diff options
Diffstat (limited to 'contrib/llvm/lib/Transforms/Scalar/JumpThreading.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/Scalar/JumpThreading.cpp | 998 |
1 files changed, 434 insertions, 564 deletions
diff --git a/contrib/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/contrib/llvm/lib/Transforms/Scalar/JumpThreading.cpp index 104d5ae..90094a8 100644 --- a/contrib/llvm/lib/Transforms/Scalar/JumpThreading.cpp +++ b/contrib/llvm/lib/Transforms/Scalar/JumpThreading.cpp @@ -40,20 +40,22 @@ STATISTIC(NumFolds, "Number of terminators folded"); STATISTIC(NumDupes, "Number of branch blocks duplicated to eliminate phi"); static cl::opt<unsigned> -Threshold("jump-threading-threshold", +Threshold("jump-threading-threshold", cl::desc("Max block size to duplicate for jump threading"), cl::init(6), cl::Hidden); -// Turn on use of LazyValueInfo. -static cl::opt<bool> -EnableLVI("enable-jump-threading-lvi", - cl::desc("Use LVI for jump threading"), - cl::init(true), - cl::ReallyHidden); - - - namespace { + // These are at global scope so static functions can use them too. + typedef SmallVectorImpl<std::pair<Constant*, BasicBlock*> > PredValueInfo; + typedef SmallVector<std::pair<Constant*, BasicBlock*>, 8> PredValueInfoTy; + + // This is used to keep track of what kind of constant we're currently hoping + // to find. + enum ConstantPreference { + WantInteger, + WantBlockAddress + }; + /// This pass performs 'jump threading', which looks at blocks that have /// multiple predecessors and multiple successors. If one or more of the /// predecessors of the block can be proven to always jump to one of the @@ -79,61 +81,59 @@ namespace { SmallSet<AssertingVH<BasicBlock>, 16> LoopHeaders; #endif DenseSet<std::pair<Value*, BasicBlock*> > RecursionSet; - + // RAII helper for updating the recursion stack. struct RecursionSetRemover { DenseSet<std::pair<Value*, BasicBlock*> > &TheSet; std::pair<Value*, BasicBlock*> ThePair; - + RecursionSetRemover(DenseSet<std::pair<Value*, BasicBlock*> > &S, std::pair<Value*, BasicBlock*> P) : TheSet(S), ThePair(P) { } - + ~RecursionSetRemover() { TheSet.erase(ThePair); } }; public: static char ID; // Pass identification - JumpThreading() : FunctionPass(ID) {} + JumpThreading() : FunctionPass(ID) { + initializeJumpThreadingPass(*PassRegistry::getPassRegistry()); + } bool runOnFunction(Function &F); - + virtual void getAnalysisUsage(AnalysisUsage &AU) const { - if (EnableLVI) { - AU.addRequired<LazyValueInfo>(); - AU.addPreserved<LazyValueInfo>(); - } + AU.addRequired<LazyValueInfo>(); + AU.addPreserved<LazyValueInfo>(); } - + void FindLoopHeaders(Function &F); bool ProcessBlock(BasicBlock *BB); bool ThreadEdge(BasicBlock *BB, const SmallVectorImpl<BasicBlock*> &PredBBs, BasicBlock *SuccBB); bool DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB, const SmallVectorImpl<BasicBlock *> &PredBBs); - - typedef SmallVectorImpl<std::pair<ConstantInt*, - BasicBlock*> > PredValueInfo; - + bool ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB, - PredValueInfo &Result); - bool ProcessThreadableEdges(Value *Cond, BasicBlock *BB); - - - bool ProcessBranchOnDuplicateCond(BasicBlock *PredBB, BasicBlock *DestBB); - bool ProcessSwitchOnDuplicateCond(BasicBlock *PredBB, BasicBlock *DestBB); + PredValueInfo &Result, + ConstantPreference Preference); + bool ProcessThreadableEdges(Value *Cond, BasicBlock *BB, + ConstantPreference Preference); bool ProcessBranchOnPHI(PHINode *PN); bool ProcessBranchOnXOR(BinaryOperator *BO); - + bool SimplifyPartiallyRedundantLoad(LoadInst *LI); }; } char JumpThreading::ID = 0; -INITIALIZE_PASS(JumpThreading, "jump-threading", - "Jump Threading", false, false); +INITIALIZE_PASS_BEGIN(JumpThreading, "jump-threading", + "Jump Threading", false, false) +INITIALIZE_PASS_DEPENDENCY(LazyValueInfo) +INITIALIZE_PASS_END(JumpThreading, "jump-threading", + "Jump Threading", false, false) // Public interface to the Jump Threading pass FunctionPass *llvm::createJumpThreadingPass() { return new JumpThreading(); } @@ -143,21 +143,21 @@ FunctionPass *llvm::createJumpThreadingPass() { return new JumpThreading(); } bool JumpThreading::runOnFunction(Function &F) { DEBUG(dbgs() << "Jump threading on function '" << F.getName() << "'\n"); TD = getAnalysisIfAvailable<TargetData>(); - LVI = EnableLVI ? &getAnalysis<LazyValueInfo>() : 0; - + LVI = &getAnalysis<LazyValueInfo>(); + FindLoopHeaders(F); - + bool Changed, EverChanged = false; do { Changed = false; for (Function::iterator I = F.begin(), E = F.end(); I != E;) { BasicBlock *BB = I; - // Thread all of the branches we can over this block. + // Thread all of the branches we can over this block. while (ProcessBlock(BB)) Changed = true; - + ++I; - + // If the block is trivially dead, zap it. This eliminates the successor // edges which simplifies the CFG. if (pred_begin(BB) == pred_end(BB) && @@ -165,48 +165,46 @@ bool JumpThreading::runOnFunction(Function &F) { DEBUG(dbgs() << " JT: Deleting dead block '" << BB->getName() << "' with terminator: " << *BB->getTerminator() << '\n'); LoopHeaders.erase(BB); - if (LVI) LVI->eraseBlock(BB); + LVI->eraseBlock(BB); DeleteDeadBlock(BB); Changed = true; - } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) { - // Can't thread an unconditional jump, but if the block is "almost - // empty", we can replace uses of it with uses of the successor and make - // this dead. - if (BI->isUnconditional() && - BB != &BB->getParent()->getEntryBlock()) { - BasicBlock::iterator BBI = BB->getFirstNonPHI(); - // Ignore dbg intrinsics. - while (isa<DbgInfoIntrinsic>(BBI)) - ++BBI; + continue; + } + + BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()); + + // Can't thread an unconditional jump, but if the block is "almost + // empty", we can replace uses of it with uses of the successor and make + // this dead. + if (BI && BI->isUnconditional() && + BB != &BB->getParent()->getEntryBlock() && // If the terminator is the only non-phi instruction, try to nuke it. - if (BBI->isTerminator()) { - // Since TryToSimplifyUncondBranchFromEmptyBlock may delete the - // block, we have to make sure it isn't in the LoopHeaders set. We - // reinsert afterward if needed. - bool ErasedFromLoopHeaders = LoopHeaders.erase(BB); - BasicBlock *Succ = BI->getSuccessor(0); - - // FIXME: It is always conservatively correct to drop the info - // for a block even if it doesn't get erased. This isn't totally - // awesome, but it allows us to use AssertingVH to prevent nasty - // dangling pointer issues within LazyValueInfo. - if (LVI) LVI->eraseBlock(BB); - if (TryToSimplifyUncondBranchFromEmptyBlock(BB)) { - Changed = true; - // If we deleted BB and BB was the header of a loop, then the - // successor is now the header of the loop. - BB = Succ; - } - - if (ErasedFromLoopHeaders) - LoopHeaders.insert(BB); - } + BB->getFirstNonPHIOrDbg()->isTerminator()) { + // Since TryToSimplifyUncondBranchFromEmptyBlock may delete the + // block, we have to make sure it isn't in the LoopHeaders set. We + // reinsert afterward if needed. + bool ErasedFromLoopHeaders = LoopHeaders.erase(BB); + BasicBlock *Succ = BI->getSuccessor(0); + + // FIXME: It is always conservatively correct to drop the info + // for a block even if it doesn't get erased. This isn't totally + // awesome, but it allows us to use AssertingVH to prevent nasty + // dangling pointer issues within LazyValueInfo. + LVI->eraseBlock(BB); + if (TryToSimplifyUncondBranchFromEmptyBlock(BB)) { + Changed = true; + // If we deleted BB and BB was the header of a loop, then the + // successor is now the header of the loop. + BB = Succ; } + + if (ErasedFromLoopHeaders) + LoopHeaders.insert(BB); } } EverChanged |= Changed; } while (Changed); - + LoopHeaders.clear(); return EverChanged; } @@ -216,25 +214,25 @@ bool JumpThreading::runOnFunction(Function &F) { static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB) { /// Ignore PHI nodes, these will be flattened when