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/Analysis/ValueTracking.h"
24 #include "llvm/Target/TargetData.h"
25 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
26 #include "llvm/ADT/DenseMap.h"
27 #include "llvm/ADT/SmallVector.h"
28 #include "llvm/ADT/SmallPtrSet.h"
29 #include "llvm/ADT/Statistic.h"
30 #include "llvm/ADT/STLExtras.h"
31 #include "llvm/Support/CFG.h"
32 #include "llvm/Support/CommandLine.h"
33 #include "llvm/Support/ConstantRange.h"
34 #include "llvm/Support/Debug.h"
35 #include "llvm/Support/IRBuilder.h"
36 #include "llvm/Support/raw_ostream.h"
42 static cl::opt<unsigned>
43 PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(1),
44 cl::desc("Control the amount of phi node folding to perform (default = 1)"));
47 DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false),
48 cl::desc("Duplicate return instructions into unconditional branches"));
50 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
53 class SimplifyCFGOpt {
54 const TargetData *const TD;
56 Value *isValueEqualityComparison(TerminatorInst *TI);
57 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
58 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases);
59 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
61 IRBuilder<> &Builder);
62 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
63 IRBuilder<> &Builder);
65 bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder);
66 bool SimplifyUnwind(UnwindInst *UI, IRBuilder<> &Builder);
67 bool SimplifyUnreachable(UnreachableInst *UI);
68 bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
69 bool SimplifyIndirectBr(IndirectBrInst *IBI);
70 bool SimplifyUncondBranch(BranchInst *BI, IRBuilder <> &Builder);
71 bool SimplifyCondBranch(BranchInst *BI, IRBuilder <>&Builder);
74 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
75 bool run(BasicBlock *BB);
79 /// SafeToMergeTerminators - Return true if it is safe to merge these two
80 /// terminator instructions together.
82 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
83 if (SI1 == SI2) return false; // Can't merge with self!
85 // It is not safe to merge these two switch instructions if they have a common
86 // successor, and if that successor has a PHI node, and if *that* PHI node has
87 // conflicting incoming values from the two switch blocks.
88 BasicBlock *SI1BB = SI1->getParent();
89 BasicBlock *SI2BB = SI2->getParent();
90 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
92 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
93 if (SI1Succs.count(*I))
94 for (BasicBlock::iterator BBI = (*I)->begin();
95 isa<PHINode>(BBI); ++BBI) {
96 PHINode *PN = cast<PHINode>(BBI);
97 if (PN->getIncomingValueForBlock(SI1BB) !=
98 PN->getIncomingValueForBlock(SI2BB))
105 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
106 /// now be entries in it from the 'NewPred' block. The values that will be
107 /// flowing into the PHI nodes will be the same as those coming in from
108 /// ExistPred, an existing predecessor of Succ.
109 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
110 BasicBlock *ExistPred) {
111 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
114 for (BasicBlock::iterator I = Succ->begin();
115 (PN = dyn_cast<PHINode>(I)); ++I)
116 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
120 /// GetIfCondition - Given a basic block (BB) with two predecessors (and at
121 /// least one PHI node in it), check to see if the merge at this block is due
122 /// to an "if condition". If so, return the boolean condition that determines
123 /// which entry into BB will be taken. Also, return by references the block
124 /// that will be entered from if the condition is true, and the block that will
125 /// be entered if the condition is false.
127 /// This does no checking to see if the true/false blocks have large or unsavory
128 /// instructions in them.
129 static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
130 BasicBlock *&IfFalse) {
131 PHINode *SomePHI = cast<PHINode>(BB->begin());
132 assert(SomePHI->getNumIncomingValues() == 2 &&
133 "Function can only handle blocks with 2 predecessors!");
134 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
135 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
137 // We can only handle branches. Other control flow will be lowered to
138 // branches if possible anyway.
139 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
140 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
141 if (Pred1Br == 0 || Pred2Br == 0)
144 // Eliminate code duplication by ensuring that Pred1Br is conditional if
146 if (Pred2Br->isConditional()) {
147 // If both branches are conditional, we don't have an "if statement". In
148 // reality, we could transform this case, but since the condition will be
149 // required anyway, we stand no chance of eliminating it, so the xform is
150 // probably not profitable.
151 if (Pred1Br->isConditional())
154 std::swap(Pred1, Pred2);
155 std::swap(Pred1Br, Pred2Br);
158 if (Pred1Br->isConditional()) {
159 // The only thing we have to watch out for here is to make sure that Pred2
160 // doesn't have incoming edges from other blocks. If it does, the condition
161 // doesn't dominate BB.
162 if (Pred2->getSinglePredecessor() == 0)
165 // If we found a conditional branch predecessor, make sure that it branches
166 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
167 if (Pred1Br->getSuccessor(0) == BB &&
168 Pred1Br->getSuccessor(1) == Pred2) {
171 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
172 Pred1Br->getSuccessor(1) == BB) {
176 // We know that one arm of the conditional goes to BB, so the other must
177 // go somewhere unrelated, and this must not be an "if statement".
181 return Pred1Br->getCondition();
184 // Ok, if we got here, both predecessors end with an unconditional branch to
185 // BB. Don't panic! If both blocks only have a single (identical)
186 // predecessor, and THAT is a conditional branch, then we're all ok!
187 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
188 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
191 // Otherwise, if this is a conditional branch, then we can use it!
192 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
193 if (BI == 0) return 0;
195 assert(BI->isConditional() && "Two successors but not conditional?");
196 if (BI->getSuccessor(0) == Pred1) {
203 return BI->getCondition();
206 /// DominatesMergePoint - If we have a merge point of an "if condition" as
207 /// accepted above, return true if the specified value dominates the block. We
208 /// don't handle the true generality of domination here, just a special case
209 /// which works well enough for us.
211 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
212 /// see if V (which must be an instruction) and its recursive operands
213 /// that do not dominate BB have a combined cost lower than CostRemaining and
214 /// are non-trapping. If both are true, the instruction is inserted into the
215 /// set and true is returned.
217 /// The cost for most non-trapping instructions is defined as 1 except for
218 /// Select whose cost is 2.
220 /// After this function returns, CostRemaining is decreased by the cost of
221 /// V plus its non-dominating operands. If that cost is greater than
222 /// CostRemaining, false is returned and CostRemaining is undefined.
223 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
224 SmallPtrSet<Instruction*, 4> *AggressiveInsts,
225 unsigned &CostRemaining) {
226 Instruction *I = dyn_cast<Instruction>(V);
228 // Non-instructions all dominate instructions, but not all constantexprs
229 // can be executed unconditionally.
230 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
235 BasicBlock *PBB = I->getParent();
237 // We don't want to allow weird loops that might have the "if condition" in
238 // the bottom of this block.
239 if (PBB == BB) return false;
241 // If this instruction is defined in a block that contains an unconditional
242 // branch to BB, then it must be in the 'conditional' part of the "if
243 // statement". If not, it definitely dominates the region.
244 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
245 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB)
248 // If we aren't allowing aggressive promotion anymore, then don't consider
249 // instructions in the 'if region'.
250 if (AggressiveInsts == 0) return false;
252 // If we have seen this instruction before, don't count it again.
253 if (AggressiveInsts->count(I)) return true;
255 // Okay, it looks like the instruction IS in the "condition". Check to
256 // see if it's a cheap instruction to unconditionally compute, and if it
257 // only uses stuff defined outside of the condition. If so, hoist it out.
258 if (!I->isSafeToSpeculativelyExecute())
263 switch (I->getOpcode()) {
264 default: return false; // Cannot hoist this out safely.
265 case Instruction::Load:
266 // We have to check to make sure there are no instructions before the
267 // load in its basic block, as we are going to hoist the load out to its
269 if (PBB->getFirstNonPHIOrDbg() != I)
273 case Instruction::GetElementPtr:
274 // GEPs are cheap if all indices are constant.
275 if (!cast<GetElementPtrInst>(I)->hasAllConstantIndices())
279 case Instruction::Add:
280 case Instruction::Sub:
281 case Instruction::And:
282 case Instruction::Or:
283 case Instruction::Xor:
284 case Instruction::Shl:
285 case Instruction::LShr:
286 case Instruction::AShr:
287 case Instruction::ICmp:
288 case Instruction::Trunc:
289 case Instruction::ZExt:
290 case Instruction::SExt:
292 break; // These are all cheap and non-trapping instructions.
294 case Instruction::Select:
299 if (Cost > CostRemaining)
302 CostRemaining -= Cost;
304 // Okay, we can only really hoist these out if their operands do
305 // not take us over the cost threshold.
306 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
307 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining))
309 // Okay, it's safe to do this! Remember this instruction.
310 AggressiveInsts->insert(I);
314 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
315 /// and PointerNullValue. Return NULL if value is not a constant int.
316 static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
317 // Normal constant int.
318 ConstantInt *CI = dyn_cast<ConstantInt>(V);
319 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
322 // This is some kind of pointer constant. Turn it into a pointer-sized
323 // ConstantInt if possible.
324 const IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
326 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
327 if (isa<ConstantPointerNull>(V))
328 return ConstantInt::get(PtrTy, 0);
330 // IntToPtr const int.
331 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
332 if (CE->getOpcode() == Instruction::IntToPtr)
333 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
334 // The constant is very likely to have the right type already.
335 if (CI->getType() == PtrTy)
338 return cast<ConstantInt>
339 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
344 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
345 /// collection of icmp eq/ne instructions that compare a value against a
346 /// constant, return the value being compared, and stick the constant into the
349 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
350 const TargetData *TD, bool isEQ, unsigned &UsedICmps) {
351 Instruction *I = dyn_cast<Instruction>(V);
352 if (I == 0) return 0;
354 // If this is an icmp against a constant, handle this as one of the cases.
