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/Target/TargetData.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(NumSpeculations, "Number of speculative executed instructions");
62 STATISTIC(NumLookupTables, "Number of switch instructions turned into lookup tables");
63 STATISTIC(NumSinkCommons, "Number of common instructions sunk down to the end block");
66 /// ValueEqualityComparisonCase - Represents a case of a switch.
67 struct ValueEqualityComparisonCase {
71 ValueEqualityComparisonCase(ConstantInt *Value, BasicBlock *Dest)
72 : Value(Value), Dest(Dest) {}
74 bool operator<(ValueEqualityComparisonCase RHS) const {
75 // Comparing pointers is ok as we only rely on the order for uniquing.
76 return Value < RHS.Value;
80 class SimplifyCFGOpt {
81 const TargetData *const TD;
83 Value *isValueEqualityComparison(TerminatorInst *TI);
84 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
85 std::vector<ValueEqualityComparisonCase> &Cases);
86 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
88 IRBuilder<> &Builder);
89 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
90 IRBuilder<> &Builder);
92 bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder);
93 bool SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder);
94 bool SimplifyUnreachable(UnreachableInst *UI);
95 bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
96 bool SimplifyIndirectBr(IndirectBrInst *IBI);
97 bool SimplifyUncondBranch(BranchInst *BI, IRBuilder <> &Builder);
98 bool SimplifyCondBranch(BranchInst *BI, IRBuilder <>&Builder);
101 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
102 bool run(BasicBlock *BB);
106 /// SafeToMergeTerminators - Return true if it is safe to merge these two
107 /// terminator instructions together.
109 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
110 if (SI1 == SI2) return false; // Can't merge with self!
112 // It is not safe to merge these two switch instructions if they have a common
113 // successor, and if that successor has a PHI node, and if *that* PHI node has
114 // conflicting incoming values from the two switch blocks.
115 BasicBlock *SI1BB = SI1->getParent();
116 BasicBlock *SI2BB = SI2->getParent();
117 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
119 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
120 if (SI1Succs.count(*I))
121 for (BasicBlock::iterator BBI = (*I)->begin();
122 isa<PHINode>(BBI); ++BBI) {
123 PHINode *PN = cast<PHINode>(BBI);
124 if (PN->getIncomingValueForBlock(SI1BB) !=
125 PN->getIncomingValueForBlock(SI2BB))
132 /// isProfitableToFoldUnconditional - Return true if it is safe and profitable
133 /// to merge these two terminator instructions together, where SI1 is an
134 /// unconditional branch. PhiNodes will store all PHI nodes in common
137 static bool isProfitableToFoldUnconditional(BranchInst *SI1,
140 SmallVectorImpl<PHINode*> &PhiNodes) {
141 if (SI1 == SI2) return false; // Can't merge with self!
142 assert(SI1->isUnconditional() && SI2->isConditional());
144 // We fold the unconditional branch if we can easily update all PHI nodes in
145 // common successors:
146 // 1> We have a constant incoming value for the conditional branch;
147 // 2> We have "Cond" as the incoming value for the unconditional branch;
148 // 3> SI2->getCondition() and Cond have same operands.
149 CmpInst *Ci2 = dyn_cast<CmpInst>(SI2->getCondition());
150 if (!Ci2) return false;
151 if (!(Cond->getOperand(0) == Ci2->getOperand(0) &&
152 Cond->getOperand(1) == Ci2->getOperand(1)) &&
153 !(Cond->getOperand(0) == Ci2->getOperand(1) &&
154 Cond->getOperand(1) == Ci2->getOperand(0)))
157 BasicBlock *SI1BB = SI1->getParent();
158 BasicBlock *SI2BB = SI2->getParent();
159 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
160 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
161 if (SI1Succs.count(*I))
162 for (BasicBlock::iterator BBI = (*I)->begin();
163 isa<PHINode>(BBI); ++BBI) {
164 PHINode *PN = cast<PHINode>(BBI);
165 if (PN->getIncomingValueForBlock(SI1BB) != Cond ||
166 !isa<ConstantInt>(PN->getIncomingValueForBlock(SI2BB)))
168 PhiNodes.push_back(PN);
173 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
174 /// now be entries in it from the 'NewPred' block. The values that will be
175 /// flowing into the PHI nodes will be the same as those coming in from
176 /// ExistPred, an existing predecessor of Succ.
177 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
178 BasicBlock *ExistPred) {
179 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
182 for (BasicBlock::iterator I = Succ->begin();
183 (PN = dyn_cast<PHINode>(I)); ++I)
184 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
188 /// GetIfCondition - Given a basic block (BB) with two predecessors (and at
189 /// least one PHI node in it), check to see if the merge at this block is due
190 /// to an "if condition". If so, return the boolean condition that determines
191 /// which entry into BB will be taken. Also, return by references the block
192 /// that will be entered from if the condition is true, and the block that will
193 /// be entered if the condition is false.
195 /// This does no checking to see if the true/false blocks have large or unsavory
196 /// instructions in them.
197 static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
198 BasicBlock *&IfFalse) {
199 PHINode *SomePHI = cast<PHINode>(BB->begin());
200 assert(SomePHI->getNumIncomingValues() == 2 &&
201 "Function can only handle blocks with 2 predecessors!");
202 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
203 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
205 // We can only handle branches. Other control flow will be lowered to
206 // branches if possible anyway.
207 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
208 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
209 if (Pred1Br == 0 || Pred2Br == 0)
212 // Eliminate code duplication by ensuring that Pred1Br is conditional if
214 if (Pred2Br->isConditional()) {
215 // If both branches are conditional, we don't have an "if statement". In
216 // reality, we could transform this case, but since the condition will be
217 // required anyway, we stand no chance of eliminating it, so the xform is
218 // probably not profitable.
219 if (Pred1Br->isConditional())
222 std::swap(Pred1, Pred2);
223 std::swap(Pred1Br, Pred2Br);
226 if (Pred1Br->isConditional()) {
227 // The only thing we have to watch out for here is to make sure that Pred2
228 // doesn't have incoming edges from other blocks. If it does, the condition
229 // doesn't dominate BB.
230 if (Pred2->getSinglePredecessor() == 0)
233 // If we found a conditional branch predecessor, make sure that it branches
234 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
235 if (Pred1Br->getSuccessor(0) == BB &&
236 Pred1Br->getSuccessor(1) == Pred2) {
239 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
240 Pred1Br->getSuccessor(1) == BB) {
244 // We know that one arm of the conditional goes to BB, so the other must
245 // go somewhere unrelated, and this must not be an "if statement".
249 return Pred1Br->getCondition();
252 // Ok, if we got here, both predecessors end with an unconditional branch to
253 // BB. Don't panic! If both blocks only have a single (identical)
254 // predecessor, and THAT is a conditional branch, then we're all ok!
255 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
256 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
259 // Otherwise, if this is a conditional branch, then we can use it!
260 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
261 if (BI == 0) return 0;
263 assert(BI->isConditional() && "Two successors but not conditional?");
264 if (BI->getSuccessor(0) == Pred1) {
271 return BI->getCondition();
274 /// ComputeSpeculuationCost - Compute an abstract "cost" of speculating the
275 /// given instruction, which is assumed to be safe to speculate. 1 means
276 /// cheap, 2 means less cheap, and UINT_MAX means prohibitively expensive.
277 static unsigned ComputeSpeculationCost(const User *I) {
278 assert(isSafeToSpeculativelyExecute(I) &&
279 "Instruction is not safe to speculatively execute!");
280 switch (Operator::getOpcode(I)) {
282 // In doubt, be conservative.
284 case Instruction::GetElementPtr:
285 // GEPs are cheap if all indices are constant.
286 if (!cast<GEPOperator>(I)->hasAllConstantIndices())
289 case Instruction::Load:
290 case Instruction::Add:
291 case Instruction::Sub:
292 case Instruction::And:
293 case Instruction::Or:
294 case Instruction::Xor:
295 case Instruction::Shl:
296 case Instruction::LShr:
297 case Instruction::AShr:
298 case Instruction::ICmp:
299 case Instruction::Trunc:
300 case Instruction::ZExt:
301 case Instruction::SExt:
302 return 1; // These are all cheap.
304 case Instruction::Call:
305 case Instruction::Select:
310 /// DominatesMergePoint - If we have a merge point of an "if condition" as
311 /// accepted above, return true if the specified value dominates the block. We
312 /// don't handle the true generality of domination here, just a special case
313 /// which works well enough for us.
315 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
316 /// see if V (which must be an instruction) and its recursive operands
317 /// that do not dominate BB have a combined cost lower than CostRemaining and
318 /// are non-trapping. If both are true, the instruction is inserted into the
319 /// set and true is returned.
321 /// The cost for most non-trapping instructions is defined as 1 except for
322 /// Select whose cost is 2.
324 /// After this function returns, CostRemaining is decreased by the cost of
325 /// V plus its non-dominating operands. If that cost is greater than
326 /// CostRemaining, false is returned and CostRemaining is undefined.
327 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
328 SmallPtrSet<Instruction*, 4> *AggressiveInsts,
329 unsigned &CostRemaining) {
330 Instruction *I = dyn_cast<Instruction>(V);
332 // Non-instructions all dominate instructions, but not all constantexprs
333 // can be executed unconditionally.
334 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
339 BasicBlock *PBB = I->getParent();
341 // We don't want to allow weird loops that might have the "if condition" in
342 // the bottom of this block.
343 if (PBB == BB) return false;
345 // If this instruction is defined in a block that contains an unconditional
346 // branch to BB, then it must be in the 'conditional' part of the "if
347 // statement". If not, it definitely dominates the region.
348 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
349 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB)
352 // If we aren't allowing aggressive promotion anymore, then don't consider
353 // instructions in the 'if region'.
354 if (AggressiveInsts == 0) return false;
356 // If we have seen this instruction before, don't count it again.
357 if (AggressiveInsts->count(I)) return true;
359 // Okay, it looks like the instruction IS in the "condition". Check to
360 // see if it's a cheap instruction to unconditionally compute, and if it
361 // only uses stuff defined outside of the condition. If so, hoist it out.
362 if (!isSafeToSpeculativelyExecute(I))
365 unsigned Cost = ComputeSpeculationCost(I);
367 if (Cost > CostRemaining)
370 CostRemaining -= Cost;
372 // Okay, we can only really hoist these out if their operands do
373 // not take us over the cost threshold.
374 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
375 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining))
377 // Okay, it's safe to do this! Remember this instruction.
378 AggressiveInsts->insert(I);
382 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
383 /// and PointerNullValue. Return NULL if value is not a constant int.
384 static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
385 // Normal constant int.
386 ConstantInt *CI = dyn_cast<ConstantInt>(V);
387 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
390 // This is some kind of pointer constant. Turn it into a pointer-sized
391 // ConstantInt if possible.
392 IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
394 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
395 if (isa<ConstantPointerNull>(V))
396 return ConstantInt::get(PtrTy, 0);
398 // IntToPtr const int.
399 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
400 if (CE->getOpcode() == Instruction::IntToPtr)
401 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
402 // The constant is very likely to have the right type already.
403 if (CI->getType() == PtrTy)
406 return cast<ConstantInt>
407 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
412 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
413 /// collection of icmp eq/ne instructions that compare a value against a
414 /// constant, return the value being compared, and stick the constant into the
417 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
418 const TargetData *TD, bool isEQ, unsigned &UsedICmps) {
419 Instruction *I = dyn_cast<Instruction>(V);
420 if (I == 0) return 0;
422 // If this is an icmp against a constant, handle this as one of the cases.
423 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
424 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
425 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
428 return I->getOperand(0);
431 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
434 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
436 // If this is an and/!= check then we want to optimize "x ugt 2" into
439 Span = Span.inverse();
441 // If there are a ton of values, we don't want to make a ginormous switch.
442 if (Span.getSetSize().ugt(8) || Span.isEmptySet())
445 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
446 Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
448 return I->getOperand(0);
453 // Otherwise, we can only handle an | or &, depending on isEQ.
454 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
457 unsigned NumValsBeforeLHS = Vals.size();
458 unsigned UsedICmpsBeforeLHS = UsedICmps;
459 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
461 unsigned NumVals = Vals.size();
462 unsigned UsedICmpsBeforeRHS = UsedICmps;
463 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
467 Vals.resize(NumVals);
468 UsedICmps = UsedICmpsBeforeRHS;
471 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
472 // set it and return success.
473 if (Extra == 0 || Extra == I->getOperand(1)) {
474 Extra = I->getOperand(1);
478 Vals.resize(NumValsBeforeLHS);
479 UsedICmps = UsedICmpsBeforeLHS;
483 // If the LHS can't be folded in, but Extra is available and RHS can, try to
485 if (Extra == 0 || Extra == I->getOperand(0)) {
486 Value *OldExtra = Extra;
487 Extra = I->getOperand(0);
488 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
491 assert(Vals.size() == NumValsBeforeLHS);
498 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
499 Instruction *Cond = 0;
500 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
501 Cond = dyn_cast<Instruction>(SI->getCondition());
502 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
503 if (BI->isConditional())
504 Cond = dyn_cast<Instruction>(BI->getCondition());
505 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
506 Cond = dyn_cast<Instruction>(IBI->getAddress());
509 TI->eraseFromParent();
510 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
513 /// isValueEqualityComparison - Return true if the specified terminator checks
514 /// to see if a value is equal to constant integer value.
515 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
517 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
518 // Do not permit merging of large switch instructions into their
519 // predecessors unless there is only one predecessor.
520 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
521 pred_end(SI->getParent())) <= 128)
522 CV = SI->getCondition();
523 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
524 if (BI->isConditional() && BI->getCondition()->hasOneUse())
525 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
526 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
527 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
528 GetConstantInt(ICI->getOperand(1), TD))
529 CV = ICI->getOperand(0);
531 // Unwrap any lossless ptrtoint cast.
532 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
533 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
534 CV = PTII->getOperand(0);
538 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
539 /// decode all of the 'cases' that it represents and return the 'default' block.
540 BasicBlock *SimplifyCFGOpt::
541 GetValueEqualityComparisonCases(TerminatorInst *TI,
542 std::vector<ValueEqualityComparisonCase>
544 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
545 Cases.reserve(SI->getNumCases());
546 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i)
547 Cases.push_back(ValueEqualityComparisonCase(i.getCaseValue(),
548 i.getCaseSuccessor()));
549 return SI->getDefaultDest();
552 BranchInst *BI = cast<BranchInst>(TI);
553 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
554 BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE);
555 Cases.push_back(ValueEqualityComparisonCase(GetConstantInt(ICI->getOperand(1),
558 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
562 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
563 /// in the list that match the specified block.
564 static void EliminateBlockCases(BasicBlock *BB,
565 std::vector<ValueEqualityComparisonCase> &Cases) {
566 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
567 if (Cases[i].Dest == BB) {
568 Cases.erase(Cases.begin()+i);
573 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
576 ValuesOverlap(std::vector<ValueEqualityComparisonCase> &C1,
577 std::vector<ValueEqualityComparisonCase > &C2) {
578 std::vector<ValueEqualityComparisonCase> *V1 = &C1, *V2 = &C2;
580 // Make V1 be smaller than V2.
581 if (V1->size() > V2->size())
584 if (V1->size() == 0) return false;
585 if (V1->size() == 1) {
587 ConstantInt *TheVal = (*V1)[0].Value;
588 for (unsigned i = 0, e = V2->size(); i != e; ++i)
589 if (TheVal == (*V2)[i].Value)
593 // Otherwise, just sort both lists and compare element by element.
