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"));
57 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
58 STATISTIC(NumLookupTables, "Number of switch instructions turned into lookup tables");
61 /// ValueEqualityComparisonCase - Represents a case of a switch.
62 struct ValueEqualityComparisonCase {
66 ValueEqualityComparisonCase(ConstantInt *Value, BasicBlock *Dest)
67 : Value(Value), Dest(Dest) {}
69 bool operator<(ValueEqualityComparisonCase RHS) const {
70 // Comparing pointers is ok as we only rely on the order for uniquing.
71 return Value < RHS.Value;
75 class SimplifyCFGOpt {
76 const TargetData *const TD;
78 Value *isValueEqualityComparison(TerminatorInst *TI);
79 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
80 std::vector<ValueEqualityComparisonCase> &Cases);
81 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
83 IRBuilder<> &Builder);
84 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
85 IRBuilder<> &Builder);
87 bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder);
88 bool SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder);
89 bool SimplifyUnreachable(UnreachableInst *UI);
90 bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
91 bool SimplifyIndirectBr(IndirectBrInst *IBI);
92 bool SimplifyUncondBranch(BranchInst *BI, IRBuilder <> &Builder);
93 bool SimplifyCondBranch(BranchInst *BI, IRBuilder <>&Builder);
96 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
97 bool run(BasicBlock *BB);
101 /// SafeToMergeTerminators - Return true if it is safe to merge these two
102 /// terminator instructions together.
104 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
105 if (SI1 == SI2) return false; // Can't merge with self!
107 // It is not safe to merge these two switch instructions if they have a common
108 // successor, and if that successor has a PHI node, and if *that* PHI node has
109 // conflicting incoming values from the two switch blocks.
110 BasicBlock *SI1BB = SI1->getParent();
111 BasicBlock *SI2BB = SI2->getParent();
112 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
114 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
115 if (SI1Succs.count(*I))
116 for (BasicBlock::iterator BBI = (*I)->begin();
117 isa<PHINode>(BBI); ++BBI) {
118 PHINode *PN = cast<PHINode>(BBI);
119 if (PN->getIncomingValueForBlock(SI1BB) !=
120 PN->getIncomingValueForBlock(SI2BB))
127 /// isProfitableToFoldUnconditional - Return true if it is safe and profitable
128 /// to merge these two terminator instructions together, where SI1 is an
129 /// unconditional branch. PhiNodes will store all PHI nodes in common
132 static bool isProfitableToFoldUnconditional(BranchInst *SI1,
135 SmallVectorImpl<PHINode*> &PhiNodes) {
136 if (SI1 == SI2) return false; // Can't merge with self!
137 assert(SI1->isUnconditional() && SI2->isConditional());
139 // We fold the unconditional branch if we can easily update all PHI nodes in
140 // common successors:
141 // 1> We have a constant incoming value for the conditional branch;
142 // 2> We have "Cond" as the incoming value for the unconditional branch;
143 // 3> SI2->getCondition() and Cond have same operands.
144 CmpInst *Ci2 = dyn_cast<CmpInst>(SI2->getCondition());
145 if (!Ci2) return false;
146 if (!(Cond->getOperand(0) == Ci2->getOperand(0) &&
147 Cond->getOperand(1) == Ci2->getOperand(1)) &&
148 !(Cond->getOperand(0) == Ci2->getOperand(1) &&
149 Cond->getOperand(1) == Ci2->getOperand(0)))
152 BasicBlock *SI1BB = SI1->getParent();
153 BasicBlock *SI2BB = SI2->getParent();
154 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
155 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
156 if (SI1Succs.count(*I))
157 for (BasicBlock::iterator BBI = (*I)->begin();
158 isa<PHINode>(BBI); ++BBI) {
159 PHINode *PN = cast<PHINode>(BBI);
160 if (PN->getIncomingValueForBlock(SI1BB) != Cond ||
161 !isa<ConstantInt>(PN->getIncomingValueForBlock(SI2BB)))
163 PhiNodes.push_back(PN);
168 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
169 /// now be entries in it from the 'NewPred' block. The values that will be
170 /// flowing into the PHI nodes will be the same as those coming in from
171 /// ExistPred, an existing predecessor of Succ.
172 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
173 BasicBlock *ExistPred) {
174 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
177 for (BasicBlock::iterator I = Succ->begin();
178 (PN = dyn_cast<PHINode>(I)); ++I)
179 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
183 /// GetIfCondition - Given a basic block (BB) with two predecessors (and at
184 /// least one PHI node in it), check to see if the merge at this block is due
185 /// to an "if condition". If so, return the boolean condition that determines
186 /// which entry into BB will be taken. Also, return by references the block
187 /// that will be entered from if the condition is true, and the block that will
188 /// be entered if the condition is false.
190 /// This does no checking to see if the true/false blocks have large or unsavory
191 /// instructions in them.
192 static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
193 BasicBlock *&IfFalse) {
194 PHINode *SomePHI = cast<PHINode>(BB->begin());
195 assert(SomePHI->getNumIncomingValues() == 2 &&
196 "Function can only handle blocks with 2 predecessors!");
197 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
198 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
200 // We can only handle branches. Other control flow will be lowered to
201 // branches if possible anyway.
202 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
203 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
204 if (Pred1Br == 0 || Pred2Br == 0)
207 // Eliminate code duplication by ensuring that Pred1Br is conditional if
209 if (Pred2Br->isConditional()) {
210 // If both branches are conditional, we don't have an "if statement". In
211 // reality, we could transform this case, but since the condition will be
212 // required anyway, we stand no chance of eliminating it, so the xform is
213 // probably not profitable.
214 if (Pred1Br->isConditional())
217 std::swap(Pred1, Pred2);
218 std::swap(Pred1Br, Pred2Br);
221 if (Pred1Br->isConditional()) {
222 // The only thing we have to watch out for here is to make sure that Pred2
223 // doesn't have incoming edges from other blocks. If it does, the condition
224 // doesn't dominate BB.
225 if (Pred2->getSinglePredecessor() == 0)
228 // If we found a conditional branch predecessor, make sure that it branches
229 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
230 if (Pred1Br->getSuccessor(0) == BB &&
231 Pred1Br->getSuccessor(1) == Pred2) {
234 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
235 Pred1Br->getSuccessor(1) == BB) {
239 // We know that one arm of the conditional goes to BB, so the other must
240 // go somewhere unrelated, and this must not be an "if statement".
244 return Pred1Br->getCondition();
247 // Ok, if we got here, both predecessors end with an unconditional branch to
248 // BB. Don't panic! If both blocks only have a single (identical)
249 // predecessor, and THAT is a conditional branch, then we're all ok!
250 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
251 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
254 // Otherwise, if this is a conditional branch, then we can use it!
255 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
256 if (BI == 0) return 0;
258 assert(BI->isConditional() && "Two successors but not conditional?");
259 if (BI->getSuccessor(0) == Pred1) {
266 return BI->getCondition();
269 /// ComputeSpeculuationCost - Compute an abstract "cost" of speculating the
270 /// given instruction, which is assumed to be safe to speculate. 1 means
271 /// cheap, 2 means less cheap, and UINT_MAX means prohibitively expensive.
272 static unsigned ComputeSpeculationCost(const User *I) {
273 assert(isSafeToSpeculativelyExecute(I) &&
274 "Instruction is not safe to speculatively execute!");
275 switch (Operator::getOpcode(I)) {
277 // In doubt, be conservative.
279 case Instruction::GetElementPtr:
280 // GEPs are cheap if all indices are constant.
281 if (!cast<GEPOperator>(I)->hasAllConstantIndices())
284 case Instruction::Load:
285 case Instruction::Add:
286 case Instruction::Sub:
287 case Instruction::And:
288 case Instruction::Or:
289 case Instruction::Xor:
290 case Instruction::Shl:
291 case Instruction::LShr:
292 case Instruction::AShr:
293 case Instruction::ICmp:
294 case Instruction::Trunc:
295 case Instruction::ZExt:
296 case Instruction::SExt:
297 return 1; // These are all cheap.
299 case Instruction::Call:
300 case Instruction::Select:
305 /// DominatesMergePoint - If we have a merge point of an "if condition" as
306 /// accepted above, return true if the specified value dominates the block. We
307 /// don't handle the true generality of domination here, just a special case
308 /// which works well enough for us.
310 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
311 /// see if V (which must be an instruction) and its recursive operands
312 /// that do not dominate BB have a combined cost lower than CostRemaining and
313 /// are non-trapping. If both are true, the instruction is inserted into the
314 /// set and true is returned.
316 /// The cost for most non-trapping instructions is defined as 1 except for
317 /// Select whose cost is 2.
319 /// After this function returns, CostRemaining is decreased by the cost of
320 /// V plus its non-dominating operands. If that cost is greater than
321 /// CostRemaining, false is returned and CostRemaining is undefined.
322 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
323 SmallPtrSet<Instruction*, 4> *AggressiveInsts,
324 unsigned &CostRemaining) {
325 Instruction *I = dyn_cast<Instruction>(V);
327 // Non-instructions all dominate instructions, but not all constantexprs
328 // can be executed unconditionally.
329 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
334 BasicBlock *PBB = I->getParent();
336 // We don't want to allow weird loops that might have the "if condition" in
337 // the bottom of this block.
338 if (PBB == BB) return false;
340 // If this instruction is defined in a block that contains an unconditional
341 // branch to BB, then it must be in the 'conditional' part of the "if
342 // statement". If not, it definitely dominates the region.
343 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
344 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB)
347 // If we aren't allowing aggressive promotion anymore, then don't consider
348 // instructions in the 'if region'.
349 if (AggressiveInsts == 0) return false;
351 // If we have seen this instruction before, don't count it again.
352 if (AggressiveInsts->count(I)) return true;
354 // Okay, it looks like the instruction IS in the "condition". Check to
355 // see if it's a cheap instruction to unconditionally compute, and if it
356 // only uses stuff defined outside of the condition. If so, hoist it out.
357 if (!isSafeToSpeculativelyExecute(I))
360 unsigned Cost = ComputeSpeculationCost(I);
362 if (Cost > CostRemaining)
365 CostRemaining -= Cost;
367 // Okay, we can only really hoist these out if their operands do
368 // not take us over the cost threshold.
369 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
370 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining))
372 // Okay, it's safe to do this! Remember this instruction.
373 AggressiveInsts->insert(I);
377 /// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
378 /// and PointerNullValue. Return NULL if value is not a constant int.
379 static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
380 // Normal constant int.
381 ConstantInt *CI = dyn_cast<ConstantInt>(V);
382 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
385 // This is some kind of pointer constant. Turn it into a pointer-sized
386 // ConstantInt if possible.
387 IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
389 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
390 if (isa<ConstantPointerNull>(V))
391 return ConstantInt::get(PtrTy, 0);
393 // IntToPtr const int.
394 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
395 if (CE->getOpcode() == Instruction::IntToPtr)
396 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
397 // The constant is very likely to have the right type already.
398 if (CI->getType() == PtrTy)
401 return cast<ConstantInt>
402 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
407 /// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
408 /// collection of icmp eq/ne instructions that compare a value against a
409 /// constant, return the value being compared, and stick the constant into the
412 GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
413 const TargetData *TD, bool isEQ, unsigned &UsedICmps) {
414 Instruction *I = dyn_cast<Instruction>(V);
415 if (I == 0) return 0;
417 // If this is an icmp against a constant, handle this as one of the cases.
418 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
419 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
420 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
423 return I->getOperand(0);
426 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
429 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
431 // If this is an and/!= check then we want to optimize "x ugt 2" into
434 Span = Span.inverse();
436 // If there are a ton of values, we don't want to make a ginormous switch.
437 if (Span.getSetSize().ugt(8) || Span.isEmptySet())
440 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
441 Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
443 return I->getOperand(0);
448 // Otherwise, we can only handle an | or &, depending on isEQ.
449 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
452 unsigned NumValsBeforeLHS = Vals.size();
453 unsigned UsedICmpsBeforeLHS = UsedICmps;
454 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
456 unsigned NumVals = Vals.size();
457 unsigned UsedICmpsBeforeRHS = UsedICmps;
458 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
462 Vals.resize(NumVals);
463 UsedICmps = UsedICmpsBeforeRHS;
466 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
467 // set it and return success.
468 if (Extra == 0 || Extra == I->getOperand(1)) {
469 Extra = I->getOperand(1);
473 Vals.resize(NumValsBeforeLHS);
474 UsedICmps = UsedICmpsBeforeLHS;
478 // If the LHS can't be folded in, but Extra is available and RHS can, try to
480 if (Extra == 0 || Extra == I->getOperand(0)) {
481 Value *OldExtra = Extra;
482 Extra = I->getOperand(0);
483 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
486 assert(Vals.size() == NumValsBeforeLHS);
493 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
494 Instruction *Cond = 0;
495 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
496 Cond = dyn_cast<Instruction>(SI->getCondition());
497 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
498 if (BI->isConditional())
499 Cond = dyn_cast<Instruction>(BI->getCondition());
500 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
501 Cond = dyn_cast<Instruction>(IBI->getAddress());
504 TI->eraseFromParent();
505 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
508 /// isValueEqualityComparison - Return true if the specified terminator checks
509 /// to see if a value is equal to constant integer value.
510 Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
512 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
513 // Do not permit merging of large switch instructions into their
514 // predecessors unless there is only one predecessor.