duplication happens. BasicBlock::const_iterator I = BB->getFirstNonPHI(); - + // FIXME: THREADING will delete values that are just used to compute the // branch, so they shouldn't count against the duplication cost. - - + + // Sum up the cost of each instruction until we get to the terminator. Don't // include the terminator because the copy won't include it. unsigned Size = 0; for (; !isa<TerminatorInst>(I); ++I) { // Debugger intrinsics don't incur code size. if (isa<DbgInfoIntrinsic>(I)) continue; - + // If this is a pointer->pointer bitcast, it is free. if (isa<BitCastInst>(I) && I->getType()->isPointerTy()) continue; - + // All other instructions count for at least one unit. ++Size; - + // Calls are more expensive. If they are non-intrinsic calls, we model them // as having cost of 4. If they are a non-vector intrinsic, we model them // as having cost of 2 total, and if they are a vector intrinsic, we model @@ -246,12 +244,16 @@ static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB) { Size += 1; } } - + // Threading through a switch statement is particularly profitable. If this // block ends in a switch, decrease its cost to make it more likely to happen. if (isa<SwitchInst>(I)) Size = Size > 6 ? Size-6 : 0; - + + // The same holds for indirect branches, but slightly more so. + if (isa<IndirectBrInst>(I)) + Size = Size > 8 ? Size-8 : 0; + return Size; } @@ -273,57 +275,64 @@ static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB) { void JumpThreading::FindLoopHeaders(Function &F) { SmallVector<std::pair<const BasicBlock*,const BasicBlock*>, 32> Edges; FindFunctionBackedges(F, Edges); - + for (unsigned i = 0, e = Edges.size(); i != e; ++i) LoopHeaders.insert(const_cast<BasicBlock*>(Edges[i].second)); } -// Helper method for ComputeValueKnownInPredecessors. If Value is a -// ConstantInt, push it. If it's an undef, push 0. Otherwise, do nothing. -static void PushConstantIntOrUndef(SmallVectorImpl<std::pair<ConstantInt*, - BasicBlock*> > &Result, - Constant *Value, BasicBlock* BB){ - if (ConstantInt *FoldedCInt = dyn_cast<ConstantInt>(Value)) - Result.push_back(std::make_pair(FoldedCInt, BB)); - else if (isa<UndefValue>(Value)) - Result.push_back(std::make_pair((ConstantInt*)0, BB)); +/// getKnownConstant - Helper method to determine if we can thread over a +/// terminator with the given value as its condition, and if so what value to +/// use for that. What kind of value this is depends on whether we want an +/// integer or a block address, but an undef is always accepted. +/// Returns null if Val is null or not an appropriate constant. +static Constant *getKnownConstant(Value *Val, ConstantPreference Preference) { + if (!Val) + return 0; + + // Undef is "known" enough. + if (UndefValue *U = dyn_cast<UndefValue>(Val)) + return U; + + if (Preference == WantBlockAddress) + return dyn_cast<BlockAddress>(Val->stripPointerCasts()); + + return dyn_cast<ConstantInt>(Val); } /// ComputeValueKnownInPredecessors - Given a basic block BB and a value V, see -/// if we can infer that the value is a known ConstantInt in any of our -/// predecessors. If so, return the known list of value and pred BB in the -/// result vector. If a value is known to be undef, it is returned as null. +/// if we can infer that the value is a known ConstantInt/BlockAddress or undef +/// in any of our predecessors. If so, return the known list of value and pred +/// BB in the result vector. /// /// This returns true if there were any known values. /// bool JumpThreading:: -ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){ +ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB, PredValueInfo &Result, + ConstantPreference Preference) { // This method walks up use-def chains recursively. Because of this, we could // get into an infinite loop going around loops in the use-def chain. To // prevent this, keep track of what (value, block) pairs we've already visited // and terminate the search if we loop back to them if (!RecursionSet.insert(std::make_pair(V, BB)).second) return false; - + // An RAII help to remove this pair from the recursion set once the recursion // stack pops back out again. RecursionSetRemover remover(RecursionSet, std::make_pair(V, BB)); - - // If V is a constantint, then it is known in all predecessors. - if (isa<ConstantInt>(V) || isa<UndefValue>(V)) { - ConstantInt *CI = dyn_cast<ConstantInt>(V); - + + // If V is a constant, then it is known in all predecessors. + if (Constant *KC = getKnownConstant(V, Preference)) { for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) - Result.push_back(std::make_pair(CI, *PI)); - + Result.push_back(std::make_pair(KC, *PI)); + return true; } - + // If V is a non-instruction value, or an instruction in a different block, // then it can't be derived from a PHI. Instruction *I = dyn_cast<Instruction>(V); if (I == 0 || I->getParent() != BB) { - + // Okay, if this is a live-in value, see if it has a known value at the end // of any of our predecessors. // @@ -331,82 +340,78 @@ ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){ /// TODO: Per PR2563, we could infer value range information about a /// predecessor based on its terminator. // - if (LVI) { - // FIXME: change this to use the more-rich 'getPredicateOnEdge' method if - // "I" is a non-local compare-with-a-constant instruction. This would be - // able to handle value inequalities better, for example if the compare is - // "X < 4" and "X < 3" is known true but "X < 4" itself is not available. - // Perhaps getConstantOnEdge should be smart enough to do this? - - for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { - BasicBlock *P = *PI; - // If the value is known by LazyValueInfo to be a constant in a - // predecessor, use that information to try to thread this block. - Constant *PredCst = LVI->getConstantOnEdge(V, P, BB); - if (PredCst == 0 || - (!isa<ConstantInt>(PredCst) && !isa<UndefValue>(PredCst))) - continue; - - Result.push_back(std::make_pair(dyn_cast<ConstantInt>(PredCst), P)); - } - - return !Result.empty(); + // FIXME: change this to use the more-rich 'getPredicateOnEdge' method if + // "I" is a non-local compare-with-a-constant instruction. This would be + // able to handle value inequalities better, for example if the compare is + // "X < 4" and "X < 3" is known true but "X < 4" itself is not available. + // Perhaps getConstantOnEdge should be smart enough to do this? + + for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { + BasicBlock *P = *PI; + // If the value is known by LazyValueInfo to be a constant in a + // predecessor, use that information to try to thread this block. + Constant *PredCst = LVI->getConstantOnEdge(V, P, BB); + if (Constant *KC = getKnownConstant(PredCst, Preference)) + Result.push_back(std::make_pair(KC, P)); } - - return false; + + return !Result.empty(); } - + /// If I is a PHI node, then we know the incoming values for any constants. if (PHINode *PN = dyn_cast<PHINode>(I)) { for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { Value *InVal = PN->getIncomingValue(i); - if (isa<ConstantInt>(InVal) || isa<UndefValue>(InVal)) { - ConstantInt *CI = dyn_cast<ConstantInt>(InVal); - Result.push_back(std::make_pair(CI, PN->getIncomingBlock(i))); - } else if (LVI) { + if (Constant *KC = getKnownConstant(InVal, Preference)) { + Result.push_back(std::make_pair(KC, PN->getIncomingBlock(i))); + } else { Constant *CI = LVI->getConstantOnEdge(InVal, PN->getIncomingBlock(i), BB); - // LVI returns null is no value could be determined. - if (!CI) continue; - PushConstantIntOrUndef(Result, CI, PN->getIncomingBlock(i)); + if (Constant *KC = getKnownConstant(CI, Preference)) + Result.push_back(std::make_pair(KC, PN->getIncomingBlock(i))); } } - + return !Result.empty(); } - - SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> LHSVals, RHSVals; + + PredValueInfoTy LHSVals, RHSVals; // Handle some boolean conditions. - if (I->getType()->getPrimitiveSizeInBits() == 