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/Support/CFG.h"
23 #include "llvm/Support/Debug.h"
24 #include "llvm/Support/raw_ostream.h"
25 #include "llvm/Analysis/ConstantFolding.h"
26 #include "llvm/Target/TargetData.h"
27 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
28 #include "llvm/ADT/DenseMap.h"
29 #include "llvm/ADT/SmallVector.h"
30 #include "llvm/ADT/SmallPtrSet.h"
31 #include "llvm/ADT/Statistic.h"
32 #include "llvm/ADT/STLExtras.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 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
98 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
99 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
102 for (BasicBlock::iterator I = Succ->begin();
103 (PN = dyn_cast<PHINode>(I)); ++I)
104 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
108 /// GetIfCondition - Given a basic block (BB) with two predecessors (and
109 /// presumably PHI nodes in it), check to see if the merge at this block is due
110 /// to an "if condition". If so, return the boolean condition that determines
111 /// which entry into BB will be taken. Also, return by references the block
112 /// that will be entered from if the condition is true, and the block that will
113 /// be entered if the condition is false.
116 static Value *GetIfCondition(BasicBlock *BB,
117 BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
118 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
119 "Function can only handle blocks with 2 predecessors!");
120 BasicBlock *Pred1 = *pred_begin(BB);
121 BasicBlock *Pred2 = *++pred_begin(BB);
123 // We can only handle branches. Other control flow will be lowered to
124 // branches if possible anyway.
125 if (!isa<BranchInst>(Pred1->getTerminator()) ||
126 !isa<BranchInst>(Pred2->getTerminator()))
128 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
129 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
131 // Eliminate code duplication by ensuring that Pred1Br is conditional if
133 if (Pred2Br->isConditional()) {
134 // If both branches are conditional, we don't have an "if statement". In
135 // reality, we could transform this case, but since the condition will be
136 // required anyway, we stand no chance of eliminating it, so the xform is
137 // probably not profitable.
138 if (Pred1Br->isConditional())
141 std::swap(Pred1, Pred2);
142 std::swap(Pred1Br, Pred2Br);
145 if (Pred1Br->isConditional()) {
146 // If we found a conditional branch predecessor, make sure that it branches
147 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
148 if (Pred1Br->getSuccessor(0) == BB &&
149 Pred1Br->getSuccessor(1) == Pred2) {
152 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
153 Pred1Br->getSuccessor(1) == BB) {
157 // We know that one arm of the conditional goes to BB, so the other must
158 // go somewhere unrelated, and this must not be an "if statement".
162 // The only thing we have to watch out for here is to make sure that Pred2
163 // doesn't have incoming edges from other blocks. If it does, the condition
164 // doesn't dominate BB.
165 if (++pred_begin(Pred2) != pred_end(Pred2))
168 return Pred1Br->getCondition();
171 // Ok, if we got here, both predecessors end with an unconditional branch to
172 // BB. Don't panic! If both blocks only have a single (identical)
173 // predecessor, and THAT is a conditional branch, then we're all ok!
174 if (pred_begin(Pred1) == pred_end(Pred1) ||
175 ++pred_begin(Pred1) != pred_end(Pred1) ||
176 pred_begin(Pred2) == pred_end(Pred2) ||
177 ++pred_begin(Pred2) != pred_end(Pred2) ||
178 *pred_begin(Pred1) != *pred_begin(Pred2))
181 // Otherwise, if this is a conditional branch, then we can use it!
182 BasicBlock *CommonPred = *pred_begin(Pred1);
183 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
184 assert(BI->isConditional() && "Two successors but not conditional?");
185 if (BI->getSuccessor(0) == Pred1) {
192 return BI->getCondition();
197 /// DominatesMergePoint - If we have a merge point of an "if condition" as
198 /// accepted above, return true if the specified value dominates the block. We
199 /// don't handle the true generality of domination here, just a special case
200 /// which works well enough for us.
202 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
203 /// see if V (which must be an instruction) is cheap to compute and is
204 /// non-trapping. If both are true, the instruction is inserted into the set
205 /// and true is returned.
206 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
207 std::set<Instruction*> *AggressiveInsts) {
208 Instruction *I = dyn_cast<Instruction>(V);
210 // Non-instructions all dominate instructions, but not all constantexprs
211 // can be executed unconditionally.
212 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
217 BasicBlock *PBB = I->getParent();
219 // We don't want to allow weird loops that might have the "if condition" in
220 // the bottom of this block.
221 if (PBB == BB) return false;
223 // If this instruction is defined in a block that contains an unconditional
224 // branch to BB, then it must be in the 'conditional' part of the "if
226 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
227 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
228 if (!AggressiveInsts) 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 loop out to
241 BasicBlock::iterator IP = PBB->begin();
242 while (isa<DbgInfoIntrinsic>(IP))
244 if (IP != BasicBlock::iterator(I))
248 case Instruction::Add:
249 case Instruction::Sub:
250 case Instruction::And:
251 case Instruction::Or:
252 case Instruction::Xor:
253 case Instruction::Shl:
254 case Instruction::LShr:
255 case Instruction::AShr:
256 case Instruction::ICmp:
257 break; // These are all cheap and non-trapping instructions.
260 // Okay, we can only really hoist these out if their operands are not
261 // defined in the conditional region.
262 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
263 if (!DominatesMergePoint(*i, BB, 0))
265 // Okay, it's safe to do this! Remember this instruction.
266 AggressiveInsts->insert(I);
272 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
273 /// and PointerNullValue. Return NULL if value is not a constant int.
274 static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
275 // Normal constant int.
276 ConstantInt *CI = dyn_cast<ConstantInt>(V);
277 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
280 // This is some kind of pointer constant. Turn it into a pointer-sized
281 // ConstantInt if possible.
282 const IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
284 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
285 if (isa<ConstantPointerNull>(V))
286 return ConstantInt::get(PtrTy, 0);
288 // IntToPtr const int.
289 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
290 if (CE->getOpcode() == Instruction::IntToPtr)
291 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
292 // The constant is very likely to have the right type already.
293 if (CI->getType() == PtrTy)
296 return cast<ConstantInt>
297 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
302 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
303 /// collection of icmp eq/ne instructions that compare a value against a
304 /// constant, return the value being compared, and stick the constant into the
307 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
308 const TargetData *TD, bool isEQ) {
309 Instruction *I = dyn_cast<Instruction>(V);
310 if (I == 0) return 0;
312 // If this is an icmp against a constant, handle this as one of the cases.
313 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
314 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE))
315 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
317 return I->getOperand(0);
322 // Otherwise, we can only handle an | or &, depending on isEQ.
323 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
326 unsigned NumValsBeforeLHS = Vals.size();
327 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
329 unsigned NumVals = Vals.size();
330 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
334 Vals.resize(NumVals);
337 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
338 // set it and return success.
339 if (Extra == 0 || Extra == I->getOperand(1)) {
340 Extra = I->getOperand(1);
344 Vals.resize(NumValsBeforeLHS);
348 // If the LHS can't be folded in, but Extra is available and RHS can, try to
350 if (Extra == 0 || Extra == I->getOperand(0)) {
351 Value *OldExtra = Extra;
352 Extra = I->getOperand(0);
353 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
356 assert(Vals.size() == NumValsBeforeLHS);
363 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
364 Instruction* Cond = 0;
365 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
366 Cond = dyn_cast<Instruction>(SI->getCondition());
367 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
368 if (BI->isConditional())
369 Cond = dyn_cast<Instruction>(BI->getCondition());
370 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
371 Cond = dyn_cast<Instruction>(IBI->getAddress());
374 TI->eraseFromParent();
375 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
378 /// isValueEqualityComparison - Return true if the specified terminator checks
379 /// to see if a value is equal to constant integer value.
380 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
382 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
383 // Do not permit merging of large switch instructions into their
384 // predecessors unless there is only one predecessor.
385 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
386 pred_end(SI->getParent())) <= 128)
387 CV = SI->getCondition();
388 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
389 if (BI->isConditional() && BI->getCondition()->hasOneUse())
390 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
391 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
392 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
393 GetConstantInt(ICI->getOperand(1), TD))
394 CV = ICI->getOperand(0);
396 // Unwrap any lossless ptrtoint cast.
397 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
398 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
399 CV = PTII->getOperand(0);
403 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
404 /// decode all of the 'cases' that it represents and return the 'default' block.
