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/ConstantRange.h"
32 #include "llvm/Support/Debug.h"
33 #include "llvm/Support/raw_ostream.h"
39 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
42 class SimplifyCFGOpt {
43 const TargetData *const TD;
45 Value *isValueEqualityComparison(TerminatorInst *TI);
46 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
47 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases);
48 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
50 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI);
52 bool SimplifyReturn(ReturnInst *RI);
53 bool SimplifyUnwind(UnwindInst *UI);
54 bool SimplifyUnreachable(UnreachableInst *UI);
55 bool SimplifySwitch(SwitchInst *SI);
56 bool SimplifyIndirectBr(IndirectBrInst *IBI);
57 bool SimplifyUncondBranch(BranchInst *BI);
58 bool SimplifyCondBranch(BranchInst *BI);
61 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
62 bool run(BasicBlock *BB);
66 /// SafeToMergeTerminators - Return true if it is safe to merge these two
67 /// terminator instructions together.
69 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
70 if (SI1 == SI2) return false; // Can't merge with self!
72 // It is not safe to merge these two switch instructions if they have a common
73 // successor, and if that successor has a PHI node, and if *that* PHI node has
74 // conflicting incoming values from the two switch blocks.
75 BasicBlock *SI1BB = SI1->getParent();
76 BasicBlock *SI2BB = SI2->getParent();
77 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
79 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
80 if (SI1Succs.count(*I))
81 for (BasicBlock::iterator BBI = (*I)->begin();
82 isa<PHINode>(BBI); ++BBI) {
83 PHINode *PN = cast<PHINode>(BBI);
84 if (PN->getIncomingValueForBlock(SI1BB) !=
85 PN->getIncomingValueForBlock(SI2BB))
92 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
93 /// now be entries in it from the 'NewPred' block. The values that will be
94 /// flowing into the PHI nodes will be the same as those coming in from
95 /// ExistPred, an existing predecessor of Succ.
96 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
97 BasicBlock *ExistPred) {
98 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
101 for (BasicBlock::iterator I = Succ->begin();
102 (PN = dyn_cast<PHINode>(I)); ++I)
103 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
107 /// GetIfCondition - Given a basic block (BB) with two predecessors (and at
108 /// least one PHI node in it), check to see if the merge at this block is due
109 /// to an "if condition". If so, return the boolean condition that determines
110 /// which entry into BB will be taken. Also, return by references the block
111 /// that will be entered from if the condition is true, and the block that will
112 /// be entered if the condition is false.
114 /// This does no checking to see if the true/false blocks have large or unsavory
115 /// instructions in them.
116 static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
117 BasicBlock *&IfFalse) {
118 PHINode *SomePHI = cast<PHINode>(BB->begin());
119 assert(SomePHI->getNumIncomingValues() == 2 &&
120 "Function can only handle blocks with 2 predecessors!");
121 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
122 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
124 // We can only handle branches. Other control flow will be lowered to
125 // branches if possible anyway.
126 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
127 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
128 if (Pred1Br == 0 || Pred2Br == 0)
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 // The only thing we have to watch out for here is to make sure that Pred2
147 // doesn't have incoming edges from other blocks. If it does, the condition
148 // doesn't dominate BB.
149 if (Pred2->getSinglePredecessor() == 0)
152 // If we found a conditional branch predecessor, make sure that it branches
153 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
154 if (Pred1Br->getSuccessor(0) == BB &&
155 Pred1Br->getSuccessor(1) == Pred2) {
158 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
159 Pred1Br->getSuccessor(1) == BB) {
163 // We know that one arm of the conditional goes to BB, so the other must
164 // go somewhere unrelated, and this must not be an "if statement".
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 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
175 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
178 // Otherwise, if this is a conditional branch, then we can use it!
179 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
180 if (BI == 0) return 0;
182 assert(BI->isConditional() && "Two successors but not conditional?");
183 if (BI->getSuccessor(0) == Pred1) {
190 return BI->getCondition();
193 /// DominatesMergePoint - If we have a merge point of an "if condition" as
194 /// accepted above, return true if the specified value dominates the block. We
195 /// don't handle the true generality of domination here, just a special case
196 /// which works well enough for us.
198 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
199 /// see if V (which must be an instruction) is cheap to compute and is
200 /// non-trapping. If both are true, the instruction is inserted into the set
201 /// and true is returned.
202 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
203 SmallPtrSet<Instruction*, 4> *AggressiveInsts) {
204 Instruction *I = dyn_cast<Instruction>(V);
206 // Non-instructions all dominate instructions, but not all constantexprs
207 // can be executed unconditionally.
208 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
213 BasicBlock *PBB = I->getParent();
215 // We don't want to allow weird loops that might have the "if condition" in
216 // the bottom of this block.
217 if (PBB == BB) return false;
219 // If this instruction is defined in a block that contains an unconditional
220 // branch to BB, then it must be in the 'conditional' part of the "if
221 // statement". If not, it definitely dominates the region.
222 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
223 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB)
226 // If we aren't allowing aggressive promotion anymore, then don't consider
227 // instructions in the 'if region'.
228 if (AggressiveInsts == 0) return false;
230 // Okay, it looks like the instruction IS in the "condition". Check to
231 // see if it's a cheap instruction to unconditionally compute, and if it
232 // only uses stuff defined outside of the condition. If so, hoist it out.
233 if (!I->isSafeToSpeculativelyExecute())
236 switch (I->getOpcode()) {
237 default: return false; // Cannot hoist this out safely.
238 case Instruction::Load:
239 // We have to check to make sure there are no instructions before the
240 // load in its basic block, as we are going to hoist the load out to its
242 if (PBB->getFirstNonPHIOrDbg() != I)
245 case Instruction::Add:
246 case Instruction::Sub:
247 case Instruction::And:
248 case Instruction::Or:
249 case Instruction::Xor:
250 case Instruction::Shl:
251 case Instruction::LShr:
252 case Instruction::AShr:
253 case Instruction::ICmp:
254 break; // These are all cheap and non-trapping instructions.
257 // Okay, we can only really hoist these out if their operands are not
258 // defined in the conditional region.
259 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
260 if (!DominatesMergePoint(*i, BB, 0))
262 // Okay, it's safe to do this! Remember this instruction.
263 AggressiveInsts->insert(I);
267 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
268 /// and PointerNullValue. Return NULL if value is not a constant int.
269 static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
270 // Normal constant int.
271 ConstantInt *CI = dyn_cast<ConstantInt>(V);
272 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
275 // This is some kind of pointer constant. Turn it into a pointer-sized
276 // ConstantInt if possible.
277 const IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
279 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
280 if (isa<ConstantPointerNull>(V))
281 return ConstantInt::get(PtrTy, 0);
283 // IntToPtr const int.
284 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
285 if (CE->getOpcode() == Instruction::IntToPtr)
286 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
287 // The constant is very likely to have the right type already.
288 if (CI->getType() == PtrTy)
291 return cast<ConstantInt>
292 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
297 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
298 /// collection of icmp eq/ne instructions that compare a value against a
299 /// constant, return the value being compared, and stick the constant into the
302 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
303 const TargetData *TD, bool isEQ) {
304 Instruction *I = dyn_cast<Instruction>(V);
305 if (I == 0) return 0;
307 // If this is an icmp against a constant, handle this as one of the cases.
308 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
309 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
310 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
312 return I->getOperand(0);
315 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
318 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
320 // If this is an and/!= check then we want to optimize "x ugt 2" into
323 Span = Span.inverse();
325 // If there are a ton of values, we don't want to make a ginormous switch.
326 if (Span.getSetSize().ugt(8) || Span.isEmptySet() ||
327 // We don't handle wrapped sets yet.
331 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
332 Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
333 return I->getOperand(0);
338 // Otherwise, we can only handle an | or &, depending on isEQ.
339 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
342 unsigned NumValsBeforeLHS = Vals.size();
343 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
345 unsigned NumVals = Vals.size();
346 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
350 Vals.resize(NumVals);
353 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
354 // set it and return success.
355 if (Extra == 0 || Extra == I->getOperand(1)) {
356 Extra = I->getOperand(1);
360 Vals.resize(NumValsBeforeLHS);
364 // If the LHS can't be folded in, but Extra is available and RHS can, try to
366 if (Extra == 0 || Extra == I->getOperand(0)) {
367 Value *OldExtra = Extra;
368 Extra = I->getOperand(0);
369 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
372 assert(Vals.size() == NumValsBeforeLHS);
379 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
380 Instruction* Cond = 0;
381 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
382 Cond = dyn_cast<Instruction>(SI->getCondition());
383 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
384 if (BI->isConditional())
385 Cond = dyn_cast<Instruction>(BI->getCondition());
386 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
387 Cond = dyn_cast<Instruction>(IBI->getAddress());
390 TI->eraseFromParent();
391 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
394 /// isValueEqualityComparison - Return true if the specified terminator checks
395 /// to see if a value is equal to constant integer value.
