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/Module.h"
26 #include "llvm/Operator.h"
27 #include "llvm/Type.h"
28 #include "llvm/ADT/DenseMap.h"
29 #include "llvm/ADT/STLExtras.h"
30 #include "llvm/ADT/SetVector.h"
31 #include "llvm/ADT/SmallPtrSet.h"
32 #include "llvm/ADT/SmallVector.h"
33 #include "llvm/ADT/Statistic.h"
34 #include "llvm/Analysis/InstructionSimplify.h"
35 #include "llvm/Analysis/ValueTracking.h"
36 #include "llvm/Support/CFG.h"
37 #include "llvm/Support/CommandLine.h"
38 #include "llvm/Support/ConstantRange.h"
39 #include "llvm/Support/Debug.h"
40 #include "llvm/Support/NoFolder.h"
41 #include "llvm/Support/raw_ostream.h"
42 #include "llvm/DataLayout.h"
43 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
49 static cl::opt<unsigned>
50 PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(1),
51 cl::desc("Control the amount of phi node folding to perform (default = 1)"));
54 DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false),
55 cl::desc("Duplicate return instructions into unconditional branches"));
58 SinkCommon("simplifycfg-sink-common", cl::Hidden, cl::init(true),
59 cl::desc("Sink common instructions down to the end block"));
61 STATISTIC(NumBitMaps, "Number of switch instructions turned into bitmaps");
62 STATISTIC(NumLookupTables, "Number of switch instructions turned into lookup tables");
63 STATISTIC(NumSinkCommons, "Number of common instructions sunk down to the end block");
64 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
67 /// ValueEqualityComparisonCase - Represents a case of a switch.
68 struct ValueEqualityComparisonCase {
72 ValueEqualityComparisonCase(ConstantInt *Value, BasicBlock *Dest)
73 : Value(Value), Dest(Dest) {}
75 bool operator<(ValueEqualityComparisonCase RHS) const {
76 // Comparing pointers is ok as we only rely on the order for uniquing.
77 return Value < RHS.Value;
80 bool operator==(BasicBlock *RHSDest) const { return Dest == RHSDest; }
83 class SimplifyCFGOpt {
84 const DataLayout *const TD;
86 Value *isValueEqualityComparison(TerminatorInst *TI);
87 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
88 std::vector<ValueEqualityComparisonCase> &Cases);
89 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
91 IRBuilder<> &Builder);
92 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
93 IRBuilder<> &Builder);
95 bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder);
96 bool SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder);
97 bool SimplifyUnreachable(UnreachableInst *UI);
98 bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
99 bool SimplifyIndirectBr(IndirectBrInst *IBI);
100 bool SimplifyUncondBranch(BranchInst *BI, IRBuilder <> &Builder);
101 bool SimplifyCondBranch(BranchInst *BI, IRBuilder <>&Builder);
104 explicit SimplifyCFGOpt(const DataLayout *td) : TD(td) {}
105 bool run(BasicBlock *BB);
109 /// SafeToMergeTerminators - Return true if it is safe to merge these two
110 /// terminator instructions together.
112 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
113 if (SI1 == SI2) return false; // Can't merge with self!
115 // It is not safe to merge these two switch instructions if they have a common
116 // successor, and if that successor has a PHI node, and if *that* PHI node has
117 // conflicting incoming values from the two switch blocks.
118 BasicBlock *SI1BB = SI1->getParent();
119 BasicBlock *SI2BB = SI2->getParent();
120 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
122 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
123 if (SI1Succs.count(*I))
124 for (BasicBlock::iterator BBI = (*I)->begin();
125 isa<PHINode>(BBI); ++BBI) {
126 PHINode *PN = cast<PHINode>(BBI);
127 if (PN->getIncomingValueForBlock(SI1BB) !=
128 PN->getIncomingValueForBlock(SI2BB))
135 /// isProfitableToFoldUnconditional - Return true if it is safe and profitable
136 /// to merge these two terminator instructions together, where SI1 is an
137 /// unconditional branch. PhiNodes will store all PHI nodes in common
140 static bool isProfitableToFoldUnconditional(BranchInst *SI1,
143 SmallVectorImpl<PHINode*> &PhiNodes) {
144 if (SI1 == SI2) return false; // Can't merge with self!
145 assert(SI1->isUnconditional() && SI2->isConditional());
147 // We fold the unconditional branch if we can easily update all PHI nodes in
148 // common successors:
149 // 1> We have a constant incoming value for the conditional branch;
150 // 2> We have "Cond" as the incoming value for the unconditional branch;
151 // 3> SI2->getCondition() and Cond have same operands.
152 CmpInst *Ci2 = dyn_cast<CmpInst>(SI2->getCondition());
153 if (!Ci2) return false;
154 if (!(Cond->getOperand(0) == Ci2->getOperand(0) &&
155 Cond->getOperand(1) == Ci2->getOperand(1)) &&
156 !(Cond->getOperand(0) == Ci2->getOperand(1) &&
157 Cond->getOperand(1) == Ci2->getOperand(0)))
160 BasicBlock *SI1BB = SI1->getParent();
161 BasicBlock *SI2BB = SI2->getParent();
162 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
163 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
164 if (SI1Succs.count(*I))
165 for (BasicBlock::iterator BBI = (*I)->begin();
166 isa<PHINode>(BBI); ++BBI) {
167 PHINode *PN = cast<PHINode>(BBI);
168 if (PN->getIncomingValueForBlock(SI1BB) != Cond ||
169 !isa<ConstantInt>(PN->getIncomingValueForBlock(SI2BB)))
171 PhiNodes.push_back(PN);
176 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
177 /// now be entries in it from the 'NewPred' block. The values that will be
178 /// flowing into the PHI nodes will be the same as those coming in from
179 /// ExistPred, an existing predecessor of Succ.
180 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
181 BasicBlock *ExistPred) {
182 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
185 for (BasicBlock::iterator I = Succ->begin();
186 (PN = dyn_cast<PHINode>(I)); ++I)
187 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
191 /// GetIfCondition - Given a basic block (BB) with two predecessors (and at
192 /// least one PHI node in it), check to see if the merge at this block is due
193 /// to an "if condition". If so, return the boolean condition that determines
194 /// which entry into BB will be taken. Also, return by references the block
195 /// that will be entered from if the condition is true, and the block that will
196 /// be entered if the condition is false.
198 /// This does no checking to see if the true/false blocks have large or unsavory
199 /// instructions in them.
200 static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
201 BasicBlock *&IfFalse) {
202 PHINode *SomePHI = cast<PHINode>(BB->begin());
203 assert(SomePHI->getNumIncomingValues() == 2 &&
204 "Function can only handle blocks with 2 predecessors!");
205 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
206 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
208 // We can only handle branches. Other control flow will be lowered to
209 // branches if possible anyway.
210 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
211 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
212 if (Pred1Br == 0 || Pred2Br == 0)
215 // Eliminate code duplication by ensuring that Pred1Br is conditional if
217 if (Pred2Br->isConditional()) {
218 // If both branches are conditional, we don't have an "if statement". In
219 // reality, we could transform this case, but since the condition will be
220 // required anyway, we stand no chance of eliminating it, so the xform is
221 // probably not profitable.
222 if (Pred1Br->isConditional())
225 std::swap(Pred1, Pred2);
226 std::swap(Pred1Br, Pred2Br);
229 if (Pred1Br->isConditional()) {
230 // The only thing we have to watch out for here is to make sure that Pred2
231 // doesn't have incoming edges from other blocks. If it does, the condition
232 // doesn't dominate BB.
233 if (Pred2->getSinglePredecessor() == 0)
236 // If we found a conditional branch predecessor, make sure that it branches
237 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
238 if (Pred1Br->getSuccessor(0) == BB &&
239 Pred1Br->getSuccessor(1) == Pred2) {
242 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
243 Pred1Br->getSuccessor(1) == BB) {
247 // We know that one arm of the conditional goes to BB, so the other must
248 // go somewhere unrelated, and this must not be an "if statement".
252 return Pred1Br->getCondition();
255 // Ok, if we got here, both predecessors end with an unconditional branch to
256 // BB. Don't panic! If both blocks only have a single (identical)
257 // predecessor, and THAT is a conditional branch, then we're all ok!
258 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
259 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
262 // Otherwise, if this is a conditional branch, then we can use it!
263 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
264 if (BI == 0) return 0;
266 assert(BI->isConditional() && "Two successors but not conditional?");
267 if (BI->getSuccessor(0) == Pred1) {
274 return BI->getCondition();
277 /// ComputeSpeculuationCost - Compute an abstract "cost" of speculating the
278 /// given instruction, which is assumed to be safe to speculate. 1 means
279 /// cheap, 2 means less cheap, and UINT_MAX means prohibitively expensive.
280 static unsigned ComputeSpeculationCost(const User *I) {
281 assert(isSafeToSpeculativelyExecute(I) &&
282 "Instruction is not safe to speculatively execute!");
283 switch (Operator::getOpcode(I)) {
285 // In doubt, be conservative.
287 case Instruction::GetElementPtr:
288 // GEPs are cheap if all indices are constant.
289 if (!cast<GEPOperator>(I)->hasAllConstantIndices())
292 case Instruction::Load:
293 case Instruction::Add:
294 case Instruction::Sub:
295 case Instruction::And:
296 case Instruction::Or:
297 case Instruction::Xor:
298 case Instruction::Shl:
299 case Instruction::LShr:
300 case Instruction::AShr:
301 case Instruction::ICmp:
302 case Instruction::Trunc:
303 case Instruction::ZExt:
304 case Instruction::SExt:
305 return 1; // These are all cheap.
307 case Instruction::Call:
308 case Instruction::Select:
313 /// DominatesMergePoint - If we have a merge point of an "if condition" as
314 /// accepted above, return true if the specified value dominates the block. We
315 /// don't handle the true generality of domination here, just a special case
316 /// which works well enough for us.
318 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
319 /// see if V (which must be an instruction) and its recursive operands
320 /// that do not dominate BB have a combined cost lower than CostRemaining and
321 /// are non-trapping. If both are true, the instruction is inserted into the
322 /// set and true is returned.
324 /// The cost for most non-trapping instructions is defined as 1 except for
325 /// Select whose cost is 2.
327 /// After this function returns, CostRemaining is decreased by the cost of
328 /// V plus its non-dominating operands. If that cost is greater than
329 /// CostRemaining, false is returned and CostRemaining is undefined.
330 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
331 SmallPtrSet<Instruction*, 4> *AggressiveInsts,
332 unsigned &CostRemaining) {
333 Instruction *I = dyn_cast<Instruction>(V);
335 // Non-instructions all dominate instructions, but not all constantexprs
336 // can be executed unconditionally.
337 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
342 BasicBlock *PBB = I->getParent();
344 // We don't want to allow weird loops that might have the "if condition" in
345 // the bottom of this block.
346 if (PBB == BB) return false;
348 // If this instruction is defined in a block that contains an unconditional
349 // branch to BB, then it must be in the 'conditional' part of the "if
350 // statement". If not, it definitely dominates the region.
351 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
352 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB)
355 // If we aren't allowing aggressive promotion anymore, then don't consider
356 // instructions in the 'if region'.
357 if (AggressiveInsts == 0) return false;
359 // If we have seen this instruction before, don't count it again.
360 if (AggressiveInsts->count(I)) return true;
362 // Okay, it looks like the instruction IS in the "condition". Check to
363 // see if it's a cheap instruction to unconditionally compute, and if it
364 // only uses stuff defined outside of the condition. If so, hoist it out.
365 if (!isSafeToSpeculativelyExecute(I))
368 unsigned Cost = ComputeSpeculationCost(I);
370 if (Cost > CostRemaining)
373 CostRemaining -= Cost;
375 // Okay, we can only really hoist these out if their operands do
376 // not take us over the cost threshold.
377 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
378 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining))
380 // Okay, it's safe to do this! Remember this instruction.
381 AggressiveInsts->insert(I);
385 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
386 /// and PointerNullValue. Return NULL if value is not a constant int.
387 static ConstantInt *GetConstantInt(Value *V, const DataLayout *TD) {
388 // Normal constant int.
389 ConstantInt *CI = dyn_cast<ConstantInt>(V);
390 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
393 // This is some kind of pointer constant. Turn it into a pointer-sized
394 // ConstantInt if possible.
395 IntegerType *PtrTy = TD->getIntPtrType(V->getType());
397 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
398 if (isa<ConstantPointerNull>(V))
399 return ConstantInt::get(PtrTy, 0);
401 // IntToPtr const int.
402 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
403 if (CE->getOpcode() == Instruction::IntToPtr)
404 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
405 // The constant is very likely to have the right type already.
406 if (CI->getType() == PtrTy)
409 return cast<ConstantInt>
410 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
415 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
416 /// collection of icmp eq/ne instructions that compare a value against a
417 /// constant, return the value being compared, and stick the constant into the
420 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
421 const DataLayout *TD, bool isEQ, unsigned &UsedICmps) {
422 Instruction *I = dyn_cast<Instruction>(V);
423 if (I == 0) return 0;
425 // If this is an icmp against a constant, handle this as one of the cases.
426 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
427 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
428 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
431 return I->getOperand(0);
434 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
437 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
439 // If this is an and/!= check then we want to optimize "x ugt 2" into
442 Span = Span.inverse();
444 // If there are a ton of values, we don't want to make a ginormous switch.
445 if (Span.getSetSize().ugt(8) || Span.isEmptySet())
448 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
449 Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
451 return I->getOperand(0);
456 // Otherwise, we can only handle an | or &, depending on isEQ.
457 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
460 unsigned NumValsBeforeLHS = Vals.size();
461 unsigned UsedICmpsBeforeLHS = UsedICmps;
462 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
464 unsigned NumVals = Vals.size();
465 unsigned UsedICmpsBeforeRHS = UsedICmps;
466 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
470 Vals.resize(NumVals);
471 UsedICmps = UsedICmpsBeforeRHS;
474 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
475 // set it and return success.
476 if (Extra == 0 || Extra == I->getOperand(1)) {
477 Extra = I->getOperand(1);
481 Vals.resize(NumValsBeforeLHS);
482 UsedICmps = UsedICmpsBeforeLHS;
486 // If the LHS can't be folded in, but Extra is available and RHS can, try to
488 if (Extra == 0 || Extra == I->getOperand(0)) {
489 Value *OldExtra = Extra;
490 Extra = I->getOperand(0);
491 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
494 assert(Vals.size() == NumValsBeforeLHS);
501 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
502 Instruction *Cond = 0;
503 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
504 Cond = dyn_cast<Instruction>(SI->getCondition());
505 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
506 if (BI->isConditional())
507 Cond = dyn_cast<Instruction>(BI->getCondition());
508 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
509 Cond = dyn_cast<Instruction>(IBI->getAddress());
512 TI->eraseFromParent();
513 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
516 /// isValueEqualityComparison - Return true if the specified terminator checks
517 /// to see if a value is equal to constant integer value.
518 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
520 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
521 // Do not permit merging of large switch instructions into their
522 // predecessors unless there is only one predecessor.
523 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
524 pred_end(SI->getParent())) <= 128)
525 CV = SI->getCondition();
526 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
527 if (BI->isConditional() && BI->getCondition()->hasOneUse())
528 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
529 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
530 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
531 GetConstantInt(ICI->getOperand(1), TD))
532 CV = ICI->getOperand(0);
534 // Unwrap any lossless ptrtoint cast.
536 PtrToIntInst *PTII = NULL;
537 if ((PTII = dyn_cast<PtrToIntInst>(CV)) &&
538 CV->getType() == TD->getIntPtrType(CV->getContext(),
539 PTII->getPointerAddressSpace()))
540 CV = PTII->getOperand(0);
545 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
546 /// decode all of the 'cases' that it represents and return the 'default' block.