355 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
356 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
357 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
360 return I->getOperand(0);
363 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
366 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
368 // If this is an and/!= check then we want to optimize "x ugt 2" into
371 Span = Span.inverse();
373 // If there are a ton of values, we don't want to make a ginormous switch.
374 if (Span.getSetSize().ugt(8) || Span.isEmptySet() ||
375 // We don't handle wrapped sets yet.
379 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
380 Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
382 return I->getOperand(0);
387 // Otherwise, we can only handle an | or &, depending on isEQ.
388 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
391 unsigned NumValsBeforeLHS = Vals.size();
392 unsigned UsedICmpsBeforeLHS = UsedICmps;
393 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
395 unsigned NumVals = Vals.size();
396 unsigned UsedICmpsBeforeRHS = UsedICmps;
397 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
401 Vals.resize(NumVals);
402 UsedICmps = UsedICmpsBeforeRHS;
405 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
406 // set it and return success.
407 if (Extra == 0 || Extra == I->getOperand(1)) {
408 Extra = I->getOperand(1);
412 Vals.resize(NumValsBeforeLHS);
413 UsedICmps = UsedICmpsBeforeLHS;
417 // If the LHS can't be folded in, but Extra is available and RHS can, try to
419 if (Extra == 0 || Extra == I->getOperand(0)) {
420 Value *OldExtra = Extra;
421 Extra = I->getOperand(0);
422 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
425 assert(Vals.size() == NumValsBeforeLHS);
432 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
433 Instruction* Cond = 0;
434 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
435 Cond = dyn_cast<Instruction>(SI->getCondition());
436 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
437 if (BI->isConditional())
438 Cond = dyn_cast<Instruction>(BI->getCondition());
439 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
440 Cond = dyn_cast<Instruction>(IBI->getAddress());
443 TI->eraseFromParent();
444 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
447 /// isValueEqualityComparison - Return true if the specified terminator checks
448 /// to see if a value is equal to constant integer value.
449 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
451 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
452 // Do not permit merging of large switch instructions into their
453 // predecessors unless there is only one predecessor.
454 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
455 pred_end(SI->getParent())) <= 128)
456 CV = SI->getCondition();
457 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
458 if (BI->isConditional() && BI->getCondition()->hasOneUse())
459 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
460 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
461 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
462 GetConstantInt(ICI->getOperand(1), TD))
463 CV = ICI->getOperand(0);
465 // Unwrap any lossless ptrtoint cast.
466 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
467 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
468 CV = PTII->getOperand(0);
472 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
473 /// decode all of the 'cases' that it represents and return the 'default' block.
474 BasicBlock *SimplifyCFGOpt::
475 GetValueEqualityComparisonCases(TerminatorInst *TI,
476 std::vector<std::pair<ConstantInt*,
477 BasicBlock*> > &Cases) {
478 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
479 Cases.reserve(SI->getNumCases());
480 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
481 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
482 return SI->getDefaultDest();
485 BranchInst *BI = cast<BranchInst>(TI);
486 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
487 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD),
488 BI->getSuccessor(ICI->getPredicate() ==
489 ICmpInst::ICMP_NE)));
490 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
494 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
495 /// in the list that match the specified block.
496 static void EliminateBlockCases(BasicBlock *BB,
497 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
498 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
499 if (Cases[i].second == BB) {
500 Cases.erase(Cases.begin()+i);
505 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
508 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
509 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
510 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
512 // Make V1 be smaller than V2.
513 if (V1->size() > V2->size())
516 if (V1->size() == 0) return false;
517 if (V1->size() == 1) {
519 ConstantInt *TheVal = (*V1)[0].first;
520 for (unsigned i = 0, e = V2->size(); i != e; ++i)
521 if (TheVal == (*V2)[i].first)
525 // Otherwise, just sort both lists and compare element by element.
526 array_pod_sort(V1->begin(), V1->end());
527 array_pod_sort(V2->begin(), V2->end());
528 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
529 while (i1 != e1 && i2 != e2) {
530 if ((*V1)[i1].first == (*V2)[i2].first)
532 if ((*V1)[i1].first < (*V2)[i2].first)
540 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
541 /// terminator instruction and its block is known to only have a single
542 /// predecessor block, check to see if that predecessor is also a value
543 /// comparison with the same value, and if that comparison determines the
544 /// outcome of this comparison. If so, simplify TI. This does a very limited
545 /// form of jump threading.
546 bool SimplifyCFGOpt::
547 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
549 IRBuilder<> &Builder) {
550 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
551 if (!PredVal) return false; // Not a value comparison in predecessor.
553 Value *ThisVal = isValueEqualityComparison(TI);
554 assert(ThisVal && "This isn't a value comparison!!");
555 if (ThisVal != PredVal) return false; // Different predicates.
557 // Find out information about when control will move from Pred to TI's block.
558 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
559 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
561 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
563 // Find information about how control leaves this block.
564 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
565 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
566 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
568 // If TI's block is the default block from Pred's comparison, potentially
569 // simplify TI based on this knowledge.
570 if (PredDef == TI->getParent()) {
571 // If we are here, we know that the value is none of those cases listed in
572 // PredCases. If there are any cases in ThisCases that are in PredCases, we
574 if (!ValuesOverlap(PredCases, ThisCases))
577 if (isa<BranchInst>(TI)) {
578 // Okay, one of the successors of this condbr is dead. Convert it to a
580 assert(ThisCases.size() == 1 && "Branch can only have one case!");
581 // Insert the new branch.
582 Instruction *NI = Builder.CreateBr(ThisDef);
585 // Remove PHI node entries for the dead edge.
586 ThisCases[0].second->removePredecessor(TI->getParent());
588 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
589 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
591 EraseTerminatorInstAndDCECond(TI);
595 SwitchInst *SI = cast<SwitchInst>(TI);
596 // Okay, TI has cases that are statically dead, prune them away.
597 SmallPtrSet<Constant*, 16> DeadCases;
598 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
599 DeadCases.insert(PredCases[i].first);
601 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
602 << "Through successor TI: " << *TI);
604 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
605 if (DeadCases.count(SI->getCaseValue(i))) {
606 SI->getSuccessor(i)->removePredecessor(TI->getParent());
610 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
614 // Otherwise, TI's block must correspond to some matched value. Find out
615 // which value (or set of values) this is.
616 ConstantInt *TIV = 0;
617 BasicBlock *TIBB = TI->getParent();
618 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
619 if (PredCases[i].second == TIBB) {
621 return false; // Cannot handle multiple values coming to this block.
622 TIV = PredCases[i].first;
624 assert(TIV && "No edge from pred to succ?");
626 // Okay, we found the one constant that our value can be if we get into TI's
627 // BB. Find out which successor will unconditionally be branched to.
628 BasicBlock *TheRealDest = 0;
629 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
630 if (ThisCases[i].first == TIV) {
631 TheRealDest = ThisCases[i].second;
635 // If not handled by any explicit cases, it is handled by the default case.
636 if (TheRealDest == 0) TheRealDest = ThisDef;
638 // Remove PHI node entries for dead edges.
639 BasicBlock *CheckEdge = TheRealDest;
640 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
641 if (*SI != CheckEdge)
642 (*SI)->removePredecessor(TIBB);
646 // Insert the new branch.
647 Instruction *NI = Builder.CreateBr(TheRealDest);
650 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
651 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
653 EraseTerminatorInstAndDCECond(TI);
658 /// ConstantIntOrdering - This class implements a stable ordering of constant
659 /// integers that does not depend on their address. This is important for
660 /// applications that sort ConstantInt's to ensure uniqueness.
661 struct ConstantIntOrdering {
662 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
663 return LHS->getValue().ult(RHS->getValue());
668 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
669 const ConstantInt *LHS = *(const ConstantInt**)P1;
670 const ConstantInt *RHS = *(const ConstantInt**)P2;
671 if (LHS->getValue().ult(RHS->getValue()))
673 if (LHS->getValue() == RHS->getValue())
678 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
679 /// equality comparison instruction (either a switch or a branch on "X == c").
680 /// See if any of the predecessors of the terminator block are value comparisons
681 /// on the same value. If so, and if safe to do so, fold them together.
682 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
683 IRBuilder<> &Builder) {
684 BasicBlock *BB = TI->getParent();
685 Value *CV = isValueEqualityComparison(TI); // CondVal
686 assert(CV && "Not a comparison?");
687 bool Changed = false;
689 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
690 while (!Preds.empty()) {
691 BasicBlock *Pred = Preds.pop_back_val();
693 // See if the predecessor is a comparison with the same value.
694 TerminatorInst *PTI = Pred->getTerminator();
695 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
697 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
698 // Figure out which 'cases' to copy from SI to PSI.
699 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
700 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
702 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
703 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
705 // Based on whether the default edge from PTI goes to BB or not, fill in
706 // PredCases and PredDefault with the new switch cases we would like to
708 SmallVector<BasicBlock*, 8> NewSuccessors;
710 if (PredDefault == BB) {
711 // If this is the default destination from PTI, only the edges in TI
712 // that don't occur in PTI, or that branch to BB will be activated.
713 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
714 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
715 if (PredCases[i].second != BB)
716 PTIHandled.insert(PredCases[i].first);
718 // The default destination is BB, we don't need explicit targets.
719 std::swap(PredCases[i], PredCases.back());
720 PredCases.pop_back();
724 // Reconstruct the new switch statement we will be building.
