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/DerivedTypes.h"
18 #include "llvm/GlobalVariable.h"
19 #include "llvm/IRBuilder.h"
20 #include "llvm/Instructions.h"
21 #include "llvm/IntrinsicInst.h"
22 #include "llvm/LLVMContext.h"
23 #include "llvm/MDBuilder.h"
24 #include "llvm/Metadata.h"
25 #include "llvm/Operator.h"
26 #include "llvm/Type.h"
27 #include "llvm/ADT/DenseMap.h"
28 #include "llvm/ADT/STLExtras.h"
29 #include "llvm/ADT/SetVector.h"
30 #include "llvm/ADT/SmallPtrSet.h"
31 #include "llvm/ADT/SmallVector.h"
32 #include "llvm/ADT/Statistic.h"
33 #include "llvm/Analysis/InstructionSimplify.h"
34 #include "llvm/Analysis/ValueTracking.h"
35 #include "llvm/Support/CFG.h"
36 #include "llvm/Support/CommandLine.h"
37 #include "llvm/Support/ConstantRange.h"
38 #include "llvm/Support/Debug.h"
39 #include "llvm/Support/NoFolder.h"
40 #include "llvm/Support/raw_ostream.h"
41 #include "llvm/Target/TargetData.h"
42 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
48 static cl::opt<unsigned>
49 PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(1),
50 cl::desc("Control the amount of phi node folding to perform (default = 1)"));
53 DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false),
54 cl::desc("Duplicate return instructions into unconditional branches"));
56 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
59 /// ValueEqualityComparisonCase - Represents a case of a switch.
60 struct ValueEqualityComparisonCase {
64 ValueEqualityComparisonCase(ConstantInt *Value, BasicBlock *Dest)
65 : Value(Value), Dest(Dest) {}
67 bool operator<(ValueEqualityComparisonCase RHS) const {
68 // Comparing pointers is ok as we only rely on the order for uniquing.
69 return Value < RHS.Value;
73 class SimplifyCFGOpt {
74 const TargetData *const TD;
76 Value *isValueEqualityComparison(TerminatorInst *TI);
77 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
78 std::vector<ValueEqualityComparisonCase> &Cases);
79 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
81 IRBuilder<> &Builder);
82 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
83 IRBuilder<> &Builder);
85 bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder);
86 bool SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder);
87 bool SimplifyUnreachable(UnreachableInst *UI);
88 bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
89 bool SimplifyIndirectBr(IndirectBrInst *IBI);
90 bool SimplifyUncondBranch(BranchInst *BI, IRBuilder <> &Builder);
91 bool SimplifyCondBranch(BranchInst *BI, IRBuilder <>&Builder);
94 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
95 bool run(BasicBlock *BB);
99 /// SafeToMergeTerminators - Return true if it is safe to merge these two
100 /// terminator instructions together.
102 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
103 if (SI1 == SI2) return false; // Can't merge with self!
105 // It is not safe to merge these two switch instructions if they have a common
106 // successor, and if that successor has a PHI node, and if *that* PHI node has
107 // conflicting incoming values from the two switch blocks.
108 BasicBlock *SI1BB = SI1->getParent();
109 BasicBlock *SI2BB = SI2->getParent();
110 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
112 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
113 if (SI1Succs.count(*I))
114 for (BasicBlock::iterator BBI = (*I)->begin();
115 isa<PHINode>(BBI); ++BBI) {
116 PHINode *PN = cast<PHINode>(BBI);
117 if (PN->getIncomingValueForBlock(SI1BB) !=
118 PN->getIncomingValueForBlock(SI2BB))
125 /// isProfitableToFoldUnconditional - Return true if it is safe and profitable
126 /// to merge these two terminator instructions together, where SI1 is an
127 /// unconditional branch. PhiNodes will store all PHI nodes in common
130 static bool isProfitableToFoldUnconditional(BranchInst *SI1,
133 SmallVectorImpl<PHINode*> &PhiNodes) {
134 if (SI1 == SI2) return false; // Can't merge with self!
135 assert(SI1->isUnconditional() && SI2->isConditional());
137 // We fold the unconditional branch if we can easily update all PHI nodes in
138 // common successors:
139 // 1> We have a constant incoming value for the conditional branch;
140 // 2> We have "Cond" as the incoming value for the unconditional branch;
141 // 3> SI2->getCondition() and Cond have same operands.
142 CmpInst *Ci2 = dyn_cast<CmpInst>(SI2->getCondition());
143 if (!Ci2) return false;
144 if (!(Cond->getOperand(0) == Ci2->getOperand(0) &&
145 Cond->getOperand(1) == Ci2->getOperand(1)) &&
146 !(Cond->getOperand(0) == Ci2->getOperand(1) &&
147 Cond->getOperand(1) == Ci2->getOperand(0)))
150 BasicBlock *SI1BB = SI1->getParent();
151 BasicBlock *SI2BB = SI2->getParent();
152 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
153 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
154 if (SI1Succs.count(*I))
155 for (BasicBlock::iterator BBI = (*I)->begin();
156 isa<PHINode>(BBI); ++BBI) {
157 PHINode *PN = cast<PHINode>(BBI);
158 if (PN->getIncomingValueForBlock(SI1BB) != Cond ||
159 !isa<ConstantInt>(PN->getIncomingValueForBlock(SI2BB)))
161 PhiNodes.push_back(PN);
166 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
167 /// now be entries in it from the 'NewPred' block. The values that will be
168 /// flowing into the PHI nodes will be the same as those coming in from
169 /// ExistPred, an existing predecessor of Succ.
170 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
171 BasicBlock *ExistPred) {
172 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
175 for (BasicBlock::iterator I = Succ->begin();
176 (PN = dyn_cast<PHINode>(I)); ++I)
177 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
181 /// GetIfCondition - Given a basic block (BB) with two predecessors (and at
182 /// least one PHI node in it), check to see if the merge at this block is due
183 /// to an "if condition". If so, return the boolean condition that determines
184 /// which entry into BB will be taken. Also, return by references the block
185 /// that will be entered from if the condition is true, and the block that will
186 /// be entered if the condition is false.
188 /// This does no checking to see if the true/false blocks have large or unsavory
189 /// instructions in them.
190 static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
191 BasicBlock *&IfFalse) {
192 PHINode *SomePHI = cast<PHINode>(BB->begin());
193 assert(SomePHI->getNumIncomingValues() == 2 &&
194 "Function can only handle blocks with 2 predecessors!");
195 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
196 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
198 // We can only handle branches. Other control flow will be lowered to
199 // branches if possible anyway.
200 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
201 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
202 if (Pred1Br == 0 || Pred2Br == 0)
205 // Eliminate code duplication by ensuring that Pred1Br is conditional if
207 if (Pred2Br->isConditional()) {
208 // If both branches are conditional, we don't have an "if statement". In
209 // reality, we could transform this case, but since the condition will be
210 // required anyway, we stand no chance of eliminating it, so the xform is
211 // probably not profitable.
212 if (Pred1Br->isConditional())
215 std::swap(Pred1, Pred2);
216 std::swap(Pred1Br, Pred2Br);
219 if (Pred1Br->isConditional()) {
220 // The only thing we have to watch out for here is to make sure that Pred2
221 // doesn't have incoming edges from other blocks. If it does, the condition
222 // doesn't dominate BB.
223 if (Pred2->getSinglePredecessor() == 0)
226 // If we found a conditional branch predecessor, make sure that it branches
227 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
228 if (Pred1Br->getSuccessor(0) == BB &&
229 Pred1Br->getSuccessor(1) == Pred2) {
232 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
233 Pred1Br->getSuccessor(1) == BB) {
237 // We know that one arm of the conditional goes to BB, so the other must
238 // go somewhere unrelated, and this must not be an "if statement".
242 return Pred1Br->getCondition();
245 // Ok, if we got here, both predecessors end with an unconditional branch to
246 // BB. Don't panic! If both blocks only have a single (identical)
247 // predecessor, and THAT is a conditional branch, then we're all ok!
248 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
249 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
252 // Otherwise, if this is a conditional branch, then we can use it!
253 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
254 if (BI == 0) return 0;
256 assert(BI->isConditional() && "Two successors but not conditional?");
257 if (BI->getSuccessor(0) == Pred1) {
264 return BI->getCondition();
267 /// ComputeSpeculuationCost - Compute an abstract "cost" of speculating the
268 /// given instruction, which is assumed to be safe to speculate. 1 means
269 /// cheap, 2 means less cheap, and UINT_MAX means prohibitively expensive.
270 static unsigned ComputeSpeculationCost(const User *I) {
271 assert(isSafeToSpeculativelyExecute(I) &&
272 "Instruction is not safe to speculatively execute!");
273 switch (Operator::getOpcode(I)) {
275 // In doubt, be conservative.
277 case Instruction::GetElementPtr:
278 // GEPs are cheap if all indices are constant.
279 if (!cast<GEPOperator>(I)->hasAllConstantIndices())
282 case Instruction::Load:
283 case Instruction::Add:
284 case Instruction::Sub:
285 case Instruction::And:
286 case Instruction::Or:
287 case Instruction::Xor:
288 case Instruction::Shl:
289 case Instruction::LShr:
290 case Instruction::AShr:
291 case Instruction::ICmp:
292 case Instruction::Trunc:
293 case Instruction::ZExt:
294 case Instruction::SExt:
295 return 1; // These are all cheap.
297 case Instruction::Call:
298 case Instruction::Select:
303 /// DominatesMergePoint - If we have a merge point of an "if condition" as
304 /// accepted above, return true if the specified value dominates the block. We
305 /// don't handle the true generality of domination here, just a special case
306 /// which works well enough for us.
308 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
309 /// see if V (which must be an instruction) and its recursive operands
310 /// that do not dominate BB have a combined cost lower than CostRemaining and
311 /// are non-trapping. If both are true, the instruction is inserted into the
312 /// set and true is returned.
314 /// The cost for most non-trapping instructions is defined as 1 except for
315 /// Select whose cost is 2.
317 /// After this function returns, CostRemaining is decreased by the cost of
318 /// V plus its non-dominating operands. If that cost is greater than
319 /// CostRemaining, false is returned and CostRemaining is undefined.
320 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
321 SmallPtrSet<Instruction*, 4> *AggressiveInsts,
322 unsigned &CostRemaining) {
323 Instruction *I = dyn_cast<Instruction>(V);
325 // Non-instructions all dominate instructions, but not all constantexprs
326 // can be executed unconditionally.
327 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
332 BasicBlock *PBB = I->getParent();
334 // We don't want to allow weird loops that might have the "if condition" in
335 // the bottom of this block.
336 if (PBB == BB) return false;
338 // If this instruction is defined in a block that contains an unconditional
339 // branch to BB, then it must be in the 'conditional' part of the "if
340 // statement". If not, it definitely dominates the region.
341 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
342 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB)
345 // If we aren't allowing aggressive promotion anymore, then don't consider
346 // instructions in the 'if region'.
347 if (AggressiveInsts == 0) return false;
349 // If we have seen this instruction before, don't count it again.
350 if (AggressiveInsts->count(I)) return true;
352 // Okay, it looks like the instruction IS in the "condition". Check to
353 // see if it's a cheap instruction to unconditionally compute, and if it
354 // only uses stuff defined outside of the condition. If so, hoist it out.
355 if (!isSafeToSpeculativelyExecute(I))
358 unsigned Cost = ComputeSpeculationCost(I);
360 if (Cost > CostRemaining)
363 CostRemaining -= Cost;
365 // Okay, we can only really hoist these out if their operands do
366 // not take us over the cost threshold.
367 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
368 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining))
370 // Okay, it's safe to do this! Remember this instruction.
371 AggressiveInsts->insert(I);
375 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
376 /// and PointerNullValue. Return NULL if value is not a constant int.
377 static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
378 // Normal constant int.
379 ConstantInt *CI = dyn_cast<ConstantInt>(V);
380 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
383 // This is some kind of pointer constant. Turn it into a pointer-sized
384 // ConstantInt if possible.
385 IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
387 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
388 if (isa<ConstantPointerNull>(V))
389 return ConstantInt::get(PtrTy, 0);
391 // IntToPtr const int.