515 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
516 pred_end(SI->getParent())) <= 128)
517 CV = SI->getCondition();
518 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
519 if (BI->isConditional() && BI->getCondition()->hasOneUse())
520 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
521 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
522 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
523 GetConstantInt(ICI->getOperand(1), TD))
524 CV = ICI->getOperand(0);
526 // Unwrap any lossless ptrtoint cast.
527 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
528 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
529 CV = PTII->getOperand(0);
533 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
534 /// decode all of the 'cases' that it represents and return the 'default' block.
535 BasicBlock *SimplifyCFGOpt::
536 GetValueEqualityComparisonCases(TerminatorInst *TI,
537 std::vector<ValueEqualityComparisonCase>
539 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
540 Cases.reserve(SI->getNumCases());
541 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i)
542 Cases.push_back(ValueEqualityComparisonCase(i.getCaseValue(),
543 i.getCaseSuccessor()));
544 return SI->getDefaultDest();
547 BranchInst *BI = cast<BranchInst>(TI);
548 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
549 BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE);
550 Cases.push_back(ValueEqualityComparisonCase(GetConstantInt(ICI->getOperand(1),
553 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
557 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
558 /// in the list that match the specified block.
559 static void EliminateBlockCases(BasicBlock *BB,
560 std::vector<ValueEqualityComparisonCase> &Cases) {
561 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
562 if (Cases[i].Dest == BB) {
563 Cases.erase(Cases.begin()+i);
568 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
571 ValuesOverlap(std::vector<ValueEqualityComparisonCase> &C1,
572 std::vector<ValueEqualityComparisonCase > &C2) {
573 std::vector<ValueEqualityComparisonCase> *V1 = &C1, *V2 = &C2;
575 // Make V1 be smaller than V2.
576 if (V1->size() > V2->size())
579 if (V1->size() == 0) return false;
580 if (V1->size() == 1) {
582 ConstantInt *TheVal = (*V1)[0].Value;
583 for (unsigned i = 0, e = V2->size(); i != e; ++i)
584 if (TheVal == (*V2)[i].Value)
588 // Otherwise, just sort both lists and compare element by element.
589 array_pod_sort(V1->begin(), V1->end());
590 array_pod_sort(V2->begin(), V2->end());
591 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
592 while (i1 != e1 && i2 != e2) {
593 if ((*V1)[i1].Value == (*V2)[i2].Value)
595 if ((*V1)[i1].Value < (*V2)[i2].Value)
603 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
604 /// terminator instruction and its block is known to only have a single
605 /// predecessor block, check to see if that predecessor is also a value
606 /// comparison with the same value, and if that comparison determines the
607 /// outcome of this comparison. If so, simplify TI. This does a very limited
608 /// form of jump threading.
609 bool SimplifyCFGOpt::
610 SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
612 IRBuilder<> &Builder) {
613 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
614 if (!PredVal) return false; // Not a value comparison in predecessor.
616 Value *ThisVal = isValueEqualityComparison(TI);
617 assert(ThisVal && "This isn't a value comparison!!");
618 if (ThisVal != PredVal) return false; // Different predicates.
620 // TODO: Preserve branch weight metadata, similarly to how
621 // FoldValueComparisonIntoPredecessors preserves it.
623 // Find out information about when control will move from Pred to TI's block.
624 std::vector<ValueEqualityComparisonCase> PredCases;
625 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
627 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
629 // Find information about how control leaves this block.
630 std::vector<ValueEqualityComparisonCase> ThisCases;
631 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
632 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
634 // If TI's block is the default block from Pred's comparison, potentially
635 // simplify TI based on this knowledge.
636 if (PredDef == TI->getParent()) {
637 // If we are here, we know that the value is none of those cases listed in
638 // PredCases. If there are any cases in ThisCases that are in PredCases, we
640 if (!ValuesOverlap(PredCases, ThisCases))
643 if (isa<BranchInst>(TI)) {
644 // Okay, one of the successors of this condbr is dead. Convert it to a
646 assert(ThisCases.size() == 1 && "Branch can only have one case!");
647 // Insert the new branch.
648 Instruction *NI = Builder.CreateBr(ThisDef);
651 // Remove PHI node entries for the dead edge.
652 ThisCases[0].Dest->removePredecessor(TI->getParent());
654 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
655 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
657 EraseTerminatorInstAndDCECond(TI);
661 SwitchInst *SI = cast<SwitchInst>(TI);
662 // Okay, TI has cases that are statically dead, prune them away.
663 SmallPtrSet<Constant*, 16> DeadCases;
664 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
665 DeadCases.insert(PredCases[i].Value);
667 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
668 << "Through successor TI: " << *TI);
670 for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) {
672 if (DeadCases.count(i.getCaseValue())) {
673 i.getCaseSuccessor()->removePredecessor(TI->getParent());
678 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
682 // Otherwise, TI's block must correspond to some matched value. Find out
683 // which value (or set of values) this is.
684 ConstantInt *TIV = 0;
685 BasicBlock *TIBB = TI->getParent();
686 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
687 if (PredCases[i].Dest == TIBB) {
689 return false; // Cannot handle multiple values coming to this block.
690 TIV = PredCases[i].Value;
692 assert(TIV && "No edge from pred to succ?");
694 // Okay, we found the one constant that our value can be if we get into TI's
695 // BB. Find out which successor will unconditionally be branched to.
696 BasicBlock *TheRealDest = 0;
697 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
698 if (ThisCases[i].Value == TIV) {
699 TheRealDest = ThisCases[i].Dest;
703 // If not handled by any explicit cases, it is handled by the default case.
704 if (TheRealDest == 0) TheRealDest = ThisDef;
706 // Remove PHI node entries for dead edges.
707 BasicBlock *CheckEdge = TheRealDest;
708 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
709 if (*SI != CheckEdge)
710 (*SI)->removePredecessor(TIBB);
714 // Insert the new branch.
715 Instruction *NI = Builder.CreateBr(TheRealDest);
718 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
719 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
721 EraseTerminatorInstAndDCECond(TI);
726 /// ConstantIntOrdering - This class implements a stable ordering of constant
727 /// integers that does not depend on their address. This is important for
728 /// applications that sort ConstantInt's to ensure uniqueness.
729 struct ConstantIntOrdering {
730 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
731 return LHS->getValue().ult(RHS->getValue());
736 static int ConstantIntSortPredicate(const void *P1, const void *P2) {
737 const ConstantInt *LHS = *(const ConstantInt*const*)P1;
738 const ConstantInt *RHS = *(const ConstantInt*const*)P2;
739 if (LHS->getValue().ult(RHS->getValue()))
741 if (LHS->getValue() == RHS->getValue())
746 static inline bool HasBranchWeights(const Instruction* I) {
747 MDNode* ProfMD = I->getMetadata(LLVMContext::MD_prof);
748 if (ProfMD && ProfMD->getOperand(0))
749 if (MDString* MDS = dyn_cast<MDString>(ProfMD->getOperand(0)))
750 return MDS->getString().equals("branch_weights");
755 /// Tries to get a branch weight for the given instruction, returns NULL if it
756 /// can't. Pos starts at 0.
757 static ConstantInt* GetWeight(Instruction* I, int Pos) {
758 MDNode* ProfMD = I->getMetadata(LLVMContext::MD_prof);
759 if (ProfMD && ProfMD->getOperand(0)) {
760 if (MDString* MDS = dyn_cast<MDString>(ProfMD->getOperand(0))) {
761 if (MDS->getString().equals("branch_weights")) {
762 assert(ProfMD->getNumOperands() >= 3);
763 return dyn_cast<ConstantInt>(ProfMD->getOperand(1 + Pos));
771 /// Scale the given weights based on the successor TI's metadata. Scaling is
772 /// done by multiplying every weight by the sum of the successor's weights.
773 static void ScaleWeights(Instruction* STI, MutableArrayRef<uint64_t> Weights) {
774 // Sum the successor's weights
775 assert(HasBranchWeights(STI));
777 MDNode* ProfMD = STI->getMetadata(LLVMContext::MD_prof);
778 for (unsigned i = 1; i < ProfMD->getNumOperands(); ++i) {
779 ConstantInt* CI = dyn_cast<ConstantInt>(ProfMD->getOperand(i));
781 Scale += CI->getValue().getZExtValue();
784 // Skip default, as it's replaced during the folding
785 for (unsigned i = 1; i < Weights.size(); ++i) {
790 /// Sees if any of the weights are too big for a uint32_t, and halves all the
791 /// weights if any are.
792 static void FitWeights(MutableArrayRef<uint64_t> Weights) {
794 for (unsigned i = 0; i < Weights.size(); ++i)
795 if (Weights[i] > UINT_MAX) {
803 for (unsigned i = 0; i < Weights.size(); ++i)
807 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
808 /// equality comparison instruction (either a switch or a branch on "X == c").
809 /// See if any of the predecessors of the terminator block are value comparisons
810 /// on the same value. If so, and if safe to do so, fold them together.
811 bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
812 IRBuilder<> &Builder) {
813 BasicBlock *BB = TI->getParent();
814 Value *CV = isValueEqualityComparison(TI); // CondVal
815 assert(CV && "Not a comparison?");
816 bool Changed = false;
818 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
819 while (!Preds.empty()) {
820 BasicBlock *Pred = Preds.pop_back_val();
822 // See if the predecessor is a comparison with the same value.
823 TerminatorInst *PTI = Pred->getTerminator();
824 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
826 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
827 // Figure out which 'cases' to copy from SI to PSI.
828 std::vector<ValueEqualityComparisonCase> BBCases;
829 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
831 std::vector<ValueEqualityComparisonCase> PredCases;
832 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
834 // Based on whether the default edge from PTI goes to BB or not, fill in
835 // PredCases and PredDefault with the new switch cases we would like to
837 SmallVector<BasicBlock*, 8> NewSuccessors;
839 // Update the branch weight metadata along the way
840 SmallVector<uint64_t, 8> Weights;
841 uint64_t PredDefaultWeight = 0;
842 bool PredHasWeights = HasBranchWeights(PTI);
843 bool SuccHasWeights = HasBranchWeights(TI);
845 if (PredHasWeights) {
846 MDNode* MD = PTI->getMetadata(LLVMContext::MD_prof);
848 for (unsigned i = 1, e = MD->getNumOperands(); i < e; ++i) {
849 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(i));
851 Weights.push_back(CI->getValue().getZExtValue());
854 // If the predecessor is a conditional eq, then swap the default weight
855 // to be the first entry.
856 if (BranchInst* BI = dyn_cast<BranchInst>(PTI)) {
857 assert(Weights.size() == 2);
858 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
860 if (ICI->getPredicate() == ICmpInst::ICMP_EQ) {
861 std::swap(Weights.front(), Weights.back());
865 PredDefaultWeight = Weights.front();
866 } else if (SuccHasWeights) {
867 // If there are no predecessor weights but there are successor weights,
868 // populate Weights with 1, which will later be scaled to the sum of
869 // successor's weights
870 Weights.assign(1 + PredCases.size(), 1);
871 PredDefaultWeight = 1;
874 uint64_t SuccDefaultWeight = 0;
875 if (SuccHasWeights) {
877 if (BranchInst* BI = dyn_cast<BranchInst>(TI)) {
878 ICmpInst* ICI = dyn_cast<ICmpInst>(BI->getCondition());
881 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
885 SuccDefaultWeight = GetWeight(TI, Index)->getValue().getZExtValue();
888 if (PredDefault == BB) {
889 // If this is the default destination from PTI, only the edges in TI
890 // that don't occur in PTI, or that branch to BB will be activated.
891 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
892 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
893 if (PredCases[i].Dest != BB)
894 PTIHandled.insert(PredCases[i].Value);
896 // The default destination is BB, we don't need explicit targets.
897 std::swap(PredCases[i], PredCases.back());
899 if (PredHasWeights) {
900 std::swap(Weights[i+1], Weights.back());
904 PredCases.pop_back();
908 // Reconstruct the new switch statement we will be building.
909 if (PredDefault != BBDefault) {
910 PredDefault->removePredecessor(Pred);
911 PredDefault = BBDefault;
912 NewSuccessors.push_back(BBDefault);
915 if (SuccHasWeights) {
916 ScaleWeights(TI, Weights);
917 Weights.front() *= SuccDefaultWeight;
918 } else if (PredHasWeights) {
919 Weights.front() /= (1 + BBCases.size());
922 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
923 if (!PTIHandled.count(BBCases[i].Value) &&
924 BBCases[i].Dest != BBDefault) {
925 PredCases.push_back(BBCases[i]);
926 NewSuccessors.push_back(BBCases[i].Dest);
927 if (SuccHasWeights) {
928 Weights.push_back(PredDefaultWeight *
929 GetWeight(TI, i)->getValue().getZExtValue());
930 } else if (PredHasWeights) {
931 // Split the old default's weight amongst the children
932 assert(PredDefaultWeight != 0);
933 Weights.push_back(PredDefaultWeight / (1 + BBCases.size()));
938 // FIXME: preserve branch weight metadata, similarly to the 'then'
939 // above. For now, drop it.
