//===- InstructionCombining.cpp - Combine multiple instructions -----------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // InstructionCombining - Combine instructions to form fewer, simple // instructions. This pass does not modify the CFG. This pass is where // algebraic simplification happens. // // This pass combines things like: // %Y = add i32 %X, 1 // %Z = add i32 %Y, 1 // into: // %Z = add i32 %X, 2 // // This is a simple worklist driven algorithm. // // This pass guarantees that the following canonicalizations are performed on // the program: // 1. If a binary operator has a constant operand, it is moved to the RHS // 2. Bitwise operators with constant operands are always grouped so that // shifts are performed first, then or's, then and's, then xor's. // 3. Compare instructions are converted from <,>,<=,>= to ==,!= if possible // 4. All cmp instructions on boolean values are replaced with logical ops // 5. add X, X is represented as (X*2) => (X << 1) // 6. Multiplies with a power-of-two constant argument are transformed into // shifts. // ... etc. // //===----------------------------------------------------------------------===// #define DEBUG_TYPE "instcombine" #include "llvm/Transforms/Scalar.h" #include "InstCombine.h" #include "llvm/IntrinsicInst.h" #include "llvm/Analysis/ConstantFolding.h" #include "llvm/Analysis/InstructionSimplify.h" #include "llvm/Analysis/MemoryBuiltins.h" #include "llvm/Target/TargetData.h" #include "llvm/Transforms/Utils/Local.h" #include "llvm/Support/CFG.h" #include "llvm/Support/Debug.h" #include "llvm/Support/GetElementPtrTypeIterator.h" #include "llvm/Support/PatternMatch.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/Statistic.h" #include "llvm-c/Initialization.h" #include #include using namespace llvm; using namespace llvm::PatternMatch; STATISTIC(NumCombined , "Number of insts combined"); STATISTIC(NumConstProp, "Number of constant folds"); STATISTIC(NumDeadInst , "Number of dead inst eliminated"); STATISTIC(NumSunkInst , "Number of instructions sunk"); // Initialization Routines void llvm::initializeInstCombine(PassRegistry &Registry) { initializeInstCombinerPass(Registry); } void LLVMInitializeInstCombine(LLVMPassRegistryRef R) { initializeInstCombine(*unwrap(R)); } char InstCombiner::ID = 0; INITIALIZE_PASS(InstCombiner, "instcombine", "Combine redundant instructions", false, false) void InstCombiner::getAnalysisUsage(AnalysisUsage &AU) const { AU.addPreservedID(LCSSAID); AU.setPreservesCFG(); } /// ShouldChangeType - Return true if it is desirable to convert a computation /// from 'From' to 'To'. We don't want to convert from a legal to an illegal /// type for example, or from a smaller to a larger illegal type. bool InstCombiner::ShouldChangeType(const Type *From, const Type *To) const { assert(From->isIntegerTy() && To->isIntegerTy()); // If we don't have TD, we don't know if the source/dest are legal. if (!TD) return false; unsigned FromWidth = From->getPrimitiveSizeInBits(); unsigned ToWidth = To->getPrimitiveSizeInBits(); bool FromLegal = TD->isLegalInteger(FromWidth); bool ToLegal = TD->isLegalInteger(ToWidth); // If this is a legal integer from type, and the result would be an illegal // type, don't do the transformation. if (FromLegal && !ToLegal) return false; // Otherwise, if both are illegal, do not increase the size of the result. We // do allow things like i160 -> i64, but not i64 -> i160. if (!FromLegal && !ToLegal && ToWidth > FromWidth) return false; return true; } /// SimplifyAssociativeOrCommutative - This performs a few simplifications for /// operators which are associative or commutative: // // Commutative operators: // // 1. Order operands such that they are listed from right (least complex) to // left (most complex). This puts constants before unary operators before // binary operators. // // Associative operators: // // 2. Transform: "(A op B) op C" ==> "A op (B op C)" if "B op C" simplifies. // 3. Transform: "A op (B op C)" ==> "(A op B) op C" if "A op B" simplifies. // // Associative and commutative operators: // // 4. Transform: "(A op B) op C" ==> "(C op A) op B" if "C op A" simplifies. // 5. Transform: "A op (B op C)" ==> "B op (C op A)" if "C op A" simplifies. // 6. Transform: "(A op C1) op (B op C2)" ==> "(A op B) op (C1 op C2)" // if C1 and C2 are constants. // bool InstCombiner::SimplifyAssociativeOrCommutative(BinaryOperator &I) { Instruction::BinaryOps Opcode = I.getOpcode(); bool Changed = false; do { // Order operands such that they are listed from right (least complex) to // left (most complex). This puts constants before unary operators before // binary operators. if (I.isCommutative() && getComplexity(I.getOperand(0)) < getComplexity(I.getOperand(1))) Changed = !I.swapOperands(); BinaryOperator *Op0 = dyn_cast(I.getOperand(0)); BinaryOperator *Op1 = dyn_cast(I.getOperand(1)); if (I.isAssociative()) { // Transform: "(A op B) op C" ==> "A op (B op C)" if "B op C" simplifies. if (Op0 && Op0->getOpcode() == Opcode) { Value *A = Op0->getOperand(0); Value *B = Op0->getOperand(1); Value *C = I.getOperand(1); // Does "B op C" simplify? if (Value *V = SimplifyBinOp(Opcode, B, C, TD)) { // It simplifies to V. Form "A op V". I.setOperand(0, A); I.setOperand(1, V); Changed = true; continue; } } // Transform: "A op (B op C)" ==> "(A op B) op C" if "A op B" simplifies. if (Op1 && Op1->getOpcode() == Opcode) { Value *A = I.getOperand(0); Value *B = Op1->getOperand(0); Value *C = Op1->getOperand(1); // Does "A op B" simplify? if (Value *V = SimplifyBinOp(Opcode, A, B, TD)) { // It simplifies to V. Form "V op C". I.setOperand(0, V); I.setOperand(1, C); Changed = true; continue; } } } if (I.isAssociative() && I.isCommutative()) { // Transform: "(A op B) op C" ==> "(C op A) op B" if "C op A" simplifies. if (Op0 && Op0->getOpcode() == Opcode) { Value *A = Op0->getOperand(0); Value *B = Op0->getOperand(1); Value *C = I.getOperand(1); // Does "C op A" simplify? if (Value *V = SimplifyBinOp(Opcode, C, A, TD)) { // It simplifies to V. Form "V op B". I.setOperand(0, V); I.setOperand(1, B); Changed = true; continue; } } // Transform: "A op (B op C)" ==> "B op (C op A)" if "C op A" simplifies. if (Op1 && Op1->getOpcode() == Opcode) { Value *A = I.getOperand(0); Value *B = Op1->getOperand(0); Value *C = Op1->getOperand(1); // Does "C op A" simplify? if (Value *V = SimplifyBinOp(Opcode, C, A, TD)) { // It simplifies to V. Form "B op V". I.setOperand(0, B); I.setOperand(1, V); Changed = true; continue; } } // Transform: "(A op C1) op (B op C2)" ==> "(A op B) op (C1 op C2)" // if C1 and C2 are constants. if (Op0 && Op1 && Op0->getOpcode() == Opcode && Op1->getOpcode() == Opcode && isa(Op0->getOperand(1)) && isa(Op1->getOperand(1)) && Op0->hasOneUse() && Op1->hasOneUse()) { Value *A = Op0->getOperand(0); Constant *C1 = cast(Op0->getOperand(1)); Value *B = Op1->getOperand(0); Constant *C2 = cast(Op1->getOperand(1)); Constant *Folded = ConstantExpr::get(Opcode, C1, C2); Instruction *New = BinaryOperator::Create(Opcode, A, B, Op1->getName(), &I); Worklist.Add(New); I.setOperand(0, New); I.setOperand(1, Folded); Changed = true; continue; } } // No further simplifications. return Changed; } while (1); } /// LeftDistributesOverRight - Whether "X LOp (Y ROp Z)" is always equal to /// "(X LOp Y) ROp (X LOp Z)". static bool LeftDistributesOverRight(Instruction::BinaryOps LOp, Instruction::BinaryOps ROp) { switch (LOp) { default: return false; case Instruction::And: // And distributes over Or and Xor. switch (ROp) { default: return false; case Instruction::Or: case Instruction::Xor: return true; } case Instruction::Mul: // Multiplication distributes over addition and subtraction. switch (ROp) { default: return false; case Instruction::Add: case Instruction::Sub: return true; } case Instruction::Or: // Or distributes over And. switch (ROp) { default: return false; case Instruction::And: return true; } } } /// RightDistributesOverLeft - Whether "(X LOp Y) ROp Z" is always equal to /// "(X ROp Z) LOp (Y ROp Z)". static bool RightDistributesOverLeft(Instruction::BinaryOps LOp, Instruction::BinaryOps ROp) { if (Instruction::isCommutative(ROp)) return LeftDistributesOverRight(ROp, LOp); // TODO: It would be nice to handle division, aka "(X + Y)/Z = X/Z + Y/Z", // but this requires knowing that the addition does not overflow and other // such subtleties. return false; } /// SimplifyByFactorizing - This tries to simplify binary operations which /// some other binary operation distributes over by factorizing out a common /// term (eg "(A*B)+(A*C)" -> "A*(B+C)"). Returns the simplified value, or /// null if no simplification was performed. Instruction *InstCombiner::SimplifyByFactorizing(BinaryOperator &I) { BinaryOperator *Op0 = dyn_cast(I.getOperand(0)); BinaryOperator *Op1 = dyn_cast(I.getOperand(1)); if (!Op0 || !Op1 || Op0->getOpcode() != Op1->getOpcode()) return 0; // The instruction has the form "(A op' B) op (C op' D)". Value *A = Op0->getOperand(0); Value *B = Op0->getOperand(1); Value *C = Op1->getOperand(0); Value *D = Op1->getOperand(1); Instruction::BinaryOps OuterOpcode = I.getOpcode(); // op Instruction::BinaryOps InnerOpcode = Op0->getOpcode(); // op' // Does "X op' Y" always equal "Y op' X"? bool InnerCommutative = Instruction::isCommutative(InnerOpcode); // Does "X op' (Y op Z)" always equal "(X op' Y) op (X op' Z)"? if (LeftDistributesOverRight(InnerOpcode, OuterOpcode)) // Does the instruction have the form "(A op' B) op (A