396 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
398 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
399 // Do not permit merging of large switch instructions into their
400 // predecessors unless there is only one predecessor.
401 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
402 pred_end(SI->getParent())) <= 128)
403 CV = SI->getCondition();
404 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
405 if (BI->isConditional() && BI->getCondition()->hasOneUse())
406 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
407 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
408 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
409 GetConstantInt(ICI->getOperand(1), TD))
410 CV = ICI->getOperand(0);
412 // Unwrap any lossless ptrtoint cast.
413 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
414 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
415 CV = PTII->getOperand(0);
419 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
420 /// decode all of the 'cases' that it represents and return the 'default' block.
421 BasicBlock *SimplifyCFGOpt::
422 GetValueEqualityComparisonCases(TerminatorInst *TI,
423 std::vector<std::pair<ConstantInt*,
424 BasicBlock*> > &Cases) {
425 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
426 Cases.reserve(SI->getNumCases());
427 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
428 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
429 return SI->getDefaultDest();
432 BranchInst *BI = cast<BranchInst>(TI);
433 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
434 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD),
435 BI->getSuccessor(ICI->getPredicate() ==
436 ICmpInst::ICMP_NE)));
437 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
441 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
442 /// in the list that match the specified block.
443 static void EliminateBlockCases(BasicBlock *BB,
444 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
445 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
446 if (Cases[i].second == BB) {
447 Cases.erase(Cases.begin()+i);
452 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
455 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
456 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
457 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
459 // Make V1 be smaller than V2.
460 if (V1->size() > V2->size())
463 if (V1->size() == 0) return false;
464 if (V1->size() == 1) {
466 ConstantInt *TheVal = (*V1)[0].first;
467 for (unsigned i = 0, e = V2->size(); i != e; ++i)
468 if (TheVal == (*V2)[i].first)
472 // Otherwise, just sort both lists and compare element by element.
473 array_pod_sort(V1->begin(), V1->end());
474 array_pod_sort(V2->begin(), V2->end());
475 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
476 while (i1 != e1 && i2 != e2) {
477 if ((*V1)[i1].first == (*V2)[i2].first)
479 if ((*V1)[i1].first < (*V2)[i2].first)
487 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
488 /// terminator instruction and its block is known to only have a single
489 /// predecessor block, check to see if that predecessor is also a value
490 /// comparison with the same value, and if that comparison determines the
491 /// outcome of this comparison. If so, simplify TI. This does a very limited
492 /// form of jump threading.
493 bool SimplifyCFGOpt::
494 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
496 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
497 if (!PredVal) return false; // Not a value comparison in predecessor.
499 Value *ThisVal = isValueEqualityComparison(TI);
500 assert(ThisVal && "This isn't a value comparison!!");
501 if (ThisVal != PredVal) return false; // Different predicates.
503 // Find out information about when control will move from Pred to TI's block.
504 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
505 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
507 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
509 // Find information about how control leaves this block.
510 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
511 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
512 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
514 // If TI's block is the default block from Pred's comparison, potentially
515 // simplify TI based on this knowledge.
516 if (PredDef == TI->getParent()) {
517 // If we are here, we know that the value is none of those cases listed in
518 // PredCases. If there are any cases in ThisCases that are in PredCases, we
520 if (!ValuesOverlap(PredCases, ThisCases))
523 if (isa<BranchInst>(TI)) {
524 // Okay, one of the successors of this condbr is dead. Convert it to a
526 assert(ThisCases.size() == 1 && "Branch can only have one case!");
527 // Insert the new branch.
528 Instruction *NI = BranchInst::Create(ThisDef, TI);
531 // Remove PHI node entries for the dead edge.
532 ThisCases[0].second->removePredecessor(TI->getParent());
534 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
535 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
537 EraseTerminatorInstAndDCECond(TI);
541 SwitchInst *SI = cast<SwitchInst>(TI);
542 // Okay, TI has cases that are statically dead, prune them away.
543 SmallPtrSet<Constant*, 16> DeadCases;
544 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
545 DeadCases.insert(PredCases[i].first);
547 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
548 << "Through successor TI: " << *TI);
550 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
551 if (DeadCases.count(SI->getCaseValue(i))) {
552 SI->getSuccessor(i)->removePredecessor(TI->getParent());
556 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
560 // Otherwise, TI's block must correspond to some matched value. Find out
561 // which value (or set of values) this is.
562 ConstantInt *TIV = 0;
563 BasicBlock *TIBB = TI->getParent();
564 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
565 if (PredCases[i].second == TIBB) {
567 return false; // Cannot handle multiple values coming to this block.
568 TIV = PredCases[i].first;
570 assert(TIV && "No edge from pred to succ?");
572 // Okay, we found the one constant that our value can be if we get into TI's
573 // BB. Find out which successor will unconditionally be branched to.
574 BasicBlock *TheRealDest = 0;
575 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
576 if (ThisCases[i].first == TIV) {
577 TheRealDest = ThisCases[i].second;
581 // If not handled by any explicit cases, it is handled by the default case.
582 if (TheRealDest == 0) TheRealDest = ThisDef;
584 // Remove PHI node entries for dead edges.
585 BasicBlock *CheckEdge = TheRealDest;
586 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
587 if (*SI != CheckEdge)
588 (*SI)->removePredecessor(TIBB);
592 // Insert the new branch.
593 Instruction *NI = BranchInst::Create(TheRealDest, TI);
596 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
597 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
599 EraseTerminatorInstAndDCECond(TI);
604 /// ConstantIntOrdering - This class implements a stable ordering of constant
605 /// integers that does not depend on their address. This is important for
606 /// applications that sort ConstantInt's to ensure uniqueness.
607 struct ConstantIntOrdering {
608 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
609 return LHS->getValue().ult(RHS->getValue());
614 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
615 const ConstantInt *LHS = *(const ConstantInt**)P1;
616 const ConstantInt *RHS = *(const ConstantInt**)P2;
617 if (LHS->getValue().ult(RHS->getValue()))
619 if (LHS->getValue() == RHS->getValue())
624 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
625 /// equality comparison instruction (either a switch or a branch on "X == c").
626 /// See if any of the predecessors of the terminator block are value comparisons
627 /// on the same value. If so, and if safe to do so, fold them together.
628 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
629 BasicBlock *BB = TI->getParent();
630 Value *CV = isValueEqualityComparison(TI); // CondVal
631 assert(CV && "Not a comparison?");
632 bool Changed = false;
634 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
635 while (!Preds.empty()) {
636 BasicBlock *Pred = Preds.pop_back_val();
638 // See if the predecessor is a comparison with the same value.
639 TerminatorInst *PTI = Pred->getTerminator();
640 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
642 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
643 // Figure out which 'cases' to copy from SI to PSI.
644 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
645 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
647 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
648 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
650 // Based on whether the default edge from PTI goes to BB or not, fill in
651 // PredCases and PredDefault with the new switch cases we would like to
653 SmallVector<BasicBlock*, 8> NewSuccessors;
655 if (PredDefault == BB) {
656 // If this is the default destination from PTI, only the edges in TI
657 // that don't occur in PTI, or that branch to BB will be activated.
658 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
659 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
660 if (PredCases[i].second != BB)
661 PTIHandled.insert(PredCases[i].first);
663 // The default destination is BB, we don't need explicit targets.
664 std::swap(PredCases[i], PredCases.back());
665 PredCases.pop_back();
669 // Reconstruct the new switch statement we will be building.
670 if (PredDefault != BBDefault) {
671 PredDefault->removePredecessor(Pred);
672 PredDefault = BBDefault;
673 NewSuccessors.push_back(BBDefault);
675 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
676 if (!PTIHandled.count(BBCases[i].first) &&
677 BBCases[i].second != BBDefault) {
678 PredCases.push_back(BBCases[i]);
679 NewSuccessors.push_back(BBCases[i].second);
683 // If this is not the default destination from PSI, only the edges
684 // in SI that occur in PSI with a destination of BB will be
686 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
687 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
688 if (PredCases[i].second == BB) {
689 PTIHandled.insert(PredCases[i].first);
690 std::swap(PredCases[i], PredCases.back());
691 PredCases.pop_back();
695 // Okay, now we know which constants were sent to BB from the
696 // predecessor. Figure out where they will all go now.
697 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
698 if (PTIHandled.count(BBCases[i].first)) {
699 // If this is one we are capable of getting...
700 PredCases.push_back(BBCases[i]);
701 NewSuccessors.push_back(BBCases[i].second);
702 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
705 // If there are any constants vectored to BB that TI doesn't handle,
706 // they must go to the default destination of TI.