725 if (PredDefault != BBDefault) {
726 PredDefault->removePredecessor(Pred);
727 PredDefault = BBDefault;
728 NewSuccessors.push_back(BBDefault);
730 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
731 if (!PTIHandled.count(BBCases[i].first) &&
732 BBCases[i].second != BBDefault) {
733 PredCases.push_back(BBCases[i]);
734 NewSuccessors.push_back(BBCases[i].second);
738 // If this is not the default destination from PSI, only the edges
739 // in SI that occur in PSI with a destination of BB will be
741 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
742 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
743 if (PredCases[i].second == BB) {
744 PTIHandled.insert(PredCases[i].first);
745 std::swap(PredCases[i], PredCases.back());
746 PredCases.pop_back();
750 // Okay, now we know which constants were sent to BB from the
751 // predecessor. Figure out where they will all go now.
752 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
753 if (PTIHandled.count(BBCases[i].first)) {
754 // If this is one we are capable of getting...
755 PredCases.push_back(BBCases[i]);
756 NewSuccessors.push_back(BBCases[i].second);
757 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
760 // If there are any constants vectored to BB that TI doesn't handle,
761 // they must go to the default destination of TI.
762 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
764 E = PTIHandled.end(); I != E; ++I) {
765 PredCases.push_back(std::make_pair(*I, BBDefault));
766 NewSuccessors.push_back(BBDefault);
770 // Okay, at this point, we know which new successor Pred will get. Make
771 // sure we update the number of entries in the PHI nodes for these
773 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
774 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
776 Builder.SetInsertPoint(PTI);
777 // Convert pointer to int before we switch.
778 if (CV->getType()->isPointerTy()) {
779 assert(TD && "Cannot switch on pointer without TargetData");
780 CV = Builder.CreatePtrToInt(CV, TD->getIntPtrType(CV->getContext()),
784 // Now that the successors are updated, create the new Switch instruction.
785 SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault,
787 NewSI->setDebugLoc(PTI->getDebugLoc());
788 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
789 NewSI->addCase(PredCases[i].first, PredCases[i].second);
791 EraseTerminatorInstAndDCECond(PTI);
793 // Okay, last check. If BB is still a successor of PSI, then we must
794 // have an infinite loop case. If so, add an infinitely looping block
795 // to handle the case to preserve the behavior of the code.
796 BasicBlock *InfLoopBlock = 0;
797 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
798 if (NewSI->getSuccessor(i) == BB) {
799 if (InfLoopBlock == 0) {
800 // Insert it at the end of the function, because it's either code,
801 // or it won't matter if it's hot. :)
802 InfLoopBlock = BasicBlock::Create(BB->getContext(),
803 "infloop", BB->getParent());
804 BranchInst::Create(InfLoopBlock, InfLoopBlock);
806 NewSI->setSuccessor(i, InfLoopBlock);
815 // isSafeToHoistInvoke - If we would need to insert a select that uses the
816 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
817 // would need to do this), we can't hoist the invoke, as there is nowhere
818 // to put the select in this case.
819 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
820 Instruction *I1, Instruction *I2) {
821 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
823 for (BasicBlock::iterator BBI = SI->begin();
824 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
825 Value *BB1V = PN->getIncomingValueForBlock(BB1);
826 Value *BB2V = PN->getIncomingValueForBlock(BB2);
827 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
835 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
836 /// BB2, hoist any common code in the two blocks up into the branch block. The
837 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
838 static bool HoistThenElseCodeToIf(BranchInst *BI) {
839 // This does very trivial matching, with limited scanning, to find identical
840 // instructions in the two blocks. In particular, we don't want to get into
841 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
842 // such, we currently just scan for obviously identical instructions in an
844 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
845 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
847 BasicBlock::iterator BB1_Itr = BB1->begin();
848 BasicBlock::iterator BB2_Itr = BB2->begin();
850 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
851 // Skip debug info if it is not identical.
852 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
853 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
854 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
855 while (isa<DbgInfoIntrinsic>(I1))
857 while (isa<DbgInfoIntrinsic>(I2))
860 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
861 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
864 // If we get here, we can hoist at least one instruction.
865 BasicBlock *BIParent = BI->getParent();
868 // If we are hoisting the terminator instruction, don't move one (making a
869 // broken BB), instead clone it, and remove BI.
870 if (isa<TerminatorInst>(I1))
871 goto HoistTerminator;
873 // For a normal instruction, we just move one to right before the branch,
874 // then replace all uses of the other with the first. Finally, we remove
875 // the now redundant second instruction.
876 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
877 if (!I2->use_empty())
878 I2->replaceAllUsesWith(I1);
879 I1->intersectOptionalDataWith(I2);
880 I2->eraseFromParent();
884 // Skip debug info if it is not identical.
885 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
886 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
887 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
888 while (isa<DbgInfoIntrinsic>(I1))
890 while (isa<DbgInfoIntrinsic>(I2))
893 } while (I1->isIdenticalToWhenDefined(I2));
898 // It may not be possible to hoist an invoke.
899 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
902 // Okay, it is safe to hoist the terminator.
903 Instruction *NT = I1->clone();
904 BIParent->getInstList().insert(BI, NT);
905 if (!NT->getType()->isVoidTy()) {
906 I1->replaceAllUsesWith(NT);
907 I2->replaceAllUsesWith(NT);
911 // Hoisting one of the terminators from our successor is a great thing.
912 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
913 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
914 // nodes, so we insert select instruction to compute the final result.
915 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
916 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
918 for (BasicBlock::iterator BBI = SI->begin();
919 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
920 Value *BB1V = PN->getIncomingValueForBlock(BB1);
921 Value *BB2V = PN->getIncomingValueForBlock(BB2);
922 if (BB1V == BB2V) continue;
924 // These values do not agree. Insert a select instruction before NT
925 // that determines the right value.
926 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
928 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
929 BB1V->getName()+"."+BB2V->getName(), NT);
930 SI->setDebugLoc(BI->getDebugLoc());
932 // Make the PHI node use the select for all incoming values for BB1/BB2
933 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
934 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
935 PN->setIncomingValue(i, SI);
939 // Update any PHI nodes in our new successors.
940 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
941 AddPredecessorToBlock(*SI, BIParent, BB1);
943 EraseTerminatorInstAndDCECond(BI);
947 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
948 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
949 /// (for now, restricted to a single instruction that's side effect free) from
950 /// the BB1 into the branch block to speculatively execute it.
951 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
952 // Only speculatively execution a single instruction (not counting the
953 // terminator) for now.
954 Instruction *HInst = NULL;
955 Instruction *Term = BB1->getTerminator();
956 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
958 Instruction *I = BBI;
960 if (isa<DbgInfoIntrinsic>(I)) continue;
961 if (I == Term) break;
970 // Be conservative for now. FP select instruction can often be expensive.
971 Value *BrCond = BI->getCondition();
972 if (isa<FCmpInst>(BrCond))
975 // If BB1 is actually on the false edge of the conditional branch, remember
976 // to swap the select operands later.
978 if (BB1 != BI->getSuccessor(0)) {
979 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
986 // br i1 %t1, label %BB1, label %BB2
995 // %t3 = select i1 %t1, %t2, %t3
996 switch (HInst->getOpcode()) {
997 default: return false; // Not safe / profitable to hoist.
998 case Instruction::Add:
999 case Instruction::Sub:
1000 // Not worth doing for vector ops.
1001 if (HInst->getType()->isVectorTy())
1004 case Instruction::And:
1005 case Instruction::Or:
1006 case Instruction::Xor:
1007 case Instruction::Shl:
1008 case Instruction::LShr:
1009 case Instruction::AShr:
1010 // Don't mess with vector operations.
1011 if (HInst->getType()->isVectorTy())
1013 break; // These are all cheap and non-trapping instructions.
1016 // If the instruction is obviously dead, don't try to predicate it.
1017 if (HInst->use_empty()) {
1018 HInst->eraseFromParent();
1022 // Can we speculatively execute the instruction? And what is the value
1023 // if the condition is false? Consider the phi uses, if the incoming value
1024 // from the "if" block are all the same V, then V is the value of the
1025 // select if the condition is false.
1026 BasicBlock *BIParent = BI->getParent();
1027 SmallVector<PHINode*, 4> PHIUses;
1028 Value *FalseV = NULL;
1030 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
1031 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
1033 // Ignore any user that is not a PHI node in BB2. These can only occur in
1034 // unreachable blocks, because they would not be dominated by the instr.
1035 PHINode *PN = dyn_cast<PHINode>(*UI);
1036 if (!PN || PN->getParent() != BB2)
1038 PHIUses.push_back(PN);
1040 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1043 else if (FalseV != PHIV)
1044 return false; // Inconsistent value when condition is false.
1047 assert(FalseV && "Must have at least one user, and it must be a PHI");
1049 // Do not hoist the instruction if any of its operands are defined but not
1050 // used in this BB. The transformation will prevent the operand from
1051 // being sunk into the use block.
1052 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1054 Instruction *OpI = dyn_cast<Instruction>(*i);
1055 if (OpI && OpI->getParent() == BIParent &&
1056 !OpI->isUsedInBasicBlock(BIParent))
1060 // If we get here, we can hoist the instruction. Try to place it
1061 // before the icmp instruction preceding the conditional branch.
1062 BasicBlock::iterator InsertPos = BI;
1063 if (InsertPos != BIParent->begin())
1065 // Skip debug info between condition and branch.
1066 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
1068 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
1069 SmallPtrSet<Instruction *, 4> BB1Insns;
1070 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
1071 BB1I != BB1E; ++BB1I)
1072 BB1Insns.insert(BB1I);
1073 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
1075 Instruction *Use = cast<Instruction>(*UI);
1076 if (!BB1Insns.count(Use)) continue;
1078 // If BrCond uses the instruction that place it just before
1079 // branch instruction.
1085 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
1087 // Create a select whose true value is the speculatively executed value and
1088 // false value is the previously determined FalseV.