547 BasicBlock *SimplifyCFGOpt::
548 GetValueEqualityComparisonCases(TerminatorInst *TI,
549 std::vector<ValueEqualityComparisonCase>
551 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
552 Cases.reserve(SI->getNumCases());
553 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i)
554 Cases.push_back(ValueEqualityComparisonCase(i.getCaseValue(),
555 i.getCaseSuccessor()));
556 return SI->getDefaultDest();
559 BranchInst *BI = cast<BranchInst>(TI);
560 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
561 BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE);
562 Cases.push_back(ValueEqualityComparisonCase(GetConstantInt(ICI->getOperand(1),
565 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
569 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
570 /// in the list that match the specified block.
571 static void EliminateBlockCases(BasicBlock *BB,
572 std::vector<ValueEqualityComparisonCase> &Cases) {
573 Cases.erase(std::remove(Cases.begin(), Cases.end(), BB), Cases.end());
576 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
579 ValuesOverlap(std::vector<ValueEqualityComparisonCase> &C1,
580 std::vector<ValueEqualityComparisonCase > &C2) {
581 std::vector<ValueEqualityComparisonCase> *V1 = &C1, *V2 = &C2;
583 // Make V1 be smaller than V2.
584 if (V1->size() > V2->size())
587 if (V1->size() == 0) return false;
588 if (V1->size() == 1) {
590 ConstantInt *TheVal = (*V1)[0].Value;
591 for (unsigned i = 0, e = V2->size(); i != e; ++i)
592 if (TheVal == (*V2)[i].Value)
596 // Otherwise, just sort both lists and compare element by element.
597 array_pod_sort(V1->begin(), V1->end());
598 array_pod_sort(V2->begin(), V2->end());
599 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
600 while (i1 != e1 && i2 != e2) {
601 if ((*V1)[i1].Value == (*V2)[i2].Value)
603 if ((*V1)[i1].Value < (*V2)[i2].Value)
611 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
612 /// terminator instruction and its block is known to only have a single
613 /// predecessor block, check to see if that predecessor is also a value
614 /// comparison with the same value, and if that comparison determines the
615 /// outcome of this comparison. If so, simplify TI. This does a very limited
616 /// form of jump threading.
617 bool SimplifyCFGOpt::
618 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
620 IRBuilder<> &Builder) {
621 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
622 if (!PredVal) return false; // Not a value comparison in predecessor.
624 Value *ThisVal = isValueEqualityComparison(TI);
625 assert(ThisVal && "This isn't a value comparison!!");
626 if (ThisVal != PredVal) return false; // Different predicates.
628 // TODO: Preserve branch weight metadata, similarly to how
629 // FoldValueComparisonIntoPredecessors preserves it.
631 // Find out information about when control will move from Pred to TI's block.
632 std::vector<ValueEqualityComparisonCase> PredCases;
633 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
635 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
637 // Find information about how control leaves this block.
638 std::vector<ValueEqualityComparisonCase> ThisCases;
639 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
640 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
642 // If TI's block is the default block from Pred's comparison, potentially
643 // simplify TI based on this knowledge.
644 if (PredDef == TI->getParent()) {
645 // If we are here, we know that the value is none of those cases listed in
646 // PredCases. If there are any cases in ThisCases that are in PredCases, we
648 if (!ValuesOverlap(PredCases, ThisCases))
651 if (isa<BranchInst>(TI)) {
652 // Okay, one of the successors of this condbr is dead. Convert it to a
654 assert(ThisCases.size() == 1 && "Branch can only have one case!");
655 // Insert the new branch.
656 Instruction *NI = Builder.CreateBr(ThisDef);
659 // Remove PHI node entries for the dead edge.
660 ThisCases[0].Dest->removePredecessor(TI->getParent());
662 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
663 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
665 EraseTerminatorInstAndDCECond(TI);
669 SwitchInst *SI = cast<SwitchInst>(TI);
670 // Okay, TI has cases that are statically dead, prune them away.
671 SmallPtrSet<Constant*, 16> DeadCases;
672 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
673 DeadCases.insert(PredCases[i].Value);
675 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
676 << "Through successor TI: " << *TI);
678 // Collect branch weights into a vector.
679 SmallVector<uint32_t, 8> Weights;
680 MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
681 bool HasWeight = MD && (MD->getNumOperands() == 2 + SI->getNumCases());
683 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
685 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(MD_i));
687 Weights.push_back(CI->getValue().getZExtValue());
689 for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) {
691 if (DeadCases.count(i.getCaseValue())) {
693 std::swap(Weights[i.getCaseIndex()+1], Weights.back());
696 i.getCaseSuccessor()->removePredecessor(TI->getParent());
700 if (HasWeight && Weights.size() >= 2)
701 SI->setMetadata(LLVMContext::MD_prof,
702 MDBuilder(SI->getParent()->getContext()).
703 createBranchWeights(Weights));
705 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
709 // Otherwise, TI's block must correspond to some matched value. Find out
710 // which value (or set of values) this is.
711 ConstantInt *TIV = 0;
712 BasicBlock *TIBB = TI->getParent();
713 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
714 if (PredCases[i].Dest == TIBB) {
716 return false; // Cannot handle multiple values coming to this block.
717 TIV = PredCases[i].Value;
719 assert(TIV && "No edge from pred to succ?");
721 // Okay, we found the one constant that our value can be if we get into TI's
722 // BB. Find out which successor will unconditionally be branched to.
723 BasicBlock *TheRealDest = 0;
724 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
725 if (ThisCases[i].Value == TIV) {
726 TheRealDest = ThisCases[i].Dest;
730 // If not handled by any explicit cases, it is handled by the default case.
731 if (TheRealDest == 0) TheRealDest = ThisDef;
733 // Remove PHI node entries for dead edges.
734 BasicBlock *CheckEdge = TheRealDest;
735 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
736 if (*SI != CheckEdge)
737 (*SI)->removePredecessor(TIBB);
741 // Insert the new branch.
742 Instruction *NI = Builder.CreateBr(TheRealDest);
745 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
746 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
748 EraseTerminatorInstAndDCECond(TI);
753 /// ConstantIntOrdering - This class implements a stable ordering of constant
754 /// integers that does not depend on their address. This is important for
755 /// applications that sort ConstantInt's to ensure uniqueness.
756 struct ConstantIntOrdering {
757 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
758 return LHS->getValue().ult(RHS->getValue());
763 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
764 const ConstantInt *LHS = *(const ConstantInt*const*)P1;
765 const ConstantInt *RHS = *(const ConstantInt*const*)P2;
766 if (LHS->getValue().ult(RHS->getValue()))
768 if (LHS->getValue() == RHS->getValue())
773 static inline bool HasBranchWeights(const Instruction* I) {
774 MDNode* ProfMD = I->getMetadata(LLVMContext::MD_prof);
775 if (ProfMD && ProfMD->getOperand(0))
776 if (MDString* MDS = dyn_cast<MDString>(ProfMD->getOperand(0)))
777 return MDS->getString().equals("branch_weights");
782 /// Get Weights of a given TerminatorInst, the default weight is at the front
783 /// of the vector. If TI is a conditional eq, we need to swap the branch-weight
785 static void GetBranchWeights(TerminatorInst *TI,
786 SmallVectorImpl<uint64_t> &Weights) {
787 MDNode* MD = TI->getMetadata(LLVMContext::MD_prof);
789 for (unsigned i = 1, e = MD->getNumOperands(); i < e; ++i) {
790 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(i));
792 Weights.push_back(CI->getValue().getZExtValue());
795 // If TI is a conditional eq, the default case is the false case,
796 // and the corresponding branch-weight data is at index 2. We swap the
797 // default weight to be the first entry.
798 if (BranchInst* BI = dyn_cast<BranchInst>(TI)) {
799 assert(Weights.size() == 2);
800 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
801 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
802 std::swap(Weights.front(), Weights.back());
806 /// Sees if any of the weights are too big for a uint32_t, and halves all the
807 /// weights if any are.
808 static void FitWeights(MutableArrayRef<uint64_t> Weights) {
810 for (unsigned i = 0; i < Weights.size(); ++i)
811 if (Weights[i] > UINT_MAX) {
819 for (unsigned i = 0; i < Weights.size(); ++i)
823 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
824 /// equality comparison instruction (either a switch or a branch on "X == c").
825 /// See if any of the predecessors of the terminator block are value comparisons
826 /// on the same value. If so, and if safe to do so, fold them together.
827 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
828 IRBuilder<> &Builder) {
829 BasicBlock *BB = TI->getParent();
830 Value *CV = isValueEqualityComparison(TI); // CondVal
831 assert(CV && "Not a comparison?");
832 bool Changed = false;
834 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
835 while (!Preds.empty()) {
836 BasicBlock *Pred = Preds.pop_back_val();
838 // See if the predecessor is a comparison with the same value.
839 TerminatorInst *PTI = Pred->getTerminator();
840 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
842 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
843 // Figure out which 'cases' to copy from SI to PSI.
844 std::vector<ValueEqualityComparisonCase> BBCases;
845 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
847 std::vector<ValueEqualityComparisonCase> PredCases;
848 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
850 // Based on whether the default edge from PTI goes to BB or not, fill in
851 // PredCases and PredDefault with the new switch cases we would like to
853 SmallVector<BasicBlock*, 8> NewSuccessors;
855 // Update the branch weight metadata along the way
856 SmallVector<uint64_t, 8> Weights;
857 bool PredHasWeights = HasBranchWeights(PTI);
858 bool SuccHasWeights = HasBranchWeights(TI);
860 if (PredHasWeights) {
861 GetBranchWeights(PTI, Weights);
862 // branch-weight metadata is inconsistant here.
863 if (Weights.size() != 1 + PredCases.size())
864 PredHasWeights = SuccHasWeights = false;
865 } else if (SuccHasWeights)
866 // If there are no predecessor weights but there are successor weights,
867 // populate Weights with 1, which will later be scaled to the sum of
868 // successor's weights
869 Weights.assign(1 + PredCases.size(), 1);
871 SmallVector<uint64_t, 8> SuccWeights;
872 if (SuccHasWeights) {
873 GetBranchWeights(TI, SuccWeights);
874 // branch-weight metadata is inconsistant here.
875 if (SuccWeights.size() != 1 + BBCases.size())
876 PredHasWeights = SuccHasWeights = false;
877 } else if (PredHasWeights)
878 SuccWeights.assign(1 + BBCases.size(), 1);
880 if (PredDefault == BB) {
881 // If this is the default destination from PTI, only the edges in TI
882 // that don't occur in PTI, or that branch to BB will be activated.
883 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
884 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
885 if (PredCases[i].Dest != BB)
886 PTIHandled.insert(PredCases[i].Value);
888 // The default destination is BB, we don't need explicit targets.
889 std::swap(PredCases[i], PredCases.back());
891 if (PredHasWeights || SuccHasWeights) {
892 // Increase weight for the default case.
893 Weights[0] += Weights[i+1];
894 std::swap(Weights[i+1], Weights.back());
898 PredCases.pop_back();
902 // Reconstruct the new switch statement we will be building.
903 if (PredDefault != BBDefault) {
904 PredDefault->removePredecessor(Pred);
905 PredDefault = BBDefault;
906 NewSuccessors.push_back(BBDefault);
909 unsigned CasesFromPred = Weights.size();
910 uint64_t ValidTotalSuccWeight = 0;
911 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
912 if (!PTIHandled.count(BBCases[i].Value) &&
913 BBCases[i].Dest != BBDefault) {
914 PredCases.push_back(BBCases[i]);
915 NewSuccessors.push_back(BBCases[i].Dest);
916 if (SuccHasWeights || PredHasWeights) {
917 // The default weight is at index 0, so weight for the ith case
918 // should be at index i+1. Scale the cases from successor by
919 // PredDefaultWeight (Weights[0]).
920 Weights.push_back(Weights[0] * SuccWeights[i+1]);
921 ValidTotalSuccWeight += SuccWeights[i+1];
925 if (SuccHasWeights || PredHasWeights) {
926 ValidTotalSuccWeight += SuccWeights[0];
927 // Scale the cases from predecessor by ValidTotalSuccWeight.
928 for (unsigned i = 1; i < CasesFromPred; ++i)
929 Weights[i] *= ValidTotalSuccWeight;
930 // Scale the default weight by SuccDefaultWeight (SuccWeights[0]).
931 Weights[0] *= SuccWeights[0];
934 // If this is not the default destination from PSI, only the edges
935 // in SI that occur in PSI with a destination of BB will be
937 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
938 std::map<ConstantInt*, uint64_t> WeightsForHandled;
939 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
940 if (PredCases[i].Dest == BB) {
941 PTIHandled.insert(PredCases[i].Value);
943 if (PredHasWeights || SuccHasWeights) {
944 WeightsForHandled[PredCases[i].Value] = Weights[i+1];
945 std::swap(Weights[i+1], Weights.back());
949 std::swap(PredCases[i], PredCases.back());
950 PredCases.pop_back();
954 // Okay, now we know which constants were sent to BB from the
955 // predecessor. Figure out where they will all go now.
956 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
957 if (PTIHandled.count(BBCases[i].Value)) {
958 // If this is one we are capable of getting...
959 if (PredHasWeights || SuccHasWeights)
960 Weights.push_back(WeightsForHandled[BBCases[i].Value]);
961 PredCases.push_back(BBCases[i]);
962 NewSuccessors.push_back(BBCases[i].Dest);
963 PTIHandled.erase(BBCases[i].Value);// This constant is taken care of
966 // If there are any constants vectored to BB that TI doesn't handle,
967 // they must go to the default destination of TI.
968 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
970 E = PTIHandled.end(); I != E; ++I) {
971 if (PredHasWeights || SuccHasWeights)
972 Weights.push_back(WeightsForHandled[*I]);
973 PredCases.push_back(ValueEqualityComparisonCase(*I, BBDefault));
974 NewSuccessors.push_back(BBDefault);
978 // Okay, at this point, we know which new successor Pred will get. Make
979 // sure we update the number of entries in the PHI nodes for these
981 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
982 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
984 Builder.SetInsertPoint(PTI);
985 // Convert pointer to int before we switch.
986 if (CV->getType()->isPointerTy()) {
987 assert(TD && "Cannot switch on pointer without DataLayout");
988 CV = Builder.CreatePtrToInt(CV, TD->getIntPtrType(CV->getType()),
992 // Now that the successors are updated, create the new Switch instruction.
993 SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault,
995 NewSI->setDebugLoc(PTI->getDebugLoc());
996 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
997 NewSI->addCase(PredCases[i].Value, PredCases[i].Dest);
999 if (PredHasWeights || SuccHasWeights) {
1000 // Halve the weights if any of them cannot fit in an uint32_t
1001 FitWeights(Weights);
1003 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
1005 NewSI->setMetadata(LLVMContext::MD_prof,
1006 MDBuilder(BB->getContext()).
1007 createBranchWeights(MDWeights));
1010 EraseTerminatorInstAndDCECond(PTI);
1012 // Okay, last check. If BB is still a successor of PSI, then we must
1013 // have an infinite loop case. If so, add an infinitely looping block
1014 // to handle the case to preserve the behavior of the code.
1015 BasicBlock *InfLoopBlock = 0;
1016 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
1017 if (NewSI->getSuccessor(i) == BB) {
1018 if (InfLoopBlock == 0) {
1019 // Insert it at the end of the function, because it's either code,
1020 // or it won't matter if it's hot. :)
1021 InfLoopBlock = BasicBlock::Create(BB->getContext(),
1022 "infloop", BB->getParent());
1023 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1025 NewSI->setSuccessor(i, InfLoopBlock);
1034 // isSafeToHoistInvoke - If we would need to insert a select that uses the
1035 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
1036 // would need to do this), we can't hoist the invoke, as there is nowhere
1037 // to put the select in this case.
1038 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
1039 Instruction *I1, Instruction *I2) {
1040 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
1042 for (BasicBlock::iterator BBI = SI->begin();
1043 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1044 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1045 Value *BB2V = PN->getIncomingValueForBlock(BB2);
1046 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
1054 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
1055 /// BB2, hoist any common code in the two blocks up into the branch block. The
1056 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
1057 static bool HoistThenElseCodeToIf(BranchInst *BI) {
1058 // This does very trivial matching, with limited scanning, to find identical
1059 // instructions in the two blocks. In particular, we don't want to get into
1060 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
1061 // such, we currently just scan for obviously identical instructions in an
1063 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
1064 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
1066 BasicBlock::iterator BB1_Itr = BB1->begin();
1067 BasicBlock::iterator BB2_Itr = BB2->begin();
1069 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
1070 // Skip debug info if it is not identical.