405 BasicBlock *SimplifyCFGOpt::
406 GetValueEqualityComparisonCases(TerminatorInst *TI,
407 std::vector<std::pair<ConstantInt*,
408 BasicBlock*> > &Cases) {
409 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
410 Cases.reserve(SI->getNumCases());
411 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
412 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
413 return SI->getDefaultDest();
416 BranchInst *BI = cast<BranchInst>(TI);
417 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
418 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD),
419 BI->getSuccessor(ICI->getPredicate() ==
420 ICmpInst::ICMP_NE)));
421 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
425 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
426 /// in the list that match the specified block.
427 static void EliminateBlockCases(BasicBlock *BB,
428 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
429 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
430 if (Cases[i].second == BB) {
431 Cases.erase(Cases.begin()+i);
436 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
439 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
440 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
441 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
443 // Make V1 be smaller than V2.
444 if (V1->size() > V2->size())
447 if (V1->size() == 0) return false;
448 if (V1->size() == 1) {
450 ConstantInt *TheVal = (*V1)[0].first;
451 for (unsigned i = 0, e = V2->size(); i != e; ++i)
452 if (TheVal == (*V2)[i].first)
456 // Otherwise, just sort both lists and compare element by element.
457 array_pod_sort(V1->begin(), V1->end());
458 array_pod_sort(V2->begin(), V2->end());
459 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
460 while (i1 != e1 && i2 != e2) {
461 if ((*V1)[i1].first == (*V2)[i2].first)
463 if ((*V1)[i1].first < (*V2)[i2].first)
471 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
472 /// terminator instruction and its block is known to only have a single
473 /// predecessor block, check to see if that predecessor is also a value
474 /// comparison with the same value, and if that comparison determines the
475 /// outcome of this comparison. If so, simplify TI. This does a very limited
476 /// form of jump threading.
477 bool SimplifyCFGOpt::
478 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
480 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
481 if (!PredVal) return false; // Not a value comparison in predecessor.
483 Value *ThisVal = isValueEqualityComparison(TI);
484 assert(ThisVal && "This isn't a value comparison!!");
485 if (ThisVal != PredVal) return false; // Different predicates.
487 // Find out information about when control will move from Pred to TI's block.
488 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
489 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
491 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
493 // Find information about how control leaves this block.
494 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
495 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
496 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
498 // If TI's block is the default block from Pred's comparison, potentially
499 // simplify TI based on this knowledge.
500 if (PredDef == TI->getParent()) {
501 // If we are here, we know that the value is none of those cases listed in
502 // PredCases. If there are any cases in ThisCases that are in PredCases, we
504 if (!ValuesOverlap(PredCases, ThisCases))
507 if (isa<BranchInst>(TI)) {
508 // Okay, one of the successors of this condbr is dead. Convert it to a
510 assert(ThisCases.size() == 1 && "Branch can only have one case!");
511 // Insert the new branch.
512 Instruction *NI = BranchInst::Create(ThisDef, TI);
515 // Remove PHI node entries for the dead edge.
516 ThisCases[0].second->removePredecessor(TI->getParent());
518 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
519 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
521 EraseTerminatorInstAndDCECond(TI);
525 SwitchInst *SI = cast<SwitchInst>(TI);
526 // Okay, TI has cases that are statically dead, prune them away.
527 SmallPtrSet<Constant*, 16> DeadCases;
528 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
529 DeadCases.insert(PredCases[i].first);
531 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
532 << "Through successor TI: " << *TI);
534 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
535 if (DeadCases.count(SI->getCaseValue(i))) {
536 SI->getSuccessor(i)->removePredecessor(TI->getParent());
540 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
544 // Otherwise, TI's block must correspond to some matched value. Find out
545 // which value (or set of values) this is.
546 ConstantInt *TIV = 0;
547 BasicBlock *TIBB = TI->getParent();
548 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
549 if (PredCases[i].second == TIBB) {
551 return false; // Cannot handle multiple values coming to this block.
552 TIV = PredCases[i].first;
554 assert(TIV && "No edge from pred to succ?");
556 // Okay, we found the one constant that our value can be if we get into TI's
557 // BB. Find out which successor will unconditionally be branched to.
558 BasicBlock *TheRealDest = 0;
559 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
560 if (ThisCases[i].first == TIV) {
561 TheRealDest = ThisCases[i].second;
565 // If not handled by any explicit cases, it is handled by the default case.
566 if (TheRealDest == 0) TheRealDest = ThisDef;
568 // Remove PHI node entries for dead edges.
569 BasicBlock *CheckEdge = TheRealDest;
570 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
571 if (*SI != CheckEdge)
572 (*SI)->removePredecessor(TIBB);
576 // Insert the new branch.
577 Instruction *NI = BranchInst::Create(TheRealDest, TI);
580 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
581 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
583 EraseTerminatorInstAndDCECond(TI);
588 /// ConstantIntOrdering - This class implements a stable ordering of constant
589 /// integers that does not depend on their address. This is important for
590 /// applications that sort ConstantInt's to ensure uniqueness.
591 struct ConstantIntOrdering {
592 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
593 return LHS->getValue().ult(RHS->getValue());
598 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
599 const ConstantInt *LHS = *(const ConstantInt**)P1;
600 const ConstantInt *RHS = *(const ConstantInt**)P2;
601 return LHS->getValue().ult(RHS->getValue()) ? 1 : -1;
604 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
605 /// equality comparison instruction (either a switch or a branch on "X == c").
606 /// See if any of the predecessors of the terminator block are value comparisons
607 /// on the same value. If so, and if safe to do so, fold them together.
608 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
609 BasicBlock *BB = TI->getParent();
610 Value *CV = isValueEqualityComparison(TI); // CondVal
611 assert(CV && "Not a comparison?");
612 bool Changed = false;
614 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
615 while (!Preds.empty()) {
616 BasicBlock *Pred = Preds.pop_back_val();
618 // See if the predecessor is a comparison with the same value.
619 TerminatorInst *PTI = Pred->getTerminator();
620 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
622 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
623 // Figure out which 'cases' to copy from SI to PSI.
624 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
625 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
627 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
628 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
630 // Based on whether the default edge from PTI goes to BB or not, fill in
631 // PredCases and PredDefault with the new switch cases we would like to
633 SmallVector<BasicBlock*, 8> NewSuccessors;
635 if (PredDefault == BB) {
636 // If this is the default destination from PTI, only the edges in TI
637 // that don't occur in PTI, or that branch to BB will be activated.
638 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
639 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
640 if (PredCases[i].second != BB)
641 PTIHandled.insert(PredCases[i].first);
643 // The default destination is BB, we don't need explicit targets.
644 std::swap(PredCases[i], PredCases.back());
645 PredCases.pop_back();
649 // Reconstruct the new switch statement we will be building.
650 if (PredDefault != BBDefault) {
651 PredDefault->removePredecessor(Pred);
652 PredDefault = BBDefault;
653 NewSuccessors.push_back(BBDefault);
655 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
656 if (!PTIHandled.count(BBCases[i].first) &&
657 BBCases[i].second != BBDefault) {
658 PredCases.push_back(BBCases[i]);
659 NewSuccessors.push_back(BBCases[i].second);
663 // If this is not the default destination from PSI, only the edges
664 // in SI that occur in PSI with a destination of BB will be
666 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
667 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
668 if (PredCases[i].second == BB) {
669 PTIHandled.insert(PredCases[i].first);
670 std::swap(PredCases[i], PredCases.back());
671 PredCases.pop_back();
675 // Okay, now we know which constants were sent to BB from the
676 // predecessor. Figure out where they will all go now.
677 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
678 if (PTIHandled.count(BBCases[i].first)) {
679 // If this is one we are capable of getting...
680 PredCases.push_back(BBCases[i]);
681 NewSuccessors.push_back(BBCases[i].second);
682 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
685 // If there are any constants vectored to BB that TI doesn't handle,
686 // they must go to the default destination of TI.
687 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
689 E = PTIHandled.end(); I != E; ++I) {
690 PredCases.push_back(std::make_pair(*I, BBDefault));
691 NewSuccessors.push_back(BBDefault);
695 // Okay, at this point, we know which new successor Pred will get. Make
696 // sure we update the number of entries in the PHI nodes for these
698 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
699 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
701 // Convert pointer to int before we switch.
702 if (CV->getType()->isPointerTy()) {
703 assert(TD && "Cannot switch on pointer without TargetData");
704 CV = new PtrToIntInst(CV, TD->getIntPtrType(CV->getContext()),
708 // Now that the successors are updated, create the new Switch instruction.
709 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
710 PredCases.size(), PTI);
711 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
712 NewSI->addCase(PredCases[i].first, PredCases[i].second);
714 EraseTerminatorInstAndDCECond(PTI);
716 // Okay, last check. If BB is still a successor of PSI, then we must
717 // have an infinite loop case. If so, add an infinitely looping block
718 // to handle the case to preserve the behavior of the code.