op' D)" or, in the // commutative case, "(A op' B) op (C op' A)"? if (A == C || (InnerCommutative && A == D)) { if (A != C) std::swap(C, D); // Consider forming "A op' (B op D)". // If "B op D" simplifies then it can be formed with no cost. Value *RHS = SimplifyBinOp(OuterOpcode, B, D, TD); // If "B op D" doesn't simplify then only proceed if both of the existing // operations "A op' B" and "C op' D" will be zapped since no longer used. if (!RHS && Op0->hasOneUse() && Op1->hasOneUse()) RHS = Builder->CreateBinOp(OuterOpcode, B, D, Op1->getName()); if (RHS) return BinaryOperator::Create(InnerOpcode, A, RHS); } // Does "(X op Y) op' Z" always equal "(X op' Z) op (Y op' Z)"? if (RightDistributesOverLeft(OuterOpcode, InnerOpcode)) // Does the instruction have the form "(A op' B) op (C op' B)" or, in the // commutative case, "(A op' B) op (B op' D)"? if (B == D || (InnerCommutative && B == C)) { if (B != D) std::swap(C, D); // Consider forming "(A op C) op' B". // If "A op C" simplifies then it can be formed with no cost. Value *LHS = SimplifyBinOp(OuterOpcode, A, C, TD); // If "A op C" doesn't simplify then only proceed if both of the existing // operations "A op' B" and "C op' D" will be zapped since no longer used. if (!LHS && Op0->hasOneUse() && Op1->hasOneUse()) LHS = Builder->CreateBinOp(OuterOpcode, A, C, Op0->getName()); if (LHS) return BinaryOperator::Create(InnerOpcode, LHS, B); } return 0; } // dyn_castNegVal - Given a 'sub' instruction, return the RHS of the instruction // if the LHS is a constant zero (which is the 'negate' form). // Value *InstCombiner::dyn_castNegVal(Value *V) const { if (BinaryOperator::isNeg(V)) return BinaryOperator::getNegArgument(V); // Constants can be considered to be negated values if they can be folded. if (ConstantInt *C = dyn_cast(V)) return ConstantExpr::getNeg(C); if (ConstantVector *C = dyn_cast(V)) if (C->getType()->getElementType()->isIntegerTy()) return ConstantExpr::getNeg(C); return 0; } // dyn_castFNegVal - Given a 'fsub' instruction, return the RHS of the // instruction if the LHS is a constant negative zero (which is the 'negate' // form). // Value *InstCombiner::dyn_castFNegVal(Value *V) const { if (BinaryOperator::isFNeg(V)) return BinaryOperator::getFNegArgument(V); // Constants can be considered to be negated values if they can be folded. if (ConstantFP *C = dyn_cast(V)) return ConstantExpr::getFNeg(C); if (ConstantVector *C = dyn_cast(V)) if (C->getType()->getElementType()->isFloatingPointTy()) return ConstantExpr::getFNeg(C); return 0; } static Value *FoldOperationIntoSelectOperand(Instruction &I, Value *SO, InstCombiner *IC) { if (CastInst *CI = dyn_cast(&I)) return IC->Builder->CreateCast(CI->getOpcode(), SO, I.getType()); // Figure out if the constant is the left or the right argument. bool ConstIsRHS = isa(I.getOperand(1)); Constant *ConstOperand = cast(I.getOperand(ConstIsRHS)); if (Constant *SOC = dyn_cast(SO)) { if (ConstIsRHS) return ConstantExpr::get(I.getOpcode(), SOC, ConstOperand); return ConstantExpr::get(I.getOpcode(), ConstOperand, SOC); } Value *Op0 = SO, *Op1 = ConstOperand; if (!ConstIsRHS) std::swap(Op0, Op1); if (BinaryOperator *BO = dyn_cast(&I)) return IC->Builder->CreateBinOp(BO->getOpcode(), Op0, Op1, SO->getName()+".op"); if (ICmpInst *CI = dyn_cast(&I)) return IC->Builder->CreateICmp(CI->getPredicate(), Op0, Op1, SO->getName()+".cmp"); if (FCmpInst *CI = dyn_cast(&I)) return IC->Builder->CreateICmp(CI->getPredicate(), Op0, Op1, SO->getName()+".cmp"); llvm_unreachable("Unknown binary instruction type!"); } // FoldOpIntoSelect - Given an instruction with a select as one operand and a // constant as the other operand, try to fold the binary operator into the // select arguments. This also works for Cast instructions, which obviously do // not have a second operand. Instruction *InstCombiner::FoldOpIntoSelect(Instruction &Op, SelectInst *SI) { // Don't modify shared select instructions if (!SI->hasOneUse()) return 0; Value *TV = SI->getOperand(1); Value *FV = SI->getOperand(2); if (isa(TV) || isa(FV)) { // Bool selects with constant operands can be folded to logical ops. if (SI->getType()->isIntegerTy(1)) return 0; Value *SelectTrueVal = FoldOperationIntoSelectOperand(Op, TV, this); Value *SelectFalseVal = FoldOperationIntoSelectOperand(Op, FV, this); return SelectInst::Create(SI->getCondition(), SelectTrueVal, SelectFalseVal); } return 0; } /// FoldOpIntoPhi - Given a binary operator, cast instruction, or select which /// has a PHI node as operand #0, see if we can fold the instruction into the /// PHI (which is only possible if all operands to the PHI are constants). /// /// If AllowAggressive is true, FoldOpIntoPhi will allow certain transforms /// that would normally be unprofitable because they strongly encourage jump /// threading. Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I, bool AllowAggressive) { AllowAggressive = false; PHINode *PN = cast(I.getOperand(0)); unsigned NumPHIValues = PN->getNumIncomingValues(); if (NumPHIValues == 0 || // We normally only transform phis with a single use, unless we're trying // hard to make jump threading happen. (!PN->hasOneUse() && !AllowAggressive)) return 0; // Check to see if all of the operands of the PHI are simple constants // (constantint/constantfp/undef). If there is one non-constant value, // remember the BB it is in. If there is more than one or if *it* is a PHI, // bail out. We don't do arbitrary constant expressions here because moving // their computation can be expensive without a cost model. BasicBlock *NonConstBB = 0; for (unsigned i = 0; i != NumPHIValues; ++i) if (!isa(PN->getIncomingValue(i)) || isa(PN->getIncomingValue(i))) { if (NonConstBB) return 0; // More than one non-const value. if (isa(PN->getIncomingValue(i))) return 0; // Itself a phi. NonConstBB = PN->getIncomingBlock(i); // If the incoming non-constant value is in I's block, we have an infinite // loop. if (NonConstBB == I.getParent()) return 0; } // If there is exactly one non-constant value, we can insert a copy of the // operation in that block. However, if this is a critical edge, we would be // inserting the computation one some other paths (e.g. inside a loop). Only // do this if the pred block is unconditionally branching into the phi block. if (NonConstBB != 0 && !AllowAggressive) { BranchInst *BI = dyn_cast(NonConstBB->getTerminator()); if (!BI || !BI->isUnconditional()) return 0; } // Okay, we can do the transformation: create the new PHI node. PHINode *NewPN = PHINode::Create(I.getType(), ""); NewPN->reserveOperandSpace(PN->getNumOperands()/2); InsertNewInstBefore(NewPN, *PN); NewPN->takeName(PN); // Next, add all of the operands to the PHI. if (SelectInst *SI = dyn_cast(&I)) { // We only currently try to fold the condition of a select when it is a phi, // not the true/false values. Value *TrueV = SI->getTrueValue(); Value *FalseV = SI->getFalseValue(); BasicBlock *PhiTransBB = PN->getParent(); for (unsigned i = 0; i != NumPHIValues; ++i) { BasicBlock *ThisBB = PN->getIncomingBlock(i); Value *TrueVInPred = TrueV->DoPHITranslation(PhiTransBB, ThisBB); Value *FalseVInPred = FalseV->DoPHITranslation(PhiTransBB, ThisBB); Value *InV = 0; if (Constant *InC = dyn_cast(PN->getIncomingValue(i))) { InV = InC->isNullValue() ? FalseVInPred : TrueVInPred; } else { assert(PN->getIncomingBlock(i) == NonConstBB); InV = SelectInst::Create(PN->getIncomingValue(i), TrueVInPred, FalseVInPred, "phitmp", NonConstBB->getTerminator()); Worklist.Add(cast(InV)); } NewPN->addIncoming(InV, ThisBB); } } else if (I.getNumOperands() == 2) { Constant *C = cast(I.getOperand(1)); for (unsigned i = 0; i != NumPHIValues; ++i) { Value *InV = 0; if (Constant *InC = dyn_cast(PN->getIncomingValue(i))) { if (CmpInst *CI = dyn_cast(&I)) InV = ConstantExpr::getCompare(CI->getPredicate(), InC, C); else InV = ConstantExpr::get(I.getOpcode(), InC, C); } else { assert(PN->getIncomingBlock(i) == NonConstBB); if (BinaryOperator *BO = dyn_cast(&I)) InV = BinaryOperator::Create(BO->getOpcode(), PN->getIncomingValue(i), C, "phitmp", NonConstBB->getTerminator()); else if (CmpInst *CI = dyn_cast(&I)) InV = CmpInst::Create(CI->getOpcode(), CI->getPredicate(), PN->getIncomingValue(i), C, "phitmp", NonConstBB->getTerminator()); else llvm_unreachable("Unknown binop!"); Worklist.Add(cast(InV)); } NewPN->addIncoming(InV, PN->getIncomingBlock(i)); } } else { CastInst *CI = cast(&I); const Type *RetTy = CI->getType(); for (unsigned i = 0; i != NumPHIValues; ++i) { Value *InV; if (Constant *InC = dyn_cast(PN->getIncomingValue(i))) { InV = ConstantExpr::getCast(CI->getOpcode(), InC, RetTy); } else { assert(PN->getIncomingBlock(i) == NonConstBB); InV = CastInst::Create(CI->getOpcode(), PN->getIncomingValue(i), I.getType(), "phitmp", NonConstBB->getTerminator()); Worklist.Add(cast(InV)); } NewPN->addIncoming(InV, PN->getIncomingBlock(i)); } } return ReplaceInstUsesWith(I, NewPN); } /// FindElementAtOffset - Given a type and a constant offset, determine whether /// or not there is a sequence of GEP indices into the type that will land us at /// the specified offset. If so, fill them into NewIndices and return the /// resultant element type, otherwise return null. const Type *InstCombiner::FindElementAtOffset(const Type *Ty, int64_t Offset, SmallVectorImpl &NewIndices) { if (!TD) return 0; if (!Ty->isSized()) return 0; // Start with the index over the outer type. Note that the type size // might be zero (even if the offset isn't zero) if the indexed