392 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
393 if (CE->getOpcode() == Instruction::IntToPtr)
394 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
395 // The constant is very likely to have the right type already.
396 if (CI->getType() == PtrTy)
399 return cast<ConstantInt>
400 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
405 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
406 /// collection of icmp eq/ne instructions that compare a value against a
407 /// constant, return the value being compared, and stick the constant into the
410 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
411 const TargetData *TD, bool isEQ, unsigned &UsedICmps) {
412 Instruction *I = dyn_cast<Instruction>(V);
413 if (I == 0) return 0;
415 // If this is an icmp against a constant, handle this as one of the cases.
416 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
417 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
418 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
421 return I->getOperand(0);
424 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
427 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
429 // If this is an and/!= check then we want to optimize "x ugt 2" into
432 Span = Span.inverse();
434 // If there are a ton of values, we don't want to make a ginormous switch.
435 if (Span.getSetSize().ugt(8) || Span.isEmptySet())
438 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
439 Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
441 return I->getOperand(0);
446 // Otherwise, we can only handle an | or &, depending on isEQ.
447 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
450 unsigned NumValsBeforeLHS = Vals.size();
451 unsigned UsedICmpsBeforeLHS = UsedICmps;
452 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
454 unsigned NumVals = Vals.size();
455 unsigned UsedICmpsBeforeRHS = UsedICmps;
456 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
460 Vals.resize(NumVals);
461 UsedICmps = UsedICmpsBeforeRHS;
464 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
465 // set it and return success.
466 if (Extra == 0 || Extra == I->getOperand(1)) {
467 Extra = I->getOperand(1);
471 Vals.resize(NumValsBeforeLHS);
472 UsedICmps = UsedICmpsBeforeLHS;
476 // If the LHS can't be folded in, but Extra is available and RHS can, try to
478 if (Extra == 0 || Extra == I->getOperand(0)) {
479 Value *OldExtra = Extra;
480 Extra = I->getOperand(0);
481 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
484 assert(Vals.size() == NumValsBeforeLHS);
491 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
492 Instruction *Cond = 0;
493 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
494 Cond = dyn_cast<Instruction>(SI->getCondition());
495 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
496 if (BI->isConditional())
497 Cond = dyn_cast<Instruction>(BI->getCondition());
498 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
499 Cond = dyn_cast<Instruction>(IBI->getAddress());
502 TI->eraseFromParent();
503 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
506 /// isValueEqualityComparison - Return true if the specified terminator checks
507 /// to see if a value is equal to constant integer value.
508 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
510 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
511 // Do not permit merging of large switch instructions into their
512 // predecessors unless there is only one predecessor.
513 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
514 pred_end(SI->getParent())) <= 128)
515 CV = SI->getCondition();
516 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
517 if (BI->isConditional() && BI->getCondition()->hasOneUse())
518 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
519 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
520 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
521 GetConstantInt(ICI->getOperand(1), TD))
522 CV = ICI->getOperand(0);
524 // Unwrap any lossless ptrtoint cast.
525 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
526 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
527 CV = PTII->getOperand(0);
531 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
532 /// decode all of the 'cases' that it represents and return the 'default' block.
533 BasicBlock *SimplifyCFGOpt::
534 GetValueEqualityComparisonCases(TerminatorInst *TI,
535 std::vector<ValueEqualityComparisonCase>
537 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
538 Cases.reserve(SI->getNumCases());
539 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i)
540 Cases.push_back(ValueEqualityComparisonCase(i.getCaseValue(),
541 i.getCaseSuccessor()));
542 return SI->getDefaultDest();
545 BranchInst *BI = cast<BranchInst>(TI);
546 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
547 BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE);
548 Cases.push_back(ValueEqualityComparisonCase(GetConstantInt(ICI->getOperand(1),
551 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
555 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
556 /// in the list that match the specified block.
557 static void EliminateBlockCases(BasicBlock *BB,
558 std::vector<ValueEqualityComparisonCase> &Cases) {
559 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
560 if (Cases[i].Dest == BB) {
561 Cases.erase(Cases.begin()+i);
566 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
569 ValuesOverlap(std::vector<ValueEqualityComparisonCase> &C1,
570 std::vector<ValueEqualityComparisonCase > &C2) {
571 std::vector<ValueEqualityComparisonCase> *V1 = &C1, *V2 = &C2;
573 // Make V1 be smaller than V2.
574 if (V1->size() > V2->size())
577 if (V1->size() == 0) return false;
578 if (V1->size() == 1) {
580 ConstantInt *TheVal = (*V1)[0].Value;
581 for (unsigned i = 0, e = V2->size(); i != e; ++i)
582 if (TheVal == (*V2)[i].Value)
586 // Otherwise, just sort both lists and compare element by element.
587 array_pod_sort(V1->begin(), V1->end());
588 array_pod_sort(V2->begin(), V2->end());
589 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
590 while (i1 != e1 && i2 != e2) {
591 if ((*V1)[i1].Value == (*V2)[i2].Value)
593 if ((*V1)[i1].Value < (*V2)[i2].Value)
601 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
602 /// terminator instruction and its block is known to only have a single
603 /// predecessor block, check to see if that predecessor is also a value
604 /// comparison with the same value, and if that comparison determines the
605 /// outcome of this comparison. If so, simplify TI. This does a very limited
606 /// form of jump threading.
607 bool SimplifyCFGOpt::
608 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
610 IRBuilder<> &Builder) {
611 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
612 if (!PredVal) return false; // Not a value comparison in predecessor.
614 Value *ThisVal = isValueEqualityComparison(TI);
615 assert(ThisVal && "This isn't a value comparison!!");
616 if (ThisVal != PredVal) return false; // Different predicates.
618 // Find out information about when control will move from Pred to TI's block.
619 std::vector<ValueEqualityComparisonCase> PredCases;
620 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
622 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
624 // Find information about how control leaves this block.
625 std::vector<ValueEqualityComparisonCase> ThisCases;
626 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
627 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
629 // If TI's block is the default block from Pred's comparison, potentially
630 // simplify TI based on this knowledge.
631 if (PredDef == TI->getParent()) {
632 // If we are here, we know that the value is none of those cases listed in
633 // PredCases. If there are any cases in ThisCases that are in PredCases, we
635 if (!ValuesOverlap(PredCases, ThisCases))
638 if (isa<BranchInst>(TI)) {
639 // Okay, one of the successors of this condbr is dead. Convert it to a
641 assert(ThisCases.size() == 1 && "Branch can only have one case!");
642 // Insert the new branch.
643 Instruction *NI = Builder.CreateBr(ThisDef);
646 // Remove PHI node entries for the dead edge.
647 ThisCases[0].Dest->removePredecessor(TI->getParent());
649 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
650 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
652 EraseTerminatorInstAndDCECond(TI);
656 SwitchInst *SI = cast<SwitchInst>(TI);
657 // Okay, TI has cases that are statically dead, prune them away.
658 SmallPtrSet<Constant*, 16> DeadCases;
659 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
660 DeadCases.insert(PredCases[i].Value);
662 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
663 << "Through successor TI: " << *TI);
665 for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) {
667 if (DeadCases.count(i.getCaseValue())) {
668 i.getCaseSuccessor()->removePredecessor(TI->getParent());
673 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
677 // Otherwise, TI's block must correspond to some matched value. Find out
678 // which value (or set of values) this is.
679 ConstantInt *TIV = 0;
680 BasicBlock *TIBB = TI->getParent();
681 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
682 if (PredCases[i].Dest == TIBB) {
684 return false; // Cannot handle multiple values coming to this block.
685 TIV = PredCases[i].Value;
687 assert(TIV && "No edge from pred to succ?");
689 // Okay, we found the one constant that our value can be if we get into TI's
690 // BB. Find out which successor will unconditionally be branched to.
691 BasicBlock *TheRealDest = 0;
692 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
693 if (ThisCases[i].Value == TIV) {
694 TheRealDest = ThisCases[i].Dest;
698 // If not handled by any explicit cases, it is handled by the default case.
699 if (TheRealDest == 0) TheRealDest = ThisDef;
701 // Remove PHI node entries for dead edges.
702 BasicBlock *CheckEdge = TheRealDest;
703 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
704 if (*SI != CheckEdge)
705 (*SI)->removePredecessor(TIBB);
709 // Insert the new branch.
710 Instruction *NI = Builder.CreateBr(TheRealDest);
713 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
714 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
716 EraseTerminatorInstAndDCECond(TI);
721 /// ConstantIntOrdering - This class implements a stable ordering of constant
722 /// integers that does not depend on their address. This is important for
723 /// applications that sort ConstantInt's to ensure uniqueness.
724 struct ConstantIntOrdering {
725 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
726 return LHS->getValue().ult(RHS->getValue());
731 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
732 const ConstantInt *LHS = *(const ConstantInt**)P1;
733 const ConstantInt *RHS = *(const ConstantInt**)P2;
734 if (LHS->getValue().ult(RHS->getValue()))
736 if (LHS->getValue() == RHS->getValue())
741 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
742 /// equality comparison instruction (either a switch or a branch on "X == c").
743 /// See if any of the predecessors of the terminator block are value comparisons
744 /// on the same value. If so, and if safe to do so, fold them together.
745 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
746 IRBuilder<> &Builder) {
747 BasicBlock *BB = TI->getParent();
748 Value *CV = isValueEqualityComparison(TI); // CondVal
749 assert(CV && "Not a comparison?");
750 bool Changed = false;
752 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
753 while (!Preds.empty()) {
754 BasicBlock *Pred = Preds.pop_back_val();
756 // See if the predecessor is a comparison with the same value.
757 TerminatorInst *PTI = Pred->getTerminator();
758 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
760 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
761 // Figure out which 'cases' to copy from SI to PSI.
762 std::vector<ValueEqualityComparisonCase> BBCases;
763 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
765 std::vector<ValueEqualityComparisonCase> PredCases;
766 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
768 // Based on whether the default edge from PTI goes to BB or not, fill in
769 // PredCases and PredDefault with the new switch cases we would like to
771 SmallVector<BasicBlock*, 8> NewSuccessors;
773 if (PredDefault == BB) {
774 // If this is the default destination from PTI, only the edges in TI
775 // that don't occur in PTI, or that branch to BB will be activated.
776 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
777 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
778 if (PredCases[i].Dest != BB)
779 PTIHandled.insert(PredCases[i].Value);
781 // The default destination is BB, we don't need explicit targets.
782 std::swap(PredCases[i], PredCases.back());
783 PredCases.pop_back();
787 // Reconstruct the new switch statement we will be building.
788 if (PredDefault != BBDefault) {
789 PredDefault->removePredecessor(Pred);
790 PredDefault = BBDefault;
791 NewSuccessors.push_back(BBDefault);
793 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
794 if (!PTIHandled.count(BBCases[i].Value) &&
795 BBCases[i].Dest != BBDefault) {
796 PredCases.push_back(BBCases[i]);
797 NewSuccessors.push_back(BBCases[i].Dest);
801 // If this is not the default destination from PSI, only the edges
802 // in SI that occur in PSI with a destination of BB will be
804 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
805 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
806 if (PredCases[i].Dest == BB) {
807 PTIHandled.insert(PredCases[i].Value);
808 std::swap(PredCases[i], PredCases.back());
809 PredCases.pop_back();
813 // Okay, now we know which constants were sent to BB from the
814 // predecessor. Figure out where they will all go now.
815 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
816 if (PTIHandled.count(BBCases[i].Value)) {
817 // If this is one we are capable of getting...
818 PredCases.push_back(BBCases[i]);
819 NewSuccessors.push_back(BBCases[i].Dest);
820 PTIHandled.erase(BBCases[i].Value);// This constant is taken care of
823 // If there are any constants vectored to BB that TI doesn't handle,
824 // they must go to the default destination of TI.
825 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
827 E = PTIHandled.end(); I != E; ++I) {
828 PredCases.push_back(ValueEqualityComparisonCase(*I, BBDefault));
829 NewSuccessors.push_back(BBDefault);
833 // Okay, at this point, we know which new successor Pred will get. Make
834 // sure we update the number of entries in the PHI nodes for these
836 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
837 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
839 Builder.SetInsertPoint(PTI);
840 // Convert pointer to int before we switch.