719 BasicBlock *InfLoopBlock = 0;
720 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
721 if (NewSI->getSuccessor(i) == BB) {
722 if (InfLoopBlock == 0) {
723 // Insert it at the end of the function, because it's either code,
724 // or it won't matter if it's hot. :)
725 InfLoopBlock = BasicBlock::Create(BB->getContext(),
726 "infloop", BB->getParent());
727 BranchInst::Create(InfLoopBlock, InfLoopBlock);
729 NewSI->setSuccessor(i, InfLoopBlock);
738 // isSafeToHoistInvoke - If we would need to insert a select that uses the
739 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
740 // would need to do this), we can't hoist the invoke, as there is nowhere
741 // to put the select in this case.
742 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
743 Instruction *I1, Instruction *I2) {
744 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
746 for (BasicBlock::iterator BBI = SI->begin();
747 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
748 Value *BB1V = PN->getIncomingValueForBlock(BB1);
749 Value *BB2V = PN->getIncomingValueForBlock(BB2);
750 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
758 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
759 /// BB2, hoist any common code in the two blocks up into the branch block. The
760 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
761 static bool HoistThenElseCodeToIf(BranchInst *BI) {
762 // This does very trivial matching, with limited scanning, to find identical
763 // instructions in the two blocks. In particular, we don't want to get into
764 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
765 // such, we currently just scan for obviously identical instructions in an
767 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
768 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
770 BasicBlock::iterator BB1_Itr = BB1->begin();
771 BasicBlock::iterator BB2_Itr = BB2->begin();
773 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
774 while (isa<DbgInfoIntrinsic>(I1))
776 while (isa<DbgInfoIntrinsic>(I2))
778 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
779 !I1->isIdenticalToWhenDefined(I2) ||
780 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
783 // If we get here, we can hoist at least one instruction.
784 BasicBlock *BIParent = BI->getParent();
787 // If we are hoisting the terminator instruction, don't move one (making a
788 // broken BB), instead clone it, and remove BI.
789 if (isa<TerminatorInst>(I1))
790 goto HoistTerminator;
792 // For a normal instruction, we just move one to right before the branch,
793 // then replace all uses of the other with the first. Finally, we remove
794 // the now redundant second instruction.
795 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
796 if (!I2->use_empty())
797 I2->replaceAllUsesWith(I1);
798 I1->intersectOptionalDataWith(I2);
799 BB2->getInstList().erase(I2);
802 while (isa<DbgInfoIntrinsic>(I1))
805 while (isa<DbgInfoIntrinsic>(I2))
807 } while (I1->getOpcode() == I2->getOpcode() &&
808 I1->isIdenticalToWhenDefined(I2));
813 // It may not be possible to hoist an invoke.
814 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
817 // Okay, it is safe to hoist the terminator.
818 Instruction *NT = I1->clone();
819 BIParent->getInstList().insert(BI, NT);
820 if (!NT->getType()->isVoidTy()) {
821 I1->replaceAllUsesWith(NT);
822 I2->replaceAllUsesWith(NT);
826 // Hoisting one of the terminators from our successor is a great thing.
827 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
828 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
829 // nodes, so we insert select instruction to compute the final result.
830 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
831 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
833 for (BasicBlock::iterator BBI = SI->begin();
834 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
835 Value *BB1V = PN->getIncomingValueForBlock(BB1);
836 Value *BB2V = PN->getIncomingValueForBlock(BB2);
837 if (BB1V == BB2V) continue;
839 // These values do not agree. Insert a select instruction before NT
840 // that determines the right value.
841 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
843 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
844 BB1V->getName()+"."+BB2V->getName(), NT);
845 // Make the PHI node use the select for all incoming values for BB1/BB2
846 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
847 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
848 PN->setIncomingValue(i, SI);
852 // Update any PHI nodes in our new successors.
853 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
854 AddPredecessorToBlock(*SI, BIParent, BB1);
856 EraseTerminatorInstAndDCECond(BI);
860 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
861 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
862 /// (for now, restricted to a single instruction that's side effect free) from
863 /// the BB1 into the branch block to speculatively execute it.
864 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
865 // Only speculatively execution a single instruction (not counting the
866 // terminator) for now.
867 Instruction *HInst = NULL;
868 Instruction *Term = BB1->getTerminator();
869 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
871 Instruction *I = BBI;
873 if (isa<DbgInfoIntrinsic>(I)) continue;
874 if (I == Term) break;
883 // Be conservative for now. FP select instruction can often be expensive.
884 Value *BrCond = BI->getCondition();
885 if (isa<FCmpInst>(BrCond))
888 // If BB1 is actually on the false edge of the conditional branch, remember
889 // to swap the select operands later.
891 if (BB1 != BI->getSuccessor(0)) {
892 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
899 // br i1 %t1, label %BB1, label %BB2
908 // %t3 = select i1 %t1, %t2, %t3
909 switch (HInst->getOpcode()) {
910 default: return false; // Not safe / profitable to hoist.
911 case Instruction::Add:
912 case Instruction::Sub:
913 // Not worth doing for vector ops.
914 if (HInst->getType()->isVectorTy())
917 case Instruction::And:
918 case Instruction::Or:
919 case Instruction::Xor:
920 case Instruction::Shl:
921 case Instruction::LShr:
922 case Instruction::AShr:
923 // Don't mess with vector operations.
924 if (HInst->getType()->isVectorTy())
926 break; // These are all cheap and non-trapping instructions.
929 // If the instruction is obviously dead, don't try to predicate it.
930 if (HInst->use_empty()) {
931 HInst->eraseFromParent();
935 // Can we speculatively execute the instruction? And what is the value
936 // if the condition is false? Consider the phi uses, if the incoming value
937 // from the "if" block are all the same V, then V is the value of the
938 // select if the condition is false.
939 BasicBlock *BIParent = BI->getParent();
940 SmallVector<PHINode*, 4> PHIUses;
941 Value *FalseV = NULL;
943 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
944 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
946 // Ignore any user that is not a PHI node in BB2. These can only occur in
947 // unreachable blocks, because they would not be dominated by the instr.
948 PHINode *PN = dyn_cast<PHINode>(*UI);
949 if (!PN || PN->getParent() != BB2)
951 PHIUses.push_back(PN);
953 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
956 else if (FalseV != PHIV)
957 return false; // Inconsistent value when condition is false.
960 assert(FalseV && "Must have at least one user, and it must be a PHI");
962 // Do not hoist the instruction if any of its operands are defined but not
963 // used in this BB. The transformation will prevent the operand from
964 // being sunk into the use block.
965 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
967 Instruction *OpI = dyn_cast<Instruction>(*i);
968 if (OpI && OpI->getParent() == BIParent &&
969 !OpI->isUsedInBasicBlock(BIParent))
973 // If we get here, we can hoist the instruction. Try to place it
974 // before the icmp instruction preceding the conditional branch.
975 BasicBlock::iterator InsertPos = BI;
976 if (InsertPos != BIParent->begin())
978 // Skip debug info between condition and branch.
979 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
981 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
982 SmallPtrSet<Instruction *, 4> BB1Insns;
983 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
984 BB1I != BB1E; ++BB1I)
985 BB1Insns.insert(BB1I);
986 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
988 Instruction *Use = cast<Instruction>(*UI);
989 if (!BB1Insns.count(Use)) continue;
991 // If BrCond uses the instruction that place it just before
992 // branch instruction.
998 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
1000 // Create a select whose true value is the speculatively executed value and
1001 // false value is the previously determined FalseV.
1004 SI = SelectInst::Create(BrCond, FalseV, HInst,
1005 FalseV->getName() + "." + HInst->getName(), BI);
1007 SI = SelectInst::Create(BrCond, HInst, FalseV,
1008 HInst->getName() + "." + FalseV->getName(), BI);
1010 // Make the PHI node use the select for all incoming values for "then" and
1012 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1013 PHINode *PN = PHIUses[i];
1014 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1015 if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent)
1016 PN->setIncomingValue(j, SI);
1023 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1024 /// across this block.
1025 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1026 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1029 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1030 if (isa<DbgInfoIntrinsic>(BBI))
1032 if (Size > 10) return false; // Don't clone large BB's.
1035 // We can only support instructions that do not define values that are
1036 // live outside of the current basic block.
1037 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1039 Instruction *U = cast<Instruction>(*UI);
1040 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1043 // Looks ok, continue checking.