type // is something like [0 x {int, int}] const Type *IntPtrTy = TD->getIntPtrType(Ty->getContext()); int64_t FirstIdx = 0; if (int64_t TySize = TD->getTypeAllocSize(Ty)) { FirstIdx = Offset/TySize; Offset -= FirstIdx*TySize; // Handle hosts where % returns negative instead of values [0..TySize). if (Offset < 0) { --FirstIdx; Offset += TySize; assert(Offset >= 0); } assert((uint64_t)Offset < (uint64_t)TySize && "Out of range offset"); } NewIndices.push_back(ConstantInt::get(IntPtrTy, FirstIdx)); // Index into the types. If we fail, set OrigBase to null. while (Offset) { // Indexing into tail padding between struct/array elements. if (uint64_t(Offset*8) >= TD->getTypeSizeInBits(Ty)) return 0; if (const StructType *STy = dyn_cast(Ty)) { const StructLayout *SL = TD->getStructLayout(STy); assert(Offset < (int64_t)SL->getSizeInBytes() && "Offset must stay within the indexed type"); unsigned Elt = SL->getElementContainingOffset(Offset); NewIndices.push_back(ConstantInt::get(Type::getInt32Ty(Ty->getContext()), Elt)); Offset -= SL->getElementOffset(Elt); Ty = STy->getElementType(Elt); } else if (const ArrayType *AT = dyn_cast(Ty)) { uint64_t EltSize = TD->getTypeAllocSize(AT->getElementType()); assert(EltSize && "Cannot index into a zero-sized array"); NewIndices.push_back(ConstantInt::get(IntPtrTy,Offset/EltSize)); Offset %= EltSize; Ty = AT->getElementType(); } else { // Otherwise, we can't index into the middle of this atomic type, bail. return 0; } } return Ty; } Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) { SmallVector Ops(GEP.op_begin(), GEP.op_end()); if (Value *V = SimplifyGEPInst(&Ops[0], Ops.size(), TD)) return ReplaceInstUsesWith(GEP, V); Value *PtrOp = GEP.getOperand(0); // Eliminate unneeded casts for indices, and replace indices which displace // by multiples of a zero size type with zero. if (TD) { bool MadeChange = false; const Type *IntPtrTy = TD->getIntPtrType(GEP.getContext()); gep_type_iterator GTI = gep_type_begin(GEP); for (User::op_iterator I = GEP.op_begin() + 1, E = GEP.op_end(); I != E; ++I, ++GTI) { // Skip indices into struct types. const SequentialType *SeqTy = dyn_cast(*GTI); if (!SeqTy) continue; // If the element type has zero size then any index over it is equivalent // to an index of zero, so replace it with zero if it is not zero already. if (SeqTy->getElementType()->isSized() && TD->getTypeAllocSize(SeqTy->getElementType()) == 0) if (!isa(*I) || !cast(*I)->isNullValue()) { *I = Constant::getNullValue(IntPtrTy); MadeChange = true; } if ((*I)->getType() != IntPtrTy) { // If we are using a wider index than needed for this platform, shrink // it to what we need. If narrower, sign-extend it to what we need. // This explicit cast can make subsequent optimizations more obvious. *I = Builder->CreateIntCast(*I, IntPtrTy, true); MadeChange = true; } } if (MadeChange) return &GEP; } // Combine Indices - If the source pointer to this getelementptr instruction // is a getelementptr instruction, combine the indices of the two // getelementptr instructions into a single instruction. // if (GEPOperator *Src = dyn_cast(PtrOp)) { // Note that if our source is a gep chain itself that we wait for that // chain to be resolved before we perform this transformation. This // avoids us creating a TON of code in some cases. // if (GetElementPtrInst *SrcGEP = dyn_cast(Src->getOperand(0))) if (SrcGEP->getNumOperands() == 2) return 0; // Wait until our source is folded to completion. SmallVector Indices; // Find out whether the last index in the source GEP is a sequential idx. bool EndsWithSequential = false; for (gep_type_iterator I = gep_type_begin(*Src), E = gep_type_end(*Src); I != E; ++I) EndsWithSequential = !(*I)->isStructTy(); // Can we combine the two pointer arithmetics offsets? if (EndsWithSequential) { // Replace: gep (gep %P, long B), long A, ... // With: T = long A+B; gep %P, T, ... // Value *Sum; Value *SO1 = Src->getOperand(Src->getNumOperands()-1); Value *GO1 = GEP.getOperand(1); if (SO1 == Constant::getNullValue(SO1->getType())) { Sum = GO1; } else if (GO1 == Constant::getNullValue(GO1->getType())) { Sum = SO1; } else { // If they aren't the same type, then the input hasn't been processed // by the loop above yet (which canonicalizes sequential index types to // intptr_t). Just avoid transforming this until the input has been // normalized. if (SO1->getType() != GO1->getType()) return 0; Sum = Builder->CreateAdd(SO1, GO1, PtrOp->getName()+".sum"); } // Update the GEP in place if possible. if (Src->getNumOperands() == 2) { GEP.setOperand(0, Src->getOperand(0)); GEP.setOperand(1, Sum); return &GEP; } Indices.append(Src->op_begin()+1, Src->op_end()-1); Indices.push_back(Sum); Indices.append(GEP.op_begin()+2, GEP.op_end()); } else