1091 SI = SelectInst::Create(BrCond, FalseV, HInst,
1092 FalseV->getName() + "." + HInst->getName(), BI);
1094 SI = SelectInst::Create(BrCond, HInst, FalseV,
1095 HInst->getName() + "." + FalseV->getName(), BI);
1096 SI->setDebugLoc(BI->getDebugLoc());
1098 // Make the PHI node use the select for all incoming values for "then" and
1100 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1101 PHINode *PN = PHIUses[i];
1102 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1103 if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent)
1104 PN->setIncomingValue(j, SI);
1111 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1112 /// across this block.
1113 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1114 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1117 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1118 if (isa<DbgInfoIntrinsic>(BBI))
1120 if (Size > 10) return false; // Don't clone large BB's.
1123 // We can only support instructions that do not define values that are
1124 // live outside of the current basic block.
1125 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1127 Instruction *U = cast<Instruction>(*UI);
1128 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1131 // Looks ok, continue checking.
1137 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1138 /// that is defined in the same block as the branch and if any PHI entries are
1139 /// constants, thread edges corresponding to that entry to be branches to their
1140 /// ultimate destination.
1141 static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
1142 BasicBlock *BB = BI->getParent();
1143 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1144 // NOTE: we currently cannot transform this case if the PHI node is used
1145 // outside of the block.
1146 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1149 // Degenerate case of a single entry PHI.
1150 if (PN->getNumIncomingValues() == 1) {
1151 FoldSingleEntryPHINodes(PN->getParent());
1155 // Now we know that this block has multiple preds and two succs.
1156 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1158 // Okay, this is a simple enough basic block. See if any phi values are
1160 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1161 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1162 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1164 // Okay, we now know that all edges from PredBB should be revectored to
1165 // branch to RealDest.
1166 BasicBlock *PredBB = PN->getIncomingBlock(i);
1167 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1169 if (RealDest == BB) continue; // Skip self loops.
1171 // The dest block might have PHI nodes, other predecessors and other
1172 // difficult cases. Instead of being smart about this, just insert a new
1173 // block that jumps to the destination block, effectively splitting
1174 // the edge we are about to create.
1175 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1176 RealDest->getName()+".critedge",
1177 RealDest->getParent(), RealDest);
1178 BranchInst::Create(RealDest, EdgeBB);
1180 // Update PHI nodes.
1181 AddPredecessorToBlock(RealDest, EdgeBB, BB);
1183 // BB may have instructions that are being threaded over. Clone these
1184 // instructions into EdgeBB. We know that there will be no uses of the
1185 // cloned instructions outside of EdgeBB.
1186 BasicBlock::iterator InsertPt = EdgeBB->begin();
1187 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1188 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1189 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1190 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1193 // Clone the instruction.
1194 Instruction *N = BBI->clone();
1195 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1197 // Update operands due to translation.
1198 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1200 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1201 if (PI != TranslateMap.end())
1205 // Check for trivial simplification.
1206 if (Value *V = SimplifyInstruction(N, TD)) {
1207 TranslateMap[BBI] = V;
1208 delete N; // Instruction folded away, don't need actual inst
1210 // Insert the new instruction into its new home.
1211 EdgeBB->getInstList().insert(InsertPt, N);
1212 if (!BBI->use_empty())
1213 TranslateMap[BBI] = N;
1217 // Loop over all of the edges from PredBB to BB, changing them to branch
1218 // to EdgeBB instead.
1219 TerminatorInst *PredBBTI = PredBB->getTerminator();
1220 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1221 if (PredBBTI->getSuccessor(i) == BB) {
1222 BB->removePredecessor(PredBB);
1223 PredBBTI->setSuccessor(i, EdgeBB);
1226 // Recurse, simplifying any other constants.
1227 return FoldCondBranchOnPHI(BI, TD) | true;
1233 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1234 /// PHI node, see if we can eliminate it.
1235 static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD,
1236 IRBuilder<> &Builder) {
1237 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1238 // statement", which has a very simple dominance structure. Basically, we
1239 // are trying to find the condition that is being branched on, which
1240 // subsequently causes this merge to happen. We really want control
1241 // dependence information for this check, but simplifycfg can't keep it up
1242 // to date, and this catches most of the cases we care about anyway.
1243 BasicBlock *BB = PN->getParent();
1244 BasicBlock *IfTrue, *IfFalse;
1245 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1247 // Don't bother if the branch will be constant folded trivially.
1248 isa<ConstantInt>(IfCond))
1251 // Okay, we found that we can merge this two-entry phi node into a select.
1252 // Doing so would require us to fold *all* two entry phi nodes in this block.
1253 // At some point this becomes non-profitable (particularly if the target
1254 // doesn't support cmov's). Only do this transformation if there are two or
1255 // fewer PHI nodes in this block.
1256 unsigned NumPhis = 0;
1257 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1261 // Loop over the PHI's seeing if we can promote them all to select
1262 // instructions. While we are at it, keep track of the instructions
1263 // that need to be moved to the dominating block.
1264 SmallPtrSet<Instruction*, 4> AggressiveInsts;
1265 unsigned MaxCostVal0 = PHINodeFoldingThreshold,
1266 MaxCostVal1 = PHINodeFoldingThreshold;
1268 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1269 PHINode *PN = cast<PHINode>(II++);
1270 if (Value *V = SimplifyInstruction(PN, TD)) {
1271 PN->replaceAllUsesWith(V);
1272 PN->eraseFromParent();
1276 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
1278 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
1283 // If we folded the the first phi, PN dangles at this point. Refresh it. If
1284 // we ran out of PHIs then we simplified them all.
1285 PN = dyn_cast<PHINode>(BB->begin());
1286 if (PN == 0) return true;
1288 // Don't fold i1 branches on PHIs which contain binary operators. These can
1289 // often be turned into switches and other things.
1290 if (PN->getType()->isIntegerTy(1) &&
1291 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1292 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1293 isa<BinaryOperator>(IfCond)))
1296 // If we all PHI nodes are promotable, check to make sure that all
1297 // instructions in the predecessor blocks can be promoted as well. If
1298 // not, we won't be able to get rid of the control flow, so it's not
1299 // worth promoting to select instructions.
1300 BasicBlock *DomBlock = 0;
1301 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1302 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1303 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1306 DomBlock = *pred_begin(IfBlock1);
1307 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1308 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1309 // This is not an aggressive instruction that we can promote.
1310 // Because of this, we won't be able to get rid of the control
1311 // flow, so the xform is not worth it.
1316 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1319 DomBlock = *pred_begin(IfBlock2);
1320 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1321 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1322 // This is not an aggressive instruction that we can promote.
1323 // Because of this, we won't be able to get rid of the control
1324 // flow, so the xform is not worth it.
1329 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1330 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1332 // If we can still promote the PHI nodes after this gauntlet of tests,
1333 // do all of the PHI's now.
1334 Instruction *InsertPt = DomBlock->getTerminator();
1335 Builder.SetInsertPoint(InsertPt);
1337 // Move all 'aggressive' instructions, which are defined in the
1338 // conditional parts of the if's up to the dominating block.
1340 DomBlock->getInstList().splice(InsertPt,
1341 IfBlock1->getInstList(), IfBlock1->begin(),
1342 IfBlock1->getTerminator());
1344 DomBlock->getInstList().splice(InsertPt,
1345 IfBlock2->getInstList(), IfBlock2->begin(),
1346 IfBlock2->getTerminator());
1348 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1349 // Change the PHI node into a select instruction.
1350 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1351 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1354 cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, ""));
1355 PN->replaceAllUsesWith(NV);
1357 PN->eraseFromParent();
1360 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1361 // has been flattened. Change DomBlock to jump directly to our new block to
1362 // avoid other simplifycfg's kicking in on the diamond.
1363 TerminatorInst *OldTI = DomBlock->getTerminator();
1364 Builder.SetInsertPoint(OldTI);
1365 Builder.CreateBr(BB);
1366 OldTI->eraseFromParent();
1370 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1371 /// to two returning blocks, try to merge them together into one return,
1372 /// introducing a select if the return values disagree.
1373 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
1374 IRBuilder<> &Builder) {
1375 assert(BI->isConditional() && "Must be a conditional branch");
1376 BasicBlock *TrueSucc = BI->getSuccessor(0);
1377 BasicBlock *FalseSucc = BI->getSuccessor(1);
1378 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1379 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1381 // Check to ensure both blocks are empty (just a return) or optionally empty
1382 // with PHI nodes. If there are other instructions, merging would cause extra
1383 // computation on one path or the other.
1384 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1386 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1389 Builder.SetInsertPoint(BI);
1390 // Okay, we found a branch that is going to two return nodes. If
1391 // there is no return value for this function, just change the
1392 // branch into a return.
1393 if (FalseRet->getNumOperands() == 0) {
1394 TrueSucc->removePredecessor(BI->getParent());
1395 FalseSucc->removePredecessor(BI->getParent());
1396 Builder.CreateRetVoid();
1397 EraseTerminatorInstAndDCECond(BI);
1401 // Otherwise, figure out what the true and false return values are
1402 // so we can insert a new select instruction.
1403 Value *TrueValue = TrueRet->getReturnValue();
1404 Value *FalseValue = FalseRet->getReturnValue();
1406 // Unwrap any PHI nodes in the return blocks.
1407 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1408 if (TVPN->getParent() == TrueSucc)
1409 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1410 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1411 if (FVPN->getParent() == FalseSucc)
1412 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1414 // In order for this transformation to be safe, we must be able to
1415 // unconditionally execute both operands to the return. This is
1416 // normally the case, but we could have a potentially-trapping
1417 // constant expression that prevents this transformation from being
1419 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1422 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1426 // Okay, we collected all the mapped values and checked them for sanity, and
1427 // defined to really do this transformation. First, update the CFG.
1428 TrueSucc->removePredecessor(BI->getParent());
1429 FalseSucc->removePredecessor(BI->getParent());
1431 // Insert select instructions where needed.
