1 //===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Peephole optimize the CFG.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "simplifycfg"
15 #include "llvm/Transforms/Utils/Local.h"
16 #include "llvm/Constants.h"
17 #include "llvm/Instructions.h"
18 #include "llvm/IntrinsicInst.h"
19 #include "llvm/Type.h"
20 #include "llvm/DerivedTypes.h"
21 #include "llvm/GlobalVariable.h"
22 #include "llvm/Support/CFG.h"
23 #include "llvm/Support/Debug.h"
24 #include "llvm/Support/raw_ostream.h"
25 #include "llvm/Analysis/ConstantFolding.h"
26 #include "llvm/Target/TargetData.h"
27 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
28 #include "llvm/ADT/DenseMap.h"
29 #include "llvm/ADT/SmallVector.h"
30 #include "llvm/ADT/SmallPtrSet.h"
31 #include "llvm/ADT/Statistic.h"
38 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
41 class SimplifyCFGOpt {
42 const TargetData *const TD;
44 ConstantInt *GetConstantInt(Value *V);
45 Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values);
46 Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values);
47 bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
48 std::vector<ConstantInt*> &Values);
49 Value *isValueEqualityComparison(TerminatorInst *TI);
50 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
51 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases);
52 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
54 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI);
57 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
58 bool run(BasicBlock *BB);
62 /// SafeToMergeTerminators - Return true if it is safe to merge these two
63 /// terminator instructions together.
65 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
66 if (SI1 == SI2) return false; // Can't merge with self!
68 // It is not safe to merge these two switch instructions if they have a common
69 // successor, and if that successor has a PHI node, and if *that* PHI node has
70 // conflicting incoming values from the two switch blocks.
71 BasicBlock *SI1BB = SI1->getParent();
72 BasicBlock *SI2BB = SI2->getParent();
73 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
75 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
76 if (SI1Succs.count(*I))
77 for (BasicBlock::iterator BBI = (*I)->begin();
78 isa<PHINode>(BBI); ++BBI) {
79 PHINode *PN = cast<PHINode>(BBI);
80 if (PN->getIncomingValueForBlock(SI1BB) !=
81 PN->getIncomingValueForBlock(SI2BB))
88 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
89 /// now be entries in it from the 'NewPred' block. The values that will be
90 /// flowing into the PHI nodes will be the same as those coming in from
91 /// ExistPred, an existing predecessor of Succ.
92 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
93 BasicBlock *ExistPred) {
94 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
95 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
96 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
99 for (BasicBlock::iterator I = Succ->begin();
100 (PN = dyn_cast<PHINode>(I)); ++I)
101 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
105 /// GetIfCondition - Given a basic block (BB) with two predecessors (and
106 /// presumably PHI nodes in it), check to see if the merge at this block is due
107 /// to an "if condition". If so, return the boolean condition that determines
108 /// which entry into BB will be taken. Also, return by references the block
109 /// that will be entered from if the condition is true, and the block that will
110 /// be entered if the condition is false.
113 static Value *GetIfCondition(BasicBlock *BB,
114 BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
115 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
116 "Function can only handle blocks with 2 predecessors!");
117 BasicBlock *Pred1 = *pred_begin(BB);
118 BasicBlock *Pred2 = *++pred_begin(BB);
120 // We can only handle branches. Other control flow will be lowered to
121 // branches if possible anyway.
122 if (!isa<BranchInst>(Pred1->getTerminator()) ||
123 !isa<BranchInst>(Pred2->getTerminator()))
125 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
126 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
128 // Eliminate code duplication by ensuring that Pred1Br is conditional if
130 if (Pred2Br->isConditional()) {
131 // If both branches are conditional, we don't have an "if statement". In
132 // reality, we could transform this case, but since the condition will be
133 // required anyway, we stand no chance of eliminating it, so the xform is
134 // probably not profitable.
135 if (Pred1Br->isConditional())
138 std::swap(Pred1, Pred2);
139 std::swap(Pred1Br, Pred2Br);
142 if (Pred1Br->isConditional()) {
143 // If we found a conditional branch predecessor, make sure that it branches
144 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
145 if (Pred1Br->getSuccessor(0) == BB &&
146 Pred1Br->getSuccessor(1) == Pred2) {
149 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
150 Pred1Br->getSuccessor(1) == BB) {
154 // We know that one arm of the conditional goes to BB, so the other must
155 // go somewhere unrelated, and this must not be an "if statement".
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 (++pred_begin(Pred2) != pred_end(Pred2))
165 return Pred1Br->getCondition();
168 // Ok, if we got here, both predecessors end with an unconditional branch to
169 // BB. Don't panic! If both blocks only have a single (identical)
170 // predecessor, and THAT is a conditional branch, then we're all ok!
171 if (pred_begin(Pred1) == pred_end(Pred1) ||
172 ++pred_begin(Pred1) != pred_end(Pred1) ||
173 pred_begin(Pred2) == pred_end(Pred2) ||
174 ++pred_begin(Pred2) != pred_end(Pred2) ||
175 *pred_begin(Pred1) != *pred_begin(Pred2))
178 // Otherwise, if this is a conditional branch, then we can use it!
179 BasicBlock *CommonPred = *pred_begin(Pred1);
180 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
181 assert(BI->isConditional() && "Two successors but not conditional?");
182 if (BI->getSuccessor(0) == Pred1) {
189 return BI->getCondition();
194 /// DominatesMergePoint - If we have a merge point of an "if condition" as
195 /// accepted above, return true if the specified value dominates the block. We
196 /// don't handle the true generality of domination here, just a special case
197 /// which works well enough for us.
199 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
200 /// see if V (which must be an instruction) is cheap to compute and is
201 /// non-trapping. If both are true, the instruction is inserted into the set
202 /// and true is returned.
203 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
204 std::set<Instruction*> *AggressiveInsts) {
205 Instruction *I = dyn_cast<Instruction>(V);
207 // Non-instructions all dominate instructions, but not all constantexprs
208 // can be executed unconditionally.
209 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
214 BasicBlock *PBB = I->getParent();
216 // We don't want to allow weird loops that might have the "if condition" in
217 // the bottom of this block.
218 if (PBB == BB) return false;
220 // If this instruction is defined in a block that contains an unconditional
221 // branch to BB, then it must be in the 'conditional' part of the "if
223 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
224 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
225 if (!AggressiveInsts) return false;
226 // Okay, it looks like the instruction IS in the "condition". Check to
227 // see if it's a cheap instruction to unconditionally compute, and if it
228 // only uses stuff defined outside of the condition. If so, hoist it out.
229 if (!I->isSafeToSpeculativelyExecute())
232 switch (I->getOpcode()) {
233 default: return false; // Cannot hoist this out safely.
234 case Instruction::Load: {
235 // We have to check to make sure there are no instructions before the
236 // load in its basic block, as we are going to hoist the loop out to
238 BasicBlock::iterator IP = PBB->begin();
239 while (isa<DbgInfoIntrinsic>(IP))
241 if (IP != BasicBlock::iterator(I))
245 case Instruction::Add:
246 case Instruction::Sub:
247 case Instruction::And:
248 case Instruction::Or:
249 case Instruction::Xor:
250 case Instruction::Shl:
251 case Instruction::LShr:
252 case Instruction::AShr:
253 case Instruction::ICmp:
254 break; // These are all cheap and non-trapping instructions.
257 // Okay, we can only really hoist these out if their operands are not
258 // defined in the conditional region.
259 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
260 if (!DominatesMergePoint(*i, BB, 0))
262 // Okay, it's safe to do this! Remember this instruction.
263 AggressiveInsts->insert(I);
269 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
270 /// and PointerNullValue. Return NULL if value is not a constant int.
271 ConstantInt *SimplifyCFGOpt::GetConstantInt(Value *V) {
272 // Normal constant int.
273 ConstantInt *CI = dyn_cast<ConstantInt>(V);
274 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
277 // This is some kind of pointer constant. Turn it into a pointer-sized
278 // ConstantInt if possible.