1071 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
1072 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
1073 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
1074 while (isa<DbgInfoIntrinsic>(I1))
1076 while (isa<DbgInfoIntrinsic>(I2))
1079 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
1080 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
1083 // If we get here, we can hoist at least one instruction.
1084 BasicBlock *BIParent = BI->getParent();
1087 // If we are hoisting the terminator instruction, don't move one (making a
1088 // broken BB), instead clone it, and remove BI.
1089 if (isa<TerminatorInst>(I1))
1090 goto HoistTerminator;
1092 // For a normal instruction, we just move one to right before the branch,
1093 // then replace all uses of the other with the first. Finally, we remove
1094 // the now redundant second instruction.
1095 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
1096 if (!I2->use_empty())
1097 I2->replaceAllUsesWith(I1);
1098 I1->intersectOptionalDataWith(I2);
1099 I2->eraseFromParent();
1103 // Skip debug info if it is not identical.
1104 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
1105 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
1106 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
1107 while (isa<DbgInfoIntrinsic>(I1))
1109 while (isa<DbgInfoIntrinsic>(I2))
1112 } while (I1->isIdenticalToWhenDefined(I2));
1117 // It may not be possible to hoist an invoke.
1118 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
1121 // Okay, it is safe to hoist the terminator.
1122 Instruction *NT = I1->clone();
1123 BIParent->getInstList().insert(BI, NT);
1124 if (!NT->getType()->isVoidTy()) {
1125 I1->replaceAllUsesWith(NT);
1126 I2->replaceAllUsesWith(NT);
1130 IRBuilder<true, NoFolder> Builder(NT);
1131 // Hoisting one of the terminators from our successor is a great thing.
1132 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
1133 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
1134 // nodes, so we insert select instruction to compute the final result.
1135 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
1136 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
1138 for (BasicBlock::iterator BBI = SI->begin();
1139 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1140 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1141 Value *BB2V = PN->getIncomingValueForBlock(BB2);
1142 if (BB1V == BB2V) continue;
1144 // These values do not agree. Insert a select instruction before NT
1145 // that determines the right value.
1146 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
1148 SI = cast<SelectInst>
1149 (Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,
1150 BB1V->getName()+"."+BB2V->getName()));
1152 // Make the PHI node use the select for all incoming values for BB1/BB2
1153 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
1154 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
1155 PN->setIncomingValue(i, SI);
1159 // Update any PHI nodes in our new successors.
1160 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
1161 AddPredecessorToBlock(*SI, BIParent, BB1);
1163 EraseTerminatorInstAndDCECond(BI);
1167 /// SinkThenElseCodeToEnd - Given an unconditional branch that goes to BBEnd,
1168 /// check whether BBEnd has only two predecessors and the other predecessor
1169 /// ends with an unconditional branch. If it is true, sink any common code
1170 /// in the two predecessors to BBEnd.
1171 static bool SinkThenElseCodeToEnd(BranchInst *BI1) {
1172 assert(BI1->isUnconditional());
1173 BasicBlock *BB1 = BI1->getParent();
1174 BasicBlock *BBEnd = BI1->getSuccessor(0);
1176 // Check that BBEnd has two predecessors and the other predecessor ends with
1177 // an unconditional branch.
1178 pred_iterator PI = pred_begin(BBEnd), PE = pred_end(BBEnd);
1179 BasicBlock *Pred0 = *PI++;
1180 if (PI == PE) // Only one predecessor.
1182 BasicBlock *Pred1 = *PI++;
1183 if (PI != PE) // More than two predecessors.
1185 BasicBlock *BB2 = (Pred0 == BB1) ? Pred1 : Pred0;
1186 BranchInst *BI2 = dyn_cast<BranchInst>(BB2->getTerminator());
1187 if (!BI2 || !BI2->isUnconditional())
1190 // Gather the PHI nodes in BBEnd.
1191 std::map<Value*, std::pair<Value*, PHINode*> > MapValueFromBB1ToBB2;
1192 Instruction *FirstNonPhiInBBEnd = 0;
1193 for (BasicBlock::iterator I = BBEnd->begin(), E = BBEnd->end();
1195 if (PHINode *PN = dyn_cast<PHINode>(I)) {
1196 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1197 Value *BB2V = PN->getIncomingValueForBlock(BB2);
1198 MapValueFromBB1ToBB2[BB1V] = std::make_pair(BB2V, PN);
1200 FirstNonPhiInBBEnd = &*I;
1204 if (!FirstNonPhiInBBEnd)
1208 // This does very trivial matching, with limited scanning, to find identical
1209 // instructions in the two blocks. We scan backward for obviously identical
1210 // instructions in an identical order.
1211 BasicBlock::InstListType::reverse_iterator RI1 = BB1->getInstList().rbegin(),
1212 RE1 = BB1->getInstList().rend(), RI2 = BB2->getInstList().rbegin(),
1213 RE2 = BB2->getInstList().rend();
1215 while (RI1 != RE1 && isa<DbgInfoIntrinsic>(&*RI1)) ++RI1;
1218 while (RI2 != RE2 && isa<DbgInfoIntrinsic>(&*RI2)) ++RI2;
1221 // Skip the unconditional branches.
1225 bool Changed = false;
1226 while (RI1 != RE1 && RI2 != RE2) {
1228 while (RI1 != RE1 && isa<DbgInfoIntrinsic>(&*RI1)) ++RI1;
1231 while (RI2 != RE2 && isa<DbgInfoIntrinsic>(&*RI2)) ++RI2;
1235 Instruction *I1 = &*RI1, *I2 = &*RI2;
1236 // I1 and I2 should have a single use in the same PHI node, and they
1237 // perform the same operation.
1238 // Cannot move control-flow-involving, volatile loads, vaarg, etc.
1239 if (isa<PHINode>(I1) || isa<PHINode>(I2) ||
1240 isa<TerminatorInst>(I1) || isa<TerminatorInst>(I2) ||
1241 isa<LandingPadInst>(I1) || isa<LandingPadInst>(I2) ||
1242 isa<AllocaInst>(I1) || isa<AllocaInst>(I2) ||
1243 I1->mayHaveSideEffects() || I2->mayHaveSideEffects() ||
1244 I1->mayReadOrWriteMemory() || I2->mayReadOrWriteMemory() ||
1245 !I1->hasOneUse() || !I2->hasOneUse() ||
1246 MapValueFromBB1ToBB2.find(I1) == MapValueFromBB1ToBB2.end() ||
1247 MapValueFromBB1ToBB2[I1].first != I2)
1250 // Check whether we should swap the operands of ICmpInst.
1251 ICmpInst *ICmp1 = dyn_cast<ICmpInst>(I1), *ICmp2 = dyn_cast<ICmpInst>(I2);
1252 bool SwapOpnds = false;
1253 if (ICmp1 && ICmp2 &&
1254 ICmp1->getOperand(0) != ICmp2->getOperand(0) &&
1255 ICmp1->getOperand(1) != ICmp2->getOperand(1) &&
1256 (ICmp1->getOperand(0) == ICmp2->getOperand(1) ||
1257 ICmp1->getOperand(1) == ICmp2->getOperand(0))) {
1258 ICmp2->swapOperands();
1261 if (!I1->isSameOperationAs(I2)) {
1263 ICmp2->swapOperands();
1267 // The operands should be either the same or they need to be generated
1268 // with a PHI node after sinking. We only handle the case where there is
1269 // a single pair of different operands.
1270 Value *DifferentOp1 = 0, *DifferentOp2 = 0;
1271 unsigned Op1Idx = 0;
1272 for (unsigned I = 0, E = I1->getNumOperands(); I != E; ++I) {
1273 if (I1->getOperand(I) == I2->getOperand(I))
1275 // Early exit if we have more-than one pair of different operands or
1276 // the different operand is already in MapValueFromBB1ToBB2.
1277 // Early exit if we need a PHI node to replace a constant.
1279 MapValueFromBB1ToBB2.find(I1->getOperand(I)) !=
1280 MapValueFromBB1ToBB2.end() ||
1281 isa<Constant>(I1->getOperand(I)) ||
1282 isa<Constant>(I2->getOperand(I))) {
1283 // If we can't sink the instructions, undo the swapping.
1285 ICmp2->swapOperands();
1288 DifferentOp1 = I1->getOperand(I);
1290 DifferentOp2 = I2->getOperand(I);
1293 // We insert the pair of different operands to MapValueFromBB1ToBB2 and
1294 // remove (I1, I2) from MapValueFromBB1ToBB2.
1296 PHINode *NewPN = PHINode::Create(DifferentOp1->getType(), 2,
1297 DifferentOp1->getName() + ".sink",
1299 MapValueFromBB1ToBB2[DifferentOp1] = std::make_pair(DifferentOp2, NewPN);
1300 // I1 should use NewPN instead of DifferentOp1.
1301 I1->setOperand(Op1Idx, NewPN);
1302 NewPN->addIncoming(DifferentOp1, BB1);
1303 NewPN->addIncoming(DifferentOp2, BB2);
1304 DEBUG(dbgs() << "Create PHI node " << *NewPN << "\n";);
1306 PHINode *OldPN = MapValueFromBB1ToBB2[I1].second;
1307 MapValueFromBB1ToBB2.erase(I1);
1309 DEBUG(dbgs() << "SINK common instructions " << *I1 << "\n";);
1310 DEBUG(dbgs() << " " << *I2 << "\n";);
1311 // We need to update RE1 and RE2 if we are going to sink the first
1312 // instruction in the basic block down.
1313 bool UpdateRE1 = (I1 == BB1->begin()), UpdateRE2 = (I2 == BB2->begin());
1314 // Sink the instruction.
1315 BBEnd->getInstList().splice(FirstNonPhiInBBEnd, BB1->getInstList(), I1);
1316 if (!OldPN->use_empty())
1317 OldPN->replaceAllUsesWith(I1);
1318 OldPN->eraseFromParent();
1320 if (!I2->use_empty())
1321 I2->replaceAllUsesWith(I1);
1322 I1->intersectOptionalDataWith(I2);
1323 I2->eraseFromParent();
1326 RE1 = BB1->getInstList().rend();
1328 RE2 = BB2->getInstList().rend();
1329 FirstNonPhiInBBEnd = I1;
1336 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
1337 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
1338 /// (for now, restricted to a single instruction that's side effect free) from
1339 /// the BB1 into the branch block to speculatively execute it.
1344 /// br i1 %t1, label %BB1, label %BB2
1346 /// %t3 = add %t2, c
1352 /// %t4 = add %t2, c
1353 /// %t3 = select i1 %t1, %t2, %t3
1354 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
1355 // Only speculatively execution a single instruction (not counting the
1356 // terminator) for now.
1357 Instruction *HInst = NULL;
1358 Instruction *Term = BB1->getTerminator();
1359 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
1360 BBI != BBE; ++BBI) {
1361 Instruction *I = BBI;
1363 if (isa<DbgInfoIntrinsic>(I)) continue;
1364 if (I == Term) break;
1371 BasicBlock *BIParent = BI->getParent();
1373 // Check the instruction to be hoisted, if there is one.
1375 // Don't hoist the instruction if it's unsafe or expensive.
1376 if (!isSafeToSpeculativelyExecute(HInst))
1378 if (ComputeSpeculationCost(HInst) > PHINodeFoldingThreshold)
1381 // Do not hoist the instruction if any of its operands are defined but not
1382 // used in this BB. The transformation will prevent the operand from
1383 // being sunk into the use block.
1384 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1386 Instruction *OpI = dyn_cast<Instruction>(*i);
1387 if (OpI && OpI->getParent() == BIParent &&
1388 !OpI->mayHaveSideEffects() &&
1389 !OpI->isUsedInBasicBlock(BIParent))
1394 // Be conservative for now. FP select instruction can often be expensive.
1395 Value *BrCond = BI->getCondition();
1396 if (isa<FCmpInst>(BrCond))
1399 // If BB1 is actually on the false edge of the conditional branch, remember
1400 // to swap the select operands later.
1401 bool Invert = false;
1402 if (BB1 != BI->getSuccessor(0)) {
1403 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
1407 // Collect interesting PHIs, and scan for hazards.
1408 SmallSetVector<std::pair<Value *, Value *>, 4> PHIs;
1409 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
1410 for (BasicBlock::iterator I = BB2->begin();
1411 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1412 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1413 Value *BIParentV = PN->getIncomingValueForBlock(BIParent);
1415 // Skip PHIs which are trivial.
1416 if (BB1V == BIParentV)
1419 // Check for saftey.
1420 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BB1V)) {
1421 // An unfolded ConstantExpr could end up getting expanded into
1422 // Instructions. Don't speculate this and another instruction at
1426 if (!isSafeToSpeculativelyExecute(CE))
1428 if (ComputeSpeculationCost(CE) > PHINodeFoldingThreshold)
1432 // Ok, we may insert a select for this PHI.
1433 PHIs.insert(std::make_pair(BB1V, BIParentV));
1436 // If there are no PHIs to process, bail early. This helps ensure idempotence
1441 // If we get here, we can hoist the instruction and if-convert.
1442 DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *BB1 << "\n";);
1444 // Hoist the instruction.
1446 BIParent->getInstList().splice(BI, BB1->getInstList(), HInst);
1448 // Insert selects and rewrite the PHI operands.
1449 IRBuilder<true, NoFolder> Builder(BI);
1450 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
1451 Value *TrueV = PHIs[i].first;
1452 Value *FalseV = PHIs[i].second;
1454 // Create a select whose true value is the speculatively executed value and
1455 // false value is the previously determined FalseV.
1458 SI = cast<SelectInst>
1459 (Builder.CreateSelect(BrCond, FalseV, TrueV,
1460 FalseV->getName() + "." + TrueV->getName()));
1462 SI = cast<SelectInst>
1463 (Builder.CreateSelect(BrCond, TrueV, FalseV,
1464 TrueV->getName() + "." + FalseV->getName()));
1466 // Make the PHI node use the select for all incoming values for "then" and
1468 for (BasicBlock::iterator I = BB2->begin();
1469 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1470 unsigned BB1I = PN->getBasicBlockIndex(BB1);
1471 unsigned BIParentI = PN->getBasicBlockIndex(BIParent);
1472 Value *BB1V = PN->getIncomingValue(BB1I);
1473 Value *BIParentV = PN->getIncomingValue(BIParentI);
1474 if (TrueV == BB1V && FalseV == BIParentV) {
1475 PN->setIncomingValue(BB1I, SI);
1476 PN->setIncomingValue(BIParentI, SI);
1485 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1486 /// across this block.
1487 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1488 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1491 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1492 if (isa<DbgInfoIntrinsic>(BBI))
1494 if (Size > 10) return false; // Don't clone large BB's.
1497 // We can only support instructions that do not define values that are
1498 // live outside of the current basic block.
1499 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1501 Instruction *U = cast<Instruction>(*UI);
1502 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1505 // Looks ok, continue checking.
1511 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1512 /// that is defined in the same block as the branch and if any PHI entries are
1513 /// constants, thread edges corresponding to that entry to be branches to their
1514 /// ultimate destination.
1515 static bool FoldCondBranchOnPHI(BranchInst *BI, const DataLayout *TD) {
1516 BasicBlock *BB = BI->getParent();
1517 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1518 // NOTE: we currently cannot transform this case if the PHI node is used
1519 // outside of the block.
1520 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1523 // Degenerate case of a single entry PHI.
1524 if (PN->getNumIncomingValues() == 1) {
1525 FoldSingleEntryPHINodes(PN->getParent());
1529 // Now we know that this block has multiple preds and two succs.
1530 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1532 // Okay, this is a simple enough basic block. See if any phi values are
1534 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1535 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1536 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1538 // Okay, we now know that all edges from PredBB should be revectored to
1539 // branch to RealDest.