841 if (CV->getType()->isPointerTy()) {
842 assert(TD && "Cannot switch on pointer without TargetData");
843 CV = Builder.CreatePtrToInt(CV, TD->getIntPtrType(CV->getContext()),
847 // Now that the successors are updated, create the new Switch instruction.
848 SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault,
850 NewSI->setDebugLoc(PTI->getDebugLoc());
851 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
852 NewSI->addCase(PredCases[i].Value, PredCases[i].Dest);
854 EraseTerminatorInstAndDCECond(PTI);
856 // Okay, last check. If BB is still a successor of PSI, then we must
857 // have an infinite loop case. If so, add an infinitely looping block
858 // to handle the case to preserve the behavior of the code.
859 BasicBlock *InfLoopBlock = 0;
860 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
861 if (NewSI->getSuccessor(i) == BB) {
862 if (InfLoopBlock == 0) {
863 // Insert it at the end of the function, because it's either code,
864 // or it won't matter if it's hot. :)
865 InfLoopBlock = BasicBlock::Create(BB->getContext(),
866 "infloop", BB->getParent());
867 BranchInst::Create(InfLoopBlock, InfLoopBlock);
869 NewSI->setSuccessor(i, InfLoopBlock);
878 // isSafeToHoistInvoke - If we would need to insert a select that uses the
879 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
880 // would need to do this), we can't hoist the invoke, as there is nowhere
881 // to put the select in this case.
882 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
883 Instruction *I1, Instruction *I2) {
884 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
886 for (BasicBlock::iterator BBI = SI->begin();
887 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
888 Value *BB1V = PN->getIncomingValueForBlock(BB1);
889 Value *BB2V = PN->getIncomingValueForBlock(BB2);
890 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
898 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
899 /// BB2, hoist any common code in the two blocks up into the branch block. The
900 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
901 static bool HoistThenElseCodeToIf(BranchInst *BI) {
902 // This does very trivial matching, with limited scanning, to find identical
903 // instructions in the two blocks. In particular, we don't want to get into
904 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
905 // such, we currently just scan for obviously identical instructions in an
907 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
908 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
910 BasicBlock::iterator BB1_Itr = BB1->begin();
911 BasicBlock::iterator BB2_Itr = BB2->begin();
913 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
914 // Skip debug info if it is not identical.
915 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
916 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
917 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
918 while (isa<DbgInfoIntrinsic>(I1))
920 while (isa<DbgInfoIntrinsic>(I2))
923 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
924 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
927 // If we get here, we can hoist at least one instruction.
928 BasicBlock *BIParent = BI->getParent();
931 // If we are hoisting the terminator instruction, don't move one (making a
932 // broken BB), instead clone it, and remove BI.
933 if (isa<TerminatorInst>(I1))
934 goto HoistTerminator;
936 // For a normal instruction, we just move one to right before the branch,
937 // then replace all uses of the other with the first. Finally, we remove
938 // the now redundant second instruction.
939 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
940 if (!I2->use_empty())
941 I2->replaceAllUsesWith(I1);
942 I1->intersectOptionalDataWith(I2);
943 I2->eraseFromParent();
947 // Skip debug info if it is not identical.
948 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
949 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
950 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
951 while (isa<DbgInfoIntrinsic>(I1))
953 while (isa<DbgInfoIntrinsic>(I2))
956 } while (I1->isIdenticalToWhenDefined(I2));
961 // It may not be possible to hoist an invoke.
962 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
965 // Okay, it is safe to hoist the terminator.
966 Instruction *NT = I1->clone();
967 BIParent->getInstList().insert(BI, NT);
968 if (!NT->getType()->isVoidTy()) {
969 I1->replaceAllUsesWith(NT);
970 I2->replaceAllUsesWith(NT);
974 IRBuilder<true, NoFolder> Builder(NT);
975 // Hoisting one of the terminators from our successor is a great thing.
976 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
977 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
978 // nodes, so we insert select instruction to compute the final result.
979 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
980 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
982 for (BasicBlock::iterator BBI = SI->begin();
983 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
984 Value *BB1V = PN->getIncomingValueForBlock(BB1);
985 Value *BB2V = PN->getIncomingValueForBlock(BB2);
986 if (BB1V == BB2V) continue;
988 // These values do not agree. Insert a select instruction before NT
989 // that determines the right value.
990 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
992 SI = cast<SelectInst>
993 (Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,
994 BB1V->getName()+"."+BB2V->getName()));
996 // Make the PHI node use the select for all incoming values for BB1/BB2
997 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
998 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
999 PN->setIncomingValue(i, SI);
1003 // Update any PHI nodes in our new successors.
1004 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
1005 AddPredecessorToBlock(*SI, BIParent, BB1);
1007 EraseTerminatorInstAndDCECond(BI);
1011 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
1012 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
1013 /// (for now, restricted to a single instruction that's side effect free) from
1014 /// the BB1 into the branch block to speculatively execute it.
1019 /// br i1 %t1, label %BB1, label %BB2
1021 /// %t3 = add %t2, c
1027 /// %t4 = add %t2, c
1028 /// %t3 = select i1 %t1, %t2, %t3
1029 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
1030 // Only speculatively execution a single instruction (not counting the
1031 // terminator) for now.
1032 Instruction *HInst = NULL;
1033 Instruction *Term = BB1->getTerminator();
1034 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
1035 BBI != BBE; ++BBI) {
1036 Instruction *I = BBI;
1038 if (isa<DbgInfoIntrinsic>(I)) continue;
1039 if (I == Term) break;
1046 BasicBlock *BIParent = BI->getParent();
1048 // Check the instruction to be hoisted, if there is one.
1050 // Don't hoist the instruction if it's unsafe or expensive.
1051 if (!isSafeToSpeculativelyExecute(HInst))
1053 if (ComputeSpeculationCost(HInst) > PHINodeFoldingThreshold)
1056 // Do not hoist the instruction if any of its operands are defined but not
1057 // used in this BB. The transformation will prevent the operand from
1058 // being sunk into the use block.
1059 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1061 Instruction *OpI = dyn_cast<Instruction>(*i);
1062 if (OpI && OpI->getParent() == BIParent &&
1063 !OpI->mayHaveSideEffects() &&
1064 !OpI->isUsedInBasicBlock(BIParent))
1069 // Be conservative for now. FP select instruction can often be expensive.
1070 Value *BrCond = BI->getCondition();
1071 if (isa<FCmpInst>(BrCond))
1074 // If BB1 is actually on the false edge of the conditional branch, remember
1075 // to swap the select operands later.
1076 bool Invert = false;
1077 if (BB1 != BI->getSuccessor(0)) {
1078 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
1082 // Collect interesting PHIs, and scan for hazards.
1083 SmallSetVector<std::pair<Value *, Value *>, 4> PHIs;
1084 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
1085 for (BasicBlock::iterator I = BB2->begin();
1086 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1087 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1088 Value *BIParentV = PN->getIncomingValueForBlock(BIParent);
1090 // Skip PHIs which are trivial.
1091 if (BB1V == BIParentV)
1094 // Check for saftey.
1095 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BB1V)) {
1096 // An unfolded ConstantExpr could end up getting expanded into
1097 // Instructions. Don't speculate this and another instruction at
1101 if (!isSafeToSpeculativelyExecute(CE))
1103 if (ComputeSpeculationCost(CE) > PHINodeFoldingThreshold)
1107 // Ok, we may insert a select for this PHI.
1108 PHIs.insert(std::make_pair(BB1V, BIParentV));
1111 // If there are no PHIs to process, bail early. This helps ensure idempotence
1116 // If we get here, we can hoist the instruction and if-convert.
1117 DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *BB1 << "\n";);
1119 // Hoist the instruction.
1121 BIParent->getInstList().splice(BI, BB1->getInstList(), HInst);
1123 // Insert selects and rewrite the PHI operands.
1124 IRBuilder<true, NoFolder> Builder(BI);
1125 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
1126 Value *TrueV = PHIs[i].first;
1127 Value *FalseV = PHIs[i].second;
1129 // Create a select whose true value is the speculatively executed value and
1130 // false value is the previously determined FalseV.
1133 SI = cast<SelectInst>
1134 (Builder.CreateSelect(BrCond, FalseV, TrueV,
1135 FalseV->getName() + "." + TrueV->getName()));
1137 SI = cast<SelectInst>
1138 (Builder.CreateSelect(BrCond, TrueV, FalseV,
1139 TrueV->getName() + "." + FalseV->getName()));
1141 // Make the PHI node use the select for all incoming values for "then" and
1143 for (BasicBlock::iterator I = BB2->begin();
1144 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1145 unsigned BB1I = PN->getBasicBlockIndex(BB1);
1146 unsigned BIParentI = PN->getBasicBlockIndex(BIParent);
1147 Value *BB1V = PN->getIncomingValue(BB1I);
1148 Value *BIParentV = PN->getIncomingValue(BIParentI);
1149 if (TrueV == BB1V && FalseV == BIParentV) {
1150 PN->setIncomingValue(BB1I, SI);
1151 PN->setIncomingValue(BIParentI, SI);
1160 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1161 /// across this block.
1162 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1163 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1166 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1167 if (isa<DbgInfoIntrinsic>(BBI))
1169 if (Size > 10) return false; // Don't clone large BB's.
1172 // We can only support instructions that do not define values that are
1173 // live outside of the current basic block.
1174 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1176 Instruction *U = cast<Instruction>(*UI);
1177 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1180 // Looks ok, continue checking.
1186 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1187 /// that is defined in the same block as the branch and if any PHI entries are
1188 /// constants, thread edges corresponding to that entry to be branches to their
1189 /// ultimate destination.
1190 static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
1191 BasicBlock *BB = BI->getParent();
1192 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1193 // NOTE: we currently cannot transform this case if the PHI node is used
1194 // outside of the block.
1195 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1198 // Degenerate case of a single entry PHI.
1199 if (PN->getNumIncomingValues() == 1) {
1200 FoldSingleEntryPHINodes(PN->getParent());
1204 // Now we know that this block has multiple preds and two succs.
1205 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1207 // Okay, this is a simple enough basic block. See if any phi values are
1209 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1210 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1211 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1213 // Okay, we now know that all edges from PredBB should be revectored to
1214 // branch to RealDest.
1215 BasicBlock *PredBB = PN->getIncomingBlock(i);
1216 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1218 if (RealDest == BB) continue; // Skip self loops.
1219 // Skip if the predecessor's terminator is an indirect branch.
1220 if (isa<IndirectBrInst>(PredBB->getTerminator())) continue;
1222 // The dest block might have PHI nodes, other predecessors and other
1223 // difficult cases. Instead of being smart about this, just insert a new
1224 // block that jumps to the destination block, effectively splitting
1225 // the edge we are about to create.
1226 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1227 RealDest->getName()+".critedge",
1228 RealDest->getParent(), RealDest);
1229 BranchInst::Create(RealDest, EdgeBB);
1231 // Update PHI nodes.
1232 AddPredecessorToBlock(RealDest, EdgeBB, BB);
1234 // BB may have instructions that are being threaded over. Clone these
1235 // instructions into EdgeBB. We know that there will be no uses of the
1236 // cloned instructions outside of EdgeBB.
1237 BasicBlock::iterator InsertPt = EdgeBB->begin();
1238 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1239 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1240 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1241 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1244 // Clone the instruction.
1245 Instruction *N = BBI->clone();
1246 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1248 // Update operands due to translation.
1249 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1251 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1252 if (PI != TranslateMap.end())
1256 // Check for trivial simplification.
1257 if (Value *V = SimplifyInstruction(N, TD)) {
1258 TranslateMap[BBI] = V;
1259 delete N; // Instruction folded away, don't need actual inst
1261 // Insert the new instruction into its new home.
1262 EdgeBB->getInstList().insert(InsertPt, N);
1263 if (!BBI->use_empty())
1264 TranslateMap[BBI] = N;
1268 // Loop over all of the edges from PredBB to BB, changing them to branch
1269 // to EdgeBB instead.