940 PredHasWeights = false;
941 SuccHasWeights = false;
943 // If this is not the default destination from PSI, only the edges
944 // in SI that occur in PSI with a destination of BB will be
946 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
947 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
948 if (PredCases[i].Dest == BB) {
949 PTIHandled.insert(PredCases[i].Value);
950 std::swap(PredCases[i], PredCases.back());
951 PredCases.pop_back();
955 // Okay, now we know which constants were sent to BB from the
956 // predecessor. Figure out where they will all go now.
957 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
958 if (PTIHandled.count(BBCases[i].Value)) {
959 // If this is one we are capable of getting...
960 PredCases.push_back(BBCases[i]);
961 NewSuccessors.push_back(BBCases[i].Dest);
962 PTIHandled.erase(BBCases[i].Value);// This constant is taken care of
965 // If there are any constants vectored to BB that TI doesn't handle,
966 // they must go to the default destination of TI.
967 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
969 E = PTIHandled.end(); I != E; ++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 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
1165 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
1166 /// (for now, restricted to a single instruction that's side effect free) from
1167 /// the BB1 into the branch block to speculatively execute it.
1172 /// br i1 %t1, label %BB1, label %BB2
1174 /// %t3 = add %t2, c
1180 /// %t4 = add %t2, c
1181 /// %t3 = select i1 %t1, %t2, %t3
1182 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
1183 // Only speculatively execution a single instruction (not counting the
1184 // terminator) for now.
1185 Instruction *HInst = NULL;
1186 Instruction *Term = BB1->getTerminator();
1187 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
1188 BBI != BBE; ++BBI) {
1189 Instruction *I = BBI;
1191 if (isa<DbgInfoIntrinsic>(I)) continue;
1192 if (I == Term) break;
1199 BasicBlock *BIParent = BI->getParent();
1201 // Check the instruction to be hoisted, if there is one.
1203 // Don't hoist the instruction if it's unsafe or expensive.
1204 if (!isSafeToSpeculativelyExecute(HInst))
1206 if (ComputeSpeculationCost(HInst) > PHINodeFoldingThreshold)
1209 // Do not hoist the instruction if any of its operands are defined but not
1210 // used in this BB. The transformation will prevent the operand from
1211 // being sunk into the use block.
1212 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1214 Instruction *OpI = dyn_cast<Instruction>(*i);
1215 if (OpI && OpI->getParent() == BIParent &&
1216 !OpI->mayHaveSideEffects() &&
1217 !OpI->isUsedInBasicBlock(BIParent))
1222 // Be conservative for now. FP select instruction can often be expensive.
1223 Value *BrCond = BI->getCondition();
1224 if (isa<FCmpInst>(BrCond))
1227 // If BB1 is actually on the false edge of the conditional branch, remember
1228 // to swap the select operands later.
1229 bool Invert = false;
1230 if (BB1 != BI->getSuccessor(0)) {
1231 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
1235 // Collect interesting PHIs, and scan for hazards.
1236 SmallSetVector<std::pair<Value *, Value *>, 4> PHIs;
1237 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
1238 for (BasicBlock::iterator I = BB2->begin();
1239 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1240 Value *BB1V = PN->getIncomingValueForBlock(BB1);
1241 Value *BIParentV = PN->getIncomingValueForBlock(BIParent);
1243 // Skip PHIs which are trivial.
1244 if (BB1V == BIParentV)
1247 // Check for saftey.
1248 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BB1V)) {
1249 // An unfolded ConstantExpr could end up getting expanded into
1250 // Instructions. Don't speculate this and another instruction at
1254 if (!isSafeToSpeculativelyExecute(CE))
1256 if (ComputeSpeculationCost(CE) > PHINodeFoldingThreshold)
1260 // Ok, we may insert a select for this PHI.
1261 PHIs.insert(std::make_pair(BB1V, BIParentV));
1264 // If there are no PHIs to process, bail early. This helps ensure idempotence
1269 // If we get here, we can hoist the instruction and if-convert.
1270 DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *BB1 << "\n";);
1272 // Hoist the instruction.
1274 BIParent->getInstList().splice(BI, BB1->getInstList(), HInst);
1276 // Insert selects and rewrite the PHI operands.
1277 IRBuilder<true, NoFolder> Builder(BI);
1278 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
1279 Value *TrueV = PHIs[i].first;
1280 Value *FalseV = PHIs[i].second;
1282 // Create a select whose true value is the speculatively executed value and
1283 // false value is the previously determined FalseV.
1286 SI = cast<SelectInst>
1287 (Builder.CreateSelect(BrCond, FalseV, TrueV,
1288 FalseV->getName() + "." + TrueV->getName()));
1290 SI = cast<SelectInst>
1291 (Builder.CreateSelect(BrCond, TrueV, FalseV,
1292 TrueV->getName() + "." + FalseV->getName()));
1294 // Make the PHI node use the select for all incoming values for "then" and
1296 for (BasicBlock::iterator I = BB2->begin();
1297 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1298 unsigned BB1I = PN->getBasicBlockIndex(BB1);
1299 unsigned BIParentI = PN->getBasicBlockIndex(BIParent);
1300 Value *BB1V = PN->getIncomingValue(BB1I);
1301 Value *BIParentV = PN->getIncomingValue(BIParentI);
1302 if (TrueV == BB1V && FalseV == BIParentV) {
1303 PN->setIncomingValue(BB1I, SI);
1304 PN->setIncomingValue(BIParentI, SI);
1313 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1314 /// across this block.
1315 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1316 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1319 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1320 if (isa<DbgInfoIntrinsic>(BBI))
1322 if (Size > 10) return false; // Don't clone large BB's.
1325 // We can only support instructions that do not define values that are
1326 // live outside of the current basic block.
1327 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1329 Instruction *U = cast<Instruction>(*UI);
1330 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1333 // Looks ok, continue checking.
1339 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1340 /// that is defined in the same block as the branch and if any PHI entries are
1341 /// constants, thread edges corresponding to that entry to be branches to their
1342 /// ultimate destination.
1343 static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
1344 BasicBlock *BB = BI->getParent();
1345 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1346 // NOTE: we currently cannot transform this case if the PHI node is used
1347 // outside of the block.
1348 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1351 // Degenerate case of a single entry PHI.
1352 if (PN->getNumIncomingValues() == 1) {
1353 FoldSingleEntryPHINodes(PN->getParent());
1357 // Now we know that this block has multiple preds and two succs.
1358 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1360 // Okay, this is a simple enough basic block. See if any phi values are
1362 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1363 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1364 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1366 // Okay, we now know that all edges from PredBB should be revectored to
1367 // branch to RealDest.
1368 BasicBlock *PredBB = PN->getIncomingBlock(i);
1369 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1371 if (RealDest == BB) continue; // Skip self loops.
1372 // Skip if the predecessor's terminator is an indirect branch.
1373 if (isa<IndirectBrInst>(PredBB->getTerminator())) continue;
1375 // The dest block might have PHI nodes, other predecessors and other
1376 // difficult cases. Instead of being smart about this, just insert a new
1377 // block that jumps to the destination block, effectively splitting
1378 // the edge we are about to create.
1379 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1380 RealDest->getName()+".critedge",
1381 RealDest->getParent(), RealDest);
1382 BranchInst::Create(RealDest, EdgeBB);
1384 // Update PHI nodes.
1385 AddPredecessorToBlock(RealDest, EdgeBB, BB);
1387 // BB may have instructions that are being threaded over. Clone these
1388 // instructions into EdgeBB. We know that there will be no uses of the
1389 // cloned instructions outside of EdgeBB.
1390 BasicBlock::iterator InsertPt = EdgeBB->begin();
1391 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1392 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1393 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1394 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1397 // Clone the instruction.
1398 Instruction *N = BBI->clone();
1399 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1401 // Update operands due to translation.
1402 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1404 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1405 if (PI != TranslateMap.end())
1409 // Check for trivial simplification.
1410 if (Value *V = SimplifyInstruction(N, TD)) {
1411 TranslateMap[BBI] = V;
1412 delete N; // Instruction folded away, don't need actual inst
1414 // Insert the new instruction into its new home.
1415 EdgeBB->getInstList().insert(InsertPt, N);
1416 if (!BBI->use_empty())
1417 TranslateMap[BBI] = N;
1421 // Loop over all of the edges from PredBB to BB, changing them to branch
1422 // to EdgeBB instead.
1423 TerminatorInst *PredBBTI = PredBB->getTerminator();
1424 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1425 if (PredBBTI->getSuccessor(i) == BB) {
1426 BB->removePredecessor(PredBB);
1427 PredBBTI->setSuccessor(i, EdgeBB);
1430 // Recurse, simplifying any other constants.
1431 return FoldCondBranchOnPHI(BI, TD) | true;
1437 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1438 /// PHI node, see if we can eliminate it.
1439 static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
1440 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1441 // statement", which has a very simple dominance structure. Basically, we
1442 // are trying to find the condition that is being branched on, which
1443 // subsequently causes this merge to happen. We really want control
1444 // dependence information for this check, but simplifycfg can't keep it up
1445 // to date, and this catches most of the cases we care about anyway.
1446 BasicBlock *BB = PN->getParent();
1447 BasicBlock *IfTrue, *IfFalse;
1448 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1450 // Don't bother if the branch will be constant folded trivially.
1451 isa<ConstantInt>(IfCond))
1454 // Okay, we found that we can merge this two-entry phi node into a select.
1455 // Doing so would require us to fold *all* two entry phi nodes in this block.
1456 // At some point this becomes non-profitable (particularly if the target
1457 // doesn't support cmov's). Only do this transformation if there are two or
1458 // fewer PHI nodes in this block.
1459 unsigned NumPhis = 0;
1460 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1464 // Loop over the PHI's seeing if we can promote them all to select
1465 // instructions. While we are at it, keep track of the instructions
1466 // that need to be moved to the dominating block.
1467 SmallPtrSet<Instruction*, 4> AggressiveInsts;
1468 unsigned MaxCostVal0 = PHINodeFoldingThreshold,
1469 MaxCostVal1 = PHINodeFoldingThreshold;
1471 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1472 PHINode *PN = cast<PHINode>(II++);
1473 if (Value *V = SimplifyInstruction(PN, TD)) {
1474 PN->replaceAllUsesWith(V);
1475 PN->eraseFromParent();
1479 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
1481 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
1486 // If we folded the first phi, PN dangles at this point. Refresh it. If
1487 // we ran out of PHIs then we simplified them all.
1488 PN = dyn_cast<PHINode>(BB->begin());
1489 if (PN == 0) return true;
1491 // Don't fold i1 branches on PHIs which contain binary operators. These can
1492 // often be turned into switches and other things.
1493 if (PN->getType()->isIntegerTy(1) &&
1494 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1495 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1496 isa<BinaryOperator>(IfCond)))
1499 // If we all PHI nodes are promotable, check to make sure that all
1500 // instructions in the predecessor blocks can be promoted as well. If
1501 // not, we won't be able to get rid of the control flow, so it's not
1502 // worth promoting to select instructions.
1503 BasicBlock *DomBlock = 0;
1504 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1505 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1506 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1509 DomBlock = *pred_begin(IfBlock1);
1510 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
1511 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1512 // This is not an aggressive instruction that we can promote.
1513 // Because of this, we won't be able to get rid of the control
1514 // flow, so the xform is not worth it.
1519 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1522 DomBlock = *pred_begin(IfBlock2);
1523 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
1524 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1525 // This is not an aggressive instruction that we can promote.
1526 // Because of this, we won't be able to get rid of the control
1527 // flow, so the xform is not worth it.
1532 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1533 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1535 // If we can still promote the PHI nodes after this gauntlet of tests,
1536 // do all of the PHI's now.
1537 Instruction *InsertPt = DomBlock->getTerminator();
1538 IRBuilder<true, NoFolder> Builder(InsertPt);
1540 // Move all 'aggressive' instructions, which are defined in the
1541 // conditional parts of the if's up to the dominating block.
1543 DomBlock->getInstList().splice(InsertPt,
1544 IfBlock1->getInstList(), IfBlock1->begin(),
1545 IfBlock1->getTerminator());
1547 DomBlock->getInstList().splice(InsertPt,
1548 IfBlock2->getInstList(), IfBlock2->begin(),
1549 IfBlock2->getTerminator());
1551 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1552 // Change the PHI node into a select instruction.
1553 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1554 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1557 cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, ""));
1558 PN->replaceAllUsesWith(NV);
1560 PN->eraseFromParent();
1563 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1564 // has been flattened. Change DomBlock to jump directly to our new block to
1565 // avoid other simplifycfg's kicking in on the diamond.
1566 TerminatorInst *OldTI = DomBlock->getTerminator();
1567 Builder.SetInsertPoint(OldTI);
1568 Builder.CreateBr(BB);
1569 OldTI->eraseFromParent();
1573 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1574 /// to two returning blocks, try to merge them together into one return,
1575 /// introducing a select if the return values disagree.
1576 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
1577 IRBuilder<> &Builder) {
1578 assert(BI->isConditional() && "Must be a conditional branch");
1579 BasicBlock *TrueSucc = BI->getSuccessor(0);
1580 BasicBlock *FalseSucc = BI->getSuccessor(1);
1581 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1582 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1584 // Check to ensure both blocks are empty (just a return) or optionally empty
1585 // with PHI nodes. If there are other instructions, merging would cause extra
1586 // computation on one path or the other.
1587 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
1589 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
1592 Builder.SetInsertPoint(BI);
1593 // Okay, we found a branch that is going to two return nodes. If
1594 // there is no return value for this function, just change the
1595 // branch into a return.