1540 BasicBlock *PredBB = PN->getIncomingBlock(i);
1541 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1543 if (RealDest == BB) continue; // Skip self loops.
1544 // Skip if the predecessor's terminator is an indirect branch.
1545 if (isa<IndirectBrInst>(PredBB->getTerminator())) continue;
1547 // The dest block might have PHI nodes, other predecessors and other
1548 // difficult cases. Instead of being smart about this, just insert a new
1549 // block that jumps to the destination block, effectively splitting
1550 // the edge we are about to create.
1551 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1552 RealDest->getName()+".critedge",
1553 RealDest->getParent(), RealDest);
1554 BranchInst::Create(RealDest, EdgeBB);
1556 // Update PHI nodes.
1557 AddPredecessorToBlock(RealDest, EdgeBB, BB);
1559 // BB may have instructions that are being threaded over. Clone these
1560 // instructions into EdgeBB. We know that there will be no uses of the
1561 // cloned instructions outside of EdgeBB.
1562 BasicBlock::iterator InsertPt = EdgeBB->begin();
1563 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1564 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1565 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1566 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1569 // Clone the instruction.
1570 Instruction *N = BBI->clone();
1571 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1573 // Update operands due to translation.
1574 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1576 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1577 if (PI != TranslateMap.end())
1581 // Check for trivial simplification.
1582 if (Value *V = SimplifyInstruction(N, TD)) {
1583 TranslateMap[BBI] = V;
1584 delete N; // Instruction folded away, don't need actual inst
1586 // Insert the new instruction into its new home.
1587 EdgeBB->getInstList().insert(InsertPt, N);
1588 if (!BBI->use_empty())
1589 TranslateMap[BBI] = N;
1593 // Loop over all of the edges from PredBB to BB, changing them to branch
1594 // to EdgeBB instead.
1595 TerminatorInst *PredBBTI = PredBB->getTerminator();
1596 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1597 if (PredBBTI->getSuccessor(i) == BB) {
1598 BB->removePredecessor(PredBB);
1599 PredBBTI->setSuccessor(i, EdgeBB);
1602 // Recurse, simplifying any other constants.
1603 return FoldCondBranchOnPHI(BI, TD) | true;
1609 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1610 /// PHI node, see if we can eliminate it.
1611 static bool FoldTwoEntryPHINode(PHINode *PN, const DataLayout *TD) {
1612 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1613 // statement", which has a very simple dominance structure. Basically, we
1614 // are trying to find the condition that is being branched on, which
1615 // subsequently causes this merge to happen. We really want control
1616 // dependence information for this check, but simplifycfg can't keep it up
1617 // to date, and this catches most of the cases we care about anyway.
1618 BasicBlock *BB = PN->getParent();
1619 BasicBlock *IfTrue, *IfFalse;
1620 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1622 // Don't bother if the branch will be constant folded trivially.
1623 isa<ConstantInt>(IfCond))
1626 // Okay, we found that we can merge this two-entry phi node into a select.
1627 // Doing so would require us to fold *all* two entry phi nodes in this block.
1628 // At some point this becomes non-profitable (particularly if the target
1629 // doesn't support cmov's). Only do this transformation if there are two or
1630 // fewer PHI nodes in this block.
1631 unsigned NumPhis = 0;
1632 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1636 // Loop over the PHI's seeing if we can promote them all to select
1637 // instructions. While we are at it, keep track of the instructions
1638 // that need to be moved to the dominating block.
1639 SmallPtrSet<Instruction*, 4> AggressiveInsts;
1640 unsigned MaxCostVal0 = PHINodeFoldingThreshold,
1641 MaxCostVal1 = PHINodeFoldingThreshold;
1643 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1644 PHINode *PN = cast<PHINode>(II++);
1645 if (Value *V = SimplifyInstruction(PN, TD)) {
1646 PN->replaceAllUsesWith(V);
1647 PN->eraseFromParent();
1651 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
1653 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
1658 // If we folded the first phi, PN dangles at this point. Refresh it. If
1659 // we ran out of PHIs then we simplified them all.
1660 PN = dyn_cast<PHINode>(BB->begin());
1661 if (PN == 0) return true;
1663 // Don't fold i1 branches on PHIs which contain binary operators. These can
1664 // often be turned into switches and other things.
1665 if (PN->getType()->isIntegerTy(1) &&
1666 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1667 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1668 isa<BinaryOperator>(IfCond)))
1671 // If we all PHI nodes are promotable, check to make sure that all
1672 // instructions in the predecessor blocks can be promoted as well. If
1673 // not, we won't be able to get rid of the control flow, so it's not
1674 // worth promoting to select instructions.
1675 BasicBlock *DomBlock = 0;
1676 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1677 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1678 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1681 DomBlock = *pred_begin(IfBlock1);
1682 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1683 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1684 // This is not an aggressive instruction that we can promote.
1685 // Because of this, we won't be able to get rid of the control
1686 // flow, so the xform is not worth it.
1691 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1694 DomBlock = *pred_begin(IfBlock2);
1695 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1696 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1697 // This is not an aggressive instruction that we can promote.
1698 // Because of this, we won't be able to get rid of the control
1699 // flow, so the xform is not worth it.
1704 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1705 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1707 // If we can still promote the PHI nodes after this gauntlet of tests,
1708 // do all of the PHI's now.
1709 Instruction *InsertPt = DomBlock->getTerminator();
1710 IRBuilder<true, NoFolder> Builder(InsertPt);
1712 // Move all 'aggressive' instructions, which are defined in the
1713 // conditional parts of the if's up to the dominating block.
1715 DomBlock->getInstList().splice(InsertPt,
1716 IfBlock1->getInstList(), IfBlock1->begin(),
1717 IfBlock1->getTerminator());
1719 DomBlock->getInstList().splice(InsertPt,
1720 IfBlock2->getInstList(), IfBlock2->begin(),
1721 IfBlock2->getTerminator());
1723 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1724 // Change the PHI node into a select instruction.
1725 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1726 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1729 cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, ""));
1730 PN->replaceAllUsesWith(NV);
1732 PN->eraseFromParent();
1735 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1736 // has been flattened. Change DomBlock to jump directly to our new block to
1737 // avoid other simplifycfg's kicking in on the diamond.
1738 TerminatorInst *OldTI = DomBlock->getTerminator();
1739 Builder.SetInsertPoint(OldTI);
1740 Builder.CreateBr(BB);
1741 OldTI->eraseFromParent();
1745 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1746 /// to two returning blocks, try to merge them together into one return,
1747 /// introducing a select if the return values disagree.
1748 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
1749 IRBuilder<> &Builder) {
1750 assert(BI->isConditional() && "Must be a conditional branch");
1751 BasicBlock *TrueSucc = BI->getSuccessor(0);
1752 BasicBlock *FalseSucc = BI->getSuccessor(1);
1753 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1754 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1756 // Check to ensure both blocks are empty (just a return) or optionally empty
1757 // with PHI nodes. If there are other instructions, merging would cause extra
1758 // computation on one path or the other.
1759 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1761 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1764 Builder.SetInsertPoint(BI);
1765 // Okay, we found a branch that is going to two return nodes. If
1766 // there is no return value for this function, just change the
1767 // branch into a return.
1768 if (FalseRet->getNumOperands() == 0) {
1769 TrueSucc->removePredecessor(BI->getParent());
1770 FalseSucc->removePredecessor(BI->getParent());
1771 Builder.CreateRetVoid();
1772 EraseTerminatorInstAndDCECond(BI);
1776 // Otherwise, figure out what the true and false return values are
1777 // so we can insert a new select instruction.
1778 Value *TrueValue = TrueRet->getReturnValue();
1779 Value *FalseValue = FalseRet->getReturnValue();
1781 // Unwrap any PHI nodes in the return blocks.
1782 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1783 if (TVPN->getParent() == TrueSucc)
1784 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1785 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1786 if (FVPN->getParent() == FalseSucc)
1787 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1789 // In order for this transformation to be safe, we must be able to
1790 // unconditionally execute both operands to the return. This is
1791 // normally the case, but we could have a potentially-trapping
1792 // constant expression that prevents this transformation from being
1794 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1797 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1801 // Okay, we collected all the mapped values and checked them for sanity, and
1802 // defined to really do this transformation. First, update the CFG.
1803 TrueSucc->removePredecessor(BI->getParent());
1804 FalseSucc->removePredecessor(BI->getParent());
1806 // Insert select instructions where needed.
1807 Value *BrCond = BI->getCondition();
1809 // Insert a select if the results differ.
1810 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1811 } else if (isa<UndefValue>(TrueValue)) {
1812 TrueValue = FalseValue;
1814 TrueValue = Builder.CreateSelect(BrCond, TrueValue,
1815 FalseValue, "retval");
1819 Value *RI = !TrueValue ?
1820 Builder.CreateRetVoid() : Builder.CreateRet(TrueValue);
1824 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1825 << "\n " << *BI << "NewRet = " << *RI
1826 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1828 EraseTerminatorInstAndDCECond(BI);
1833 /// ExtractBranchMetadata - Given a conditional BranchInstruction, retrieve the
1834 /// probabilities of the branch taking each edge. Fills in the two APInt
1835 /// parameters and return true, or returns false if no or invalid metadata was
1837 static bool ExtractBranchMetadata(BranchInst *BI,
1838 uint64_t &ProbTrue, uint64_t &ProbFalse) {
1839 assert(BI->isConditional() &&
1840 "Looking for probabilities on unconditional branch?");
1841 MDNode *ProfileData = BI->getMetadata(LLVMContext::MD_prof);
1842 if (!ProfileData || ProfileData->getNumOperands() != 3) return false;
1843 ConstantInt *CITrue = dyn_cast<ConstantInt>(ProfileData->getOperand(1));
1844 ConstantInt *CIFalse = dyn_cast<ConstantInt>(ProfileData->getOperand(2));
1845 if (!CITrue || !CIFalse) return false;
1846 ProbTrue = CITrue->getValue().getZExtValue();
1847 ProbFalse = CIFalse->getValue().getZExtValue();
1851 /// checkCSEInPredecessor - Return true if the given instruction is available
1852 /// in its predecessor block. If yes, the instruction will be removed.
1854 static bool checkCSEInPredecessor(Instruction *Inst, BasicBlock *PB) {
1855 if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst))
1857 for (BasicBlock::iterator I = PB->begin(), E = PB->end(); I != E; I++) {
1858 Instruction *PBI = &*I;
1859 // Check whether Inst and PBI generate the same value.
1860 if (Inst->isIdenticalTo(PBI)) {
1861 Inst->replaceAllUsesWith(PBI);
1862 Inst->eraseFromParent();
1869 /// FoldBranchToCommonDest - If this basic block is simple enough, and if a
1870 /// predecessor branches to us and one of our successors, fold the block into
1871 /// the predecessor and use logical operations to pick the right destination.
1872 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1873 BasicBlock *BB = BI->getParent();
1875 Instruction *Cond = 0;
1876 if (BI->isConditional())
1877 Cond = dyn_cast<Instruction>(BI->getCondition());
1879 // For unconditional branch, check for a simple CFG pattern, where
1880 // BB has a single predecessor and BB's successor is also its predecessor's
1881 // successor. If such pattern exisits, check for CSE between BB and its
1883 if (BasicBlock *PB = BB->getSinglePredecessor())
1884 if (BranchInst *PBI = dyn_cast<BranchInst>(PB->getTerminator()))
1885 if (PBI->isConditional() &&
1886 (BI->getSuccessor(0) == PBI->getSuccessor(0) ||
1887 BI->getSuccessor(0) == PBI->getSuccessor(1))) {
1888 for (BasicBlock::iterator I = BB->begin(), E = BB->end();
1890 Instruction *Curr = I++;
1891 if (isa<CmpInst>(Curr)) {
1895 // Quit if we can't remove this instruction.
1896 if (!checkCSEInPredecessor(Curr, PB))
1905 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1906 Cond->getParent() != BB || !Cond->hasOneUse())
1909 // Only allow this if the condition is a simple instruction that can be
1910 // executed unconditionally. It must be in the same block as the branch, and
1911 // must be at the front of the block.
1912 BasicBlock::iterator FrontIt = BB->front();
1914 // Ignore dbg intrinsics.
1915 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1917 // Allow a single instruction to be hoisted in addition to the compare
1918 // that feeds the branch. We later ensure that any values that _it_ uses
1919 // were also live in the predecessor, so that we don't unnecessarily create
1920 // register pressure or inhibit out-of-order execution.
1921 Instruction *BonusInst = 0;
1922 if (&*FrontIt != Cond &&
1923 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1924 isSafeToSpeculativelyExecute(FrontIt)) {
1925 BonusInst = &*FrontIt;
1928 // Ignore dbg intrinsics.
1929 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1932 // Only a single bonus inst is allowed.
1933 if (&*FrontIt != Cond)
1936 // Make sure the instruction after the condition is the cond branch.
1937 BasicBlock::iterator CondIt = Cond; ++CondIt;
1939 // Ingore dbg intrinsics.
1940 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
1945 // Cond is known to be a compare or binary operator. Check to make sure that
1946 // neither operand is a potentially-trapping constant expression.
1947 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1950 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1954 // Finally, don't infinitely unroll conditional loops.
1955 BasicBlock *TrueDest = BI->getSuccessor(0);
1956 BasicBlock *FalseDest = (BI->isConditional()) ? BI->getSuccessor(1) : 0;
1957 if (TrueDest == BB || FalseDest == BB)
1960 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1961 BasicBlock *PredBlock = *PI;
1962 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1964 // Check that we have two conditional branches. If there is a PHI node in
1965 // the common successor, verify that the same value flows in from both
1967 SmallVector<PHINode*, 4> PHIs;
1968 if (PBI == 0 || PBI->isUnconditional() ||
1969 (BI->isConditional() &&
1970 !SafeToMergeTerminators(BI, PBI)) ||
1971 (!BI->isConditional() &&
1972 !isProfitableToFoldUnconditional(BI, PBI, Cond, PHIs)))
1975 // Determine if the two branches share a common destination.
1976 Instruction::BinaryOps Opc = Instruction::BinaryOpsEnd;
1977 bool InvertPredCond = false;
1979 if (BI->isConditional()) {
1980 if (PBI->getSuccessor(0) == TrueDest)
1981 Opc = Instruction::Or;
1982 else if (PBI->getSuccessor(1) == FalseDest)
1983 Opc = Instruction::And;
1984 else if (PBI->getSuccessor(0) == FalseDest)
1985 Opc = Instruction::And, InvertPredCond = true;
1986 else if (PBI->getSuccessor(1) == TrueDest)
1987 Opc = Instruction::Or, InvertPredCond = true;
1991 if (PBI->getSuccessor(0) != TrueDest && PBI->getSuccessor(1) != TrueDest)
1995 // Ensure that any values used in the bonus instruction are also used
1996 // by the terminator of the predecessor. This means that those values
1997 // must already have been resolved, so we won't be inhibiting the
1998 // out-of-order core by speculating them earlier.
2000 // Collect the values used by the bonus inst
2001 SmallPtrSet<Value*, 4> UsedValues;
2002 for (Instruction::op_iterator OI = BonusInst->op_begin(),
2003 OE = BonusInst->op_end(); OI != OE; ++OI) {
2005 if (!isa<Constant>(V))
2006 UsedValues.insert(V);
2009 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
2010 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
2012 // Walk up to four levels back up the use-def chain of the predecessor's
2013 // terminator to see if all those values were used. The choice of four
2014 // levels is arbitrary, to provide a compile-time-cost bound.
2015 while (!Worklist.empty()) {
2016 std::pair<Value*, unsigned> Pair = Worklist.back();
2017 Worklist.pop_back();
2019 if (Pair.second >= 4) continue;
2020 UsedValues.erase(Pair.first);
2021 if (UsedValues.empty()) break;
2023 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
2024 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
2026 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
2030 if (!UsedValues.empty()) return false;
2033 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
2034 IRBuilder<> Builder(PBI);
2036 // If we need to invert the condition in the pred block to match, do so now.