1270 TerminatorInst *PredBBTI = PredBB->getTerminator();
1271 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1272 if (PredBBTI->getSuccessor(i) == BB) {
1273 BB->removePredecessor(PredBB);
1274 PredBBTI->setSuccessor(i, EdgeBB);
1277 // Recurse, simplifying any other constants.
1278 return FoldCondBranchOnPHI(BI, TD) | true;
1284 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1285 /// PHI node, see if we can eliminate it.
1286 static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
1287 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1288 // statement", which has a very simple dominance structure. Basically, we
1289 // are trying to find the condition that is being branched on, which
1290 // subsequently causes this merge to happen. We really want control
1291 // dependence information for this check, but simplifycfg can't keep it up
1292 // to date, and this catches most of the cases we care about anyway.
1293 BasicBlock *BB = PN->getParent();
1294 BasicBlock *IfTrue, *IfFalse;
1295 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1297 // Don't bother if the branch will be constant folded trivially.
1298 isa<ConstantInt>(IfCond))
1301 // Okay, we found that we can merge this two-entry phi node into a select.
1302 // Doing so would require us to fold *all* two entry phi nodes in this block.
1303 // At some point this becomes non-profitable (particularly if the target
1304 // doesn't support cmov's). Only do this transformation if there are two or
1305 // fewer PHI nodes in this block.
1306 unsigned NumPhis = 0;
1307 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1311 // Loop over the PHI's seeing if we can promote them all to select
1312 // instructions. While we are at it, keep track of the instructions
1313 // that need to be moved to the dominating block.
1314 SmallPtrSet<Instruction*, 4> AggressiveInsts;
1315 unsigned MaxCostVal0 = PHINodeFoldingThreshold,
1316 MaxCostVal1 = PHINodeFoldingThreshold;
1318 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1319 PHINode *PN = cast<PHINode>(II++);
1320 if (Value *V = SimplifyInstruction(PN, TD)) {
1321 PN->replaceAllUsesWith(V);
1322 PN->eraseFromParent();
1326 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
1328 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
1333 // If we folded the first phi, PN dangles at this point. Refresh it. If
1334 // we ran out of PHIs then we simplified them all.
1335 PN = dyn_cast<PHINode>(BB->begin());
1336 if (PN == 0) return true;
1338 // Don't fold i1 branches on PHIs which contain binary operators. These can
1339 // often be turned into switches and other things.
1340 if (PN->getType()->isIntegerTy(1) &&
1341 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1342 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1343 isa<BinaryOperator>(IfCond)))
1346 // If we all PHI nodes are promotable, check to make sure that all
1347 // instructions in the predecessor blocks can be promoted as well. If
1348 // not, we won't be able to get rid of the control flow, so it's not
1349 // worth promoting to select instructions.
1350 BasicBlock *DomBlock = 0;
1351 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1352 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1353 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1356 DomBlock = *pred_begin(IfBlock1);
1357 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1358 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1359 // This is not an aggressive instruction that we can promote.
1360 // Because of this, we won't be able to get rid of the control
1361 // flow, so the xform is not worth it.
1366 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1369 DomBlock = *pred_begin(IfBlock2);
1370 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1371 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1372 // This is not an aggressive instruction that we can promote.
1373 // Because of this, we won't be able to get rid of the control
1374 // flow, so the xform is not worth it.
1379 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1380 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1382 // If we can still promote the PHI nodes after this gauntlet of tests,
1383 // do all of the PHI's now.
1384 Instruction *InsertPt = DomBlock->getTerminator();
1385 IRBuilder<true, NoFolder> Builder(InsertPt);
1387 // Move all 'aggressive' instructions, which are defined in the
1388 // conditional parts of the if's up to the dominating block.
1390 DomBlock->getInstList().splice(InsertPt,
1391 IfBlock1->getInstList(), IfBlock1->begin(),
1392 IfBlock1->getTerminator());
1394 DomBlock->getInstList().splice(InsertPt,
1395 IfBlock2->getInstList(), IfBlock2->begin(),
1396 IfBlock2->getTerminator());
1398 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1399 // Change the PHI node into a select instruction.
1400 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1401 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1404 cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, ""));
1405 PN->replaceAllUsesWith(NV);
1407 PN->eraseFromParent();
1410 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1411 // has been flattened. Change DomBlock to jump directly to our new block to
1412 // avoid other simplifycfg's kicking in on the diamond.
1413 TerminatorInst *OldTI = DomBlock->getTerminator();
1414 Builder.SetInsertPoint(OldTI);
1415 Builder.CreateBr(BB);
1416 OldTI->eraseFromParent();
1420 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1421 /// to two returning blocks, try to merge them together into one return,
1422 /// introducing a select if the return values disagree.
1423 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
1424 IRBuilder<> &Builder) {
1425 assert(BI->isConditional() && "Must be a conditional branch");
1426 BasicBlock *TrueSucc = BI->getSuccessor(0);
1427 BasicBlock *FalseSucc = BI->getSuccessor(1);
1428 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1429 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1431 // Check to ensure both blocks are empty (just a return) or optionally empty
1432 // with PHI nodes. If there are other instructions, merging would cause extra
1433 // computation on one path or the other.
1434 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1436 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1439 Builder.SetInsertPoint(BI);
1440 // Okay, we found a branch that is going to two return nodes. If
1441 // there is no return value for this function, just change the
1442 // branch into a return.
1443 if (FalseRet->getNumOperands() == 0) {
1444 TrueSucc->removePredecessor(BI->getParent());
1445 FalseSucc->removePredecessor(BI->getParent());
1446 Builder.CreateRetVoid();
1447 EraseTerminatorInstAndDCECond(BI);
1451 // Otherwise, figure out what the true and false return values are
1452 // so we can insert a new select instruction.
1453 Value *TrueValue = TrueRet->getReturnValue();
1454 Value *FalseValue = FalseRet->getReturnValue();
1456 // Unwrap any PHI nodes in the return blocks.
1457 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1458 if (TVPN->getParent() == TrueSucc)
1459 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1460 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1461 if (FVPN->getParent() == FalseSucc)
1462 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1464 // In order for this transformation to be safe, we must be able to
1465 // unconditionally execute both operands to the return. This is
1466 // normally the case, but we could have a potentially-trapping
1467 // constant expression that prevents this transformation from being
1469 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1472 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1476 // Okay, we collected all the mapped values and checked them for sanity, and
1477 // defined to really do this transformation. First, update the CFG.
1478 TrueSucc->removePredecessor(BI->getParent());
1479 FalseSucc->removePredecessor(BI->getParent());
1481 // Insert select instructions where needed.
1482 Value *BrCond = BI->getCondition();
1484 // Insert a select if the results differ.
1485 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1486 } else if (isa<UndefValue>(TrueValue)) {
1487 TrueValue = FalseValue;
1489 TrueValue = Builder.CreateSelect(BrCond, TrueValue,
1490 FalseValue, "retval");
1494 Value *RI = !TrueValue ?
1495 Builder.CreateRetVoid() : Builder.CreateRet(TrueValue);
1499 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1500 << "\n " << *BI << "NewRet = " << *RI
1501 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1503 EraseTerminatorInstAndDCECond(BI);
1508 /// ExtractBranchMetadata - Given a conditional BranchInstruction, retrieve the
1509 /// probabilities of the branch taking each edge. Fills in the two APInt
1510 /// parameters and return true, or returns false if no or invalid metadata was
1512 static bool ExtractBranchMetadata(BranchInst *BI,
1513 APInt &ProbTrue, APInt &ProbFalse) {
1514 assert(BI->isConditional() &&
1515 "Looking for probabilities on unconditional branch?");
1516 MDNode *ProfileData = BI->getMetadata(LLVMContext::MD_prof);
1517 if (!ProfileData || ProfileData->getNumOperands() != 3) return false;
1518 ConstantInt *CITrue = dyn_cast<ConstantInt>(ProfileData->getOperand(1));
1519 ConstantInt *CIFalse = dyn_cast<ConstantInt>(ProfileData->getOperand(2));
1520 if (!CITrue || !CIFalse) return false;
1521 ProbTrue = CITrue->getValue();
1522 ProbFalse = CIFalse->getValue();
1523 assert(ProbTrue.getBitWidth() == 32 && ProbFalse.getBitWidth() == 32 &&
1524 "Branch probability metadata must be 32-bit integers");
1528 /// MultiplyAndLosePrecision - Multiplies A and B, then returns the result. In
1529 /// the event of overflow, logically-shifts all four inputs right until the
1531 static APInt MultiplyAndLosePrecision(APInt &A, APInt &B, APInt &C, APInt &D,
1532 unsigned &BitsLost) {
1534 bool Overflow = false;
1535 APInt Result = A.umul_ov(B, Overflow);
1537 APInt MaxB = APInt::getMaxValue(A.getBitWidth()).udiv(A);
1541 } while (B.ugt(MaxB));
1542 A = A.lshr(BitsLost);
1543 C = C.lshr(BitsLost);
1544 D = D.lshr(BitsLost);
1550 /// checkCSEInPredecessor - Return true if the given instruction is available
1551 /// in its predecessor block. If yes, the instruction will be removed.
1553 static bool checkCSEInPredecessor(Instruction *Inst, BasicBlock *PB) {
1554 if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst))
1556 for (BasicBlock::iterator I = PB->begin(), E = PB->end(); I != E; I++) {
1557 Instruction *PBI = &*I;
1558 // Check whether Inst and PBI generate the same value.
1559 if (Inst->isIdenticalTo(PBI)) {
1560 Inst->replaceAllUsesWith(PBI);
1561 Inst->eraseFromParent();
1568 /// FoldBranchToCommonDest - If this basic block is simple enough, and if a
1569 /// predecessor branches to us and one of our successors, fold the block into
1570 /// the predecessor and use logical operations to pick the right destination.
1571 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1572 BasicBlock *BB = BI->getParent();
1574 Instruction *Cond = 0;
1575 if (BI->isConditional())
1576 Cond = dyn_cast<Instruction>(BI->getCondition());
1578 // For unconditional branch, check for a simple CFG pattern, where
1579 // BB has a single predecessor and BB's successor is also its predecessor's
1580 // successor. If such pattern exisits, check for CSE between BB and its
1582 if (BasicBlock *PB = BB->getSinglePredecessor())
1583 if (BranchInst *PBI = dyn_cast<BranchInst>(PB->getTerminator()))
1584 if (PBI->isConditional() &&
1585 (BI->getSuccessor(0) == PBI->getSuccessor(0) ||
1586 BI->getSuccessor(0) == PBI->getSuccessor(1))) {
1587 for (BasicBlock::iterator I = BB->begin(), E = BB->end();
1589 Instruction *Curr = I++;
1590 if (isa<CmpInst>(Curr)) {
1594 // Quit if we can't remove this instruction.
1595 if (!checkCSEInPredecessor(Curr, PB))
1604 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1605 Cond->getParent() != BB || !Cond->hasOneUse())
1608 // Only allow this if the condition is a simple instruction that can be
1609 // executed unconditionally. It must be in the same block as the branch, and
1610 // must be at the front of the block.
1611 BasicBlock::iterator FrontIt = BB->front();
1613 // Ignore dbg intrinsics.
1614 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1616 // Allow a single instruction to be hoisted in addition to the compare
1617 // that feeds the branch. We later ensure that any values that _it_ uses
1618 // were also live in the predecessor, so that we don't unnecessarily create
1619 // register pressure or inhibit out-of-order execution.
1620 Instruction *BonusInst = 0;
1621 if (&*FrontIt != Cond &&
1622 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1623 isSafeToSpeculativelyExecute(FrontIt)) {
1624 BonusInst = &*FrontIt;
1627 // Ignore dbg intrinsics.
1628 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1631 // Only a single bonus inst is allowed.
1632 if (&*FrontIt != Cond)
1635 // Make sure the instruction after the condition is the cond branch.
1636 BasicBlock::iterator CondIt = Cond; ++CondIt;
1638 // Ingore dbg intrinsics.
1639 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
1644 // Cond is known to be a compare or binary operator. Check to make sure that
1645 // neither operand is a potentially-trapping constant expression.
1646 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1649 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1653 // Finally, don't infinitely unroll conditional loops.