1) { + if (I->getType()->getPrimitiveSizeInBits() == 1) { + assert(Preference == WantInteger && "One-bit non-integer type?"); // X | true -> true // X & false -> false if (I->getOpcode() == Instruction::Or || I->getOpcode() == Instruction::And) { - ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals); - ComputeValueKnownInPredecessors(I->getOperand(1), BB, RHSVals); - + ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals, + WantInteger); + ComputeValueKnownInPredecessors(I->getOperand(1), BB, RHSVals, + WantInteger); + if (LHSVals.empty() && RHSVals.empty()) return false; - + ConstantInt *InterestingVal; if (I->getOpcode() == Instruction::Or) InterestingVal = ConstantInt::getTrue(I->getContext()); else InterestingVal = ConstantInt::getFalse(I->getContext()); - + SmallPtrSet<BasicBlock*, 4> LHSKnownBBs; - + // Scan for the sentinel. If we find an undef, force it to the // interesting value: x|undef -> true and x&undef -> false. for (unsigned i = 0, e = LHSVals.size(); i != e; ++i) - if (LHSVals[i].first == InterestingVal || LHSVals[i].first == 0) { + if (LHSVals[i].first == InterestingVal || + isa<UndefValue>(LHSVals[i].first)) { Result.push_back(LHSVals[i]); Result.back().first = InterestingVal; LHSKnownBBs.insert(LHSVals[i].second); } for (unsigned i = 0, e = RHSVals.size(); i != e; ++i) - if (RHSVals[i].first == InterestingVal || RHSVals[i].first == 0) { + if (RHSVals[i].first == InterestingVal || + isa<UndefValue>(RHSVals[i].first)) { // If we already inferred a value for this block on the LHS, don't // re-add it. if (!LHSKnownBBs.count(RHSVals[i].second)) { @@ -414,48 +419,51 @@ ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){ Result.back().first = InterestingVal; } } - + return !Result.empty(); } - + // Handle the NOT form of XOR. if (I->getOpcode() == Instruction::Xor && isa<ConstantInt>(I->getOperand(1)) && cast<ConstantInt>(I->getOperand(1))->isOne()) { - ComputeValueKnownInPredecessors(I->getOperand(0), BB, Result); + ComputeValueKnownInPredecessors(I->getOperand(0), BB, Result, + WantInteger); if (Result.empty()) return false; // Invert the known values. for (unsigned i = 0, e = Result.size(); i != e; ++i) - if (Result[i].first) - Result[i].first = - cast<ConstantInt>(ConstantExpr::getNot(Result[i].first)); - + Result[i].first = ConstantExpr::getNot(Result[i].first); + return true; } - + // Try to simplify some other binary operator values. } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(I)) { + assert(Preference != WantBlockAddress + && "A binary operator creating a block address?"); if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->getOperand(1))) { - SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> LHSVals; - ComputeValueKnownInPredecessors(BO->getOperand(0), BB, LHSVals); - + PredValueInfoTy LHSVals; + ComputeValueKnownInPredecessors(BO->getOperand(0), BB, LHSVals, + WantInteger); + // Try to use constant folding to simplify the binary operator. for (unsigned i = 0, e = LHSVals.size(); i != e; ++i) { - Constant *V = LHSVals[i].first ? LHSVals[i].first : - cast<Constant>(UndefValue::get(BO->getType())); + Constant *V = LHSVals[i].first; Constant *Folded = ConstantExpr::get(BO->getOpcode(), V, CI); - - PushConstantIntOrUndef(Result, Folded, LHSVals[i].second); + + if (Constant *KC = getKnownConstant(Folded, WantInteger)) + Result.push_back(std::make_pair(KC, LHSVals[i].second)); } } - + return !Result.empty(); } - + // Handle compare with phi operand, where the PHI is defined in this block. if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) { + assert(Preference == WantInteger && "Compares only produce integers"); PHINode *PN = dyn_cast<PHINode>(Cmp->getOperand(0)); if (PN && PN->getParent() == BB) { // We can do this simplification if any comparisons fold to true or false. @@ -464,32 +472,31 @@ ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){ BasicBlock *PredBB = PN->getIncomingBlock(i); Value *LHS = PN->getIncomingValue(i); Value *RHS = Cmp->getOperand(1)->DoPHITranslation(BB, PredBB); - + Value *Res = SimplifyCmpInst(Cmp->getPredicate(), LHS, RHS, TD); if (Res == 0) { - if (!LVI || !isa<Constant>(RHS)) + if (!isa<Constant>(RHS)) continue; - - LazyValueInfo::Tristate + + LazyValueInfo::Tristate ResT = LVI->getPredicateOnEdge(Cmp->getPredicate(), LHS, cast<Constant>(RHS), PredBB, BB); if (ResT == LazyValueInfo::Unknown) continue; Res = ConstantInt::get(Type::getInt1Ty(LHS->getContext()), ResT); } - - if (Constant *ConstRes = dyn_cast<Constant>(Res)) - PushConstantIntOrUndef(Result, ConstRes, PredBB); + + if (Constant *KC = getKnownConstant(Res, WantInteger)) + Result.push_back(std::make_pair(KC, PredBB)); } - + return !Result.empty(); } - - + + // If comparing a live-in value against a constant, see if we know the // live-in value on any predecessors. - if (LVI && isa<Constant>(Cmp->getOperand(1)) && - Cmp->getType()->isIntegerTy()) { + if (isa<Constant>(Cmp->getOperand(1)) && Cmp->getType()->isIntegerTy()) { if (!isa<Instruction>(Cmp->getOperand(0)) || cast<Instruction>(Cmp->getOperand(0))->getParent() != BB) { Constant *RHSCst = cast<Constant>(Cmp->getOperand(1)); @@ -505,44 +512,74 @@ ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){ continue; Constant *ResC = ConstantInt::get(Cmp->getType(), Res); - Result.push_back(std::make_pair(cast<ConstantInt>(ResC), P)); + Result.push_back(std::make_pair(ResC, P)); } return !Result.empty(); } - + // Try to find a constant value for the LHS of a comparison, // and evaluate it statically if we can. if (Constant *CmpConst = dyn_cast<Constant>(Cmp->getOperand(1))) { - SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> LHSVals; - ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals); - + PredValueInfoTy LHSVals; + ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals, + WantInteger); + for (unsigned i = 0, e = LHSVals.size(); i != e; ++i) { - Constant *V = LHSVals[i].first ? LHSVals[i].first : - cast<Constant>(UndefValue::get(CmpConst->getType())); + Constant *V = LHSVals[i].first; Constant *Folded = ConstantExpr::getCompare(Cmp->getPredicate(), V, CmpConst); - PushConstantIntOrUndef(Result, Folded, LHSVals[i].second); + if (Constant *KC = getKnownConstant(Folded, WantInteger)) + Result.push_back(std::make_pair(KC, LHSVals[i].second)); } - + return !Result.empty(); } } } - - if (LVI) { - // If all else fails, see if LVI can figure out a constant value for us. - Constant *CI = LVI->getConstant(V, BB); - ConstantInt *CInt = dyn_cast_or_null<ConstantInt>(CI); - if (CInt) { - for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) - Result.push_back(std::make_pair(CInt, *PI)); + + if (SelectInst *SI = dyn_cast<SelectInst>(I)) { + // Handle select instructions where at least one operand is a known constant + // and we can figure out the condition value for any predecessor block. + Constant *TrueVal = getKnownConstant(SI->getTrueValue(), Preference); + Constant *FalseVal = getKnownConstant(SI->getFalseValue(), Preference); + PredValueInfoTy Conds; + if ((TrueVal || FalseVal) && + ComputeValueKnownInPredecessors(SI->getCondition(), BB, Conds, + WantInteger)) { + for (unsigned i = 0, e = Conds.size(); i != e; ++i) { + Constant *Cond = Conds[i].first; + + // Figure out what value to use for the condition. + bool KnownCond; + if (ConstantInt *CI = dyn_cast<ConstantInt>(Cond)) { + // A known boolean. + KnownCond = CI->isOne(); + } else { + assert(isa<UndefValue>(Cond) && "Unexpected condition value"); + // Either operand will do, so be sure to pick the one that's a known + // constant. + // FIXME: Do this more cleverly if both values are known constants? + KnownCond = (TrueVal != 0); + } + + // See if the select has a known constant value for this predecessor. + if (Constant *Val = KnownCond ? TrueVal : FalseVal) + Result.push_back(std::make_pair(Val, Conds[i].second)); + } + + return !Result.empty(); } - - return !Result.empty(); } - - return false; + + // If all else fails, see if