1049 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1050 /// that is defined in the same block as the branch and if any PHI entries are
1051 /// constants, thread edges corresponding to that entry to be branches to their
1052 /// ultimate destination.
1053 static bool FoldCondBranchOnPHI(BranchInst *BI) {
1054 BasicBlock *BB = BI->getParent();
1055 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1056 // NOTE: we currently cannot transform this case if the PHI node is used
1057 // outside of the block.
1058 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1061 // Degenerate case of a single entry PHI.
1062 if (PN->getNumIncomingValues() == 1) {
1063 FoldSingleEntryPHINodes(PN->getParent());
1067 // Now we know that this block has multiple preds and two succs.
1068 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1070 // Okay, this is a simple enough basic block. See if any phi values are
1072 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1073 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1074 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1076 // Okay, we now know that all edges from PredBB should be revectored to
1077 // branch to RealDest.
1078 BasicBlock *PredBB = PN->getIncomingBlock(i);
1079 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1081 if (RealDest == BB) continue; // Skip self loops.
1083 // The dest block might have PHI nodes, other predecessors and other
1084 // difficult cases. Instead of being smart about this, just insert a new
1085 // block that jumps to the destination block, effectively splitting
1086 // the edge we are about to create.
1087 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1088 RealDest->getName()+".critedge",
1089 RealDest->getParent(), RealDest);
1090 BranchInst::Create(RealDest, EdgeBB);
1092 for (BasicBlock::iterator BBI = RealDest->begin();
1093 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1094 Value *V = PN->getIncomingValueForBlock(BB);
1095 PN->addIncoming(V, EdgeBB);
1098 // BB may have instructions that are being threaded over. Clone these
1099 // instructions into EdgeBB. We know that there will be no uses of the
1100 // cloned instructions outside of EdgeBB.
1101 BasicBlock::iterator InsertPt = EdgeBB->begin();
1102 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1103 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1104 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1105 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1108 // Clone the instruction.
1109 Instruction *N = BBI->clone();
1110 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1112 // Update operands due to translation.
1113 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1115 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1116 if (PI != TranslateMap.end())
1120 // Check for trivial simplification.
1121 if (Constant *C = ConstantFoldInstruction(N)) {
1122 TranslateMap[BBI] = C;
1123 delete N; // Constant folded away, don't need actual inst
1125 // Insert the new instruction into its new home.
1126 EdgeBB->getInstList().insert(InsertPt, N);
1127 if (!BBI->use_empty())
1128 TranslateMap[BBI] = N;
1132 // Loop over all of the edges from PredBB to BB, changing them to branch
1133 // to EdgeBB instead.
1134 TerminatorInst *PredBBTI = PredBB->getTerminator();
1135 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1136 if (PredBBTI->getSuccessor(i) == BB) {
1137 BB->removePredecessor(PredBB);
1138 PredBBTI->setSuccessor(i, EdgeBB);
1141 // Recurse, simplifying any other constants.
1142 return FoldCondBranchOnPHI(BI) | true;
1148 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1149 /// PHI node, see if we can eliminate it.
1150 static bool FoldTwoEntryPHINode(PHINode *PN) {
1151 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1152 // statement", which has a very simple dominance structure. Basically, we
1153 // are trying to find the condition that is being branched on, which
1154 // subsequently causes this merge to happen. We really want control
1155 // dependence information for this check, but simplifycfg can't keep it up
1156 // to date, and this catches most of the cases we care about anyway.
1158 BasicBlock *BB = PN->getParent();
1159 BasicBlock *IfTrue, *IfFalse;
1160 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1161 if (!IfCond) return false;
1163 // Okay, we found that we can merge this two-entry phi node into a select.
1164 // Doing so would require us to fold *all* two entry phi nodes in this block.
1165 // At some point this becomes non-profitable (particularly if the target
1166 // doesn't support cmov's). Only do this transformation if there are two or
1167 // fewer PHI nodes in this block.
1168 unsigned NumPhis = 0;
1169 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1173 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1174 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1176 // Loop over the PHI's seeing if we can promote them all to select
1177 // instructions. While we are at it, keep track of the instructions
1178 // that need to be moved to the dominating block.
1179 std::set<Instruction*> AggressiveInsts;
1181 BasicBlock::iterator AfterPHIIt = BB->begin();
1182 while (isa<PHINode>(AfterPHIIt)) {
1183 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1184 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1185 if (PN->getIncomingValue(0) != PN)
1186 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1188 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1189 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1190 &AggressiveInsts) ||
1191 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1192 &AggressiveInsts)) {
1197 // If we all PHI nodes are promotable, check to make sure that all
1198 // instructions in the predecessor blocks can be promoted as well. If
1199 // not, we won't be able to get rid of the control flow, so it's not
1200 // worth promoting to select instructions.
1201 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1202 PN = cast<PHINode>(BB->begin());
1203 BasicBlock *Pred = PN->getIncomingBlock(0);
1204 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1206 DomBlock = *pred_begin(Pred);
1207 for (BasicBlock::iterator I = Pred->begin();
1208 !isa<TerminatorInst>(I); ++I)
1209 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1210 // This is not an aggressive instruction that we can promote.
1211 // Because of this, we won't be able to get rid of the control
1212 // flow, so the xform is not worth it.
1217 Pred = PN->getIncomingBlock(1);
1218 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1220 DomBlock = *pred_begin(Pred);
1221 for (BasicBlock::iterator I = Pred->begin();
1222 !isa<TerminatorInst>(I); ++I)
1223 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1224 // This is not an aggressive instruction that we can promote.
1225 // Because of this, we won't be able to get rid of the control
1226 // flow, so the xform is not worth it.
1231 // If we can still promote the PHI nodes after this gauntlet of tests,
1232 // do all of the PHI's now.
1234 // Move all 'aggressive' instructions, which are defined in the
1235 // conditional parts of the if's up to the dominating block.
1237 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1238 IfBlock1->getInstList(), IfBlock1->begin(),
1239 IfBlock1->getTerminator());
1241 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1242 IfBlock2->getInstList(), IfBlock2->begin(),
1243 IfBlock2->getTerminator());
1245 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1246 // Change the PHI node into a select instruction.
1247 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1248 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1250 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1251 PN->replaceAllUsesWith(NV);
1254 BB->getInstList().erase(PN);
1259 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1260 /// to two returning blocks, try to merge them together into one return,
1261 /// introducing a select if the return values disagree.
1262 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1263 assert(BI->isConditional() && "Must be a conditional branch");
1264 BasicBlock *TrueSucc = BI->getSuccessor(0);
1265 BasicBlock *FalseSucc = BI->getSuccessor(1);
1266 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1267 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1269 // Check to ensure both blocks are empty (just a return) or optionally empty
1270 // with PHI nodes. If there are other instructions, merging would cause extra
1271 // computation on one path or the other.
1272 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1274 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1277 // Okay, we found a branch that is going to two return nodes. If
1278 // there is no return value for this function, just change the
1279 // branch into a return.
1280 if (FalseRet->getNumOperands() == 0) {
1281 TrueSucc->removePredecessor(BI->getParent());
1282 FalseSucc->removePredecessor(BI->getParent());
1283 ReturnInst::Create(BI->getContext(), 0, BI);
1284 EraseTerminatorInstAndDCECond(BI);
1288 // Otherwise, figure out what the true and false return values are
1289 // so we can insert a new select instruction.
1290 Value *TrueValue = TrueRet->getReturnValue();
1291 Value *FalseValue = FalseRet->getReturnValue();
1293 // Unwrap any PHI nodes in the return blocks.
1294 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1295 if (TVPN->getParent() == TrueSucc)
1296 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1297 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1298 if (FVPN->getParent() == FalseSucc)
1299 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1301 // In order for this transformation to be safe, we must be able to
1302 // unconditionally execute both operands to the return. This is
1303 // normally the case, but we could have a potentially-trapping
1304 // constant expression that prevents this transformation from being
1306 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1309 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1313 // Okay, we collected all the mapped values and checked them for sanity, and
1314 // defined to really do this transformation. First, update the CFG.
1315 TrueSucc->removePredecessor(BI->getParent());
1316 FalseSucc->removePredecessor(BI->getParent());
1318 // Insert select instructions where needed.
1319 Value *BrCond = BI->getCondition();
1321 // Insert a select if the results differ.