1596 if (FalseRet->getNumOperands() == 0) {
1597 TrueSucc->removePredecessor(BI->getParent());
1598 FalseSucc->removePredecessor(BI->getParent());
1599 Builder.CreateRetVoid();
1600 EraseTerminatorInstAndDCECond(BI);
1604 // Otherwise, figure out what the true and false return values are
1605 // so we can insert a new select instruction.
1606 Value *TrueValue = TrueRet->getReturnValue();
1607 Value *FalseValue = FalseRet->getReturnValue();
1609 // Unwrap any PHI nodes in the return blocks.
1610 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1611 if (TVPN->getParent() == TrueSucc)
1612 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1613 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1614 if (FVPN->getParent() == FalseSucc)
1615 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1617 // In order for this transformation to be safe, we must be able to
1618 // unconditionally execute both operands to the return. This is
1619 // normally the case, but we could have a potentially-trapping
1620 // constant expression that prevents this transformation from being
1622 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1625 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1629 // Okay, we collected all the mapped values and checked them for sanity, and
1630 // defined to really do this transformation. First, update the CFG.
1631 TrueSucc->removePredecessor(BI->getParent());
1632 FalseSucc->removePredecessor(BI->getParent());
1634 // Insert select instructions where needed.
1635 Value *BrCond = BI->getCondition();
1637 // Insert a select if the results differ.
1638 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1639 } else if (isa<UndefValue>(TrueValue)) {
1640 TrueValue = FalseValue;
1642 TrueValue = Builder.CreateSelect(BrCond, TrueValue,
1643 FalseValue, "retval");
1647 Value *RI = !TrueValue ?
1648 Builder.CreateRetVoid() : Builder.CreateRet(TrueValue);
1652 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1653 << "\n " << *BI << "NewRet = " << *RI
1654 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1656 EraseTerminatorInstAndDCECond(BI);
1661 /// ExtractBranchMetadata - Given a conditional BranchInstruction, retrieve the
1662 /// probabilities of the branch taking each edge. Fills in the two APInt
1663 /// parameters and return true, or returns false if no or invalid metadata was
1665 static bool ExtractBranchMetadata(BranchInst *BI,
1666 APInt &ProbTrue, APInt &ProbFalse) {
1667 assert(BI->isConditional() &&
1668 "Looking for probabilities on unconditional branch?");
1669 MDNode *ProfileData = BI->getMetadata(LLVMContext::MD_prof);
1670 if (!ProfileData || ProfileData->getNumOperands() != 3) return false;
1671 ConstantInt *CITrue = dyn_cast<ConstantInt>(ProfileData->getOperand(1));
1672 ConstantInt *CIFalse = dyn_cast<ConstantInt>(ProfileData->getOperand(2));
1673 if (!CITrue || !CIFalse) return false;
1674 ProbTrue = CITrue->getValue();
1675 ProbFalse = CIFalse->getValue();
1676 assert(ProbTrue.getBitWidth() == 32 && ProbFalse.getBitWidth() == 32 &&
1677 "Branch probability metadata must be 32-bit integers");
1681 /// MultiplyAndLosePrecision - Multiplies A and B, then returns the result. In
1682 /// the event of overflow, logically-shifts all four inputs right until the
1684 static APInt MultiplyAndLosePrecision(APInt &A, APInt &B, APInt &C, APInt &D,
1685 unsigned &BitsLost) {
1687 bool Overflow = false;
1688 APInt Result = A.umul_ov(B, Overflow);
1690 APInt MaxB = APInt::getMaxValue(A.getBitWidth()).udiv(A);
1694 } while (B.ugt(MaxB));
1695 A = A.lshr(BitsLost);
1696 C = C.lshr(BitsLost);
1697 D = D.lshr(BitsLost);
1703 /// checkCSEInPredecessor - Return true if the given instruction is available
1704 /// in its predecessor block. If yes, the instruction will be removed.
1706 static bool checkCSEInPredecessor(Instruction *Inst, BasicBlock *PB) {
1707 if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst))
1709 for (BasicBlock::iterator I = PB->begin(), E = PB->end(); I != E; I++) {
1710 Instruction *PBI = &*I;
1711 // Check whether Inst and PBI generate the same value.
1712 if (Inst->isIdenticalTo(PBI)) {
1713 Inst->replaceAllUsesWith(PBI);
1714 Inst->eraseFromParent();
1721 /// FoldBranchToCommonDest - If this basic block is simple enough, and if a
1722 /// predecessor branches to us and one of our successors, fold the block into
1723 /// the predecessor and use logical operations to pick the right destination.
1724 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1725 BasicBlock *BB = BI->getParent();
1727 Instruction *Cond = 0;
1728 if (BI->isConditional())
1729 Cond = dyn_cast<Instruction>(BI->getCondition());
1731 // For unconditional branch, check for a simple CFG pattern, where
1732 // BB has a single predecessor and BB's successor is also its predecessor's
1733 // successor. If such pattern exisits, check for CSE between BB and its
1735 if (BasicBlock *PB = BB->getSinglePredecessor())
1736 if (BranchInst *PBI = dyn_cast<BranchInst>(PB->getTerminator()))
1737 if (PBI->isConditional() &&
1738 (BI->getSuccessor(0) == PBI->getSuccessor(0) ||
1739 BI->getSuccessor(0) == PBI->getSuccessor(1))) {
1740 for (BasicBlock::iterator I = BB->begin(), E = BB->end();
1742 Instruction *Curr = I++;
1743 if (isa<CmpInst>(Curr)) {
1747 // Quit if we can't remove this instruction.
1748 if (!checkCSEInPredecessor(Curr, PB))
1757 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1758 Cond->getParent() != BB || !Cond->hasOneUse())
1761 // Only allow this if the condition is a simple instruction that can be
1762 // executed unconditionally. It must be in the same block as the branch, and
1763 // must be at the front of the block.
1764 BasicBlock::iterator FrontIt = BB->front();
1766 // Ignore dbg intrinsics.
1767 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1769 // Allow a single instruction to be hoisted in addition to the compare
1770 // that feeds the branch. We later ensure that any values that _it_ uses
1771 // were also live in the predecessor, so that we don't unnecessarily create
1772 // register pressure or inhibit out-of-order execution.
1773 Instruction *BonusInst = 0;
1774 if (&*FrontIt != Cond &&
1775 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1776 isSafeToSpeculativelyExecute(FrontIt)) {
1777 BonusInst = &*FrontIt;
1780 // Ignore dbg intrinsics.
1781 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
1784 // Only a single bonus inst is allowed.
1785 if (&*FrontIt != Cond)
1788 // Make sure the instruction after the condition is the cond branch.
1789 BasicBlock::iterator CondIt = Cond; ++CondIt;
1791 // Ingore dbg intrinsics.
1792 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
1797 // Cond is known to be a compare or binary operator. Check to make sure that
1798 // neither operand is a potentially-trapping constant expression.
1799 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1802 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1806 // Finally, don't infinitely unroll conditional loops.
1807 BasicBlock *TrueDest = BI->getSuccessor(0);
1808 BasicBlock *FalseDest = (BI->isConditional()) ? BI->getSuccessor(1) : 0;
1809 if (TrueDest == BB || FalseDest == BB)
1812 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1813 BasicBlock *PredBlock = *PI;
1814 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1816 // Check that we have two conditional branches. If there is a PHI node in
1817 // the common successor, verify that the same value flows in from both
1819 SmallVector<PHINode*, 4> PHIs;
1820 if (PBI == 0 || PBI->isUnconditional() ||
1821 (BI->isConditional() &&
1822 !SafeToMergeTerminators(BI, PBI)) ||
1823 (!BI->isConditional() &&
1824 !isProfitableToFoldUnconditional(BI, PBI, Cond, PHIs)))
1827 // Determine if the two branches share a common destination.
1828 Instruction::BinaryOps Opc;
1829 bool InvertPredCond = false;
1831 if (BI->isConditional()) {
1832 if (PBI->getSuccessor(0) == TrueDest)
1833 Opc = Instruction::Or;
1834 else if (PBI->getSuccessor(1) == FalseDest)
1835 Opc = Instruction::And;
1836 else if (PBI->getSuccessor(0) == FalseDest)
1837 Opc = Instruction::And, InvertPredCond = true;
1838 else if (PBI->getSuccessor(1) == TrueDest)
1839 Opc = Instruction::Or, InvertPredCond = true;
1843 if (PBI->getSuccessor(0) != TrueDest && PBI->getSuccessor(1) != TrueDest)
1847 // Ensure that any values used in the bonus instruction are also used
1848 // by the terminator of the predecessor. This means that those values
1849 // must already have been resolved, so we won't be inhibiting the
1850 // out-of-order core by speculating them earlier.
1852 // Collect the values used by the bonus inst
1853 SmallPtrSet<Value*, 4> UsedValues;
1854 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1855 OE = BonusInst->op_end(); OI != OE; ++OI) {
1857 if (!isa<Constant>(V))
1858 UsedValues.insert(V);
1861 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1862 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1864 // Walk up to four levels back up the use-def chain of the predecessor's
1865 // terminator to see if all those values were used. The choice of four
1866 // levels is arbitrary, to provide a compile-time-cost bound.
1867 while (!Worklist.empty()) {
1868 std::pair<Value*, unsigned> Pair = Worklist.back();
1869 Worklist.pop_back();
1871 if (Pair.second >= 4) continue;
1872 UsedValues.erase(Pair.first);
1873 if (UsedValues.empty()) break;
1875 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
1876 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1878 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1882 if (!UsedValues.empty()) return false;
1885 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1886 IRBuilder<> Builder(PBI);
1888 // If we need to invert the condition in the pred block to match, do so now.
1889 if (InvertPredCond) {
1890 Value *NewCond = PBI->getCondition();
1892 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
1893 CmpInst *CI = cast<CmpInst>(NewCond);
1894 CI->setPredicate(CI->getInversePredicate());
1896 NewCond = Builder.CreateNot(NewCond,
1897 PBI->getCondition()->getName()+".not");
1900 PBI->setCondition(NewCond);
1901 PBI->swapSuccessors();
1904 // If we have a bonus inst, clone it into the predecessor block.
1905 Instruction *NewBonus = 0;
1907 NewBonus = BonusInst->clone();
1908 PredBlock->getInstList().insert(PBI, NewBonus);
1909 NewBonus->takeName(BonusInst);
1910 BonusInst->setName(BonusInst->getName()+".old");
1913 // Clone Cond into the predecessor basic block, and or/and the
1914 // two conditions together.
1915 Instruction *New = Cond->clone();
1916 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
1917 PredBlock->getInstList().insert(PBI, New);
1918 New->takeName(Cond);
1919 Cond->setName(New->getName()+".old");
1921 if (BI->isConditional()) {
1922 Instruction *NewCond =
1923 cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(),
1925 PBI->setCondition(NewCond);
1927 if (PBI->getSuccessor(0) == BB) {
1928 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1929 PBI->setSuccessor(0, TrueDest);
1931 if (PBI->getSuccessor(1) == BB) {
1932 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1933 PBI->setSuccessor(1, FalseDest);
1936 // Update PHI nodes in the common successors.
1937 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
1938 ConstantInt *PBI_C = cast<ConstantInt>(
1939 PHIs[i]->getIncomingValueForBlock(PBI->getParent()));
1940 assert(PBI_C->getType()->isIntegerTy(1));
1941 Instruction *MergedCond = 0;
1942 if (PBI->getSuccessor(0) == TrueDest) {
1943 // Create (PBI_Cond and PBI_C) or (!PBI_Cond and BI_Value)
1944 // PBI_C is true: PBI_Cond or (!PBI_Cond and BI_Value)
1945 // is false: !PBI_Cond and BI_Value
1946 Instruction *NotCond =
1947 cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
1950 cast<Instruction>(Builder.CreateBinOp(Instruction::And,
1955 cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
1956 PBI->getCondition(), MergedCond,
1959 // Create (PBI_Cond and BI_Value) or (!PBI_Cond and PBI_C)
1960 // PBI_C is true: (PBI_Cond and BI_Value) or (!PBI_Cond)
1961 // is false: PBI_Cond and BI_Value
1963 cast<Instruction>(Builder.CreateBinOp(Instruction::And,
1964 PBI->getCondition(), New,
1966 if (PBI_C->isOne()) {
1967 Instruction *NotCond =
1968 cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
1971 cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
1972 NotCond, MergedCond,
1977 PHIs[i]->setIncomingValue(PHIs[i]->getBasicBlockIndex(PBI->getParent()),
1980 // Change PBI from Conditional to Unconditional.
1981 BranchInst *New_PBI = BranchInst::Create(TrueDest, PBI);
1982 EraseTerminatorInstAndDCECond(PBI);
1986 // TODO: If BB is reachable from all paths through PredBlock, then we
1987 // could replace PBI's branch probabilities with BI's.
1989 // Merge probability data into PredBlock's branch.
1991 if (PBI->isConditional() && BI->isConditional() &&
1992 ExtractBranchMetadata(PBI, C, D) && ExtractBranchMetadata(BI, A, B)) {
1993 // Given IR which does:
1995 // br i1 %x, label %bbB, label %bbC
1997 // br i1 %y, label %bbD, label %bbC
1998 // Let's call the probability that we take the edge from %bbA to %bbB
1999 // 'a', from %bbA to %bbC, 'b', from %bbB to %bbD 'c' and from %bbB to
2000 // %bbC probability 'd'.