LVI can figure out a constant value for us. + Constant *CI = LVI->getConstant(V, BB); + if (Constant *KC = getKnownConstant(CI, Preference)) { + for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) + Result.push_back(std::make_pair(KC, *PI)); + } + + return !Result.empty(); } @@ -565,10 +602,20 @@ static unsigned GetBestDestForJumpOnUndef(BasicBlock *BB) { if (NumPreds < MinNumPreds) MinSucc = i; } - + return MinSucc; } +static bool hasAddressTakenAndUsed(BasicBlock *BB) { + if (!BB->hasAddressTaken()) return false; + + // If the block has its address taken, it may be a tree of dead constants + // hanging off of it. These shouldn't keep the block alive. + BlockAddress *BA = BlockAddress::get(BB); + BA->removeDeadConstantUsers(); + return !BA->use_empty(); +} + /// ProcessBlock - If there are any predecessors whose control can be threaded /// through to a successor, transform them now. bool JumpThreading::ProcessBlock(BasicBlock *BB) { @@ -577,167 +624,122 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) { if (pred_begin(BB) == pred_end(BB) && BB != &BB->getParent()->getEntryBlock()) return false; - + // If this block has a single predecessor, and if that pred has a single // successor, merge the blocks. This encourages recursive jump threading // because now the condition in this block can be threaded through // predecessors of our predecessor block. if (BasicBlock *SinglePred = BB->getSinglePredecessor()) { if (SinglePred->getTerminator()->getNumSuccessors() == 1 && - SinglePred != BB) { + SinglePred != BB && !hasAddressTakenAndUsed(BB)) { // If SinglePred was a loop header, BB becomes one. if (LoopHeaders.erase(SinglePred)) LoopHeaders.insert(BB); - + // Remember if SinglePred was the entry block of the function. If so, we // will need to move BB back to the entry position. bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock(); - if (LVI) LVI->eraseBlock(SinglePred); + LVI->eraseBlock(SinglePred); MergeBasicBlockIntoOnlyPred(BB); - + if (isEntry && BB != &BB->getParent()->getEntryBlock()) BB->moveBefore(&BB->getParent()->getEntryBlock()); return true; } } - // Look to see if the terminator is a branch of switch, if not we can't thread - // it. + // What kind of constant we're looking for. + ConstantPreference Preference = WantInteger; + + // Look to see if the terminator is a conditional branch, switch or indirect + // branch, if not we can't thread it. Value *Condition; - if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) { + Instruction *Terminator = BB->getTerminator(); + if (BranchInst *BI = dyn_cast<BranchInst>(Terminator)) { // Can't thread an unconditional jump. if (BI->isUnconditional()) return false; Condition = BI->getCondition(); - } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) + } else if (SwitchInst *SI = dyn_cast<SwitchInst>(Terminator)) { Condition = SI->getCondition(); - else + } else if (IndirectBrInst *IB = dyn_cast<IndirectBrInst>(Terminator)) { + Condition = IB->getAddress()->stripPointerCasts(); + Preference = WantBlockAddress; + } else { return false; // Must be an invoke. - - // If the terminator of this block is branching on a constant, simplify the - // terminator to an unconditional branch. This can occur due to threading in - // other blocks. - if (isa<ConstantInt>(Condition)) { - DEBUG(dbgs() << " In block '" << BB->getName() - << "' folding terminator: " << *BB->getTerminator() << '\n'); - ++NumFolds; - ConstantFoldTerminator(BB); - return true; } - + // If the terminator is branching on an undef, we can pick any of the // successors to branch to. Let GetBestDestForJumpOnUndef decide. if (isa<UndefValue>(Condition)) { unsigned BestSucc = GetBestDestForJumpOnUndef(BB); - + // Fold the branch/switch. TerminatorInst *BBTerm = BB->getTerminator(); for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) { if (i == BestSucc) continue; - RemovePredecessorAndSimplify(BBTerm->getSuccessor(i), BB, TD); + BBTerm->getSuccessor(i)->removePredecessor(BB, true); } - + DEBUG(dbgs() << " In block '" << BB->getName() << "' folding undef terminator: " << *BBTerm << '\n'); BranchInst::Create(BBTerm->getSuccessor(BestSucc), BBTerm); BBTerm->eraseFromParent(); return true; } - - Instruction *CondInst = dyn_cast<Instruction>(Condition); - // If the condition is an instruction defined in another block, see if a - // predecessor has the same condition: - // br COND, BBX, BBY - // BBX: - // br COND, BBZ, BBW - if (!LVI && - !Condition->hasOneUse() && // Multiple uses. - (CondInst == 0 || CondInst->getParent() != BB)) { // Non-local definition. - pred_iterator PI = pred_begin(BB), E = pred_end(BB); - if (isa<BranchInst>(BB->getTerminator())) { - for (; PI != E; ++PI) { - BasicBlock *P = *PI; - if (BranchInst *PBI = dyn_cast<BranchInst>(P->getTerminator())) - if (PBI->isConditional() && PBI->getCondition() == Condition && - ProcessBranchOnDuplicateCond(P, BB)) - return true; - } - } else { - assert(isa<SwitchInst>(BB->getTerminator()) && "Unknown jump terminator"); - for (; PI != E; ++PI) { - BasicBlock *P = *PI; - if (SwitchInst *PSI = dyn_cast<SwitchInst>(P->getTerminator())) - if (PSI->getCondition() == Condition && - ProcessSwitchOnDuplicateCond(P, BB)) - return true; - } - } + // If the terminator of this block is branching on a constant, simplify the + // terminator to an unconditional branch. This can occur due to threading in + // other blocks. + if (getKnownConstant(Condition, Preference)) { + DEBUG(dbgs() << " In block '" << BB->getName() + << "' folding terminator: " << *BB->getTerminator() << '\n'); + ++NumFolds; + ConstantFoldTerminator(BB); + return true; } + Instruction *CondInst = dyn_cast<Instruction>(Condition); + // All the rest of our checks depend on the condition being an instruction. if (CondInst == 0) { // FIXME: Unify this with code below. - if (LVI && ProcessThreadableEdges(Condition, BB)) + if (ProcessThreadableEdges(Condition, BB, Preference)) return true; return false; - } - - + } + + if (CmpInst *CondCmp = dyn_cast<CmpInst>(CondInst)) { - if (!LVI && - (!isa<PHINode>(CondCmp->getOperand(0)) || - cast<PHINode>(CondCmp->getOperand(0))->getParent() != BB)) { - // If we have a comparison, loop over the predecessors to see if there is - // a condition with a lexically identical value. - pred_iterator PI = pred_begin(BB), E = pred_end(BB); - for (; PI != E; ++PI) { - BasicBlock *P = *PI; - if (BranchInst *PBI = dyn_cast<BranchInst>(P->getTerminator())) - if (PBI->isConditional() && P != BB) { - if (CmpInst *CI = dyn_cast<CmpInst>(PBI->getCondition())) { - if (CI->getOperand(0) == CondCmp->getOperand(0) && - CI->getOperand(1) == CondCmp->getOperand(1) && - CI->getPredicate() == CondCmp->getPredicate()) { - // TODO: Could handle things like (x != 4) --> (x == 17) - if (ProcessBranchOnDuplicateCond(P, BB)) - return true; - } - } - } - } - } - // For a comparison where the LHS is outside this block, it's possible // that we've branched on it before. Used LVI to see if we can simplify // the branch based on that. BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator()); Constant *CondConst = dyn_cast<Constant>(CondCmp->getOperand(1)); pred_iterator PI = pred_begin(BB), PE = pred_end(BB); - if (LVI && CondBr && CondConst && CondBr->isConditional() && PI != PE && + if (CondBr && CondConst && CondBr->isConditional() && PI != PE && (!isa<Instruction>(CondCmp->getOperand(0)) || cast<Instruction>(CondCmp->getOperand(0))->getParent() != BB)) { // For predecessor edge, determine if the comparison is true or false // on that edge. If they're all true or all false, we can simplify the // branch. // FIXME: We could handle mixed true/false by duplicating code. - LazyValueInfo::Tristate Baseline = + LazyValueInfo::Tristate Baseline = LVI->getPredicateOnEdge(CondCmp->getPredicate(), CondCmp->getOperand(0), CondConst, *PI, BB); if (Baseline != LazyValueInfo::Unknown) { // Check that all remaining incoming values match the first one. while (++PI != PE) { - LazyValueInfo::Tristate Ret = LVI->getPredicateOnEdge( - CondCmp->getPredicate(), - CondCmp->getOperand(0), - CondConst, *PI, BB); + LazyValueInfo::Tristate Ret = + LVI->getPredicateOnEdge(CondCmp->getPredicate(), + CondCmp->getOperand(0), CondConst, *PI, BB); if (Ret != Baseline) break; } - + // If we terminated early, then one of the values didn't match. if (PI == PE) { unsigned ToRemove = Baseline == LazyValueInfo::True ? 