707 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
709 E = PTIHandled.end(); I != E; ++I) {
710 PredCases.push_back(std::make_pair(*I, BBDefault));
711 NewSuccessors.push_back(BBDefault);
715 // Okay, at this point, we know which new successor Pred will get. Make
716 // sure we update the number of entries in the PHI nodes for these
718 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
719 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
721 // Convert pointer to int before we switch.
722 if (CV->getType()->isPointerTy()) {
723 assert(TD && "Cannot switch on pointer without TargetData");
724 CV = new PtrToIntInst(CV, TD->getIntPtrType(CV->getContext()),
728 // Now that the successors are updated, create the new Switch instruction.
729 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
730 PredCases.size(), PTI);
731 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
732 NewSI->addCase(PredCases[i].first, PredCases[i].second);
734 EraseTerminatorInstAndDCECond(PTI);
736 // Okay, last check. If BB is still a successor of PSI, then we must
737 // have an infinite loop case. If so, add an infinitely looping block
738 // to handle the case to preserve the behavior of the code.
739 BasicBlock *InfLoopBlock = 0;
740 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
741 if (NewSI->getSuccessor(i) == BB) {
742 if (InfLoopBlock == 0) {
743 // Insert it at the end of the function, because it's either code,
744 // or it won't matter if it's hot. :)
745 InfLoopBlock = BasicBlock::Create(BB->getContext(),
746 "infloop", BB->getParent());
747 BranchInst::Create(InfLoopBlock, InfLoopBlock);
749 NewSI->setSuccessor(i, InfLoopBlock);
758 // isSafeToHoistInvoke - If we would need to insert a select that uses the
759 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
760 // would need to do this), we can't hoist the invoke, as there is nowhere
761 // to put the select in this case.
762 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
763 Instruction *I1, Instruction *I2) {
764 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
766 for (BasicBlock::iterator BBI = SI->begin();
767 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
768 Value *BB1V = PN->getIncomingValueForBlock(BB1);
769 Value *BB2V = PN->getIncomingValueForBlock(BB2);
770 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
778 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
779 /// BB2, hoist any common code in the two blocks up into the branch block. The
780 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
781 static bool HoistThenElseCodeToIf(BranchInst *BI) {
782 // This does very trivial matching, with limited scanning, to find identical
783 // instructions in the two blocks. In particular, we don't want to get into
784 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
785 // such, we currently just scan for obviously identical instructions in an
787 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
788 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
790 BasicBlock::iterator BB1_Itr = BB1->begin();
791 BasicBlock::iterator BB2_Itr = BB2->begin();
793 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
794 while (isa<DbgInfoIntrinsic>(I1))
796 while (isa<DbgInfoIntrinsic>(I2))
798 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
799 !I1->isIdenticalToWhenDefined(I2) ||
800 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
803 // If we get here, we can hoist at least one instruction.
804 BasicBlock *BIParent = BI->getParent();
807 // If we are hoisting the terminator instruction, don't move one (making a
808 // broken BB), instead clone it, and remove BI.
809 if (isa<TerminatorInst>(I1))
810 goto HoistTerminator;
812 // For a normal instruction, we just move one to right before the branch,
813 // then replace all uses of the other with the first. Finally, we remove
814 // the now redundant second instruction.
815 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
816 if (!I2->use_empty())
817 I2->replaceAllUsesWith(I1);
818 I1->intersectOptionalDataWith(I2);
819 I2->eraseFromParent();
822 while (isa<DbgInfoIntrinsic>(I1))
825 while (isa<DbgInfoIntrinsic>(I2))
827 } while (I1->getOpcode() == I2->getOpcode() &&
828 I1->isIdenticalToWhenDefined(I2));
833 // It may not be possible to hoist an invoke.
834 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
837 // Okay, it is safe to hoist the terminator.
838 Instruction *NT = I1->clone();
839 BIParent->getInstList().insert(BI, NT);
840 if (!NT->getType()->isVoidTy()) {
841 I1->replaceAllUsesWith(NT);
842 I2->replaceAllUsesWith(NT);
846 // Hoisting one of the terminators from our successor is a great thing.
847 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
848 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
849 // nodes, so we insert select instruction to compute the final result.
850 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
851 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
853 for (BasicBlock::iterator BBI = SI->begin();
854 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
855 Value *BB1V = PN->getIncomingValueForBlock(BB1);
856 Value *BB2V = PN->getIncomingValueForBlock(BB2);
857 if (BB1V == BB2V) continue;
859 // These values do not agree. Insert a select instruction before NT
860 // that determines the right value.
861 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
863 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
864 BB1V->getName()+"."+BB2V->getName(), NT);
865 // Make the PHI node use the select for all incoming values for BB1/BB2
866 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
867 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
868 PN->setIncomingValue(i, SI);
872 // Update any PHI nodes in our new successors.
873 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
874 AddPredecessorToBlock(*SI, BIParent, BB1);
876 EraseTerminatorInstAndDCECond(BI);
880 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
881 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
882 /// (for now, restricted to a single instruction that's side effect free) from
883 /// the BB1 into the branch block to speculatively execute it.
884 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
885 // Only speculatively execution a single instruction (not counting the
886 // terminator) for now.
887 Instruction *HInst = NULL;
888 Instruction *Term = BB1->getTerminator();
889 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
891 Instruction *I = BBI;
893 if (isa<DbgInfoIntrinsic>(I)) continue;
894 if (I == Term) break;
903 // Be conservative for now. FP select instruction can often be expensive.
904 Value *BrCond = BI->getCondition();
905 if (isa<FCmpInst>(BrCond))
908 // If BB1 is actually on the false edge of the conditional branch, remember
909 // to swap the select operands later.
911 if (BB1 != BI->getSuccessor(0)) {
912 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
919 // br i1 %t1, label %BB1, label %BB2
928 // %t3 = select i1 %t1, %t2, %t3
929 switch (HInst->getOpcode()) {
930 default: return false; // Not safe / profitable to hoist.
931 case Instruction::Add:
932 case Instruction::Sub:
933 // Not worth doing for vector ops.
934 if (HInst->getType()->isVectorTy())
937 case Instruction::And:
938 case Instruction::Or:
939 case Instruction::Xor:
940 case Instruction::Shl:
941 case Instruction::LShr:
942 case Instruction::AShr:
943 // Don't mess with vector operations.
944 if (HInst->getType()->isVectorTy())
946 break; // These are all cheap and non-trapping instructions.
949 // If the instruction is obviously dead, don't try to predicate it.
950 if (HInst->use_empty()) {
951 HInst->eraseFromParent();
955 // Can we speculatively execute the instruction? And what is the value
956 // if the condition is false? Consider the phi uses, if the incoming value
957 // from the "if" block are all the same V, then V is the value of the
958 // select if the condition is false.
959 BasicBlock *BIParent = BI->getParent();
960 SmallVector<PHINode*, 4> PHIUses;
961 Value *FalseV = NULL;
963 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
964 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
966 // Ignore any user that is not a PHI node in BB2. These can only occur in
967 // unreachable blocks, because they would not be dominated by the instr.
968 PHINode *PN = dyn_cast<PHINode>(*UI);
969 if (!PN || PN->getParent() != BB2)
971 PHIUses.push_back(PN);
973 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
976 else if (FalseV != PHIV)
977 return false; // Inconsistent value when condition is false.
980 assert(FalseV && "Must have at least one user, and it must be a PHI");
982 // Do not hoist the instruction if any of its operands are defined but not
983 // used in this BB. The transformation will prevent the operand from
984 // being sunk into the use block.
985 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
987 Instruction *OpI = dyn_cast<Instruction>(*i);
988 if (OpI && OpI->getParent() == BIParent &&
989 !OpI->isUsedInBasicBlock(BIParent))
993 // If we get here, we can hoist the instruction. Try to place it
994 // before the icmp instruction preceding the conditional branch.
995 BasicBlock::iterator InsertPos = BI;
996 if (InsertPos != BIParent->begin())
998 // Skip debug info between condition and branch.
999 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
1001 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
1002 SmallPtrSet<Instruction *, 4> BB1Insns;
1003 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
1004 BB1I != BB1E; ++BB1I)
1005 BB1Insns.insert(BB1I);
1006 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
1008 Instruction *Use = cast<Instruction>(*UI);
1009 if (!BB1Insns.count(Use)) continue;
1011 // If BrCond uses the instruction that place it just before
1012 // branch instruction.
1018 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
1020 // Create a select whose true value is the speculatively executed value and
1021 // false value is the previously determined FalseV.
1024 SI = SelectInst::Create(BrCond, FalseV, HInst,
1025 FalseV->getName() + "." + HInst->getName(), BI);
1027 SI = SelectInst::Create(BrCond, HInst, FalseV,
1028 HInst->getName() + "." + FalseV->getName(), BI);
1030 // Make the PHI node use the select for all incoming values for "then" and
1032 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1033 PHINode *PN = PHIUses[i];
1034 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1035 if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent)
1036 PN->setIncomingValue(j, SI);
1043 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1044 /// across this block.