2002 // We transform the IR into:
2004 // br i1 %z, label %bbD, label %bbC
2005 // where the probability of going to %bbD is (a*c) and going to bbC is
2008 // Probabilities aren't stored as ratios directly. Using branch weights,
2010 // (a*c)% = A*C, (b+(a*d))% = A*D+B*C+B*D.
2012 // In the event of overflow, we want to drop the LSB of the input
2016 // Ignore overflow result on ProbTrue.
2017 APInt ProbTrue = MultiplyAndLosePrecision(A, C, B, D, BitsLost);
2019 APInt Tmp1 = MultiplyAndLosePrecision(B, D, A, C, BitsLost);
2021 ProbTrue = ProbTrue.lshr(BitsLost*2);
2024 APInt Tmp2 = MultiplyAndLosePrecision(A, D, C, B, BitsLost);
2026 ProbTrue = ProbTrue.lshr(BitsLost*2);
2027 Tmp1 = Tmp1.lshr(BitsLost*2);
2030 APInt Tmp3 = MultiplyAndLosePrecision(B, C, A, D, BitsLost);
2032 ProbTrue = ProbTrue.lshr(BitsLost*2);
2033 Tmp1 = Tmp1.lshr(BitsLost*2);
2034 Tmp2 = Tmp2.lshr(BitsLost*2);
2037 bool Overflow1 = false, Overflow2 = false;
2038 APInt Tmp4 = Tmp2.uadd_ov(Tmp3, Overflow1);
2039 APInt ProbFalse = Tmp4.uadd_ov(Tmp1, Overflow2);
2041 if (Overflow1 || Overflow2) {
2042 ProbTrue = ProbTrue.lshr(1);
2043 Tmp1 = Tmp1.lshr(1);
2044 Tmp2 = Tmp2.lshr(1);
2045 Tmp3 = Tmp3.lshr(1);
2047 ProbFalse = Tmp4 + Tmp1;
2050 // The sum of branch weights must fit in 32-bits.
2051 if (ProbTrue.isNegative() && ProbFalse.isNegative()) {
2052 ProbTrue = ProbTrue.lshr(1);
2053 ProbFalse = ProbFalse.lshr(1);
2056 if (ProbTrue != ProbFalse) {
2057 // Normalize the result.
2058 APInt GCD = APIntOps::GreatestCommonDivisor(ProbTrue, ProbFalse);
2059 ProbTrue = ProbTrue.udiv(GCD);
2060 ProbFalse = ProbFalse.udiv(GCD);
2062 MDBuilder MDB(BI->getContext());
2063 MDNode *N = MDB.createBranchWeights(ProbTrue.getZExtValue(),
2064 ProbFalse.getZExtValue());
2065 PBI->setMetadata(LLVMContext::MD_prof, N);
2067 PBI->setMetadata(LLVMContext::MD_prof, NULL);
2070 PBI->setMetadata(LLVMContext::MD_prof, NULL);
2073 // Copy any debug value intrinsics into the end of PredBlock.
2074 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
2075 if (isa<DbgInfoIntrinsic>(*I))
2076 I->clone()->insertBefore(PBI);
2083 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
2084 /// predecessor of another block, this function tries to simplify it. We know
2085 /// that PBI and BI are both conditional branches, and BI is in one of the
2086 /// successor blocks of PBI - PBI branches to BI.
2087 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
2088 assert(PBI->isConditional() && BI->isConditional());
2089 BasicBlock *BB = BI->getParent();
2091 // If this block ends with a branch instruction, and if there is a
2092 // predecessor that ends on a branch of the same condition, make
2093 // this conditional branch redundant.
2094 if (PBI->getCondition() == BI->getCondition() &&
2095 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
2096 // Okay, the outcome of this conditional branch is statically
2097 // knowable. If this block had a single pred, handle specially.
2098 if (BB->getSinglePredecessor()) {
2099 // Turn this into a branch on constant.
2100 bool CondIsTrue = PBI->getSuccessor(0) == BB;
2101 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
2103 return true; // Nuke the branch on constant.
2106 // Otherwise, if there are multiple predecessors, insert a PHI that merges
2107 // in the constant and simplify the block result. Subsequent passes of
2108 // simplifycfg will thread the block.
2109 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
2110 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
2111 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
2112 std::distance(PB, PE),
2113 BI->getCondition()->getName() + ".pr",
2115 // Okay, we're going to insert the PHI node. Since PBI is not the only
2116 // predecessor, compute the PHI'd conditional value for all of the preds.
2117 // Any predecessor where the condition is not computable we keep symbolic.
2118 for (pred_iterator PI = PB; PI != PE; ++PI) {
2119 BasicBlock *P = *PI;
2120 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
2121 PBI != BI && PBI->isConditional() &&
2122 PBI->getCondition() == BI->getCondition() &&
2123 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
2124 bool CondIsTrue = PBI->getSuccessor(0) == BB;
2125 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
2128 NewPN->addIncoming(BI->getCondition(), P);
2132 BI->setCondition(NewPN);
2137 // If this is a conditional branch in an empty block, and if any
2138 // predecessors is a conditional branch to one of our destinations,
2139 // fold the conditions into logical ops and one cond br.
2140 BasicBlock::iterator BBI = BB->begin();
2141 // Ignore dbg intrinsics.
2142 while (isa<DbgInfoIntrinsic>(BBI))
2148 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
2153 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
2155 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
2156 PBIOp = 0, BIOp = 1;
2157 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
2158 PBIOp = 1, BIOp = 0;
2159 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
2164 // Check to make sure that the other destination of this branch
2165 // isn't BB itself. If so, this is an infinite loop that will
2166 // keep getting unwound.
2167 if (PBI->getSuccessor(PBIOp) == BB)
2170 // Do not perform this transformation if it would require
2171 // insertion of a large number of select instructions. For targets
2172 // without predication/cmovs, this is a big pessimization.
2173 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
2175 unsigned NumPhis = 0;
2176 for (BasicBlock::iterator II = CommonDest->begin();
2177 isa<PHINode>(II); ++II, ++NumPhis)
2178 if (NumPhis > 2) // Disable this xform.
2181 // Finally, if everything is ok, fold the branches to logical ops.
2182 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
2184 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
2185 << "AND: " << *BI->getParent());
2188 // If OtherDest *is* BB, then BB is a basic block with a single conditional
2189 // branch in it, where one edge (OtherDest) goes back to itself but the other
2190 // exits. We don't *know* that the program avoids the infinite loop
2191 // (even though that seems likely). If we do this xform naively, we'll end up
2192 // recursively unpeeling the loop. Since we know that (after the xform is
2193 // done) that the block *is* infinite if reached, we just make it an obviously
2194 // infinite loop with no cond branch.
2195 if (OtherDest == BB) {
2196 // Insert it at the end of the function, because it's either code,
2197 // or it won't matter if it's hot. :)
2198 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
2199 "infloop", BB->getParent());
2200 BranchInst::Create(InfLoopBlock, InfLoopBlock);
2201 OtherDest = InfLoopBlock;
2204 DEBUG(dbgs() << *PBI->getParent()->getParent());
2206 // BI may have other predecessors. Because of this, we leave
2207 // it alone, but modify PBI.
2209 // Make sure we get to CommonDest on True&True directions.
2210 Value *PBICond = PBI->getCondition();
2211 IRBuilder<true, NoFolder> Builder(PBI);
2213 PBICond = Builder.CreateNot(PBICond, PBICond->getName()+".not");
2215 Value *BICond = BI->getCondition();
2217 BICond = Builder.CreateNot(BICond, BICond->getName()+".not");
2219 // Merge the conditions.
2220 Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge");
2222 // Modify PBI to branch on the new condition to the new dests.
2223 PBI->setCondition(Cond);
2224 PBI->setSuccessor(0, CommonDest);
2225 PBI->setSuccessor(1, OtherDest);
2227 // OtherDest may have phi nodes. If so, add an entry from PBI's
2228 // block that are identical to the entries for BI's block.
2229 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
2231 // We know that the CommonDest already had an edge from PBI to
2232 // it. If it has PHIs though, the PHIs may have different
2233 // entries for BB and PBI's BB. If so, insert a select to make
2236 for (BasicBlock::iterator II = CommonDest->begin();
2237 (PN = dyn_cast<PHINode>(II)); ++II) {
2238 Value *BIV = PN->getIncomingValueForBlock(BB);
2239 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
2240 Value *PBIV = PN->getIncomingValue(PBBIdx);
2242 // Insert a select in PBI to pick the right value.
2243 Value *NV = cast<SelectInst>
2244 (Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName()+".mux"));
2245 PN->setIncomingValue(PBBIdx, NV);
2249 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
2250 DEBUG(dbgs() << *PBI->getParent()->getParent());
2252 // This basic block is probably dead. We know it has at least
2253 // one fewer predecessor.
2257 // SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
2258 // branch to TrueBB if Cond is true or to FalseBB if Cond is false.
2259 // Takes care of updating the successors and removing the old terminator.
2260 // Also makes sure not to introduce new successors by assuming that edges to
2261 // non-successor TrueBBs and FalseBBs aren't reachable.
2262 static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
2263 BasicBlock *TrueBB, BasicBlock *FalseBB){
2264 // Remove any superfluous successor edges from the CFG.
2265 // First, figure out which successors to preserve.
2266 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
2268 BasicBlock *KeepEdge1 = TrueBB;
2269 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
2271 // Then remove the rest.
2272 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
2273 BasicBlock *Succ = OldTerm->getSuccessor(I);
2274 // Make sure only to keep exactly one copy of each edge.
2275 if (Succ == KeepEdge1)
2277 else if (Succ == KeepEdge2)
2280 Succ->removePredecessor(OldTerm->getParent());
2283 IRBuilder<> Builder(OldTerm);
2284 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
2286 // Insert an appropriate new terminator.
2287 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
2288 if (TrueBB == FalseBB)
2289 // We were only looking for one successor, and it was present.
2290 // Create an unconditional branch to it.
2291 Builder.CreateBr(TrueBB);
2293 // We found both of the successors we were looking for.
2294 // Create a conditional branch sharing the condition of the select.
2295 Builder.CreateCondBr(Cond, TrueBB, FalseBB);
2296 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
2297 // Neither of the selected blocks were successors, so this
2298 // terminator must be unreachable.
2299 new UnreachableInst(OldTerm->getContext(), OldTerm);
2301 // One of the selected values was a successor, but the other wasn't.
2302 // Insert an unconditional branch to the one that was found;
2303 // the edge to the one that wasn't must be unreachable.
2305 // Only TrueBB was found.
2306 Builder.CreateBr(TrueBB);
2308 // Only FalseBB was found.
2309 Builder.CreateBr(FalseBB);
2312 EraseTerminatorInstAndDCECond(OldTerm);
2316 // SimplifySwitchOnSelect - Replaces
2317 // (switch (select cond, X, Y)) on constant X, Y
2318 // with a branch - conditional if X and Y lead to distinct BBs,
2319 // unconditional otherwise.
2320 static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
2321 // Check for constant integer values in the select.
2322 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
2323 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
2324 if (!TrueVal || !FalseVal)
2327 // Find the relevant condition and destinations.
2328 Value *Condition = Select->getCondition();
2329 BasicBlock *TrueBB = SI->findCaseValue(TrueVal).getCaseSuccessor();
2330 BasicBlock *FalseBB = SI->findCaseValue(FalseVal).getCaseSuccessor();
2332 // Perform the actual simplification.
2333 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB);
2336 // SimplifyIndirectBrOnSelect - Replaces
2337 // (indirectbr (select cond, blockaddress(@fn, BlockA),
2338 // blockaddress(@fn, BlockB)))
2340 // (br cond, BlockA, BlockB).
2341 static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
2342 // Check that both operands of the select are block addresses.
2343 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
2344 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
2348 // Extract the actual blocks.
2349 BasicBlock *TrueBB = TBA->getBasicBlock();
2350 BasicBlock *FalseBB = FBA->getBasicBlock();
2352 // Perform the actual simplification.
2353 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB);
2356 /// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
2357 /// instruction (a seteq/setne with a constant) as the only instruction in a
2358 /// block that ends with an uncond branch. We are looking for a very specific
2359 /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
2360 /// this case, we merge the first two "or's of icmp" into a switch, but then the
2361 /// default value goes to an uncond block with a seteq in it, we get something
2364 /// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
2366 /// %tmp = icmp eq i8 %A, 92
2369 /// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
2371 /// We prefer to split the edge to 'end' so that there is a true/false entry to
2372 /// the PHI, merging the third icmp into the switch.
2373 static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
2374 const TargetData *TD,
2375 IRBuilder<> &Builder) {
2376 BasicBlock *BB = ICI->getParent();
2378 // If the block has any PHIs in it or the icmp has multiple uses, it is too
2380 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
2382 Value *V = ICI->getOperand(0);
2383 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
2385 // The pattern we're looking for is where our only predecessor is a switch on
2386 // 'V' and this block is the default case for the switch. In this case we can
2387 // fold the compared value into the switch to simplify things.