1 : 0; unsigned ToKeep = Baseline == LazyValueInfo::True ? 0 : 1; - RemovePredecessorAndSimplify(CondBr->getSuccessor(ToRemove), BB, TD); + CondBr->getSuccessor(ToRemove)->removePredecessor(BB, true); BranchInst::Create(CondBr->getSuccessor(ToKeep), CondBr); CondBr->eraseFromParent(); return true; @@ -755,174 +757,37 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) { if (CmpInst *CondCmp = dyn_cast<CmpInst>(SimplifyValue)) if (isa<Constant>(CondCmp->getOperand(1))) SimplifyValue = CondCmp->getOperand(0); - + // TODO: There are other places where load PRE would be profitable, such as // more complex comparisons. if (LoadInst *LI = dyn_cast<LoadInst>(SimplifyValue)) if (SimplifyPartiallyRedundantLoad(LI)) return true; - - + + // Handle a variety of cases where we are branching on something derived from // a PHI node in the current block. If we can prove that any predecessors // compute a predictable value based on a PHI node, thread those predecessors. // - if (ProcessThreadableEdges(CondInst, BB)) + if (ProcessThreadableEdges(CondInst, BB, Preference)) return true; - + // If this is an otherwise-unfoldable branch on a phi node in the current // block, see if we can simplify. if (PHINode *PN = dyn_cast<PHINode>(CondInst)) if (PN->getParent() == BB && isa<BranchInst>(BB->getTerminator())) return ProcessBranchOnPHI(PN); - - + + // If this is an otherwise-unfoldable branch on a XOR, see if we can simplify. if (CondInst->getOpcode() == Instruction::Xor && CondInst->getParent() == BB && isa<BranchInst>(BB->getTerminator())) return ProcessBranchOnXOR(cast<BinaryOperator>(CondInst)); - - - // TODO: If we have: "br (X > 0)" and we have a predecessor where we know - // "(X == 4)", thread through this block. - - return false; -} -/// ProcessBranchOnDuplicateCond - We found a block and a predecessor of that -/// block that jump on exactly the same condition. This means that we almost -/// always know the direction of the edge in the DESTBB: -/// PREDBB: -/// br COND, DESTBB, BBY -/// DESTBB: -/// br COND, BBZ, BBW -/// -/// If DESTBB has multiple predecessors, we can't just constant fold the branch -/// in DESTBB, we have to thread over it. -bool JumpThreading::ProcessBranchOnDuplicateCond(BasicBlock *PredBB, - BasicBlock *BB) { - BranchInst *PredBI = cast<BranchInst>(PredBB->getTerminator()); - - // If both successors of PredBB go to DESTBB, we don't know anything. We can - // fold the branch to an unconditional one, which allows other recursive - // simplifications. - bool BranchDir; - if (PredBI->getSuccessor(1) != BB) - BranchDir = true; - else if (PredBI->getSuccessor(0) != BB) - BranchDir = false; - else { - DEBUG(dbgs() << " In block '" << PredBB->getName() - << "' folding terminator: " << *PredBB->getTerminator() << '\n'); - ++NumFolds; - ConstantFoldTerminator(PredBB); - return true; - } - - BranchInst *DestBI = cast<BranchInst>(BB->getTerminator()); - // If the dest block has one predecessor, just fix the branch condition to a - // constant and fold it. - if (BB->getSinglePredecessor()) { - DEBUG(dbgs() << " In block '" << BB->getName() - << "' folding condition to '" << BranchDir << "': " - << *BB->getTerminator() << '\n'); - ++NumFolds; - Value *OldCond = DestBI->getCondition(); - DestBI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()), - BranchDir)); - // Delete dead instructions before we fold the branch. Folding the branch - // can eliminate edges from the CFG which can end up deleting OldCond. - RecursivelyDeleteTriviallyDeadInstructions(OldCond); - ConstantFoldTerminator(BB); - return true; - } - - - // Next, figure out which successor we are threading to. - BasicBlock *SuccBB = DestBI->getSuccessor(!BranchDir); - - SmallVector<BasicBlock*, 2> Preds; - Preds.push_back(PredBB); - - // Ok, try to thread it! - return ThreadEdge(BB, Preds, SuccBB); -} - -/// ProcessSwitchOnDuplicateCond - We found a block and a predecessor of that -/// block that switch on exactly the same condition. This means that we almost -/// always know the direction of the edge in the DESTBB: -/// PREDBB: -/// switch COND [... DESTBB, BBY ... ] -/// DESTBB: -/// switch COND [... BBZ, BBW ] -/// -/// Optimizing switches like this is very important, because simplifycfg builds -/// switches out of repeated 'if' conditions. -bool JumpThreading::ProcessSwitchOnDuplicateCond(BasicBlock *PredBB, - BasicBlock *DestBB) { - // Can't thread edge to self. - if (PredBB == DestBB) - return false; - - SwitchInst *PredSI = cast<SwitchInst>(PredBB->getTerminator()); - SwitchInst *DestSI = cast<SwitchInst>(DestBB->getTerminator()); - - // There are a variety of optimizations that we can potentially do on these - // blocks: we order them from most to least preferable. - - // If DESTBB *just* contains the switch, then we can forward edges from PREDBB - // directly to their destination. This does not introduce *any* code size - // growth. Skip debug info first. - BasicBlock::iterator BBI = DestBB->begin(); - while (isa<DbgInfoIntrinsic>(BBI)) - BBI++; - - // FIXME: Thread if it just contains a PHI. - if (isa<SwitchInst>(BBI)) { - bool MadeChange = false; - // Ignore the default edge for now. - for (unsigned i = 1, e = DestSI->getNumSuccessors(); i != e; ++i) { - ConstantInt *DestVal = DestSI->getCaseValue(i); - BasicBlock *DestSucc = DestSI->getSuccessor(i); - - // Okay, DestSI has a case for 'DestVal' that goes to 'DestSucc'. See if - // PredSI has an explicit case for it. If so, forward. If it is covered - // by the default case, we can't update PredSI. - unsigned PredCase = PredSI->findCaseValue(DestVal); - if (PredCase == 0) continue; - - // If PredSI doesn't go to DestBB on this value, then it won't reach the - // case on this condition. - if (PredSI->getSuccessor(PredCase) != DestBB && - DestSI->getSuccessor(i) != DestBB) - continue; - - // Do not forward this if it already goes to this destination, this would - // be an infinite loop. - if (PredSI->getSuccessor(PredCase) == DestSucc) - continue; - - // Otherwise, we're safe to make the change. Make sure that the edge from - // DestSI to DestSucc is not critical and has no PHI nodes. - DEBUG(dbgs() << "FORWARDING EDGE " << *DestVal << " FROM: " << *PredSI); - DEBUG(dbgs() << "THROUGH: " << *DestSI); + // TODO: If we have: "br (X > 0)" and we have a predecessor where we know + // "(X == 4)", thread through this block. - // If the destination has PHI nodes, just split the edge for updating - // simplicity. - if (isa<PHINode>(DestSucc->begin()) && !DestSucc->getSinglePredecessor()){ - SplitCriticalEdge(DestSI, i, this); - DestSucc = DestSI->getSuccessor(i); - } - FoldSingleEntryPHINodes(DestSucc); - PredSI->setSuccessor(PredCase, DestSucc); - MadeChange = true; - } - - if (MadeChange) - return true; - } - return false; } @@ -934,13 +799,13 @@ bool JumpThreading::ProcessSwitchOnDuplicateCond(BasicBlock *PredBB, bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) { // Don't hack volatile loads. if (LI->isVolatile()) return false; - + // If the load is defined in a block with exactly one predecessor, it can't be // partially redundant. BasicBlock *LoadBB = LI->getParent(); if (LoadBB->getSinglePredecessor()) return false; - + Value *LoadedPtr = LI->getOperand(0); // If the loaded operand is defined in the LoadBB, it can't be available. @@ -948,17 +813,17 @@ bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) { if (Instruction *PtrOp = dyn_cast<Instruction>(LoadedPtr)) if (PtrOp->getParent() == LoadBB) return false; - + // Scan a few instructions