279 const IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
281 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
282 if (isa<ConstantPointerNull>(V))
283 return ConstantInt::get(PtrTy, 0);
285 // IntToPtr const int.
286 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
287 if (CE->getOpcode() == Instruction::IntToPtr)
288 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
289 // The constant is very likely to have the right type already.
290 if (CI->getType() == PtrTy)
293 return cast<ConstantInt>
294 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
299 /// GatherConstantSetEQs - Given a potentially 'or'd together collection of
300 /// icmp_eq instructions that compare a value against a constant, return the
301 /// value being compared, and stick the constant into the Values vector.
302 Value *SimplifyCFGOpt::
303 GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values) {
304 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
305 if (Inst->getOpcode() == Instruction::ICmp &&
306 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_EQ) {
307 if (ConstantInt *C = GetConstantInt(Inst->getOperand(1))) {
309 return Inst->getOperand(0);
310 } else if (ConstantInt *C = GetConstantInt(Inst->getOperand(0))) {
312 return Inst->getOperand(1);
314 } else if (Inst->getOpcode() == Instruction::Or) {
315 if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
316 if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
324 /// GatherConstantSetNEs - Given a potentially 'and'd together collection of
325 /// setne instructions that compare a value against a constant, return the value
326 /// being compared, and stick the constant into the Values vector.
327 Value *SimplifyCFGOpt::
328 GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values) {
329 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
330 if (Inst->getOpcode() == Instruction::ICmp &&
331 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_NE) {
332 if (ConstantInt *C = GetConstantInt(Inst->getOperand(1))) {
334 return Inst->getOperand(0);
335 } else if (ConstantInt *C = GetConstantInt(Inst->getOperand(0))) {
337 return Inst->getOperand(1);
339 } else if (Inst->getOpcode() == Instruction::And) {
340 if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
341 if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
349 /// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
350 /// bunch of comparisons of one value against constants, return the value and
351 /// the constants being compared.
352 bool SimplifyCFGOpt::GatherValueComparisons(Instruction *Cond, Value *&CompVal,
353 std::vector<ConstantInt*> &Values) {
354 if (Cond->getOpcode() == Instruction::Or) {
355 CompVal = GatherConstantSetEQs(Cond, Values);
357 // Return true to indicate that the condition is true if the CompVal is
358 // equal to one of the constants.
360 } else if (Cond->getOpcode() == Instruction::And) {
361 CompVal = GatherConstantSetNEs(Cond, Values);
363 // Return false to indicate that the condition is false if the CompVal is
364 // equal to one of the constants.
370 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
371 Instruction* Cond = 0;
372 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
373 Cond = dyn_cast<Instruction>(SI->getCondition());
374 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
375 if (BI->isConditional())
376 Cond = dyn_cast<Instruction>(BI->getCondition());
379 TI->eraseFromParent();
380 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
383 /// isValueEqualityComparison - Return true if the specified terminator checks
384 /// to see if a value is equal to constant integer value.
385 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
387 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
388 // Do not permit merging of large switch instructions into their
389 // predecessors unless there is only one predecessor.
390 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
391 pred_end(SI->getParent())) <= 128)
392 CV = SI->getCondition();
393 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
394 if (BI->isConditional() && BI->getCondition()->hasOneUse())
395 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
396 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
397 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
398 GetConstantInt(ICI->getOperand(1)))
399 CV = ICI->getOperand(0);
401 // Unwrap any lossless ptrtoint cast.
402 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
403 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
404 CV = PTII->getOperand(0);
408 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
409 /// decode all of the 'cases' that it represents and return the 'default' block.
410 BasicBlock *SimplifyCFGOpt::
411 GetValueEqualityComparisonCases(TerminatorInst *TI,
412 std::vector<std::pair<ConstantInt*,
413 BasicBlock*> > &Cases) {
414 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
415 Cases.reserve(SI->getNumCases());
416 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
417 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
418 return SI->getDefaultDest();
421 BranchInst *BI = cast<BranchInst>(TI);
422 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
423 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1)),
424 BI->getSuccessor(ICI->getPredicate() ==
425 ICmpInst::ICMP_NE)));
426 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
430 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
431 /// in the list that match the specified block.
432 static void EliminateBlockCases(BasicBlock *BB,
433 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
434 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
435 if (Cases[i].second == BB) {
436 Cases.erase(Cases.begin()+i);
441 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
444 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
445 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
446 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
448 // Make V1 be smaller than V2.
449 if (V1->size() > V2->size())
452 if (V1->size() == 0) return false;
453 if (V1->size() == 1) {
455 ConstantInt *TheVal = (*V1)[0].first;
456 for (unsigned i = 0, e = V2->size(); i != e; ++i)
457 if (TheVal == (*V2)[i].first)
461 // Otherwise, just sort both lists and compare element by element.
462 std::sort(V1->begin(), V1->end());
463 std::sort(V2->begin(), V2->end());
464 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
465 while (i1 != e1 && i2 != e2) {
466 if ((*V1)[i1].first == (*V2)[i2].first)
468 if ((*V1)[i1].first < (*V2)[i2].first)
476 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
477 /// terminator instruction and its block is known to only have a single
478 /// predecessor block, check to see if that predecessor is also a value
479 /// comparison with the same value, and if that comparison determines the
480 /// outcome of this comparison. If so, simplify TI. This does a very limited
481 /// form of jump threading.
482 bool SimplifyCFGOpt::
483 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
485 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
486 if (!PredVal) return false; // Not a value comparison in predecessor.
488 Value *ThisVal = isValueEqualityComparison(TI);
489 assert(ThisVal && "This isn't a value comparison!!");
490 if (ThisVal != PredVal) return false; // Different predicates.
492 // Find out information about when control will move from Pred to TI's block.
493 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
494 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
496 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
498 // Find information about how control leaves this block.
499 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
500 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
501 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
503 // If TI's block is the default block from Pred's comparison, potentially
504 // simplify TI based on this knowledge.
505 if (PredDef == TI->getParent()) {
506 // If we are here, we know that the value is none of those cases listed in
507 // PredCases. If there are any cases in ThisCases that are in PredCases, we
509 if (ValuesOverlap(PredCases, ThisCases)) {
510 if (isa<BranchInst>(TI)) {
511 // Okay, one of the successors of this condbr is dead. Convert it to a
513 assert(ThisCases.size() == 1 && "Branch can only have one case!");
514 // Insert the new branch.
515 Instruction *NI = BranchInst::Create(ThisDef, TI);
518 // Remove PHI node entries for the dead edge.
519 ThisCases[0].second->removePredecessor(TI->getParent());
521 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
522 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
524 EraseTerminatorInstAndDCECond(TI);
528 SwitchInst *SI = cast<SwitchInst>(TI);
529 // Okay, TI has cases that are statically dead, prune them away.
530 SmallPtrSet<Constant*, 16> DeadCases;
531 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
532 DeadCases.insert(PredCases[i].first);
534 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
535 << "Through successor TI: " << *TI);
537 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
538 if (DeadCases.count(SI->getCaseValue(i))) {
539 SI->getSuccessor(i)->removePredecessor(TI->getParent());
543 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
549 // Otherwise, TI's block must correspond to some matched value. Find out
550 // which value (or set of values) this is.
551 ConstantInt *TIV = 0;
552 BasicBlock *TIBB = TI->getParent();
553 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
554 if (PredCases[i].second == TIBB) {
556 TIV = PredCases[i].first;
558 return false; // Cannot handle multiple values coming to this block.
560 assert(TIV && "No edge from pred to succ?");
562 // Okay, we found the one constant that our value can be if we get into TI's
563 // BB. Find out which successor will unconditionally be branched to.
564 BasicBlock *TheRealDest = 0;
565 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
566 if (ThisCases[i].first == TIV) {
567 TheRealDest = ThisCases[i].second;
571 // If not handled by any explicit cases, it is handled by the default case.
572 if (TheRealDest == 0) TheRealDest = ThisDef;
574 // Remove PHI node entries for dead edges.