1432 Value *BrCond = BI->getCondition();
1434 // Insert a select if the results differ.
1435 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1436 } else if (isa<UndefValue>(TrueValue)) {
1437 TrueValue = FalseValue;
1439 TrueValue = Builder.CreateSelect(BrCond, TrueValue,
1440 FalseValue, "retval");
1444 Value *RI = !TrueValue ?
1445 Builder.CreateRetVoid() : Builder.CreateRet(TrueValue);
1449 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1450 << "\n " << *BI << "NewRet = " << *RI
1451 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1453 EraseTerminatorInstAndDCECond(BI);
1458 /// FoldBranchToCommonDest - If this basic block is simple enough, and if a
1459 /// predecessor branches to us and one of our successors, fold the block into
1460 /// the predecessor and use logical operations to pick the right destination.
1461 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1462 BasicBlock *BB = BI->getParent();
1463 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1464 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1465 Cond->getParent() != BB || !Cond->hasOneUse())
1468 // Only allow this if the condition is a simple instruction that can be
1469 // executed unconditionally. It must be in the same block as the branch, and
1470 // must be at the front of the block.
1471 BasicBlock::iterator FrontIt = BB->front();
1473 // Ignore dbg intrinsics.
1474 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1476 // Allow a single instruction to be hoisted in addition to the compare
1477 // that feeds the branch. We later ensure that any values that _it_ uses
1478 // were also live in the predecessor, so that we don't unnecessarily create
1479 // register pressure or inhibit out-of-order execution.
1480 Instruction *BonusInst = 0;
1481 if (&*FrontIt != Cond &&
1482 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1483 FrontIt->isSafeToSpeculativelyExecute()) {
1484 BonusInst = &*FrontIt;
1487 // Ignore dbg intrinsics.
1488 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1491 // Only a single bonus inst is allowed.
1492 if (&*FrontIt != Cond)
1495 // Make sure the instruction after the condition is the cond branch.
1496 BasicBlock::iterator CondIt = Cond; ++CondIt;
1498 // Ingore dbg intrinsics.
1499 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
1504 // Cond is known to be a compare or binary operator. Check to make sure that
1505 // neither operand is a potentially-trapping constant expression.
1506 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1509 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1513 // Finally, don't infinitely unroll conditional loops.
1514 BasicBlock *TrueDest = BI->getSuccessor(0);
1515 BasicBlock *FalseDest = BI->getSuccessor(1);
1516 if (TrueDest == BB || FalseDest == BB)
1519 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1520 BasicBlock *PredBlock = *PI;
1521 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1523 // Check that we have two conditional branches. If there is a PHI node in
1524 // the common successor, verify that the same value flows in from both
1526 if (PBI == 0 || PBI->isUnconditional() || !SafeToMergeTerminators(BI, PBI))
1529 // Determine if the two branches share a common destination.
1530 Instruction::BinaryOps Opc;
1531 bool InvertPredCond = false;
1533 if (PBI->getSuccessor(0) == TrueDest)
1534 Opc = Instruction::Or;
1535 else if (PBI->getSuccessor(1) == FalseDest)
1536 Opc = Instruction::And;
1537 else if (PBI->getSuccessor(0) == FalseDest)
1538 Opc = Instruction::And, InvertPredCond = true;
1539 else if (PBI->getSuccessor(1) == TrueDest)
1540 Opc = Instruction::Or, InvertPredCond = true;
1544 // Ensure that any values used in the bonus instruction are also used
1545 // by the terminator of the predecessor. This means that those values
1546 // must already have been resolved, so we won't be inhibiting the
1547 // out-of-order core by speculating them earlier.
1549 // Collect the values used by the bonus inst
1550 SmallPtrSet<Value*, 4> UsedValues;
1551 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1552 OE = BonusInst->op_end(); OI != OE; ++OI) {
1554 if (!isa<Constant>(V))
1555 UsedValues.insert(V);
1558 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1559 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1561 // Walk up to four levels back up the use-def chain of the predecessor's
1562 // terminator to see if all those values were used. The choice of four
1563 // levels is arbitrary, to provide a compile-time-cost bound.
1564 while (!Worklist.empty()) {
1565 std::pair<Value*, unsigned> Pair = Worklist.back();
1566 Worklist.pop_back();
1568 if (Pair.second >= 4) continue;
1569 UsedValues.erase(Pair.first);
1570 if (UsedValues.empty()) break;
1572 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
1573 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1575 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1579 if (!UsedValues.empty()) return false;
1582 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1584 // If we need to invert the condition in the pred block to match, do so now.
1585 if (InvertPredCond) {
1586 Value *NewCond = PBI->getCondition();
1588 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
1589 CmpInst *CI = cast<CmpInst>(NewCond);
1590 CI->setPredicate(CI->getInversePredicate());
1592 NewCond = BinaryOperator::CreateNot(NewCond,
1593 PBI->getCondition()->getName()+".not", PBI);
1596 PBI->setCondition(NewCond);
1597 BasicBlock *OldTrue = PBI->getSuccessor(0);
1598 BasicBlock *OldFalse = PBI->getSuccessor(1);
1599 PBI->setSuccessor(0, OldFalse);
1600 PBI->setSuccessor(1, OldTrue);
1603 // If we have a bonus inst, clone it into the predecessor block.
1604 Instruction *NewBonus = 0;
1606 NewBonus = BonusInst->clone();
1607 PredBlock->getInstList().insert(PBI, NewBonus);
1608 NewBonus->takeName(BonusInst);
1609 BonusInst->setName(BonusInst->getName()+".old");
1612 // Clone Cond into the predecessor basic block, and or/and the
1613 // two conditions together.
1614 Instruction *New = Cond->clone();
1615 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1616 PredBlock->getInstList().insert(PBI, New);
1617 New->takeName(Cond);
1618 Cond->setName(New->getName()+".old");
1620 Instruction *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1621 New, "or.cond", PBI);
1622 NewCond->setDebugLoc(PBI->getDebugLoc());
1623 PBI->setCondition(NewCond);
1624 if (PBI->getSuccessor(0) == BB) {
1625 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1626 PBI->setSuccessor(0, TrueDest);
1628 if (PBI->getSuccessor(1) == BB) {
1629 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1630 PBI->setSuccessor(1, FalseDest);
1633 // Copy any debug value intrinsics into the end of PredBlock.
1634 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
1635 if (isa<DbgInfoIntrinsic>(*I))
1636 I->clone()->insertBefore(PBI);
1643 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1644 /// predecessor of another block, this function tries to simplify it. We know
1645 /// that PBI and BI are both conditional branches, and BI is in one of the
1646 /// successor blocks of PBI - PBI branches to BI.
1647 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1648 assert(PBI->isConditional() && BI->isConditional());
1649 BasicBlock *BB = BI->getParent();
1651 // If this block ends with a branch instruction, and if there is a
1652 // predecessor that ends on a branch of the same condition, make
1653 // this conditional branch redundant.
1654 if (PBI->getCondition() == BI->getCondition() &&
1655 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1656 // Okay, the outcome of this conditional branch is statically
1657 // knowable. If this block had a single pred, handle specially.
1658 if (BB->getSinglePredecessor()) {
1659 // Turn this into a branch on constant.
1660 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1661 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1663 return true; // Nuke the branch on constant.
1666 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1667 // in the constant and simplify the block result. Subsequent passes of
1668 // simplifycfg will thread the block.
1669 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1670 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
1671 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1672 std::distance(PB, PE),
1673 BI->getCondition()->getName() + ".pr",
1675 // Okay, we're going to insert the PHI node. Since PBI is not the only
1676 // predecessor, compute the PHI'd conditional value for all of the preds.
1677 // Any predecessor where the condition is not computable we keep symbolic.
1678 for (pred_iterator PI = PB; PI != PE; ++PI) {
1679 BasicBlock *P = *PI;
1680 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
1681 PBI != BI && PBI->isConditional() &&
1682 PBI->getCondition() == BI->getCondition() &&
1683 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1684 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1685 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1688 NewPN->addIncoming(BI->getCondition(), P);
1692 BI->setCondition(NewPN);
1697 // If this is a conditional branch in an empty block, and if any
1698 // predecessors is a conditional branch to one of our destinations,
1699 // fold the conditions into logical ops and one cond br.
1700 BasicBlock::iterator BBI = BB->begin();
1701 // Ignore dbg intrinsics.
1702 while (isa<DbgInfoIntrinsic>(BBI))
1708 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1713 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1715 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1716 PBIOp = 0, BIOp = 1;
1717 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1718 PBIOp = 1, BIOp = 0;
1719 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1724 // Check to make sure that the other destination of this branch
1725 // isn't BB itself. If so, this is an infinite loop that will
1726 // keep getting unwound.
1727 if (PBI->getSuccessor(PBIOp) == BB)
1730 // Do not perform this transformation if it would require
1731 // insertion of a large number of select instructions. For targets
1732 // without predication/cmovs, this is a big pessimization.
1733 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1735 unsigned NumPhis = 0;
1736 for (BasicBlock::iterator II = CommonDest->begin();
1737 isa<PHINode>(II); ++II, ++NumPhis)
1738 if (NumPhis > 2) // Disable this xform.
1741 // Finally, if everything is ok, fold the branches to logical ops.
1742 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1744 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
1745 << "AND: " << *BI->getParent());
1748 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1749 // branch in it, where one edge (OtherDest) goes back to itself but the other
1750 // exits. We don't *know* that the program avoids the infinite loop
1751 // (even though that seems likely). If we do this xform naively, we'll end up
1752 // recursively unpeeling the loop. Since we know that (after the xform is
1753 // done) that the block *is* infinite if reached, we just make it an obviously
1754 // infinite loop with no cond branch.