up from the load, to see if it is obviously live at // the entry to its block. BasicBlock::iterator BBIt = LI; - if (Value *AvailableVal = + if (Value *AvailableVal = FindAvailableLoadedValue(LoadedPtr, LoadBB, BBIt, 6)) { // If the value if the load is locally available within the block, just use // it. This frequently occurs for reg2mem'd allocas. //cerr << "LOAD ELIMINATED:\n" << *BBIt << *LI << "\n"; - + // If the returned value is the load itself, replace with an undef. This can // only happen in dead loops. if (AvailableVal == LI) AvailableVal = UndefValue::get(LI->getType()); @@ -972,13 +837,13 @@ bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) { // might clobber its value. if (BBIt != LoadBB->begin()) return false; - - + + SmallPtrSet<BasicBlock*, 8> PredsScanned; typedef SmallVector<std::pair<BasicBlock*, Value*>, 8> AvailablePredsTy; AvailablePredsTy AvailablePreds; BasicBlock *OneUnavailablePred = 0; - + // If we got here, the loaded value is transparent through to the start of the // block. Check to see if it is available in any of the predecessor blocks. for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB); @@ -996,23 +861,23 @@ bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) { OneUnavailablePred = PredBB; continue; } - + // If so, this load is partially redundant. Remember this info so that we // can create a PHI node. AvailablePreds.push_back(std::make_pair(PredBB, PredAvailable)); } - + // If the loaded value isn't available in any predecessor, it isn't partially // redundant. if (AvailablePreds.empty()) return false; - + // Okay, the loaded value is available in at least one (and maybe all!) // predecessors. If the value is unavailable in more than one unique // predecessor, we want to insert a merge block for those common predecessors. // This ensures that we only have to insert one reload, thus not increasing // code size. BasicBlock *UnavailablePred = 0; - + // If there is exactly one predecessor where the value is unavailable, the // already computed 'OneUnavailablePred' block is it. If it ends in an // unconditional branch, we know that it isn't a critical edge. @@ -1035,17 +900,17 @@ bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) { // If the predecessor is an indirect goto, we can't split the edge. if (isa<IndirectBrInst>(P->getTerminator())) return false; - + if (!AvailablePredSet.count(P)) PredsToSplit.push_back(P); } - + // Split them out to their own block. UnavailablePred = SplitBlockPredecessors(LoadBB, &PredsToSplit[0], PredsToSplit.size(), "thread-pre-split", this); } - + // If the value isn't available in all predecessors, then there will be // exactly one where it isn't available. Insert a load on that edge and add // it to the AvailablePreds list. @@ -1057,35 +922,35 @@ bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) { UnavailablePred->getTerminator()); AvailablePreds.push_back(std::make_pair(UnavailablePred, NewVal)); } - + // Now we know that each predecessor of this block has a value in // AvailablePreds, sort them for efficient access as we're walking the preds. array_pod_sort(AvailablePreds.begin(), AvailablePreds.end()); - + // Create a PHI node at the start of the block for the PRE'd load value. PHINode *PN = PHINode::Create(LI->getType(), "", LoadBB->begin()); PN->takeName(LI); - + // Insert new entries into the PHI for each predecessor. A single block may // have multiple entries here. for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); PI != E; ++PI) { BasicBlock *P = *PI; - AvailablePredsTy::iterator I = + AvailablePredsTy::iterator I = std::lower_bound(AvailablePreds.begin(), AvailablePreds.end(), std::make_pair(P, (Value*)0)); - + assert(I != AvailablePreds.end() && I->first == P && "Didn't find entry for predecessor!"); - + PN->addIncoming(I->second, I->first); } - + //cerr << "PRE: " << *LI << *PN << "\n"; - + LI->replaceAllUsesWith(PN); LI->eraseFromParent(); - + return true; } @@ -1097,7 +962,7 @@ FindMostPopularDest(BasicBlock *BB, const SmallVectorImpl<std::pair<BasicBlock*, BasicBlock*> > &PredToDestList) { assert(!PredToDestList.empty()); - + // Determine popularity. If there are multiple possible destinations, we // explicitly choose to ignore 'undef' destinations. We prefer to thread // blocks with known and real destinations to threading undef. We'll handle @@ -1106,13 +971,13 @@ FindMostPopularDest(BasicBlock *BB, for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i) if (PredToDestList[i].second) DestPopularity[PredToDestList[i].second]++; - + // Find the most popular dest. DenseMap<BasicBlock*, unsigned>::iterator DPI = DestPopularity.begin(); BasicBlock *MostPopularDest = DPI->first; unsigned Popularity = DPI->second; SmallVector<BasicBlock*, 4> SamePopularity; - + for (++DPI; DPI != DestPopularity.end(); ++DPI) { // If the popularity of this entry isn't higher than the popularity we've // seen so far, ignore it. @@ -1126,10 +991,10 @@ FindMostPopularDest(BasicBlock *BB, SamePopularity.clear(); MostPopularDest = DPI->first; Popularity = DPI->second; - } + } } - - // Okay, now we know the most popular destination. If there is more than + + // Okay, now we know the most popular destination. If there is more than one // destination, we need to determine one. This is arbitrary, but we need // to make a deterministic decision. Pick the first one that appears in the // successor list. @@ -1138,105 +1003,105 @@ FindMostPopularDest(BasicBlock *BB, TerminatorInst *TI = BB->getTerminator(); for (unsigned i = 0; ; ++i) { assert(i != TI->getNumSuccessors() && "Didn't find any successor!"); - + if (std::find(SamePopularity.begin(), SamePopularity.end(), TI->getSuccessor(i)) == SamePopularity.end()) continue; - + MostPopularDest = TI->getSuccessor(i); break; } } - + // Okay, we have finally picked the most popular destination. return MostPopularDest; } -bool JumpThreading::ProcessThreadableEdges(Value *Cond, BasicBlock *BB) { +bool JumpThreading::ProcessThreadableEdges(Value *Cond, BasicBlock *BB, + ConstantPreference Preference) { // If threading this would thread across a loop header, don't even try to // thread the edge. if (LoopHeaders.count(BB)) return false; - - SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> PredValues; - if (!ComputeValueKnownInPredecessors(Cond, BB, PredValues)) + + PredValueInfoTy PredValues; + if (!ComputeValueKnownInPredecessors(Cond, BB, PredValues, Preference)) return false; - + assert(!PredValues.empty() && "ComputeValueKnownInPredecessors returned true with no values"); DEBUG(dbgs() << "IN BB: " << *BB; for (unsigned i = 0, e = PredValues.size(); i != e; ++i) { - dbgs() << " BB '" << BB->getName() << "': FOUND condition = "; - if (PredValues[i].first) - dbgs() << *PredValues[i].first; - else - dbgs() << "UNDEF"; - dbgs() << " for pred '" << PredValues[i].second->getName() - << "'.\n"; + dbgs() << " BB '" << BB->getName() << "': FOUND condition = " + << *PredValues[i].first + << " for pred '" << PredValues[i].second->getName() << "'.