2037 if (InvertPredCond) {
2038 Value *NewCond = PBI->getCondition();
2040 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
2041 CmpInst *CI = cast<CmpInst>(NewCond);
2042 CI->setPredicate(CI->getInversePredicate());
2044 NewCond = Builder.CreateNot(NewCond,
2045 PBI->getCondition()->getName()+".not");
2048 PBI->setCondition(NewCond);
2049 PBI->swapSuccessors();
2052 // If we have a bonus inst, clone it into the predecessor block.
2053 Instruction *NewBonus = 0;
2055 NewBonus = BonusInst->clone();
2056 PredBlock->getInstList().insert(PBI, NewBonus);
2057 NewBonus->takeName(BonusInst);
2058 BonusInst->setName(BonusInst->getName()+".old");
2061 // Clone Cond into the predecessor basic block, and or/and the
2062 // two conditions together.
2063 Instruction *New = Cond->clone();
2064 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
2065 PredBlock->getInstList().insert(PBI, New);
2066 New->takeName(Cond);
2067 Cond->setName(New->getName()+".old");
2069 if (BI->isConditional()) {
2070 Instruction *NewCond =
2071 cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(),
2073 PBI->setCondition(NewCond);
2075 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
2076 bool PredHasWeights = ExtractBranchMetadata(PBI, PredTrueWeight,
2078 bool SuccHasWeights = ExtractBranchMetadata(BI, SuccTrueWeight,
2080 SmallVector<uint64_t, 8> NewWeights;
2082 if (PBI->getSuccessor(0) == BB) {
2083 if (PredHasWeights && SuccHasWeights) {
2084 // PBI: br i1 %x, BB, FalseDest
2085 // BI: br i1 %y, TrueDest, FalseDest
2086 //TrueWeight is TrueWeight for PBI * TrueWeight for BI.
2087 NewWeights.push_back(PredTrueWeight * SuccTrueWeight);
2088 //FalseWeight is FalseWeight for PBI * TotalWeight for BI +
2089 // TrueWeight for PBI * FalseWeight for BI.
2090 // We assume that total weights of a BranchInst can fit into 32 bits.
2091 // Therefore, we will not have overflow using 64-bit arithmetic.
2092 NewWeights.push_back(PredFalseWeight * (SuccFalseWeight +
2093 SuccTrueWeight) + PredTrueWeight * SuccFalseWeight);
2095 AddPredecessorToBlock(TrueDest, PredBlock, BB);
2096 PBI->setSuccessor(0, TrueDest);
2098 if (PBI->getSuccessor(1) == BB) {
2099 if (PredHasWeights && SuccHasWeights) {
2100 // PBI: br i1 %x, TrueDest, BB
2101 // BI: br i1 %y, TrueDest, FalseDest
2102 //TrueWeight is TrueWeight for PBI * TotalWeight for BI +
2103 // FalseWeight for PBI * TrueWeight for BI.
2104 NewWeights.push_back(PredTrueWeight * (SuccFalseWeight +
2105 SuccTrueWeight) + PredFalseWeight * SuccTrueWeight);
2106 //FalseWeight is FalseWeight for PBI * FalseWeight for BI.
2107 NewWeights.push_back(PredFalseWeight * SuccFalseWeight);
2109 AddPredecessorToBlock(FalseDest, PredBlock, BB);
2110 PBI->setSuccessor(1, FalseDest);
2112 if (NewWeights.size() == 2) {
2113 // Halve the weights if any of them cannot fit in an uint32_t
2114 FitWeights(NewWeights);
2116 SmallVector<uint32_t, 8> MDWeights(NewWeights.begin(),NewWeights.end());
2117 PBI->setMetadata(LLVMContext::MD_prof,
2118 MDBuilder(BI->getContext()).
2119 createBranchWeights(MDWeights));
2121 PBI->setMetadata(LLVMContext::MD_prof, NULL);
2123 // Update PHI nodes in the common successors.
2124 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
2125 ConstantInt *PBI_C = cast<ConstantInt>(
2126 PHIs[i]->getIncomingValueForBlock(PBI->getParent()));
2127 assert(PBI_C->getType()->isIntegerTy(1));
2128 Instruction *MergedCond = 0;
2129 if (PBI->getSuccessor(0) == TrueDest) {
2130 // Create (PBI_Cond and PBI_C) or (!PBI_Cond and BI_Value)
2131 // PBI_C is true: PBI_Cond or (!PBI_Cond and BI_Value)
2132 // is false: !PBI_Cond and BI_Value
2133 Instruction *NotCond =
2134 cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
2137 cast<Instruction>(Builder.CreateBinOp(Instruction::And,
2142 cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
2143 PBI->getCondition(), MergedCond,
2146 // Create (PBI_Cond and BI_Value) or (!PBI_Cond and PBI_C)
2147 // PBI_C is true: (PBI_Cond and BI_Value) or (!PBI_Cond)
2148 // is false: PBI_Cond and BI_Value
2150 cast<Instruction>(Builder.CreateBinOp(Instruction::And,
2151 PBI->getCondition(), New,
2153 if (PBI_C->isOne()) {
2154 Instruction *NotCond =
2155 cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
2158 cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
2159 NotCond, MergedCond,
2164 PHIs[i]->setIncomingValue(PHIs[i]->getBasicBlockIndex(PBI->getParent()),
2167 // Change PBI from Conditional to Unconditional.
2168 BranchInst *New_PBI = BranchInst::Create(TrueDest, PBI);
2169 EraseTerminatorInstAndDCECond(PBI);
2173 // TODO: If BB is reachable from all paths through PredBlock, then we
2174 // could replace PBI's branch probabilities with BI's.
2176 // Copy any debug value intrinsics into the end of PredBlock.
2177 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
2178 if (isa<DbgInfoIntrinsic>(*I))
2179 I->clone()->insertBefore(PBI);
2186 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
2187 /// predecessor of another block, this function tries to simplify it. We know
2188 /// that PBI and BI are both conditional branches, and BI is in one of the
2189 /// successor blocks of PBI - PBI branches to BI.
2190 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
2191 assert(PBI->isConditional() && BI->isConditional());
2192 BasicBlock *BB = BI->getParent();
2194 // If this block ends with a branch instruction, and if there is a
2195 // predecessor that ends on a branch of the same condition, make
2196 // this conditional branch redundant.
2197 if (PBI->getCondition() == BI->getCondition() &&
2198 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
2199 // Okay, the outcome of this conditional branch is statically
2200 // knowable. If this block had a single pred, handle specially.
2201 if (BB->getSinglePredecessor()) {
2202 // Turn this into a branch on constant.
2203 bool CondIsTrue = PBI->getSuccessor(0) == BB;
2204 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
2206 return true; // Nuke the branch on constant.
2209 // Otherwise, if there are multiple predecessors, insert a PHI that merges
2210 // in the constant and simplify the block result. Subsequent passes of
2211 // simplifycfg will thread the block.
2212 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
2213 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
2214 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
2215 std::distance(PB, PE),
2216 BI->getCondition()->getName() + ".pr",
2218 // Okay, we're going to insert the PHI node. Since PBI is not the only
2219 // predecessor, compute the PHI'd conditional value for all of the preds.
2220 // Any predecessor where the condition is not computable we keep symbolic.
2221 for (pred_iterator PI = PB; PI != PE; ++PI) {
2222 BasicBlock *P = *PI;
2223 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
2224 PBI != BI && PBI->isConditional() &&
2225 PBI->getCondition() == BI->getCondition() &&
2226 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
2227 bool CondIsTrue = PBI->getSuccessor(0) == BB;
2228 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
2231 NewPN->addIncoming(BI->getCondition(), P);
2235 BI->setCondition(NewPN);
2240 // If this is a conditional branch in an empty block, and if any
2241 // predecessors is a conditional branch to one of our destinations,
2242 // fold the conditions into logical ops and one cond br.
2243 BasicBlock::iterator BBI = BB->begin();
2244 // Ignore dbg intrinsics.
2245 while (isa<DbgInfoIntrinsic>(BBI))
2251 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
2256 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
2258 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
2259 PBIOp = 0, BIOp = 1;
2260 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
2261 PBIOp = 1, BIOp = 0;
2262 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
2267 // Check to make sure that the other destination of this branch
2268 // isn't BB itself. If so, this is an infinite loop that will
2269 // keep getting unwound.
2270 if (PBI->getSuccessor(PBIOp) == BB)
2273 // Do not perform this transformation if it would require
2274 // insertion of a large number of select instructions. For targets
2275 // without predication/cmovs, this is a big pessimization.
2276 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
2278 unsigned NumPhis = 0;
2279 for (BasicBlock::iterator II = CommonDest->begin();
2280 isa<PHINode>(II); ++II, ++NumPhis)
2281 if (NumPhis > 2) // Disable this xform.
2284 // Finally, if everything is ok, fold the branches to logical ops.
2285 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
2287 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
2288 << "AND: " << *BI->getParent());
2291 // If OtherDest *is* BB, then BB is a basic block with a single conditional
2292 // branch in it, where one edge (OtherDest) goes back to itself but the other
2293 // exits. We don't *know* that the program avoids the infinite loop
2294 // (even though that seems likely). If we do this xform naively, we'll end up
2295 // recursively unpeeling the loop. Since we know that (after the xform is
2296 // done) that the block *is* infinite if reached, we just make it an obviously
2297 // infinite loop with no cond branch.
2298 if (OtherDest == BB) {
2299 // Insert it at the end of the function, because it's either code,
2300 // or it won't matter if it's hot. :)
2301 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
2302 "infloop", BB->getParent());
2303 BranchInst::Create(InfLoopBlock, InfLoopBlock);
2304 OtherDest = InfLoopBlock;
2307 DEBUG(dbgs() << *PBI->getParent()->getParent());
2309 // BI may have other predecessors. Because of this, we leave
2310 // it alone, but modify PBI.
2312 // Make sure we get to CommonDest on True&True directions.
2313 Value *PBICond = PBI->getCondition();
2314 IRBuilder<true, NoFolder> Builder(PBI);
2316 PBICond = Builder.CreateNot(PBICond, PBICond->getName()+".not");
2318 Value *BICond = BI->getCondition();
2320 BICond = Builder.CreateNot(BICond, BICond->getName()+".not");
2322 // Merge the conditions.
2323 Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge");
2325 // Modify PBI to branch on the new condition to the new dests.
2326 PBI->setCondition(Cond);
2327 PBI->setSuccessor(0, CommonDest);
2328 PBI->setSuccessor(1, OtherDest);
2330 // Update branch weight for PBI.
2331 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
2332 bool PredHasWeights = ExtractBranchMetadata(PBI, PredTrueWeight,
2334 bool SuccHasWeights = ExtractBranchMetadata(BI, SuccTrueWeight,
2336 if (PredHasWeights && SuccHasWeights) {
2337 uint64_t PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
2338 uint64_t PredOther = PBIOp ?PredTrueWeight : PredFalseWeight;
2339 uint64_t SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
2340 uint64_t SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
2341 // The weight to CommonDest should be PredCommon * SuccTotal +
2342 // PredOther * SuccCommon.
2343 // The weight to OtherDest should be PredOther * SuccOther.
2344 SmallVector<uint64_t, 2> NewWeights;
2345 NewWeights.push_back(PredCommon * (SuccCommon + SuccOther) +
2346 PredOther * SuccCommon);
2347 NewWeights.push_back(PredOther * SuccOther);
2348 // Halve the weights if any of them cannot fit in an uint32_t
2349 FitWeights(NewWeights);
2351 SmallVector<uint32_t, 2> MDWeights(NewWeights.begin(),NewWeights.end());
2352 PBI->setMetadata(LLVMContext::MD_prof,
2353 MDBuilder(BI->getContext()).
2354 createBranchWeights(MDWeights));
2357 // OtherDest may have phi nodes. If so, add an entry from PBI's
2358 // block that are identical to the entries for BI's block.
2359 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
2361 // We know that the CommonDest already had an edge from PBI to
2362 // it. If it has PHIs though, the PHIs may have different
2363 // entries for BB and PBI's BB. If so, insert a select to make
2366 for (BasicBlock::iterator II = CommonDest->begin();
2367 (PN = dyn_cast<PHINode>(II)); ++II) {
2368 Value *BIV = PN->getIncomingValueForBlock(BB);
2369 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
2370 Value *PBIV = PN->getIncomingValue(PBBIdx);
2372 // Insert a select in PBI to pick the right value.
2373 Value *NV = cast<SelectInst>
2374 (Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName()+".mux"));
2375 PN->setIncomingValue(PBBIdx, NV);
2379 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
2380 DEBUG(dbgs() << *PBI->getParent()->getParent());
2382 // This basic block is probably dead. We know it has at least
2383 // one fewer predecessor.
2387 // SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
2388 // branch to TrueBB if Cond is true or to FalseBB if Cond is false.
2389 // Takes care of updating the successors and removing the old terminator.
2390 // Also makes sure not to introduce new successors by assuming that edges to
2391 // non-successor TrueBBs and FalseBBs aren't reachable.
2392 static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
2393 BasicBlock *TrueBB, BasicBlock *FalseBB,
2394 uint32_t TrueWeight,
2395 uint32_t FalseWeight){
2396 // Remove any superfluous successor edges from the CFG.
2397 // First, figure out which successors to preserve.
2398 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
2400 BasicBlock *KeepEdge1 = TrueBB;
2401 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
2403 // Then remove the rest.
2404 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
2405 BasicBlock *Succ = OldTerm->getSuccessor(I);
2406 // Make sure only to keep exactly one copy of each edge.
2407 if (Succ == KeepEdge1)
2409 else if (Succ == KeepEdge2)
2412 Succ->removePredecessor(OldTerm->getParent());
2415 IRBuilder<> Builder(OldTerm);
2416 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
2418 // Insert an appropriate new terminator.
2419 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
2420 if (TrueBB == FalseBB)
2421 // We were only looking for one successor, and it was present.
2422 // Create an unconditional branch to it.
2423 Builder.CreateBr(TrueBB);
2425 // We found both of the successors we were looking for.
2426 // Create a conditional branch sharing the condition of the select.
2427 BranchInst *NewBI = Builder.CreateCondBr(Cond, TrueBB, FalseBB);
2428 if (TrueWeight != FalseWeight)
2429 NewBI->setMetadata(LLVMContext::MD_prof,
2430 MDBuilder(OldTerm->getContext()).
2431 createBranchWeights(TrueWeight, FalseWeight));
2433 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
2434 // Neither of the selected blocks were successors, so this
2435 // terminator must be unreachable.
2436 new UnreachableInst(OldTerm->getContext(), OldTerm);
2438 // One of the selected values was a successor, but the other wasn't.
2439 // Insert an unconditional branch to the one that was found;
2440 // the edge to the one that wasn't must be unreachable.
2442 // Only TrueBB was found.
2443 Builder.CreateBr(TrueBB);
2445 // Only FalseBB was found.
2446 Builder.CreateBr(FalseBB);
2449 EraseTerminatorInstAndDCECond(OldTerm);
2453 // SimplifySwitchOnSelect - Replaces
2454 // (switch (select cond, X, Y)) on constant X, Y
2455 // with a branch - conditional if X and Y lead to distinct BBs,
2456 // unconditional otherwise.
2457 static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
2458 // Check for constant integer values in the select.
2459 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
2460 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
2461 if (!TrueVal || !FalseVal)
2464 // Find the relevant condition and destinations.
2465 Value *Condition = Select->getCondition();
2466 BasicBlock *TrueBB = SI->findCaseValue(TrueVal).getCaseSuccessor();
2467 BasicBlock *FalseBB = SI->findCaseValue(FalseVal).getCaseSuccessor();
2469 // Get weight for TrueBB and FalseBB.