594 array_pod_sort(V1->begin(), V1->end());
595 array_pod_sort(V2->begin(), V2->end());
596 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
597 while (i1 != e1 && i2 != e2) {
598 if ((*V1)[i1].Value == (*V2)[i2].Value)
600 if ((*V1)[i1].Value < (*V2)[i2].Value)
608 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
609 /// terminator instruction and its block is known to only have a single
610 /// predecessor block, check to see if that predecessor is also a value
611 /// comparison with the same value, and if that comparison determines the
612 /// outcome of this comparison. If so, simplify TI. This does a very limited
613 /// form of jump threading.
614 bool SimplifyCFGOpt::
615 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
617 IRBuilder<> &Builder) {
618 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
619 if (!PredVal) return false; // Not a value comparison in predecessor.
621 Value *ThisVal = isValueEqualityComparison(TI);
622 assert(ThisVal && "This isn't a value comparison!!");
623 if (ThisVal != PredVal) return false; // Different predicates.
625 // TODO: Preserve branch weight metadata, similarly to how
626 // FoldValueComparisonIntoPredecessors preserves it.
628 // Find out information about when control will move from Pred to TI's block.
629 std::vector<ValueEqualityComparisonCase> PredCases;
630 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
632 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
634 // Find information about how control leaves this block.
635 std::vector<ValueEqualityComparisonCase> ThisCases;
636 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
637 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
639 // If TI's block is the default block from Pred's comparison, potentially
640 // simplify TI based on this knowledge.
641 if (PredDef == TI->getParent()) {
642 // If we are here, we know that the value is none of those cases listed in
643 // PredCases. If there are any cases in ThisCases that are in PredCases, we
645 if (!ValuesOverlap(PredCases, ThisCases))
648 if (isa<BranchInst>(TI)) {
649 // Okay, one of the successors of this condbr is dead. Convert it to a
651 assert(ThisCases.size() == 1 && "Branch can only have one case!");
652 // Insert the new branch.
653 Instruction *NI = Builder.CreateBr(ThisDef);
656 // Remove PHI node entries for the dead edge.
657 ThisCases[0].Dest->removePredecessor(TI->getParent());
659 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
660 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
662 EraseTerminatorInstAndDCECond(TI);
666 SwitchInst *SI = cast<SwitchInst>(TI);
667 // Okay, TI has cases that are statically dead, prune them away.
668 SmallPtrSet<Constant*, 16> DeadCases;
669 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
670 DeadCases.insert(PredCases[i].Value);
672 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
673 << "Through successor TI: " << *TI);
675 // Collect branch weights into a vector.
676 SmallVector<uint32_t, 8> Weights;
677 MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
678 bool HasWeight = MD && (MD->getNumOperands() == 2 + SI->getNumCases());
680 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
682 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(MD_i));
684 Weights.push_back(CI->getValue().getZExtValue());
686 for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) {
688 if (DeadCases.count(i.getCaseValue())) {
690 std::swap(Weights[i.getCaseIndex()+1], Weights.back());
693 i.getCaseSuccessor()->removePredecessor(TI->getParent());
698 SI->setMetadata(LLVMContext::MD_prof,
699 MDBuilder(SI->getParent()->getContext()).
700 createBranchWeights(Weights));
702 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
706 // Otherwise, TI's block must correspond to some matched value. Find out
707 // which value (or set of values) this is.
708 ConstantInt *TIV = 0;
709 BasicBlock *TIBB = TI->getParent();
710 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
711 if (PredCases[i].Dest == TIBB) {
713 return false; // Cannot handle multiple values coming to this block.
714 TIV = PredCases[i].Value;
716 assert(TIV && "No edge from pred to succ?");
718 // Okay, we found the one constant that our value can be if we get into TI's
719 // BB. Find out which successor will unconditionally be branched to.
720 BasicBlock *TheRealDest = 0;
721 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
722 if (ThisCases[i].Value == TIV) {
723 TheRealDest = ThisCases[i].Dest;
727 // If not handled by any explicit cases, it is handled by the default case.
728 if (TheRealDest == 0) TheRealDest = ThisDef;
730 // Remove PHI node entries for dead edges.
731 BasicBlock *CheckEdge = TheRealDest;
732 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
733 if (*SI != CheckEdge)
734 (*SI)->removePredecessor(TIBB);
738 // Insert the new branch.
739 Instruction *NI = Builder.CreateBr(TheRealDest);
742 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
743 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
745 EraseTerminatorInstAndDCECond(TI);
750 /// ConstantIntOrdering - This class implements a stable ordering of constant
751 /// integers that does not depend on their address. This is important for
752 /// applications that sort ConstantInt's to ensure uniqueness.
753 struct ConstantIntOrdering {
754 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
755 return LHS->getValue().ult(RHS->getValue());
760 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
761 const ConstantInt *LHS = *(const ConstantInt*const*)P1;
762 const ConstantInt *RHS = *(const ConstantInt*const*)P2;
763 if (LHS->getValue().ult(RHS->getValue()))
765 if (LHS->getValue() == RHS->getValue())
770 static inline bool HasBranchWeights(const Instruction* I) {
771 MDNode* ProfMD = I->getMetadata(LLVMContext::MD_prof);
772 if (ProfMD && ProfMD->getOperand(0))
773 if (MDString* MDS = dyn_cast<MDString>(ProfMD->getOperand(0)))
774 return MDS->getString().equals("branch_weights");
779 /// Get Weights of a given TerminatorInst, the default weight is at the front
780 /// of the vector. If TI is a conditional eq, we need to swap the branch-weight
782 static void GetBranchWeights(TerminatorInst *TI,
783 SmallVectorImpl<uint64_t> &Weights) {
784 MDNode* MD = TI->getMetadata(LLVMContext::MD_prof);
786 for (unsigned i = 1, e = MD->getNumOperands(); i < e; ++i) {
787 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(i));
789 Weights.push_back(CI->getValue().getZExtValue());
792 // If TI is a conditional eq, the default case is the false case,
793 // and the corresponding branch-weight data is at index 2. We swap the
794 // default weight to be the first entry.
795 if (BranchInst* BI = dyn_cast<BranchInst>(TI)) {
796 assert(Weights.size() == 2);
797 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
798 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
799 std::swap(Weights.front(), Weights.back());
803 /// Sees if any of the weights are too big for a uint32_t, and halves all the
804 /// weights if any are.
805 static void FitWeights(MutableArrayRef<uint64_t> Weights) {
807 for (unsigned i = 0; i < Weights.size(); ++i)
808 if (Weights[i] > UINT_MAX) {
816 for (unsigned i = 0; i < Weights.size(); ++i)
820 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
821 /// equality comparison instruction (either a switch or a branch on "X == c").
822 /// See if any of the predecessors of the terminator block are value comparisons
823 /// on the same value. If so, and if safe to do so, fold them together.
824 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
825 IRBuilder<> &Builder) {
826 BasicBlock *BB = TI->getParent();
827 Value *CV = isValueEqualityComparison(TI); // CondVal
828 assert(CV && "Not a comparison?");
829 bool Changed = false;
831 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
832 while (!Preds.empty()) {
833 BasicBlock *Pred = Preds.pop_back_val();
835 // See if the predecessor is a comparison with the same value.
836 TerminatorInst *PTI = Pred->getTerminator();
837 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
839 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
840 // Figure out which 'cases' to copy from SI to PSI.
841 std::vector<ValueEqualityComparisonCase> BBCases;
842 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
844 std::vector<ValueEqualityComparisonCase> PredCases;
845 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
847 // Based on whether the default edge from PTI goes to BB or not, fill in
848 // PredCases and PredDefault with the new switch cases we would like to
850 SmallVector<BasicBlock*, 8> NewSuccessors;
852 // Update the branch weight metadata along the way
853 SmallVector<uint64_t, 8> Weights;
854 bool PredHasWeights = HasBranchWeights(PTI);
855 bool SuccHasWeights = HasBranchWeights(TI);
857 if (PredHasWeights) {
858 GetBranchWeights(PTI, Weights);
859 // branch-weight metadata is inconsistant here.
860 if (Weights.size() != 1 + PredCases.size())
861 PredHasWeights = SuccHasWeights = false;
862 } else if (SuccHasWeights)
863 // If there are no predecessor weights but there are successor weights,
864 // populate Weights with 1, which will later be scaled to the sum of
865 // successor's weights
866 Weights.assign(1 + PredCases.size(), 1);
868 SmallVector<uint64_t, 8> SuccWeights;
869 if (SuccHasWeights) {
870 GetBranchWeights(TI, SuccWeights);
871 // branch-weight metadata is inconsistant here.
872 if (SuccWeights.size() != 1 + BBCases.size())
873 PredHasWeights = SuccHasWeights = false;
874 } else if (PredHasWeights)
875 SuccWeights.assign(1 + BBCases.size(), 1);
877 if (PredDefault == BB) {
878 // If this is the default destination from PTI, only the edges in TI
879 // that don't occur in PTI, or that branch to BB will be activated.
880 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
881 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
882 if (PredCases[i].Dest != BB)
883 PTIHandled.insert(PredCases[i].Value);
885 // The default destination is BB, we don't need explicit targets.
886 std::swap(PredCases[i], PredCases.back());
888 if (PredHasWeights || SuccHasWeights) {
889 // Increase weight for the default case.
890 Weights[0] += Weights[i+1];
891 std::swap(Weights[i+1], Weights.back());
895 PredCases.pop_back();
899 // Reconstruct the new switch statement we will be building.
900 if (PredDefault != BBDefault) {
901 PredDefault->removePredecessor(Pred);
902 PredDefault = BBDefault;
903 NewSuccessors.push_back(BBDefault);
906 unsigned CasesFromPred = Weights.size();
907 uint64_t ValidTotalSuccWeight = 0;
908 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
909 if (!PTIHandled.count(BBCases[i].Value) &&
910 BBCases[i].Dest != BBDefault) {
911 PredCases.push_back(BBCases[i]);
912 NewSuccessors.push_back(BBCases[i].Dest);
913 if (SuccHasWeights || PredHasWeights) {
914 // The default weight is at index 0, so weight for the ith case
915 // should be at index i+1. Scale the cases from successor by
916 // PredDefaultWeight (Weights[0]).
917 Weights.push_back(Weights[0] * SuccWeights[i+1]);
918 ValidTotalSuccWeight += SuccWeights[i+1];
922 if (SuccHasWeights || PredHasWeights) {
923 ValidTotalSuccWeight += SuccWeights[0];
924 // Scale the cases from predecessor by ValidTotalSuccWeight.
925 for (unsigned i = 1; i < CasesFromPred; ++i)
926 Weights[i] *= ValidTotalSuccWeight;
927 // Scale the default weight by SuccDefaultWeight (SuccWeights[0]).
928 Weights[0] *= SuccWeights[0];
931 // If this is not the default destination from PSI, only the edges
932 // in SI that occur in PSI with a destination of BB will be
934 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
935 std::map<ConstantInt*, uint64_t> WeightsForHandled;
936 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
937 if (PredCases[i].Dest == BB) {
938 PTIHandled.insert(PredCases[i].Value);
940 if (PredHasWeights || SuccHasWeights) {
941 WeightsForHandled[PredCases[i].Value] = Weights[i+1];
942 std::swap(Weights[i+1], Weights.back());
946 std::swap(PredCases[i], PredCases.back());
947 PredCases.pop_back();
951 // Okay, now we know which constants were sent to BB from the
952 // predecessor. Figure out where they will all go now.
953 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
954 if (PTIHandled.count(BBCases[i].Value)) {
955 // If this is one we are capable of getting...
956 if (PredHasWeights || SuccHasWeights)
957 Weights.push_back(WeightsForHandled[BBCases[i].Value]);
958 PredCases.push_back(BBCases[i]);
959 NewSuccessors.push_back(BBCases[i].Dest);
960 PTIHandled.erase(BBCases[i].Value);// This constant is taken care of
963 // If there are any constants vectored to BB that TI doesn't handle,
964 // they must go to the default destination of TI.
965 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
967 E = PTIHandled.end(); I != E; ++I) {
968 if (PredHasWeights || SuccHasWeights)
969 Weights.push_back(WeightsForHandled[*I]);
970 PredCases.push_back(ValueEqualityComparisonCase(*I, BBDefault));
971 NewSuccessors.push_back(BBDefault);
975 // Okay, at this point, we know which new successor Pred will get. Make
976 // sure we update the number of entries in the PHI nodes for these
978 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
979 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
981 Builder.SetInsertPoint(PTI);
982 // Convert pointer to int before we switch.
983 if (CV->getType()->isPointerTy()) {
984 assert(TD && "Cannot switch on pointer without TargetData");
985 CV = Builder.CreatePtrToInt(CV, TD->getIntPtrType(CV->getContext()),
989 // Now that the successors are updated, create the new Switch instruction.
990 SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault,
992 NewSI->setDebugLoc(PTI->getDebugLoc());
993 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
994 NewSI->addCase(PredCases[i].Value, PredCases[i].Dest);
996 if (PredHasWeights || SuccHasWeights) {
997 // Halve the weights if any of them cannot fit in an uint32_t
1000 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
1002 NewSI->setMetadata(LLVMContext::MD_prof,
1003 MDBuilder(BB->getContext()).
1004 createBranchWeights(MDWeights));
1007 EraseTerminatorInstAndDCECond(PTI);
1009 // Okay, last check. If BB is still a successor of PSI, then we must
1010 // have an infinite loop case. If so, add an infinitely looping block
1011 // to handle the case to preserve the behavior of the code.
1012 BasicBlock *InfLoopBlock = 0;
1013 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
1014 if (NewSI->getSuccessor(i) == BB) {
1015 if (InfLoopBlock == 0) {
1016 // Insert it at the end of the function, because it's either code,
1017 // or it won't matter if it's hot. :)
1018 InfLoopBlock = BasicBlock::Create(BB->getContext(),
1019 "infloop", BB->getParent());
1020 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1022 NewSI->setSuccessor(i, InfLoopBlock);
1031 // isSafeToHoistInvoke - If we would need to insert a select that uses the
1032 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
1033 // would need to do this), we can't hoist the invoke, as there is nowhere
1034 // to put the select in this case.
1035 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
1036 Instruction *I1, Instruction *I2) {
1037 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
1039 for (BasicBlock::iterator BBI = SI->begin();
1040 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1041 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1042 Value *BB2V = PN->getIncomingValueForBlock(BB2);
1043 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
1051 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
1052 /// BB2, hoist any common code in the two blocks up into the branch block. The
1053 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
1054 static bool HoistThenElseCodeToIf(BranchInst *BI) {
1055 // This does very trivial matching, with limited scanning, to find identical
1056 // instructions in the two blocks. In particular, we don't want to get into
1057 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
1058 // such, we currently just scan for obviously identical instructions in an
1060 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
1061 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
1063 BasicBlock::iterator BB1_Itr = BB1->begin();
1064 BasicBlock::iterator BB2_Itr = BB2->begin();
1066 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
1067 // Skip debug info if it is not identical.
1068 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
1069 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
1070 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
1071 while (isa<DbgInfoIntrinsic>(I1))
1073 while (isa<DbgInfoIntrinsic>(I2))
1076 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
1077 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
1080 // If we get here, we can hoist at least one instruction.