575 BasicBlock *CheckEdge = TheRealDest;
576 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
577 if (*SI != CheckEdge)
578 (*SI)->removePredecessor(TIBB);
582 // Insert the new branch.
583 Instruction *NI = BranchInst::Create(TheRealDest, TI);
586 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
587 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
589 EraseTerminatorInstAndDCECond(TI);
596 /// ConstantIntOrdering - This class implements a stable ordering of constant
597 /// integers that does not depend on their address. This is important for
598 /// applications that sort ConstantInt's to ensure uniqueness.
599 struct ConstantIntOrdering {
600 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
601 return LHS->getValue().ult(RHS->getValue());
606 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
607 /// equality comparison instruction (either a switch or a branch on "X == c").
608 /// See if any of the predecessors of the terminator block are value comparisons
609 /// on the same value. If so, and if safe to do so, fold them together.
610 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
611 BasicBlock *BB = TI->getParent();
612 Value *CV = isValueEqualityComparison(TI); // CondVal
613 assert(CV && "Not a comparison?");
614 bool Changed = false;
616 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
617 while (!Preds.empty()) {
618 BasicBlock *Pred = Preds.pop_back_val();
620 // See if the predecessor is a comparison with the same value.
621 TerminatorInst *PTI = Pred->getTerminator();
622 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
624 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
625 // Figure out which 'cases' to copy from SI to PSI.
626 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
627 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
629 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
630 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
632 // Based on whether the default edge from PTI goes to BB or not, fill in
633 // PredCases and PredDefault with the new switch cases we would like to
635 SmallVector<BasicBlock*, 8> NewSuccessors;
637 if (PredDefault == BB) {
638 // If this is the default destination from PTI, only the edges in TI
639 // that don't occur in PTI, or that branch to BB will be activated.
640 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
641 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
642 if (PredCases[i].second != BB)
643 PTIHandled.insert(PredCases[i].first);
645 // The default destination is BB, we don't need explicit targets.
646 std::swap(PredCases[i], PredCases.back());
647 PredCases.pop_back();
651 // Reconstruct the new switch statement we will be building.
652 if (PredDefault != BBDefault) {
653 PredDefault->removePredecessor(Pred);
654 PredDefault = BBDefault;
655 NewSuccessors.push_back(BBDefault);
657 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
658 if (!PTIHandled.count(BBCases[i].first) &&
659 BBCases[i].second != BBDefault) {
660 PredCases.push_back(BBCases[i]);
661 NewSuccessors.push_back(BBCases[i].second);
665 // If this is not the default destination from PSI, only the edges
666 // in SI that occur in PSI with a destination of BB will be
668 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
669 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
670 if (PredCases[i].second == BB) {
671 PTIHandled.insert(PredCases[i].first);
672 std::swap(PredCases[i], PredCases.back());
673 PredCases.pop_back();
677 // Okay, now we know which constants were sent to BB from the
678 // predecessor. Figure out where they will all go now.
679 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
680 if (PTIHandled.count(BBCases[i].first)) {
681 // If this is one we are capable of getting...
682 PredCases.push_back(BBCases[i]);
683 NewSuccessors.push_back(BBCases[i].second);
684 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
687 // If there are any constants vectored to BB that TI doesn't handle,
688 // they must go to the default destination of TI.
689 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
691 E = PTIHandled.end(); I != E; ++I) {
692 PredCases.push_back(std::make_pair(*I, BBDefault));
693 NewSuccessors.push_back(BBDefault);
697 // Okay, at this point, we know which new successor Pred will get. Make
698 // sure we update the number of entries in the PHI nodes for these
700 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
701 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
703 // Convert pointer to int before we switch.
704 if (CV->getType()->isPointerTy()) {
705 assert(TD && "Cannot switch on pointer without TargetData");
706 CV = new PtrToIntInst(CV, TD->getIntPtrType(CV->getContext()),
710 // Now that the successors are updated, create the new Switch instruction.
711 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
712 PredCases.size(), PTI);
713 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
714 NewSI->addCase(PredCases[i].first, PredCases[i].second);
716 EraseTerminatorInstAndDCECond(PTI);
718 // Okay, last check. If BB is still a successor of PSI, then we must
719 // have an infinite loop case. If so, add an infinitely looping block
720 // to handle the case to preserve the behavior of the code.
721 BasicBlock *InfLoopBlock = 0;
722 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
723 if (NewSI->getSuccessor(i) == BB) {
724 if (InfLoopBlock == 0) {
725 // Insert it at the end of the function, because it's either code,
726 // or it won't matter if it's hot. :)
727 InfLoopBlock = BasicBlock::Create(BB->getContext(),
728 "infloop", BB->getParent());
729 BranchInst::Create(InfLoopBlock, InfLoopBlock);
731 NewSI->setSuccessor(i, InfLoopBlock);
740 // isSafeToHoistInvoke - If we would need to insert a select that uses the
741 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
742 // would need to do this), we can't hoist the invoke, as there is nowhere
743 // to put the select in this case.
744 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
745 Instruction *I1, Instruction *I2) {
746 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
748 for (BasicBlock::iterator BBI = SI->begin();
749 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
750 Value *BB1V = PN->getIncomingValueForBlock(BB1);
751 Value *BB2V = PN->getIncomingValueForBlock(BB2);
752 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
760 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
761 /// BB2, hoist any common code in the two blocks up into the branch block. The
762 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
763 static bool HoistThenElseCodeToIf(BranchInst *BI) {
764 // This does very trivial matching, with limited scanning, to find identical
765 // instructions in the two blocks. In particular, we don't want to get into
766 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
767 // such, we currently just scan for obviously identical instructions in an
769 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
770 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
772 BasicBlock::iterator BB1_Itr = BB1->begin();
773 BasicBlock::iterator BB2_Itr = BB2->begin();
775 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
776 while (isa<DbgInfoIntrinsic>(I1))
778 while (isa<DbgInfoIntrinsic>(I2))
780 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
781 !I1->isIdenticalToWhenDefined(I2) ||
782 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
785 // If we get here, we can hoist at least one instruction.
786 BasicBlock *BIParent = BI->getParent();
789 // If we are hoisting the terminator instruction, don't move one (making a
790 // broken BB), instead clone it, and remove BI.
791 if (isa<TerminatorInst>(I1))
792 goto HoistTerminator;
794 // For a normal instruction, we just move one to right before the branch,
795 // then replace all uses of the other with the first. Finally, we remove
796 // the now redundant second instruction.
797 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
798 if (!I2->use_empty())
799 I2->replaceAllUsesWith(I1);
800 I1->intersectOptionalDataWith(I2);
801 BB2->getInstList().erase(I2);
804 while (isa<DbgInfoIntrinsic>(I1))
807 while (isa<DbgInfoIntrinsic>(I2))
809 } while (I1->getOpcode() == I2->getOpcode() &&
810 I1->isIdenticalToWhenDefined(I2));
815 // It may not be possible to hoist an invoke.
816 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
819 // Okay, it is safe to hoist the terminator.
820 Instruction *NT = I1->clone();
821 BIParent->getInstList().insert(BI, NT);
822 if (!NT->getType()->isVoidTy()) {
823 I1->replaceAllUsesWith(NT);
824 I2->replaceAllUsesWith(NT);
828 // Hoisting one of the terminators from our successor is a great thing.
829 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
830 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
831 // nodes, so we insert select instruction to compute the final result.
832 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
833 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
835 for (BasicBlock::iterator BBI = SI->begin();
836 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
837 Value *BB1V = PN->getIncomingValueForBlock(BB1);
838 Value *BB2V = PN->getIncomingValueForBlock(BB2);
840 // These values do not agree. Insert a select instruction before NT
841 // that determines the right value.
842 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
844 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
845 BB1V->getName()+"."+BB2V->getName(), NT);
846 // Make the PHI node use the select for all incoming values for BB1/BB2
847 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
848 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
849 PN->setIncomingValue(i, SI);
854 // Update any PHI nodes in our new successors.