2470 uint32_t TrueWeight = 0, FalseWeight = 0;
2471 SmallVector<uint64_t, 8> Weights;
2472 bool HasWeights = HasBranchWeights(SI);
2474 GetBranchWeights(SI, Weights);
2475 if (Weights.size() == 1 + SI->getNumCases()) {
2476 TrueWeight = (uint32_t)Weights[SI->findCaseValue(TrueVal).
2477 getSuccessorIndex()];
2478 FalseWeight = (uint32_t)Weights[SI->findCaseValue(FalseVal).
2479 getSuccessorIndex()];
2483 // Perform the actual simplification.
2484 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB,
2485 TrueWeight, FalseWeight);
2488 // SimplifyIndirectBrOnSelect - Replaces
2489 // (indirectbr (select cond, blockaddress(@fn, BlockA),
2490 // blockaddress(@fn, BlockB)))
2492 // (br cond, BlockA, BlockB).
2493 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
2494 // Check that both operands of the select are block addresses.
2495 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
2496 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
2500 // Extract the actual blocks.
2501 BasicBlock *TrueBB = TBA->getBasicBlock();
2502 BasicBlock *FalseBB = FBA->getBasicBlock();
2504 // Perform the actual simplification.
2505 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB,
2509 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
2510 /// instruction (a seteq/setne with a constant) as the only instruction in a
2511 /// block that ends with an uncond branch. We are looking for a very specific
2512 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
2513 /// this case, we merge the first two "or's of icmp" into a switch, but then the
2514 /// default value goes to an uncond block with a seteq in it, we get something
2517 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
2519 /// %tmp = icmp eq i8 %A, 92
2522 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
2524 /// We prefer to split the edge to 'end' so that there is a true/false entry to
2525 /// the PHI, merging the third icmp into the switch.
2526 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
2527 const DataLayout *TD,
2528 IRBuilder<> &Builder) {
2529 BasicBlock *BB = ICI->getParent();
2531 // If the block has any PHIs in it or the icmp has multiple uses, it is too
2533 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
2535 Value *V = ICI->getOperand(0);
2536 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
2538 // The pattern we're looking for is where our only predecessor is a switch on
2539 // 'V' and this block is the default case for the switch. In this case we can
2540 // fold the compared value into the switch to simplify things.
2541 BasicBlock *Pred = BB->getSinglePredecessor();
2542 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
2544 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
2545 if (SI->getCondition() != V)
2548 // If BB is reachable on a non-default case, then we simply know the value of
2549 // V in this block. Substitute it and constant fold the icmp instruction
2551 if (SI->getDefaultDest() != BB) {
2552 ConstantInt *VVal = SI->findCaseDest(BB);
2553 assert(VVal && "Should have a unique destination value");
2554 ICI->setOperand(0, VVal);
2556 if (Value *V = SimplifyInstruction(ICI, TD)) {
2557 ICI->replaceAllUsesWith(V);
2558 ICI->eraseFromParent();
2560 // BB is now empty, so it is likely to simplify away.
2561 return SimplifyCFG(BB) | true;
2564 // Ok, the block is reachable from the default dest. If the constant we're
2565 // comparing exists in one of the other edges, then we can constant fold ICI
2567 if (SI->findCaseValue(Cst) != SI->case_default()) {
2569 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2570 V = ConstantInt::getFalse(BB->getContext());
2572 V = ConstantInt::getTrue(BB->getContext());
2574 ICI->replaceAllUsesWith(V);
2575 ICI->eraseFromParent();
2576 // BB is now empty, so it is likely to simplify away.
2577 return SimplifyCFG(BB) | true;
2580 // The use of the icmp has to be in the 'end' block, by the only PHI node in
2582 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
2583 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
2584 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
2585 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
2588 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
2590 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
2591 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
2593 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2594 std::swap(DefaultCst, NewCst);
2596 // Replace ICI (which is used by the PHI for the default value) with true or
2597 // false depending on if it is EQ or NE.
2598 ICI->replaceAllUsesWith(DefaultCst);
2599 ICI->eraseFromParent();
2601 // Okay, the switch goes to this block on a default value. Add an edge from
2602 // the switch to the merge point on the compared value.
2603 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
2604 BB->getParent(), BB);
2605 SmallVector<uint64_t, 8> Weights;
2606 bool HasWeights = HasBranchWeights(SI);
2608 GetBranchWeights(SI, Weights);
2609 if (Weights.size() == 1 + SI->getNumCases()) {
2610 // Split weight for default case to case for "Cst".
2611 Weights[0] = (Weights[0]+1) >> 1;
2612 Weights.push_back(Weights[0]);
2614 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
2615 SI->setMetadata(LLVMContext::MD_prof,
2616 MDBuilder(SI->getContext()).
2617 createBranchWeights(MDWeights));
2620 SI->addCase(Cst, NewBB);
2622 // NewBB branches to the phi block, add the uncond branch and the phi entry.
2623 Builder.SetInsertPoint(NewBB);
2624 Builder.SetCurrentDebugLocation(SI->getDebugLoc());
2625 Builder.CreateBr(SuccBlock);
2626 PHIUse->addIncoming(NewCst, NewBB);
2630 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
2631 /// Check to see if it is branching on an or/and chain of icmp instructions, and
2632 /// fold it into a switch instruction if so.
2633 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const DataLayout *TD,
2634 IRBuilder<> &Builder) {
2635 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
2636 if (Cond == 0) return false;
2639 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2640 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2641 // 'setne's and'ed together, collect them.
2643 std::vector<ConstantInt*> Values;
2644 bool TrueWhenEqual = true;
2645 Value *ExtraCase = 0;
2646 unsigned UsedICmps = 0;
2648 if (Cond->getOpcode() == Instruction::Or) {
2649 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
2651 } else if (Cond->getOpcode() == Instruction::And) {
2652 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
2654 TrueWhenEqual = false;
2657 // If we didn't have a multiply compared value, fail.
2658 if (CompVal == 0) return false;
2660 // Avoid turning single icmps into a switch.
2664 // There might be duplicate constants in the list, which the switch
2665 // instruction can't handle, remove them now.
2666 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
2667 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2669 // If Extra was used, we require at least two switch values to do the
2670 // transformation. A switch with one value is just an cond branch.
2671 if (ExtraCase && Values.size() < 2) return false;
2673 // TODO: Preserve branch weight metadata, similarly to how
2674 // FoldValueComparisonIntoPredecessors preserves it.
2676 // Figure out which block is which destination.
2677 BasicBlock *DefaultBB = BI->getSuccessor(1);
2678 BasicBlock *EdgeBB = BI->getSuccessor(0);
2679 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2681 BasicBlock *BB = BI->getParent();
2683 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
2684 << " cases into SWITCH. BB is:\n" << *BB);
2686 // If there are any extra values that couldn't be folded into the switch
2687 // then we evaluate them with an explicit branch first. Split the block
2688 // right before the condbr to handle it.
2690 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
2691 // Remove the uncond branch added to the old block.
2692 TerminatorInst *OldTI = BB->getTerminator();
2693 Builder.SetInsertPoint(OldTI);
2696 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
2698 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
2700 OldTI->eraseFromParent();
2702 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
2703 // for the edge we just added.
2704 AddPredecessorToBlock(EdgeBB, BB, NewBB);
2706 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
2707 << "\nEXTRABB = " << *BB);
2711 Builder.SetInsertPoint(BI);
2712 // Convert pointer to int before we switch.
2713 if (CompVal->getType()->isPointerTy()) {
2714 assert(TD && "Cannot switch on pointer without DataLayout");
2715 CompVal = Builder.CreatePtrToInt(CompVal,
2716 TD->getIntPtrType(CompVal->getType()),
2720 // Create the new switch instruction now.
2721 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
2723 // Add all of the 'cases' to the switch instruction.
2724 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2725 New->addCase(Values[i], EdgeBB);
2727 // We added edges from PI to the EdgeBB. As such, if there were any
2728 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2729 // the number of edges added.
2730 for (BasicBlock::iterator BBI = EdgeBB->begin();
2731 isa<PHINode>(BBI); ++BBI) {
2732 PHINode *PN = cast<PHINode>(BBI);
2733 Value *InVal = PN->getIncomingValueForBlock(BB);
2734 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2735 PN->addIncoming(InVal, BB);
2738 // Erase the old branch instruction.
2739 EraseTerminatorInstAndDCECond(BI);
2741 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
2745 bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
2746 // If this is a trivial landing pad that just continues unwinding the caught
2747 // exception then zap the landing pad, turning its invokes into calls.
2748 BasicBlock *BB = RI->getParent();
2749 LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI());
2750 if (RI->getValue() != LPInst)
2751 // Not a landing pad, or the resume is not unwinding the exception that
2752 // caused control to branch here.
2755 // Check that there are no other instructions except for debug intrinsics.
2756 BasicBlock::iterator I = LPInst, E = RI;
2758 if (!isa<DbgInfoIntrinsic>(I))
2761 // Turn all invokes that unwind here into calls and delete the basic block.
2762 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
2763 InvokeInst *II = cast<InvokeInst>((*PI++)->getTerminator());
2764 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
2765 // Insert a call instruction before the invoke.
2766 CallInst *Call = CallInst::Create(II->getCalledValue(), Args, "", II);
2768 Call->setCallingConv(II->getCallingConv());
2769 Call->setAttributes(II->getAttributes());
2770 Call->setDebugLoc(II->getDebugLoc());
2772 // Anything that used the value produced by the invoke instruction now uses
2773 // the value produced by the call instruction. Note that we do this even
2774 // for void functions and calls with no uses so that the callgraph edge is
2776 II->replaceAllUsesWith(Call);
2777 BB->removePredecessor(II->getParent());
2779 // Insert a branch to the normal destination right before the invoke.
2780 BranchInst::Create(II->getNormalDest(), II);
2782 // Finally, delete the invoke instruction!
2783 II->eraseFromParent();
2786 // The landingpad is now unreachable. Zap it.
2787 BB->eraseFromParent();
2791 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
2792 BasicBlock *BB = RI->getParent();
2793 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2795 // Find predecessors that end with branches.
2796 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2797 SmallVector<BranchInst*, 8> CondBranchPreds;
2798 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2799 BasicBlock *P = *PI;
2800 TerminatorInst *PTI = P->getTerminator();
2801 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2802 if (BI->isUnconditional())
2803 UncondBranchPreds.push_back(P);
2805 CondBranchPreds.push_back(BI);
2809 // If we found some, do the transformation!
2810 if (!UncondBranchPreds.empty() && DupRet) {
2811 while (!UncondBranchPreds.empty()) {
2812 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2813 DEBUG(dbgs() << "FOLDING: " << *BB
2814 << "INTO UNCOND BRANCH PRED: " << *Pred);
2815 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
2818 // If we eliminated all predecessors of the block, delete the block now.
2819 if (pred_begin(BB) == pred_end(BB))
2820 // We know there are no successors, so just nuke the block.
2821 BB->eraseFromParent();
2826 // Check out all of the conditional branches going to this return
2827 // instruction. If any of them just select between returns, change the
2828 // branch itself into a select/return pair.
2829 while (!CondBranchPreds.empty()) {
2830 BranchInst *BI = CondBranchPreds.pop_back_val();
2832 // Check to see if the non-BB successor is also a return block.
2833 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2834 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2835 SimplifyCondBranchToTwoReturns(BI, Builder))
2841 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2842 BasicBlock *BB = UI->getParent();
2844 bool Changed = false;
2846 // If there are any instructions immediately before the unreachable that can
2847 // be removed, do so.
2848 while (UI != BB->begin()) {
2849 BasicBlock::iterator BBI = UI;
2851 // Do not delete instructions that can have side effects which might cause
2852 // the unreachable to not be reachable; specifically, calls and volatile
2853 // operations may have this effect.
2854 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2856 if (BBI->mayHaveSideEffects()) {
2857 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
2858 if (SI->isVolatile())
2860 } else if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
2861 if (LI->isVolatile())
2863 } else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(BBI)) {
2864 if (RMWI->isVolatile())
2866 } else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) {
2867 if (CXI->isVolatile())
2869 } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) &&
2870 !isa<LandingPadInst>(BBI)) {
2873 // Note that deleting LandingPad's here is in fact okay, although it
2874 // involves a bit of subtle reasoning. If this inst is a LandingPad,
2875 // all the predecessors of this block will be the unwind edges of Invokes,
2876 // and we can therefore guarantee this block will be erased.
2879 // Delete this instruction (any uses are guaranteed to be dead)
2880 if (!BBI->use_empty())
2881 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
2882 BBI->eraseFromParent();
2886 // If the unreachable instruction is the first in the block, take a gander
2887 // at all of the predecessors of this instruction, and simplify them.
2888 if (&BB->front() != UI) return Changed;
2890 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2891 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2892 TerminatorInst *TI = Preds[i]->getTerminator();
2893 IRBuilder<> Builder(TI);
2894 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2895 if (BI->isUnconditional()) {
2896 if (BI->getSuccessor(0) == BB) {
2897 new UnreachableInst(TI->getContext(), TI);
2898 TI->eraseFromParent();
2902 if (BI->getSuccessor(0) == BB) {
2903 Builder.CreateBr(BI->getSuccessor(1));
2904 EraseTerminatorInstAndDCECond(BI);
2905 } else if (BI->getSuccessor(1) == BB) {
2906 Builder.CreateBr(BI->getSuccessor(0));
2907 EraseTerminatorInstAndDCECond(BI);
2911 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2912 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2914 if (i.getCaseSuccessor() == BB) {
2915 BB->removePredecessor(SI->getParent());
2920 // If the default value is unreachable, figure out the most popular
2921 // destination and make it the default.
2922 if (SI->getDefaultDest() == BB) {
2923 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
2924 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2926 std::pair<unsigned, unsigned> &entry =
2927 Popularity[i.getCaseSuccessor()];
2928 if (entry.first == 0) {
2930 entry.second = i.getCaseIndex();
2936 // Find the most popular block.
2937 unsigned MaxPop = 0;
2938 unsigned MaxIndex = 0;
2939 BasicBlock *MaxBlock = 0;
2940 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
2941 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2942 if (I->second.first > MaxPop ||
2943 (I->second.first == MaxPop && MaxIndex > I->second.second)) {
2944 MaxPop = I->second.first;
2945 MaxIndex = I->second.second;
2946 MaxBlock = I->first;
2950 // Make this the new default, allowing us to delete any explicit
2952 SI->setDefaultDest(MaxBlock);
2955 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2957 if (isa<PHINode>(MaxBlock->begin()))
2958 for (unsigned i = 0; i != MaxPop-1; ++i)
2959 MaxBlock->removePredecessor(SI->getParent());
2961 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2963 if (i.getCaseSuccessor() == MaxBlock) {
2969 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2970 if (II->getUnwindDest() == BB) {
2971 // Convert the invoke to a call instruction. This would be a good
2972 // place to note that the call does not throw though.
2973 BranchInst *BI = Builder.CreateBr(II->getNormalDest());
2974 II->removeFromParent(); // Take out of symbol table
2976 // Insert the call now...
2977 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2978 Builder.SetInsertPoint(BI);
2979 CallInst *CI = Builder.CreateCall(II->getCalledValue(),
2980 Args, II->getName());
2981 CI->setCallingConv(II->getCallingConv());
2982 CI->setAttributes(II->getAttributes());
2983 // If the invoke produced a value, the call does now instead.
2984 II->replaceAllUsesWith(CI);
2991 // If this block is now dead, remove it.
2992 if (pred_begin(BB) == pred_end(BB) &&
2993 BB != &BB->getParent()->getEntryBlock()) {
2994 // We know there are no successors, so just nuke the block.
2995 BB->eraseFromParent();
3002 /// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
3003 /// integer range comparison into a sub, an icmp and a branch.
3004 static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
3005 assert(SI->getNumCases() > 1 && "Degenerate switch?");
3007 // Make sure all cases point to the same destination and gather the values.
3008 SmallVector<ConstantInt *, 16> Cases;
3009 SwitchInst::CaseIt I = SI->case_begin();
3010 Cases.push_back(I.getCaseValue());
3011 SwitchInst::CaseIt PrevI = I++;
3012 for (SwitchInst::CaseIt E = SI->case_end(); I != E; PrevI = I++) {
3013 if (PrevI.getCaseSuccessor() != I.getCaseSuccessor())
3015 Cases.push_back(I.getCaseValue());
3017 assert(Cases.size() == SI->getNumCases() && "Not all cases gathered");
3019 // Sort the case values, then check if they form a range we can transform.