1081 BasicBlock *BIParent = BI->getParent();
1084 // If we are hoisting the terminator instruction, don't move one (making a
1085 // broken BB), instead clone it, and remove BI.
1086 if (isa<TerminatorInst>(I1))
1087 goto HoistTerminator;
1089 // For a normal instruction, we just move one to right before the branch,
1090 // then replace all uses of the other with the first. Finally, we remove
1091 // the now redundant second instruction.
1092 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
1093 if (!I2->use_empty())
1094 I2->replaceAllUsesWith(I1);
1095 I1->intersectOptionalDataWith(I2);
1096 I2->eraseFromParent();
1100 // Skip debug info if it is not identical.
1101 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
1102 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
1103 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
1104 while (isa<DbgInfoIntrinsic>(I1))
1106 while (isa<DbgInfoIntrinsic>(I2))
1109 } while (I1->isIdenticalToWhenDefined(I2));
1114 // It may not be possible to hoist an invoke.
1115 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
1118 // Okay, it is safe to hoist the terminator.
1119 Instruction *NT = I1->clone();
1120 BIParent->getInstList().insert(BI, NT);
1121 if (!NT->getType()->isVoidTy()) {
1122 I1->replaceAllUsesWith(NT);
1123 I2->replaceAllUsesWith(NT);
1127 IRBuilder<true, NoFolder> Builder(NT);
1128 // Hoisting one of the terminators from our successor is a great thing.
1129 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
1130 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
1131 // nodes, so we insert select instruction to compute the final result.
1132 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
1133 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
1135 for (BasicBlock::iterator BBI = SI->begin();
1136 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1137 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1138 Value *BB2V = PN->getIncomingValueForBlock(BB2);
1139 if (BB1V == BB2V) continue;
1141 // These values do not agree. Insert a select instruction before NT
1142 // that determines the right value.
1143 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
1145 SI = cast<SelectInst>
1146 (Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,
1147 BB1V->getName()+"."+BB2V->getName()));
1149 // Make the PHI node use the select for all incoming values for BB1/BB2
1150 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
1151 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
1152 PN->setIncomingValue(i, SI);
1156 // Update any PHI nodes in our new successors.
1157 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
1158 AddPredecessorToBlock(*SI, BIParent, BB1);
1160 EraseTerminatorInstAndDCECond(BI);
1164 /// SinkThenElseCodeToEnd - Given an unconditional branch that goes to BBEnd,
1165 /// check whether BBEnd has only two predecessors and the other predecessor
1166 /// ends with an unconditional branch. If it is true, sink any common code
1167 /// in the two predecessors to BBEnd.
1168 static bool SinkThenElseCodeToEnd(BranchInst *BI1) {
1169 assert(BI1->isUnconditional());
1170 BasicBlock *BB1 = BI1->getParent();
1171 BasicBlock *BBEnd = BI1->getSuccessor(0);
1173 // Check that BBEnd has two predecessors and the other predecessor ends with
1174 // an unconditional branch.
1175 SmallVector<BasicBlock*, 16> Preds(pred_begin(BBEnd), pred_end(BBEnd));
1176 if (Preds.size() != 2)
1178 BasicBlock *BB2 = (Preds[0] == BB1) ? Preds[1] : Preds[0];
1179 BranchInst *BI2 = dyn_cast<BranchInst>(BB2->getTerminator());
1180 if (!BI2 || !BI2->isUnconditional())
1183 // Gather the PHI nodes in BBEnd.
1184 std::map<Value*, std::pair<Value*, PHINode*> > MapValueFromBB1ToBB2;
1185 Instruction *FirstNonPhiInBBEnd = 0;
1186 for (BasicBlock::iterator I = BBEnd->begin(), E = BBEnd->end();
1188 if (PHINode *PN = dyn_cast<PHINode>(I)) {
1189 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1190 Value *BB2V = PN->getIncomingValueForBlock(BB2);
1191 MapValueFromBB1ToBB2[BB1V] = std::make_pair(BB2V, PN);
1193 FirstNonPhiInBBEnd = &*I;
1197 if (!FirstNonPhiInBBEnd)
1201 // This does very trivial matching, with limited scanning, to find identical
1202 // instructions in the two blocks. We scan backward for obviously identical
1203 // instructions in an identical order.
1204 BasicBlock::InstListType::reverse_iterator RI1 = BB1->getInstList().rbegin(),
1205 RE1 = BB1->getInstList().rend(), RI2 = BB2->getInstList().rbegin(),
1206 RE2 = BB2->getInstList().rend();
1208 while (RI1 != RE1 && isa<DbgInfoIntrinsic>(&*RI1)) ++RI1;
1211 while (RI2 != RE2 && isa<DbgInfoIntrinsic>(&*RI2)) ++RI2;
1214 // Skip the unconditional branches.
1218 bool Changed = false;
1219 while (RI1 != RE1 && RI2 != RE2) {
1221 while (RI1 != RE1 && isa<DbgInfoIntrinsic>(&*RI1)) ++RI1;
1224 while (RI2 != RE2 && isa<DbgInfoIntrinsic>(&*RI2)) ++RI2;
1228 Instruction *I1 = &*RI1, *I2 = &*RI2;
1229 // I1 and I2 should have a single use in the same PHI node, and they
1230 // perform the same operation.
1231 // Cannot move control-flow-involving, volatile loads, vaarg, etc.
1232 if (isa<PHINode>(I1) || isa<PHINode>(I2) ||
1233 isa<TerminatorInst>(I1) || isa<TerminatorInst>(I2) ||
1234 isa<LandingPadInst>(I1) || isa<LandingPadInst>(I2) ||
1235 isa<AllocaInst>(I1) || isa<AllocaInst>(I2) ||
1236 I1->mayHaveSideEffects() || I2->mayHaveSideEffects() ||
1237 I1->mayReadOrWriteMemory() || I2->mayReadOrWriteMemory() ||
1238 !I1->hasOneUse() || !I2->hasOneUse() ||
1239 MapValueFromBB1ToBB2.find(I1) == MapValueFromBB1ToBB2.end() ||
1240 MapValueFromBB1ToBB2[I1].first != I2)
1243 // Check whether we should swap the operands of ICmpInst.
1244 ICmpInst *ICmp1 = dyn_cast<ICmpInst>(I1), *ICmp2 = dyn_cast<ICmpInst>(I2);
1245 bool SwapOpnds = false;
1246 if (ICmp1 && ICmp2 &&
1247 ICmp1->getOperand(0) != ICmp2->getOperand(0) &&
1248 ICmp1->getOperand(1) != ICmp2->getOperand(1) &&
1249 (ICmp1->getOperand(0) == ICmp2->getOperand(1) ||
1250 ICmp1->getOperand(1) == ICmp2->getOperand(0))) {
1251 ICmp2->swapOperands();
1254 if (!I1->isSameOperationAs(I2)) {
1256 ICmp2->swapOperands();
1260 // The operands should be either the same or they need to be generated
1261 // with a PHI node after sinking. We only handle the case where there is
1262 // a single pair of different operands.
1263 Value *DifferentOp1 = 0, *DifferentOp2 = 0;
1264 unsigned Op1Idx = 0;
1265 for (unsigned I = 0, E = I1->getNumOperands(); I != E; ++I) {
1266 if (I1->getOperand(I) == I2->getOperand(I))
1268 // Early exit if we have more-than one pair of different operands or
1269 // the different operand is already in MapValueFromBB1ToBB2.
1270 // Early exit if we need a PHI node to replace a constant.
1272 MapValueFromBB1ToBB2.find(I1->getOperand(I)) !=
1273 MapValueFromBB1ToBB2.end() ||
1274 isa<Constant>(I1->getOperand(I)) ||
1275 isa<Constant>(I2->getOperand(I))) {
1276 // If we can't sink the instructions, undo the swapping.
1278 ICmp2->swapOperands();
1281 DifferentOp1 = I1->getOperand(I);
1283 DifferentOp2 = I2->getOperand(I);
1286 // We insert the pair of different operands to MapValueFromBB1ToBB2 and
1287 // remove (I1, I2) from MapValueFromBB1ToBB2.
1289 PHINode *NewPN = PHINode::Create(DifferentOp1->getType(), 2,
1290 DifferentOp1->getName() + ".sink",
1292 MapValueFromBB1ToBB2[DifferentOp1] = std::make_pair(DifferentOp2, NewPN);
1293 // I1 should use NewPN instead of DifferentOp1.
1294 I1->setOperand(Op1Idx, NewPN);
1295 NewPN->addIncoming(DifferentOp1, BB1);
1296 NewPN->addIncoming(DifferentOp2, BB2);
1297 DEBUG(dbgs() << "Create PHI node " << *NewPN << "\n";);
1299 PHINode *OldPN = MapValueFromBB1ToBB2[I1].second;
1300 MapValueFromBB1ToBB2.erase(I1);
1302 DEBUG(dbgs() << "SINK common instructions " << *I1 << "\n";);
1303 DEBUG(dbgs() << " " << *I2 << "\n";);
1304 // We need to update RE1 and RE2 if we are going to sink the first
1305 // instruction in the basic block down.
1306 bool UpdateRE1 = (I1 == BB1->begin()), UpdateRE2 = (I2 == BB2->begin());
1307 // Sink the instruction.
1308 BBEnd->getInstList().splice(FirstNonPhiInBBEnd, BB1->getInstList(), I1);
1309 if (!OldPN->use_empty())
1310 OldPN->replaceAllUsesWith(I1);
1311 OldPN->eraseFromParent();
1313 if (!I2->use_empty())
1314 I2->replaceAllUsesWith(I1);
1315 I1->intersectOptionalDataWith(I2);
1316 I2->eraseFromParent();
1319 RE1 = BB1->getInstList().rend();
1321 RE2 = BB2->getInstList().rend();
1322 FirstNonPhiInBBEnd = I1;
1329 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
1330 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
1331 /// (for now, restricted to a single instruction that's side effect free) from
1332 /// the BB1 into the branch block to speculatively execute it.
1337 /// br i1 %t1, label %BB1, label %BB2
1339 /// %t3 = add %t2, c
1345 /// %t4 = add %t2, c
1346 /// %t3 = select i1 %t1, %t2, %t3
1347 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
1348 // Only speculatively execution a single instruction (not counting the
1349 // terminator) for now.
1350 Instruction *HInst = NULL;
1351 Instruction *Term = BB1->getTerminator();
1352 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
1353 BBI != BBE; ++BBI) {
1354 Instruction *I = BBI;
1356 if (isa<DbgInfoIntrinsic>(I)) continue;
1357 if (I == Term) break;
1364 BasicBlock *BIParent = BI->getParent();
1366 // Check the instruction to be hoisted, if there is one.
1368 // Don't hoist the instruction if it's unsafe or expensive.
1369 if (!isSafeToSpeculativelyExecute(HInst))
1371 if (ComputeSpeculationCost(HInst) > PHINodeFoldingThreshold)
1374 // Do not hoist the instruction if any of its operands are defined but not
1375 // used in this BB. The transformation will prevent the operand from
1376 // being sunk into the use block.
1377 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1379 Instruction *OpI = dyn_cast<Instruction>(*i);
1380 if (OpI && OpI->getParent() == BIParent &&
1381 !OpI->mayHaveSideEffects() &&
1382 !OpI->isUsedInBasicBlock(BIParent))
1387 // Be conservative for now. FP select instruction can often be expensive.
1388 Value *BrCond = BI->getCondition();
1389 if (isa<FCmpInst>(BrCond))
1392 // If BB1 is actually on the false edge of the conditional branch, remember
1393 // to swap the select operands later.
1394 bool Invert = false;
1395 if (BB1 != BI->getSuccessor(0)) {
1396 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
1400 // Collect interesting PHIs, and scan for hazards.
1401 SmallSetVector<std::pair<Value *, Value *>, 4> PHIs;
1402 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
1403 for (BasicBlock::iterator I = BB2->begin();
1404 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1405 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1406 Value *BIParentV = PN->getIncomingValueForBlock(BIParent);
1408 // Skip PHIs which are trivial.
1409 if (BB1V == BIParentV)
1412 // Check for saftey.
1413 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BB1V)) {
1414 // An unfolded ConstantExpr could end up getting expanded into
1415 // Instructions. Don't speculate this and another instruction at
1419 if (!isSafeToSpeculativelyExecute(CE))
1421 if (ComputeSpeculationCost(CE) > PHINodeFoldingThreshold)
1425 // Ok, we may insert a select for this PHI.
1426 PHIs.insert(std::make_pair(BB1V, BIParentV));
1429 // If there are no PHIs to process, bail early. This helps ensure idempotence
1434 // If we get here, we can hoist the instruction and if-convert.
1435 DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *BB1 << "\n";);
1437 // Hoist the instruction.
1439 BIParent->getInstList().splice(BI, BB1->getInstList(), HInst);
1441 // Insert selects and rewrite the PHI operands.
1442 IRBuilder<true, NoFolder> Builder(BI);
1443 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
1444 Value *TrueV = PHIs[i].first;
1445 Value *FalseV = PHIs[i].second;
1447 // Create a select whose true value is the speculatively executed value and
1448 // false value is the previously determined FalseV.
1451 SI = cast<SelectInst>
1452 (Builder.CreateSelect(BrCond, FalseV, TrueV,
1453 FalseV->getName() + "." + TrueV->getName()));
1455 SI = cast<SelectInst>
1456 (Builder.CreateSelect(BrCond, TrueV, FalseV,
1457 TrueV->getName() + "." + FalseV->getName()));
1459 // Make the PHI node use the select for all incoming values for "then" and
1461 for (BasicBlock::iterator I = BB2->begin();
1462 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1463 unsigned BB1I = PN->getBasicBlockIndex(BB1);
1464 unsigned BIParentI = PN->getBasicBlockIndex(BIParent);
1465 Value *BB1V = PN->getIncomingValue(BB1I);
1466 Value *BIParentV = PN->getIncomingValue(BIParentI);
1467 if (TrueV == BB1V && FalseV == BIParentV) {
1468 PN->setIncomingValue(BB1I, SI);
1469 PN->setIncomingValue(BIParentI, SI);
1478 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1479 /// across this block.
1480 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1481 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1484 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1485 if (isa<DbgInfoIntrinsic>(BBI))
1487 if (Size > 10) return false; // Don't clone large BB's.
1490 // We can only support instructions that do not define values that are
1491 // live outside of the current basic block.
1492 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1494 Instruction *U = cast<Instruction>(*UI);
1495 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1498 // Looks ok, continue checking.
1504 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1505 /// that is defined in the same block as the branch and if any PHI entries are
1506 /// constants, thread edges corresponding to that entry to be branches to their
1507 /// ultimate destination.
1508 static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
1509 BasicBlock *BB = BI->getParent();
1510 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1511 // NOTE: we currently cannot transform this case if the PHI node is used
1512 // outside of the block.
1513 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1516 // Degenerate case of a single entry PHI.
1517 if (PN->getNumIncomingValues() == 1) {
1518 FoldSingleEntryPHINodes(PN->getParent());
1522 // Now we know that this block has multiple preds and two succs.
1523 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1525 // Okay, this is a simple enough basic block. See if any phi values are
1527 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1528 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1529 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1531 // Okay, we now know that all edges from PredBB should be revectored to
1532 // branch to RealDest.