1654 BasicBlock *TrueDest = BI->getSuccessor(0);
1655 BasicBlock *FalseDest = (BI->isConditional()) ? BI->getSuccessor(1) : 0;
1656 if (TrueDest == BB || FalseDest == BB)
1659 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1660 BasicBlock *PredBlock = *PI;
1661 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1663 // Check that we have two conditional branches. If there is a PHI node in
1664 // the common successor, verify that the same value flows in from both
1666 SmallVector<PHINode*, 4> PHIs;
1667 if (PBI == 0 || PBI->isUnconditional() ||
1668 (BI->isConditional() &&
1669 !SafeToMergeTerminators(BI, PBI)) ||
1670 (!BI->isConditional() &&
1671 !isProfitableToFoldUnconditional(BI, PBI, Cond, PHIs)))
1674 // Determine if the two branches share a common destination.
1675 Instruction::BinaryOps Opc;
1676 bool InvertPredCond = false;
1678 if (BI->isConditional()) {
1679 if (PBI->getSuccessor(0) == TrueDest)
1680 Opc = Instruction::Or;
1681 else if (PBI->getSuccessor(1) == FalseDest)
1682 Opc = Instruction::And;
1683 else if (PBI->getSuccessor(0) == FalseDest)
1684 Opc = Instruction::And, InvertPredCond = true;
1685 else if (PBI->getSuccessor(1) == TrueDest)
1686 Opc = Instruction::Or, InvertPredCond = true;
1690 if (PBI->getSuccessor(0) != TrueDest && PBI->getSuccessor(1) != TrueDest)
1694 // Ensure that any values used in the bonus instruction are also used
1695 // by the terminator of the predecessor. This means that those values
1696 // must already have been resolved, so we won't be inhibiting the
1697 // out-of-order core by speculating them earlier.
1699 // Collect the values used by the bonus inst
1700 SmallPtrSet<Value*, 4> UsedValues;
1701 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1702 OE = BonusInst->op_end(); OI != OE; ++OI) {
1704 if (!isa<Constant>(V))
1705 UsedValues.insert(V);
1708 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1709 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1711 // Walk up to four levels back up the use-def chain of the predecessor's
1712 // terminator to see if all those values were used. The choice of four
1713 // levels is arbitrary, to provide a compile-time-cost bound.
1714 while (!Worklist.empty()) {
1715 std::pair<Value*, unsigned> Pair = Worklist.back();
1716 Worklist.pop_back();
1718 if (Pair.second >= 4) continue;
1719 UsedValues.erase(Pair.first);
1720 if (UsedValues.empty()) break;
1722 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
1723 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1725 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1729 if (!UsedValues.empty()) return false;
1732 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1733 IRBuilder<> Builder(PBI);
1735 // If we need to invert the condition in the pred block to match, do so now.
1736 if (InvertPredCond) {
1737 Value *NewCond = PBI->getCondition();
1739 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
1740 CmpInst *CI = cast<CmpInst>(NewCond);
1741 CI->setPredicate(CI->getInversePredicate());
1743 NewCond = Builder.CreateNot(NewCond,
1744 PBI->getCondition()->getName()+".not");
1747 PBI->setCondition(NewCond);
1748 PBI->swapSuccessors();
1751 // If we have a bonus inst, clone it into the predecessor block.
1752 Instruction *NewBonus = 0;
1754 NewBonus = BonusInst->clone();
1755 PredBlock->getInstList().insert(PBI, NewBonus);
1756 NewBonus->takeName(BonusInst);
1757 BonusInst->setName(BonusInst->getName()+".old");
1760 // Clone Cond into the predecessor basic block, and or/and the
1761 // two conditions together.
1762 Instruction *New = Cond->clone();
1763 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1764 PredBlock->getInstList().insert(PBI, New);
1765 New->takeName(Cond);
1766 Cond->setName(New->getName()+".old");
1768 if (BI->isConditional()) {
1769 Instruction *NewCond =
1770 cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(),
1772 PBI->setCondition(NewCond);
1774 if (PBI->getSuccessor(0) == BB) {
1775 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1776 PBI->setSuccessor(0, TrueDest);
1778 if (PBI->getSuccessor(1) == BB) {
1779 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1780 PBI->setSuccessor(1, FalseDest);
1783 // Update PHI nodes in the common successors.
1784 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
1785 ConstantInt *PBI_C = cast<ConstantInt>(
1786 PHIs[i]->getIncomingValueForBlock(PBI->getParent()));
1787 assert(PBI_C->getType()->isIntegerTy(1));
1788 Instruction *MergedCond = 0;
1789 if (PBI->getSuccessor(0) == TrueDest) {
1790 // Create (PBI_Cond and PBI_C) or (!PBI_Cond and BI_Value)
1791 // PBI_C is true: PBI_Cond or (!PBI_Cond and BI_Value)
1792 // is false: !PBI_Cond and BI_Value
1793 Instruction *NotCond =
1794 cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
1797 cast<Instruction>(Builder.CreateBinOp(Instruction::And,
1802 cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
1803 PBI->getCondition(), MergedCond,
1806 // Create (PBI_Cond and BI_Value) or (!PBI_Cond and PBI_C)
1807 // PBI_C is true: (PBI_Cond and BI_Value) or (!PBI_Cond)
1808 // is false: PBI_Cond and BI_Value
1810 cast<Instruction>(Builder.CreateBinOp(Instruction::And,
1811 PBI->getCondition(), New,
1813 if (PBI_C->isOne()) {
1814 Instruction *NotCond =
1815 cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
1818 cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
1819 NotCond, MergedCond,
1824 PHIs[i]->setIncomingValue(PHIs[i]->getBasicBlockIndex(PBI->getParent()),
1827 // Change PBI from Conditional to Unconditional.
1828 BranchInst *New_PBI = BranchInst::Create(TrueDest, PBI);
1829 EraseTerminatorInstAndDCECond(PBI);
1833 // TODO: If BB is reachable from all paths through PredBlock, then we
1834 // could replace PBI's branch probabilities with BI's.
1836 // Merge probability data into PredBlock's branch.
1838 if (PBI->isConditional() && BI->isConditional() &&
1839 ExtractBranchMetadata(PBI, C, D) && ExtractBranchMetadata(BI, A, B)) {
1840 // Given IR which does:
1842 // br i1 %x, label %bbB, label %bbC
1844 // br i1 %y, label %bbD, label %bbC
1845 // Let's call the probability that we take the edge from %bbA to %bbB
1846 // 'a', from %bbA to %bbC, 'b', from %bbB to %bbD 'c' and from %bbB to
1847 // %bbC probability 'd'.
1849 // We transform the IR into:
1851 // br i1 %z, label %bbD, label %bbC
1852 // where the probability of going to %bbD is (a*c) and going to bbC is
1855 // Probabilities aren't stored as ratios directly. Using branch weights,
1857 // (a*c)% = A*C, (b+(a*d))% = A*D+B*C+B*D.
1859 // In the event of overflow, we want to drop the LSB of the input
1863 // Ignore overflow result on ProbTrue.
1864 APInt ProbTrue = MultiplyAndLosePrecision(A, C, B, D, BitsLost);
1866 APInt Tmp1 = MultiplyAndLosePrecision(B, D, A, C, BitsLost);
1868 ProbTrue = ProbTrue.lshr(BitsLost*2);
1871 APInt Tmp2 = MultiplyAndLosePrecision(A, D, C, B, BitsLost);
1873 ProbTrue = ProbTrue.lshr(BitsLost*2);
1874 Tmp1 = Tmp1.lshr(BitsLost*2);
1877 APInt Tmp3 = MultiplyAndLosePrecision(B, C, A, D, BitsLost);
1879 ProbTrue = ProbTrue.lshr(BitsLost*2);
1880 Tmp1 = Tmp1.lshr(BitsLost*2);
1881 Tmp2 = Tmp2.lshr(BitsLost*2);
1884 bool Overflow1 = false, Overflow2 = false;
1885 APInt Tmp4 = Tmp2.uadd_ov(Tmp3, Overflow1);
1886 APInt ProbFalse = Tmp4.uadd_ov(Tmp1, Overflow2);
1888 if (Overflow1 || Overflow2) {
1889 ProbTrue = ProbTrue.lshr(1);
1890 Tmp1 = Tmp1.lshr(1);
1891 Tmp2 = Tmp2.lshr(1);
1892 Tmp3 = Tmp3.lshr(1);
1894 ProbFalse = Tmp4 + Tmp1;
1897 // The sum of branch weights must fit in 32-bits.
1898 if (ProbTrue.isNegative() && ProbFalse.isNegative()) {
1899 ProbTrue = ProbTrue.lshr(1);
1900 ProbFalse = ProbFalse.lshr(1);
1903 if (ProbTrue != ProbFalse) {
1904 // Normalize the result.
1905 APInt GCD = APIntOps::GreatestCommonDivisor(ProbTrue, ProbFalse);
1906 ProbTrue = ProbTrue.udiv(GCD);
1907 ProbFalse = ProbFalse.udiv(GCD);
1909 MDBuilder MDB(BI->getContext());
1910 MDNode *N = MDB.createBranchWeights(ProbTrue.getZExtValue(),
1911 ProbFalse.getZExtValue());
1912 PBI->setMetadata(LLVMContext::MD_prof, N);
1914 PBI->setMetadata(LLVMContext::MD_prof, NULL);
1917 PBI->setMetadata(LLVMContext::MD_prof, NULL);
1920 // Copy any debug value intrinsics into the end of PredBlock.
1921 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
1922 if (isa<DbgInfoIntrinsic>(*I))
1923 I->clone()->insertBefore(PBI);
1930 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1931 /// predecessor of another block, this function tries to simplify it. We know
1932 /// that PBI and BI are both conditional branches, and BI is in one of the
1933 /// successor blocks of PBI - PBI branches to BI.
1934 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1935 assert(PBI->isConditional() && BI->isConditional());
1936 BasicBlock *BB = BI->getParent();
1938 // If this block ends with a branch instruction, and if there is a
1939 // predecessor that ends on a branch of the same condition, make
1940 // this conditional branch redundant.
1941 if (PBI->getCondition() == BI->getCondition() &&
1942 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1943 // Okay, the outcome of this conditional branch is statically
1944 // knowable. If this block had a single pred, handle specially.
1945 if (BB->getSinglePredecessor()) {
1946 // Turn this into a branch on constant.
1947 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1948 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1950 return true; // Nuke the branch on constant.
1953 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1954 // in the constant and simplify the block result. Subsequent passes of
1955 // simplifycfg will thread the block.
1956 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1957 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
1958 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1959 std::distance(PB, PE),
1960 BI->getCondition()->getName() + ".pr",
1962 // Okay, we're going to insert the PHI node. Since PBI is not the only
1963 // predecessor, compute the PHI'd conditional value for all of the preds.
1964 // Any predecessor where the condition is not computable we keep symbolic.
1965 for (pred_iterator PI = PB; PI != PE; ++PI) {
1966 BasicBlock *P = *PI;
1967 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
1968 PBI != BI && PBI->isConditional() &&
1969 PBI->getCondition() == BI->getCondition() &&
1970 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1971 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1972 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1975 NewPN->addIncoming(BI->getCondition(), P);
1979 BI->setCondition(NewPN);
1984 // If this is a conditional branch in an empty block, and if any
1985 // predecessors is a conditional branch to one of our destinations,
1986 // fold the conditions into logical ops and one cond br.
1987 BasicBlock::iterator BBI = BB->begin();
1988 // Ignore dbg intrinsics.
1989 while (isa<DbgInfoIntrinsic>(BBI))
1995 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
2000 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
2002 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
2003 PBIOp = 0, BIOp = 1;
2004 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
2005 PBIOp = 1, BIOp = 0;
2006 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
2011 // Check to make sure that the other destination of this branch
2012 // isn't BB itself. If so, this is an infinite loop that will
2013 // keep getting unwound.
2014 if (PBI->getSuccessor(PBIOp) == BB)
2017 // Do not perform this transformation if it would require
2018 // insertion of a large number of select instructions. For targets
2019 // without predication/cmovs, this is a big pessimization.