855 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
856 AddPredecessorToBlock(*SI, BIParent, BB1);
858 EraseTerminatorInstAndDCECond(BI);
862 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
863 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
864 /// (for now, restricted to a single instruction that's side effect free) from
865 /// the BB1 into the branch block to speculatively execute it.
866 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
867 // Only speculatively execution a single instruction (not counting the
868 // terminator) for now.
869 Instruction *HInst = NULL;
870 Instruction *Term = BB1->getTerminator();
871 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
873 Instruction *I = BBI;
875 if (isa<DbgInfoIntrinsic>(I)) continue;
876 if (I == Term) break;
886 // Be conservative for now. FP select instruction can often be expensive.
887 Value *BrCond = BI->getCondition();
888 if (isa<Instruction>(BrCond) &&
889 cast<Instruction>(BrCond)->getOpcode() == Instruction::FCmp)
892 // If BB1 is actually on the false edge of the conditional branch, remember
893 // to swap the select operands later.
895 if (BB1 != BI->getSuccessor(0)) {
896 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
903 // br i1 %t1, label %BB1, label %BB2
912 // %t3 = select i1 %t1, %t2, %t3
913 switch (HInst->getOpcode()) {
914 default: return false; // Not safe / profitable to hoist.
915 case Instruction::Add:
916 case Instruction::Sub:
917 // Not worth doing for vector ops.
918 if (HInst->getType()->isVectorTy())
921 case Instruction::And:
922 case Instruction::Or:
923 case Instruction::Xor:
924 case Instruction::Shl:
925 case Instruction::LShr:
926 case Instruction::AShr:
927 // Don't mess with vector operations.
928 if (HInst->getType()->isVectorTy())
930 break; // These are all cheap and non-trapping instructions.
933 // If the instruction is obviously dead, don't try to predicate it.
934 if (HInst->use_empty()) {
935 HInst->eraseFromParent();
939 // Can we speculatively execute the instruction? And what is the value
940 // if the condition is false? Consider the phi uses, if the incoming value
941 // from the "if" block are all the same V, then V is the value of the
942 // select if the condition is false.
943 BasicBlock *BIParent = BI->getParent();
944 SmallVector<PHINode*, 4> PHIUses;
945 Value *FalseV = NULL;
947 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
948 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
950 // Ignore any user that is not a PHI node in BB2. These can only occur in
951 // unreachable blocks, because they would not be dominated by the instr.
952 PHINode *PN = dyn_cast<PHINode>(*UI);
953 if (!PN || PN->getParent() != BB2)
955 PHIUses.push_back(PN);
957 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
960 else if (FalseV != PHIV)
961 return false; // Inconsistent value when condition is false.
964 assert(FalseV && "Must have at least one user, and it must be a PHI");
966 // Do not hoist the instruction if any of its operands are defined but not
967 // used in this BB. The transformation will prevent the operand from
968 // being sunk into the use block.
969 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
971 Instruction *OpI = dyn_cast<Instruction>(*i);
972 if (OpI && OpI->getParent() == BIParent &&
973 !OpI->isUsedInBasicBlock(BIParent))
977 // If we get here, we can hoist the instruction. Try to place it
978 // before the icmp instruction preceding the conditional branch.
979 BasicBlock::iterator InsertPos = BI;
980 if (InsertPos != BIParent->begin())
982 // Skip debug info between condition and branch.
983 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
985 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
986 SmallPtrSet<Instruction *, 4> BB1Insns;
987 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
988 BB1I != BB1E; ++BB1I)
989 BB1Insns.insert(BB1I);
990 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
992 Instruction *Use = cast<Instruction>(*UI);
993 if (BB1Insns.count(Use)) {
994 // If BrCond uses the instruction that place it just before
995 // branch instruction.
1002 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
1004 // Create a select whose true value is the speculatively executed value and
1005 // false value is the previously determined FalseV.
1008 SI = SelectInst::Create(BrCond, FalseV, HInst,
1009 FalseV->getName() + "." + HInst->getName(), BI);
1011 SI = SelectInst::Create(BrCond, HInst, FalseV,
1012 HInst->getName() + "." + FalseV->getName(), BI);
1014 // Make the PHI node use the select for all incoming values for "then" and
1016 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1017 PHINode *PN = PHIUses[i];
1018 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1019 if (PN->getIncomingBlock(j) == BB1 ||
1020 PN->getIncomingBlock(j) == BIParent)
1021 PN->setIncomingValue(j, SI);
1028 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1029 /// across this block.
1030 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1031 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1034 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1035 if (isa<DbgInfoIntrinsic>(BBI))
1037 if (Size > 10) return false; // Don't clone large BB's.
1040 // We can only support instructions that do not define values that are
1041 // live outside of the current basic block.
1042 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1044 Instruction *U = cast<Instruction>(*UI);
1045 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1048 // Looks ok, continue checking.
1054 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1055 /// that is defined in the same block as the branch and if any PHI entries are
1056 /// constants, thread edges corresponding to that entry to be branches to their
1057 /// ultimate destination.
1058 static bool FoldCondBranchOnPHI(BranchInst *BI) {
1059 BasicBlock *BB = BI->getParent();
1060 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1061 // NOTE: we currently cannot transform this case if the PHI node is used
1062 // outside of the block.
1063 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1066 // Degenerate case of a single entry PHI.
1067 if (PN->getNumIncomingValues() == 1) {
1068 FoldSingleEntryPHINodes(PN->getParent());
1072 // Now we know that this block has multiple preds and two succs.
1073 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1075 // Okay, this is a simple enough basic block. See if any phi values are
1077 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1079 if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
1080 CB->getType()->isIntegerTy(1)) {
1081 // Okay, we now know that all edges from PredBB should be revectored to
1082 // branch to RealDest.
1083 BasicBlock *PredBB = PN->getIncomingBlock(i);
1084 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1086 if (RealDest == BB) continue; // Skip self loops.
1088 // The dest block might have PHI nodes, other predecessors and other
1089 // difficult cases. Instead of being smart about this, just insert a new
1090 // block that jumps to the destination block, effectively splitting
1091 // the edge we are about to create.
1092 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1093 RealDest->getName()+".critedge",
1094 RealDest->getParent(), RealDest);
1095 BranchInst::Create(RealDest, EdgeBB);
1097 for (BasicBlock::iterator BBI = RealDest->begin();
1098 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1099 Value *V = PN->getIncomingValueForBlock(BB);
1100 PN->addIncoming(V, EdgeBB);
1103 // BB may have instructions that are being threaded over. Clone these
1104 // instructions into EdgeBB. We know that there will be no uses of the
1105 // cloned instructions outside of EdgeBB.
1106 BasicBlock::iterator InsertPt = EdgeBB->begin();
1107 std::map<Value*, Value*> TranslateMap; // Track translated values.
1108 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1109 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1110 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1112 // Clone the instruction.
1113 Instruction *N = BBI->clone();
1114 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1116 // Update operands due to translation.
1117 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1119 std::map<Value*, Value*>::iterator PI =
1120 TranslateMap.find(*i);
1121 if (PI != TranslateMap.end())
1125 // Check for trivial simplification.
1126 if (Constant *C = ConstantFoldInstruction(N)) {
1127 TranslateMap[BBI] = C;
1128 delete N; // Constant folded away, don't need actual inst
1130 // Insert the new instruction into its new home.
1131 EdgeBB->getInstList().insert(InsertPt, N);
1132 if (!BBI->use_empty())
1133 TranslateMap[BBI] = N;
1138 // Loop over all of the edges from PredBB to BB, changing them to branch
1139 // to EdgeBB instead.
1140 TerminatorInst *PredBBTI = PredBB->getTerminator();
1141 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1142 if (PredBBTI->getSuccessor(i) == BB) {
1143 BB->removePredecessor(PredBB);
1144 PredBBTI->setSuccessor(i, EdgeBB);
1147 // Recurse, simplifying any other constants.
1148 return FoldCondBranchOnPHI(BI) | true;
1155 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1156 /// PHI node, see if we can eliminate it.