1045 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1046 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1049 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1050 if (isa<DbgInfoIntrinsic>(BBI))
1052 if (Size > 10) return false; // Don't clone large BB's.
1055 // We can only support instructions that do not define values that are
1056 // live outside of the current basic block.
1057 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1059 Instruction *U = cast<Instruction>(*UI);
1060 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1063 // Looks ok, continue checking.
1069 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1070 /// that is defined in the same block as the branch and if any PHI entries are
1071 /// constants, thread edges corresponding to that entry to be branches to their
1072 /// ultimate destination.
1073 static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
1074 BasicBlock *BB = BI->getParent();
1075 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1076 // NOTE: we currently cannot transform this case if the PHI node is used
1077 // outside of the block.
1078 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1081 // Degenerate case of a single entry PHI.
1082 if (PN->getNumIncomingValues() == 1) {
1083 FoldSingleEntryPHINodes(PN->getParent());
1087 // Now we know that this block has multiple preds and two succs.
1088 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1090 // Okay, this is a simple enough basic block. See if any phi values are
1092 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1093 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1094 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1096 // Okay, we now know that all edges from PredBB should be revectored to
1097 // branch to RealDest.
1098 BasicBlock *PredBB = PN->getIncomingBlock(i);
1099 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1101 if (RealDest == BB) continue; // Skip self loops.
1103 // The dest block might have PHI nodes, other predecessors and other
1104 // difficult cases. Instead of being smart about this, just insert a new
1105 // block that jumps to the destination block, effectively splitting
1106 // the edge we are about to create.
1107 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1108 RealDest->getName()+".critedge",
1109 RealDest->getParent(), RealDest);
1110 BranchInst::Create(RealDest, EdgeBB);
1112 // Update PHI nodes.
1113 AddPredecessorToBlock(RealDest, EdgeBB, BB);
1115 // BB may have instructions that are being threaded over. Clone these
1116 // instructions into EdgeBB. We know that there will be no uses of the
1117 // cloned instructions outside of EdgeBB.
1118 BasicBlock::iterator InsertPt = EdgeBB->begin();
1119 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1120 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1121 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1122 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1125 // Clone the instruction.
1126 Instruction *N = BBI->clone();
1127 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1129 // Update operands due to translation.
1130 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1132 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1133 if (PI != TranslateMap.end())
1137 // Check for trivial simplification.
1138 if (Value *V = SimplifyInstruction(N, TD)) {
1139 TranslateMap[BBI] = V;
1140 delete N; // Instruction folded away, don't need actual inst
1142 // Insert the new instruction into its new home.
1143 EdgeBB->getInstList().insert(InsertPt, N);
1144 if (!BBI->use_empty())
1145 TranslateMap[BBI] = N;
1149 // Loop over all of the edges from PredBB to BB, changing them to branch
1150 // to EdgeBB instead.
1151 TerminatorInst *PredBBTI = PredBB->getTerminator();
1152 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1153 if (PredBBTI->getSuccessor(i) == BB) {
1154 BB->removePredecessor(PredBB);
1155 PredBBTI->setSuccessor(i, EdgeBB);
1158 // Recurse, simplifying any other constants.
1159 return FoldCondBranchOnPHI(BI, TD) | true;
1165 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1166 /// PHI node, see if we can eliminate it.
1167 static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
1168 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1169 // statement", which has a very simple dominance structure. Basically, we
1170 // are trying to find the condition that is being branched on, which
1171 // subsequently causes this merge to happen. We really want control
1172 // dependence information for this check, but simplifycfg can't keep it up
1173 // to date, and this catches most of the cases we care about anyway.
1174 BasicBlock *BB = PN->getParent();
1175 BasicBlock *IfTrue, *IfFalse;
1176 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1178 // Don't bother if the branch will be constant folded trivially.
1179 isa<ConstantInt>(IfCond))
1182 // Okay, we found that we can merge this two-entry phi node into a select.
1183 // Doing so would require us to fold *all* two entry phi nodes in this block.
1184 // At some point this becomes non-profitable (particularly if the target
1185 // doesn't support cmov's). Only do this transformation if there are two or
1186 // fewer PHI nodes in this block.
1187 unsigned NumPhis = 0;
1188 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1192 // Loop over the PHI's seeing if we can promote them all to select
1193 // instructions. While we are at it, keep track of the instructions
1194 // that need to be moved to the dominating block.
1195 SmallPtrSet<Instruction*, 4> AggressiveInsts;
1197 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1198 PHINode *PN = cast<PHINode>(II++);
1199 if (Value *V = SimplifyInstruction(PN, TD)) {
1200 PN->replaceAllUsesWith(V);
1201 PN->eraseFromParent();
1205 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts) ||
1206 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts))
1210 // If we folded the the first phi, PN dangles at this point. Refresh it. If
1211 // we ran out of PHIs then we simplified them all.
1212 PN = dyn_cast<PHINode>(BB->begin());
1213 if (PN == 0) return true;
1215 // Don't fold i1 branches on PHIs which contain binary operators. These can
1216 // often be turned into switches and other things.
1217 if (PN->getType()->isIntegerTy(1) &&
1218 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1219 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1220 isa<BinaryOperator>(IfCond)))
1223 // If we all PHI nodes are promotable, check to make sure that all
1224 // instructions in the predecessor blocks can be promoted as well. If
1225 // not, we won't be able to get rid of the control flow, so it's not
1226 // worth promoting to select instructions.
1227 BasicBlock *DomBlock = 0;
1228 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1229 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1230 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1233 DomBlock = *pred_begin(IfBlock1);
1234 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1235 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1236 // This is not an aggressive instruction that we can promote.
1237 // Because of this, we won't be able to get rid of the control
1238 // flow, so the xform is not worth it.
1243 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1246 DomBlock = *pred_begin(IfBlock2);
1247 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1248 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1249 // This is not an aggressive instruction that we can promote.
1250 // Because of this, we won't be able to get rid of the control
1251 // flow, so the xform is not worth it.
1256 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1257 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1259 // If we can still promote the PHI nodes after this gauntlet of tests,
1260 // do all of the PHI's now.
1261 Instruction *InsertPt = DomBlock->getTerminator();
1263 // Move all 'aggressive' instructions, which are defined in the
1264 // conditional parts of the if's up to the dominating block.
1266 DomBlock->getInstList().splice(InsertPt,
1267 IfBlock1->getInstList(), IfBlock1->begin(),
1268 IfBlock1->getTerminator());
1270 DomBlock->getInstList().splice(InsertPt,
1271 IfBlock2->getInstList(), IfBlock2->begin(),
1272 IfBlock2->getTerminator());
1274 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1275 // Change the PHI node into a select instruction.
1276 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1277 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1279 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", InsertPt);
1280 PN->replaceAllUsesWith(NV);
1282 PN->eraseFromParent();
1285 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1286 // has been flattened. Change DomBlock to jump directly to our new block to
1287 // avoid other simplifycfg's kicking in on the diamond.
1288 TerminatorInst *OldTI = DomBlock->getTerminator();
1289 BranchInst::Create(BB, OldTI);
1290 OldTI->eraseFromParent();
1294 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1295 /// to two returning blocks, try to merge them together into one return,
1296 /// introducing a select if the return values disagree.
1297 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1298 assert(BI->isConditional() && "Must be a conditional branch");
1299 BasicBlock *TrueSucc = BI->getSuccessor(0);
1300 BasicBlock *FalseSucc = BI->getSuccessor(1);
1301 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1302 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1304 // Check to ensure both blocks are empty (just a return) or optionally empty
1305 // with PHI nodes. If there are other instructions, merging would cause extra
1306 // computation on one path or the other.
1307 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1309 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1312 // Okay, we found a branch that is going to two return nodes. If
1313 // there is no return value for this function, just change the
1314 // branch into a return.
1315 if (FalseRet->getNumOperands() == 0) {
1316 TrueSucc->removePredecessor(BI->getParent());
1317 FalseSucc->removePredecessor(BI->getParent());
1318 ReturnInst::Create(BI->getContext(), 0, BI);
1319 EraseTerminatorInstAndDCECond(BI);
1323 // Otherwise, figure out what the true and false return values are
1324 // so we can insert a new select instruction.
1325 Value *TrueValue = TrueRet->getReturnValue();
1326 Value *FalseValue = FalseRet->getReturnValue();
1328 // Unwrap any PHI nodes in the return blocks.
1329 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1330 if (TVPN->getParent() == TrueSucc)
1331 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1332 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1333 if (FVPN->getParent() == FalseSucc)
1334 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1336 // In order for this transformation to be safe, we must be able to
1337 // unconditionally execute both operands to the return. This is
1338 // normally the case, but we could have a potentially-trapping
1339 // constant expression that prevents this transformation from being
1341 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1344 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1348 // Okay, we collected all the mapped values and checked them for sanity, and
1349 // defined to really do this transformation. First, update the CFG.