\n"; }); - + // Decide what we want to thread through. Convert our list of known values to // a list of known destinations for each pred. This also discards duplicate // predecessors and keeps track of the undefined inputs (which are represented // as a null dest in the PredToDestList). SmallPtrSet<BasicBlock*, 16> SeenPreds; SmallVector<std::pair<BasicBlock*, BasicBlock*>, 16> PredToDestList; - + BasicBlock *OnlyDest = 0; BasicBlock *MultipleDestSentinel = (BasicBlock*)(intptr_t)~0ULL; - + for (unsigned i = 0, e = PredValues.size(); i != e; ++i) { BasicBlock *Pred = PredValues[i].second; if (!SeenPreds.insert(Pred)) continue; // Duplicate predecessor entry. - + // If the predecessor ends with an indirect goto, we can't change its // destination. if (isa<IndirectBrInst>(Pred->getTerminator())) continue; - - ConstantInt *Val = PredValues[i].first; - + + Constant *Val = PredValues[i].first; + BasicBlock *DestBB; - if (Val == 0) // Undef. + if (isa<UndefValue>(Val)) DestBB = 0; else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) - DestBB = BI->getSuccessor(Val->isZero()); + DestBB = BI->getSuccessor(cast<ConstantInt>(Val)->isZero()); + else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) + DestBB = SI->getSuccessor(SI->findCaseValue(cast<ConstantInt>(Val))); else { - SwitchInst *SI = cast<SwitchInst>(BB->getTerminator()); - DestBB = SI->getSuccessor(SI->findCaseValue(Val)); + assert(isa<IndirectBrInst>(BB->getTerminator()) + && "Unexpected terminator"); + DestBB = cast<BlockAddress>(Val)->getBasicBlock(); } // If we have exactly one destination, remember it for efficiency below. - if (i == 0) + if (PredToDestList.empty()) OnlyDest = DestBB; else if (OnlyDest != DestBB) OnlyDest = MultipleDestSentinel; - + PredToDestList.push_back(std::make_pair(Pred, DestBB)); } - + // If all edges were unthreadable, we fail. if (PredToDestList.empty()) return false; - + // Determine which is the most common successor. If we have many inputs and // this block is a switch, we want to start by threading the batch that goes // to the most popular destination first. If we only know about one // threadable destination (the common case) we can avoid this. BasicBlock *MostPopularDest = OnlyDest; - + if (MostPopularDest == MultipleDestSentinel) MostPopularDest = FindMostPopularDest(BB, PredToDestList); - + // Now that we know what the most popular destination is, factor all // predecessors that will jump to it into a single predecessor. SmallVector<BasicBlock*, 16> PredsToFactor; for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i) if (PredToDestList[i].second == MostPopularDest) { BasicBlock *Pred = PredToDestList[i].first; - + // This predecessor may be a switch or something else that has multiple // edges to the block. Factor each of these edges by listing them // according to # occurrences in PredsToFactor. @@ -1251,7 +1116,7 @@ bool JumpThreading::ProcessThreadableEdges(Value *Cond, BasicBlock *BB) { if (MostPopularDest == 0) MostPopularDest = BB->getTerminator()-> getSuccessor(GetBestDestForJumpOnUndef(BB)); - + // Ok, try to thread it! return ThreadEdge(BB, PredsToFactor, MostPopularDest); } @@ -1259,15 +1124,15 @@ bool JumpThreading::ProcessThreadableEdges(Value *Cond, BasicBlock *BB) { /// ProcessBranchOnPHI - We have an otherwise unthreadable conditional branch on /// a PHI node in the current block. See if there are any simplifications we /// can do based on inputs to the phi node. -/// +/// bool JumpThreading::ProcessBranchOnPHI(PHINode *PN) { BasicBlock *BB = PN->getParent(); - + // TODO: We could make use of this to do it once for blocks with common PHI // values. SmallVector<BasicBlock*, 1> PredBBs; PredBBs.resize(1); - + // If any of the predecessor blocks end in an unconditional branch, we can // *duplicate* the conditional branch into that block in order to further // encourage jump threading and to eliminate cases where we have branch on a @@ -1289,21 +1154,21 @@ bool JumpThreading::ProcessBranchOnPHI(PHINode *PN) { /// ProcessBranchOnXOR - We have an otherwise unthreadable conditional branch on /// a xor instruction in the current block. See if there are any /// simplifications we can do based on inputs to the xor. -/// +/// bool JumpThreading::ProcessBranchOnXOR(BinaryOperator *BO) { BasicBlock *BB = BO->getParent(); - + // If either the LHS or RHS of the xor is a constant, don't do this // optimization. if (isa<ConstantInt>(BO->getOperand(0)) || isa<ConstantInt>(BO->getOperand(1))) return false; - + // If the first instruction in BB isn't a phi, we won't be able to infer // anything special about any particular predecessor. if (!isa<PHINode>(BB->front())) return false; - + // If we have a xor as the branch input to this block, and we know that the // LHS or RHS of the xor in any predecessor is true/false, then we can clone // the condition into the predecessor and fix that value to true, saving some @@ -1322,15 +1187,17 @@ bool JumpThreading::ProcessBranchOnXOR(BinaryOperator *BO) { // %Y = icmp ne i32 %A, %B // br i1 %Z, ... - SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> XorOpValues; + PredValueInfoTy XorOpValues; bool isLHS = true; - if (!ComputeValueKnownInPredecessors(BO->getOperand(0), BB, XorOpValues)) { + if (!ComputeValueKnownInPredecessors(BO->getOperand(0), BB, XorOpValues, + WantInteger)) { assert(XorOpValues.empty()); - if (!ComputeValueKnownInPredecessors(BO->getOperand(1), BB, XorOpValues)) + if (!ComputeValueKnownInPredecessors(BO->getOperand(1), BB, XorOpValues, + WantInteger)) return false; isLHS = false; } - + assert(!XorOpValues.empty() && "ComputeValueKnownInPredecessors returned true with no values"); @@ -1338,29 +1205,33 @@ bool JumpThreading::ProcessBranchOnXOR(BinaryOperator *BO) { // predecessors can be of the set true, false, or undef. unsigned NumTrue = 0, NumFalse = 0; for (unsigned i = 0, e = XorOpValues.size(); i != e; ++i) { - if (!XorOpValues[i].first) continue; // Ignore undefs for the count. - if (XorOpValues[i].first->isZero()) + if (isa<UndefValue>(XorOpValues[i].first)) + // Ignore undefs for the count. + continue; + if (cast<ConstantInt>(XorOpValues[i].first)->isZero()) ++NumFalse; else ++NumTrue; } - + // Determine which value to split on, true, false, or undef if neither. ConstantInt *SplitVal = 0; if (NumTrue > NumFalse) SplitVal = ConstantInt::getTrue(BB->getContext()); else if (NumTrue != 0 || NumFalse != 0) SplitVal = ConstantInt::getFalse(BB->getContext()); - + // Collect all of the blocks that this can be folded into so that we can // factor this once and clone it once. SmallVector<BasicBlock*, 8> BlocksToFoldInto; for (unsigned i = 0, e = XorOpValues.size(); i != e; ++i) { - if (XorOpValues[i].first != SplitVal && XorOpValues[i].first != 0) continue; + if (XorOpValues[i].first != SplitVal && + !isa<UndefValue>(XorOpValues[i].first)) + continue; BlocksToFoldInto.push_back(XorOpValues[i].second); } - + // If we inferred a value for all of the predecessors, then duplication won't // help us. However, we can just replace the LHS or RHS with the constant. if (BlocksToFoldInto.size() == @@ -1377,10 +1248,10 @@ bool JumpThreading::ProcessBranchOnXOR(BinaryOperator *BO) { // If all preds provide 1, set the computed value to 1. BO->setOperand(!isLHS, SplitVal); } - + return true; } - + // Try to duplicate BB into PredBB. return DuplicateCondBranchOnPHIIntoPred(BB, BlocksToFoldInto); } @@ -1398,14 +1269,14 @@ static void AddPHINodeEntriesForMappedBlock(BasicBlock *PHIBB, // Ok, we have a PHI node. Figure out what the incoming value was for the // DestBlock. Value *IV = PN->getIncomingValueForBlock(OldPred); - + // Remap the value if necessary. if (Instruction *Inst = dyn_cast<Instruction>(IV)) { DenseMap<Instruction*, Value*>::iterator I = ValueMap.find(Inst); if (I != ValueMap.end()) IV = I->second; } - + PN->addIncoming(IV, NewPred); } } @@ -1413,8 +1284,8 @@ static void AddPHINodeEntriesForMappedBlock(BasicBlock *PHIBB, /// ThreadEdge - We have decided that it is safe and profitable to factor the /// blocks in PredBBs to one predecessor, then thread an edge from it to SuccBB /// across BB. Transform the IR to reflect this change. -bool JumpThreading::ThreadEdge(BasicBlock *BB, - const SmallVectorImpl<BasicBlock*> &PredBBs, +bool JumpThreading::ThreadEdge(BasicBlock *BB, + const SmallVectorImpl<BasicBlock*> &PredBBs, BasicBlock *SuccBB) { // If threading to the same block as we come from, we would infinite loop. if (SuccBB == BB) { @@ -1422,7 +1293,7 @@ bool JumpThreading::ThreadEdge(BasicBlock *BB, << "' - would thread to self!