1157 static bool FoldTwoEntryPHINode(PHINode *PN) {
1158 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1159 // statement", which has a very simple dominance structure. Basically, we
1160 // are trying to find the condition that is being branched on, which
1161 // subsequently causes this merge to happen. We really want control
1162 // dependence information for this check, but simplifycfg can't keep it up
1163 // to date, and this catches most of the cases we care about anyway.
1165 BasicBlock *BB = PN->getParent();
1166 BasicBlock *IfTrue, *IfFalse;
1167 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1168 if (!IfCond) return false;
1170 // Okay, we found that we can merge this two-entry phi node into a select.
1171 // Doing so would require us to fold *all* two entry phi nodes in this block.
1172 // At some point this becomes non-profitable (particularly if the target
1173 // doesn't support cmov's). Only do this transformation if there are two or
1174 // fewer PHI nodes in this block.
1175 unsigned NumPhis = 0;
1176 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1180 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1181 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1183 // Loop over the PHI's seeing if we can promote them all to select
1184 // instructions. While we are at it, keep track of the instructions
1185 // that need to be moved to the dominating block.
1186 std::set<Instruction*> AggressiveInsts;
1188 BasicBlock::iterator AfterPHIIt = BB->begin();
1189 while (isa<PHINode>(AfterPHIIt)) {
1190 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1191 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1192 if (PN->getIncomingValue(0) != PN)
1193 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1195 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1196 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1197 &AggressiveInsts) ||
1198 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1199 &AggressiveInsts)) {
1204 // If we all PHI nodes are promotable, check to make sure that all
1205 // instructions in the predecessor blocks can be promoted as well. If
1206 // not, we won't be able to get rid of the control flow, so it's not
1207 // worth promoting to select instructions.
1208 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1209 PN = cast<PHINode>(BB->begin());
1210 BasicBlock *Pred = PN->getIncomingBlock(0);
1211 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1213 DomBlock = *pred_begin(Pred);
1214 for (BasicBlock::iterator I = Pred->begin();
1215 !isa<TerminatorInst>(I); ++I)
1216 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1217 // This is not an aggressive instruction that we can promote.
1218 // Because of this, we won't be able to get rid of the control
1219 // flow, so the xform is not worth it.
1224 Pred = PN->getIncomingBlock(1);
1225 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1227 DomBlock = *pred_begin(Pred);
1228 for (BasicBlock::iterator I = Pred->begin();
1229 !isa<TerminatorInst>(I); ++I)
1230 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1231 // This is not an aggressive instruction that we can promote.
1232 // Because of this, we won't be able to get rid of the control
1233 // flow, so the xform is not worth it.
1238 // If we can still promote the PHI nodes after this gauntlet of tests,
1239 // do all of the PHI's now.
1241 // Move all 'aggressive' instructions, which are defined in the
1242 // conditional parts of the if's up to the dominating block.
1244 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1245 IfBlock1->getInstList(),
1247 IfBlock1->getTerminator());
1250 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1251 IfBlock2->getInstList(),
1253 IfBlock2->getTerminator());
1256 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1257 // Change the PHI node into a select instruction.
1259 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1261 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1263 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1264 PN->replaceAllUsesWith(NV);
1267 BB->getInstList().erase(PN);
1272 /// isTerminatorFirstRelevantInsn - Return true if Term is very first
1273 /// instruction ignoring Phi nodes and dbg intrinsics.
1274 static bool isTerminatorFirstRelevantInsn(BasicBlock *BB, Instruction *Term) {
1275 BasicBlock::iterator BBI = Term;
1276 while (BBI != BB->begin()) {
1278 if (!isa<DbgInfoIntrinsic>(BBI))
1282 if (isa<PHINode>(BBI) || &*BBI == Term || isa<DbgInfoIntrinsic>(BBI))
1287 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1288 /// to two returning blocks, try to merge them together into one return,
1289 /// introducing a select if the return values disagree.
1290 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1291 assert(BI->isConditional() && "Must be a conditional branch");
1292 BasicBlock *TrueSucc = BI->getSuccessor(0);
1293 BasicBlock *FalseSucc = BI->getSuccessor(1);
1294 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1295 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1297 // Check to ensure both blocks are empty (just a return) or optionally empty
1298 // with PHI nodes. If there are other instructions, merging would cause extra
1299 // computation on one path or the other.
1300 if (!isTerminatorFirstRelevantInsn(TrueSucc, TrueRet))
1302 if (!isTerminatorFirstRelevantInsn(FalseSucc, FalseRet))
1305 // Okay, we found a branch that is going to two return nodes. If
1306 // there is no return value for this function, just change the
1307 // branch into a return.
1308 if (FalseRet->getNumOperands() == 0) {
1309 TrueSucc->removePredecessor(BI->getParent());
1310 FalseSucc->removePredecessor(BI->getParent());
1311 ReturnInst::Create(BI->getContext(), 0, BI);
1312 EraseTerminatorInstAndDCECond(BI);
1316 // Otherwise, figure out what the true and false return values are
1317 // so we can insert a new select instruction.
1318 Value *TrueValue = TrueRet->getReturnValue();
1319 Value *FalseValue = FalseRet->getReturnValue();
1321 // Unwrap any PHI nodes in the return blocks.
1322 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1323 if (TVPN->getParent() == TrueSucc)
1324 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1325 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1326 if (FVPN->getParent() == FalseSucc)
1327 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1329 // In order for this transformation to be safe, we must be able to
1330 // unconditionally execute both operands to the return. This is
1331 // normally the case, but we could have a potentially-trapping
1332 // constant expression that prevents this transformation from being
1334 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1337 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1341 // Okay, we collected all the mapped values and checked them for sanity, and
1342 // defined to really do this transformation. First, update the CFG.
1343 TrueSucc->removePredecessor(BI->getParent());
1344 FalseSucc->removePredecessor(BI->getParent());
1346 // Insert select instructions where needed.
1347 Value *BrCond = BI->getCondition();
1349 // Insert a select if the results differ.
1350 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1351 } else if (isa<UndefValue>(TrueValue)) {
1352 TrueValue = FalseValue;
1354 TrueValue = SelectInst::Create(BrCond, TrueValue,
1355 FalseValue, "retval", BI);
1359 Value *RI = !TrueValue ?
1360 ReturnInst::Create(BI->getContext(), BI) :
1361 ReturnInst::Create(BI->getContext(), TrueValue, BI);
1364 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1365 << "\n " << *BI << "NewRet = " << *RI
1366 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1368 EraseTerminatorInstAndDCECond(BI);
1373 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1374 /// and if a predecessor branches to us and one of our successors, fold the
1375 /// setcc into the predecessor and use logical operations to pick the right
1377 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1378 BasicBlock *BB = BI->getParent();
1379 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1380 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1381 Cond->getParent() != BB || !Cond->hasOneUse())
1384 // Only allow this if the condition is a simple instruction that can be
1385 // executed unconditionally. It must be in the same block as the branch, and
1386 // must be at the front of the block.
1387 BasicBlock::iterator FrontIt = BB->front();
1388 // Ignore dbg intrinsics.
1389 while(isa<DbgInfoIntrinsic>(FrontIt))
1392 // Allow a single instruction to be hoisted in addition to the compare
1393 // that feeds the branch. We later ensure that any values that _it_ uses
1394 // were also live in the predecessor, so that we don't unnecessarily create
1395 // register pressure or inhibit out-of-order execution.
1396 Instruction *BonusInst = 0;
1397 if (&*FrontIt != Cond &&
1398 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1399 FrontIt->isSafeToSpeculativelyExecute()) {
1400 BonusInst = &*FrontIt;
1404 // Only a single bonus inst is allowed.
1405 if (&*FrontIt != Cond)
1408 // Make sure the instruction after the condition is the cond branch.
1409 BasicBlock::iterator CondIt = Cond; ++CondIt;
1410 // Ingore dbg intrinsics.