1533 BasicBlock *PredBB = PN->getIncomingBlock(i);
1534 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1536 if (RealDest == BB) continue; // Skip self loops.
1537 // Skip if the predecessor's terminator is an indirect branch.
1538 if (isa<IndirectBrInst>(PredBB->getTerminator())) continue;
1540 // The dest block might have PHI nodes, other predecessors and other
1541 // difficult cases. Instead of being smart about this, just insert a new
1542 // block that jumps to the destination block, effectively splitting
1543 // the edge we are about to create.
1544 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1545 RealDest->getName()+".critedge",
1546 RealDest->getParent(), RealDest);
1547 BranchInst::Create(RealDest, EdgeBB);
1549 // Update PHI nodes.
1550 AddPredecessorToBlock(RealDest, EdgeBB, BB);
1552 // BB may have instructions that are being threaded over. Clone these
1553 // instructions into EdgeBB. We know that there will be no uses of the
1554 // cloned instructions outside of EdgeBB.
1555 BasicBlock::iterator InsertPt = EdgeBB->begin();
1556 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1557 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1558 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1559 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1562 // Clone the instruction.
1563 Instruction *N = BBI->clone();
1564 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1566 // Update operands due to translation.
1567 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1569 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1570 if (PI != TranslateMap.end())
1574 // Check for trivial simplification.
1575 if (Value *V = SimplifyInstruction(N, TD)) {
1576 TranslateMap[BBI] = V;
1577 delete N; // Instruction folded away, don't need actual inst
1579 // Insert the new instruction into its new home.
1580 EdgeBB->getInstList().insert(InsertPt, N);
1581 if (!BBI->use_empty())
1582 TranslateMap[BBI] = N;
1586 // Loop over all of the edges from PredBB to BB, changing them to branch
1587 // to EdgeBB instead.
1588 TerminatorInst *PredBBTI = PredBB->getTerminator();
1589 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1590 if (PredBBTI->getSuccessor(i) == BB) {
1591 BB->removePredecessor(PredBB);
1592 PredBBTI->setSuccessor(i, EdgeBB);
1595 // Recurse, simplifying any other constants.
1596 return FoldCondBranchOnPHI(BI, TD) | true;
1602 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1603 /// PHI node, see if we can eliminate it.
1604 static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
1605 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1606 // statement", which has a very simple dominance structure. Basically, we
1607 // are trying to find the condition that is being branched on, which
1608 // subsequently causes this merge to happen. We really want control
1609 // dependence information for this check, but simplifycfg can't keep it up
1610 // to date, and this catches most of the cases we care about anyway.
1611 BasicBlock *BB = PN->getParent();
1612 BasicBlock *IfTrue, *IfFalse;
1613 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1615 // Don't bother if the branch will be constant folded trivially.
1616 isa<ConstantInt>(IfCond))
1619 // Okay, we found that we can merge this two-entry phi node into a select.
1620 // Doing so would require us to fold *all* two entry phi nodes in this block.
1621 // At some point this becomes non-profitable (particularly if the target
1622 // doesn't support cmov's). Only do this transformation if there are two or
1623 // fewer PHI nodes in this block.
1624 unsigned NumPhis = 0;
1625 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1629 // Loop over the PHI's seeing if we can promote them all to select
1630 // instructions. While we are at it, keep track of the instructions
1631 // that need to be moved to the dominating block.
1632 SmallPtrSet<Instruction*, 4> AggressiveInsts;
1633 unsigned MaxCostVal0 = PHINodeFoldingThreshold,
1634 MaxCostVal1 = PHINodeFoldingThreshold;
1636 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1637 PHINode *PN = cast<PHINode>(II++);
1638 if (Value *V = SimplifyInstruction(PN, TD)) {
1639 PN->replaceAllUsesWith(V);
1640 PN->eraseFromParent();
1644 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
1646 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
1651 // If we folded the first phi, PN dangles at this point. Refresh it. If
1652 // we ran out of PHIs then we simplified them all.
1653 PN = dyn_cast<PHINode>(BB->begin());
1654 if (PN == 0) return true;
1656 // Don't fold i1 branches on PHIs which contain binary operators. These can
1657 // often be turned into switches and other things.
1658 if (PN->getType()->isIntegerTy(1) &&
1659 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1660 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1661 isa<BinaryOperator>(IfCond)))
1664 // If we all PHI nodes are promotable, check to make sure that all
1665 // instructions in the predecessor blocks can be promoted as well. If
1666 // not, we won't be able to get rid of the control flow, so it's not
1667 // worth promoting to select instructions.
1668 BasicBlock *DomBlock = 0;
1669 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1670 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1671 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1674 DomBlock = *pred_begin(IfBlock1);
1675 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1676 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1677 // This is not an aggressive instruction that we can promote.
1678 // Because of this, we won't be able to get rid of the control
1679 // flow, so the xform is not worth it.
1684 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1687 DomBlock = *pred_begin(IfBlock2);
1688 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1689 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1690 // This is not an aggressive instruction that we can promote.
1691 // Because of this, we won't be able to get rid of the control
1692 // flow, so the xform is not worth it.
1697 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1698 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1700 // If we can still promote the PHI nodes after this gauntlet of tests,
1701 // do all of the PHI's now.
1702 Instruction *InsertPt = DomBlock->getTerminator();
1703 IRBuilder<true, NoFolder> Builder(InsertPt);
1705 // Move all 'aggressive' instructions, which are defined in the
1706 // conditional parts of the if's up to the dominating block.
1708 DomBlock->getInstList().splice(InsertPt,
1709 IfBlock1->getInstList(), IfBlock1->begin(),
1710 IfBlock1->getTerminator());
1712 DomBlock->getInstList().splice(InsertPt,
1713 IfBlock2->getInstList(), IfBlock2->begin(),
1714 IfBlock2->getTerminator());
1716 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1717 // Change the PHI node into a select instruction.
1718 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1719 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1722 cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, ""));
1723 PN->replaceAllUsesWith(NV);
1725 PN->eraseFromParent();
1728 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1729 // has been flattened. Change DomBlock to jump directly to our new block to
1730 // avoid other simplifycfg's kicking in on the diamond.
1731 TerminatorInst *OldTI = DomBlock->getTerminator();
1732 Builder.SetInsertPoint(OldTI);
1733 Builder.CreateBr(BB);
1734 OldTI->eraseFromParent();
1738 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1739 /// to two returning blocks, try to merge them together into one return,
1740 /// introducing a select if the return values disagree.
1741 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
1742 IRBuilder<> &Builder) {
1743 assert(BI->isConditional() && "Must be a conditional branch");
1744 BasicBlock *TrueSucc = BI->getSuccessor(0);
1745 BasicBlock *FalseSucc = BI->getSuccessor(1);
1746 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1747 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1749 // Check to ensure both blocks are empty (just a return) or optionally empty
1750 // with PHI nodes. If there are other instructions, merging would cause extra
1751 // computation on one path or the other.
1752 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1754 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1757 Builder.SetInsertPoint(BI);
1758 // Okay, we found a branch that is going to two return nodes. If
1759 // there is no return value for this function, just change the
1760 // branch into a return.
1761 if (FalseRet->getNumOperands() == 0) {
1762 TrueSucc->removePredecessor(BI->getParent());
1763 FalseSucc->removePredecessor(BI->getParent());
1764 Builder.CreateRetVoid();
1765 EraseTerminatorInstAndDCECond(BI);
1769 // Otherwise, figure out what the true and false return values are
1770 // so we can insert a new select instruction.
1771 Value *TrueValue = TrueRet->getReturnValue();
1772 Value *FalseValue = FalseRet->getReturnValue();
1774 // Unwrap any PHI nodes in the return blocks.
1775 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1776 if (TVPN->getParent() == TrueSucc)
1777 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1778 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1779 if (FVPN->getParent() == FalseSucc)
1780 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1782 // In order for this transformation to be safe, we must be able to
1783 // unconditionally execute both operands to the return. This is
1784 // normally the case, but we could have a potentially-trapping
1785 // constant expression that prevents this transformation from being
1787 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1790 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1794 // Okay, we collected all the mapped values and checked them for sanity, and
1795 // defined to really do this transformation. First, update the CFG.
1796 TrueSucc->removePredecessor(BI->getParent());
1797 FalseSucc->removePredecessor(BI->getParent());
1799 // Insert select instructions where needed.
1800 Value *BrCond = BI->getCondition();
1802 // Insert a select if the results differ.
1803 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1804 } else if (isa<UndefValue>(TrueValue)) {
1805 TrueValue = FalseValue;
1807 TrueValue = Builder.CreateSelect(BrCond, TrueValue,
1808 FalseValue, "retval");
1812 Value *RI = !TrueValue ?
1813 Builder.CreateRetVoid() : Builder.CreateRet(TrueValue);
1817 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1818 << "\n " << *BI << "NewRet = " << *RI
1819 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1821 EraseTerminatorInstAndDCECond(BI);
1826 /// ExtractBranchMetadata - Given a conditional BranchInstruction, retrieve the
1827 /// probabilities of the branch taking each edge. Fills in the two APInt
1828 /// parameters and return true, or returns false if no or invalid metadata was
1830 static bool ExtractBranchMetadata(BranchInst *BI,
1831 uint64_t &ProbTrue, uint64_t &ProbFalse) {
1832 assert(BI->isConditional() &&
1833 "Looking for probabilities on unconditional branch?");
1834 MDNode *ProfileData = BI->getMetadata(LLVMContext::MD_prof);
1835 if (!ProfileData || ProfileData->getNumOperands() != 3) return false;
1836 ConstantInt *CITrue = dyn_cast<ConstantInt>(ProfileData->getOperand(1));
1837 ConstantInt *CIFalse = dyn_cast<ConstantInt>(ProfileData->getOperand(2));
1838 if (!CITrue || !CIFalse) return false;
1839 ProbTrue = CITrue->getValue().getZExtValue();
1840 ProbFalse = CIFalse->getValue().getZExtValue();
1844 /// checkCSEInPredecessor - Return true if the given instruction is available
1845 /// in its predecessor block. If yes, the instruction will be removed.
1847 static bool checkCSEInPredecessor(Instruction *Inst, BasicBlock *PB) {
1848 if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst))
1850 for (BasicBlock::iterator I = PB->begin(), E = PB->end(); I != E; I++) {
1851 Instruction *PBI = &*I;
1852 // Check whether Inst and PBI generate the same value.
1853 if (Inst->isIdenticalTo(PBI)) {
1854 Inst->replaceAllUsesWith(PBI);
1855 Inst->eraseFromParent();
1862 /// FoldBranchToCommonDest - If this basic block is simple enough, and if a
1863 /// predecessor branches to us and one of our successors, fold the block into
1864 /// the predecessor and use logical operations to pick the right destination.
1865 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1866 BasicBlock *BB = BI->getParent();
1868 Instruction *Cond = 0;
1869 if (BI->isConditional())
1870 Cond = dyn_cast<Instruction>(BI->getCondition());
1872 // For unconditional branch, check for a simple CFG pattern, where
1873 // BB has a single predecessor and BB's successor is also its predecessor's
1874 // successor. If such pattern exisits, check for CSE between BB and its
1876 if (BasicBlock *PB = BB->getSinglePredecessor())
1877 if (BranchInst *PBI = dyn_cast<BranchInst>(PB->getTerminator()))
1878 if (PBI->isConditional() &&
1879 (BI->getSuccessor(0) == PBI->getSuccessor(0) ||
1880 BI->getSuccessor(0) == PBI->getSuccessor(1))) {
1881 for (BasicBlock::iterator I = BB->begin(), E = BB->end();
1883 Instruction *Curr = I++;
1884 if (isa<CmpInst>(Curr)) {
1888 // Quit if we can't remove this instruction.
1889 if (!checkCSEInPredecessor(Curr, PB))
1898 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1899 Cond->getParent() != BB || !Cond->hasOneUse())
1902 // Only allow this if the condition is a simple instruction that can be
1903 // executed unconditionally. It must be in the same block as the branch, and
1904 // must be at the front of the block.
1905 BasicBlock::iterator FrontIt = BB->front();
1907 // Ignore dbg intrinsics.
1908 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1910 // Allow a single instruction to be hoisted in addition to the compare
1911 // that feeds the branch. We later ensure that any values that _it_ uses
1912 // were also live in the predecessor, so that we don't unnecessarily create
1913 // register pressure or inhibit out-of-order execution.
1914 Instruction *BonusInst = 0;
1915 if (&*FrontIt != Cond &&
1916 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1917 isSafeToSpeculativelyExecute(FrontIt)) {
1918 BonusInst = &*FrontIt;
1921 // Ignore dbg intrinsics.
1922 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1925 // Only a single bonus inst is allowed.
1926 if (&*FrontIt != Cond)
1929 // Make sure the instruction after the condition is the cond branch.
1930 BasicBlock::iterator CondIt = Cond; ++CondIt;
1932 // Ingore dbg intrinsics.
1933 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
1938 // Cond is known to be a compare or binary operator. Check to make sure that
1939 // neither operand is a potentially-trapping constant expression.
1940 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1943 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1947 // Finally, don't infinitely unroll conditional loops.
1948 BasicBlock *TrueDest = BI->getSuccessor(0);
1949 BasicBlock *FalseDest = (BI->isConditional()) ? BI->getSuccessor(1) : 0;
1950 if (TrueDest == BB || FalseDest == BB)
1953 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1954 BasicBlock *PredBlock = *PI;
1955 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1957 // Check that we have two conditional branches. If there is a PHI node in
1958 // the common successor, verify that the same value flows in from both
1960 SmallVector<PHINode*, 4> PHIs;
1961 if (PBI == 0 || PBI->isUnconditional() ||
1962 (BI->isConditional() &&
1963 !SafeToMergeTerminators(BI, PBI)) ||
1964 (!BI->isConditional() &&
1965 !isProfitableToFoldUnconditional(BI, PBI, Cond, PHIs)))
1968 // Determine if the two branches share a common destination.
1969 Instruction::BinaryOps Opc = Instruction::BinaryOpsEnd;
1970 bool InvertPredCond = false;
1972 if (BI->isConditional()) {
1973 if (PBI->getSuccessor(0) == TrueDest)
1974 Opc = Instruction::Or;
1975 else if (PBI->getSuccessor(1) == FalseDest)
1976 Opc = Instruction::And;
1977 else if (PBI->getSuccessor(0) == FalseDest)
1978 Opc = Instruction::And, InvertPredCond = true;
1979 else if (PBI->getSuccessor(1) == TrueDest)
1980 Opc = Instruction::Or, InvertPredCond = true;
1984 if (PBI->getSuccessor(0) != TrueDest && PBI->getSuccessor(1) != TrueDest)
1988 // Ensure that any values used in the bonus instruction are also used
1989 // by the terminator of the predecessor. This means that those values
1990 // must already have been resolved, so we won't be inhibiting the
1991 // out-of-order core by speculating them earlier.
1993 // Collect the values used by the bonus inst
1994 SmallPtrSet<Value*, 4> UsedValues;
1995 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1996 OE = BonusInst->op_end(); OI != OE; ++OI) {
1998 if (!isa<Constant>(V))
1999 UsedValues.insert(V);
2002 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
2003 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
2005 // Walk up to four levels back up the use-def chain of the predecessor's
2006 // terminator to see if all those values were used. The choice of four
2007 // levels is arbitrary, to provide a compile-time-cost bound.