1350 TrueSucc->removePredecessor(BI->getParent());
1351 FalseSucc->removePredecessor(BI->getParent());
1353 // Insert select instructions where needed.
1354 Value *BrCond = BI->getCondition();
1356 // Insert a select if the results differ.
1357 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1358 } else if (isa<UndefValue>(TrueValue)) {
1359 TrueValue = FalseValue;
1361 TrueValue = SelectInst::Create(BrCond, TrueValue,
1362 FalseValue, "retval", BI);
1366 Value *RI = !TrueValue ?
1367 ReturnInst::Create(BI->getContext(), BI) :
1368 ReturnInst::Create(BI->getContext(), TrueValue, BI);
1371 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1372 << "\n " << *BI << "NewRet = " << *RI
1373 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1375 EraseTerminatorInstAndDCECond(BI);
1380 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1381 /// and if a predecessor branches to us and one of our successors, fold the
1382 /// setcc into the predecessor and use logical operations to pick the right
1384 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1385 BasicBlock *BB = BI->getParent();
1386 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1387 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1388 Cond->getParent() != BB || !Cond->hasOneUse())
1391 // Only allow this if the condition is a simple instruction that can be
1392 // executed unconditionally. It must be in the same block as the branch, and
1393 // must be at the front of the block.
1394 BasicBlock::iterator FrontIt = BB->front();
1395 // Ignore dbg intrinsics.
1396 while (isa<DbgInfoIntrinsic>(FrontIt))
1399 // Allow a single instruction to be hoisted in addition to the compare
1400 // that feeds the branch. We later ensure that any values that _it_ uses
1401 // were also live in the predecessor, so that we don't unnecessarily create
1402 // register pressure or inhibit out-of-order execution.
1403 Instruction *BonusInst = 0;
1404 if (&*FrontIt != Cond &&
1405 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1406 FrontIt->isSafeToSpeculativelyExecute()) {
1407 BonusInst = &*FrontIt;
1411 // Only a single bonus inst is allowed.
1412 if (&*FrontIt != Cond)
1415 // Make sure the instruction after the condition is the cond branch.
1416 BasicBlock::iterator CondIt = Cond; ++CondIt;
1417 // Ingore dbg intrinsics.
1418 while(isa<DbgInfoIntrinsic>(CondIt))
1420 if (&*CondIt != BI) {
1421 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!");
1425 // Cond is known to be a compare or binary operator. Check to make sure that
1426 // neither operand is a potentially-trapping constant expression.
1427 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1430 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1435 // Finally, don't infinitely unroll conditional loops.
1436 BasicBlock *TrueDest = BI->getSuccessor(0);
1437 BasicBlock *FalseDest = BI->getSuccessor(1);
1438 if (TrueDest == BB || FalseDest == BB)
1441 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1442 BasicBlock *PredBlock = *PI;
1443 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1445 // Check that we have two conditional branches. If there is a PHI node in
1446 // the common successor, verify that the same value flows in from both
1448 if (PBI == 0 || PBI->isUnconditional() ||
1449 !SafeToMergeTerminators(BI, PBI))
1452 // Ensure that any values used in the bonus instruction are also used
1453 // by the terminator of the predecessor. This means that those values
1454 // must already have been resolved, so we won't be inhibiting the
1455 // out-of-order core by speculating them earlier.
1457 // Collect the values used by the bonus inst
1458 SmallPtrSet<Value*, 4> UsedValues;
1459 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1460 OE = BonusInst->op_end(); OI != OE; ++OI) {
1462 if (!isa<Constant>(V))
1463 UsedValues.insert(V);
1466 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1467 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1469 // Walk up to four levels back up the use-def chain of the predecessor's
1470 // terminator to see if all those values were used. The choice of four
1471 // levels is arbitrary, to provide a compile-time-cost bound.
1472 while (!Worklist.empty()) {
1473 std::pair<Value*, unsigned> Pair = Worklist.back();
1474 Worklist.pop_back();
1476 if (Pair.second >= 4) continue;
1477 UsedValues.erase(Pair.first);
1478 if (UsedValues.empty()) break;
1480 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
1481 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1483 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1487 if (!UsedValues.empty()) return false;
1490 Instruction::BinaryOps Opc;
1491 bool InvertPredCond = false;
1493 if (PBI->getSuccessor(0) == TrueDest)
1494 Opc = Instruction::Or;
1495 else if (PBI->getSuccessor(1) == FalseDest)
1496 Opc = Instruction::And;
1497 else if (PBI->getSuccessor(0) == FalseDest)
1498 Opc = Instruction::And, InvertPredCond = true;
1499 else if (PBI->getSuccessor(1) == TrueDest)
1500 Opc = Instruction::Or, InvertPredCond = true;
1504 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1506 // If we need to invert the condition in the pred block to match, do so now.
1507 if (InvertPredCond) {
1508 Value *NewCond = PBI->getCondition();
1510 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
1511 CmpInst *CI = cast<CmpInst>(NewCond);
1512 CI->setPredicate(CI->getInversePredicate());
1514 NewCond = BinaryOperator::CreateNot(NewCond,
1515 PBI->getCondition()->getName()+".not", PBI);
1518 PBI->setCondition(NewCond);
1519 BasicBlock *OldTrue = PBI->getSuccessor(0);
1520 BasicBlock *OldFalse = PBI->getSuccessor(1);
1521 PBI->setSuccessor(0, OldFalse);
1522 PBI->setSuccessor(1, OldTrue);
1525 // If we have a bonus inst, clone it into the predecessor block.
1526 Instruction *NewBonus = 0;
1528 NewBonus = BonusInst->clone();
1529 PredBlock->getInstList().insert(PBI, NewBonus);
1530 NewBonus->takeName(BonusInst);
1531 BonusInst->setName(BonusInst->getName()+".old");
1534 // Clone Cond into the predecessor basic block, and or/and the
1535 // two conditions together.
1536 Instruction *New = Cond->clone();
1537 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1538 PredBlock->getInstList().insert(PBI, New);
1539 New->takeName(Cond);
1540 Cond->setName(New->getName()+".old");
1542 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1543 New, "or.cond", PBI);
1544 PBI->setCondition(NewCond);
1545 if (PBI->getSuccessor(0) == BB) {
1546 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1547 PBI->setSuccessor(0, TrueDest);
1549 if (PBI->getSuccessor(1) == BB) {
1550 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1551 PBI->setSuccessor(1, FalseDest);
1558 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1559 /// predecessor of another block, this function tries to simplify it. We know
1560 /// that PBI and BI are both conditional branches, and BI is in one of the
1561 /// successor blocks of PBI - PBI branches to BI.
1562 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1563 assert(PBI->isConditional() && BI->isConditional());
1564 BasicBlock *BB = BI->getParent();
1566 // If this block ends with a branch instruction, and if there is a
1567 // predecessor that ends on a branch of the same condition, make
1568 // this conditional branch redundant.
1569 if (PBI->getCondition() == BI->getCondition() &&
1570 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1571 // Okay, the outcome of this conditional branch is statically
1572 // knowable. If this block had a single pred, handle specially.
1573 if (BB->getSinglePredecessor()) {
1574 // Turn this into a branch on constant.
1575 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1576 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1578 return true; // Nuke the branch on constant.
1581 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1582 // in the constant and simplify the block result. Subsequent passes of
1583 // simplifycfg will thread the block.
1584 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1585 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1586 BI->getCondition()->getName() + ".pr",
1588 // Okay, we're going to insert the PHI node. Since PBI is not the only
1589 // predecessor, compute the PHI'd conditional value for all of the preds.
1590 // Any predecessor where the condition is not computable we keep symbolic.
1591 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1592 BasicBlock *P = *PI;
1593 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
1594 PBI != BI && PBI->isConditional() &&
1595 PBI->getCondition() == BI->getCondition() &&
1596 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1597 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1598 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1601 NewPN->addIncoming(BI->getCondition(), P);
1605 BI->setCondition(NewPN);
1610 // If this is a conditional branch in an empty block, and if any
1611 // predecessors is a conditional branch to one of our destinations,
1612 // fold the conditions into logical ops and one cond br.
1613 BasicBlock::iterator BBI = BB->begin();
1614 // Ignore dbg intrinsics.
1615 while (isa<DbgInfoIntrinsic>(BBI))
1621 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1626 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1628 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1629 PBIOp = 0, BIOp = 1;
1630 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1631 PBIOp = 1, BIOp = 0;
1632 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1637 // Check to make sure that the other destination of this branch
1638 // isn't BB itself. If so, this is an infinite loop that will
1639 // keep getting unwound.