3020 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
3021 for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
3022 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
3026 Constant *Offset = ConstantExpr::getNeg(Cases.back());
3027 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases());
3029 Value *Sub = SI->getCondition();
3030 if (!Offset->isNullValue())
3031 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off");
3032 Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
3033 BranchInst *NewBI = Builder.CreateCondBr(
3034 Cmp, SI->case_begin().getCaseSuccessor(), SI->getDefaultDest());
3036 // Update weight for the newly-created conditional branch.
3037 SmallVector<uint64_t, 8> Weights;
3038 bool HasWeights = HasBranchWeights(SI);
3040 GetBranchWeights(SI, Weights);
3041 if (Weights.size() == 1 + SI->getNumCases()) {
3042 // Combine all weights for the cases to be the true weight of NewBI.
3043 // We assume that the sum of all weights for a Terminator can fit into 32
3045 uint32_t NewTrueWeight = 0;
3046 for (unsigned I = 1, E = Weights.size(); I != E; ++I)
3047 NewTrueWeight += (uint32_t)Weights[I];
3048 NewBI->setMetadata(LLVMContext::MD_prof,
3049 MDBuilder(SI->getContext()).
3050 createBranchWeights(NewTrueWeight,
3051 (uint32_t)Weights[0]));
3055 // Prune obsolete incoming values off the successor's PHI nodes.
3056 for (BasicBlock::iterator BBI = SI->case_begin().getCaseSuccessor()->begin();
3057 isa<PHINode>(BBI); ++BBI) {
3058 for (unsigned I = 0, E = SI->getNumCases()-1; I != E; ++I)
3059 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
3061 SI->eraseFromParent();
3066 /// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch
3067 /// and use it to remove dead cases.
3068 static bool EliminateDeadSwitchCases(SwitchInst *SI) {
3069 Value *Cond = SI->getCondition();
3070 unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth();
3071 APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
3072 ComputeMaskedBits(Cond, KnownZero, KnownOne);
3074 // Gather dead cases.
3075 SmallVector<ConstantInt*, 8> DeadCases;
3076 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
3077 if ((I.getCaseValue()->getValue() & KnownZero) != 0 ||
3078 (I.getCaseValue()->getValue() & KnownOne) != KnownOne) {
3079 DeadCases.push_back(I.getCaseValue());
3080 DEBUG(dbgs() << "SimplifyCFG: switch case '"
3081 << I.getCaseValue() << "' is dead.\n");
3085 SmallVector<uint64_t, 8> Weights;
3086 bool HasWeight = HasBranchWeights(SI);
3088 GetBranchWeights(SI, Weights);
3089 HasWeight = (Weights.size() == 1 + SI->getNumCases());
3092 // Remove dead cases from the switch.
3093 for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) {
3094 SwitchInst::CaseIt Case = SI->findCaseValue(DeadCases[I]);
3095 assert(Case != SI->case_default() &&
3096 "Case was not found. Probably mistake in DeadCases forming.");
3098 std::swap(Weights[Case.getCaseIndex()+1], Weights.back());
3102 // Prune unused values from PHI nodes.
3103 Case.getCaseSuccessor()->removePredecessor(SI->getParent());
3104 SI->removeCase(Case);
3107 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
3108 SI->setMetadata(LLVMContext::MD_prof,
3109 MDBuilder(SI->getParent()->getContext()).
3110 createBranchWeights(MDWeights));
3113 return !DeadCases.empty();
3116 /// FindPHIForConditionForwarding - If BB would be eligible for simplification
3117 /// by TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated
3118 /// by an unconditional branch), look at the phi node for BB in the successor
3119 /// block and see if the incoming value is equal to CaseValue. If so, return
3120 /// the phi node, and set PhiIndex to BB's index in the phi node.
3121 static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
3124 if (BB->getFirstNonPHIOrDbg() != BB->getTerminator())
3125 return NULL; // BB must be empty to be a candidate for simplification.
3126 if (!BB->getSinglePredecessor())
3127 return NULL; // BB must be dominated by the switch.
3129 BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
3130 if (!Branch || !Branch->isUnconditional())
3131 return NULL; // Terminator must be unconditional branch.
3133 BasicBlock *Succ = Branch->getSuccessor(0);
3135 BasicBlock::iterator I = Succ->begin();
3136 while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
3137 int Idx = PHI->getBasicBlockIndex(BB);
3138 assert(Idx >= 0 && "PHI has no entry for predecessor?");
3140 Value *InValue = PHI->getIncomingValue(Idx);
3141 if (InValue != CaseValue) continue;
3150 /// ForwardSwitchConditionToPHI - Try to forward the condition of a switch
3151 /// instruction to a phi node dominated by the switch, if that would mean that
3152 /// some of the destination blocks of the switch can be folded away.
3153 /// Returns true if a change is made.
3154 static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
3155 typedef DenseMap<PHINode*, SmallVector<int,4> > ForwardingNodesMap;
3156 ForwardingNodesMap ForwardingNodes;
3158 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
3159 ConstantInt *CaseValue = I.getCaseValue();
3160 BasicBlock *CaseDest = I.getCaseSuccessor();
3163 PHINode *PHI = FindPHIForConditionForwarding(CaseValue, CaseDest,
3167 ForwardingNodes[PHI].push_back(PhiIndex);
3170 bool Changed = false;
3172 for (ForwardingNodesMap::iterator I = ForwardingNodes.begin(),
3173 E = ForwardingNodes.end(); I != E; ++I) {
3174 PHINode *Phi = I->first;
3175 SmallVector<int,4> &Indexes = I->second;
3177 if (Indexes.size() < 2) continue;
3179 for (size_t I = 0, E = Indexes.size(); I != E; ++I)
3180 Phi->setIncomingValue(Indexes[I], SI->getCondition());
3187 /// ValidLookupTableConstant - Return true if the backend will be able to handle
3188 /// initializing an array of constants like C.
3189 static bool ValidLookupTableConstant(Constant *C) {
3190 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C))
3191 return CE->isGEPWithNoNotionalOverIndexing();
3193 return isa<ConstantFP>(C) ||
3194 isa<ConstantInt>(C) ||
3195 isa<ConstantPointerNull>(C) ||
3196 isa<GlobalValue>(C) ||
3200 /// GetCaseResulsts - Try to determine the resulting constant values in phi
3201 /// nodes at the common destination basic block for one of the case
3202 /// destinations of a switch instruction.
3203 static bool GetCaseResults(SwitchInst *SI,
3204 BasicBlock *CaseDest,
3205 BasicBlock **CommonDest,
3206 SmallVector<std::pair<PHINode*,Constant*>, 4> &Res) {
3207 // The block from which we enter the common destination.
3208 BasicBlock *Pred = SI->getParent();
3210 // If CaseDest is empty, continue to its successor.
3211 if (CaseDest->getFirstNonPHIOrDbg() == CaseDest->getTerminator() &&
3212 !isa<PHINode>(CaseDest->begin())) {
3214 TerminatorInst *Terminator = CaseDest->getTerminator();
3215 if (Terminator->getNumSuccessors() != 1)
3219 CaseDest = Terminator->getSuccessor(0);
3222 // If we did not have a CommonDest before, use the current one.
3224 *CommonDest = CaseDest;
3225 // If the destination isn't the common one, abort.
3226 if (CaseDest != *CommonDest)
3229 // Get the values for this case from phi nodes in the destination block.
3230 BasicBlock::iterator I = (*CommonDest)->begin();
3231 while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
3232 int Idx = PHI->getBasicBlockIndex(Pred);
3236 Constant *ConstVal = dyn_cast<Constant>(PHI->getIncomingValue(Idx));
3240 // Be conservative about which kinds of constants we support.
3241 if (!ValidLookupTableConstant(ConstVal))
3244 Res.push_back(std::make_pair(PHI, ConstVal));
3251 /// SwitchLookupTable - This class represents a lookup table that can be used
3252 /// to replace a switch.
3253 class SwitchLookupTable {
3255 /// SwitchLookupTable - Create a lookup table to use as a switch replacement
3256 /// with the contents of Values, using DefaultValue to fill any holes in the
3258 SwitchLookupTable(Module &M,
3260 ConstantInt *Offset,
3261 const SmallVector<std::pair<ConstantInt*, Constant*>, 4>& Values,
3262 Constant *DefaultValue,
3263 const DataLayout *TD);
3265 /// BuildLookup - Build instructions with Builder to retrieve the value at
3266 /// the position given by Index in the lookup table.
3267 Value *BuildLookup(Value *Index, IRBuilder<> &Builder);
3269 /// WouldFitInRegister - Return true if a table with TableSize elements of
3270 /// type ElementType would fit in a target-legal register.
3271 static bool WouldFitInRegister(const DataLayout *TD,
3273 const Type *ElementType);
3276 // Depending on the contents of the table, it can be represented in
3279 // For tables where each element contains the same value, we just have to
3280 // store that single value and return it for each lookup.
3283 // For small tables with integer elements, we can pack them into a bitmap
3284 // that fits into a target-legal register. Values are retrieved by
3285 // shift and mask operations.
3288 // The table is stored as an array of values. Values are retrieved by load
3289 // instructions from the table.
3293 // For SingleValueKind, this is the single value.
3294 Constant *SingleValue;
3296 // For BitMapKind, this is the bitmap.
3297 ConstantInt *BitMap;
3298 IntegerType *BitMapElementTy;
3300 // For ArrayKind, this is the array.
3301 GlobalVariable *Array;
3305 SwitchLookupTable::SwitchLookupTable(Module &M,
3307 ConstantInt *Offset,
3308 const SmallVector<std::pair<ConstantInt*, Constant*>, 4>& Values,
3309 Constant *DefaultValue,
3310 const DataLayout *TD) {
3311 assert(Values.size() && "Can't build lookup table without values!");
3312 assert(TableSize >= Values.size() && "Can't fit values in table!");
3314 // If all values in the table are equal, this is that value.
3315 SingleValue = Values.begin()->second;
3317 // Build up the table contents.
3318 SmallVector<Constant*, 64> TableContents(TableSize);
3319 for (size_t I = 0, E = Values.size(); I != E; ++I) {
3320 ConstantInt *CaseVal = Values[I].first;
3321 Constant *CaseRes = Values[I].second;
3322 assert(CaseRes->getType() == DefaultValue->getType());
3324 uint64_t Idx = (CaseVal->getValue() - Offset->getValue())
3326 TableContents[Idx] = CaseRes;
3328 if (CaseRes != SingleValue)
3332 // Fill in any holes in the table with the default result.
3333 if (Values.size() < TableSize) {
3334 for (uint64_t I = 0; I < TableSize; ++I) {
3335 if (!TableContents[I])
3336 TableContents[I] = DefaultValue;
3339 if (DefaultValue != SingleValue)
3343 // If each element in the table contains the same value, we only need to store
3344 // that single value.
3346 Kind = SingleValueKind;
3350 // If the type is integer and the table fits in a register, build a bitmap.
3351 if (WouldFitInRegister(TD, TableSize, DefaultValue->getType())) {
3352 IntegerType *IT = cast<IntegerType>(DefaultValue->getType());
3353 APInt TableInt(TableSize * IT->getBitWidth(), 0);
3354 for (uint64_t I = TableSize; I > 0; --I) {
3355 TableInt <<= IT->getBitWidth();
3356 // Insert values into the bitmap. Undef values are set to zero.
3357 if (!isa<UndefValue>(TableContents[I - 1])) {
3358 ConstantInt *Val = cast<ConstantInt>(TableContents[I - 1]);
3359 TableInt |= Val->getValue().zext(TableInt.getBitWidth());
3362 BitMap = ConstantInt::get(M.getContext(), TableInt);
3363 BitMapElementTy = IT;
3369 // Store the table in an array.
3370 ArrayType *ArrayTy = ArrayType::get(DefaultValue->getType(), TableSize);
3371 Constant *Initializer = ConstantArray::get(ArrayTy, TableContents);
3373 Array = new GlobalVariable(M, ArrayTy, /*constant=*/ true,
3374 GlobalVariable::PrivateLinkage,
3377 Array->setUnnamedAddr(true);
3381 Value *SwitchLookupTable::BuildLookup(Value *Index, IRBuilder<> &Builder) {
3383 case SingleValueKind:
3386 // Type of the bitmap (e.g. i59).
3387 IntegerType *MapTy = BitMap->getType();
3389 // Cast Index to the same type as the bitmap.
3390 // Note: The Index is <= the number of elements in the table, so
3391 // truncating it to the width of the bitmask is safe.
3392 Value *ShiftAmt = Builder.CreateZExtOrTrunc(Index, MapTy, "switch.cast");
3394 // Multiply the shift amount by the element width.
3395 ShiftAmt = Builder.CreateMul(ShiftAmt,
3396 ConstantInt::get(MapTy, BitMapElementTy->getBitWidth()),
3400 Value *DownShifted = Builder.CreateLShr(BitMap, ShiftAmt,
3401 "switch.downshift");
3403 return Builder.CreateTrunc(DownShifted, BitMapElementTy,
3407 Value *GEPIndices[] = { Builder.getInt32(0), Index };
3408 Value *GEP = Builder.CreateInBoundsGEP(Array, GEPIndices,
3410 return Builder.CreateLoad(GEP, "switch.load");
3413 llvm_unreachable("Unknown lookup table kind!");
3416 bool SwitchLookupTable::WouldFitInRegister(const DataLayout *TD,
3418 const Type *ElementType) {
3421 const IntegerType *IT = dyn_cast<IntegerType>(ElementType);
3424 // FIXME: If the type is wider than it needs to be, e.g. i8 but all values
3425 // are <= 15, we could try to narrow the type.
3427 // Avoid overflow, fitsInLegalInteger uses unsigned int for the width.
3428 if (TableSize >= UINT_MAX/IT->getBitWidth())
3430 return TD->fitsInLegalInteger(TableSize * IT->getBitWidth());
3433 /// ShouldBuildLookupTable - Determine whether a lookup table should be built
3434 /// for this switch, based on the number of caes, size of the table and the
3435 /// types of the results.
3436 static bool ShouldBuildLookupTable(SwitchInst *SI,
3438 const DataLayout *TD,
3439 const SmallDenseMap<PHINode*, Type*>& ResultTypes) {
3440 // The table density should be at least 40%. This is the same criterion as for
3441 // jump tables, see SelectionDAGBuilder::handleJTSwitchCase.
3442 // FIXME: Find the best cut-off.
3443 if (SI->getNumCases() > TableSize || TableSize >= UINT64_MAX / 10)
3444 return false; // TableSize overflowed, or mul below might overflow.
3445 if (SI->getNumCases() * 10 >= TableSize * 4)
3448 // If each table would fit in a register, we should build it anyway.
3449 for (SmallDenseMap<PHINode*, Type*>::const_iterator I = ResultTypes.begin(),
3450 E = ResultTypes.end(); I != E; ++I) {
3451 if (!SwitchLookupTable::WouldFitInRegister(TD, TableSize, I->second))
3457 /// SwitchToLookupTable - If the switch is only used to initialize one or more
3458 /// phi nodes in a common successor block with different constant values,
3459 /// replace the switch with lookup tables.
3460 static bool SwitchToLookupTable(SwitchInst *SI,
3461 IRBuilder<> &Builder,
3462 const DataLayout* TD) {
3463 assert(SI->getNumCases() > 1 && "Degenerate switch?");
3464 // FIXME: Handle unreachable cases.
3466 // FIXME: If the switch is too sparse for a lookup table, perhaps we could
3467 // split off a dense part and build a lookup table for that.
3469 // FIXME: This creates arrays of GEPs to constant strings, which means each
3470 // GEP needs a runtime relocation in PIC code. We should just build one big
3471 // string and lookup indices into that.
3473 // Ignore the switch if the number of cases is too small.