2008 while (!Worklist.empty()) {
2009 std::pair<Value*, unsigned> Pair = Worklist.back();
2010 Worklist.pop_back();
2012 if (Pair.second >= 4) continue;
2013 UsedValues.erase(Pair.first);
2014 if (UsedValues.empty()) break;
2016 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
2017 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
2019 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
2023 if (!UsedValues.empty()) return false;
2026 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
2027 IRBuilder<> Builder(PBI);
2029 // If we need to invert the condition in the pred block to match, do so now.
2030 if (InvertPredCond) {
2031 Value *NewCond = PBI->getCondition();
2033 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
2034 CmpInst *CI = cast<CmpInst>(NewCond);
2035 CI->setPredicate(CI->getInversePredicate());
2037 NewCond = Builder.CreateNot(NewCond,
2038 PBI->getCondition()->getName()+".not");
2041 PBI->setCondition(NewCond);
2042 PBI->swapSuccessors();
2045 // If we have a bonus inst, clone it into the predecessor block.
2046 Instruction *NewBonus = 0;
2048 NewBonus = BonusInst->clone();
2049 PredBlock->getInstList().insert(PBI, NewBonus);
2050 NewBonus->takeName(BonusInst);
2051 BonusInst->setName(BonusInst->getName()+".old");
2054 // Clone Cond into the predecessor basic block, and or/and the
2055 // two conditions together.
2056 Instruction *New = Cond->clone();
2057 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
2058 PredBlock->getInstList().insert(PBI, New);
2059 New->takeName(Cond);
2060 Cond->setName(New->getName()+".old");
2062 if (BI->isConditional()) {
2063 Instruction *NewCond =
2064 cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(),
2066 PBI->setCondition(NewCond);
2068 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
2069 bool PredHasWeights = ExtractBranchMetadata(PBI, PredTrueWeight,
2071 bool SuccHasWeights = ExtractBranchMetadata(BI, SuccTrueWeight,
2073 SmallVector<uint64_t, 8> NewWeights;
2075 if (PBI->getSuccessor(0) == BB) {
2076 if (PredHasWeights && SuccHasWeights) {
2077 // PBI: br i1 %x, BB, FalseDest
2078 // BI: br i1 %y, TrueDest, FalseDest
2079 //TrueWeight is TrueWeight for PBI * TrueWeight for BI.
2080 NewWeights.push_back(PredTrueWeight * SuccTrueWeight);
2081 //FalseWeight is FalseWeight for PBI * TotalWeight for BI +
2082 // TrueWeight for PBI * FalseWeight for BI.
2083 // We assume that total weights of a BranchInst can fit into 32 bits.
2084 // Therefore, we will not have overflow using 64-bit arithmetic.
2085 NewWeights.push_back(PredFalseWeight * (SuccFalseWeight +
2086 SuccTrueWeight) + PredTrueWeight * SuccFalseWeight);
2088 AddPredecessorToBlock(TrueDest, PredBlock, BB);
2089 PBI->setSuccessor(0, TrueDest);
2091 if (PBI->getSuccessor(1) == BB) {
2092 if (PredHasWeights && SuccHasWeights) {
2093 // PBI: br i1 %x, TrueDest, BB
2094 // BI: br i1 %y, TrueDest, FalseDest
2095 //TrueWeight is TrueWeight for PBI * TotalWeight for BI +
2096 // FalseWeight for PBI * TrueWeight for BI.
2097 NewWeights.push_back(PredTrueWeight * (SuccFalseWeight +
2098 SuccTrueWeight) + PredFalseWeight * SuccTrueWeight);
2099 //FalseWeight is FalseWeight for PBI * FalseWeight for BI.
2100 NewWeights.push_back(PredFalseWeight * SuccFalseWeight);
2102 AddPredecessorToBlock(FalseDest, PredBlock, BB);
2103 PBI->setSuccessor(1, FalseDest);
2105 if (NewWeights.size() == 2) {
2106 // Halve the weights if any of them cannot fit in an uint32_t
2107 FitWeights(NewWeights);
2109 SmallVector<uint32_t, 8> MDWeights(NewWeights.begin(),NewWeights.end());
2110 PBI->setMetadata(LLVMContext::MD_prof,
2111 MDBuilder(BI->getContext()).
2112 createBranchWeights(MDWeights));
2114 PBI->setMetadata(LLVMContext::MD_prof, NULL);
2116 // Update PHI nodes in the common successors.
2117 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
2118 ConstantInt *PBI_C = cast<ConstantInt>(
2119 PHIs[i]->getIncomingValueForBlock(PBI->getParent()));
2120 assert(PBI_C->getType()->isIntegerTy(1));
2121 Instruction *MergedCond = 0;
2122 if (PBI->getSuccessor(0) == TrueDest) {
2123 // Create (PBI_Cond and PBI_C) or (!PBI_Cond and BI_Value)
2124 // PBI_C is true: PBI_Cond or (!PBI_Cond and BI_Value)
2125 // is false: !PBI_Cond and BI_Value
2126 Instruction *NotCond =
2127 cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
2130 cast<Instruction>(Builder.CreateBinOp(Instruction::And,
2135 cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
2136 PBI->getCondition(), MergedCond,
2139 // Create (PBI_Cond and BI_Value) or (!PBI_Cond and PBI_C)
2140 // PBI_C is true: (PBI_Cond and BI_Value) or (!PBI_Cond)
2141 // is false: PBI_Cond and BI_Value
2143 cast<Instruction>(Builder.CreateBinOp(Instruction::And,
2144 PBI->getCondition(), New,
2146 if (PBI_C->isOne()) {
2147 Instruction *NotCond =
2148 cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
2151 cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
2152 NotCond, MergedCond,
2157 PHIs[i]->setIncomingValue(PHIs[i]->getBasicBlockIndex(PBI->getParent()),
2160 // Change PBI from Conditional to Unconditional.
2161 BranchInst *New_PBI = BranchInst::Create(TrueDest, PBI);
2162 EraseTerminatorInstAndDCECond(PBI);
2166 // TODO: If BB is reachable from all paths through PredBlock, then we
2167 // could replace PBI's branch probabilities with BI's.
2169 // Copy any debug value intrinsics into the end of PredBlock.
2170 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
2171 if (isa<DbgInfoIntrinsic>(*I))
2172 I->clone()->insertBefore(PBI);
2179 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
2180 /// predecessor of another block, this function tries to simplify it. We know
2181 /// that PBI and BI are both conditional branches, and BI is in one of the
2182 /// successor blocks of PBI - PBI branches to BI.
2183 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
2184 assert(PBI->isConditional() && BI->isConditional());
2185 BasicBlock *BB = BI->getParent();
2187 // If this block ends with a branch instruction, and if there is a
2188 // predecessor that ends on a branch of the same condition, make
2189 // this conditional branch redundant.
2190 if (PBI->getCondition() == BI->getCondition() &&
2191 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
2192 // Okay, the outcome of this conditional branch is statically
2193 // knowable. If this block had a single pred, handle specially.
2194 if (BB->getSinglePredecessor()) {
2195 // Turn this into a branch on constant.
2196 bool CondIsTrue = PBI->getSuccessor(0) == BB;
2197 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
2199 return true; // Nuke the branch on constant.
2202 // Otherwise, if there are multiple predecessors, insert a PHI that merges
2203 // in the constant and simplify the block result. Subsequent passes of
2204 // simplifycfg will thread the block.
2205 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
2206 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
2207 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
2208 std::distance(PB, PE),
2209 BI->getCondition()->getName() + ".pr",
2211 // Okay, we're going to insert the PHI node. Since PBI is not the only
2212 // predecessor, compute the PHI'd conditional value for all of the preds.
2213 // Any predecessor where the condition is not computable we keep symbolic.
2214 for (pred_iterator PI = PB; PI != PE; ++PI) {
2215 BasicBlock *P = *PI;
2216 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
2217 PBI != BI && PBI->isConditional() &&
2218 PBI->getCondition() == BI->getCondition() &&
2219 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
2220 bool CondIsTrue = PBI->getSuccessor(0) == BB;
2221 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
2224 NewPN->addIncoming(BI->getCondition(), P);
2228 BI->setCondition(NewPN);
2233 // If this is a conditional branch in an empty block, and if any
2234 // predecessors is a conditional branch to one of our destinations,
2235 // fold the conditions into logical ops and one cond br.
2236 BasicBlock::iterator BBI = BB->begin();
2237 // Ignore dbg intrinsics.
2238 while (isa<DbgInfoIntrinsic>(BBI))
2244 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
2249 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
2251 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
2252 PBIOp = 0, BIOp = 1;
2253 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
2254 PBIOp = 1, BIOp = 0;
2255 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
2260 // Check to make sure that the other destination of this branch
2261 // isn't BB itself. If so, this is an infinite loop that will
2262 // keep getting unwound.
2263 if (PBI->getSuccessor(PBIOp) == BB)
2266 // Do not perform this transformation if it would require
2267 // insertion of a large number of select instructions. For targets
2268 // without predication/cmovs, this is a big pessimization.
2269 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
2271 unsigned NumPhis = 0;
2272 for (BasicBlock::iterator II = CommonDest->begin();
2273 isa<PHINode>(II); ++II, ++NumPhis)
2274 if (NumPhis > 2) // Disable this xform.
2277 // Finally, if everything is ok, fold the branches to logical ops.
2278 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
2280 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
2281 << "AND: " << *BI->getParent());
2284 // If OtherDest *is* BB, then BB is a basic block with a single conditional
2285 // branch in it, where one edge (OtherDest) goes back to itself but the other
2286 // exits. We don't *know* that the program avoids the infinite loop
2287 // (even though that seems likely). If we do this xform naively, we'll end up
2288 // recursively unpeeling the loop. Since we know that (after the xform is
2289 // done) that the block *is* infinite if reached, we just make it an obviously
2290 // infinite loop with no cond branch.
2291 if (OtherDest == BB) {
2292 // Insert it at the end of the function, because it's either code,
2293 // or it won't matter if it's hot. :)
2294 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
2295 "infloop", BB->getParent());
2296 BranchInst::Create(InfLoopBlock, InfLoopBlock);
2297 OtherDest = InfLoopBlock;
2300 DEBUG(dbgs() << *PBI->getParent()->getParent());
2302 // BI may have other predecessors. Because of this, we leave
2303 // it alone, but modify PBI.
2305 // Make sure we get to CommonDest on True&True directions.
2306 Value *PBICond = PBI->getCondition();
2307 IRBuilder<true, NoFolder> Builder(PBI);
2309 PBICond = Builder.CreateNot(PBICond, PBICond->getName()+".not");
2311 Value *BICond = BI->getCondition();
2313 BICond = Builder.CreateNot(BICond, BICond->getName()+".not");
2315 // Merge the conditions.
2316 Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge");
2318 // Modify PBI to branch on the new condition to the new dests.
2319 PBI->setCondition(Cond);
2320 PBI->setSuccessor(0, CommonDest);
2321 PBI->setSuccessor(1, OtherDest);
2323 // Update branch weight for PBI.
2324 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
2325 bool PredHasWeights = ExtractBranchMetadata(PBI, PredTrueWeight,
2327 bool SuccHasWeights = ExtractBranchMetadata(BI, SuccTrueWeight,
2329 if (PredHasWeights && SuccHasWeights) {
2330 uint64_t PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
2331 uint64_t PredOther = PBIOp ?PredTrueWeight : PredFalseWeight;
2332 uint64_t SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
2333 uint64_t SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
2334 // The weight to CommonDest should be PredCommon * SuccTotal +
2335 // PredOther * SuccCommon.
2336 // The weight to OtherDest should be PredOther * SuccOther.
2337 SmallVector<uint64_t, 2> NewWeights;
2338 NewWeights.push_back(PredCommon * (SuccCommon + SuccOther) +
2339 PredOther * SuccCommon);
2340 NewWeights.push_back(PredOther * SuccOther);
2341 // Halve the weights if any of them cannot fit in an uint32_t
2342 FitWeights(NewWeights);
2344 SmallVector<uint32_t, 2> MDWeights(NewWeights.begin(),NewWeights.end());
2345 PBI->setMetadata(LLVMContext::MD_prof,
2346 MDBuilder(BI->getContext()).
2347 createBranchWeights(MDWeights));
2350 // OtherDest may have phi nodes. If so, add an entry from PBI's
2351 // block that are identical to the entries for BI's block.
2352 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
2354 // We know that the CommonDest already had an edge from PBI to
2355 // it. If it has PHIs though, the PHIs may have different
2356 // entries for BB and PBI's BB. If so, insert a select to make
2359 for (BasicBlock::iterator II = CommonDest->begin();
2360 (PN = dyn_cast<PHINode>(II)); ++II) {
2361 Value *BIV = PN->getIncomingValueForBlock(BB);
2362 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
2363 Value *PBIV = PN->getIncomingValue(PBBIdx);
2365 // Insert a select in PBI to pick the right value.
2366 Value *NV = cast<SelectInst>
2367 (Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName()+".mux"));
2368 PN->setIncomingValue(PBBIdx, NV);
2372 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
2373 DEBUG(dbgs() << *PBI->getParent()->getParent());
2375 // This basic block is probably dead. We know it has at least
2376 // one fewer predecessor.
2380 // SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
2381 // branch to TrueBB if Cond is true or to FalseBB if Cond is false.
2382 // Takes care of updating the successors and removing the old terminator.
2383 // Also makes sure not to introduce new successors by assuming that edges to
2384 // non-successor TrueBBs and FalseBBs aren't reachable.
2385 static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
2386 BasicBlock *TrueBB, BasicBlock *FalseBB,
2387 uint32_t TrueWeight,
2388 uint32_t FalseWeight){
2389 // Remove any superfluous successor edges from the CFG.
2390 // First, figure out which successors to preserve.
2391 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
2393 BasicBlock *KeepEdge1 = TrueBB;
2394 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
2396 // Then remove the rest.
2397 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
2398 BasicBlock *Succ = OldTerm->getSuccessor(I);
2399 // Make sure only to keep exactly one copy of each edge.
2400 if (Succ == KeepEdge1)
2402 else if (Succ == KeepEdge2)
2405 Succ->removePredecessor(OldTerm->getParent());
2408 IRBuilder<> Builder(OldTerm);
2409 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
2411 // Insert an appropriate new terminator.
2412 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
2413 if (TrueBB == FalseBB)
2414 // We were only looking for one successor, and it was present.
2415 // Create an unconditional branch to it.
2416 Builder.CreateBr(TrueBB);
2418 // We found both of the successors we were looking for.
2419 // Create a conditional branch sharing the condition of the select.
2420 BranchInst *NewBI = Builder.CreateCondBr(Cond, TrueBB, FalseBB);
2421 if (TrueWeight != FalseWeight)
2422 NewBI->setMetadata(LLVMContext::MD_prof,
2423 MDBuilder(OldTerm->getContext()).
2424 createBranchWeights(TrueWeight, FalseWeight));
2426 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
2427 // Neither of the selected blocks were successors, so this
2428 // terminator must be unreachable.
2429 new UnreachableInst(OldTerm->getContext(), OldTerm);
2431 // One of the selected values was a successor, but the other wasn't.
2432 // Insert an unconditional branch to the one that was found;
2433 // the edge to the one that wasn't must be unreachable.
2435 // Only TrueBB was found.
2436 Builder.CreateBr(TrueBB);
2438 // Only FalseBB was found.