1640 if (PBI->getSuccessor(PBIOp) == BB)
1643 // Do not perform this transformation if it would require
1644 // insertion of a large number of select instructions. For targets
1645 // without predication/cmovs, this is a big pessimization.
1646 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1648 unsigned NumPhis = 0;
1649 for (BasicBlock::iterator II = CommonDest->begin();
1650 isa<PHINode>(II); ++II, ++NumPhis)
1651 if (NumPhis > 2) // Disable this xform.
1654 // Finally, if everything is ok, fold the branches to logical ops.
1655 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1657 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
1658 << "AND: " << *BI->getParent());
1661 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1662 // branch in it, where one edge (OtherDest) goes back to itself but the other
1663 // exits. We don't *know* that the program avoids the infinite loop
1664 // (even though that seems likely). If we do this xform naively, we'll end up
1665 // recursively unpeeling the loop. Since we know that (after the xform is
1666 // done) that the block *is* infinite if reached, we just make it an obviously
1667 // infinite loop with no cond branch.
1668 if (OtherDest == BB) {
1669 // Insert it at the end of the function, because it's either code,
1670 // or it won't matter if it's hot. :)
1671 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1672 "infloop", BB->getParent());
1673 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1674 OtherDest = InfLoopBlock;
1677 DEBUG(dbgs() << *PBI->getParent()->getParent());
1679 // BI may have other predecessors. Because of this, we leave
1680 // it alone, but modify PBI.
1682 // Make sure we get to CommonDest on True&True directions.
1683 Value *PBICond = PBI->getCondition();
1685 PBICond = BinaryOperator::CreateNot(PBICond,
1686 PBICond->getName()+".not",
1688 Value *BICond = BI->getCondition();
1690 BICond = BinaryOperator::CreateNot(BICond,
1691 BICond->getName()+".not",
1693 // Merge the conditions.
1694 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1696 // Modify PBI to branch on the new condition to the new dests.
1697 PBI->setCondition(Cond);
1698 PBI->setSuccessor(0, CommonDest);
1699 PBI->setSuccessor(1, OtherDest);
1701 // OtherDest may have phi nodes. If so, add an entry from PBI's
1702 // block that are identical to the entries for BI's block.
1703 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
1705 // We know that the CommonDest already had an edge from PBI to
1706 // it. If it has PHIs though, the PHIs may have different
1707 // entries for BB and PBI's BB. If so, insert a select to make
1710 for (BasicBlock::iterator II = CommonDest->begin();
1711 (PN = dyn_cast<PHINode>(II)); ++II) {
1712 Value *BIV = PN->getIncomingValueForBlock(BB);
1713 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1714 Value *PBIV = PN->getIncomingValue(PBBIdx);
1716 // Insert a select in PBI to pick the right value.
1717 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1718 PBIV->getName()+".mux", PBI);
1719 PN->setIncomingValue(PBBIdx, NV);
1723 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1724 DEBUG(dbgs() << *PBI->getParent()->getParent());
1726 // This basic block is probably dead. We know it has at least
1727 // one fewer predecessor.
1731 // SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
1732 // branch to TrueBB if Cond is true or to FalseBB if Cond is false.
1733 // Takes care of updating the successors and removing the old terminator.
1734 // Also makes sure not to introduce new successors by assuming that edges to
1735 // non-successor TrueBBs and FalseBBs aren't reachable.
1736 static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
1737 BasicBlock *TrueBB, BasicBlock *FalseBB){
1738 // Remove any superfluous successor edges from the CFG.
1739 // First, figure out which successors to preserve.
1740 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
1742 BasicBlock *KeepEdge1 = TrueBB;
1743 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
1745 // Then remove the rest.
1746 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
1747 BasicBlock *Succ = OldTerm->getSuccessor(I);
1748 // Make sure only to keep exactly one copy of each edge.
1749 if (Succ == KeepEdge1)
1751 else if (Succ == KeepEdge2)
1754 Succ->removePredecessor(OldTerm->getParent());
1757 // Insert an appropriate new terminator.
1758 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
1759 if (TrueBB == FalseBB)
1760 // We were only looking for one successor, and it was present.
1761 // Create an unconditional branch to it.
1762 BranchInst::Create(TrueBB, OldTerm);
1764 // We found both of the successors we were looking for.
1765 // Create a conditional branch sharing the condition of the select.
1766 BranchInst::Create(TrueBB, FalseBB, Cond, OldTerm);
1767 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
1768 // Neither of the selected blocks were successors, so this
1769 // terminator must be unreachable.
1770 new UnreachableInst(OldTerm->getContext(), OldTerm);
1772 // One of the selected values was a successor, but the other wasn't.
1773 // Insert an unconditional branch to the one that was found;
1774 // the edge to the one that wasn't must be unreachable.
1776 // Only TrueBB was found.
1777 BranchInst::Create(TrueBB, OldTerm);
1779 // Only FalseBB was found.
1780 BranchInst::Create(FalseBB, OldTerm);
1783 EraseTerminatorInstAndDCECond(OldTerm);
1787 // SimplifyIndirectBrOnSelect - Replaces
1788 // (indirectbr (select cond, blockaddress(@fn, BlockA),
1789 // blockaddress(@fn, BlockB)))
1791 // (br cond, BlockA, BlockB).
1792 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
1793 // Check that both operands of the select are block addresses.
1794 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
1795 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
1799 // Extract the actual blocks.
1800 BasicBlock *TrueBB = TBA->getBasicBlock();
1801 BasicBlock *FalseBB = FBA->getBasicBlock();
1803 // Perform the actual simplification.
1804 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB);
1807 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
1808 /// instruction (a seteq/setne with a constant) as the only instruction in a
1809 /// block that ends with an uncond branch. We are looking for a very specific
1810 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
1811 /// this case, we merge the first two "or's of icmp" into a switch, but then the
1812 /// default value goes to an uncond block with a seteq in it, we get something
1815 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
1817 /// %tmp = icmp eq i8 %A, 92
1820 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
1822 /// We prefer to split the edge to 'end' so that there is a true/false entry to
1823 /// the PHI, merging the third icmp into the switch.
1824 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
1825 const TargetData *TD) {
1826 BasicBlock *BB = ICI->getParent();
1827 // If the block has any PHIs in it or the icmp has multiple uses, it is too
1829 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
1831 Value *V = ICI->getOperand(0);
1832 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
1834 // The pattern we're looking for is where our only predecessor is a switch on
1835 // 'V' and this block is the default case for the switch. In this case we can
1836 // fold the compared value into the switch to simplify things.
1837 BasicBlock *Pred = BB->getSinglePredecessor();
1838 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
1840 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
1841 if (SI->getCondition() != V)
1844 // If BB is reachable on a non-default case, then we simply know the value of
1845 // V in this block. Substitute it and constant fold the icmp instruction
1847 if (SI->getDefaultDest() != BB) {
1848 ConstantInt *VVal = SI->findCaseDest(BB);
1849 assert(VVal && "Should have a unique destination value");
1850 ICI->setOperand(0, VVal);
1852 if (Value *V = SimplifyInstruction(ICI, TD)) {
1853 ICI->replaceAllUsesWith(V);
1854 ICI->eraseFromParent();
1856 // BB is now empty, so it is likely to simplify away.
1857 return SimplifyCFG(BB) | true;
1860 // Ok, the block is reachable from the default dest. If the constant we're
1861 // comparing exists in one of the other edges, then we can constant fold ICI
1863 if (SI->findCaseValue(Cst) != 0) {
1865 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1866 V = ConstantInt::getFalse(BB->getContext());
1868 V = ConstantInt::getTrue(BB->getContext());
1870 ICI->replaceAllUsesWith(V);
1871 ICI->eraseFromParent();
1872 // BB is now empty, so it is likely to simplify away.
1873 return SimplifyCFG(BB) | true;
1876 // The use of the icmp has to be in the 'end' block, by the only PHI node in
1878 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
1879 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
1880 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
1881 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
1884 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
1886 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
1887 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
1889 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1890 std::swap(DefaultCst, NewCst);
1892 // Replace ICI (which is used by the PHI for the default value) with true or
1893 // false depending on if it is EQ or NE.
1894 ICI->replaceAllUsesWith(DefaultCst);
1895 ICI->eraseFromParent();
1897 // Okay, the switch goes to this block on a default value. Add an edge from
1898 // the switch to the merge point on the compared value.
1899 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
1900 BB->getParent(), BB);
1901 SI->addCase(Cst, NewBB);
1903 // NewBB branches to the phi block, add the uncond branch and the phi entry.
1904 BranchInst::Create(SuccBlock, NewBB);
1905 PHIUse->addIncoming(NewCst, NewBB);
1909 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
1910 /// Check to see if it is branching on an or/and chain of icmp instructions, and
1911 /// fold it into a switch instruction if so.