3474 // This is similar to the check when building jump tables in
3475 // SelectionDAGBuilder::handleJTSwitchCase.
3476 // FIXME: Determine the best cut-off.
3477 if (SI->getNumCases() < 4)
3480 // Figure out the corresponding result for each case value and phi node in the
3481 // common destination, as well as the the min and max case values.
3482 assert(SI->case_begin() != SI->case_end());
3483 SwitchInst::CaseIt CI = SI->case_begin();
3484 ConstantInt *MinCaseVal = CI.getCaseValue();
3485 ConstantInt *MaxCaseVal = CI.getCaseValue();
3487 BasicBlock *CommonDest = NULL;
3488 typedef SmallVector<std::pair<ConstantInt*, Constant*>, 4> ResultListTy;
3489 SmallDenseMap<PHINode*, ResultListTy> ResultLists;
3490 SmallDenseMap<PHINode*, Constant*> DefaultResults;
3491 SmallDenseMap<PHINode*, Type*> ResultTypes;
3492 SmallVector<PHINode*, 4> PHIs;
3494 for (SwitchInst::CaseIt E = SI->case_end(); CI != E; ++CI) {
3495 ConstantInt *CaseVal = CI.getCaseValue();
3496 if (CaseVal->getValue().slt(MinCaseVal->getValue()))
3497 MinCaseVal = CaseVal;
3498 if (CaseVal->getValue().sgt(MaxCaseVal->getValue()))
3499 MaxCaseVal = CaseVal;
3501 // Resulting value at phi nodes for this case value.
3502 typedef SmallVector<std::pair<PHINode*, Constant*>, 4> ResultsTy;
3504 if (!GetCaseResults(SI, CI.getCaseSuccessor(), &CommonDest, Results))
3507 // Append the result from this case to the list for each phi.
3508 for (ResultsTy::iterator I = Results.begin(), E = Results.end(); I!=E; ++I) {
3509 if (!ResultLists.count(I->first))
3510 PHIs.push_back(I->first);
3511 ResultLists[I->first].push_back(std::make_pair(CaseVal, I->second));
3515 // Get the resulting values for the default case.
3516 SmallVector<std::pair<PHINode*, Constant*>, 4> DefaultResultsList;
3517 if (!GetCaseResults(SI, SI->getDefaultDest(), &CommonDest, DefaultResultsList))
3519 for (size_t I = 0, E = DefaultResultsList.size(); I != E; ++I) {
3520 PHINode *PHI = DefaultResultsList[I].first;
3521 Constant *Result = DefaultResultsList[I].second;
3522 DefaultResults[PHI] = Result;
3523 ResultTypes[PHI] = Result->getType();
3526 APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
3527 uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
3528 if (!ShouldBuildLookupTable(SI, TableSize, TD, ResultTypes))
3531 // Create the BB that does the lookups.
3532 Module &Mod = *CommonDest->getParent()->getParent();
3533 BasicBlock *LookupBB = BasicBlock::Create(Mod.getContext(),
3535 CommonDest->getParent(),
3538 // Check whether the condition value is within the case range, and branch to
3540 Builder.SetInsertPoint(SI);
3541 Value *TableIndex = Builder.CreateSub(SI->getCondition(), MinCaseVal,
3543 Value *Cmp = Builder.CreateICmpULT(TableIndex, ConstantInt::get(
3544 MinCaseVal->getType(), TableSize));
3545 Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest());
3547 // Populate the BB that does the lookups.
3548 Builder.SetInsertPoint(LookupBB);
3549 bool ReturnedEarly = false;
3550 for (size_t I = 0, E = PHIs.size(); I != E; ++I) {
3551 PHINode *PHI = PHIs[I];
3553 SwitchLookupTable Table(Mod, TableSize, MinCaseVal, ResultLists[PHI],
3554 DefaultResults[PHI], TD);
3556 Value *Result = Table.BuildLookup(TableIndex, Builder);
3558 // If the result is used to return immediately from the function, we want to
3559 // do that right here.
3560 if (PHI->hasOneUse() && isa<ReturnInst>(*PHI->use_begin()) &&
3561 *PHI->use_begin() == CommonDest->getFirstNonPHIOrDbg()) {
3562 Builder.CreateRet(Result);
3563 ReturnedEarly = true;
3567 PHI->addIncoming(Result, LookupBB);
3571 Builder.CreateBr(CommonDest);
3573 // Remove the switch.
3574 for (unsigned i = 0; i < SI->getNumSuccessors(); ++i) {
3575 BasicBlock *Succ = SI->getSuccessor(i);
3576 if (Succ == SI->getDefaultDest()) continue;
3577 Succ->removePredecessor(SI->getParent());
3579 SI->eraseFromParent();
3585 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
3586 BasicBlock *BB = SI->getParent();
3588 if (isValueEqualityComparison(SI)) {
3589 // If we only have one predecessor, and if it is a branch on this value,
3590 // see if that predecessor totally determines the outcome of this switch.
3591 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
3592 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
3593 return SimplifyCFG(BB) | true;
3595 Value *Cond = SI->getCondition();
3596 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
3597 if (SimplifySwitchOnSelect(SI, Select))
3598 return SimplifyCFG(BB) | true;
3600 // If the block only contains the switch, see if we can fold the block
3601 // away into any preds.
3602 BasicBlock::iterator BBI = BB->begin();
3603 // Ignore dbg intrinsics.
3604 while (isa<DbgInfoIntrinsic>(BBI))
3607 if (FoldValueComparisonIntoPredecessors(SI, Builder))
3608 return SimplifyCFG(BB) | true;
3611 // Try to transform the switch into an icmp and a branch.
3612 if (TurnSwitchRangeIntoICmp(SI, Builder))
3613 return SimplifyCFG(BB) | true;
3615 // Remove unreachable cases.
3616 if (EliminateDeadSwitchCases(SI))
3617 return SimplifyCFG(BB) | true;
3619 if (ForwardSwitchConditionToPHI(SI))
3620 return SimplifyCFG(BB) | true;
3622 if (SwitchToLookupTable(SI, Builder, TD))
3623 return SimplifyCFG(BB) | true;
3628 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
3629 BasicBlock *BB = IBI->getParent();
3630 bool Changed = false;
3632 // Eliminate redundant destinations.
3633 SmallPtrSet<Value *, 8> Succs;
3634 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
3635 BasicBlock *Dest = IBI->getDestination(i);
3636 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
3637 Dest->removePredecessor(BB);
3638 IBI->removeDestination(i);
3644 if (IBI->getNumDestinations() == 0) {
3645 // If the indirectbr has no successors, change it to unreachable.
3646 new UnreachableInst(IBI->getContext(), IBI);
3647 EraseTerminatorInstAndDCECond(IBI);
3651 if (IBI->getNumDestinations() == 1) {
3652 // If the indirectbr has one successor, change it to a direct branch.
3653 BranchInst::Create(IBI->getDestination(0), IBI);
3654 EraseTerminatorInstAndDCECond(IBI);
3658 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
3659 if (SimplifyIndirectBrOnSelect(IBI, SI))
3660 return SimplifyCFG(BB) | true;
3665 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
3666 BasicBlock *BB = BI->getParent();
3668 if (SinkCommon && SinkThenElseCodeToEnd(BI))
3671 // If the Terminator is the only non-phi instruction, simplify the block.
3672 BasicBlock::iterator I = BB->getFirstNonPHIOrDbgOrLifetime();
3673 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
3674 TryToSimplifyUncondBranchFromEmptyBlock(BB))
3677 // If the only instruction in the block is a seteq/setne comparison
3678 // against a constant, try to simplify the block.
3679 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
3680 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
3681 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
3683 if (I->isTerminator() &&
3684 TryToSimplifyUncondBranchWithICmpInIt(ICI, TD, Builder))
3688 // If this basic block is ONLY a compare and a branch, and if a predecessor
3689 // branches to us and our successor, fold the comparison into the
3690 // predecessor and use logical operations to update the incoming value
3691 // for PHI nodes in common successor.
3692 if (FoldBranchToCommonDest(BI))
3693 return SimplifyCFG(BB) | true;
3698 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
3699 BasicBlock *BB = BI->getParent();
3701 // Conditional branch
3702 if (isValueEqualityComparison(BI)) {
3703 // If we only have one predecessor, and if it is a branch on this value,
3704 // see if that predecessor totally determines the outcome of this
3706 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
3707 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
3708 return SimplifyCFG(BB) | true;
3710 // This block must be empty, except for the setcond inst, if it exists.
3711 // Ignore dbg intrinsics.
3712 BasicBlock::iterator I = BB->begin();
3713 // Ignore dbg intrinsics.
3714 while (isa<DbgInfoIntrinsic>(I))
3717 if (FoldValueComparisonIntoPredecessors(BI, Builder))
3718 return SimplifyCFG(BB) | true;
3719 } else if (&*I == cast<Instruction>(BI->getCondition())){
3721 // Ignore dbg intrinsics.
3722 while (isa<DbgInfoIntrinsic>(I))
3724 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
3725 return SimplifyCFG(BB) | true;
3729 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
3730 if (SimplifyBranchOnICmpChain(BI, TD, Builder))
3733 // If this basic block is ONLY a compare and a branch, and if a predecessor
3734 // branches to us and one of our successors, fold the comparison into the
3735 // predecessor and use logical operations to pick the right destination.
3736 if (FoldBranchToCommonDest(BI))
3737 return SimplifyCFG(BB) | true;
3739 // We have a conditional branch to two blocks that are only reachable
3740 // from BI. We know that the condbr dominates the two blocks, so see if
3741 // there is any identical code in the "then" and "else" blocks. If so, we
3742 // can hoist it up to the branching block.
3743 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
3744 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
3745 if (HoistThenElseCodeToIf(BI))
3746 return SimplifyCFG(BB) | true;
3748 // If Successor #1 has multiple preds, we may be able to conditionally
3749 // execute Successor #0 if it branches to successor #1.
3750 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
3751 if (Succ0TI->getNumSuccessors() == 1 &&
3752 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
3753 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
3754 return SimplifyCFG(BB) | true;
3756 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
3757 // If Successor #0 has multiple preds, we may be able to conditionally
3758 // execute Successor #1 if it branches to successor #0.
3759 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
3760 if (Succ1TI->getNumSuccessors() == 1 &&
3761 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
3762 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
3763 return SimplifyCFG(BB) | true;
3766 // If this is a branch on a phi node in the current block, thread control
3767 // through this block if any PHI node entries are constants.
3768 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
3769 if (PN->getParent() == BI->getParent())
3770 if (FoldCondBranchOnPHI(BI, TD))
3771 return SimplifyCFG(BB) | true;
3773 // Scan predecessor blocks for conditional branches.
3774 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
3775 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
3776 if (PBI != BI && PBI->isConditional())
3777 if (SimplifyCondBranchToCondBranch(PBI, BI))
3778 return SimplifyCFG(BB) | true;
3783 /// Check if passing a value to an instruction will cause undefined behavior.
3784 static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
3785 Constant *C = dyn_cast<Constant>(V);
3792 if (C->isNullValue()) {
3793 // Only look at the first use, avoid hurting compile time with long uselists
3794 User *Use = *I->use_begin();
3796 // Now make sure that there are no instructions in between that can alter
3797 // control flow (eg. calls)
3798 for (BasicBlock::iterator i = ++BasicBlock::iterator(I); &*i != Use; ++i)
3799 if (i == I->getParent()->end() || i->mayHaveSideEffects())
3802 // Look through GEPs. A load from a GEP derived from NULL is still undefined
3803 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))
3804 if (GEP->getPointerOperand() == I)
3805 return passingValueIsAlwaysUndefined(V, GEP);
3807 // Look through bitcasts.
3808 if (BitCastInst *BC = dyn_cast<BitCastInst>(Use))
3809 return passingValueIsAlwaysUndefined(V, BC);
3811 // Load from null is undefined.
3812 if (LoadInst *LI = dyn_cast<LoadInst>(Use))
3813 return LI->getPointerAddressSpace() == 0;
3815 // Store to null is undefined.
3816 if (StoreInst *SI = dyn_cast<StoreInst>(Use))
3817 return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I;
3822 /// If BB has an incoming value that will always trigger undefined behavior
3823 /// (eg. null pointer dereference), remove the branch leading here.
3824 static bool removeUndefIntroducingPredecessor(BasicBlock *BB) {
3825 for (BasicBlock::iterator i = BB->begin();
3826 PHINode *PHI = dyn_cast<PHINode>(i); ++i)
3827 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
3828 if (passingValueIsAlwaysUndefined(PHI->getIncomingValue(i), PHI)) {
3829 TerminatorInst *T = PHI->getIncomingBlock(i)->getTerminator();
3830 IRBuilder<> Builder(T);
3831 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
3832 BB->removePredecessor(PHI->getIncomingBlock(i));
3833 // Turn uncoditional branches into unreachables and remove the dead
3834 // destination from conditional branches.
3835 if (BI->isUnconditional())
3836 Builder.CreateUnreachable();
3838 Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1) :
3839 BI->getSuccessor(0));
3840 BI->eraseFromParent();
3843 // TODO: SwitchInst.
3849 bool SimplifyCFGOpt::run(BasicBlock *BB) {
3850 bool Changed = false;
3852 assert(BB && BB->getParent() && "Block not embedded in function!");
3853 assert(BB->getTerminator() && "Degenerate basic block encountered!");
3855 // Remove basic blocks that have no predecessors (except the entry block)...
3856 // or that just have themself as a predecessor. These are unreachable.
3857 if ((pred_begin(BB) == pred_end(BB) &&
3858 BB != &BB->getParent()->getEntryBlock()) ||
3859 BB->getSinglePredecessor() == BB) {
3860 DEBUG(dbgs() << "Removing BB: \n" << *BB);
3861 DeleteDeadBlock(BB);
3865 // Check to see if we can constant propagate this terminator instruction
3867 Changed |= ConstantFoldTerminator(BB, true);
3869 // Check for and eliminate duplicate PHI nodes in this block.
3870 Changed |= EliminateDuplicatePHINodes(BB);
3872 // Check for and remove branches that will always cause undefined behavior.
3873 Changed |= removeUndefIntroducingPredecessor(BB);
3875 // Merge basic blocks into their predecessor if there is only one distinct
3876 // pred, and if there is only one distinct successor of the predecessor, and
3877 // if there are no PHI nodes.
3879 if (MergeBlockIntoPredecessor(BB))
3882 IRBuilder<> Builder(BB);
3884 // If there is a trivial two-entry PHI node in this basic block, and we can
3885 // eliminate it, do so now.
3886 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
3887 if (PN->getNumIncomingValues() == 2)
3888 Changed |= FoldTwoEntryPHINode(PN, TD);
3890 Builder.SetInsertPoint(BB->getTerminator());
3891 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
3892 if (BI->isUnconditional()) {
3893 if (SimplifyUncondBranch(BI, Builder)) return true;
3895 if (SimplifyCondBranch(BI, Builder)) return true;
3897 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
3898 if (SimplifyReturn(RI, Builder)) return true;
3899 } else if (ResumeInst *RI = dyn_cast<ResumeInst>(BB->getTerminator())) {
3900 if (SimplifyResume(RI, Builder)) return true;
3901 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
3902 if (SimplifySwitch(SI, Builder)) return true;
3903 } else if (UnreachableInst *UI =
3904 dyn_cast<UnreachableInst>(BB->getTerminator())) {
3905 if (SimplifyUnreachable(UI)) return true;
3906 } else if (IndirectBrInst *IBI =
3907 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
3908 if (SimplifyIndirectBr(IBI)) return true;
3914 /// SimplifyCFG - This function is used to do simplification of a CFG. For
3915 /// example, it adjusts branches to branches to eliminate the extra hop, it
3916 /// eliminates unreachable basic blocks, and does other "peephole" optimization
3917 /// of the CFG. It returns true if a modification was made.
3919 bool llvm::SimplifyCFG(BasicBlock *BB, const DataLayout *TD) {
3920 return SimplifyCFGOpt(TD).run(BB);