2439 Builder.CreateBr(FalseBB);
2442 EraseTerminatorInstAndDCECond(OldTerm);
2446 // SimplifySwitchOnSelect - Replaces
2447 // (switch (select cond, X, Y)) on constant X, Y
2448 // with a branch - conditional if X and Y lead to distinct BBs,
2449 // unconditional otherwise.
2450 static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
2451 // Check for constant integer values in the select.
2452 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
2453 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
2454 if (!TrueVal || !FalseVal)
2457 // Find the relevant condition and destinations.
2458 Value *Condition = Select->getCondition();
2459 BasicBlock *TrueBB = SI->findCaseValue(TrueVal).getCaseSuccessor();
2460 BasicBlock *FalseBB = SI->findCaseValue(FalseVal).getCaseSuccessor();
2462 // Get weight for TrueBB and FalseBB.
2463 uint32_t TrueWeight = 0, FalseWeight = 0;
2464 SmallVector<uint64_t, 8> Weights;
2465 bool HasWeights = HasBranchWeights(SI);
2467 GetBranchWeights(SI, Weights);
2468 if (Weights.size() == 1 + SI->getNumCases()) {
2469 TrueWeight = (uint32_t)Weights[SI->findCaseValue(TrueVal).
2470 getSuccessorIndex()];
2471 FalseWeight = (uint32_t)Weights[SI->findCaseValue(FalseVal).
2472 getSuccessorIndex()];
2476 // Perform the actual simplification.
2477 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB,
2478 TrueWeight, FalseWeight);
2481 // SimplifyIndirectBrOnSelect - Replaces
2482 // (indirectbr (select cond, blockaddress(@fn, BlockA),
2483 // blockaddress(@fn, BlockB)))
2485 // (br cond, BlockA, BlockB).
2486 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
2487 // Check that both operands of the select are block addresses.
2488 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
2489 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
2493 // Extract the actual blocks.
2494 BasicBlock *TrueBB = TBA->getBasicBlock();
2495 BasicBlock *FalseBB = FBA->getBasicBlock();
2497 // Perform the actual simplification.
2498 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB,
2502 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
2503 /// instruction (a seteq/setne with a constant) as the only instruction in a
2504 /// block that ends with an uncond branch. We are looking for a very specific
2505 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
2506 /// this case, we merge the first two "or's of icmp" into a switch, but then the
2507 /// default value goes to an uncond block with a seteq in it, we get something
2510 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
2512 /// %tmp = icmp eq i8 %A, 92
2515 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
2517 /// We prefer to split the edge to 'end' so that there is a true/false entry to
2518 /// the PHI, merging the third icmp into the switch.
2519 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
2520 const TargetData *TD,
2521 IRBuilder<> &Builder) {
2522 BasicBlock *BB = ICI->getParent();
2524 // If the block has any PHIs in it or the icmp has multiple uses, it is too
2526 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
2528 Value *V = ICI->getOperand(0);
2529 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
2531 // The pattern we're looking for is where our only predecessor is a switch on
2532 // 'V' and this block is the default case for the switch. In this case we can
2533 // fold the compared value into the switch to simplify things.
2534 BasicBlock *Pred = BB->getSinglePredecessor();
2535 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
2537 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
2538 if (SI->getCondition() != V)
2541 // If BB is reachable on a non-default case, then we simply know the value of
2542 // V in this block. Substitute it and constant fold the icmp instruction
2544 if (SI->getDefaultDest() != BB) {
2545 ConstantInt *VVal = SI->findCaseDest(BB);
2546 assert(VVal && "Should have a unique destination value");
2547 ICI->setOperand(0, VVal);
2549 if (Value *V = SimplifyInstruction(ICI, TD)) {
2550 ICI->replaceAllUsesWith(V);
2551 ICI->eraseFromParent();
2553 // BB is now empty, so it is likely to simplify away.
2554 return SimplifyCFG(BB) | true;
2557 // Ok, the block is reachable from the default dest. If the constant we're
2558 // comparing exists in one of the other edges, then we can constant fold ICI
2560 if (SI->findCaseValue(Cst) != SI->case_default()) {
2562 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2563 V = ConstantInt::getFalse(BB->getContext());
2565 V = ConstantInt::getTrue(BB->getContext());
2567 ICI->replaceAllUsesWith(V);
2568 ICI->eraseFromParent();
2569 // BB is now empty, so it is likely to simplify away.
2570 return SimplifyCFG(BB) | true;
2573 // The use of the icmp has to be in the 'end' block, by the only PHI node in
2575 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
2576 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
2577 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
2578 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
2581 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
2583 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
2584 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
2586 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2587 std::swap(DefaultCst, NewCst);
2589 // Replace ICI (which is used by the PHI for the default value) with true or
2590 // false depending on if it is EQ or NE.
2591 ICI->replaceAllUsesWith(DefaultCst);
2592 ICI->eraseFromParent();
2594 // Okay, the switch goes to this block on a default value. Add an edge from
2595 // the switch to the merge point on the compared value.
2596 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
2597 BB->getParent(), BB);
2598 SmallVector<uint64_t, 8> Weights;
2599 bool HasWeights = HasBranchWeights(SI);
2601 GetBranchWeights(SI, Weights);
2602 if (Weights.size() == 1 + SI->getNumCases()) {
2603 // Split weight for default case to case for "Cst".
2604 Weights[0] = (Weights[0]+1) >> 1;
2605 Weights.push_back(Weights[0]);
2607 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
2608 SI->setMetadata(LLVMContext::MD_prof,
2609 MDBuilder(SI->getContext()).
2610 createBranchWeights(MDWeights));
2613 SI->addCase(Cst, NewBB);
2615 // NewBB branches to the phi block, add the uncond branch and the phi entry.
2616 Builder.SetInsertPoint(NewBB);
2617 Builder.SetCurrentDebugLocation(SI->getDebugLoc());
2618 Builder.CreateBr(SuccBlock);
2619 PHIUse->addIncoming(NewCst, NewBB);
2623 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
2624 /// Check to see if it is branching on an or/and chain of icmp instructions, and
2625 /// fold it into a switch instruction if so.
2626 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD,
2627 IRBuilder<> &Builder) {
2628 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
2629 if (Cond == 0) return false;
2632 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2633 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2634 // 'setne's and'ed together, collect them.
2636 std::vector<ConstantInt*> Values;
2637 bool TrueWhenEqual = true;
2638 Value *ExtraCase = 0;
2639 unsigned UsedICmps = 0;
2641 if (Cond->getOpcode() == Instruction::Or) {
2642 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
2644 } else if (Cond->getOpcode() == Instruction::And) {
2645 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
2647 TrueWhenEqual = false;
2650 // If we didn't have a multiply compared value, fail.
2651 if (CompVal == 0) return false;
2653 // Avoid turning single icmps into a switch.
2657 // There might be duplicate constants in the list, which the switch
2658 // instruction can't handle, remove them now.
2659 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
2660 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2662 // If Extra was used, we require at least two switch values to do the
2663 // transformation. A switch with one value is just an cond branch.
2664 if (ExtraCase && Values.size() < 2) return false;
2666 // TODO: Preserve branch weight metadata, similarly to how
2667 // FoldValueComparisonIntoPredecessors preserves it.
2669 // Figure out which block is which destination.
2670 BasicBlock *DefaultBB = BI->getSuccessor(1);
2671 BasicBlock *EdgeBB = BI->getSuccessor(0);
2672 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2674 BasicBlock *BB = BI->getParent();
2676 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
2677 << " cases into SWITCH. BB is:\n" << *BB);
2679 // If there are any extra values that couldn't be folded into the switch
2680 // then we evaluate them with an explicit branch first. Split the block
2681 // right before the condbr to handle it.
2683 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
2684 // Remove the uncond branch added to the old block.
2685 TerminatorInst *OldTI = BB->getTerminator();
2686 Builder.SetInsertPoint(OldTI);
2689 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
2691 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
2693 OldTI->eraseFromParent();
2695 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
2696 // for the edge we just added.
2697 AddPredecessorToBlock(EdgeBB, BB, NewBB);
2699 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
2700 << "\nEXTRABB = " << *BB);
2704 Builder.SetInsertPoint(BI);
2705 // Convert pointer to int before we switch.
2706 if (CompVal->getType()->isPointerTy()) {
2707 assert(TD && "Cannot switch on pointer without TargetData");
2708 CompVal = Builder.CreatePtrToInt(CompVal,
2709 TD->getIntPtrType(CompVal->getContext()),
2713 // Create the new switch instruction now.
2714 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
2716 // Add all of the 'cases' to the switch instruction.
2717 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2718 New->addCase(Values[i], EdgeBB);
2720 // We added edges from PI to the EdgeBB. As such, if there were any
2721 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2722 // the number of edges added.
2723 for (BasicBlock::iterator BBI = EdgeBB->begin();
2724 isa<PHINode>(BBI); ++BBI) {
2725 PHINode *PN = cast<PHINode>(BBI);
2726 Value *InVal = PN->getIncomingValueForBlock(BB);
2727 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2728 PN->addIncoming(InVal, BB);
2731 // Erase the old branch instruction.
2732 EraseTerminatorInstAndDCECond(BI);
2734 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
2738 bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
2739 // If this is a trivial landing pad that just continues unwinding the caught
2740 // exception then zap the landing pad, turning its invokes into calls.
2741 BasicBlock *BB = RI->getParent();
2742 LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI());
2743 if (RI->getValue() != LPInst)
2744 // Not a landing pad, or the resume is not unwinding the exception that
2745 // caused control to branch here.
2748 // Check that there are no other instructions except for debug intrinsics.
2749 BasicBlock::iterator I = LPInst, E = RI;
2751 if (!isa<DbgInfoIntrinsic>(I))
2754 // Turn all invokes that unwind here into calls and delete the basic block.
2755 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
2756 InvokeInst *II = cast<InvokeInst>((*PI++)->getTerminator());
2757 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
2758 // Insert a call instruction before the invoke.
2759 CallInst *Call = CallInst::Create(II->getCalledValue(), Args, "", II);
2761 Call->setCallingConv(II->getCallingConv());
2762 Call->setAttributes(II->getAttributes());
2763 Call->setDebugLoc(II->getDebugLoc());
2765 // Anything that used the value produced by the invoke instruction now uses
2766 // the value produced by the call instruction. Note that we do this even
2767 // for void functions and calls with no uses so that the callgraph edge is
2769 II->replaceAllUsesWith(Call);
2770 BB->removePredecessor(II->getParent());
2772 // Insert a branch to the normal destination right before the invoke.
2773 BranchInst::Create(II->getNormalDest(), II);
2775 // Finally, delete the invoke instruction!
2776 II->eraseFromParent();
2779 // The landingpad is now unreachable. Zap it.
2780 BB->eraseFromParent();
2784 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
2785 BasicBlock *BB = RI->getParent();
2786 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2788 // Find predecessors that end with branches.
2789 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2790 SmallVector<BranchInst*, 8> CondBranchPreds;
2791 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2792 BasicBlock *P = *PI;
2793 TerminatorInst *PTI = P->getTerminator();
2794 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2795 if (BI->isUnconditional())
2796 UncondBranchPreds.push_back(P);
2798 CondBranchPreds.push_back(BI);
2802 // If we found some, do the transformation!
2803 if (!UncondBranchPreds.empty() && DupRet) {
2804 while (!UncondBranchPreds.empty()) {
2805 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2806 DEBUG(dbgs() << "FOLDING: " << *BB
2807 << "INTO UNCOND BRANCH PRED: " << *Pred);
2808 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
2811 // If we eliminated all predecessors of the block, delete the block now.
2812 if (pred_begin(BB) == pred_end(BB))
2813 // We know there are no successors, so just nuke the block.
2814 BB->eraseFromParent();
2819 // Check out all of the conditional branches going to this return
2820 // instruction. If any of them just select between returns, change the
2821 // branch itself into a select/return pair.
2822 while (!CondBranchPreds.empty()) {
2823 BranchInst *BI = CondBranchPreds.pop_back_val();
2825 // Check to see if the non-BB successor is also a return block.
2826 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2827 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2828 SimplifyCondBranchToTwoReturns(BI, Builder))
2834 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2835 BasicBlock *BB = UI->getParent();
2837 bool Changed = false;
2839 // If there are any instructions immediately before the unreachable that can
2840 // be removed, do so.
2841 while (UI != BB->begin()) {
2842 BasicBlock::iterator BBI = UI;
2844 // Do not delete instructions that can have side effects which might cause
2845 // the unreachable to not be reachable; specifically, calls and volatile
2846 // operations may have this effect.
2847 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2849 if (BBI->mayHaveSideEffects()) {
2850 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
2851 if (SI->isVolatile())
2853 } else if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
2854 if (LI->isVolatile())
2856 } else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(BBI)) {
2857 if (RMWI->isVolatile())
2859 } else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) {
2860 if (CXI->isVolatile())
2862 } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) &&
2863 !isa<LandingPadInst>(BBI)) {
2866 // Note that deleting LandingPad's here is in fact okay, although it
2867 // involves a bit of subtle reasoning. If this inst is a LandingPad,
2868 // all the predecessors of this block will be the unwind edges of Invokes,
2869 // and we can therefore guarantee this block will be erased.
2872 // Delete this instruction (any uses are guaranteed to be dead)
2873 if (!BBI->use_empty())
2874 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
2875 BBI->eraseFromParent();
2879 // If the unreachable instruction is the first in the block, take a gander
2880 // at all of the predecessors of this instruction, and simplify them.
2881 if (&BB->front() != UI) return Changed;
2883 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2884 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2885 TerminatorInst *TI = Preds[i]->getTerminator();
2886 IRBuilder<> Builder(TI);
2887 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2888 if (BI->isUnconditional()) {
2889 if (BI->getSuccessor(0) == BB) {
2890 new UnreachableInst(TI->getContext(), TI);
2891 TI->eraseFromParent();
2895 if (BI->getSuccessor(0) == BB) {
2896 Builder.CreateBr(BI->getSuccessor(1));
2897 EraseTerminatorInstAndDCECond(BI);
2898 } else if (BI->getSuccessor(1) == BB) {
2899 Builder.CreateBr(BI->getSuccessor(0));
2900 EraseTerminatorInstAndDCECond(BI);
2904 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2905 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2907 if (i.getCaseSuccessor() == BB) {
2908 BB->removePredecessor(SI->getParent());
2913 // If the default value is unreachable, figure out the most popular
2914 // destination and make it the default.
2915 if (SI->getDefaultDest() == BB) {
2916 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
2917 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2919 std::pair<unsigned, unsigned> &entry =
2920 Popularity[i.getCaseSuccessor()];
2921 if (entry.first == 0) {
2923 entry.second = i.getCaseIndex();
2929 // Find the most popular block.
2930 unsigned MaxPop = 0;
2931 unsigned MaxIndex = 0;
2932 BasicBlock *MaxBlock = 0;
2933 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
2934 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2935 if (I->second.first > MaxPop ||
2936 (I->second.first == MaxPop && MaxIndex > I->second.second)) {
2937 MaxPop = I->second.first;
2938 MaxIndex = I->second.second;
2939 MaxBlock = I->first;
2943 // Make this the new default, allowing us to delete any explicit
2945 SI->setDefaultDest(MaxBlock);
2948 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2950 if (isa<PHINode>(MaxBlock->begin()))
2951 for (unsigned i = 0; i != MaxPop-1; ++i)
2952 MaxBlock->removePredecessor(SI->getParent());
2954 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2956 if (i.getCaseSuccessor() == MaxBlock) {
2962 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2963 if (II->getUnwindDest() == BB) {
2964 // Convert the invoke to a call instruction. This would be a good
2965 // place to note that the call does not throw though.