2388 BasicBlock *Pred = BB->getSinglePredecessor();
2389 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
2391 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
2392 if (SI->getCondition() != V)
2395 // If BB is reachable on a non-default case, then we simply know the value of
2396 // V in this block. Substitute it and constant fold the icmp instruction
2398 if (SI->getDefaultDest() != BB) {
2399 ConstantInt *VVal = SI->findCaseDest(BB);
2400 assert(VVal && "Should have a unique destination value");
2401 ICI->setOperand(0, VVal);
2403 if (Value *V = SimplifyInstruction(ICI, TD)) {
2404 ICI->replaceAllUsesWith(V);
2405 ICI->eraseFromParent();
2407 // BB is now empty, so it is likely to simplify away.
2408 return SimplifyCFG(BB) | true;
2411 // Ok, the block is reachable from the default dest. If the constant we're
2412 // comparing exists in one of the other edges, then we can constant fold ICI
2414 if (SI->findCaseValue(Cst) != SI->case_default()) {
2416 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2417 V = ConstantInt::getFalse(BB->getContext());
2419 V = ConstantInt::getTrue(BB->getContext());
2421 ICI->replaceAllUsesWith(V);
2422 ICI->eraseFromParent();
2423 // BB is now empty, so it is likely to simplify away.
2424 return SimplifyCFG(BB) | true;
2427 // The use of the icmp has to be in the 'end' block, by the only PHI node in
2429 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
2430 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
2431 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
2432 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
2435 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
2437 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
2438 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
2440 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2441 std::swap(DefaultCst, NewCst);
2443 // Replace ICI (which is used by the PHI for the default value) with true or
2444 // false depending on if it is EQ or NE.
2445 ICI->replaceAllUsesWith(DefaultCst);
2446 ICI->eraseFromParent();
2448 // Okay, the switch goes to this block on a default value. Add an edge from
2449 // the switch to the merge point on the compared value.
2450 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
2451 BB->getParent(), BB);
2452 SI->addCase(Cst, NewBB);
2454 // NewBB branches to the phi block, add the uncond branch and the phi entry.
2455 Builder.SetInsertPoint(NewBB);
2456 Builder.SetCurrentDebugLocation(SI->getDebugLoc());
2457 Builder.CreateBr(SuccBlock);
2458 PHIUse->addIncoming(NewCst, NewBB);
2462 /// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
2463 /// Check to see if it is branching on an or/and chain of icmp instructions, and
2464 /// fold it into a switch instruction if so.
2465 static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD,
2466 IRBuilder<> &Builder) {
2467 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
2468 if (Cond == 0) return false;
2471 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2472 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2473 // 'setne's and'ed together, collect them.
2475 std::vector<ConstantInt*> Values;
2476 bool TrueWhenEqual = true;
2477 Value *ExtraCase = 0;
2478 unsigned UsedICmps = 0;
2480 if (Cond->getOpcode() == Instruction::Or) {
2481 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
2483 } else if (Cond->getOpcode() == Instruction::And) {
2484 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
2486 TrueWhenEqual = false;
2489 // If we didn't have a multiply compared value, fail.
2490 if (CompVal == 0) return false;
2492 // Avoid turning single icmps into a switch.
2496 // There might be duplicate constants in the list, which the switch
2497 // instruction can't handle, remove them now.
2498 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
2499 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2501 // If Extra was used, we require at least two switch values to do the
2502 // transformation. A switch with one value is just an cond branch.
2503 if (ExtraCase && Values.size() < 2) return false;
2505 // TODO: Preserve branch weight metadata, similarly to how
2506 // FoldValueComparisonIntoPredecessors preserves it.
2508 // Figure out which block is which destination.
2509 BasicBlock *DefaultBB = BI->getSuccessor(1);
2510 BasicBlock *EdgeBB = BI->getSuccessor(0);
2511 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2513 BasicBlock *BB = BI->getParent();
2515 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
2516 << " cases into SWITCH. BB is:\n" << *BB);
2518 // If there are any extra values that couldn't be folded into the switch
2519 // then we evaluate them with an explicit branch first. Split the block
2520 // right before the condbr to handle it.
2522 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
2523 // Remove the uncond branch added to the old block.
2524 TerminatorInst *OldTI = BB->getTerminator();
2525 Builder.SetInsertPoint(OldTI);
2528 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
2530 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
2532 OldTI->eraseFromParent();
2534 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
2535 // for the edge we just added.
2536 AddPredecessorToBlock(EdgeBB, BB, NewBB);
2538 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
2539 << "\nEXTRABB = " << *BB);
2543 Builder.SetInsertPoint(BI);
2544 // Convert pointer to int before we switch.
2545 if (CompVal->getType()->isPointerTy()) {
2546 assert(TD && "Cannot switch on pointer without TargetData");
2547 CompVal = Builder.CreatePtrToInt(CompVal,
2548 TD->getIntPtrType(CompVal->getContext()),
2552 // Create the new switch instruction now.
2553 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
2555 // Add all of the 'cases' to the switch instruction.
2556 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2557 New->addCase(Values[i], EdgeBB);
2559 // We added edges from PI to the EdgeBB. As such, if there were any
2560 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2561 // the number of edges added.
2562 for (BasicBlock::iterator BBI = EdgeBB->begin();
2563 isa<PHINode>(BBI); ++BBI) {
2564 PHINode *PN = cast<PHINode>(BBI);
2565 Value *InVal = PN->getIncomingValueForBlock(BB);
2566 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2567 PN->addIncoming(InVal, BB);
2570 // Erase the old branch instruction.
2571 EraseTerminatorInstAndDCECond(BI);
2573 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
2577 bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
2578 // If this is a trivial landing pad that just continues unwinding the caught
2579 // exception then zap the landing pad, turning its invokes into calls.
2580 BasicBlock *BB = RI->getParent();
2581 LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI());
2582 if (RI->getValue() != LPInst)
2583 // Not a landing pad, or the resume is not unwinding the exception that
2584 // caused control to branch here.
2587 // Check that there are no other instructions except for debug intrinsics.
2588 BasicBlock::iterator I = LPInst, E = RI;
2590 if (!isa<DbgInfoIntrinsic>(I))
2593 // Turn all invokes that unwind here into calls and delete the basic block.
2594 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
2595 InvokeInst *II = cast<InvokeInst>((*PI++)->getTerminator());
2596 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
2597 // Insert a call instruction before the invoke.
2598 CallInst *Call = CallInst::Create(II->getCalledValue(), Args, "", II);
2600 Call->setCallingConv(II->getCallingConv());
2601 Call->setAttributes(II->getAttributes());
2602 Call->setDebugLoc(II->getDebugLoc());
2604 // Anything that used the value produced by the invoke instruction now uses
2605 // the value produced by the call instruction. Note that we do this even
2606 // for void functions and calls with no uses so that the callgraph edge is
2608 II->replaceAllUsesWith(Call);
2609 BB->removePredecessor(II->getParent());
2611 // Insert a branch to the normal destination right before the invoke.
2612 BranchInst::Create(II->getNormalDest(), II);
2614 // Finally, delete the invoke instruction!
2615 II->eraseFromParent();
2618 // The landingpad is now unreachable. Zap it.
2619 BB->eraseFromParent();
2623 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
2624 BasicBlock *BB = RI->getParent();
2625 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2627 // Find predecessors that end with branches.
2628 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2629 SmallVector<BranchInst*, 8> CondBranchPreds;
2630 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2631 BasicBlock *P = *PI;
2632 TerminatorInst *PTI = P->getTerminator();
2633 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2634 if (BI->isUnconditional())
2635 UncondBranchPreds.push_back(P);
2637 CondBranchPreds.push_back(BI);
2641 // If we found some, do the transformation!
2642 if (!UncondBranchPreds.empty() && DupRet) {
2643 while (!UncondBranchPreds.empty()) {
2644 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2645 DEBUG(dbgs() << "FOLDING: " << *BB
2646 << "INTO UNCOND BRANCH PRED: " << *Pred);
2647 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
2650 // If we eliminated all predecessors of the block, delete the block now.
2651 if (pred_begin(BB) == pred_end(BB))
2652 // We know there are no successors, so just nuke the block.
2653 BB->eraseFromParent();
2658 // Check out all of the conditional branches going to this return
2659 // instruction. If any of them just select between returns, change the
2660 // branch itself into a select/return pair.
2661 while (!CondBranchPreds.empty()) {
2662 BranchInst *BI = CondBranchPreds.pop_back_val();
2664 // Check to see if the non-BB successor is also a return block.
2665 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2666 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2667 SimplifyCondBranchToTwoReturns(BI, Builder))
2673 bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2674 BasicBlock *BB = UI->getParent();
2676 bool Changed = false;
2678 // If there are any instructions immediately before the unreachable that can
2679 // be removed, do so.
2680 while (UI != BB->begin()) {
2681 BasicBlock::iterator BBI = UI;
2683 // Do not delete instructions that can have side effects which might cause
2684 // the unreachable to not be reachable; specifically, calls and volatile
2685 // operations may have this effect.
2686 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2688 if (BBI->mayHaveSideEffects()) {
2689 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
2690 if (SI->isVolatile())
2692 } else if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
2693 if (LI->isVolatile())
2695 } else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(BBI)) {
2696 if (RMWI->isVolatile())
2698 } else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) {
2699 if (CXI->isVolatile())
2701 } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) &&
2702 !isa<LandingPadInst>(BBI)) {
2705 // Note that deleting LandingPad's here is in fact okay, although it
2706 // involves a bit of subtle reasoning. If this inst is a LandingPad,
2707 // all the predecessors of this block will be the unwind edges of Invokes,
2708 // and we can therefore guarantee this block will be erased.
2711 // Delete this instruction (any uses are guaranteed to be dead)
2712 if (!BBI->use_empty())
2713 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
2714 BBI->eraseFromParent();
2718 // If the unreachable instruction is the first in the block, take a gander
2719 // at all of the predecessors of this instruction, and simplify them.
2720 if (&BB->front() != UI) return Changed;
2722 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2723 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2724 TerminatorInst *TI = Preds[i]->getTerminator();
2725 IRBuilder<> Builder(TI);
2726 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2727 if (BI->isUnconditional()) {
2728 if (BI->getSuccessor(0) == BB) {
2729 new UnreachableInst(TI->getContext(), TI);
2730 TI->eraseFromParent();
2734 if (BI->getSuccessor(0) == BB) {
2735 Builder.CreateBr(BI->getSuccessor(1));
2736 EraseTerminatorInstAndDCECond(BI);
2737 } else if (BI->getSuccessor(1) == BB) {
2738 Builder.CreateBr(BI->getSuccessor(0));
2739 EraseTerminatorInstAndDCECond(BI);
2743 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2744 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2746 if (i.getCaseSuccessor() == BB) {
2747 BB->removePredecessor(SI->getParent());
2752 // If the default value is unreachable, figure out the most popular
2753 // destination and make it the default.
2754 if (SI->getDefaultDest() == BB) {
2755 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
2756 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2758 std::pair<unsigned, unsigned> &entry =
2759 Popularity[i.getCaseSuccessor()];
2760 if (entry.first == 0) {
2762 entry.second = i.getCaseIndex();
2768 // Find the most popular block.
2769 unsigned MaxPop = 0;
2770 unsigned MaxIndex = 0;
2771 BasicBlock *MaxBlock = 0;
2772 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
2773 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2774 if (I->second.first > MaxPop ||
2775 (I->second.first == MaxPop && MaxIndex > I->second.second)) {
2776 MaxPop = I->second.first;
2777 MaxIndex = I->second.second;
2778 MaxBlock = I->first;
2782 // Make this the new default, allowing us to delete any explicit
2784 SI->setDefaultDest(MaxBlock);
2787 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2789 if (isa<PHINode>(MaxBlock->begin()))
2790 for (unsigned i = 0; i != MaxPop-1; ++i)
2791 MaxBlock->removePredecessor(SI->getParent());
2793 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
2795 if (i.getCaseSuccessor() == MaxBlock) {
2801 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2802 if (II->getUnwindDest() == BB) {
2803 // Convert the invoke to a call instruction. This would be a good
2804 // place to note that the call does not throw though.
2805 BranchInst *BI = Builder.CreateBr(II->getNormalDest());
2806 II->removeFromParent(); // Take out of symbol table
2808 // Insert the call now...
2809 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2810 Builder.SetInsertPoint(BI);
2811 CallInst *CI = Builder.CreateCall(II->getCalledValue(),
2812 Args, II->getName());
2813 CI->setCallingConv(II->getCallingConv());
2814 CI->setAttributes(II->getAttributes());
2815 // If the invoke produced a value, the call does now instead.
2816 II->replaceAllUsesWith(CI);
2823 // If this block is now dead, remove it.
2824 if (pred_begin(BB) == pred_end(BB) &&
2825 BB != &BB->getParent()->getEntryBlock()) {
2826 // We know there are no successors, so just nuke the block.
2827 BB->eraseFromParent();
2834 /// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
2835 /// integer range comparison into a sub, an icmp and a branch.
2836 static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
2837 assert(SI->getNumCases() > 1 && "Degenerate switch?");
2839 // Make sure all cases point to the same destination and gather the values.
2840 SmallVector<ConstantInt *, 16> Cases;
2841 SwitchInst::CaseIt I = SI->case_begin();
2842 Cases.push_back(I.getCaseValue());
2843 SwitchInst::CaseIt PrevI = I++;
2844 for (SwitchInst::CaseIt E = SI->case_end(); I != E; PrevI = I++) {
2845 if (PrevI.getCaseSuccessor() != I.getCaseSuccessor())
2847 Cases.push_back(I.getCaseValue());
2849 assert(Cases.size() == SI->getNumCases() && "Not all cases gathered");
2851 // Sort the case values, then check if they form a range we can transform.
