->getParent();
2049 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2051 bool Changed = false;
2052 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2053 while (!Preds.empty()) {
2054 BasicBlock *Pred = Preds.back();
2055 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
2056 if (II && II->getUnwindDest() == BB) {
2057 // Insert a new branch instruction before the invoke, because this
2058 // is now a fall through.
2059 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2060 Pred->getInstList().remove(II); // Take out of symbol table
2062 // Insert the call now.
2063 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
2064 CallInst *CI = CallInst::Create(II->getCalledValue(),
2065 Args.begin(), Args.end(),
2067 CI->setCallingConv(II->getCallingConv());
2068 CI->setAttributes(II->getAttributes());
2069 // If the invoke produced a value, the Call now does instead.
2070 II->replaceAllUsesWith(CI);
2078 // If this block is now dead (and isn't the entry block), remove it.
2079 if (pred_begin(BB) == pred_end(BB) &&
2080 BB != &BB->getParent()->getEntryBlock()) {
2081 // We know there are no successors, so just nuke the block.
2082 BB->eraseFromParent();
2089 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2090 BasicBlock *BB = UI->getParent();
2092 bool Changed = false;
2094 // If there are any instructions immediately before the unreachable that can
2095 // be removed, do so.
2096 while (UI != BB->begin()) {
2097 BasicBlock::iterator BBI = UI;
2099 // Do not delete instructions that can have side effects, like calls
2100 // (which may never return) and volatile loads and stores.
2101 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2103 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
2104 if (SI->isVolatile())
2107 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
2108 if (LI->isVolatile())
2111 // Delete this instruction
2112 BBI->eraseFromParent();
2116 // If the unreachable instruction is the first in the block, take a gander
2117 // at all of the predecessors of this instruction, and simplify them.
2118 if (&BB->front() != UI) return Changed;
2120 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2121 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2122 TerminatorInst *TI = Preds[i]->getTerminator();
2124 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2125 if (BI->isUnconditional()) {
2126 if (BI->getSuccessor(0) == BB) {
2127 new UnreachableInst(TI->getContext(), TI);
2128 TI->eraseFromParent();
2132 if (BI->getSuccessor(0) == BB) {
2133 BranchInst::Create(BI->getSuccessor(1), BI);
2134 EraseTerminatorInstAndDCECond(BI);
2135 } else if (BI->getSuccessor(1) == BB) {
2136 BranchInst::Create(BI->getSuccessor(0), BI);
2137 EraseTerminatorInstAndDCECond(BI);
2141 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2142 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2143 if (SI->getSuccessor(i) == BB) {
2144 BB->removePredecessor(SI->getParent());
2149 // If the default value is unreachable, figure out the most popular
2150 // destination and make it the default.
2151 if (SI->getSuccessor(0) == BB) {
2152 std::map<BasicBlock*, unsigned> Popularity;
2153 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2154 Popularity[SI->getSuccessor(i)]++;
2156 // Find the most popular block.
2157 unsigned MaxPop = 0;
2158 BasicBlock *MaxBlock = 0;
2159 for (std::map<BasicBlock*, unsigned>::iterator
2160 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2161 if (I->second > MaxPop) {
2163 MaxBlock = I->first;
2167 // Make this the new default, allowing us to delete any explicit
2169 SI->setSuccessor(0, MaxBlock);
2172 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2174 if (isa<PHINode>(MaxBlock->begin()))
2175 for (unsigned i = 0; i != MaxPop-1; ++i)
2176 MaxBlock->removePredecessor(SI->getParent());
2178 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2179 if (SI->getSuccessor(i) == MaxBlock) {
2185 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2186 if (II->getUnwindDest() == BB) {
2187 // Convert the invoke to a call instruction. This would be a good
2188 // place to note that the call does not throw though.
2189 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2190 II->removeFromParent(); // Take out of symbol table
2192 // Insert the call now...
2193 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2194 CallInst *CI = CallInst::Create(II->getCalledValue(),
2195 Args.begin(), Args.end(),
2197 CI->setCallingConv(II->getCallingConv());
2198 CI->setAttributes(II->getAttributes());
2199 // If the invoke produced a value, the call does now instead.