2020 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
2022 unsigned NumPhis = 0;
2023 for (BasicBlock::iterator II = CommonDest->begin();
2024 isa<PHINode>(II); ++II, ++NumPhis)
2025 if (NumPhis > 2) // Disable this xform.
2028 // Finally, if everything is ok, fold the branches to logical ops.
2029 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
2031 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
2032 << "AND: " << *BI->getParent());
2035 // If OtherDest *is* BB, then BB is a basic block with a single conditional
2036 // branch in it, where one edge (OtherDest) goes back to itself but the other
2037 // exits. We don't *know* that the program avoids the infinite loop
2038 // (even though that seems likely). If we do this xform naively, we'll end up
2039 // recursively unpeeling the loop. Since we know that (after the xform is
2040 // done) that the block *is* infinite if reached, we just make it an obviously
2041 // infinite loop with no cond branch.
2042 if (OtherDest == BB) {
2043 // Insert it at the end of the function, because it's either code,
2044 // or it won't matter if it's hot. :)
2045 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
2046 "infloop", BB->getParent());
2047 BranchInst::Create(InfLoopBlock, InfLoopBlock);
2048 OtherDest = InfLoopBlock;
2051 DEBUG(dbgs() << *PBI->getParent()->getParent());
2053 // BI may have other predecessors. Because of this, we leave
2054 // it alone, but modify PBI.
2056 // Make sure we get to CommonDest on True&True directions.
2057 Value *PBICond = PBI->getCondition();
2058 IRBuilder<true, NoFolder> Builder(PBI);
2060 PBICond = Builder.CreateNot(PBICond, PBICond->getName()+".not");
2062 Value *BICond = BI->getCondition();
2064 BICond = Builder.CreateNot(BICond, BICond->getName()+".not");
2066 // Merge the conditions.
2067 Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge");
2069 // Modify PBI to branch on the new condition to the new dests.
2070 PBI->setCondition(Cond);
2071 PBI->setSuccessor(0, CommonDest);
2072 PBI->setSuccessor(1, OtherDest);
2074 // OtherDest may have phi nodes. If so, add an entry from PBI's
2075 // block that are identical to the entries for BI's block.
2076 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
2078 // We know that the CommonDest already had an edge from PBI to
2079 // it. If it has PHIs though, the PHIs may have different
2080 // entries for BB and PBI's BB. If so, insert a select to make
2083 for (BasicBlock::iterator II = CommonDest->begin();
2084 (PN = dyn_cast<PHINode>(II)); ++II) {
2085 Value *BIV = PN->getIncomingValueForBlock(BB);
2086 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
2087 Value *PBIV = PN->getIncomingValue(PBBIdx);
2089 // Insert a select in PBI to pick the right value.
2090 Value *NV = cast<SelectInst>
2091 (Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName()+".mux"));
2092 PN->setIncomingValue(PBBIdx, NV);
2096 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
2097 DEBUG(dbgs() << *PBI->getParent()->getParent());
2099 // This basic block is probably dead. We know it has at least
2100 // one fewer predecessor.
2104 // SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
2105 // branch to TrueBB if Cond is true or to FalseBB if Cond is false.
2106 // Takes care of updating the successors and removing the old terminator.
2107 // Also makes sure not to introduce new successors by assuming that edges to
2108 // non-successor TrueBBs and FalseBBs aren't reachable.
2109 static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
2110 BasicBlock *TrueBB, BasicBlock *FalseBB){
2111 // Remove any superfluous successor edges from the CFG.
2112 // First, figure out which successors to preserve.
2113 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
2115 BasicBlock *KeepEdge1 = TrueBB;
2116 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
2118 // Then remove the rest.
2119 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
2120 BasicBlock *Succ = OldTerm->getSuccessor(I);
2121 // Make sure only to keep exactly one copy of each edge.
2122 if (Succ == KeepEdge1)
2124 else if (Succ == KeepEdge2)
2127 Succ->removePredecessor(OldTerm->getParent());
2130 IRBuilder<> Builder(OldTerm);
2131 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
2133 // Insert an appropriate new terminator.
2134 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
2135 if (TrueBB == FalseBB)
2136 // We were only looking for one successor, and it was present.
2137 // Create an unconditional branch to it.
2138 Builder.CreateBr(TrueBB);
2140 // We found both of the successors we were looking for.
2141 // Create a conditional branch sharing the condition of the select.
2142 Builder.CreateCondBr(Cond, TrueBB, FalseBB);
2143 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
2144 // Neither of the selected blocks were successors, so this
2145 // terminator must be unreachable.
2146 new UnreachableInst(OldTerm->getContext(), OldTerm);
2148 // One of the selected values was a successor, but the other wasn't.
2149 // Insert an unconditional branch to the one that was found;
2150 // the edge to the one that wasn't must be unreachable.
2152 // Only TrueBB was found.
2153 Builder.CreateBr(TrueBB);
2155 // Only FalseBB was found.
2156 Builder.CreateBr(FalseBB);
2159 EraseTerminatorInstAndDCECond(OldTerm);
2163 // SimplifySwitchOnSelect - Replaces
2164 // (switch (select cond, X, Y)) on constant X, Y
2165 // with a branch - conditional if X and Y lead to distinct BBs,
2166 // unconditional otherwise.
2167 static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
2168 // Check for constant integer values in the select.
2169 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
2170 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
2171 if (!TrueVal || !FalseVal)
2174 // Find the relevant condition and destinations.
2175 Value *Condition = Select->getCondition();
2176 BasicBlock *TrueBB = SI->findCaseValue(TrueVal).getCaseSuccessor();
2177 BasicBlock *FalseBB = SI->findCaseValue(FalseVal).getCaseSuccessor();
2179 // Perform the actual simplification.
2180 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB);
2183 // SimplifyIndirectBrOnSelect - Replaces
2184 // (indirectbr (select cond, blockaddress(@fn, BlockA),
2185 // blockaddress(@fn, BlockB)))
2187 // (br cond, BlockA, BlockB).
2188 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
2189 // Check that both operands of the select are block addresses.
2190 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
2191 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
2195 // Extract the actual blocks.
2196 BasicBlock *TrueBB = TBA->getBasicBlock();
2197 BasicBlock *FalseBB = FBA->getBasicBlock();
2199 // Perform the actual simplification.
2200 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB);
2203 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
2204 /// instruction (a seteq/setne with a constant) as the only instruction in a
2205 /// block that ends with an uncond branch. We are looking for a very specific
2206 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
2207 /// this case, we merge the first two "or's of icmp" into a switch, but then the
2208 /// default value goes to an uncond block with a seteq in it, we get something
2211 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
2213 /// %tmp = icmp eq i8 %A, 92
2216 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
2218 /// We prefer to split the edge to 'end' so that there is a true/false entry to
2219 /// the PHI, merging the third icmp into the switch.
2220 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
2221 const TargetData *TD,
2222 IRBuilder<> &Builder) {
2223 BasicBlock *BB = ICI->getParent();
2225 // If the block has any PHIs in it or the icmp has multiple uses, it is too
2227 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
2229 Value *V = ICI->getOperand(0);
2230 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
2232 // The pattern we're looking for is where our only predecessor is a switch on
2233 // 'V' and this block is the default case for the switch. In this case we can
2234 // fold the compared value into the switch to simplify things.
2235 BasicBlock *Pred = BB->getSinglePredecessor();
2236 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
2238 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
2239 if (SI->getCondition() != V)
2242 // If BB is reachable on a non-default case, then we simply know the value of
2243 // V in this block. Substitute it and constant fold the icmp instruction
2245 if (SI->getDefaultDest() != BB) {
2246 ConstantInt *VVal = SI->findCaseDest(BB);
2247 assert(VVal && "Should have a unique destination value");
2248 ICI->setOperand(0, VVal);
2250 if (Value *V = SimplifyInstruction(ICI, TD)) {
2251 ICI->replaceAllUsesWith(V);
2252 ICI->eraseFromParent();
2254 // BB is now empty, so it is likely to simplify away.
2255 return SimplifyCFG(BB) | true;
2258 // Ok, the block is reachable from the default dest. If the constant we're
2259 // comparing exists in one of the other edges, then we can constant fold ICI
2261 if (SI->findCaseValue(Cst) != SI->case_default()) {
2263 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2264 V = ConstantInt::getFalse(BB->getContext());
2266 V = ConstantInt::getTrue(BB->getContext());
2268 ICI->replaceAllUsesWith(V);
2269 ICI->eraseFromParent();
2270 // BB is now empty, so it is likely to simplify away.
2271 return SimplifyCFG(BB) | true;
2274 // The use of the icmp has to be in the 'end' block, by the only PHI node in
2276 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
2277 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
2278 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
2279 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
2282 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
2284 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
2285 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
2287 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2288 std::swap(DefaultCst, NewCst);
2290 // Replace ICI (which is used by the PHI for the default value) with true or
2291 // false depending on if it is EQ or NE.
2292 ICI->replaceAllUsesWith(DefaultCst);
2293 ICI->eraseFromParent();
2295 // Okay, the switch goes to this block on a default value. Add an edge from
2296 // the switch to the merge point on the compared value.
2297 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
2298 BB->getParent(), BB);
2299 SI->addCase(Cst, NewBB);
2301 // NewBB branches to the phi block, add the uncond branch and the phi entry.
2302 Builder.SetInsertPoint(NewBB);
2303 Builder.SetCurrentDebugLocation(SI->getDebugLoc());
2304 Builder.CreateBr(SuccBlock);
2305 PHIUse->addIncoming(NewCst, NewBB);
2309 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
2310 /// Check to see if it is branching on an or/and chain of icmp instructions, and
2311 /// fold it into a switch instruction if so.
2312 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD,
2313 IRBuilder<> &Builder) {
2314 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
2315 if (Cond == 0) return false;
2318 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2319 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2320 // 'setne's and'ed together, collect them.
2322 std::vector<ConstantInt*> Values;
2323 bool TrueWhenEqual = true;
2324 Value *ExtraCase = 0;
2325 unsigned UsedICmps = 0;
2327 if (Cond->getOpcode() == Instruction::Or) {
2328 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
2330 } else if (Cond->getOpcode() == Instruction::And) {
2331 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
2333 TrueWhenEqual = false;
2336 // If we didn't have a multiply compared value, fail.
2337 if (CompVal == 0) return false;
2339 // Avoid turning single icmps into a switch.
2343 // There might be duplicate constants in the list, which the switch
2344 // instruction can't handle, remove them now.
2345 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
2346 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2348 // If Extra was used, we require at least two switch values to do the
2349 // transformation. A switch with one value is just an cond branch.
2350 if (ExtraCase && Values.size() < 2) return false;
2352 // Figure out which block is which destination.
2353 BasicBlock *DefaultBB = BI->getSuccessor(1);
2354 BasicBlock *EdgeBB = BI->getSuccessor(0);
2355 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2357 BasicBlock *BB = BI->getParent();
2359 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
2360 << " cases into SWITCH. BB is:\n" << *BB);
2362 // If there are any extra values that couldn't be folded into the switch
2363 // then we evaluate them with an explicit branch first. Split the block
2364 // right before the condbr to handle it.
2366 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
2367 // Remove the uncond branch added to the old block.
2368 TerminatorInst *OldTI = BB->getTerminator();
2369 Builder.SetInsertPoint(OldTI);
2372 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
2374 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
2376 OldTI->eraseFromParent();
2378 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
2379 // for the edge we just added.
2380 AddPredecessorToBlock(EdgeBB, BB, NewBB);
2382 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
2383 << "\nEXTRABB = " << *BB);
2387 Builder.SetInsertPoint(BI);
2388 // Convert pointer to int before we switch.
2389 if (CompVal->getType()->isPointerTy()) {
2390 assert(TD && "Cannot switch on pointer without TargetData");
2391 CompVal = Builder.CreatePtrToInt(CompVal,
2392 TD->getIntPtrType(CompVal->getContext()),
2396 // Create the new switch instruction now.
2397 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
2399 // Add all of the 'cases' to the switch instruction.
2400 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2401 New->addCase(Values[i], EdgeBB);
2403 // We added edges from PI to the EdgeBB. As such, if there were any
2404 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2405 // the number of edges added.