1411 while(isa<DbgInfoIntrinsic>(CondIt))
1413 if (&*CondIt != BI) {
1414 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!");
1418 // Cond is known to be a compare or binary operator. Check to make sure that
1419 // neither operand is a potentially-trapping constant expression.
1420 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1423 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1428 // Finally, don't infinitely unroll conditional loops.
1429 BasicBlock *TrueDest = BI->getSuccessor(0);
1430 BasicBlock *FalseDest = BI->getSuccessor(1);
1431 if (TrueDest == BB || FalseDest == BB)
1434 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1435 BasicBlock *PredBlock = *PI;
1436 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1438 // Check that we have two conditional branches. If there is a PHI node in
1439 // the common successor, verify that the same value flows in from both
1441 if (PBI == 0 || PBI->isUnconditional() ||
1442 !SafeToMergeTerminators(BI, PBI))
1445 // Ensure that any values used in the bonus instruction are also used
1446 // by the terminator of the predecessor. This means that those values
1447 // must already have been resolved, so we won't be inhibiting the
1448 // out-of-order core by speculating them earlier.
1450 // Collect the values used by the bonus inst
1451 SmallPtrSet<Value*, 4> UsedValues;
1452 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1453 OE = BonusInst->op_end(); OI != OE; ++OI) {
1455 if (!isa<Constant>(V))
1456 UsedValues.insert(V);
1459 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1460 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1462 // Walk up to four levels back up the use-def chain of the predecessor's
1463 // terminator to see if all those values were used. The choice of four
1464 // levels is arbitrary, to provide a compile-time-cost bound.
1465 while (!Worklist.empty()) {
1466 std::pair<Value*, unsigned> Pair = Worklist.back();
1467 Worklist.pop_back();
1469 if (Pair.second >= 4) continue;
1470 UsedValues.erase(Pair.first);
1471 if (UsedValues.empty()) break;
1473 if (Instruction* I = dyn_cast<Instruction>(Pair.first)) {
1474 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1476 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1480 if (!UsedValues.empty()) return false;
1483 Instruction::BinaryOps Opc;
1484 bool InvertPredCond = false;
1486 if (PBI->getSuccessor(0) == TrueDest)
1487 Opc = Instruction::Or;
1488 else if (PBI->getSuccessor(1) == FalseDest)
1489 Opc = Instruction::And;
1490 else if (PBI->getSuccessor(0) == FalseDest)
1491 Opc = Instruction::And, InvertPredCond = true;
1492 else if (PBI->getSuccessor(1) == TrueDest)
1493 Opc = Instruction::Or, InvertPredCond = true;
1497 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1499 // If we need to invert the condition in the pred block to match, do so now.
1500 if (InvertPredCond) {
1502 BinaryOperator::CreateNot(PBI->getCondition(),
1503 PBI->getCondition()->getName()+".not", PBI);
1504 PBI->setCondition(NewCond);
1505 BasicBlock *OldTrue = PBI->getSuccessor(0);
1506 BasicBlock *OldFalse = PBI->getSuccessor(1);
1507 PBI->setSuccessor(0, OldFalse);
1508 PBI->setSuccessor(1, OldTrue);
1511 // If we have a bonus inst, clone it into the predecessor block.
1512 Instruction *NewBonus = 0;
1514 NewBonus = BonusInst->clone();
1515 PredBlock->getInstList().insert(PBI, NewBonus);
1516 NewBonus->takeName(BonusInst);
1517 BonusInst->setName(BonusInst->getName()+".old");
1520 // Clone Cond into the predecessor basic block, and or/and the
1521 // two conditions together.
1522 Instruction *New = Cond->clone();
1523 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1524 PredBlock->getInstList().insert(PBI, New);
1525 New->takeName(Cond);
1526 Cond->setName(New->getName()+".old");
1528 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1529 New, "or.cond", PBI);
1530 PBI->setCondition(NewCond);
1531 if (PBI->getSuccessor(0) == BB) {
1532 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1533 PBI->setSuccessor(0, TrueDest);
1535 if (PBI->getSuccessor(1) == BB) {
1536 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1537 PBI->setSuccessor(1, FalseDest);
1544 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1545 /// predecessor of another block, this function tries to simplify it. We know
1546 /// that PBI and BI are both conditional branches, and BI is in one of the
1547 /// successor blocks of PBI - PBI branches to BI.
1548 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1549 assert(PBI->isConditional() && BI->isConditional());
1550 BasicBlock *BB = BI->getParent();
1552 // If this block ends with a branch instruction, and if there is a
1553 // predecessor that ends on a branch of the same condition, make
1554 // this conditional branch redundant.
1555 if (PBI->getCondition() == BI->getCondition() &&
1556 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1557 // Okay, the outcome of this conditional branch is statically
1558 // knowable. If this block had a single pred, handle specially.
1559 if (BB->getSinglePredecessor()) {
1560 // Turn this into a branch on constant.
1561 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1562 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1564 return true; // Nuke the branch on constant.
1567 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1568 // in the constant and simplify the block result. Subsequent passes of
1569 // simplifycfg will thread the block.
1570 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1571 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1572 BI->getCondition()->getName() + ".pr",
1574 // Okay, we're going to insert the PHI node. Since PBI is not the only
1575 // predecessor, compute the PHI'd conditional value for all of the preds.
1576 // Any predecessor where the condition is not computable we keep symbolic.
1577 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1578 BasicBlock *P = *PI;
1579 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
1580 PBI != BI && PBI->isConditional() &&
1581 PBI->getCondition() == BI->getCondition() &&
1582 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1583 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1584 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1587 NewPN->addIncoming(BI->getCondition(), P);
1591 BI->setCondition(NewPN);
1596 // If this is a conditional branch in an empty block, and if any
1597 // predecessors is a conditional branch to one of our destinations,
1598 // fold the conditions into logical ops and one cond br.
1599 BasicBlock::iterator BBI = BB->begin();
1600 // Ignore dbg intrinsics.
1601 while (isa<DbgInfoIntrinsic>(BBI))
1607 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1612 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1614 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1615 PBIOp = 0, BIOp = 1;
1616 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1617 PBIOp = 1, BIOp = 0;
1618 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1623 // Check to make sure that the other destination of this branch
1624 // isn't BB itself. If so, this is an infinite loop that will
1625 // keep getting unwound.
1626 if (PBI->getSuccessor(PBIOp) == BB)
1629 // Do not perform this transformation if it would require
1630 // insertion of a large number of select instructions. For targets
1631 // without predication/cmovs, this is a big pessimization.
1632 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1634 unsigned NumPhis = 0;
1635 for (BasicBlock::iterator II = CommonDest->begin();
1636 isa<PHINode>(II); ++II, ++NumPhis)
1637 if (NumPhis > 2) // Disable this xform.
1640 // Finally, if everything is ok, fold the branches to logical ops.
1641 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1643 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
1644 << "AND: " << *BI->getParent());
1647 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1648 // branch in it, where one edge (OtherDest) goes back to itself but the other
1649 // exits. We don't *know* that the program avoids the infinite loop
1650 // (even though that seems likely). If we do this xform naively, we'll end up
1651 // recursively unpeeling the loop. Since we know that (after the xform is
1652 // done) that the block *is* infinite if reached, we just make it an obviously
1653 // infinite loop with no cond branch.
1654 if (OtherDest == BB) {
1655 // Insert it at the end of the function, because it's either code,
1656 // or it won't matter if it's hot. :)
1657 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1658 "infloop", BB->getParent());
1659 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1660 OtherDest = InfLoopBlock;
1663 DEBUG(dbgs() << *PBI->getParent()->getParent());
1665 // BI may have other predecessors. Because of this, we leave
1666 // it alone, but modify PBI.
1668 // Make sure we get to CommonDest on True&True directions.
1669 Value *PBICond = PBI->getCondition();
1671 PBICond = BinaryOperator::CreateNot(PBICond,
1672 PBICond->getName()+".not",
1674 Value *BICond = BI->getCondition();
1676 BICond = BinaryOperator::CreateNot(BICond,
1677 BICond->getName()+".not",
1679 // Merge the conditions.