1322 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1323 } else if (isa<UndefValue>(TrueValue)) {
1324 TrueValue = FalseValue;
1326 TrueValue = SelectInst::Create(BrCond, TrueValue,
1327 FalseValue, "retval", BI);
1331 Value *RI = !TrueValue ?
1332 ReturnInst::Create(BI->getContext(), BI) :
1333 ReturnInst::Create(BI->getContext(), TrueValue, BI);
1336 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1337 << "\n " << *BI << "NewRet = " << *RI
1338 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1340 EraseTerminatorInstAndDCECond(BI);
1345 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1346 /// and if a predecessor branches to us and one of our successors, fold the
1347 /// setcc into the predecessor and use logical operations to pick the right
1349 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1350 BasicBlock *BB = BI->getParent();
1351 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1352 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1353 Cond->getParent() != BB || !Cond->hasOneUse())
1356 // Only allow this if the condition is a simple instruction that can be
1357 // executed unconditionally. It must be in the same block as the branch, and
1358 // must be at the front of the block.
1359 BasicBlock::iterator FrontIt = BB->front();
1360 // Ignore dbg intrinsics.
1361 while (isa<DbgInfoIntrinsic>(FrontIt))
1364 // Allow a single instruction to be hoisted in addition to the compare
1365 // that feeds the branch. We later ensure that any values that _it_ uses
1366 // were also live in the predecessor, so that we don't unnecessarily create
1367 // register pressure or inhibit out-of-order execution.
1368 Instruction *BonusInst = 0;
1369 if (&*FrontIt != Cond &&
1370 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1371 FrontIt->isSafeToSpeculativelyExecute()) {
1372 BonusInst = &*FrontIt;
1376 // Only a single bonus inst is allowed.
1377 if (&*FrontIt != Cond)
1380 // Make sure the instruction after the condition is the cond branch.
1381 BasicBlock::iterator CondIt = Cond; ++CondIt;
1382 // Ingore dbg intrinsics.
1383 while(isa<DbgInfoIntrinsic>(CondIt))
1385 if (&*CondIt != BI) {
1386 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!");
1390 // Cond is known to be a compare or binary operator. Check to make sure that
1391 // neither operand is a potentially-trapping constant expression.
1392 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1395 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1400 // Finally, don't infinitely unroll conditional loops.
1401 BasicBlock *TrueDest = BI->getSuccessor(0);
1402 BasicBlock *FalseDest = BI->getSuccessor(1);
1403 if (TrueDest == BB || FalseDest == BB)
1406 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1407 BasicBlock *PredBlock = *PI;
1408 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1410 // Check that we have two conditional branches. If there is a PHI node in
1411 // the common successor, verify that the same value flows in from both
1413 if (PBI == 0 || PBI->isUnconditional() ||
1414 !SafeToMergeTerminators(BI, PBI))
1417 // Ensure that any values used in the bonus instruction are also used
1418 // by the terminator of the predecessor. This means that those values
1419 // must already have been resolved, so we won't be inhibiting the
1420 // out-of-order core by speculating them earlier.
1422 // Collect the values used by the bonus inst
1423 SmallPtrSet<Value*, 4> UsedValues;
1424 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1425 OE = BonusInst->op_end(); OI != OE; ++OI) {
1427 if (!isa<Constant>(V))
1428 UsedValues.insert(V);
1431 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1432 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1434 // Walk up to four levels back up the use-def chain of the predecessor's
1435 // terminator to see if all those values were used. The choice of four
1436 // levels is arbitrary, to provide a compile-time-cost bound.
1437 while (!Worklist.empty()) {
1438 std::pair<Value*, unsigned> Pair = Worklist.back();
1439 Worklist.pop_back();
1441 if (Pair.second >= 4) continue;
1442 UsedValues.erase(Pair.first);
1443 if (UsedValues.empty()) break;
1445 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
1446 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1448 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1452 if (!UsedValues.empty()) return false;
1455 Instruction::BinaryOps Opc;
1456 bool InvertPredCond = false;
1458 if (PBI->getSuccessor(0) == TrueDest)
1459 Opc = Instruction::Or;
1460 else if (PBI->getSuccessor(1) == FalseDest)
1461 Opc = Instruction::And;
1462 else if (PBI->getSuccessor(0) == FalseDest)
1463 Opc = Instruction::And, InvertPredCond = true;
1464 else if (PBI->getSuccessor(1) == TrueDest)
1465 Opc = Instruction::Or, InvertPredCond = true;
1469 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1471 // If we need to invert the condition in the pred block to match, do so now.
1472 if (InvertPredCond) {
1473 Value *NewCond = PBI->getCondition();
1475 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
1476 CmpInst *CI = cast<CmpInst>(NewCond);
1477 CI->setPredicate(CI->getInversePredicate());
1479 NewCond = BinaryOperator::CreateNot(NewCond,
1480 PBI->getCondition()->getName()+".not", PBI);
1483 PBI->setCondition(NewCond);
1484 BasicBlock *OldTrue = PBI->getSuccessor(0);
1485 BasicBlock *OldFalse = PBI->getSuccessor(1);
1486 PBI->setSuccessor(0, OldFalse);
1487 PBI->setSuccessor(1, OldTrue);
1490 // If we have a bonus inst, clone it into the predecessor block.
1491 Instruction *NewBonus = 0;
1493 NewBonus = BonusInst->clone();
1494 PredBlock->getInstList().insert(PBI, NewBonus);
1495 NewBonus->takeName(BonusInst);
1496 BonusInst->setName(BonusInst->getName()+".old");
1499 // Clone Cond into the predecessor basic block, and or/and the
1500 // two conditions together.
1501 Instruction *New = Cond->clone();
1502 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1503 PredBlock->getInstList().insert(PBI, New);
1504 New->takeName(Cond);
1505 Cond->setName(New->getName()+".old");
1507 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1508 New, "or.cond", PBI);
1509 PBI->setCondition(NewCond);
1510 if (PBI->getSuccessor(0) == BB) {
1511 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1512 PBI->setSuccessor(0, TrueDest);
1514 if (PBI->getSuccessor(1) == BB) {
1515 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1516 PBI->setSuccessor(1, FalseDest);
1518 return SimplifyCFG(PBI->getParent()) | true;
1523 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1524 /// predecessor of another block, this function tries to simplify it. We know
1525 /// that PBI and BI are both conditional branches, and BI is in one of the
1526 /// successor blocks of PBI - PBI branches to BI.
1527 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1528 assert(PBI->isConditional() && BI->isConditional());
1529 BasicBlock *BB = BI->getParent();
1531 // If this block ends with a branch instruction, and if there is a
1532 // predecessor that ends on a branch of the same condition, make
1533 // this conditional branch redundant.
1534 if (PBI->getCondition() == BI->getCondition() &&
1535 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1536 // Okay, the outcome of this conditional branch is statically
1537 // knowable. If this block had a single pred, handle specially.
1538 if (BB->getSinglePredecessor()) {
1539 // Turn this into a branch on constant.
1540 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1541 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1543 return true; // Nuke the branch on constant.
1546 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1547 // in the constant and simplify the block result. Subsequent passes of
1548 // simplifycfg will thread the block.
1549 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1550 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1551 BI->getCondition()->getName() + ".pr",
1553 // Okay, we're going to insert the PHI node. Since PBI is not the only
1554 // predecessor, compute the PHI'd conditional value for all of the preds.
1555 // Any predecessor where the condition is not computable we keep symbolic.
1556 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1557 BasicBlock *P = *PI;
1558 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
1559 PBI != BI && PBI->isConditional() &&
1560 PBI->getCondition() == BI->getCondition() &&
1561 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1562 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1563 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1566 NewPN->addIncoming(BI->getCondition(), P);
1570 BI->setCondition(NewPN);
1575 // If this is a conditional branch in an empty block, and if any
1576 // predecessors is a conditional branch to one of our destinations,
1577 // fold the conditions into logical ops and one cond br.
1578 BasicBlock::iterator BBI = BB->begin();
1579 // Ignore dbg intrinsics.
1580 while (isa<DbgInfoIntrinsic>(BBI))
1586 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1591 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1593 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1594 PBIOp = 0, BIOp = 1;
1595 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1596 PBIOp = 1, BIOp = 0;
1597 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1602 // Check to make sure that the other destination of this branch
1603 // isn't BB itself. If so, this is an infinite loop that will
1604 // keep getting unwound.
1605 if (PBI->getSuccessor(PBIOp) == BB)
1608 // Do not perform this transformation if it would require
1609 // insertion of a large number of select instructions. For targets
1610 // without predication/cmovs, this is a big pessimization.
1611 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1613 unsigned NumPhis = 0;
1614 for (BasicBlock::iterator II = CommonDest->begin();
1615 isa<PHINode>(II); ++II, ++NumPhis)
1616 if (NumPhis > 2) // Disable this xform.