2966 BranchInst *BI = Builder.CreateBr(II->getNormalDest());
2967 II->removeFromParent(); // Take out of symbol table
2969 // Insert the call now...
2970 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2971 Builder.SetInsertPoint(BI);
2972 CallInst *CI = Builder.CreateCall(II->getCalledValue(),
2973 Args, II->getName());
2974 CI->setCallingConv(II->getCallingConv());
2975 CI->setAttributes(II->getAttributes());
2976 // If the invoke produced a value, the call does now instead.
2977 II->replaceAllUsesWith(CI);
2984 // If this block is now dead, remove it.
2985 if (pred_begin(BB) == pred_end(BB) &&
2986 BB != &BB->getParent()->getEntryBlock()) {
2987 // We know there are no successors, so just nuke the block.
2988 BB->eraseFromParent();
2995 /// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
2996 /// integer range comparison into a sub, an icmp and a branch.
2997 static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
2998 assert(SI->getNumCases() > 1 && "Degenerate switch?");
3000 // Make sure all cases point to the same destination and gather the values.
3001 SmallVector<ConstantInt *, 16> Cases;
3002 SwitchInst::CaseIt I = SI->case_begin();
3003 Cases.push_back(I.getCaseValue());
3004 SwitchInst::CaseIt PrevI = I++;
3005 for (SwitchInst::CaseIt E = SI->case_end(); I != E; PrevI = I++) {
3006 if (PrevI.getCaseSuccessor() != I.getCaseSuccessor())
3008 Cases.push_back(I.getCaseValue());
3010 assert(Cases.size() == SI->getNumCases() && "Not all cases gathered");
3012 // Sort the case values, then check if they form a range we can transform.
3013 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
3014 for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
3015 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
3019 Constant *Offset = ConstantExpr::getNeg(Cases.back());
3020 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases());
3022 Value *Sub = SI->getCondition();
3023 if (!Offset->isNullValue())
3024 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off");
3025 Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
3026 BranchInst *NewBI = Builder.CreateCondBr(
3027 Cmp, SI->case_begin().getCaseSuccessor(), SI->getDefaultDest());
3029 // Update weight for the newly-created conditional branch.
3030 SmallVector<uint64_t, 8> Weights;
3031 bool HasWeights = HasBranchWeights(SI);
3033 GetBranchWeights(SI, Weights);
3034 if (Weights.size() == 1 + SI->getNumCases()) {
3035 // Combine all weights for the cases to be the true weight of NewBI.
3036 // We assume that the sum of all weights for a Terminator can fit into 32
3038 uint32_t NewTrueWeight = 0;
3039 for (unsigned I = 1, E = Weights.size(); I != E; ++I)
3040 NewTrueWeight += (uint32_t)Weights[I];
3041 NewBI->setMetadata(LLVMContext::MD_prof,
3042 MDBuilder(SI->getContext()).
3043 createBranchWeights(NewTrueWeight,
3044 (uint32_t)Weights[0]));
3048 // Prune obsolete incoming values off the successor's PHI nodes.
3049 for (BasicBlock::iterator BBI = SI->case_begin().getCaseSuccessor()->begin();
3050 isa<PHINode>(BBI); ++BBI) {
3051 for (unsigned I = 0, E = SI->getNumCases()-1; I != E; ++I)
3052 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
3054 SI->eraseFromParent();
3059 /// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch
3060 /// and use it to remove dead cases.
3061 static bool EliminateDeadSwitchCases(SwitchInst *SI) {
3062 Value *Cond = SI->getCondition();
3063 unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth();
3064 APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
3065 ComputeMaskedBits(Cond, KnownZero, KnownOne);
3067 // Gather dead cases.
3068 SmallVector<ConstantInt*, 8> DeadCases;
3069 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
3070 if ((I.getCaseValue()->getValue() & KnownZero) != 0 ||
3071 (I.getCaseValue()->getValue() & KnownOne) != KnownOne) {
3072 DeadCases.push_back(I.getCaseValue());
3073 DEBUG(dbgs() << "SimplifyCFG: switch case '"
3074 << I.getCaseValue() << "' is dead.\n");
3078 SmallVector<uint64_t, 8> Weights;
3079 bool HasWeight = HasBranchWeights(SI);
3081 GetBranchWeights(SI, Weights);
3082 HasWeight = (Weights.size() == 1 + SI->getNumCases());
3085 // Remove dead cases from the switch.
3086 for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) {
3087 SwitchInst::CaseIt Case = SI->findCaseValue(DeadCases[I]);
3088 assert(Case != SI->case_default() &&
3089 "Case was not found. Probably mistake in DeadCases forming.");
3091 std::swap(Weights[Case.getCaseIndex()+1], Weights.back());
3095 // Prune unused values from PHI nodes.
3096 Case.getCaseSuccessor()->removePredecessor(SI->getParent());
3097 SI->removeCase(Case);
3100 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
3101 SI->setMetadata(LLVMContext::MD_prof,
3102 MDBuilder(SI->getParent()->getContext()).
3103 createBranchWeights(MDWeights));
3106 return !DeadCases.empty();
3109 /// FindPHIForConditionForwarding - If BB would be eligible for simplification
3110 /// by TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated
3111 /// by an unconditional branch), look at the phi node for BB in the successor
3112 /// block and see if the incoming value is equal to CaseValue. If so, return
3113 /// the phi node, and set PhiIndex to BB's index in the phi node.
3114 static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
3117 if (BB->getFirstNonPHIOrDbg() != BB->getTerminator())
3118 return NULL; // BB must be empty to be a candidate for simplification.
3119 if (!BB->getSinglePredecessor())
3120 return NULL; // BB must be dominated by the switch.
3122 BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
3123 if (!Branch || !Branch->isUnconditional())
3124 return NULL; // Terminator must be unconditional branch.
3126 BasicBlock *Succ = Branch->getSuccessor(0);
3128 BasicBlock::iterator I = Succ->begin();
3129 while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
3130 int Idx = PHI->getBasicBlockIndex(BB);
3131 assert(Idx >= 0 && "PHI has no entry for predecessor?");
3133 Value *InValue = PHI->getIncomingValue(Idx);
3134 if (InValue != CaseValue) continue;
3143 /// ForwardSwitchConditionToPHI - Try to forward the condition of a switch
3144 /// instruction to a phi node dominated by the switch, if that would mean that
3145 /// some of the destination blocks of the switch can be folded away.
3146 /// Returns true if a change is made.
3147 static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
3148 typedef DenseMap<PHINode*, SmallVector<int,4> > ForwardingNodesMap;
3149 ForwardingNodesMap ForwardingNodes;
3151 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
3152 ConstantInt *CaseValue = I.getCaseValue();
3153 BasicBlock *CaseDest = I.getCaseSuccessor();
3156 PHINode *PHI = FindPHIForConditionForwarding(CaseValue, CaseDest,
3160 ForwardingNodes[PHI].push_back(PhiIndex);
3163 bool Changed = false;
3165 for (ForwardingNodesMap::iterator I = ForwardingNodes.begin(),
3166 E = ForwardingNodes.end(); I != E; ++I) {
3167 PHINode *Phi = I->first;
3168 SmallVector<int,4> &Indexes = I->second;
3170 if (Indexes.size() < 2) continue;
3172 for (size_t I = 0, E = Indexes.size(); I != E; ++I)
3173 Phi->setIncomingValue(Indexes[I], SI->getCondition());
3180 /// ValidLookupTableConstant - Return true if the backend will be able to handle
3181 /// initializing an array of constants like C.
3182 static bool ValidLookupTableConstant(Constant *C) {
3183 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C))
3184 return CE->isGEPWithNoNotionalOverIndexing();
3186 return isa<ConstantFP>(C) ||
3187 isa<ConstantInt>(C) ||
3188 isa<ConstantPointerNull>(C) ||
3189 isa<GlobalValue>(C) ||
3193 /// GetCaseResulsts - Try to determine the resulting constant values in phi
3194 /// nodes at the common destination basic block for one of the case
3195 /// destinations of a switch instruction.
3196 static bool GetCaseResults(SwitchInst *SI,
3197 BasicBlock *CaseDest,
3198 BasicBlock **CommonDest,
3199 SmallVector<std::pair<PHINode*,Constant*>, 4> &Res) {
3200 // The block from which we enter the common destination.
3201 BasicBlock *Pred = SI->getParent();
3203 // If CaseDest is empty, continue to its successor.
3204 if (CaseDest->getFirstNonPHIOrDbg() == CaseDest->getTerminator() &&
3205 !isa<PHINode>(CaseDest->begin())) {
3207 TerminatorInst *Terminator = CaseDest->getTerminator();
3208 if (Terminator->getNumSuccessors() != 1)
3212 CaseDest = Terminator->getSuccessor(0);
3215 // If we did not have a CommonDest before, use the current one.
3217 *CommonDest = CaseDest;
3218 // If the destination isn't the common one, abort.
3219 if (CaseDest != *CommonDest)
3222 // Get the values for this case from phi nodes in the destination block.
3223 BasicBlock::iterator I = (*CommonDest)->begin();
3224 while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
3225 int Idx = PHI->getBasicBlockIndex(Pred);
3229 Constant *ConstVal = dyn_cast<Constant>(PHI->getIncomingValue(Idx));
3233 // Be conservative about which kinds of constants we support.
3234 if (!ValidLookupTableConstant(ConstVal))
3237 Res.push_back(std::make_pair(PHI, ConstVal));
3244 /// SwitchLookupTable - This class represents a lookup table that can be used
3245 /// to replace a switch.
3246 class SwitchLookupTable {
3248 /// SwitchLookupTable - Create a lookup table to use as a switch replacement
3249 /// with the contents of Values, using DefaultValue to fill any holes in the
3251 SwitchLookupTable(Module &M,
3253 ConstantInt *Offset,
3254 const SmallVector<std::pair<ConstantInt*, Constant*>, 4>& Values,
3255 Constant *DefaultValue);
3257 /// BuildLookup - Build instructions with Builder to retrieve the value at
3258 /// the position given by Index in the lookup table.
3259 Value *BuildLookup(Value *Index, IRBuilder<> &Builder);
3262 // Depending on the contents of the table, it can be represented in
3265 // For tables where each element contains the same value, we just have to
3266 // store that single value and return it for each lookup.
3269 // The table is stored as an array of values. Values are retrieved by load
3270 // instructions from the table.
3274 // For SingleValueKind, this is the single value.
3275 Constant *SingleValue;
3277 // For ArrayKind, this is the array.
3278 GlobalVariable *Array;
3282 SwitchLookupTable::SwitchLookupTable(Module &M,
3284 ConstantInt *Offset,
3285 const SmallVector<std::pair<ConstantInt*, Constant*>, 4>& Values,
3286 Constant *DefaultValue) {
3287 assert(Values.size() && "Can't build lookup table without values.");
3288 assert(TableSize >= Values.size() && "Can't fit values in table.");
3290 // If all values in the table are equal, this is that value.
3291 SingleValue = Values.begin()->second;
3293 // Build up the table contents.
3294 SmallVector<Constant*, 64> TableContents(TableSize);
3295 for (size_t I = 0, E = Values.size(); I != E; ++I) {
3296 ConstantInt *CaseVal = Values[I].first;
3297 Constant *CaseRes = Values[I].second;
3298 assert(CaseRes->getType() == DefaultValue->getType());
3300 uint64_t Idx = (CaseVal->getValue() - Offset->getValue())
3302 TableContents[Idx] = CaseRes;
3304 if (CaseRes != SingleValue)
3308 // Fill in any holes in the table with the default result.
3309 if (Values.size() < TableSize) {
3310 for (uint64_t I = 0; I < TableSize; ++I) {
3311 if (!TableContents[I])
3312 TableContents[I] = DefaultValue;
3315 if (DefaultValue != SingleValue)
3319 // If each element in the table contains the same value, we only need to store
3320 // that single value.
3322 Kind = SingleValueKind;
3326 // Store the table in an array.
3327 ArrayType *ArrayTy = ArrayType::get(DefaultValue->getType(), TableSize);
3328 Constant *Initializer = ConstantArray::get(ArrayTy, TableContents);
3330 Array = new GlobalVariable(M, ArrayTy, /*constant=*/ true,
3331 GlobalVariable::PrivateLinkage,
3334 Array->setUnnamedAddr(true);
3338 Value *SwitchLookupTable::BuildLookup(Value *Index, IRBuilder<> &Builder) {
3340 case SingleValueKind:
3343 Value *GEPIndices[] = { Builder.getInt32(0), Index };
3344 Value *GEP = Builder.CreateInBoundsGEP(Array, GEPIndices,
3346 return Builder.CreateLoad(GEP, "switch.load");
3349 llvm_unreachable("Unknown lookup table kind!");
3352 /// ShouldBuildLookupTable - Determine whether a lookup table should be built
3353 /// for this switch, based on the number of caes, size of the table and the
3354 /// types of the results.
3355 static bool ShouldBuildLookupTable(SwitchInst *SI,
3356 uint64_t TableSize) {
3357 // The table density should be at least 40%. This is the same criterion as for
3358 // jump tables, see SelectionDAGBuilder::handleJTSwitchCase.
3359 // FIXME: Find the best cut-off.
3360 if (SI->getNumCases() * 10 >= TableSize * 4)
3366 /// SwitchToLookupTable - If the switch is only used to initialize one or more
3367 /// phi nodes in a common successor block with different constant values,
3368 /// replace the switch with lookup tables.
3369 static bool SwitchToLookupTable(SwitchInst *SI,
3370 IRBuilder<> &Builder) {
3371 assert(SI->getNumCases() > 1 && "Degenerate switch?");
3372 // FIXME: Handle unreachable cases.
3374 // FIXME: If the switch is too sparse for a lookup table, perhaps we could
3375 // split off a dense part and build a lookup table for that.
3377 // FIXME: If the results are all integers and the lookup table would fit in a
3378 // target-legal register, we should store them as a bitmap and use shift/mask
3379 // to look up the result.
3381 // FIXME: This creates arrays of GEPs to constant strings, which means each
3382 // GEP needs a runtime relocation in PIC code. We should just build one big
3383 // string and lookup indices into that.
3385 // Ignore the switch if the number of cases is too small.
3386 // This is similar to the check when building jump tables in
3387 // SelectionDAGBuilder::handleJTSwitchCase.
3388 // FIXME: Determine the best cut-off.
3389 if (SI->getNumCases() < 4)
3392 // Figure out the corresponding result for each case value and phi node in the
3393 // common destination, as well as the the min and max case values.