1680 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1682 // Modify PBI to branch on the new condition to the new dests.
1683 PBI->setCondition(Cond);
1684 PBI->setSuccessor(0, CommonDest);
1685 PBI->setSuccessor(1, OtherDest);
1687 // OtherDest may have phi nodes. If so, add an entry from PBI's
1688 // block that are identical to the entries for BI's block.
1690 for (BasicBlock::iterator II = OtherDest->begin();
1691 (PN = dyn_cast<PHINode>(II)); ++II) {
1692 Value *V = PN->getIncomingValueForBlock(BB);
1693 PN->addIncoming(V, PBI->getParent());
1696 // We know that the CommonDest already had an edge from PBI to
1697 // it. If it has PHIs though, the PHIs may have different
1698 // entries for BB and PBI's BB. If so, insert a select to make
1700 for (BasicBlock::iterator II = CommonDest->begin();
1701 (PN = dyn_cast<PHINode>(II)); ++II) {
1702 Value *BIV = PN->getIncomingValueForBlock(BB);
1703 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1704 Value *PBIV = PN->getIncomingValue(PBBIdx);
1706 // Insert a select in PBI to pick the right value.
1707 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1708 PBIV->getName()+".mux", PBI);
1709 PN->setIncomingValue(PBBIdx, NV);
1713 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1714 DEBUG(dbgs() << *PBI->getParent()->getParent());
1716 // This basic block is probably dead. We know it has at least
1717 // one fewer predecessor.
1721 bool SimplifyCFGOpt::run(BasicBlock *BB) {
1722 bool Changed = false;
1723 Function *M = BB->getParent();
1725 assert(BB && BB->getParent() && "Block not embedded in function!");
1726 assert(BB->getTerminator() && "Degenerate basic block encountered!");
1727 assert(&BB->getParent()->getEntryBlock() != BB &&
1728 "Can't Simplify entry block!");
1730 // Remove basic blocks that have no predecessors... or that just have themself
1731 // as a predecessor. These are unreachable.
1732 if (pred_begin(BB) == pred_end(BB) || BB->getSinglePredecessor() == BB) {
1733 DEBUG(dbgs() << "Removing BB: \n" << *BB);
1734 DeleteDeadBlock(BB);
1738 // Check to see if we can constant propagate this terminator instruction
1740 Changed |= ConstantFoldTerminator(BB);
1742 // Check for and eliminate duplicate PHI nodes in this block.
1743 Changed |= EliminateDuplicatePHINodes(BB);
1745 // If there is a trivial two-entry PHI node in this basic block, and we can
1746 // eliminate it, do so now.
1747 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1748 if (PN->getNumIncomingValues() == 2)
1749 Changed |= FoldTwoEntryPHINode(PN);
1751 // If this is a returning block with only PHI nodes in it, fold the return
1752 // instruction into any unconditional branch predecessors.
1754 // If any predecessor is a conditional branch that just selects among
1755 // different return values, fold the replace the branch/return with a select
1757 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1758 if (isTerminatorFirstRelevantInsn(BB, BB->getTerminator())) {
1759 // Find predecessors that end with branches.
1760 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1761 SmallVector<BranchInst*, 8> CondBranchPreds;
1762 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1763 BasicBlock *P = *PI;
1764 TerminatorInst *PTI = P->getTerminator();
1765 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1766 if (BI->isUnconditional())
1767 UncondBranchPreds.push_back(P);
1769 CondBranchPreds.push_back(BI);
1773 // If we found some, do the transformation!
1774 if (!UncondBranchPreds.empty()) {
1775 while (!UncondBranchPreds.empty()) {
1776 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
1777 DEBUG(dbgs() << "FOLDING: " << *BB
1778 << "INTO UNCOND BRANCH PRED: " << *Pred);
1779 Instruction *UncondBranch = Pred->getTerminator();
1780 // Clone the return and add it to the end of the predecessor.
1781 Instruction *NewRet = RI->clone();
1782 Pred->getInstList().push_back(NewRet);
1784 // If the return instruction returns a value, and if the value was a
1785 // PHI node in "BB", propagate the right value into the return.
1786 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
1788 if (PHINode *PN = dyn_cast<PHINode>(*i))
1789 if (PN->getParent() == BB)
1790 *i = PN->getIncomingValueForBlock(Pred);
1792 // Update any PHI nodes in the returning block to realize that we no
1793 // longer branch to them.
1794 BB->removePredecessor(Pred);
1795 Pred->getInstList().erase(UncondBranch);
1798 // If we eliminated all predecessors of the block, delete the block now.
1799 if (pred_begin(BB) == pred_end(BB))
1800 // We know there are no successors, so just nuke the block.
1801 M->getBasicBlockList().erase(BB);
1806 // Check out all of the conditional branches going to this return
1807 // instruction. If any of them just select between returns, change the
1808 // branch itself into a select/return pair.
1809 while (!CondBranchPreds.empty()) {
1810 BranchInst *BI = CondBranchPreds.pop_back_val();
1812 // Check to see if the non-BB successor is also a return block.
1813 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
1814 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
1815 SimplifyCondBranchToTwoReturns(BI))
1819 } else if (isa<UnwindInst>(BB->begin())) {
1820 // Check to see if the first instruction in this block is just an unwind.
1821 // If so, replace any invoke instructions which use this as an exception
1822 // destination with call instructions.
1824 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1825 while (!Preds.empty()) {
1826 BasicBlock *Pred = Preds.back();
1827 if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
1828 if (II->getUnwindDest() == BB) {
1829 // Insert a new branch instruction before the invoke, because this
1830 // is now a fall through.
1831 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1832 Pred->getInstList().remove(II); // Take out of symbol table
1834 // Insert the call now.
1835 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
1836 CallInst *CI = CallInst::Create(II->getCalledValue(),
1837 Args.begin(), Args.end(),
1839 CI->setCallingConv(II->getCallingConv());
1840 CI->setAttributes(II->getAttributes());
1841 // If the invoke produced a value, the Call now does instead.
1842 II->replaceAllUsesWith(CI);
1850 // If this block is now dead, remove it.
1851 if (pred_begin(BB) == pred_end(BB)) {
1852 // We know there are no successors, so just nuke the block.
1853 M->getBasicBlockList().erase(BB);
1857 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1858 if (isValueEqualityComparison(SI)) {
1859 // If we only have one predecessor, and if it is a branch on this value,
1860 // see if that predecessor totally determines the outcome of this switch.
1861 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1862 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
1863 return SimplifyCFG(BB) || 1;
1865 // If the block only contains the switch, see if we can fold the block
1866 // away into any preds.
1867 BasicBlock::iterator BBI = BB->begin();
1868 // Ignore dbg intrinsics.
1869 while (isa<DbgInfoIntrinsic>(BBI))
1872 if (FoldValueComparisonIntoPredecessors(SI))
1873 return SimplifyCFG(BB) || 1;
1875 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1876 if (BI->isUnconditional()) {
1877 BasicBlock::iterator BBI = BB->getFirstNonPHI();
1879 // Ignore dbg intrinsics.
1880 while (isa<DbgInfoIntrinsic>(BBI))
1882 if (BBI->isTerminator()) // Terminator is the only non-phi instruction!
1883 if (TryToSimplifyUncondBranchFromEmptyBlock(BB))
1886 } else { // Conditional branch
1887 if (isValueEqualityComparison(BI)) {
1888 // If we only have one predecessor, and if it is a branch on this value,
1889 // see if that predecessor totally determines the outcome of this
1891 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1892 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
1893 return SimplifyCFG(BB) | true;
1895 // This block must be empty, except for the setcond inst, if it exists.
1896 // Ignore dbg intrinsics.
1897 BasicBlock::iterator I = BB->begin();
1898 // Ignore dbg intrinsics.
1899 while (isa<DbgInfoIntrinsic>(I))
1902 if (FoldValueComparisonIntoPredecessors(BI))
1903 return SimplifyCFG(BB) | true;
1904 } else if (&*I == cast<Instruction>(BI->getCondition())){
1906 // Ignore dbg intrinsics.