1755 if (OtherDest == BB) {
1756 // Insert it at the end of the function, because it's either code,
1757 // or it won't matter if it's hot. :)
1758 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1759 "infloop", BB->getParent());
1760 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1761 OtherDest = InfLoopBlock;
1764 DEBUG(dbgs() << *PBI->getParent()->getParent());
1766 // BI may have other predecessors. Because of this, we leave
1767 // it alone, but modify PBI.
1769 // Make sure we get to CommonDest on True&True directions.
1770 Value *PBICond = PBI->getCondition();
1772 PBICond = BinaryOperator::CreateNot(PBICond,
1773 PBICond->getName()+".not",
1775 Value *BICond = BI->getCondition();
1777 BICond = BinaryOperator::CreateNot(BICond,
1778 BICond->getName()+".not",
1780 // Merge the conditions.
1781 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1783 // Modify PBI to branch on the new condition to the new dests.
1784 PBI->setCondition(Cond);
1785 PBI->setSuccessor(0, CommonDest);
1786 PBI->setSuccessor(1, OtherDest);
1788 // OtherDest may have phi nodes. If so, add an entry from PBI's
1789 // block that are identical to the entries for BI's block.
1790 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
1792 // We know that the CommonDest already had an edge from PBI to
1793 // it. If it has PHIs though, the PHIs may have different
1794 // entries for BB and PBI's BB. If so, insert a select to make
1797 for (BasicBlock::iterator II = CommonDest->begin();
1798 (PN = dyn_cast<PHINode>(II)); ++II) {
1799 Value *BIV = PN->getIncomingValueForBlock(BB);
1800 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1801 Value *PBIV = PN->getIncomingValue(PBBIdx);
1803 // Insert a select in PBI to pick the right value.
1804 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1805 PBIV->getName()+".mux", PBI);
1806 PN->setIncomingValue(PBBIdx, NV);
1810 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1811 DEBUG(dbgs() << *PBI->getParent()->getParent());
1813 // This basic block is probably dead. We know it has at least
1814 // one fewer predecessor.
1818 // SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
1819 // branch to TrueBB if Cond is true or to FalseBB if Cond is false.
1820 // Takes care of updating the successors and removing the old terminator.
1821 // Also makes sure not to introduce new successors by assuming that edges to
1822 // non-successor TrueBBs and FalseBBs aren't reachable.
1823 static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
1824 BasicBlock *TrueBB, BasicBlock *FalseBB){
1825 // Remove any superfluous successor edges from the CFG.
1826 // First, figure out which successors to preserve.
1827 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
1829 BasicBlock *KeepEdge1 = TrueBB;
1830 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
1832 // Then remove the rest.
1833 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
1834 BasicBlock *Succ = OldTerm->getSuccessor(I);
1835 // Make sure only to keep exactly one copy of each edge.
1836 if (Succ == KeepEdge1)
1838 else if (Succ == KeepEdge2)
1841 Succ->removePredecessor(OldTerm->getParent());
1844 IRBuilder<> Builder(OldTerm);
1845 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
1847 // Insert an appropriate new terminator.
1848 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
1849 if (TrueBB == FalseBB)
1850 // We were only looking for one successor, and it was present.
1851 // Create an unconditional branch to it.
1852 Builder.CreateBr(TrueBB);
1854 // We found both of the successors we were looking for.
1855 // Create a conditional branch sharing the condition of the select.
1856 Builder.CreateCondBr(Cond, TrueBB, FalseBB);
1857 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
1858 // Neither of the selected blocks were successors, so this
1859 // terminator must be unreachable.
1860 new UnreachableInst(OldTerm->getContext(), OldTerm);
1862 // One of the selected values was a successor, but the other wasn't.
1863 // Insert an unconditional branch to the one that was found;
1864 // the edge to the one that wasn't must be unreachable.
1866 // Only TrueBB was found.
1867 Builder.CreateBr(TrueBB);
1869 // Only FalseBB was found.
1870 Builder.CreateBr(FalseBB);
1873 EraseTerminatorInstAndDCECond(OldTerm);
1877 // SimplifySwitchOnSelect - Replaces
1878 // (switch (select cond, X, Y)) on constant X, Y
1879 // with a branch - conditional if X and Y lead to distinct BBs,
1880 // unconditional otherwise.
1881 static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
1882 // Check for constant integer values in the select.
1883 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
1884 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
1885 if (!TrueVal || !FalseVal)
1888 // Find the relevant condition and destinations.
1889 Value *Condition = Select->getCondition();
1890 BasicBlock *TrueBB = SI->getSuccessor(SI->findCaseValue(TrueVal));
1891 BasicBlock *FalseBB = SI->getSuccessor(SI->findCaseValue(FalseVal));
1893 // Perform the actual simplification.
1894 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB);
1897 // SimplifyIndirectBrOnSelect - Replaces
1898 // (indirectbr (select cond, blockaddress(@fn, BlockA),
1899 // blockaddress(@fn, BlockB)))
1901 // (br cond, BlockA, BlockB).
1902 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
1903 // Check that both operands of the select are block addresses.
1904 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
1905 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
1909 // Extract the actual blocks.
1910 BasicBlock *TrueBB = TBA->getBasicBlock();
1911 BasicBlock *FalseBB = FBA->getBasicBlock();
1913 // Perform the actual simplification.
1914 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB);
1917 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
1918 /// instruction (a seteq/setne with a constant) as the only instruction in a
1919 /// block that ends with an uncond branch. We are looking for a very specific
1920 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
1921 /// this case, we merge the first two "or's of icmp" into a switch, but then the
1922 /// default value goes to an uncond block with a seteq in it, we get something
1925 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
1927 /// %tmp = icmp eq i8 %A, 92
1930 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
1932 /// We prefer to split the edge to 'end' so that there is a true/false entry to
1933 /// the PHI, merging the third icmp into the switch.
1934 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
1935 const TargetData *TD,
1936 IRBuilder<> &Builder) {
1937 BasicBlock *BB = ICI->getParent();
1939 // If the block has any PHIs in it or the icmp has multiple uses, it is too
1941 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
1943 Value *V = ICI->getOperand(0);
1944 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
1946 // The pattern we're looking for is where our only predecessor is a switch on
1947 // 'V' and this block is the default case for the switch. In this case we can
1948 // fold the compared value into the switch to simplify things.
1949 BasicBlock *Pred = BB->getSinglePredecessor();
1950 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
1952 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
1953 if (SI->getCondition() != V)
1956 // If BB is reachable on a non-default case, then we simply know the value of
1957 // V in this block. Substitute it and constant fold the icmp instruction
1959 if (SI->getDefaultDest() != BB) {
1960 ConstantInt *VVal = SI->findCaseDest(BB);
1961 assert(VVal && "Should have a unique destination value");
1962 ICI->setOperand(0, VVal);
1964 if (Value *V = SimplifyInstruction(ICI, TD)) {
1965 ICI->replaceAllUsesWith(V);
1966 ICI->eraseFromParent();
1968 // BB is now empty, so it is likely to simplify away.
1969 return SimplifyCFG(BB) | true;
1972 // Ok, the block is reachable from the default dest. If the constant we're
1973 // comparing exists in one of the other edges, then we can constant fold ICI
1975 if (SI->findCaseValue(Cst) != 0) {
1977 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1978 V = ConstantInt::getFalse(BB->getContext());
1980 V = ConstantInt::getTrue(BB->getContext());
1982 ICI->replaceAllUsesWith(V);
1983 ICI->eraseFromParent();
1984 // BB is now empty, so it is likely to simplify away.
1985 return SimplifyCFG(BB) | true;
1988 // The use of the icmp has to be in the 'end' block, by the only PHI node in
1990 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
1991 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
1992 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
1993 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
1996 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
1998 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
1999 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
2001 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2002 std::swap(DefaultCst, NewCst);
2004 // Replace ICI (which is used by the PHI for the default value) with true or
2005 // false depending on if it is EQ or NE.
2006 ICI->replaceAllUsesWith(DefaultCst);
2007 ICI->eraseFromParent();
2009 // Okay, the switch goes to this block on a default value. Add an edge from
2010 // the switch to the merge point on the compared value.
2011 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
2012 BB->getParent(), BB);
2013 SI->addCase(Cst, NewBB);
2015 // NewBB branches to the phi block, add the uncond branch and the phi entry.
2016 Builder.SetInsertPoint(NewBB);
2017 Builder.SetCurrentDebugLocation(SI->getDebugLoc());
2018 Builder.CreateBr(SuccBlock);
2019 PHIUse->addIncoming(NewCst, NewBB);
2023 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
2024 /// Check to see if it is branching on an or/and chain of icmp instructions, and
2025 /// fold it into a switch instruction if so.
2026 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD,
2027 IRBuilder<> &Builder) {
2028 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
2029 if (Cond == 0) return false;
2032 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2033 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2034 // 'setne's and'ed together, collect them.
2036 std::vector<ConstantInt*> Values;
2037 bool TrueWhenEqual = true;
2038 Value *ExtraCase = 0;
2039 unsigned UsedICmps = 0;
2041 if (Cond->getOpcode() == Instruction::Or) {
2042 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
2044 } else if (Cond->getOpcode() == Instruction::And) {
2045 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
2047 TrueWhenEqual = false;
2050 // If we didn't have a multiply compared value, fail.
2051 if (CompVal == 0) return false;
2053 // Avoid turning single icmps into a switch.
2057 // There might be duplicate constants in the list, which the switch
2058 // instruction can't handle, remove them now.
2059 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
2060 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2062 // If Extra was used, we require at least two switch values to do the
2063 // transformation. A switch with one value is just an cond branch.
2064 if (ExtraCase && Values.size() < 2) return false;
2066 // Figure out which block is which destination.