2852 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
2853 for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
2854 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
2858 Constant *Offset = ConstantExpr::getNeg(Cases.back());
2859 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases());
2861 Value *Sub = SI->getCondition();
2862 if (!Offset->isNullValue())
2863 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off");
2864 Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
2865 Builder.CreateCondBr(
2866 Cmp, SI->case_begin().getCaseSuccessor(), SI->getDefaultDest());
2868 // Prune obsolete incoming values off the successor's PHI nodes.
2869 for (BasicBlock::iterator BBI = SI->case_begin().getCaseSuccessor()->begin();
2870 isa<PHINode>(BBI); ++BBI) {
2871 for (unsigned I = 0, E = SI->getNumCases()-1; I != E; ++I)
2872 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
2874 SI->eraseFromParent();
2879 /// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch
2880 /// and use it to remove dead cases.
2881 static bool EliminateDeadSwitchCases(SwitchInst *SI) {
2882 Value *Cond = SI->getCondition();
2883 unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth();
2884 APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
2885 ComputeMaskedBits(Cond, KnownZero, KnownOne);
2887 // Gather dead cases.
2888 SmallVector<ConstantInt*, 8> DeadCases;
2889 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
2890 if ((I.getCaseValue()->getValue() & KnownZero) != 0 ||
2891 (I.getCaseValue()->getValue() & KnownOne) != KnownOne) {
2892 DeadCases.push_back(I.getCaseValue());
2893 DEBUG(dbgs() << "SimplifyCFG: switch case '"
2894 << I.getCaseValue() << "' is dead.\n");
2898 // Remove dead cases from the switch.
2899 for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) {
2900 SwitchInst::CaseIt Case = SI->findCaseValue(DeadCases[I]);
2901 assert(Case != SI->case_default() &&
2902 "Case was not found. Probably mistake in DeadCases forming.");
2903 // Prune unused values from PHI nodes.
2904 Case.getCaseSuccessor()->removePredecessor(SI->getParent());
2905 SI->removeCase(Case);
2908 return !DeadCases.empty();
2911 /// FindPHIForConditionForwarding - If BB would be eligible for simplification
2912 /// by TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated
2913 /// by an unconditional branch), look at the phi node for BB in the successor
2914 /// block and see if the incoming value is equal to CaseValue. If so, return
2915 /// the phi node, and set PhiIndex to BB's index in the phi node.
2916 static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
2919 if (BB->getFirstNonPHIOrDbg() != BB->getTerminator())
2920 return NULL; // BB must be empty to be a candidate for simplification.
2921 if (!BB->getSinglePredecessor())
2922 return NULL; // BB must be dominated by the switch.
2924 BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
2925 if (!Branch || !Branch->isUnconditional())
2926 return NULL; // Terminator must be unconditional branch.
2928 BasicBlock *Succ = Branch->getSuccessor(0);
2930 BasicBlock::iterator I = Succ->begin();
2931 while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
2932 int Idx = PHI->getBasicBlockIndex(BB);
2933 assert(Idx >= 0 && "PHI has no entry for predecessor?");
2935 Value *InValue = PHI->getIncomingValue(Idx);
2936 if (InValue != CaseValue) continue;
2945 /// ForwardSwitchConditionToPHI - Try to forward the condition of a switch
2946 /// instruction to a phi node dominated by the switch, if that would mean that
2947 /// some of the destination blocks of the switch can be folded away.
2948 /// Returns true if a change is made.
2949 static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
2950 typedef DenseMap<PHINode*, SmallVector<int,4> > ForwardingNodesMap;
2951 ForwardingNodesMap ForwardingNodes;
2953 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
2954 ConstantInt *CaseValue = I.getCaseValue();
2955 BasicBlock *CaseDest = I.getCaseSuccessor();
2958 PHINode *PHI = FindPHIForConditionForwarding(CaseValue, CaseDest,
2962 ForwardingNodes[PHI].push_back(PhiIndex);
2965 bool Changed = false;
2967 for (ForwardingNodesMap::iterator I = ForwardingNodes.begin(),
2968 E = ForwardingNodes.end(); I != E; ++I) {
2969 PHINode *Phi = I->first;
2970 SmallVector<int,4> &Indexes = I->second;
2972 if (Indexes.size() < 2) continue;
2974 for (size_t I = 0, E = Indexes.size(); I != E; ++I)
2975 Phi->setIncomingValue(Indexes[I], SI->getCondition());
2982 /// ValidLookupTableConstant - Return true if the backend will be able to handle
2983 /// initializing an array of constants like C.
2984 static bool ValidLookupTableConstant(Constant *C) {
2985 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C))
2986 return CE->isGEPWithNoNotionalOverIndexing();
2988 return isa<ConstantFP>(C) ||
2989 isa<ConstantInt>(C) ||
2990 isa<ConstantPointerNull>(C) ||
2991 isa<GlobalValue>(C) ||
2995 /// GetCaseResulsts - Try to determine the resulting constant values in phi
2996 /// nodes at the common destination basic block for one of the case
2997 /// destinations of a switch instruction.
2998 static bool GetCaseResults(SwitchInst *SI,
2999 BasicBlock *CaseDest,
3000 BasicBlock **CommonDest,
3001 SmallVector<std::pair<PHINode*,Constant*>, 4> &Res) {
3002 // The block from which we enter the common destination.
3003 BasicBlock *Pred = SI->getParent();
3005 // If CaseDest is empty, continue to its successor.
3006 if (CaseDest->getFirstNonPHIOrDbg() == CaseDest->getTerminator() &&
3007 !isa<PHINode>(CaseDest->begin())) {
3009 TerminatorInst *Terminator = CaseDest->getTerminator();
3010 if (Terminator->getNumSuccessors() != 1)
3014 CaseDest = Terminator->getSuccessor(0);
3017 // If we did not have a CommonDest before, use the current one.
3019 *CommonDest = CaseDest;
3020 // If the destination isn't the common one, abort.
3021 if (CaseDest != *CommonDest)
3024 // Get the values for this case from phi nodes in the destination block.
3025 BasicBlock::iterator I = (*CommonDest)->begin();
3026 while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
3027 int Idx = PHI->getBasicBlockIndex(Pred);
3031 Constant *ConstVal = dyn_cast<Constant>(PHI->getIncomingValue(Idx));
3035 // Be conservative about which kinds of constants we support.
3036 if (!ValidLookupTableConstant(ConstVal))
3039 Res.push_back(std::make_pair(PHI, ConstVal));
3045 /// BuildLookupTable - Build a lookup table with the contents of Results, using
3046 /// DefaultResult to fill the holes in the table. If the table ends up
3047 /// containing the same result in each element, set *SingleResult to that value
3048 /// and return NULL.
3049 static GlobalVariable *BuildLookupTable(
3052 ConstantInt *Offset,
3053 const std::vector<std::pair<ConstantInt*,Constant*> >& Results,
3054 Constant *DefaultResult,
3055 Constant **SingleResult) {
3056 assert(Results.size() && "Need values to build lookup table");
3057 assert(TableSize >= Results.size() && "Table needs to hold all values");
3059 // If all values in the table are equal, this is that value.
3060 Constant *SameResult = Results.begin()->second;
3062 // Build up the table contents.
3063 std::vector<Constant*> TableContents(TableSize);
3064 for (size_t I = 0, E = Results.size(); I != E; ++I) {
3065 ConstantInt *CaseVal = Results[I].first;
3066 Constant *CaseRes = Results[I].second;
3068 uint64_t Idx = (CaseVal->getValue() - Offset->getValue()).getLimitedValue();
3069 TableContents[Idx] = CaseRes;
3071 if (CaseRes != SameResult)
3075 // Fill in any holes in the table with the default result.
3076 if (Results.size() < TableSize) {
3077 for (unsigned i = 0; i < TableSize; ++i) {
3078 if (!TableContents[i])
3079 TableContents[i] = DefaultResult;
3082 if (DefaultResult != SameResult)
3086 // Same result was used in the entire table; just return that.
3088 *SingleResult = SameResult;
3092 ArrayType *ArrayTy = ArrayType::get(DefaultResult->getType(), TableSize);
3093 Constant *Initializer = ConstantArray::get(ArrayTy, TableContents);
3095 GlobalVariable *GV = new GlobalVariable(M, ArrayTy, /*constant=*/ true,
3096 GlobalVariable::PrivateLinkage,
3099 GV->setUnnamedAddr(true);
3103 /// SwitchToLookupTable - If the switch is only used to initialize one or more
3104 /// phi nodes in a common successor block with different constant values,
3105 /// replace the switch with lookup tables.
3106 static bool SwitchToLookupTable(SwitchInst *SI,
3107 IRBuilder<> &Builder) {
3108 assert(SI->getNumCases() > 1 && "Degenerate switch?");
3109 // FIXME: Handle unreachable cases.
3111 // FIXME: If the switch is too sparse for a lookup table, perhaps we could
3112 // split off a dense part and build a lookup table for that.
3114 // FIXME: If the results are all integers and the lookup table would fit in a
3115 // target-legal register, we should store them as a bitmap and use shift/mask
3116 // to look up the result.
3118 // FIXME: This creates arrays of GEPs to constant strings, which means each
3119 // GEP needs a runtime relocation in PIC code. We should just build one big
3120 // string and lookup indices into that.
3122 // Ignore the switch if the number of cases are too small.
3123 // This is similar to the check when building jump tables in
3124 // SelectionDAGBuilder::handleJTSwitchCase.
3125 // FIXME: Determine the best cut-off.
3126 if (SI->getNumCases() < 4)
3129 // Figure out the corresponding result for each case value and phi node in the
3130 // common destination, as well as the the min and max case values.
3131 assert(SI->case_begin() != SI->case_end());
3132 SwitchInst::CaseIt CI = SI->case_begin();
3133 ConstantInt *MinCaseVal = CI.getCaseValue();
3134 ConstantInt *MaxCaseVal = CI.getCaseValue();
3136 BasicBlock *CommonDest = NULL;
3137 typedef std::vector<std::pair<ConstantInt*, Constant*> > ResultListTy;
3138 SmallDenseMap<PHINode*, ResultListTy> ResultLists;
3139 SmallDenseMap<PHINode*, Constant*> DefaultResults;
3140 SmallDenseMap<PHINode*, Type*> ResultTypes;
3141 SmallVector<PHINode*, 4> PHIs;
3143 for (SwitchInst::CaseIt E = SI->case_end(); CI != E; ++CI) {
3144 ConstantInt *CaseVal = CI.getCaseValue();
3145 if (CaseVal->getValue().slt(MinCaseVal->getValue()))
3146 MinCaseVal = CaseVal;
3147 if (CaseVal->getValue().sgt(MaxCaseVal->getValue()))
3148 MaxCaseVal = CaseVal;
3150 // Resulting value at phi nodes for this case value.
3151 typedef SmallVector<std::pair<PHINode*, Constant*>, 4> ResultsTy;
3153 if (!GetCaseResults(SI, CI.getCaseSuccessor(), &CommonDest, Results))
3156 // Append the result from this case to the list for each phi.
3157 for (ResultsTy::iterator I = Results.begin(), E = Results.end(); I!=E; ++I) {
3158 if (!ResultLists.count(I->first))
3159 PHIs.push_back(I->first);
3160 ResultLists[I->first].push_back(std::make_pair(CaseVal, I->second));
3164 // Get the resulting values for the default case.
3166 SmallVector<std::pair<PHINode*, Constant*>, 4> DefaultResultsList;
3167 if (!GetCaseResults(SI, SI->getDefaultDest(), &CommonDest, DefaultResultsList))
3169 for (size_t I = 0, E = DefaultResultsList.size(); I != E; ++I) {
3170 PHINode *PHI = DefaultResultsList[I].first;
3171 Constant *Result = DefaultResultsList[I].second;
3172 DefaultResults[PHI] = Result;
3173 ResultTypes[PHI] = Result->getType();
3177 APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
3178 // The table density should be at lest 40%. This is the same criterion as for
3179 // jump tables, see SelectionDAGBuilder::handleJTSwitchCase.
3180 // FIXME: Find the best cut-off.
3181 // Be careful to avoid overlow in the density computation.
3182 if (RangeSpread.zextOrSelf(64).ugt(UINT64_MAX / 4 - 1))
3184 uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
3185 if (SI->getNumCases() * 10 < TableSize * 4)
3188 // Build the lookup tables.
3189 SmallDenseMap<PHINode*, GlobalVariable*> LookupTables;
3190 SmallDenseMap<PHINode*, Constant*> SingleResults;
3192 Module &Mod = *CommonDest->getParent()->getParent();
3193 for (SmallVector<PHINode*, 4>::iterator I = PHIs.begin(), E = PHIs.end();
3197 Constant *SingleResult = NULL;
3198 LookupTables[PHI] = BuildLookupTable(Mod, TableSize, MinCaseVal,
3199 ResultLists[PHI], DefaultResults[PHI],
3201 SingleResults[PHI] = SingleResult;
3204 // Create the BB that does the lookups.