1907 while (isa<DbgInfoIntrinsic>(I))
1910 if (FoldValueComparisonIntoPredecessors(BI))
1911 return SimplifyCFG(BB) | true;
1916 // If this is a branch on a phi node in the current block, thread control
1917 // through this block if any PHI node entries are constants.
1918 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
1919 if (PN->getParent() == BI->getParent())
1920 if (FoldCondBranchOnPHI(BI))
1921 return SimplifyCFG(BB) | true;
1923 // If this basic block is ONLY a setcc and a branch, and if a predecessor
1924 // branches to us and one of our successors, fold the setcc into the
1925 // predecessor and use logical operations to pick the right destination.
1926 if (FoldBranchToCommonDest(BI))
1927 return SimplifyCFG(BB) | true;
1930 // Scan predecessor blocks for conditional branches.
1931 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1932 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1933 if (PBI != BI && PBI->isConditional())
1934 if (SimplifyCondBranchToCondBranch(PBI, BI))
1935 return SimplifyCFG(BB) | true;
1937 } else if (isa<UnreachableInst>(BB->getTerminator())) {
1938 // If there are any instructions immediately before the unreachable that can
1939 // be removed, do so.
1940 Instruction *Unreachable = BB->getTerminator();
1941 while (Unreachable != BB->begin()) {
1942 BasicBlock::iterator BBI = Unreachable;
1944 // Do not delete instructions that can have side effects, like calls
1945 // (which may never return) and volatile loads and stores.
1946 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
1948 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
1949 if (SI->isVolatile())
1952 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
1953 if (LI->isVolatile())
1956 // Delete this instruction
1957 BB->getInstList().erase(BBI);
1961 // If the unreachable instruction is the first in the block, take a gander
1962 // at all of the predecessors of this instruction, and simplify them.
1963 if (&BB->front() == Unreachable) {
1964 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1965 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1966 TerminatorInst *TI = Preds[i]->getTerminator();
1968 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1969 if (BI->isUnconditional()) {
1970 if (BI->getSuccessor(0) == BB) {
1971 new UnreachableInst(TI->getContext(), TI);
1972 TI->eraseFromParent();
1976 if (BI->getSuccessor(0) == BB) {
1977 BranchInst::Create(BI->getSuccessor(1), BI);
1978 EraseTerminatorInstAndDCECond(BI);
1979 } else if (BI->getSuccessor(1) == BB) {
1980 BranchInst::Create(BI->getSuccessor(0), BI);
1981 EraseTerminatorInstAndDCECond(BI);
1985 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1986 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1987 if (SI->getSuccessor(i) == BB) {
1988 BB->removePredecessor(SI->getParent());
1993 // If the default value is unreachable, figure out the most popular
1994 // destination and make it the default.
1995 if (SI->getSuccessor(0) == BB) {
1996 std::map<BasicBlock*, unsigned> Popularity;
1997 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1998 Popularity[SI->getSuccessor(i)]++;
2000 // Find the most popular block.
2001 unsigned MaxPop = 0;
2002 BasicBlock *MaxBlock = 0;
2003 for (std::map<BasicBlock*, unsigned>::iterator
2004 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2005 if (I->second > MaxPop) {
2007 MaxBlock = I->first;
2011 // Make this the new default, allowing us to delete any explicit
2013 SI->setSuccessor(0, MaxBlock);
2016 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2018 if (isa<PHINode>(MaxBlock->begin()))
2019 for (unsigned i = 0; i != MaxPop-1; ++i)
2020 MaxBlock->removePredecessor(SI->getParent());
2022 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2023 if (SI->getSuccessor(i) == MaxBlock) {
2029 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2030 if (II->getUnwindDest() == BB) {
2031 // Convert the invoke to a call instruction. This would be a good
2032 // place to note that the call does not throw though.
2033 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2034 II->removeFromParent(); // Take out of symbol table
2036 // Insert the call now...
2037 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2038 CallInst *CI = CallInst::Create(II->getCalledValue(),
2039 Args.begin(), Args.end(),
2041 CI->setCallingConv(II->getCallingConv());
2042 CI->setAttributes(II->getAttributes());
2043 // If the invoke produced a value, the call does now instead.
2044 II->replaceAllUsesWith(CI);
2051 // If this block is now dead, remove it.
2052 if (pred_begin(BB) == pred_end(BB)) {
2053 // We know there are no successors, so just nuke the block.
2054 M->getBasicBlockList().erase(BB);
2060 // Merge basic blocks into their predecessor if there is only one distinct
2061 // pred, and if there is only one distinct successor of the predecessor, and
2062 // if there are no PHI nodes.
2064 if (MergeBlockIntoPredecessor(BB))
2067 // Otherwise, if this block only has a single predecessor, and if that block
2068 // is a conditional branch, see if we can hoist any code from this block up
2069 // into our predecessor.
2070 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
2071 BasicBlock *OnlyPred = *PI++;
2072 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
2073 if (*PI != OnlyPred) {
2074 OnlyPred = 0; // There are multiple different predecessors...
2079 if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
2080 if (BI->isConditional()) {
2081 // Get the other block.
2082 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
2083 PI = pred_begin(OtherBB);
2086 if (PI == pred_end(OtherBB)) {
2087 // We have a conditional branch to two blocks that are only reachable
2088 // from the condbr. We know that the condbr dominates the two blocks,
2089 // so see if there is any identical code in the "then" and "else"
2090 // blocks. If so, we can hoist it up to the branching block.
2091 Changed |= HoistThenElseCodeToIf(BI);
2093 BasicBlock* OnlySucc = NULL;
2094 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
2098 else if (*SI != OnlySucc) {
2099 OnlySucc = 0; // There are multiple distinct successors!
2104 if (OnlySucc == OtherBB) {
2105 // If BB's only successor is the other successor of the predecessor,
2106 // i.e. a triangle, see if we can hoist any code from this block up
2107 // to the "if" block.
2108 Changed |= SpeculativelyExecuteBB(BI, BB);
2113 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2114 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2115 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2116 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
2117 Instruction *Cond = cast<Instruction>(BI->getCondition());
2118 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2119 // 'setne's and'ed together, collect them.
2121 std::vector<ConstantInt*> Values;
2122 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
2124 // There might be duplicate constants in the list, which the switch
2125 // instruction can't handle, remove them now.
2126 std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
2127 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2129 // Figure out which block is which destination.
2130 BasicBlock *DefaultBB = BI->getSuccessor(1);
2131 BasicBlock *EdgeBB = BI->getSuccessor(0);
2132 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2134 // Convert pointer to int before we switch.
2135 if (CompVal->getType()->isPointerTy()) {
2136 assert(TD && "Cannot switch on pointer without TargetData");
2137 CompVal = new PtrToIntInst(CompVal,
2138 TD->getIntPtrType(CompVal->getContext()),
2142 // Create the new switch instruction now.
2143 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
2146 // Add all of the 'cases' to the switch instruction.
2147 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2148 New->addCase(Values[i], EdgeBB);
2150 // We added edges from PI to the EdgeBB. As such, if there were any
2151 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2152 // the number of edges added.
2153 for (BasicBlock::iterator BBI = EdgeBB->begin();
2154 isa<PHINode>(BBI); ++BBI) {
2155 PHINode *PN = cast<PHINode>(BBI);
2156 Value *InVal = PN->getIncomingValueForBlock(*PI);
2157 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2158 PN->addIncoming(InVal, *PI);
2161 // Erase the old branch instruction.
2162 EraseTerminatorInstAndDCECond(BI);
2170 /// SimplifyCFG - This function is used to do simplification of a CFG. For
2171 /// example, it adjusts branches to branches to eliminate the extra hop, it
2172 /// eliminates unreachable basic blocks, and does other "peephole" optimization
2173 /// of the CFG. It returns true if a modification was made.
2175 /// WARNING: The entry node of a function may not be simplified.
2177 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
2178 return SimplifyCFGOpt(TD).run(BB);