2067 BasicBlock *DefaultBB = BI->getSuccessor(1);
2068 BasicBlock *EdgeBB = BI->getSuccessor(0);
2069 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2071 BasicBlock *BB = BI->getParent();
2073 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
2074 << " cases into SWITCH. BB is:\n" << *BB);
2076 // If there are any extra values that couldn't be folded into the switch
2077 // then we evaluate them with an explicit branch first. Split the block
2078 // right before the condbr to handle it.
2080 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
2081 // Remove the uncond branch added to the old block.
2082 TerminatorInst *OldTI = BB->getTerminator();
2083 Builder.SetInsertPoint(OldTI);
2086 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
2088 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
2090 OldTI->eraseFromParent();
2092 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
2093 // for the edge we just added.
2094 AddPredecessorToBlock(EdgeBB, BB, NewBB);
2096 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
2097 << "\nEXTRABB = " << *BB);
2101 Builder.SetInsertPoint(BI);
2102 // Convert pointer to int before we switch.
2103 if (CompVal->getType()->isPointerTy()) {
2104 assert(TD && "Cannot switch on pointer without TargetData");
2105 CompVal = Builder.CreatePtrToInt(CompVal,
2106 TD->getIntPtrType(CompVal->getContext()),
2110 // Create the new switch instruction now.
2111 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
2113 // Add all of the 'cases' to the switch instruction.
2114 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2115 New->addCase(Values[i], EdgeBB);
2117 // We added edges from PI to the EdgeBB. As such, if there were any
2118 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2119 // the number of edges added.
2120 for (BasicBlock::iterator BBI = EdgeBB->begin();
2121 isa<PHINode>(BBI); ++BBI) {
2122 PHINode *PN = cast<PHINode>(BBI);
2123 Value *InVal = PN->getIncomingValueForBlock(BB);
2124 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2125 PN->addIncoming(InVal, BB);
2128 // Erase the old branch instruction.
2129 EraseTerminatorInstAndDCECond(BI);
2131 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
2135 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
2136 BasicBlock *BB = RI->getParent();
2137 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2139 // Find predecessors that end with branches.
2140 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2141 SmallVector<BranchInst*, 8> CondBranchPreds;
2142 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2143 BasicBlock *P = *PI;
2144 TerminatorInst *PTI = P->getTerminator();
2145 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2146 if (BI->isUnconditional())
2147 UncondBranchPreds.push_back(P);
2149 CondBranchPreds.push_back(BI);
2153 // If we found some, do the transformation!
2154 if (!UncondBranchPreds.empty() && DupRet) {
2155 while (!UncondBranchPreds.empty()) {
2156 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2157 DEBUG(dbgs() << "FOLDING: " << *BB
2158 << "INTO UNCOND BRANCH PRED: " << *Pred);
2159 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
2162 // If we eliminated all predecessors of the block, delete the block now.
2163 if (pred_begin(BB) == pred_end(BB))
2164 // We know there are no successors, so just nuke the block.
2165 BB->eraseFromParent();
2170 // Check out all of the conditional branches going to this return
2171 // instruction. If any of them just select between returns, change the
2172 // branch itself into a select/return pair.
2173 while (!CondBranchPreds.empty()) {
2174 BranchInst *BI = CondBranchPreds.pop_back_val();
2176 // Check to see if the non-BB successor is also a return block.
2177 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2178 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2179 SimplifyCondBranchToTwoReturns(BI, Builder))
2185 bool SimplifyCFGOpt::SimplifyUnwind(UnwindInst *UI, IRBuilder<> &Builder) {
2186 // Check to see if the first instruction in this block is just an unwind.
2187 // If so, replace any invoke instructions which use this as an exception
2188 // destination with call instructions.
2189 BasicBlock *BB = UI->getParent();
2190 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2192 bool Changed = false;
2193 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2194 while (!Preds.empty()) {
2195 BasicBlock *Pred = Preds.back();
2196 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
2197 if (II && II->getUnwindDest() == BB) {
2198 // Insert a new branch instruction before the invoke, because this
2199 // is now a fall through.
2200 Builder.SetInsertPoint(II);
2201 BranchInst *BI = Builder.CreateBr(II->getNormalDest());
2202 Pred->getInstList().remove(II); // Take out of symbol table
2204 // Insert the call now.
2205 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
2206 Builder.SetInsertPoint(BI);
2207 CallInst *CI = Builder.CreateCall(II->getCalledValue(),
2208 Args.begin(), Args.end(),
2210 CI->setCallingConv(II->getCallingConv());
2211 CI->setAttributes(II->getAttributes());
2212 // If the invoke produced a value, the Call now does instead.
2213 II->replaceAllUsesWith(CI);
2221 // If this block is now dead (and isn't the entry block), remove it.
2222 if (pred_begin(BB) == pred_end(BB) &&
2223 BB != &BB->getParent()->getEntryBlock()) {
2224 // We know there are no successors, so just nuke the block.
2225 BB->eraseFromParent();
2232 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2233 BasicBlock *BB = UI->getParent();
2235 bool Changed = false;
2237 // If there are any instructions immediately before the unreachable that can
2238 // be removed, do so.
2239 while (UI != BB->begin()) {
2240 BasicBlock::iterator BBI = UI;
2242 // Do not delete instructions that can have side effects, like calls
2243 // (which may never return) and volatile loads and stores.
2244 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2246 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
2247 if (SI->isVolatile())
2250 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
2251 if (LI->isVolatile())
2254 // Delete this instruction (any uses are guaranteed to be dead)
2255 if (!BBI->use_empty())
2256 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
2257 BBI->eraseFromParent();
2261 // If the unreachable instruction is the first in the block, take a gander
2262 // at all of the predecessors of this instruction, and simplify them.
2263 if (&BB->front() != UI) return Changed;
2265 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2266 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2267 TerminatorInst *TI = Preds[i]->getTerminator();
2268 IRBuilder<> Builder(TI);
2269 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2270 if (BI->isUnconditional()) {
2271 if (BI->getSuccessor(0) == BB) {
2272 new UnreachableInst(TI->getContext(), TI);
2273 TI->eraseFromParent();
2277 if (BI->getSuccessor(0) == BB) {
2278 Builder.CreateBr(BI->getSuccessor(1));
2279 EraseTerminatorInstAndDCECond(BI);
2280 } else if (BI->getSuccessor(1) == BB) {
2281 Builder.CreateBr(BI->getSuccessor(0));
2282 EraseTerminatorInstAndDCECond(BI);
2286 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2287 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2288 if (SI->getSuccessor(i) == BB) {
2289 BB->removePredecessor(SI->getParent());
2294 // If the default value is unreachable, figure out the most popular
2295 // destination and make it the default.
2296 if (SI->getSuccessor(0) == BB) {
2297 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
2298 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
2299 std::pair<unsigned, unsigned>& entry =
2300 Popularity[SI->getSuccessor(i)];
2301 if (entry.first == 0) {
2309 // Find the most popular block.
2310 unsigned MaxPop = 0;
2311 unsigned MaxIndex = 0;
2312 BasicBlock *MaxBlock = 0;
2313 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
2314 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2315 if (I->second.first > MaxPop ||
2316 (I->second.first == MaxPop && MaxIndex > I->second.second)) {
2317 MaxPop = I->second.first;
2318 MaxIndex = I->second.second;
2319 MaxBlock = I->first;
2323 // Make this the new default, allowing us to delete any explicit
2325 SI->setSuccessor(0, MaxBlock);
2328 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2330 if (isa<PHINode>(MaxBlock->begin()))
2331 for (unsigned i = 0; i != MaxPop-1; ++i)
2332 MaxBlock->removePredecessor(SI->getParent());
2334 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2335 if (SI->getSuccessor(i) == MaxBlock) {
2341 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2342 if (II->getUnwindDest() == BB) {
2343 // Convert the invoke to a call instruction. This would be a good
2344 // place to note that the call does not throw though.
2345 BranchInst *BI = Builder.CreateBr(II->getNormalDest());
2346 II->removeFromParent(); // Take out of symbol table
2348 // Insert the call now...
2349 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2350 Builder.SetInsertPoint(BI);
2351 CallInst *CI = Builder.CreateCall(II->getCalledValue(),
2352 Args.begin(), Args.end(),
2354 CI->setCallingConv(II->getCallingConv());
2355 CI->setAttributes(II->getAttributes());
2356 // If the invoke produced a value, the call does now instead.
2357 II->replaceAllUsesWith(CI);
2364 // If this block is now dead, remove it.
2365 if (pred_begin(BB) == pred_end(BB) &&
2366 BB != &BB->getParent()->getEntryBlock()) {
2367 // We know there are no successors, so just nuke the block.
2368 BB->eraseFromParent();
2375 /// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
2376 /// integer range comparison into a sub, an icmp and a branch.
2377 static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
2378 assert(SI->getNumCases() > 2 && "Degenerate switch?");
2380 // Make sure all cases point to the same destination and gather the values.
2381 SmallVector<ConstantInt *, 16> Cases;
2382 Cases.push_back(SI->getCaseValue(1));
2383 for (unsigned I = 2, E = SI->getNumCases(); I != E; ++I) {
2384 if (SI->getSuccessor(I-1) != SI->getSuccessor(I))
2386 Cases.push_back(SI->getCaseValue(I));
2388 assert(Cases.size() == SI->getNumCases()-1 && "Not all cases gathered");
2390 // Sort the case values, then check if they form a range we can transform.
2391 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
2392 for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
2393 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
2397 Constant *Offset = ConstantExpr::getNeg(Cases.back());
2398 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases()-1);
2400 Value *Sub = SI->getCondition();
2401 if (!Offset->isNullValue())
2402 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off");
2403 Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
2404 Builder.CreateCondBr(Cmp, SI->getSuccessor(1), SI->getDefaultDest());
2406 // Prune obsolete incoming values off the successor's PHI nodes.