1619 // Finally, if everything is ok, fold the branches to logical ops.
1620 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1622 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
1623 << "AND: " << *BI->getParent());
1626 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1627 // branch in it, where one edge (OtherDest) goes back to itself but the other
1628 // exits. We don't *know* that the program avoids the infinite loop
1629 // (even though that seems likely). If we do this xform naively, we'll end up
1630 // recursively unpeeling the loop. Since we know that (after the xform is
1631 // done) that the block *is* infinite if reached, we just make it an obviously
1632 // infinite loop with no cond branch.
1633 if (OtherDest == BB) {
1634 // Insert it at the end of the function, because it's either code,
1635 // or it won't matter if it's hot. :)
1636 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1637 "infloop", BB->getParent());
1638 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1639 OtherDest = InfLoopBlock;
1642 DEBUG(dbgs() << *PBI->getParent()->getParent());
1644 // BI may have other predecessors. Because of this, we leave
1645 // it alone, but modify PBI.
1647 // Make sure we get to CommonDest on True&True directions.
1648 Value *PBICond = PBI->getCondition();
1650 PBICond = BinaryOperator::CreateNot(PBICond,
1651 PBICond->getName()+".not",
1653 Value *BICond = BI->getCondition();
1655 BICond = BinaryOperator::CreateNot(BICond,
1656 BICond->getName()+".not",
1658 // Merge the conditions.
1659 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1661 // Modify PBI to branch on the new condition to the new dests.
1662 PBI->setCondition(Cond);
1663 PBI->setSuccessor(0, CommonDest);
1664 PBI->setSuccessor(1, OtherDest);
1666 // OtherDest may have phi nodes. If so, add an entry from PBI's
1667 // block that are identical to the entries for BI's block.
1669 for (BasicBlock::iterator II = OtherDest->begin();
1670 (PN = dyn_cast<PHINode>(II)); ++II) {
1671 Value *V = PN->getIncomingValueForBlock(BB);
1672 PN->addIncoming(V, PBI->getParent());
1675 // We know that the CommonDest already had an edge from PBI to
1676 // it. If it has PHIs though, the PHIs may have different
1677 // entries for BB and PBI's BB. If so, insert a select to make
1679 for (BasicBlock::iterator II = CommonDest->begin();
1680 (PN = dyn_cast<PHINode>(II)); ++II) {
1681 Value *BIV = PN->getIncomingValueForBlock(BB);
1682 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1683 Value *PBIV = PN->getIncomingValue(PBBIdx);
1685 // Insert a select in PBI to pick the right value.
1686 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1687 PBIV->getName()+".mux", PBI);
1688 PN->setIncomingValue(PBBIdx, NV);
1692 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1693 DEBUG(dbgs() << *PBI->getParent()->getParent());
1695 // This basic block is probably dead. We know it has at least
1696 // one fewer predecessor.
1700 // SimplifyIndirectBrOnSelect - Replaces
1701 // (indirectbr (select cond, blockaddress(@fn, BlockA),
1702 // blockaddress(@fn, BlockB)))
1704 // (br cond, BlockA, BlockB).
1705 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
1706 // Check that both operands of the select are block addresses.
1707 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
1708 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
1712 // Extract the actual blocks.
1713 BasicBlock *TrueBB = TBA->getBasicBlock();
1714 BasicBlock *FalseBB = FBA->getBasicBlock();
1716 // Remove any superfluous successor edges from the CFG.
1717 // First, figure out which successors to preserve.
1718 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
1720 BasicBlock *KeepEdge1 = TrueBB;
1721 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
1723 // Then remove the rest.
1724 for (unsigned I = 0, E = IBI->getNumSuccessors(); I != E; ++I) {
1725 BasicBlock *Succ = IBI->getSuccessor(I);
1726 // Make sure only to keep exactly one copy of each edge.
1727 if (Succ == KeepEdge1)
1729 else if (Succ == KeepEdge2)
1732 Succ->removePredecessor(IBI->getParent());
1735 // Insert an appropriate new terminator.
1736 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
1737 if (TrueBB == FalseBB)
1738 // We were only looking for one successor, and it was present.
1739 // Create an unconditional branch to it.
1740 BranchInst::Create(TrueBB, IBI);
1742 // We found both of the successors we were looking for.
1743 // Create a conditional branch sharing the condition of the select.
1744 BranchInst::Create(TrueBB, FalseBB, SI->getCondition(), IBI);
1745 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
1746 // Neither of the selected blocks were successors, so this
1747 // indirectbr must be unreachable.
1748 new UnreachableInst(IBI->getContext(), IBI);
1750 // One of the selected values was a successor, but the other wasn't.
1751 // Insert an unconditional branch to the one that was found;
1752 // the edge to the one that wasn't must be unreachable.
1754 // Only TrueBB was found.
1755 BranchInst::Create(TrueBB, IBI);
1757 // Only FalseBB was found.
1758 BranchInst::Create(FalseBB, IBI);
1761 EraseTerminatorInstAndDCECond(IBI);
1765 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
1766 /// instruction (a seteq/setne with a constant) as the only instruction in a
1767 /// block that ends with an uncond branch. We are looking for a very specific
1768 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
1769 /// this case, we merge the first two "or's of icmp" into a switch, but then the
1770 /// default value goes to an uncond block with a seteq in it, we get something
1773 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
1775 /// %tmp = icmp eq i8 %A, 92
1778 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
1780 /// We prefer to split the edge to 'end' so that there is a true/false entry to
1781 /// the PHI, merging the third icmp into the switch.
1782 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI) {
1783 BasicBlock *BB = ICI->getParent();
1784 // If the block has any PHIs in it or the icmp has multiple uses, it is too
1786 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
1788 Value *V = ICI->getOperand(0);
1789 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
1791 // The pattern we're looking for is where our only predecessor is a switch on
1792 // 'V' and this block is the default case for the switch. In this case we can
1793 // fold the compared value into the switch to simplify things.
1794 BasicBlock *Pred = BB->getSinglePredecessor();
1795 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
1797 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
1798 if (SI->getCondition() != V)
1801 // If BB is reachable on a non-default case, then we simply know the value of
1802 // V in this block. Substitute it and constant fold the icmp instruction
1804 if (SI->getDefaultDest() != BB) {
1805 ConstantInt *VVal = SI->findCaseDest(BB);
1806 assert(VVal && "Should have a unique destination value");
1807 ICI->setOperand(0, VVal);
1809 if (Constant *C = ConstantFoldInstruction(ICI)) {
1810 ICI->replaceAllUsesWith(C);
1811 ICI->eraseFromParent();
1813 // BB is now empty, so it is likely to simplify away.
1814 return SimplifyCFG(BB) | true;
1817 // Ok, the block is reachable from the default dest. If the constant we're
1818 // comparing exists in one of the other edges, then we can constant fold ICI
1820 if (SI->findCaseValue(Cst) != 0) {
1822 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1823 V = ConstantInt::getFalse(BB->getContext());
1825 V = ConstantInt::getTrue(BB->getContext());
1827 ICI->replaceAllUsesWith(V);
1828 ICI->eraseFromParent();
1829 // BB is now empty, so it is likely to simplify away.
1830 return SimplifyCFG(BB) | true;
1833 // The use of the icmp has to be in the 'end' block, by the only PHI node in
1835 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
1836 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
1837 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
1838 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
1841 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
1843 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
1844 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
1846 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1847 std::swap(DefaultCst, NewCst);
1849 // Replace ICI (which is used by the PHI for the default value) with true or
1850 // false depending on if it is EQ or NE.
1851 ICI->replaceAllUsesWith(DefaultCst);
1852 ICI->eraseFromParent();
1854 // Okay, the switch goes to this block on a default value. Add an edge from
1855 // the switch to the merge point on the compared value.
1856 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
1857 BB->getParent(), BB);
1858 SI->addCase(Cst, NewBB);
1860 // NewBB branches to the phi block, add the uncond branch and the phi entry.
1861 BranchInst::Create(SuccBlock, NewBB);
1862 PHIUse->addIncoming(NewCst, NewBB);
1866 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
1867 /// Check to see if it is branching on an or/and chain of icmp instructions, and
1868 /// fold it into a switch instruction if so.
1869 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD) {
1870 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1871 if (Cond == 0) return false;
1874 // Change br (X == 0 | X == 1), T, F into a switch instruction.
1875 // If this is a bunch of seteq's or'd together, or if it's a bunch of
1876 // 'setne's and'ed together, collect them.