3205 BasicBlock *LookupBB = BasicBlock::Create(Mod.getContext(),
3207 CommonDest->getParent(),
3210 // Check whether the condition value is within the case range, and branch to
3212 Builder.SetInsertPoint(SI);
3213 Value *TableIndex = Builder.CreateSub(SI->getCondition(), MinCaseVal,
3215 Value *Cmp = Builder.CreateICmpULT(TableIndex, ConstantInt::get(
3216 MinCaseVal->getType(), TableSize));
3217 Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest());
3219 // Populate the BB that does the lookups.
3220 Builder.SetInsertPoint(LookupBB);
3221 bool ReturnedEarly = false;
3222 for (SmallVector<PHINode*, 4>::iterator I = PHIs.begin(), E = PHIs.end();
3225 // There was a single result for this phi; just use that.
3226 if (Constant *SingleResult = SingleResults[PHI]) {
3227 PHI->addIncoming(SingleResult, LookupBB);
3231 Value *GEPIndices[] = { Builder.getInt32(0), TableIndex };
3232 Value *GEP = Builder.CreateInBoundsGEP(LookupTables[PHI], GEPIndices,
3234 Value *Result = Builder.CreateLoad(GEP, "switch.load");
3236 // If the result is only going to be used to return from the function,
3237 // we want to do that right here.
3238 if (PHI->hasOneUse() && isa<ReturnInst>(*PHI->use_begin())) {
3239 if (CommonDest->getFirstNonPHIOrDbg() == CommonDest->getTerminator()) {
3240 Builder.CreateRet(Result);
3241 ReturnedEarly = true;
3246 PHI->addIncoming(Result, LookupBB);
3250 Builder.CreateBr(CommonDest);
3252 // Remove the switch.
3253 for (unsigned i = 0; i < SI->getNumSuccessors(); ++i) {
3254 BasicBlock *Succ = SI->getSuccessor(i);
3255 if (Succ == SI->getDefaultDest()) continue;
3256 Succ->removePredecessor(SI->getParent());
3258 SI->eraseFromParent();
3264 bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
3265 // If this switch is too complex to want to look at, ignore it.
3266 if (!isValueEqualityComparison(SI))
3269 BasicBlock *BB = SI->getParent();
3271 // If we only have one predecessor, and if it is a branch on this value,
3272 // see if that predecessor totally determines the outcome of this switch.
3273 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
3274 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
3275 return SimplifyCFG(BB) | true;
3277 Value *Cond = SI->getCondition();
3278 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
3279 if (SimplifySwitchOnSelect(SI, Select))
3280 return SimplifyCFG(BB) | true;
3282 // If the block only contains the switch, see if we can fold the block
3283 // away into any preds.
3284 BasicBlock::iterator BBI = BB->begin();
3285 // Ignore dbg intrinsics.
3286 while (isa<DbgInfoIntrinsic>(BBI))
3289 if (FoldValueComparisonIntoPredecessors(SI, Builder))
3290 return SimplifyCFG(BB) | true;
3292 // Try to transform the switch into an icmp and a branch.
3293 if (TurnSwitchRangeIntoICmp(SI, Builder))
3294 return SimplifyCFG(BB) | true;
3296 // Remove unreachable cases.
3297 if (EliminateDeadSwitchCases(SI))
3298 return SimplifyCFG(BB) | true;
3300 if (ForwardSwitchConditionToPHI(SI))
3301 return SimplifyCFG(BB) | true;
3303 if (SwitchToLookupTable(SI, Builder))
3304 return SimplifyCFG(BB) | true;
3309 bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
3310 BasicBlock *BB = IBI->getParent();
3311 bool Changed = false;
3313 // Eliminate redundant destinations.
3314 SmallPtrSet<Value *, 8> Succs;
3315 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
3316 BasicBlock *Dest = IBI->getDestination(i);
3317 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
3318 Dest->removePredecessor(BB);
3319 IBI->removeDestination(i);
3325 if (IBI->getNumDestinations() == 0) {
3326 // If the indirectbr has no successors, change it to unreachable.
3327 new UnreachableInst(IBI->getContext(), IBI);
3328 EraseTerminatorInstAndDCECond(IBI);
3332 if (IBI->getNumDestinations() == 1) {
3333 // If the indirectbr has one successor, change it to a direct branch.
3334 BranchInst::Create(IBI->getDestination(0), IBI);
3335 EraseTerminatorInstAndDCECond(IBI);
3339 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
3340 if (SimplifyIndirectBrOnSelect(IBI, SI))
3341 return SimplifyCFG(BB) | true;
3346 bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
3347 BasicBlock *BB = BI->getParent();
3349 // If the Terminator is the only non-phi instruction, simplify the block.
3350 BasicBlock::iterator I = BB->getFirstNonPHIOrDbgOrLifetime();
3351 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
3352 TryToSimplifyUncondBranchFromEmptyBlock(BB))
3355 // If the only instruction in the block is a seteq/setne comparison
3356 // against a constant, try to simplify the block.
3357 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
3358 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
3359 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
3361 if (I->isTerminator() &&
3362 TryToSimplifyUncondBranchWithICmpInIt(ICI, TD, Builder))
3366 // If this basic block is ONLY a compare and a branch, and if a predecessor
3367 // branches to us and our successor, fold the comparison into the
3368 // predecessor and use logical operations to update the incoming value
3369 // for PHI nodes in common successor.
3370 if (FoldBranchToCommonDest(BI))
3371 return SimplifyCFG(BB) | true;
3376 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
3377 BasicBlock *BB = BI->getParent();
3379 // Conditional branch
3380 if (isValueEqualityComparison(BI)) {
3381 // If we only have one predecessor, and if it is a branch on this value,
3382 // see if that predecessor totally determines the outcome of this
3384 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
3385 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
3386 return SimplifyCFG(BB) | true;
3388 // This block must be empty, except for the setcond inst, if it exists.
3389 // Ignore dbg intrinsics.
3390 BasicBlock::iterator I = BB->begin();
3391 // Ignore dbg intrinsics.
3392 while (isa<DbgInfoIntrinsic>(I))
3395 if (FoldValueComparisonIntoPredecessors(BI, Builder))
3396 return SimplifyCFG(BB) | true;
3397 } else if (&*I == cast<Instruction>(BI->getCondition())){
3399 // Ignore dbg intrinsics.
3400 while (isa<DbgInfoIntrinsic>(I))
3402 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
3403 return SimplifyCFG(BB) | true;
3407 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
3408 if (SimplifyBranchOnICmpChain(BI, TD, Builder))
3411 // If this basic block is ONLY a compare and a branch, and if a predecessor
3412 // branches to us and one of our successors, fold the comparison into the
3413 // predecessor and use logical operations to pick the right destination.
3414 if (FoldBranchToCommonDest(BI))
3415 return SimplifyCFG(BB) | true;
3417 // We have a conditional branch to two blocks that are only reachable
3418 // from BI. We know that the condbr dominates the two blocks, so see if
3419 // there is any identical code in the "then" and "else" blocks. If so, we
3420 // can hoist it up to the branching block.
3421 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
3422 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
3423 if (HoistThenElseCodeToIf(BI))
3424 return SimplifyCFG(BB) | true;
3426 // If Successor #1 has multiple preds, we may be able to conditionally
3427 // execute Successor #0 if it branches to successor #1.
3428 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
3429 if (Succ0TI->getNumSuccessors() == 1 &&
3430 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
3431 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
3432 return SimplifyCFG(BB) | true;
3434 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
3435 // If Successor #0 has multiple preds, we may be able to conditionally
3436 // execute Successor #1 if it branches to successor #0.
3437 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
3438 if (Succ1TI->getNumSuccessors() == 1 &&
3439 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
3440 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
3441 return SimplifyCFG(BB) | true;
3444 // If this is a branch on a phi node in the current block, thread control
3445 // through this block if any PHI node entries are constants.
3446 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
3447 if (PN->getParent() == BI->getParent())
3448 if (FoldCondBranchOnPHI(BI, TD))
3449 return SimplifyCFG(BB) | true;
3451 // Scan predecessor blocks for conditional branches.
3452 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
3453 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
3454 if (PBI != BI && PBI->isConditional())
3455 if (SimplifyCondBranchToCondBranch(PBI, BI))
3456 return SimplifyCFG(BB) | true;
3461 /// Check if passing a value to an instruction will cause undefined behavior.
3462 static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
3463 Constant *C = dyn_cast<Constant>(V);
3467 if (!I->hasOneUse()) // Only look at single-use instructions, for compile time
3470 if (C->isNullValue()) {
3471 Instruction *Use = I->use_back();
3473 // Now make sure that there are no instructions in between that can alter
3474 // control flow (eg. calls)
3475 for (BasicBlock::iterator i = ++BasicBlock::iterator(I); &*i != Use; ++i)
3476 if (i == I->getParent()->end() || i->mayHaveSideEffects())
3479 // Look through GEPs. A load from a GEP derived from NULL is still undefined
3480 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))
3481 if (GEP->getPointerOperand() == I)
3482 return passingValueIsAlwaysUndefined(V, GEP);
3484 // Look through bitcasts.
3485 if (BitCastInst *BC = dyn_cast<BitCastInst>(Use))
3486 return passingValueIsAlwaysUndefined(V, BC);
3488 // Load from null is undefined.
3489 if (LoadInst *LI = dyn_cast<LoadInst>(Use))
3490 return LI->getPointerAddressSpace() == 0;
3492 // Store to null is undefined.
3493 if (StoreInst *SI = dyn_cast<StoreInst>(Use))
3494 return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I;
3499 /// If BB has an incoming value that will always trigger undefined behavior
3500 /// (eg. null pointer dereference), remove the branch leading here.
3501 static bool removeUndefIntroducingPredecessor(BasicBlock *BB) {
3502 for (BasicBlock::iterator i = BB->begin();
3503 PHINode *PHI = dyn_cast<PHINode>(i); ++i)
3504 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
3505 if (passingValueIsAlwaysUndefined(PHI->getIncomingValue(i), PHI)) {
3506 TerminatorInst *T = PHI->getIncomingBlock(i)->getTerminator();
3507 IRBuilder<> Builder(T);
3508 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
3509 BB->removePredecessor(PHI->getIncomingBlock(i));
3510 // Turn uncoditional branches into unreachables and remove the dead
3511 // destination from conditional branches.
3512 if (BI->isUnconditional())
3513 Builder.CreateUnreachable();
3515 Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1) :
3516 BI->getSuccessor(0));
3517 BI->eraseFromParent();
3520 // TODO: SwitchInst.
3526 bool SimplifyCFGOpt::run(BasicBlock *BB) {
3527 bool Changed = false;
3529 assert(BB && BB->getParent() && "Block not embedded in function!");
3530 assert(BB->getTerminator() && "Degenerate basic block encountered!");
3532 // Remove basic blocks that have no predecessors (except the entry block)...
3533 // or that just have themself as a predecessor. These are unreachable.
3534 if ((pred_begin(BB) == pred_end(BB) &&
3535 BB != &BB->getParent()->getEntryBlock()) ||
3536 BB->getSinglePredecessor() == BB) {
3537 DEBUG(dbgs() << "Removing BB: \n" << *BB);
3538 DeleteDeadBlock(BB);
3542 // Check to see if we can constant propagate this terminator instruction
3544 Changed |= ConstantFoldTerminator(BB, true);
3546 // Check for and eliminate duplicate PHI nodes in this block.
3547 Changed |= EliminateDuplicatePHINodes(BB);
3549 // Check for and remove branches that will always cause undefined behavior.
3550 Changed |= removeUndefIntroducingPredecessor(BB);
3552 // Merge basic blocks into their predecessor if there is only one distinct
3553 // pred, and if there is only one distinct successor of the predecessor, and
3554 // if there are no PHI nodes.
3556 if (MergeBlockIntoPredecessor(BB))
3559 IRBuilder<> Builder(BB);
3561 // If there is a trivial two-entry PHI node in this basic block, and we can
3562 // eliminate it, do so now.
3563 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
3564 if (PN->getNumIncomingValues() == 2)
3565 Changed |= FoldTwoEntryPHINode(PN, TD);
3567 Builder.SetInsertPoint(BB->getTerminator());
3568 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
3569 if (BI->isUnconditional()) {
3570 if (SimplifyUncondBranch(BI, Builder)) return true;
3572 if (SimplifyCondBranch(BI, Builder)) return true;
3574 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
3575 if (SimplifyReturn(RI, Builder)) return true;
3576 } else if (ResumeInst *RI = dyn_cast<ResumeInst>(BB->getTerminator())) {
3577 if (SimplifyResume(RI, Builder)) return true;
3578 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
3579 if (SimplifySwitch(SI, Builder)) return true;
3580 } else if (UnreachableInst *UI =
3581 dyn_cast<UnreachableInst>(BB->getTerminator())) {
3582 if (SimplifyUnreachable(UI)) return true;
3583 } else if (IndirectBrInst *IBI =
3584 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
3585 if (SimplifyIndirectBr(IBI)) return true;
3591 /// SimplifyCFG - This function is used to do simplification of a CFG. For
3592 /// example, it adjusts branches to branches to eliminate the extra hop, it
3593 /// eliminates unreachable basic blocks, and does other "peephole" optimization
3594 /// of the CFG. It returns true if a modification was made.
3596 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
3597 return SimplifyCFGOpt(TD).run(BB);