1912 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD) {
1913 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1914 if (Cond == 0) return false;
1917 // Change br (X == 0 | X == 1), T, F into a switch instruction.
1918 // If this is a bunch of seteq's or'd together, or if it's a bunch of
1919 // 'setne's and'ed together, collect them.
1921 std::vector<ConstantInt*> Values;
1922 bool TrueWhenEqual = true;
1923 Value *ExtraCase = 0;
1925 if (Cond->getOpcode() == Instruction::Or) {
1926 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true);
1927 } else if (Cond->getOpcode() == Instruction::And) {
1928 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false);
1929 TrueWhenEqual = false;
1932 // If we didn't have a multiply compared value, fail.
1933 if (CompVal == 0) return false;
1935 // There might be duplicate constants in the list, which the switch
1936 // instruction can't handle, remove them now.
1937 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
1938 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
1940 // If Extra was used, we require at least two switch values to do the
1941 // transformation. A switch with one value is just an cond branch.
1942 if (ExtraCase && Values.size() < 2) return false;
1944 // Figure out which block is which destination.
1945 BasicBlock *DefaultBB = BI->getSuccessor(1);
1946 BasicBlock *EdgeBB = BI->getSuccessor(0);
1947 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
1949 BasicBlock *BB = BI->getParent();
1951 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
1952 << " cases into SWITCH. BB is:\n" << *BB);
1954 // If there are any extra values that couldn't be folded into the switch
1955 // then we evaluate them with an explicit branch first. Split the block
1956 // right before the condbr to handle it.
1958 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
1959 // Remove the uncond branch added to the old block.
1960 TerminatorInst *OldTI = BB->getTerminator();
1963 BranchInst::Create(EdgeBB, NewBB, ExtraCase, OldTI);
1965 BranchInst::Create(NewBB, EdgeBB, ExtraCase, OldTI);
1967 OldTI->eraseFromParent();
1969 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
1970 // for the edge we just added.
1971 AddPredecessorToBlock(EdgeBB, BB, NewBB);
1973 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
1974 << "\nEXTRABB = " << *BB);
1978 // Convert pointer to int before we switch.
1979 if (CompVal->getType()->isPointerTy()) {
1980 assert(TD && "Cannot switch on pointer without TargetData");
1981 CompVal = new PtrToIntInst(CompVal,
1982 TD->getIntPtrType(CompVal->getContext()),
1986 // Create the new switch instruction now.
1987 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB, Values.size(), BI);
1989 // Add all of the 'cases' to the switch instruction.
1990 for (unsigned i = 0, e = Values.size(); i != e; ++i)
1991 New->addCase(Values[i], EdgeBB);
1993 // We added edges from PI to the EdgeBB. As such, if there were any
1994 // PHI nodes in EdgeBB, they need entries to be added corresponding to
1995 // the number of edges added.
1996 for (BasicBlock::iterator BBI = EdgeBB->begin();
1997 isa<PHINode>(BBI); ++BBI) {
1998 PHINode *PN = cast<PHINode>(BBI);
1999 Value *InVal = PN->getIncomingValueForBlock(BB);
2000 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2001 PN->addIncoming(InVal, BB);
2004 // Erase the old branch instruction.
2005 EraseTerminatorInstAndDCECond(BI);
2007 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
2011 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI) {
2012 BasicBlock *BB = RI->getParent();
2013 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2015 // Find predecessors that end with branches.
2016 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2017 SmallVector<BranchInst*, 8> CondBranchPreds;
2018 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2019 BasicBlock *P = *PI;
2020 TerminatorInst *PTI = P->getTerminator();
2021 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2022 if (BI->isUnconditional())
2023 UncondBranchPreds.push_back(P);
2025 CondBranchPreds.push_back(BI);
2029 // If we found some, do the transformation!
2030 if (!UncondBranchPreds.empty()) {
2031 while (!UncondBranchPreds.empty()) {
2032 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2033 DEBUG(dbgs() << "FOLDING: " << *BB
2034 << "INTO UNCOND BRANCH PRED: " << *Pred);
2035 Instruction *UncondBranch = Pred->getTerminator();
2036 // Clone the return and add it to the end of the predecessor.
2037 Instruction *NewRet = RI->clone();
2038 Pred->getInstList().push_back(NewRet);
2040 // If the return instruction returns a value, and if the value was a
2041 // PHI node in "BB", propagate the right value into the return.
2042 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
2044 if (PHINode *PN = dyn_cast<PHINode>(*i))
2045 if (PN->getParent() == BB)
2046 *i = PN->getIncomingValueForBlock(Pred);
2048 // Update any PHI nodes in the returning block to realize that we no
2049 // longer branch to them.
2050 BB->removePredecessor(Pred);
2051 UncondBranch->eraseFromParent();
2054 // If we eliminated all predecessors of the block, delete the block now.
2055 if (pred_begin(BB) == pred_end(BB))
2056 // We know there are no successors, so just nuke the block.
2057 BB->eraseFromParent();
2062 // Check out all of the conditional branches going to this return
2063 // instruction. If any of them just select between returns, change the
2064 // branch itself into a select/return pair.
2065 while (!CondBranchPreds.empty()) {
2066 BranchInst *BI = CondBranchPreds.pop_back_val();
2068 // Check to see if the non-BB successor is also a return block.
2069 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2070 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2071 SimplifyCondBranchToTwoReturns(BI))
2077 bool SimplifyCFGOpt::SimplifyUnwind(UnwindInst *UI) {
2078 // Check to see if the first instruction in this block is just an unwind.
2079 // If so, replace any invoke instructions which use this as an exception
2080 // destination with call instructions.
2081 BasicBlock *BB = UI->getParent();
2082 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2084 bool Changed = false;
2085 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2086 while (!Preds.empty()) {
2087 BasicBlock *Pred = Preds.back();
2088 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
2089 if (II && II->getUnwindDest() == BB) {
2090 // Insert a new branch instruction before the invoke, because this
2091 // is now a fall through.
2092 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2093 Pred->getInstList().remove(II); // Take out of symbol table
2095 // Insert the call now.
2096 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
2097 CallInst *CI = CallInst::Create(II->getCalledValue(),
2098 Args.begin(), Args.end(),
2100 CI->setCallingConv(II->getCallingConv());
2101 CI->setAttributes(II->getAttributes());
2102 // If the invoke produced a value, the Call now does instead.
2103 II->replaceAllUsesWith(CI);
2111 // If this block is now dead (and isn't the entry block), remove it.
2112 if (pred_begin(BB) == pred_end(BB) &&
2113 BB != &BB->getParent()->getEntryBlock()) {
2114 // We know there are no successors, so just nuke the block.
2115 BB->eraseFromParent();
2122 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2123 BasicBlock *BB = UI->getParent();
2125 bool Changed = false;
2127 // If there are any instructions immediately before the unreachable that can
2128 // be removed, do so.
2129 while (UI != BB->begin()) {
2130 BasicBlock::iterator BBI = UI;
2132 // Do not delete instructions that can have side effects, like calls
2133 // (which may never return) and volatile loads and stores.
2134 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2136 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
2137 if (SI->isVolatile())
2140 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
2141 if (LI->isVolatile())
2144 // Delete this instruction
2145 BBI->eraseFromParent();
2149 // If the unreachable instruction is the first in the block, take a gander
2150 // at all of the predecessors of this instruction, and simplify them.
2151 if (&BB->front() != UI) return Changed;
2153 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2154 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2155 TerminatorInst *TI = Preds[i]->getTerminator();
2157 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2158 if (BI->isUnconditional()) {
2159 if (BI->getSuccessor(0) == BB) {
2160 new UnreachableInst(TI->getContext(), TI);
2161 TI->eraseFromParent();
2165 if (BI->getSuccessor(0) == BB) {
2166 BranchInst::Create(BI->getSuccessor(1), BI);
2167 EraseTerminatorInstAndDCECond(BI);
2168 } else if (BI->getSuccessor(1) == BB) {
2169 BranchInst::Create(BI->getSuccessor(0), BI);
2170 EraseTerminatorInstAndDCECond(BI);
2174 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2175 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2176 if (SI->getSuccessor(i) == BB) {
2177 BB->removePredecessor(SI->getParent());
2182 // If the default value is unreachable, figure out the most popular
2183 // destination and make it the default.
2184 if (SI->getSuccessor(0) == BB) {
2185 std::map<BasicBlock*, unsigned> Popularity;
2186 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2187 Popularity[SI->getSuccessor(i)]++;
2189 // Find the most popular block.