if (isa(*GEP.idx_begin()) && cast(*GEP.idx_begin())->isNullValue() && Src->getNumOperands() != 1) { // Otherwise we can do the fold if the first index of the GEP is a zero Indices.append(Src->op_begin()+1, Src->op_end()); Indices.append(GEP.idx_begin()+1, GEP.idx_end()); } if (!Indices.empty()) return (GEP.isInBounds() && Src->isInBounds()) ? GetElementPtrInst::CreateInBounds(Src->getOperand(0), Indices.begin(), Indices.end(), GEP.getName()) : GetElementPtrInst::Create(Src->getOperand(0), Indices.begin(), Indices.end(), GEP.getName()); } // Handle gep(bitcast x) and gep(gep x, 0, 0, 0). Value *StrippedPtr = PtrOp->stripPointerCasts(); if (StrippedPtr != PtrOp) { const PointerType *StrippedPtrTy =cast(StrippedPtr->getType()); bool HasZeroPointerIndex = false; if (ConstantInt *C = dyn_cast(GEP.getOperand(1))) HasZeroPointerIndex = C->isZero(); // Transform: GEP (bitcast [10 x i8]* X to [0 x i8]*), i32 0, ... // into : GEP [10 x i8]* X, i32 0, ... // // Likewise, transform: GEP (bitcast i8* X to [0 x i8]*), i32 0, ... // into : GEP i8* X, ... // // This occurs when the program declares an array extern like "int X[];" if (HasZeroPointerIndex) { const PointerType *CPTy = cast(PtrOp->getType()); if (const ArrayType *CATy = dyn_cast(CPTy->getElementType())) { // GEP (bitcast i8* X to [0 x i8]*), i32 0, ... ? if (CATy->getElementType() == StrippedPtrTy->getElementType()) { // -> GEP i8* X, ... SmallVector Idx(GEP.idx_begin()+1, GEP.idx_end()); GetElementPtrInst *Res = GetElementPtrInst::Create(StrippedPtr, Idx.begin(), Idx.end(), GEP.getName()); Res->setIsInBounds(GEP.isInBounds()); return Res; } if (const ArrayType *XATy = dyn_cast(StrippedPtrTy->getElementType())){ // GEP (bitcast [10 x i8]* X to [0 x i8]*), i32 0, ... ? if (CATy->getElementType() == XATy->getElementType()) { // -> GEP [10 x i8]* X, i32 0, ... // At this point, we know that the cast source type is a pointer // to an array of the same type as the destination pointer // array. Because the array type is never stepped over (there // is a leading zero) we can fold the cast into this GEP. GEP.setOperand(0, StrippedPtr); return &GEP; } } } } else if (GEP.getNumOperands() == 2) { // Transform things like: // %t = getelementptr i32* bitcast ([2 x i32]* %str to i32*), i32 %V // into: %t1 = getelementptr [2 x i32]* %str, i32 0, i32 %V; bitcast const Type *SrcElTy = StrippedPtrTy->getElementType(); const Type *ResElTy=cast(PtrOp->getType())->getElementType(); if (TD && SrcElTy->isArrayTy() && TD->getTypeAllocSize(cast(SrcElTy)->getElementType()) == TD->getTypeAllocSize(ResElTy)) { Value *Idx[2]; Idx[0] = Constant::getNullValue(Type::getInt32Ty(GEP.getContext())); Idx[1] = GEP.getOperand(1); Value *NewGEP = GEP.isInBounds() ? Builder->CreateInBoundsGEP(StrippedPtr, Idx, Idx + 2, GEP.getName()) : Builder->CreateGEP(StrippedPtr, Idx, Idx + 2, GEP.getName()); // V and GEP are both pointer types --> BitCast return new BitCastInst(NewGEP, GEP.getType()); } // Transform things like: // getelementptr i8* bitcast ([100 x double]* X to i8*), i32 %tmp // (where tmp = 8*tmp2) into: // getelementptr [100 x double]* %arr, i32 0, i32 %tmp2; bitcast if (TD && SrcElTy->isArrayTy() && ResElTy->isIntegerTy(8)) { uint64_t ArrayEltSize = TD->getTypeAllocSize(cast(SrcElTy)->getElementType()); // Check to see if "tmp" is a scale by a multiple of ArrayEltSize. We // allow either a mul, shift, or constant here. Value *NewIdx = 0; ConstantInt *Scale = 0; if (ArrayEltSize == 1) { NewIdx = GEP.getOperand(1); Scale = ConstantInt::get(cast(NewIdx->getType()), 1); } else if (ConstantInt *CI = dyn_cast(GEP.getOperand(1))) { NewIdx = ConstantInt::get(CI->getType(), 1); Scale = CI; } else if (Instruction *Inst =dyn_cast(GEP.getOperand(1))){ if (Inst->getOpcode() == Instruction::Shl && isa(Inst->getOperand(1))) { ConstantInt *ShAmt = cast(Inst->getOperand(1)); uint32_t ShAmtVal = ShAmt->getLimitedValue(64); Scale = ConstantInt::get(cast(Inst->getType()), 1ULL << ShAmtVal); NewIdx = Inst->getOperand(0); } else if (Inst->getOpcode() == Instruction::Mul && isa(Inst->getOperand(1))) { Scale = cast(Inst->getOperand(1)); NewIdx = Inst->getOperand(0); } } // If the index will be to exactly the right offset with the scale taken // out, perform the transformation. Note, we don't know whether Scale is // signed or not. We'll use unsigned version of division/modulo // operation after making sure Scale doesn't have the sign bit set. if (ArrayEltSize && Scale && Scale->getSExtValue() >= 0LL && Scale->getZExtValue() % ArrayEltSize == 0) { Scale = ConstantInt::get(Scale->getType(), Scale->getZExtValue() / ArrayEltSize); if (Scale->getZExtValue() != 1) { Constant *C = ConstantExpr::getIntegerCast(Scale, NewIdx->getType(), false /*ZExt*/); NewIdx = Builder->CreateMul(NewIdx, C, "idxscale"); } // Insert the new GEP instruction. Value *Idx[2]; Idx[0] = Constant::getNullValue(Type::getInt32Ty(GEP.getContext())); Idx[1] = NewIdx; Value *NewGEP = GEP.isInBounds() ? Builder->CreateInBoundsGEP(StrippedPtr, Idx, Idx + 2,GEP.getName()): Builder->CreateGEP(StrippedPtr, Idx, Idx + 2, GEP.getName()); // The NewGEP must be pointer typed, so must the old one -> BitCast return new BitCastInst(NewGEP, GEP.getType()); } } } } /// See if we can simplify: /// X = bitcast A* to B* /// Y = gep X, <...constant indices...