1878 std::vector<ConstantInt*> Values;
1879 bool TrueWhenEqual = true;
1880 Value *ExtraCase = 0;
1882 if (Cond->getOpcode() == Instruction::Or) {
1883 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true);
1884 } else if (Cond->getOpcode() == Instruction::And) {
1885 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false);
1886 TrueWhenEqual = false;
1889 // If we didn't have a multiply compared value, fail.
1890 if (CompVal == 0) return false;
1892 // There might be duplicate constants in the list, which the switch
1893 // instruction can't handle, remove them now.
1894 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
1895 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
1897 // If Extra was used, we require at least two switch values to do the
1898 // transformation. A switch with one value is just an cond branch.
1899 if (ExtraCase && Values.size() < 2) return false;
1901 // Figure out which block is which destination.
1902 BasicBlock *DefaultBB = BI->getSuccessor(1);
1903 BasicBlock *EdgeBB = BI->getSuccessor(0);
1904 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
1906 BasicBlock *BB = BI->getParent();
1908 // If there are any extra values that couldn't be folded into the switch
1909 // then we evaluate them with an explicit branch first. Split the block
1910 // right before the condbr to handle it.
1914 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
1915 // Remove the uncond branch added to the old block.
1916 TerminatorInst *OldTI = BB->getTerminator();
1918 BranchInst::Create(EdgeBB, NewBB, ExtraCase, OldTI);
1919 OldTI->eraseFromParent();
1921 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
1922 // for the edge we just added.
1923 for (BasicBlock::iterator I = EdgeBB->begin(); isa<PHINode>(I); ++I) {
1924 PHINode *PN = cast<PHINode>(I);
1925 PN->addIncoming(PN->getIncomingValueForBlock(NewBB), BB);
1930 // Convert pointer to int before we switch.
1931 if (CompVal->getType()->isPointerTy()) {
1932 assert(TD && "Cannot switch on pointer without TargetData");
1933 CompVal = new PtrToIntInst(CompVal,
1934 TD->getIntPtrType(CompVal->getContext()),
1938 // Create the new switch instruction now.
1939 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB, Values.size(), BI);
1941 // Add all of the 'cases' to the switch instruction.
1942 for (unsigned i = 0, e = Values.size(); i != e; ++i)
1943 New->addCase(Values[i], EdgeBB);
1945 // We added edges from PI to the EdgeBB. As such, if there were any
1946 // PHI nodes in EdgeBB, they need entries to be added corresponding to
1947 // the number of edges added.
1948 for (BasicBlock::iterator BBI = EdgeBB->begin();
1949 isa<PHINode>(BBI); ++BBI) {
1950 PHINode *PN = cast<PHINode>(BBI);
1951 Value *InVal = PN->getIncomingValueForBlock(BB);
1952 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
1953 PN->addIncoming(InVal, BB);
1956 // Erase the old branch instruction.
1957 EraseTerminatorInstAndDCECond(BI);
1961 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI) {
1962 BasicBlock *BB = RI->getParent();
1963 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
1965 // Find predecessors that end with branches.
1966 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1967 SmallVector<BranchInst*, 8> CondBranchPreds;
1968 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1969 BasicBlock *P = *PI;
1970 TerminatorInst *PTI = P->getTerminator();
1971 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1972 if (BI->isUnconditional())
1973 UncondBranchPreds.push_back(P);
1975 CondBranchPreds.push_back(BI);
1979 // If we found some, do the transformation!
1980 if (!UncondBranchPreds.empty()) {
1981 while (!UncondBranchPreds.empty()) {
1982 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
1983 DEBUG(dbgs() << "FOLDING: " << *BB
1984 << "INTO UNCOND BRANCH PRED: " << *Pred);
1985 Instruction *UncondBranch = Pred->getTerminator();
1986 // Clone the return and add it to the end of the predecessor.
1987 Instruction *NewRet = RI->clone();
1988 Pred->getInstList().push_back(NewRet);
1990 // If the return instruction returns a value, and if the value was a
1991 // PHI node in "BB", propagate the right value into the return.
1992 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
1994 if (PHINode *PN = dyn_cast<PHINode>(*i))
1995 if (PN->getParent() == BB)
1996 *i = PN->getIncomingValueForBlock(Pred);
1998 // Update any PHI nodes in the returning block to realize that we no
1999 // longer branch to them.
2000 BB->removePredecessor(Pred);
2001 Pred->getInstList().erase(UncondBranch);
2004 // If we eliminated all predecessors of the block, delete the block now.
2005 if (pred_begin(BB) == pred_end(BB))
2006 // We know there are no successors, so just nuke the block.
2007 BB->eraseFromParent();
2012 // Check out all of the conditional branches going to this return
2013 // instruction. If any of them just select between returns, change the
2014 // branch itself into a select/return pair.
2015 while (!CondBranchPreds.empty()) {
2016 BranchInst *BI = CondBranchPreds.pop_back_val();
2018 // Check to see if the non-BB successor is also a return block.
2019 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2020 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2021 SimplifyCondBranchToTwoReturns(BI))
2027 bool SimplifyCFGOpt::SimplifyUnwind(UnwindInst *UI) {
2028 // Check to see if the first instruction in this block is just an unwind.
2029 // If so, replace any invoke instructions which use this as an exception
2030 // destination with call instructions.
2031 BasicBlock *BB = UI->getParent();
2032 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2034 bool Changed = false;
2035 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2036 while (!Preds.empty()) {
2037 BasicBlock *Pred = Preds.back();
2038 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
2039 if (II && II->getUnwindDest() == BB) {
2040 // Insert a new branch instruction before the invoke, because this
2041 // is now a fall through.
2042 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2043 Pred->getInstList().remove(II); // Take out of symbol table
2045 // Insert the call now.
2046 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
2047 CallInst *CI = CallInst::Create(II->getCalledValue(),
2048 Args.begin(), Args.end(),
2050 CI->setCallingConv(II->getCallingConv());
2051 CI->setAttributes(II->getAttributes());
2052 // If the invoke produced a value, the Call now does instead.
2053 II->replaceAllUsesWith(CI);
2061 // If this block is now dead (and isn't the entry block), remove it.
2062 if (pred_begin(BB) == pred_end(BB) &&
2063 BB != &BB->getParent()->getEntryBlock()) {
2064 // We know there are no successors, so just nuke the block.
2065 BB->eraseFromParent();
2072 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2073 BasicBlock *BB = UI->getParent();
2075 bool Changed = false;
2077 // If there are any instructions immediately before the unreachable that can
2078 // be removed, do so.
2079 while (UI != BB->begin()) {
2080 BasicBlock::iterator BBI = UI;
2082 // Do not delete instructions that can have side effects, like calls
2083 // (which may never return) and volatile loads and stores.
2084 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2086 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
2087 if (SI->isVolatile())
2090 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
2091 if (LI->isVolatile())
2094 // Delete this instruction
2095 BB->getInstList().erase(BBI);
2099 // If the unreachable instruction is the first in the block, take a gander
2100 // at all of the predecessors of this instruction, and simplify them.
2101 if (&BB->front() != UI) return Changed;
2103 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2104 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2105 TerminatorInst *TI = Preds[i]->getTerminator();
2107 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2108 if (BI->isUnconditional()) {
2109 if (BI->getSuccessor(0) == BB) {
2110 new UnreachableInst(TI->getContext(), TI);
2111 TI->eraseFromParent();
2115 if (BI->getSuccessor(0) == BB) {
2116 BranchInst::Create(BI->getSuccessor(1), BI);
2117 EraseTerminatorInstAndDCECond(BI);
2118 } else if (BI->getSuccessor(1) == BB) {
2119 BranchInst::Create(BI->getSuccessor(0), BI);
2120 EraseTerminatorInstAndDCECond(BI);
2124 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2125 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2126 if (SI->getSuccessor(i) == BB) {
2127 BB->removePredecessor(SI->getParent());
2132 // If the default value is unreachable, figure out the most popular
2133 // destination and make it the default.
2134 if (SI->getSuccessor(0) == BB) {
2135 std::map<BasicBlock*, unsigned> Popularity;
2136 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2137 Popularity[SI->getSuccessor(i)]++;
2139 // Find the most popular block.
2140 unsigned MaxPop = 0;
2141 BasicBlock *MaxBlock = 0;
2142 for (std::map<BasicBlock*, unsigned>::iterator
2143 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2144 if (I->second > MaxPop) {
2146 MaxBlock = I->first;
2150 // Make this the new default, allowing us to delete any explicit
2152 SI->setSuccessor(0, MaxBlock);
2155 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2157 if (isa<PHINode>(MaxBlock->begin()))
2158 for (unsigned i = 0; i != MaxPop-1; ++i)
2159 MaxBlock->removePredecessor(SI->getParent());
2161 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2162 if (SI->getSuccessor(i) == MaxBlock) {
2168 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2169 if (II->getUnwindDest() == BB) {
2170 // Convert the invoke to a call instruction. This would be a good
2171 // place to note that the call does not throw though.