2406 for (BasicBlock::iterator BBI = EdgeBB->begin();
2407 isa<PHINode>(BBI); ++BBI) {
2408 PHINode *PN = cast<PHINode>(BBI);
2409 Value *InVal = PN->getIncomingValueForBlock(BB);
2410 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2411 PN->addIncoming(InVal, BB);
2414 // Erase the old branch instruction.
2415 EraseTerminatorInstAndDCECond(BI);
2417 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
2421 bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
2422 // If this is a trivial landing pad that just continues unwinding the caught
2423 // exception then zap the landing pad, turning its invokes into calls.
2424 BasicBlock *BB = RI->getParent();
2425 LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI());
2426 if (RI->getValue() != LPInst)
2427 // Not a landing pad, or the resume is not unwinding the exception that
2428 // caused control to branch here.
2431 // Check that there are no other instructions except for debug intrinsics.
2432 BasicBlock::iterator I = LPInst, E = RI;
2434 if (!isa<DbgInfoIntrinsic>(I))
2437 // Turn all invokes that unwind here into calls and delete the basic block.
2438 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
2439 InvokeInst *II = cast<InvokeInst>((*PI++)->getTerminator());
2440 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
2441 // Insert a call instruction before the invoke.
2442 CallInst *Call = CallInst::Create(II->getCalledValue(), Args, "", II);
2444 Call->setCallingConv(II->getCallingConv());
2445 Call->setAttributes(II->getAttributes());
2446 Call->setDebugLoc(II->getDebugLoc());
2448 // Anything that used the value produced by the invoke instruction now uses
2449 // the value produced by the call instruction. Note that we do this even
2450 // for void functions and calls with no uses so that the callgraph edge is
2452 II->replaceAllUsesWith(Call);
2453 BB->removePredecessor(II->getParent());
2455 // Insert a branch to the normal destination right before the invoke.
2456 BranchInst::Create(II->getNormalDest(), II);
2458 // Finally, delete the invoke instruction!
2459 II->eraseFromParent();
2462 // The landingpad is now unreachable. Zap it.
2463 BB->eraseFromParent();
2467 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
2468 BasicBlock *BB = RI->getParent();
2469 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2471 // Find predecessors that end with branches.
2472 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2473 SmallVector<BranchInst*, 8> CondBranchPreds;
2474 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2475 BasicBlock *P = *PI;
2476 TerminatorInst *PTI = P->getTerminator();
2477 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2478 if (BI->isUnconditional())
2479 UncondBranchPreds.push_back(P);
2481 CondBranchPreds.push_back(BI);
2485 // If we found some, do the transformation!
2486 if (!UncondBranchPreds.empty() && DupRet) {
2487 while (!UncondBranchPreds.empty()) {
2488 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2489 DEBUG(dbgs() << "FOLDING: " << *BB
2490 << "INTO UNCOND BRANCH PRED: " << *Pred);
2491 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
2494 // If we eliminated all predecessors of the block, delete the block now.
2495 if (pred_begin(BB) == pred_end(BB))
2496 // We know there are no successors, so just nuke the block.
2497 BB->eraseFromParent();
2502 // Check out all of the conditional branches going to this return
2503 // instruction. If any of them just select between returns, change the
2504 // branch itself into a select/return pair.
2505 while (!CondBranchPreds.empty()) {
2506 BranchInst *BI = CondBranchPreds.pop_back_val();
2508 // Check to see if the non-BB successor is also a return block.
2509 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2510 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2511 SimplifyCondBranchToTwoReturns(BI, Builder))
2517 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2518 BasicBlock *BB = UI->getParent();
2520 bool Changed = false;
2522 // If there are any instructions immediately before the unreachable that can
2523 // be removed, do so.
2524 while (UI != BB->begin()) {
2525 BasicBlock::iterator BBI = UI;
2527 // Do not delete instructions that can have side effects which might cause
2528 // the unreachable to not be reachable; specifically, calls and volatile
2529 // operations may have this effect.
2530 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2532 if (BBI->mayHaveSideEffects()) {
2533 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
2534 if (SI->isVolatile())
2536 } else if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
2537 if (LI->isVolatile())
2539 } else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(BBI)) {
2540 if (RMWI->isVolatile())
2542 } else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) {
2543 if (CXI->isVolatile())
2545 } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) &&
2546 !isa<LandingPadInst>(BBI)) {
2549 // Note that deleting LandingPad's here is in fact okay, although it
2550 // involves a bit of subtle reasoning. If this inst is a LandingPad,
2551 // all the predecessors of this block will be the unwind edges of Invokes,
2552 // and we can therefore guarantee this block will be erased.
2555 // Delete this instruction (any uses are guaranteed to be dead)
2556 if (!BBI->use_empty())
2557 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
2558 BBI->eraseFromParent();
2562 // If the unreachable instruction is the first in the block, take a gander
2563 // at all of the predecessors of this instruction, and simplify them.
2564 if (&BB->front() != UI) return Changed;
2566 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2567 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2568 TerminatorInst *TI = Preds[i]->getTerminator();
2569 IRBuilder<> Builder(TI);
2570 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2571 if (BI->isUnconditional()) {
2572 if (BI->getSuccessor(0) == BB) {
2573 new UnreachableInst(TI->getContext(), TI);
2574 TI->eraseFromParent();
2578 if (BI->getSuccessor(0) == BB) {
2579 Builder.CreateBr(BI->getSuccessor(1));
2580 EraseTerminatorInstAndDCECond(BI);
2581 } else if (BI->getSuccessor(1) == BB) {
2582 Builder.CreateBr(BI->getSuccessor(0));
2583 EraseTerminatorInstAndDCECond(BI);
2587 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2588 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2590 if (i.getCaseSuccessor() == BB) {
2591 BB->removePredecessor(SI->getParent());
2596 // If the default value is unreachable, figure out the most popular
2597 // destination and make it the default.
2598 if (SI->getDefaultDest() == BB) {
2599 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
2600 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2602 std::pair<unsigned, unsigned> &entry =
2603 Popularity[i.getCaseSuccessor()];
2604 if (entry.first == 0) {
2606 entry.second = i.getCaseIndex();
2612 // Find the most popular block.
2613 unsigned MaxPop = 0;
2614 unsigned MaxIndex = 0;
2615 BasicBlock *MaxBlock = 0;
2616 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
2617 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2618 if (I->second.first > MaxPop ||
2619 (I->second.first == MaxPop && MaxIndex > I->second.second)) {
2620 MaxPop = I->second.first;
2621 MaxIndex = I->second.second;
2622 MaxBlock = I->first;
2626 // Make this the new default, allowing us to delete any explicit
2628 SI->setDefaultDest(MaxBlock);
2631 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2633 if (isa<PHINode>(MaxBlock->begin()))
2634 for (unsigned i = 0; i != MaxPop-1; ++i)
2635 MaxBlock->removePredecessor(SI->getParent());
2637 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2639 if (i.getCaseSuccessor() == MaxBlock) {
2645 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2646 if (II->getUnwindDest() == BB) {
2647 // Convert the invoke to a call instruction. This would be a good
2648 // place to note that the call does not throw though.
2649 BranchInst *BI = Builder.CreateBr(II->getNormalDest());
2650 II->removeFromParent(); // Take out of symbol table
2652 // Insert the call now...
2653 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2654 Builder.SetInsertPoint(BI);
2655 CallInst *CI = Builder.CreateCall(II->getCalledValue(),
2656 Args, II->getName());
2657 CI->setCallingConv(II->getCallingConv());
2658 CI->setAttributes(II->getAttributes());
2659 // If the invoke produced a value, the call does now instead.
2660 II->replaceAllUsesWith(CI);
2667 // If this block is now dead, remove it.
2668 if (pred_begin(BB) == pred_end(BB) &&
2669 BB != &BB->getParent()->getEntryBlock()) {
2670 // We know there are no successors, so just nuke the block.
2671 BB->eraseFromParent();
2678 /// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
2679 /// integer range comparison into a sub, an icmp and a branch.
2680 static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
2681 assert(SI->getNumCases() > 1 && "Degenerate switch?");
2683 // Make sure all cases point to the same destination and gather the values.
2684 SmallVector<ConstantInt *, 16> Cases;
2685 SwitchInst::CaseIt I = SI->case_begin();
2686 Cases.push_back(I.getCaseValue());
2687 SwitchInst::CaseIt PrevI = I++;
2688 for (SwitchInst::CaseIt E = SI->case_end(); I != E; PrevI = I++) {
2689 if (PrevI.getCaseSuccessor() != I.getCaseSuccessor())
2691 Cases.push_back(I.getCaseValue());
2693 assert(Cases.size() == SI->getNumCases() && "Not all cases gathered");
2695 // Sort the case values, then check if they form a range we can transform.
2696 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
2697 for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
2698 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
2702 Constant *Offset = ConstantExpr::getNeg(Cases.back());
2703 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases());
2705 Value *Sub = SI->getCondition();
2706 if (!Offset->isNullValue())
2707 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off");
2708 Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
2709 Builder.CreateCondBr(
2710 Cmp, SI->case_begin().getCaseSuccessor(), SI->getDefaultDest());
2712 // Prune obsolete incoming values off the successor's PHI nodes.
2713 for (BasicBlock::iterator BBI = SI->case_begin().getCaseSuccessor()->begin();
2714 isa<PHINode>(BBI); ++BBI) {
2715 for (unsigned I = 0, E = SI->getNumCases()-1; I != E; ++I)
2716 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
2718 SI->eraseFromParent();
2723 /// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch
2724 /// and use it to remove dead cases.
2725 static bool EliminateDeadSwitchCases(SwitchInst *SI) {
2726 Value *Cond = SI->getCondition();
2727 unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth();
2728 APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
2729 ComputeMaskedBits(Cond, KnownZero, KnownOne);
2731 // Gather dead cases.
2732 SmallVector<ConstantInt*, 8> DeadCases;
2733 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
2734 if ((I.getCaseValue()->getValue() & KnownZero) != 0 ||
2735 (I.getCaseValue()->getValue() & KnownOne) != KnownOne) {
2736 DeadCases.push_back(I.getCaseValue());
2737 DEBUG(dbgs() << "SimplifyCFG: switch case '"
2738 << I.getCaseValue() << "' is dead.\n");
2742 // Remove dead cases from the switch.
2743 for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) {
2744 SwitchInst::CaseIt Case = SI->findCaseValue(DeadCases[I]);
2745 assert(Case != SI->case_default() &&
2746 "Case was not found. Probably mistake in DeadCases forming.");
2747 // Prune unused values from PHI nodes.
2748 Case.getCaseSuccessor()->removePredecessor(SI->getParent());
2749 SI->removeCase(Case);
2752 return !DeadCases.empty();
2755 /// FindPHIForConditionForwarding - If BB would be eligible for simplification
2756 /// by TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated
2757 /// by an unconditional branch), look at the phi node for BB in the successor
2758 /// block and see if the incoming value is equal to CaseValue. If so, return
2759 /// the phi node, and set PhiIndex to BB's index in the phi node.
2760 static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
2763 if (BB->getFirstNonPHIOrDbg() != BB->getTerminator())
2764 return NULL; // BB must be empty to be a candidate for simplification.
2765 if (!BB->getSinglePredecessor())
2766 return NULL; // BB must be dominated by the switch.
2768 BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
2769 if (!Branch || !Branch->isUnconditional())
2770 return NULL; // Terminator must be unconditional branch.
2772 BasicBlock *Succ = Branch->getSuccessor(0);
2774 BasicBlock::iterator I = Succ->begin();
2775 while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
2776 int Idx = PHI->getBasicBlockIndex(BB);
2777 assert(Idx >= 0 && "PHI has no entry for predecessor?");
2779 Value *InValue = PHI->getIncomingValue(Idx);
2780 if (InValue != CaseValue) continue;
2789 /// ForwardSwitchConditionToPHI - Try to forward the condition of a switch
2790 /// instruction to a phi node dominated by the switch, if that would mean that
2791 /// some of the destination blocks of the switch can be folded away.
2792 /// Returns true if a change is made.