2200 II->replaceAllUsesWith(CI);
2207 // If this block is now dead, remove it.
2208 if (pred_begin(BB) == pred_end(BB) &&
2209 BB != &BB->getParent()->getEntryBlock()) {
2210 // We know there are no successors, so just nuke the block.
2211 BB->eraseFromParent();
2219 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI) {
2220 // If this switch is too complex to want to look at, ignore it.
2221 if (!isValueEqualityComparison(SI))
2224 BasicBlock *BB = SI->getParent();
2226 // If we only have one predecessor, and if it is a branch on this value,
2227 // see if that predecessor totally determines the outcome of this switch.
2228 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2229 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
2230 return SimplifyCFG(BB) | true;
2232 // If the block only contains the switch, see if we can fold the block
2233 // away into any preds.
2234 BasicBlock::iterator BBI = BB->begin();
2235 // Ignore dbg intrinsics.
2236 while (isa<DbgInfoIntrinsic>(BBI))
2239 if (FoldValueComparisonIntoPredecessors(SI))
2240 return SimplifyCFG(BB) | true;
2245 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
2246 BasicBlock *BB = IBI->getParent();
2247 bool Changed = false;
2249 // Eliminate redundant destinations.
2250 SmallPtrSet<Value *, 8> Succs;
2251 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2252 BasicBlock *Dest = IBI->getDestination(i);
2253 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2254 Dest->removePredecessor(BB);
2255 IBI->removeDestination(i);
2261 if (IBI->getNumDestinations() == 0) {
2262 // If the indirectbr has no successors, change it to unreachable.
2263 new UnreachableInst(IBI->getContext(), IBI);
2264 EraseTerminatorInstAndDCECond(IBI);
2268 if (IBI->getNumDestinations() == 1) {
2269 // If the indirectbr has one successor, change it to a direct branch.
2270 BranchInst::Create(IBI->getDestination(0), IBI);
2271 EraseTerminatorInstAndDCECond(IBI);
2275 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2276 if (SimplifyIndirectBrOnSelect(IBI, SI))
2277 return SimplifyCFG(BB) | true;
2282 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI) {
2283 BasicBlock *BB = BI->getParent();
2285 // If the Terminator is the only non-phi instruction, simplify the block.
2286 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg();
2287 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
2288 TryToSimplifyUncondBranchFromEmptyBlock(BB))
2291 // If the only instruction in the block is a seteq/setne comparison
2292 // against a constant, try to simplify the block.
2293 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
2294 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
2295 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
2297 if (I->isTerminator() && TryToSimplifyUncondBranchWithICmpInIt(ICI, TD))
2305 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI) {
2306 BasicBlock *BB = BI->getParent();
2308 // Conditional branch
2309 if (isValueEqualityComparison(BI)) {
2310 // If we only have one predecessor, and if it is a branch on this value,
2311 // see if that predecessor totally determines the outcome of this
2313 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2314 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
2315 return SimplifyCFG(BB) | true;
2317 // This block must be empty, except for the setcond inst, if it exists.
2318 // Ignore dbg intrinsics.
2319 BasicBlock::iterator I = BB->begin();
2320 // Ignore dbg intrinsics.
2321 while (isa<DbgInfoIntrinsic>(I))
2324 if (FoldValueComparisonIntoPredecessors(BI))
2325 return SimplifyCFG(BB) | true;
2326 } else if (&*I == cast<Instruction>(BI->getCondition())){
2328 // Ignore dbg intrinsics.
2329 while (isa<DbgInfoIntrinsic>(I))
2331 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI))
2332 return SimplifyCFG(BB) | true;
2336 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
2337 if (SimplifyBranchOnICmpChain(BI, TD))
2340 // We have a conditional branch to two blocks that are only reachable
2341 // from BI. We know that the condbr dominates the two blocks, so see if
2342 // there is any identical code in the "then" and "else" blocks. If so, we
2343 // can hoist it up to the branching block.