2172 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2173 II->removeFromParent(); // Take out of symbol table
2175 // Insert the call now...
2176 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2177 CallInst *CI = CallInst::Create(II->getCalledValue(),
2178 Args.begin(), Args.end(),
2180 CI->setCallingConv(II->getCallingConv());
2181 CI->setAttributes(II->getAttributes());
2182 // If the invoke produced a value, the call does now instead.
2183 II->replaceAllUsesWith(CI);
2190 // If this block is now dead, remove it.
2191 if (pred_begin(BB) == pred_end(BB) &&
2192 BB != &BB->getParent()->getEntryBlock()) {
2193 // We know there are no successors, so just nuke the block.
2194 BB->eraseFromParent();
2202 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI) {
2203 // If this switch is too complex to want to look at, ignore it.
2204 if (!isValueEqualityComparison(SI))
2207 BasicBlock *BB = SI->getParent();
2209 // If we only have one predecessor, and if it is a branch on this value,
2210 // see if that predecessor totally determines the outcome of this switch.
2211 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2212 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
2213 return SimplifyCFG(BB) | true;
2215 // If the block only contains the switch, see if we can fold the block
2216 // away into any preds.
2217 BasicBlock::iterator BBI = BB->begin();
2218 // Ignore dbg intrinsics.
2219 while (isa<DbgInfoIntrinsic>(BBI))
2222 if (FoldValueComparisonIntoPredecessors(SI))
2223 return SimplifyCFG(BB) | true;
2228 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
2229 BasicBlock *BB = IBI->getParent();
2230 bool Changed = false;
2232 // Eliminate redundant destinations.
2233 SmallPtrSet<Value *, 8> Succs;
2234 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2235 BasicBlock *Dest = IBI->getDestination(i);
2236 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2237 Dest->removePredecessor(BB);
2238 IBI->removeDestination(i);
2244 if (IBI->getNumDestinations() == 0) {
2245 // If the indirectbr has no successors, change it to unreachable.
2246 new UnreachableInst(IBI->getContext(), IBI);
2247 EraseTerminatorInstAndDCECond(IBI);
2251 if (IBI->getNumDestinations() == 1) {
2252 // If the indirectbr has one successor, change it to a direct branch.
2253 BranchInst::Create(IBI->getDestination(0), IBI);
2254 EraseTerminatorInstAndDCECond(IBI);
2258 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2259 if (SimplifyIndirectBrOnSelect(IBI, SI))
2260 return SimplifyCFG(BB) | true;
2265 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI) {
2266 BasicBlock *BB = BI->getParent();
2268 // If the Terminator is the only non-phi instruction, simplify the block.
2269 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg();
2270 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
2271 TryToSimplifyUncondBranchFromEmptyBlock(BB))
2274 // If the only instruction in the block is a seteq/setne comparison
2275 // against a constant, try to simplify the block.
2276 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
2277 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
2278 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
2280 if (I->isTerminator() && TryToSimplifyUncondBranchWithICmpInIt(ICI))
2288 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI) {
2289 BasicBlock *BB = BI->getParent();
2291 // Conditional branch
2292 if (isValueEqualityComparison(BI)) {
2293 // If we only have one predecessor, and if it is a branch on this value,
2294 // see if that predecessor totally determines the outcome of this
2296 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2297 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
2298 return SimplifyCFG(BB) | true;
2300 // This block must be empty, except for the setcond inst, if it exists.
2301 // Ignore dbg intrinsics.
2302 BasicBlock::iterator I = BB->begin();
2303 // Ignore dbg intrinsics.
2304 while (isa<DbgInfoIntrinsic>(I))
2307 if (FoldValueComparisonIntoPredecessors(BI))
2308 return SimplifyCFG(BB) | true;
2309 } else if (&*I == cast<Instruction>(BI->getCondition())){
2311 // Ignore dbg intrinsics.
2312 while (isa<DbgInfoIntrinsic>(I))
2314 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI))
2315 return SimplifyCFG(BB) | true;
2319 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
2320 if (SimplifyBranchOnICmpChain(BI, TD))
2323 // We have a conditional branch to two blocks that are only reachable
2324 // from BI. We know that the condbr dominates the two blocks, so see if
2325 // there is any identical code in the "then" and "else" blocks. If so, we
2326 // can hoist it up to the branching block.
2327 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
2328 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2329 if (HoistThenElseCodeToIf(BI))
2330 return SimplifyCFG(BB) | true;
2332 // If Successor #1 has multiple preds, we may be able to conditionally
2333 // execute Successor #0 if it branches to successor #1.
2334 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
2335 if (Succ0TI->getNumSuccessors() == 1 &&
2336 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
2337 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
2338 return SimplifyCFG(BB) | true;
2340 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2341 // If Successor #0 has multiple preds, we may be able to conditionally
2342 // execute Successor #1 if it branches to successor #0.
2343 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
2344 if (Succ1TI->getNumSuccessors() == 1 &&
2345 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
2346 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
2347 return SimplifyCFG(BB) | true;
2350 // If this is a branch on a phi node in the current block, thread control
2351 // through this block if any PHI node entries are constants.
2352 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
2353 if (PN->getParent() == BI->getParent())
2354 if (FoldCondBranchOnPHI(BI))
2355 return SimplifyCFG(BB) | true;
2357 // If this basic block is ONLY a setcc and a branch, and if a predecessor
2358 // branches to us and one of our successors, fold the setcc into the
2359 // predecessor and use logical operations to pick the right destination.
2360 if (FoldBranchToCommonDest(BI))
2361 return SimplifyCFG(BB) | true;
2363 // Scan predecessor blocks for conditional branches.
2364 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2365 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2366 if (PBI != BI && PBI->isConditional())
2367 if (SimplifyCondBranchToCondBranch(PBI, BI))
2368 return SimplifyCFG(BB) | true;
2373 bool SimplifyCFGOpt::run(BasicBlock *BB) {
2374 bool Changed = false;
2375 Function *Fn = BB->getParent();
2377 assert(BB && Fn && "Block not embedded in function!");
2378 assert(BB->getTerminator() && "Degenerate basic block encountered!");
2380 // Remove basic blocks that have no predecessors (except the entry block)...
2381 // or that just have themself as a predecessor. These are unreachable.
2382 if ((pred_begin(BB) == pred_end(BB) && BB != &Fn->getEntryBlock()) ||
2383 BB->getSinglePredecessor() == BB) {
2384 DEBUG(dbgs() << "Removing BB: \n" << *BB);
2385 DeleteDeadBlock(BB);
2389 // Check to see if we can constant propagate this terminator instruction
2391 Changed |= ConstantFoldTerminator(BB);
2393 // Check for and eliminate duplicate PHI nodes in this block.
2394 Changed |= EliminateDuplicatePHINodes(BB);
2396 // Merge basic blocks into their predecessor if there is only one distinct
2397 // pred, and if there is only one distinct successor of the predecessor, and
2398 // if there are no PHI nodes.
2400 if (MergeBlockIntoPredecessor(BB))
2403 // If there is a trivial two-entry PHI node in this basic block, and we can
2404 // eliminate it, do so now.
2405 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
2406 if (PN->getNumIncomingValues() == 2)
2407 Changed |= FoldTwoEntryPHINode(PN);
2409 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
2410 if (BI->isUnconditional()) {
2411 if (SimplifyUncondBranch(BI)) return true;
2413 if (SimplifyCondBranch(BI))
2416 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
2417 if (SimplifyReturn(RI)) return true;
2418 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
2419 if (SimplifySwitch(SI)) return true;
2420 } else if (UnreachableInst *UI =
2421 dyn_cast<UnreachableInst>(BB->getTerminator())) {
2422 if (SimplifyUnreachable(UI)) return true;
2423 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
2424 if (SimplifyUnwind(UI)) return true;
2425 } else if (IndirectBrInst *IBI =
2426 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
2427 if (SimplifyIndirectBr(IBI)) return true;
2433 /// SimplifyCFG - This function is used to do simplification of a CFG. For
2434 /// example, it adjusts branches to branches to eliminate the extra hop, it
2435 /// eliminates unreachable basic blocks, and does other "peephole" optimization
2436 /// of the CFG. It returns true if a modification was made.
2438 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
2439 return SimplifyCFGOpt(TD).run(BB);