\n"); return false; } - + // If threading this would thread across a loop header, don't thread the edge. // See the comments above FindLoopHeaders for justifications and caveats. if (LoopHeaders.count(BB)) { @@ -1438,7 +1309,7 @@ bool JumpThreading::ThreadEdge(BasicBlock *BB, << "' - Cost is too high: " << JumpThreadCost << "\n"); return false; } - + // And finally, do it! Start by factoring the predecessors is needed. BasicBlock *PredBB; if (PredBBs.size() == 1) @@ -1449,30 +1320,29 @@ bool JumpThreading::ThreadEdge(BasicBlock *BB, PredBB = SplitBlockPredecessors(BB, &PredBBs[0], PredBBs.size(), ".thr_comm", this); } - + // And finally, do it! DEBUG(dbgs() << " Threading edge from '" << PredBB->getName() << "' to '" << SuccBB->getName() << "' with cost: " << JumpThreadCost << ", across block:\n " << *BB << "\n"); - - if (LVI) - LVI->threadEdge(PredBB, BB, SuccBB); - + + LVI->threadEdge(PredBB, BB, SuccBB); + // We are going to have to map operands from the original BB block to the new // copy of the block 'NewBB'. If there are PHI nodes in BB, evaluate them to // account for entry from PredBB. DenseMap<Instruction*, Value*> ValueMapping; - - BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), - BB->getName()+".thread", + + BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), + BB->getName()+".thread", BB->getParent(), BB); NewBB->moveAfter(PredBB); - + BasicBlock::iterator BI = BB->begin(); for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI) ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB); - + // Clone the non-phi instructions of BB into NewBB, keeping track of the // mapping and using it to remap operands in the cloned instructions. for (; !isa<TerminatorInst>(BI); ++BI) { @@ -1480,7 +1350,7 @@ bool JumpThreading::ThreadEdge(BasicBlock *BB, New->setName(BI->getName()); NewBB->getInstList().push_back(New); ValueMapping[BI] = New; - + // Remap operands to patch up intra-block references. for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i) if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) { @@ -1489,15 +1359,15 @@ bool JumpThreading::ThreadEdge(BasicBlock *BB, New->setOperand(i, I->second); } } - + // We didn't copy the terminator from BB over to NewBB, because there is now // an unconditional jump to SuccBB. Insert the unconditional jump. BranchInst::Create(SuccBB, NewBB); - + // Check to see if SuccBB has PHI nodes. If so, we need to add entries to the // PHI nodes for NewBB now. AddPHINodeEntriesForMappedBlock(SuccBB, BB, NewBB, ValueMapping); - + // If there were values defined in BB that are used outside the block, then we // now have to update all uses of the value to use either the original value, // the cloned value, or some PHI derived value. This can require arbitrary @@ -1515,14 +1385,14 @@ bool JumpThreading::ThreadEdge(BasicBlock *BB, continue; } else if (User->getParent() == BB) continue; - + UsesToRename.push_back(&UI.getUse()); } - + // If there are no uses outside the block, we're done with this instruction. if (UsesToRename.empty()) continue; - + DEBUG(dbgs() << "JT: Renaming non-local uses of: " << *I << "\n"); // We found a use of I outside of BB. Rename all uses of I that are outside @@ -1531,28 +1401,28 @@ bool JumpThreading::ThreadEdge(BasicBlock *BB, SSAUpdate.Initialize(I->getType(), I->getName()); SSAUpdate.AddAvailableValue(BB, I); SSAUpdate.AddAvailableValue(NewBB, ValueMapping[I]); - + while (!UsesToRename.empty()) SSAUpdate.RewriteUse(*UsesToRename.pop_back_val()); DEBUG(dbgs() << "\n"); } - - + + // Ok, NewBB is good to go. Update the terminator of PredBB to jump to // NewBB instead of BB. This eliminates predecessors from BB, which requires // us to simplify any PHI nodes in BB. TerminatorInst *PredTerm = PredBB->getTerminator(); for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i) if (PredTerm->getSuccessor(i) == BB) { - RemovePredecessorAndSimplify(BB, PredBB, TD); + BB->removePredecessor(PredBB, true); PredTerm->setSuccessor(i, NewBB); } - + // At this point, the IR is fully up to date and consistent. Do a quick scan // over the new instructions and zap any that are constants or dead. This // frequently happens because of phi translation. SimplifyInstructionsInBlock(NewBB, TD); - + // Threaded an edge! ++NumThreads; return true; @@ -1576,14 +1446,14 @@ bool JumpThreading::DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB, << "' - it might create an irreducible loop!\n"); return false; } - + unsigned DuplicationCost = getJumpThreadDuplicationCost(BB); if (DuplicationCost > Threshold) { DEBUG(dbgs() << " Not duplicating BB '" << BB->getName() << "' - Cost is too high: " << DuplicationCost << "\n"); return false; } - + // And finally, do it! Start by factoring the predecessors is needed. BasicBlock *PredBB; if (PredBBs.size() == 1) @@ -1594,35 +1464,35 @@ bool JumpThreading::DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB, PredBB = SplitBlockPredecessors(BB, &PredBBs[0], PredBBs.size(), ".thr_comm", this); } - + // Okay, we decided to do this! Clone all the instructions in BB onto the end // of PredBB. DEBUG(dbgs() << " Duplicating block '" << BB->getName() << "' into end of '" << PredBB->getName() << "' to eliminate branch on phi. Cost: " << DuplicationCost << " block is:" << *BB << "\n"); - + // Unless PredBB ends with an unconditional branch, split the edge so that we // can just clone the bits from BB into the end of the new PredBB. BranchInst *OldPredBranch = dyn_cast<BranchInst>(PredBB->getTerminator()); - + if (OldPredBranch == 0 || !OldPredBranch->isUnconditional()) { PredBB = SplitEdge(PredBB, BB, this); OldPredBranch = cast<BranchInst>(PredBB->getTerminator()); } - + // We are going to have to map operands from the original BB block into the // PredBB block. Evaluate PHI nodes in BB. DenseMap<Instruction*, Value*> ValueMapping; - + BasicBlock::iterator BI = BB->begin(); for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI) ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB); - + // Clone the non-phi instructions of BB into PredBB, keeping track of the // mapping and using it to remap operands in the cloned instructions. for (; BI != BB->end(); ++BI) { Instruction *New = BI->clone(); - + // Remap operands to patch up intra-block references. for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i) if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) { @@ -1644,7 +1514,7 @@ bool JumpThreading::DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB, ValueMapping[BI] = New; } } - + // Check to see if the targets of the branch had PHI nodes. If so, we need to // add entries to the PHI nodes for branch from PredBB now. BranchInst *BBBranch = cast<BranchInst>(BB->getTerminator()); @@ -1652,7 +1522,7 @@ bool JumpThreading::DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB, ValueMapping); AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(1), BB, PredBB, ValueMapping); - + // If there were values defined in BB that are used outside the block, then we // now have to update all uses of the value to use either the original value, // the cloned value, or some PHI derived value. This can require arbitrary @@ -1670,35 +1540,35 @@ bool JumpThreading::DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB, continue; } else if (User->getParent() == BB) continue; - + UsesToRename.push_back(&UI.getUse()); } - + // If there are no uses outside the block, we're done with this instruction. if (UsesToRename.empty()) continue; - + DEBUG(dbgs() << "JT: Renaming non-local uses of: " << *I << "\n"); - + // We found a use of I outside of BB. Rename all uses of I that are outside // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks // with the two values we know. SSAUpdate.Initialize(I->getType(), I->getName()); SSAUpdate.AddAvailableValue(BB, I); SSAUpdate.AddAvailableValue(PredBB, ValueMapping[I]); - + while (!UsesToRename.empty()) SSAUpdate.RewriteUse(*UsesToRename.pop_back_val()); DEBUG(dbgs() << "\n"); } - + // PredBB no longer jumps to BB, remove entries in the PHI node for the edge // that we nuked. - RemovePredecessorAndSimplify(BB, PredBB, TD); - + BB->removePredecessor(PredBB, true); + // Remove the unconditional branch at the end of the PredBB block. OldPredBranch->eraseFromParent(); - + ++NumDupes; return true; } |