3394 assert(SI->case_begin() != SI->case_end());
3395 SwitchInst::CaseIt CI = SI->case_begin();
3396 ConstantInt *MinCaseVal = CI.getCaseValue();
3397 ConstantInt *MaxCaseVal = CI.getCaseValue();
3399 BasicBlock *CommonDest = NULL;
3400 typedef SmallVector<std::pair<ConstantInt*, Constant*>, 4> ResultListTy;
3401 SmallDenseMap<PHINode*, ResultListTy> ResultLists;
3402 SmallDenseMap<PHINode*, Constant*> DefaultResults;
3403 SmallDenseMap<PHINode*, Type*> ResultTypes;
3404 SmallVector<PHINode*, 4> PHIs;
3406 for (SwitchInst::CaseIt E = SI->case_end(); CI != E; ++CI) {
3407 ConstantInt *CaseVal = CI.getCaseValue();
3408 if (CaseVal->getValue().slt(MinCaseVal->getValue()))
3409 MinCaseVal = CaseVal;
3410 if (CaseVal->getValue().sgt(MaxCaseVal->getValue()))
3411 MaxCaseVal = CaseVal;
3413 // Resulting value at phi nodes for this case value.
3414 typedef SmallVector<std::pair<PHINode*, Constant*>, 4> ResultsTy;
3416 if (!GetCaseResults(SI, CI.getCaseSuccessor(), &CommonDest, Results))
3419 // Append the result from this case to the list for each phi.
3420 for (ResultsTy::iterator I = Results.begin(), E = Results.end(); I!=E; ++I) {
3421 if (!ResultLists.count(I->first))
3422 PHIs.push_back(I->first);
3423 ResultLists[I->first].push_back(std::make_pair(CaseVal, I->second));
3427 // Get the resulting values for the default case.
3428 SmallVector<std::pair<PHINode*, Constant*>, 4> DefaultResultsList;
3429 if (!GetCaseResults(SI, SI->getDefaultDest(), &CommonDest, DefaultResultsList))
3431 for (size_t I = 0, E = DefaultResultsList.size(); I != E; ++I) {
3432 PHINode *PHI = DefaultResultsList[I].first;
3433 Constant *Result = DefaultResultsList[I].second;
3434 DefaultResults[PHI] = Result;
3435 ResultTypes[PHI] = Result->getType();
3438 APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
3439 // Be careful to avoid overflow when TableSize is used in
3440 // ShouldBuildLookupTable.
3441 if (RangeSpread.zextOrSelf(64).ugt(UINT64_MAX / 4 - 1))
3443 uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
3444 if (!ShouldBuildLookupTable(SI, TableSize))
3447 // Create the BB that does the lookups.
3448 Module &Mod = *CommonDest->getParent()->getParent();
3449 BasicBlock *LookupBB = BasicBlock::Create(Mod.getContext(),
3451 CommonDest->getParent(),
3454 // Check whether the condition value is within the case range, and branch to
3456 Builder.SetInsertPoint(SI);
3457 Value *TableIndex = Builder.CreateSub(SI->getCondition(), MinCaseVal,
3459 Value *Cmp = Builder.CreateICmpULT(TableIndex, ConstantInt::get(
3460 MinCaseVal->getType(), TableSize));
3461 Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest());
3463 // Populate the BB that does the lookups.
3464 Builder.SetInsertPoint(LookupBB);
3465 bool ReturnedEarly = false;
3466 for (size_t I = 0, E = PHIs.size(); I != E; ++I) {
3467 PHINode *PHI = PHIs[I];
3469 SwitchLookupTable Table(Mod, TableSize, MinCaseVal, ResultLists[PHI],
3470 DefaultResults[PHI]);
3472 Value *Result = Table.BuildLookup(TableIndex, Builder);
3474 // If the result is used to return immediately from the function, we want to
3475 // do that right here.
3476 if (PHI->hasOneUse() && isa<ReturnInst>(*PHI->use_begin()) &&
3477 *PHI->use_begin() == CommonDest->getFirstNonPHIOrDbg()) {
3478 Builder.CreateRet(Result);
3479 ReturnedEarly = true;
3483 PHI->addIncoming(Result, LookupBB);
3487 Builder.CreateBr(CommonDest);
3489 // Remove the switch.
3490 for (unsigned i = 0; i < SI->getNumSuccessors(); ++i) {
3491 BasicBlock *Succ = SI->getSuccessor(i);
3492 if (Succ == SI->getDefaultDest()) continue;
3493 Succ->removePredecessor(SI->getParent());
3495 SI->eraseFromParent();
3501 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
3502 // If this switch is too complex to want to look at, ignore it.
3503 if (!isValueEqualityComparison(SI))
3506 BasicBlock *BB = SI->getParent();
3508 // If we only have one predecessor, and if it is a branch on this value,
3509 // see if that predecessor totally determines the outcome of this switch.
3510 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
3511 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
3512 return SimplifyCFG(BB) | true;
3514 Value *Cond = SI->getCondition();
3515 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
3516 if (SimplifySwitchOnSelect(SI, Select))
3517 return SimplifyCFG(BB) | true;
3519 // If the block only contains the switch, see if we can fold the block
3520 // away into any preds.
3521 BasicBlock::iterator BBI = BB->begin();
3522 // Ignore dbg intrinsics.
3523 while (isa<DbgInfoIntrinsic>(BBI))
3526 if (FoldValueComparisonIntoPredecessors(SI, Builder))
3527 return SimplifyCFG(BB) | true;
3529 // Try to transform the switch into an icmp and a branch.
3530 if (TurnSwitchRangeIntoICmp(SI, Builder))
3531 return SimplifyCFG(BB) | true;
3533 // Remove unreachable cases.
3534 if (EliminateDeadSwitchCases(SI))
3535 return SimplifyCFG(BB) | true;
3537 if (ForwardSwitchConditionToPHI(SI))
3538 return SimplifyCFG(BB) | true;
3540 if (SwitchToLookupTable(SI, Builder))
3541 return SimplifyCFG(BB) | true;
3546 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
3547 BasicBlock *BB = IBI->getParent();
3548 bool Changed = false;
3550 // Eliminate redundant destinations.
3551 SmallPtrSet<Value *, 8> Succs;
3552 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
3553 BasicBlock *Dest = IBI->getDestination(i);
3554 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
3555 Dest->removePredecessor(BB);
3556 IBI->removeDestination(i);
3562 if (IBI->getNumDestinations() == 0) {
3563 // If the indirectbr has no successors, change it to unreachable.
3564 new UnreachableInst(IBI->getContext(), IBI);
3565 EraseTerminatorInstAndDCECond(IBI);
3569 if (IBI->getNumDestinations() == 1) {
3570 // If the indirectbr has one successor, change it to a direct branch.
3571 BranchInst::Create(IBI->getDestination(0), IBI);
3572 EraseTerminatorInstAndDCECond(IBI);
3576 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
3577 if (SimplifyIndirectBrOnSelect(IBI, SI))
3578 return SimplifyCFG(BB) | true;
3583 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
3584 BasicBlock *BB = BI->getParent();
3586 if (SinkCommon && SinkThenElseCodeToEnd(BI))
3589 // If the Terminator is the only non-phi instruction, simplify the block.
3590 BasicBlock::iterator I = BB->getFirstNonPHIOrDbgOrLifetime();
3591 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
3592 TryToSimplifyUncondBranchFromEmptyBlock(BB))
3595 // If the only instruction in the block is a seteq/setne comparison
3596 // against a constant, try to simplify the block.
3597 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
3598 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
3599 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
3601 if (I->isTerminator() &&
3602 TryToSimplifyUncondBranchWithICmpInIt(ICI, TD, Builder))
3606 // If this basic block is ONLY a compare and a branch, and if a predecessor
3607 // branches to us and our successor, fold the comparison into the
3608 // predecessor and use logical operations to update the incoming value
3609 // for PHI nodes in common successor.
3610 if (FoldBranchToCommonDest(BI))
3611 return SimplifyCFG(BB) | true;
3616 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
3617 BasicBlock *BB = BI->getParent();
3619 // Conditional branch
3620 if (isValueEqualityComparison(BI)) {
3621 // If we only have one predecessor, and if it is a branch on this value,
3622 // see if that predecessor totally determines the outcome of this
3624 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
3625 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
3626 return SimplifyCFG(BB) | true;
3628 // This block must be empty, except for the setcond inst, if it exists.
3629 // Ignore dbg intrinsics.
3630 BasicBlock::iterator I = BB->begin();
3631 // Ignore dbg intrinsics.
3632 while (isa<DbgInfoIntrinsic>(I))
3635 if (FoldValueComparisonIntoPredecessors(BI, Builder))
3636 return SimplifyCFG(BB) | true;
3637 } else if (&*I == cast<Instruction>(BI->getCondition())){
3639 // Ignore dbg intrinsics.
3640 while (isa<DbgInfoIntrinsic>(I))
3642 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
3643 return SimplifyCFG(BB) | true;
3647 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
3648 if (SimplifyBranchOnICmpChain(BI, TD, Builder))
3651 // If this basic block is ONLY a compare and a branch, and if a predecessor
3652 // branches to us and one of our successors, fold the comparison into the
3653 // predecessor and use logical operations to pick the right destination.
3654 if (FoldBranchToCommonDest(BI))
3655 return SimplifyCFG(BB) | true;
3657 // We have a conditional branch to two blocks that are only reachable
3658 // from BI. We know that the condbr dominates the two blocks, so see if
3659 // there is any identical code in the "then" and "else" blocks. If so, we
3660 // can hoist it up to the branching block.
3661 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
3662 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
3663 if (HoistThenElseCodeToIf(BI))
3664 return SimplifyCFG(BB) | true;
3666 // If Successor #1 has multiple preds, we may be able to conditionally
3667 // execute Successor #0 if it branches to successor #1.
3668 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
3669 if (Succ0TI->getNumSuccessors() == 1 &&
3670 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
3671 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
3672 return SimplifyCFG(BB) | true;
3674 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
3675 // If Successor #0 has multiple preds, we may be able to conditionally
3676 // execute Successor #1 if it branches to successor #0.
3677 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
3678 if (Succ1TI->getNumSuccessors() == 1 &&
3679 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
3680 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
3681 return SimplifyCFG(BB) | true;
3684 // If this is a branch on a phi node in the current block, thread control
3685 // through this block if any PHI node entries are constants.
3686 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
3687 if (PN->getParent() == BI->getParent())
3688 if (FoldCondBranchOnPHI(BI, TD))
3689 return SimplifyCFG(BB) | true;
3691 // Scan predecessor blocks for conditional branches.
3692 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
3693 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
3694 if (PBI != BI && PBI->isConditional())
3695 if (SimplifyCondBranchToCondBranch(PBI, BI))
3696 return SimplifyCFG(BB) | true;
3701 /// Check if passing a value to an instruction will cause undefined behavior.
3702 static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
3703 Constant *C = dyn_cast<Constant>(V);
3707 if (!I->hasOneUse()) // Only look at single-use instructions, for compile time
3710 if (C->isNullValue()) {
3711 Instruction *Use = I->use_back();
3713 // Now make sure that there are no instructions in between that can alter
3714 // control flow (eg. calls)
3715 for (BasicBlock::iterator i = ++BasicBlock::iterator(I); &*i != Use; ++i)
3716 if (i == I->getParent()->end() || i->mayHaveSideEffects())
3719 // Look through GEPs. A load from a GEP derived from NULL is still undefined
3720 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))
3721 if (GEP->getPointerOperand() == I)
3722 return passingValueIsAlwaysUndefined(V, GEP);
3724 // Look through bitcasts.
3725 if (BitCastInst *BC = dyn_cast<BitCastInst>(Use))
3726 return passingValueIsAlwaysUndefined(V, BC);
3728 // Load from null is undefined.
3729 if (LoadInst *LI = dyn_cast<LoadInst>(Use))
3730 return LI->getPointerAddressSpace() == 0;
3732 // Store to null is undefined.
3733 if (StoreInst *SI = dyn_cast<StoreInst>(Use))
3734 return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I;
3739 /// If BB has an incoming value that will always trigger undefined behavior
3740 /// (eg. null pointer dereference), remove the branch leading here.
3741 static bool removeUndefIntroducingPredecessor(BasicBlock *BB) {
3742 for (BasicBlock::iterator i = BB->begin();
3743 PHINode *PHI = dyn_cast<PHINode>(i); ++i)
3744 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
3745 if (passingValueIsAlwaysUndefined(PHI->getIncomingValue(i), PHI)) {
3746 TerminatorInst *T = PHI->getIncomingBlock(i)->getTerminator();
3747 IRBuilder<> Builder(T);
3748 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
3749 BB->removePredecessor(PHI->getIncomingBlock(i));
3750 // Turn uncoditional branches into unreachables and remove the dead
3751 // destination from conditional branches.
3752 if (BI->isUnconditional())
3753 Builder.CreateUnreachable();
3755 Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1) :
3756 BI->getSuccessor(0));
3757 BI->eraseFromParent();
3760 // TODO: SwitchInst.
3766 bool SimplifyCFGOpt::run(BasicBlock *BB) {
3767 bool Changed = false;
3769 assert(BB && BB->getParent() && "Block not embedded in function!");
3770 assert(BB->getTerminator() && "Degenerate basic block encountered!");
3772 // Remove basic blocks that have no predecessors (except the entry block)...
3773 // or that just have themself as a predecessor. These are unreachable.
3774 if ((pred_begin(BB) == pred_end(BB) &&
3775 BB != &BB->getParent()->getEntryBlock()) ||
3776 BB->getSinglePredecessor() == BB) {
3777 DEBUG(dbgs() << "Removing BB: \n" << *BB);
3778 DeleteDeadBlock(BB);
3782 // Check to see if we can constant propagate this terminator instruction
3784 Changed |= ConstantFoldTerminator(BB, true);
3786 // Check for and eliminate duplicate PHI nodes in this block.
3787 Changed |= EliminateDuplicatePHINodes(BB);
3789 // Check for and remove branches that will always cause undefined behavior.
3790 Changed |= removeUndefIntroducingPredecessor(BB);
3792 // Merge basic blocks into their predecessor if there is only one distinct
3793 // pred, and if there is only one distinct successor of the predecessor, and
3794 // if there are no PHI nodes.
3796 if (MergeBlockIntoPredecessor(BB))
3799 IRBuilder<> Builder(BB);
3801 // If there is a trivial two-entry PHI node in this basic block, and we can
3802 // eliminate it, do so now.
3803 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
3804 if (PN->getNumIncomingValues() == 2)
3805 Changed |= FoldTwoEntryPHINode(PN, TD);
3807 Builder.SetInsertPoint(BB->getTerminator());
3808 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
3809 if (BI->isUnconditional()) {
3810 if (SimplifyUncondBranch(BI, Builder)) return true;
3812 if (SimplifyCondBranch(BI, Builder)) return true;
3814 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
3815 if (SimplifyReturn(RI, Builder)) return true;
3816 } else if (ResumeInst *RI = dyn_cast<ResumeInst>(BB->getTerminator())) {
3817 if (SimplifyResume(RI, Builder)) return true;
3818 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
3819 if (SimplifySwitch(SI, Builder)) return true;
3820 } else if (UnreachableInst *UI =
3821 dyn_cast<UnreachableInst>(BB->getTerminator())) {
3822 if (SimplifyUnreachable(UI)) return true;
3823 } else if (IndirectBrInst *IBI =
3824 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
3825 if (SimplifyIndirectBr(IBI)) return true;
3831 /// SimplifyCFG - This function is used to do simplification of a CFG. For
3832 /// example, it adjusts branches to branches to eliminate the extra hop, it
3833 /// eliminates unreachable basic blocks, and does other "peephole" optimization
3834 /// of the CFG. It returns true if a modification was made.
3836 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
3837 return SimplifyCFGOpt(TD).run(BB);