2793 static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
2794 typedef DenseMap<PHINode*, SmallVector<int,4> > ForwardingNodesMap;
2795 ForwardingNodesMap ForwardingNodes;
2797 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
2798 ConstantInt *CaseValue = I.getCaseValue();
2799 BasicBlock *CaseDest = I.getCaseSuccessor();
2802 PHINode *PHI = FindPHIForConditionForwarding(CaseValue, CaseDest,
2806 ForwardingNodes[PHI].push_back(PhiIndex);
2809 bool Changed = false;
2811 for (ForwardingNodesMap::iterator I = ForwardingNodes.begin(),
2812 E = ForwardingNodes.end(); I != E; ++I) {
2813 PHINode *Phi = I->first;
2814 SmallVector<int,4> &Indexes = I->second;
2816 if (Indexes.size() < 2) continue;
2818 for (size_t I = 0, E = Indexes.size(); I != E; ++I)
2819 Phi->setIncomingValue(Indexes[I], SI->getCondition());
2826 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
2827 // If this switch is too complex to want to look at, ignore it.
2828 if (!isValueEqualityComparison(SI))
2831 BasicBlock *BB = SI->getParent();
2833 // If we only have one predecessor, and if it is a branch on this value,
2834 // see if that predecessor totally determines the outcome of this switch.
2835 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2836 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
2837 return SimplifyCFG(BB) | true;
2839 Value *Cond = SI->getCondition();
2840 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
2841 if (SimplifySwitchOnSelect(SI, Select))
2842 return SimplifyCFG(BB) | true;
2844 // If the block only contains the switch, see if we can fold the block
2845 // away into any preds.
2846 BasicBlock::iterator BBI = BB->begin();
2847 // Ignore dbg intrinsics.
2848 while (isa<DbgInfoIntrinsic>(BBI))
2851 if (FoldValueComparisonIntoPredecessors(SI, Builder))
2852 return SimplifyCFG(BB) | true;
2854 // Try to transform the switch into an icmp and a branch.
2855 if (TurnSwitchRangeIntoICmp(SI, Builder))
2856 return SimplifyCFG(BB) | true;
2858 // Remove unreachable cases.
2859 if (EliminateDeadSwitchCases(SI))
2860 return SimplifyCFG(BB) | true;
2862 if (ForwardSwitchConditionToPHI(SI))
2863 return SimplifyCFG(BB) | true;
2868 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
2869 BasicBlock *BB = IBI->getParent();
2870 bool Changed = false;
2872 // Eliminate redundant destinations.
2873 SmallPtrSet<Value *, 8> Succs;
2874 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2875 BasicBlock *Dest = IBI->getDestination(i);
2876 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2877 Dest->removePredecessor(BB);
2878 IBI->removeDestination(i);
2884 if (IBI->getNumDestinations() == 0) {
2885 // If the indirectbr has no successors, change it to unreachable.
2886 new UnreachableInst(IBI->getContext(), IBI);
2887 EraseTerminatorInstAndDCECond(IBI);
2891 if (IBI->getNumDestinations() == 1) {
2892 // If the indirectbr has one successor, change it to a direct branch.
2893 BranchInst::Create(IBI->getDestination(0), IBI);
2894 EraseTerminatorInstAndDCECond(IBI);
2898 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2899 if (SimplifyIndirectBrOnSelect(IBI, SI))
2900 return SimplifyCFG(BB) | true;
2905 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
2906 BasicBlock *BB = BI->getParent();
2908 // If the Terminator is the only non-phi instruction, simplify the block.
2909 BasicBlock::iterator I = BB->getFirstNonPHIOrDbgOrLifetime();
2910 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
2911 TryToSimplifyUncondBranchFromEmptyBlock(BB))
2914 // If the only instruction in the block is a seteq/setne comparison
2915 // against a constant, try to simplify the block.
2916 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
2917 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
2918 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
2920 if (I->isTerminator() &&
2921 TryToSimplifyUncondBranchWithICmpInIt(ICI, TD, Builder))
2925 // If this basic block is ONLY a compare and a branch, and if a predecessor
2926 // branches to us and our successor, fold the comparison into the
2927 // predecessor and use logical operations to update the incoming value
2928 // for PHI nodes in common successor.
2929 if (FoldBranchToCommonDest(BI))
2930 return SimplifyCFG(BB) | true;
2935 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
2936 BasicBlock *BB = BI->getParent();
2938 // Conditional branch
2939 if (isValueEqualityComparison(BI)) {
2940 // If we only have one predecessor, and if it is a branch on this value,
2941 // see if that predecessor totally determines the outcome of this
2943 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2944 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
2945 return SimplifyCFG(BB) | true;
2947 // This block must be empty, except for the setcond inst, if it exists.
2948 // Ignore dbg intrinsics.
2949 BasicBlock::iterator I = BB->begin();
2950 // Ignore dbg intrinsics.
2951 while (isa<DbgInfoIntrinsic>(I))
2954 if (FoldValueComparisonIntoPredecessors(BI, Builder))
2955 return SimplifyCFG(BB) | true;
2956 } else if (&*I == cast<Instruction>(BI->getCondition())){
2958 // Ignore dbg intrinsics.
2959 while (isa<DbgInfoIntrinsic>(I))
2961 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
2962 return SimplifyCFG(BB) | true;
2966 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
2967 if (SimplifyBranchOnICmpChain(BI, TD, Builder))
2970 // If this basic block is ONLY a compare and a branch, and if a predecessor
2971 // branches to us and one of our successors, fold the comparison into the
2972 // predecessor and use logical operations to pick the right destination.
2973 if (FoldBranchToCommonDest(BI))
2974 return SimplifyCFG(BB) | true;
2976 // We have a conditional branch to two blocks that are only reachable
2977 // from BI. We know that the condbr dominates the two blocks, so see if
2978 // there is any identical code in the "then" and "else" blocks. If so, we
2979 // can hoist it up to the branching block.
2980 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
2981 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2982 if (HoistThenElseCodeToIf(BI))
2983 return SimplifyCFG(BB) | true;
2985 // If Successor #1 has multiple preds, we may be able to conditionally
2986 // execute Successor #0 if it branches to successor #1.
2987 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
2988 if (Succ0TI->getNumSuccessors() == 1 &&
2989 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
2990 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
2991 return SimplifyCFG(BB) | true;
2993 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2994 // If Successor #0 has multiple preds, we may be able to conditionally
2995 // execute Successor #1 if it branches to successor #0.
2996 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
2997 if (Succ1TI->getNumSuccessors() == 1 &&
2998 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
2999 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
3000 return SimplifyCFG(BB) | true;
3003 // If this is a branch on a phi node in the current block, thread control
3004 // through this block if any PHI node entries are constants.
3005 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
3006 if (PN->getParent() == BI->getParent())
3007 if (FoldCondBranchOnPHI(BI, TD))
3008 return SimplifyCFG(BB) | true;
3010 // Scan predecessor blocks for conditional branches.
3011 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
3012 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
3013 if (PBI != BI && PBI->isConditional())
3014 if (SimplifyCondBranchToCondBranch(PBI, BI))
3015 return SimplifyCFG(BB) | true;
3020 /// Check if passing a value to an instruction will cause undefined behavior.
3021 static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
3022 Constant *C = dyn_cast<Constant>(V);
3026 if (!I->hasOneUse()) // Only look at single-use instructions, for compile time
3029 if (C->isNullValue()) {
3030 Instruction *Use = I->use_back();
3032 // Now make sure that there are no instructions in between that can alter
3033 // control flow (eg. calls)
3034 for (BasicBlock::iterator i = ++BasicBlock::iterator(I); &*i != Use; ++i)
3035 if (i == I->getParent()->end() || i->mayHaveSideEffects())
3038 // Look through GEPs. A load from a GEP derived from NULL is still undefined
3039 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))
3040 if (GEP->getPointerOperand() == I)
3041 return passingValueIsAlwaysUndefined(V, GEP);
3043 // Look through bitcasts.
3044 if (BitCastInst *BC = dyn_cast<BitCastInst>(Use))
3045 return passingValueIsAlwaysUndefined(V, BC);
3047 // Load from null is undefined.
3048 if (LoadInst *LI = dyn_cast<LoadInst>(Use))
3049 return LI->getPointerAddressSpace() == 0;
3051 // Store to null is undefined.
3052 if (StoreInst *SI = dyn_cast<StoreInst>(Use))
3053 return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I;
3058 /// If BB has an incoming value that will always trigger undefined behavior
3059 /// (eg. null pointer dereference), remove the branch leading here.
3060 static bool removeUndefIntroducingPredecessor(BasicBlock *BB) {
3061 for (BasicBlock::iterator i = BB->begin();
3062 PHINode *PHI = dyn_cast<PHINode>(i); ++i)
3063 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
3064 if (passingValueIsAlwaysUndefined(PHI->getIncomingValue(i), PHI)) {
3065 TerminatorInst *T = PHI->getIncomingBlock(i)->getTerminator();
3066 IRBuilder<> Builder(T);
3067 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
3068 BB->removePredecessor(PHI->getIncomingBlock(i));
3069 // Turn uncoditional branches into unreachables and remove the dead
3070 // destination from conditional branches.
3071 if (BI->isUnconditional())
3072 Builder.CreateUnreachable();
3074 Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1) :
3075 BI->getSuccessor(0));
3076 BI->eraseFromParent();
3079 // TODO: SwitchInst.
3085 bool SimplifyCFGOpt::run(BasicBlock *BB) {
3086 bool Changed = false;
3088 assert(BB && BB->getParent() && "Block not embedded in function!");
3089 assert(BB->getTerminator() && "Degenerate basic block encountered!");
3091 // Remove basic blocks that have no predecessors (except the entry block)...
3092 // or that just have themself as a predecessor. These are unreachable.
3093 if ((pred_begin(BB) == pred_end(BB) &&
3094 BB != &BB->getParent()->getEntryBlock()) ||
3095 BB->getSinglePredecessor() == BB) {
3096 DEBUG(dbgs() << "Removing BB: \n" << *BB);
3097 DeleteDeadBlock(BB);
3101 // Check to see if we can constant propagate this terminator instruction
3103 Changed |= ConstantFoldTerminator(BB, true);
3105 // Check for and eliminate duplicate PHI nodes in this block.
3106 Changed |= EliminateDuplicatePHINodes(BB);
3108 // Check for and remove branches that will always cause undefined behavior.
3109 Changed |= removeUndefIntroducingPredecessor(BB);
3111 // Merge basic blocks into their predecessor if there is only one distinct
3112 // pred, and if there is only one distinct successor of the predecessor, and
3113 // if there are no PHI nodes.
3115 if (MergeBlockIntoPredecessor(BB))
3118 IRBuilder<> Builder(BB);
3120 // If there is a trivial two-entry PHI node in this basic block, and we can
3121 // eliminate it, do so now.
3122 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
3123 if (PN->getNumIncomingValues() == 2)
3124 Changed |= FoldTwoEntryPHINode(PN, TD);
3126 Builder.SetInsertPoint(BB->getTerminator());
3127 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
3128 if (BI->isUnconditional()) {
3129 if (SimplifyUncondBranch(BI, Builder)) return true;
3131 if (SimplifyCondBranch(BI, Builder)) return true;
3133 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
3134 if (SimplifyReturn(RI, Builder)) return true;
3135 } else if (ResumeInst *RI = dyn_cast<ResumeInst>(BB->getTerminator())) {
3136 if (SimplifyResume(RI, Builder)) return true;
3137 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
3138 if (SimplifySwitch(SI, Builder)) return true;
3139 } else if (UnreachableInst *UI =
3140 dyn_cast<UnreachableInst>(BB->getTerminator())) {
3141 if (SimplifyUnreachable(UI)) return true;
3142 } else if (IndirectBrInst *IBI =
3143 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
3144 if (SimplifyIndirectBr(IBI)) return true;
3150 /// SimplifyCFG - This function is used to do simplification of a CFG. For
3151 /// example, it adjusts branches to branches to eliminate the extra hop, it
3152 /// eliminates unreachable basic blocks, and does other "peephole" optimization
3153 /// of the CFG. It returns true if a modification was made.
3155 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
3156 return SimplifyCFGOpt(TD).run(BB);