2190 unsigned MaxPop = 0;
2191 BasicBlock *MaxBlock = 0;
2192 for (std::map<BasicBlock*, unsigned>::iterator
2193 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2194 if (I->second > MaxPop) {
2196 MaxBlock = I->first;
2200 // Make this the new default, allowing us to delete any explicit
2202 SI->setSuccessor(0, MaxBlock);
2205 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2207 if (isa<PHINode>(MaxBlock->begin()))
2208 for (unsigned i = 0; i != MaxPop-1; ++i)
2209 MaxBlock->removePredecessor(SI->getParent());
2211 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2212 if (SI->getSuccessor(i) == MaxBlock) {
2218 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2219 if (II->getUnwindDest() == BB) {
2220 // Convert the invoke to a call instruction. This would be a good
2221 // place to note that the call does not throw though.
2222 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2223 II->removeFromParent(); // Take out of symbol table
2225 // Insert the call now...
2226 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2227 CallInst *CI = CallInst::Create(II->getCalledValue(),
2228 Args.begin(), Args.end(),
2230 CI->setCallingConv(II->getCallingConv());
2231 CI->setAttributes(II->getAttributes());
2232 // If the invoke produced a value, the call does now instead.
2233 II->replaceAllUsesWith(CI);
2240 // If this block is now dead, remove it.
2241 if (pred_begin(BB) == pred_end(BB) &&
2242 BB != &BB->getParent()->getEntryBlock()) {
2243 // We know there are no successors, so just nuke the block.
2244 BB->eraseFromParent();
2252 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI) {
2253 // If this switch is too complex to want to look at, ignore it.
2254 if (!isValueEqualityComparison(SI))
2257 BasicBlock *BB = SI->getParent();
2259 // If we only have one predecessor, and if it is a branch on this value,
2260 // see if that predecessor totally determines the outcome of this switch.
2261 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2262 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
2263 return SimplifyCFG(BB) | true;
2265 // If the block only contains the switch, see if we can fold the block
2266 // away into any preds.
2267 BasicBlock::iterator BBI = BB->begin();
2268 // Ignore dbg intrinsics.
2269 while (isa<DbgInfoIntrinsic>(BBI))
2272 if (FoldValueComparisonIntoPredecessors(SI))
2273 return SimplifyCFG(BB) | true;
2278 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
2279 BasicBlock *BB = IBI->getParent();
2280 bool Changed = false;
2282 // Eliminate redundant destinations.
2283 SmallPtrSet<Value *, 8> Succs;
2284 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2285 BasicBlock *Dest = IBI->getDestination(i);
2286 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2287 Dest->removePredecessor(BB);
2288 IBI->removeDestination(i);
2294 if (IBI->getNumDestinations() == 0) {
2295 // If the indirectbr has no successors, change it to unreachable.
2296 new UnreachableInst(IBI->getContext(), IBI);
2297 EraseTerminatorInstAndDCECond(IBI);
2301 if (IBI->getNumDestinations() == 1) {
2302 // If the indirectbr has one successor, change it to a direct branch.
2303 BranchInst::Create(IBI->getDestination(0), IBI);
2304 EraseTerminatorInstAndDCECond(IBI);
2308 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2309 if (SimplifyIndirectBrOnSelect(IBI, SI))
2310 return SimplifyCFG(BB) | true;
2315 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI) {
2316 BasicBlock *BB = BI->getParent();
2318 // If the Terminator is the only non-phi instruction, simplify the block.
2319 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg();
2320 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
2321 TryToSimplifyUncondBranchFromEmptyBlock(BB))
2324 // If the only instruction in the block is a seteq/setne comparison
2325 // against a constant, try to simplify the block.
2326 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
2327 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
2328 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
2330 if (I->isTerminator() && TryToSimplifyUncondBranchWithICmpInIt(ICI, TD))
2338 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI) {
2339 BasicBlock *BB = BI->getParent();
2341 // Conditional branch
2342 if (isValueEqualityComparison(BI)) {
2343 // If we only have one predecessor, and if it is a branch on this value,
2344 // see if that predecessor totally determines the outcome of this
2346 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2347 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
2348 return SimplifyCFG(BB) | true;
2350 // This block must be empty, except for the setcond inst, if it exists.
2351 // Ignore dbg intrinsics.
2352 BasicBlock::iterator I = BB->begin();
2353 // Ignore dbg intrinsics.
2354 while (isa<DbgInfoIntrinsic>(I))
2357 if (FoldValueComparisonIntoPredecessors(BI))
2358 return SimplifyCFG(BB) | true;
2359 } else if (&*I == cast<Instruction>(BI->getCondition())){
2361 // Ignore dbg intrinsics.
2362 while (isa<DbgInfoIntrinsic>(I))
2364 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI))
2365 return SimplifyCFG(BB) | true;
2369 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
2370 if (SimplifyBranchOnICmpChain(BI, TD))
2373 // We have a conditional branch to two blocks that are only reachable
2374 // from BI. We know that the condbr dominates the two blocks, so see if
2375 // there is any identical code in the "then" and "else" blocks. If so, we
2376 // can hoist it up to the branching block.
2377 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
2378 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2379 if (HoistThenElseCodeToIf(BI))
2380 return SimplifyCFG(BB) | true;
2382 // If Successor #1 has multiple preds, we may be able to conditionally
2383 // execute Successor #0 if it branches to successor #1.
2384 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
2385 if (Succ0TI->getNumSuccessors() == 1 &&
2386 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
2387 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
2388 return SimplifyCFG(BB) | true;
2390 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2391 // If Successor #0 has multiple preds, we may be able to conditionally
2392 // execute Successor #1 if it branches to successor #0.
2393 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
2394 if (Succ1TI->getNumSuccessors() == 1 &&
2395 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
2396 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
2397 return SimplifyCFG(BB) | true;
2400 // If this is a branch on a phi node in the current block, thread control
2401 // through this block if any PHI node entries are constants.
2402 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
2403 if (PN->getParent() == BI->getParent())
2404 if (FoldCondBranchOnPHI(BI, TD))
2405 return SimplifyCFG(BB) | true;
2407 // If this basic block is ONLY a setcc and a branch, and if a predecessor
2408 // branches to us and one of our successors, fold the setcc into the
2409 // predecessor and use logical operations to pick the right destination.
2410 if (FoldBranchToCommonDest(BI))
2411 return SimplifyCFG(BB) | true;
2413 // Scan predecessor blocks for conditional branches.
2414 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2415 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2416 if (PBI != BI && PBI->isConditional())
2417 if (SimplifyCondBranchToCondBranch(PBI, BI))
2418 return SimplifyCFG(BB) | true;
2423 bool SimplifyCFGOpt::run(BasicBlock *BB) {
2424 bool Changed = false;
2426 assert(BB && BB->getParent() && "Block not embedded in function!");
2427 assert(BB->getTerminator() && "Degenerate basic block encountered!");
2429 // Remove basic blocks that have no predecessors (except the entry block)...
2430 // or that just have themself as a predecessor. These are unreachable.
2431 if ((pred_begin(BB) == pred_end(BB) &&
2432 BB != &BB->getParent()->getEntryBlock()) ||
2433 BB->getSinglePredecessor() == BB) {
2434 DEBUG(dbgs() << "Removing BB: \n" << *BB);
2435 DeleteDeadBlock(BB);
2439 // Check to see if we can constant propagate this terminator instruction
2441 Changed |= ConstantFoldTerminator(BB);
2443 // Check for and eliminate duplicate PHI nodes in this block.
2444 Changed |= EliminateDuplicatePHINodes(BB);
2446 // Merge basic blocks into their predecessor if there is only one distinct
2447 // pred, and if there is only one distinct successor of the predecessor, and
2448 // if there are no PHI nodes.
2450 if (MergeBlockIntoPredecessor(BB))
2453 // If there is a trivial two-entry PHI node in this basic block, and we can
2454 // eliminate it, do so now.
2455 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
2456 if (PN->getNumIncomingValues() == 2)
2457 Changed |= FoldTwoEntryPHINode(PN, TD);
2459 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
2460 if (BI->isUnconditional()) {
2461 if (SimplifyUncondBranch(BI)) return true;
2463 if (SimplifyCondBranch(BI)) return true;
2465 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
2466 if (SimplifyReturn(RI)) return true;
2467 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
2468 if (SimplifySwitch(SI)) return true;
2469 } else if (UnreachableInst *UI =
2470 dyn_cast<UnreachableInst>(BB->getTerminator())) {
2471 if (SimplifyUnreachable(UI)) return true;
2472 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
2473 if (SimplifyUnwind(UI)) return true;
2474 } else if (IndirectBrInst *IBI =
2475 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
2476 if (SimplifyIndirectBr(IBI)) return true;
2482 /// SimplifyCFG - This function is used to do simplification of a CFG. For
2483 /// example, it adjusts branches to branches to eliminate the extra hop, it
2484 /// eliminates unreachable basic blocks, and does other "peephole" optimization
2485 /// of the CFG. It returns true if a modification was made.
2487 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
2488 return SimplifyCFGOpt(TD).run(BB);