2407 for (BasicBlock::iterator BBI = SI->getSuccessor(1)->begin();
2408 isa<PHINode>(BBI); ++BBI) {
2409 for (unsigned I = 0, E = SI->getNumCases()-2; I != E; ++I)
2410 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
2412 SI->eraseFromParent();
2417 /// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch
2418 /// and use it to remove dead cases.
2419 static bool EliminateDeadSwitchCases(SwitchInst *SI) {
2420 Value *Cond = SI->getCondition();
2421 unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth();
2422 APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
2423 ComputeMaskedBits(Cond, APInt::getAllOnesValue(Bits), KnownZero, KnownOne);
2425 // Gather dead cases.
2426 SmallVector<ConstantInt*, 8> DeadCases;
2427 for (unsigned I = 1, E = SI->getNumCases(); I != E; ++I) {
2428 if ((SI->getCaseValue(I)->getValue() & KnownZero) != 0 ||
2429 (SI->getCaseValue(I)->getValue() & KnownOne) != KnownOne) {
2430 DeadCases.push_back(SI->getCaseValue(I));
2431 DEBUG(dbgs() << "SimplifyCFG: switch case '"
2432 << SI->getCaseValue(I)->getValue() << "' is dead.\n");
2436 // Remove dead cases from the switch.
2437 for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) {
2438 unsigned Case = SI->findCaseValue(DeadCases[I]);
2439 // Prune unused values from PHI nodes.
2440 SI->getSuccessor(Case)->removePredecessor(SI->getParent());
2441 SI->removeCase(Case);
2444 return !DeadCases.empty();
2447 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
2448 // If this switch is too complex to want to look at, ignore it.
2449 if (!isValueEqualityComparison(SI))
2452 BasicBlock *BB = SI->getParent();
2454 // If we only have one predecessor, and if it is a branch on this value,
2455 // see if that predecessor totally determines the outcome of this switch.
2456 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2457 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
2458 return SimplifyCFG(BB) | true;
2460 Value *Cond = SI->getCondition();
2461 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
2462 if (SimplifySwitchOnSelect(SI, Select))
2463 return SimplifyCFG(BB) | true;
2465 // If the block only contains the switch, see if we can fold the block
2466 // away into any preds.
2467 BasicBlock::iterator BBI = BB->begin();
2468 // Ignore dbg intrinsics.
2469 while (isa<DbgInfoIntrinsic>(BBI))
2472 if (FoldValueComparisonIntoPredecessors(SI, Builder))
2473 return SimplifyCFG(BB) | true;
2475 // Try to transform the switch into an icmp and a branch.
2476 if (TurnSwitchRangeIntoICmp(SI, Builder))
2477 return SimplifyCFG(BB) | true;
2479 // Remove unreachable cases.
2480 if (EliminateDeadSwitchCases(SI))
2481 return SimplifyCFG(BB) | true;
2486 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
2487 BasicBlock *BB = IBI->getParent();
2488 bool Changed = false;
2490 // Eliminate redundant destinations.
2491 SmallPtrSet<Value *, 8> Succs;
2492 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2493 BasicBlock *Dest = IBI->getDestination(i);
2494 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2495 Dest->removePredecessor(BB);
2496 IBI->removeDestination(i);
2502 if (IBI->getNumDestinations() == 0) {
2503 // If the indirectbr has no successors, change it to unreachable.
2504 new UnreachableInst(IBI->getContext(), IBI);
2505 EraseTerminatorInstAndDCECond(IBI);
2509 if (IBI->getNumDestinations() == 1) {
2510 // If the indirectbr has one successor, change it to a direct branch.
2511 BranchInst::Create(IBI->getDestination(0), IBI);
2512 EraseTerminatorInstAndDCECond(IBI);
2516 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2517 if (SimplifyIndirectBrOnSelect(IBI, SI))
2518 return SimplifyCFG(BB) | true;
2523 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
2524 BasicBlock *BB = BI->getParent();
2526 // If the Terminator is the only non-phi instruction, simplify the block.
2527 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg();
2528 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
2529 TryToSimplifyUncondBranchFromEmptyBlock(BB))
2532 // If the only instruction in the block is a seteq/setne comparison
2533 // against a constant, try to simplify the block.
2534 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
2535 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
2536 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
2538 if (I->isTerminator()
2539 && TryToSimplifyUncondBranchWithICmpInIt(ICI, TD, Builder))
2547 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
2548 BasicBlock *BB = BI->getParent();
2550 // Conditional branch
2551 if (isValueEqualityComparison(BI)) {
2552 // If we only have one predecessor, and if it is a branch on this value,
2553 // see if that predecessor totally determines the outcome of this
2555 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2556 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
2557 return SimplifyCFG(BB) | true;
2559 // This block must be empty, except for the setcond inst, if it exists.
2560 // Ignore dbg intrinsics.
2561 BasicBlock::iterator I = BB->begin();
2562 // Ignore dbg intrinsics.
2563 while (isa<DbgInfoIntrinsic>(I))
2566 if (FoldValueComparisonIntoPredecessors(BI, Builder))
2567 return SimplifyCFG(BB) | true;
2568 } else if (&*I == cast<Instruction>(BI->getCondition())){
2570 // Ignore dbg intrinsics.
2571 while (isa<DbgInfoIntrinsic>(I))
2573 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
2574 return SimplifyCFG(BB) | true;
2578 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
2579 if (SimplifyBranchOnICmpChain(BI, TD, Builder))
2582 // We have a conditional branch to two blocks that are only reachable
2583 // from BI. We know that the condbr dominates the two blocks, so see if
2584 // there is any identical code in the "then" and "else" blocks. If so, we
2585 // can hoist it up to the branching block.
2586 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
2587 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2588 if (HoistThenElseCodeToIf(BI))
2589 return SimplifyCFG(BB) | true;
2591 // If Successor #1 has multiple preds, we may be able to conditionally
2592 // execute Successor #0 if it branches to successor #1.
2593 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
2594 if (Succ0TI->getNumSuccessors() == 1 &&
2595 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
2596 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
2597 return SimplifyCFG(BB) | true;
2599 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2600 // If Successor #0 has multiple preds, we may be able to conditionally
2601 // execute Successor #1 if it branches to successor #0.
2602 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
2603 if (Succ1TI->getNumSuccessors() == 1 &&
2604 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
2605 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
2606 return SimplifyCFG(BB) | true;
2609 // If this is a branch on a phi node in the current block, thread control
2610 // through this block if any PHI node entries are constants.
2611 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
2612 if (PN->getParent() == BI->getParent())
2613 if (FoldCondBranchOnPHI(BI, TD))
2614 return SimplifyCFG(BB) | true;
2616 // If this basic block is ONLY a setcc and a branch, and if a predecessor
2617 // branches to us and one of our successors, fold the setcc into the
2618 // predecessor and use logical operations to pick the right destination.
2619 if (FoldBranchToCommonDest(BI))
2620 return SimplifyCFG(BB) | true;
2622 // Scan predecessor blocks for conditional branches.
2623 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2624 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2625 if (PBI != BI && PBI->isConditional())
2626 if (SimplifyCondBranchToCondBranch(PBI, BI))
2627 return SimplifyCFG(BB) | true;
2632 bool SimplifyCFGOpt::run(BasicBlock *BB) {
2633 bool Changed = false;
2635 assert(BB && BB->getParent() && "Block not embedded in function!");
2636 assert(BB->getTerminator() && "Degenerate basic block encountered!");
2638 // Remove basic blocks that have no predecessors (except the entry block)...
2639 // or that just have themself as a predecessor. These are unreachable.
2640 if ((pred_begin(BB) == pred_end(BB) &&
2641 BB != &BB->getParent()->getEntryBlock()) ||
2642 BB->getSinglePredecessor() == BB) {
2643 DEBUG(dbgs() << "Removing BB: \n" << *BB);
2644 DeleteDeadBlock(BB);
2648 // Check to see if we can constant propagate this terminator instruction
2650 Changed |= ConstantFoldTerminator(BB);
2652 // Check for and eliminate duplicate PHI nodes in this block.
2653 Changed |= EliminateDuplicatePHINodes(BB);
2655 // Merge basic blocks into their predecessor if there is only one distinct
2656 // pred, and if there is only one distinct successor of the predecessor, and
2657 // if there are no PHI nodes.
2659 if (MergeBlockIntoPredecessor(BB))
2662 IRBuilder<> Builder(BB);
2664 // If there is a trivial two-entry PHI node in this basic block, and we can
2665 // eliminate it, do so now.
2666 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
2667 if (PN->getNumIncomingValues() == 2)
2668 Changed |= FoldTwoEntryPHINode(PN, TD, Builder);
2670 Builder.SetInsertPoint(BB->getTerminator());
2671 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
2672 if (BI->isUnconditional()) {
2673 if (SimplifyUncondBranch(BI, Builder)) return true;
2675 if (SimplifyCondBranch(BI, Builder)) return true;
2677 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
2678 if (SimplifyReturn(RI, Builder)) return true;
2679 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
2680 if (SimplifySwitch(SI, Builder)) return true;
2681 } else if (UnreachableInst *UI =
2682 dyn_cast<UnreachableInst>(BB->getTerminator())) {
2683 if (SimplifyUnreachable(UI)) return true;
2684 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
2685 if (SimplifyUnwind(UI, Builder)) return true;
2686 } else if (IndirectBrInst *IBI =
2687 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
2688 if (SimplifyIndirectBr(IBI)) return true;
2694 /// SimplifyCFG - This function is used to do simplification of a CFG. For
2695 /// example, it adjusts branches to branches to eliminate the extra hop, it
2696 /// eliminates unreachable basic blocks, and does other "peephole" optimization
2697 /// of the CFG. It returns true if a modification was made.
2699 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
2700 return SimplifyCFGOpt(TD).run(BB);