2344 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
2345 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2346 if (HoistThenElseCodeToIf(BI))
2347 return SimplifyCFG(BB) | true;
2349 // If Successor #1 has multiple preds, we may be able to conditionally
2350 // execute Successor #0 if it branches to successor #1.
2351 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
2352 if (Succ0TI->getNumSuccessors() == 1 &&
2353 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
2354 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
2355 return SimplifyCFG(BB) | true;
2357 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2358 // If Successor #0 has multiple preds, we may be able to conditionally
2359 // execute Successor #1 if it branches to successor #0.
2360 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
2361 if (Succ1TI->getNumSuccessors() == 1 &&
2362 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
2363 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
2364 return SimplifyCFG(BB) | true;
2367 // If this is a branch on a phi node in the current block, thread control
2368 // through this block if any PHI node entries are constants.
2369 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
2370 if (PN->getParent() == BI->getParent())
2371 if (FoldCondBranchOnPHI(BI, TD))
2372 return SimplifyCFG(BB) | true;
2374 // If this basic block is ONLY a setcc and a branch, and if a predecessor
2375 // branches to us and one of our successors, fold the setcc into the
2376 // predecessor and use logical operations to pick the right destination.
2377 if (FoldBranchToCommonDest(BI))
2378 return SimplifyCFG(BB) | true;
2380 // Scan predecessor blocks for conditional branches.
2381 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2382 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2383 if (PBI != BI && PBI->isConditional())
2384 if (SimplifyCondBranchToCondBranch(PBI, BI))
2385 return SimplifyCFG(BB) | true;
2390 bool SimplifyCFGOpt::run(BasicBlock *BB) {
2391 bool Changed = false;
2393 assert(BB && BB->getParent() && "Block not embedded in function!");
2394 assert(BB->getTerminator() && "Degenerate basic block encountered!");
2396 // Remove basic blocks that have no predecessors (except the entry block)...
2397 // or that just have themself as a predecessor. These are unreachable.
2398 if ((pred_begin(BB) == pred_end(BB) &&
2399 BB != &BB->getParent()->getEntryBlock()) ||
2400 BB->getSinglePredecessor() == BB) {
2401 DEBUG(dbgs() << "Removing BB: \n" << *BB);
2402 DeleteDeadBlock(BB);
2406 // Check to see if we can constant propagate this terminator instruction
2408 Changed |= ConstantFoldTerminator(BB);
2410 // Check for and eliminate duplicate PHI nodes in this block.
2411 Changed |= EliminateDuplicatePHINodes(BB);
2413 // Merge basic blocks into their predecessor if there is only one distinct
2414 // pred, and if there is only one distinct successor of the predecessor, and
2415 // if there are no PHI nodes.
2417 if (MergeBlockIntoPredecessor(BB))
2420 // If there is a trivial two-entry PHI node in this basic block, and we can
2421 // eliminate it, do so now.
2422 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
2423 if (PN->getNumIncomingValues() == 2)
2424 Changed |= FoldTwoEntryPHINode(PN, TD);
2426 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
2427 if (BI->isUnconditional()) {
2428 if (SimplifyUncondBranch(BI)) return true;
2430 if (SimplifyCondBranch(BI)) return true;
2432 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
2433 if (SimplifyReturn(RI)) return true;
2434 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
2435 if (SimplifySwitch(SI)) return true;
2436 } else if (UnreachableInst *UI =
2437 dyn_cast<UnreachableInst>(BB->getTerminator())) {
2438 if (SimplifyUnreachable(UI)) return true;
2439 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
2440 if (SimplifyUnwind(UI)) return true;
2441 } else if (IndirectBrInst *IBI =
2442 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
2443 if (SimplifyIndirectBr(IBI)) return true;
2449 /// SimplifyCFG - This function is used to do simplification of a CFG. For
2450 /// example, it adjusts branches to branches to eliminate the extra hop, it
2451 /// eliminates unreachable basic blocks, and does other "peephole" optimization
2452 /// of the CFG. It returns true if a modification was made.
2454 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
2455 return SimplifyCFGOpt(TD).run(BB);