> /// into a gep of the original struct. This is important for SROA and alias /// analysis of unions. If "A" is also a bitcast, wait for A/X to be merged. if (BitCastInst *BCI = dyn_cast(PtrOp)) { if (TD && !isa(BCI->getOperand(0)) && GEP.hasAllConstantIndices()) { // Determine how much the GEP moves the pointer. We are guaranteed to get // a constant back from EmitGEPOffset. ConstantInt *OffsetV = cast(EmitGEPOffset(&GEP)); int64_t Offset = OffsetV->getSExtValue(); // If this GEP instruction doesn't move the pointer, just replace the GEP // with a bitcast of the real input to the dest type. if (Offset == 0) { // If the bitcast is of an allocation, and the allocation will be // converted to match the type of the cast, don't touch this. if (isa(BCI->getOperand(0)) || isMalloc(BCI->getOperand(0))) { // See if the bitcast simplifies, if so, don't nuke this GEP yet. if (Instruction *I = visitBitCast(*BCI)) { if (I != BCI) { I->takeName(BCI); BCI->getParent()->getInstList().insert(BCI, I); ReplaceInstUsesWith(*BCI, I); } return &GEP; } } return new BitCastInst(BCI->getOperand(0), GEP.getType()); } // Otherwise, if the offset is non-zero, we need to find out if there is a // field at Offset in 'A's type. If so, we can pull the cast through the // GEP. SmallVector NewIndices; const Type *InTy = cast(BCI->getOperand(0)->getType())->getElementType(); if (FindElementAtOffset(InTy, Offset, NewIndices)) { Value *NGEP = GEP.isInBounds() ? Builder->CreateInBoundsGEP(BCI->getOperand(0), NewIndices.begin(), NewIndices.end()) : Builder->CreateGEP(BCI->getOperand(0), NewIndices.begin(), NewIndices.end()); if (NGEP->getType() == GEP.getType()) return ReplaceInstUsesWith(GEP, NGEP); NGEP->takeName(&GEP); return new BitCastInst(NGEP, GEP.getType()); } } } return 0; } static bool IsOnlyNullComparedAndFreed(const Value &V) { for (Value::const_use_iterator UI = V.use_begin(), UE = V.use_end(); UI != UE; ++UI) { const User *U = *UI; if (isFreeCall(U)) continue; if (const ICmpInst *ICI = dyn_cast(U)) if (ICI->isEquality() && isa(ICI->getOperand(1))) continue; return false; } return true; } Instruction *InstCombiner::visitMalloc(Instruction &MI) { // If we have a malloc call which is only used in any amount of comparisons // to null and free calls, delete the calls and replace the comparisons with // true or false as appropriate. if (IsOnlyNullComparedAndFreed(MI)) { for (Value::use_iterator UI = MI.use_begin(), UE = MI.use_end(); UI != UE;) { // We can assume that every remaining use is a free call or an icmp eq/ne // to null, so the cast is safe. Instruction *I = cast(*UI); // Early increment here, as we're about to get rid of the user. ++UI; if (isFreeCall(I)) { EraseInstFromFunction(*cast(I)); continue; } // Again, the cast is safe. ICmpInst *C = cast(I); ReplaceInstUsesWith(*C, ConstantInt::get(Type::getInt1Ty(C->getContext()), C->isFalseWhenEqual())); EraseInstFromFunction(*C); } return EraseInstFromFunction(MI); } return 0; } Instruction *InstCombiner::visitFree(CallInst &FI) { Value *Op = FI.getArgOperand(0); // free undef -> unreachable. if (isa(Op)) { // Insert a new store to null because we cannot modify the CFG here. new StoreInst(ConstantInt::getTrue(FI.getContext()), UndefValue::get(Type::getInt1PtrTy(FI.getContext())), &FI); return EraseInstFromFunction(FI); } // If we have 'free null' delete the instruction. This can happen in stl code // when lots of inlining happens. if (isa(Op)) return EraseInstFromFunction(FI); return 0; } Instruction *InstCombiner::visitBranchInst(BranchInst &BI) { // Change br (not X), label True, label False to: br X, label False, True Value *X = 0; BasicBlock *TrueDest; BasicBlock *FalseDest; if (match(&BI, m_Br(m_Not(m_Value(X)), TrueDest, FalseDest)) && !isa(X)) { // Swap Destinations and condition... BI.setCondition(X); BI.setSuccessor(0, FalseDest); BI.setSuccessor(1, TrueDest); return &BI; } // Cannonicalize fcmp_one -> fcmp_oeq FCmpInst::Predicate FPred; Value *Y; if (match(&BI, m_Br(m_FCmp(FPred, m_Value(X), m_Value(Y)), TrueDest, FalseDest)) && BI.getCondition()->hasOneUse()) if (FPred == FCmpInst::FCMP_ONE || FPred == FCmpInst::FCMP_OLE || FPred == FCmpInst::FCMP_OGE) { FCmpInst *Cond = cast(BI.getCondition()); Cond->setPredicate(FCmpInst::getInversePredicate(FPred)); // Swap Destinations and condition. BI.setSuccessor(0, FalseDest); BI.setSuccessor(1, TrueDest); Worklist.Add(Cond); return &BI; } // Cannonicalize icmp_ne -> icmp_eq ICmpInst::Predicate IPred; if (match(&BI, m_Br(m_ICmp(IPred, m_Value(X), m_Value(Y)), TrueDest, FalseDest)) && BI.getCondition()->hasOneUse()) if (IPred == ICmpInst::ICMP_NE || IPred == ICmpInst::ICMP_ULE || IPred == ICmpInst::ICMP_SLE || IPred == ICmpInst::ICMP_UGE || IPred == ICmpInst::ICMP_SGE) { ICmpInst *Cond = cast(BI.getCondition()); Cond->setPredicate(ICmpInst::getInversePredicate(IPred)); // Swap Destinations and condition. BI.setSuccessor(0, FalseDest); BI.setSuccessor(1, TrueDest); Worklist.Add(Cond); return &BI; } return 0; } Instruction *InstCombiner::visitSwitchInst(SwitchInst &SI) { Value *Cond = SI.getCondition(); if (Instruction *I = dyn_cast(Cond)) { if (I->getOpcode() == Instruction::Add) if (ConstantInt *AddRHS = dyn_cast(I->getOperand(1))) { // change 'switch (X+4) case 1:' into 'switch (X) case -3' for (unsigned i = 2, e = SI.getNumOperands(); i != e; i += 2) SI.setOperand(i, ConstantExpr::getSub(cast(SI.getOperand(i)), AddRHS)); SI.setOperand(0, I->getOperand(0)); Worklist.Add(I); return &SI; } } return 0; } Instruction *InstCombiner::visitExtractValueInst(ExtractValueInst &EV) { Value *Agg = EV.getAggregateOperand(); if (!EV.hasIndices()) return ReplaceInstUsesWith(EV, Agg); if (Constant *C = dyn_cast(Agg)) { if (isa(C)) return ReplaceInstUsesWith(EV, UndefValue::get(EV.getType())); if (isa(C)) return ReplaceInstUsesWith(EV, Constant::getNullValue(EV.getType())); if (isa(C) || isa(C)) { // Extract the element indexed by the first index out of the constant Value *V = C->getOperand(*EV.idx_begin()); if (EV.getNumIndices() > 1) // Extract the remaining indices out of the constant indexed by the // first index return ExtractValueInst::Create(V, EV.idx_begin() + 1, EV.idx_end()); else return ReplaceInstUsesWith(EV, V); } return 0; // Can't handle other constants } if (InsertValueInst *IV = dyn_cast(Agg)) { // We're extracting from an insertvalue instruction, compare the indices const unsigned *exti, *exte, *insi, *inse; for (exti = EV.idx_begin(), insi = IV->idx_begin(), exte = EV.idx_end(), inse = IV->idx_end(); exti != exte && insi != inse; ++exti, ++insi) { if (*insi != *exti) // The insert and extract both reference distinctly different elements. // This means the extract is not influenced by the insert, and we can // replace the aggregate operand of the extract with the aggregate // operand of the insert. i.e., replace // %I = insertvalue { i32, { i32 } } %A, { i32 } { i32 42 }, 1 // %E = extractvalue { i32, { i32 } } %I, 0 // with // %E = extractvalue { i32, { i32 } } %A, 0 return ExtractValueInst::Create(IV->getAggregateOperand(), EV.idx_begin(), EV.idx_end()); } if (exti == exte && insi == inse) // Both iterators are at the end: Index lists are identical. Replace // %B = insertvalue { i32, { i32 } } %A, i32 42, 1, 0 // %C = extractvalue { i32, { i32 } } %B, 1, 0 // with "i32 42" return ReplaceInstUsesWith(EV, IV->getInsertedValueOperand()); if (exti == exte) { // The extract list is a prefix of the insert list. i.e. replace // %I = insertvalue { i32, { i32 } } %A, i32 42, 1, 0 // %E = extractvalue { i32, { i32 } } %I, 1 // with // %X = extractvalue { i32, { i32 } } %A, 1 // %E = insertvalue { i32 } %X, i32 42, 0 // by switching the order of the insert and extract (though the // insertvalue should be left in, since it may have other uses). Value *NewEV = Builder->CreateExtractValue(IV->getAggregateOperand(), EV.idx_begin(), EV.idx_end()); return InsertValueInst::Create(NewEV, IV->getInsertedValueOperand(), insi, inse); } if (insi == inse) // The insert list is a prefix of the extract list // We can simply remove the common indices from the extract and make it // operate on the inserted value instead of the insertvalue result. // i.e., replace // %I = insertvalue { i32, { i32 } } %A, { i32 } { i32 42 }, 1 // %E = extractvalue { i32, { i32 } } %I, 1, 0 // with // %E extractvalue { i32 } { i32 42 }, 0 return ExtractValueInst::Create(IV->getInsertedValueOperand(), exti, exte); } if (IntrinsicInst *II = dyn_cast(Agg)) { // We're extracting from an intrinsic, see if we're the only user, which // allows us to simplify multiple result intrinsics to simpler things that // just get one value. if (II->hasOneUse()) { // Check if we're grabbing the overflow bit or the result of a 'with // overflow' intrinsic. If it's the latter we can remove the intrinsic // and replace it with a traditional binary instruction. switch (II->getIntrinsicID()) { case Intrinsic::uadd_with_overflow: case Intrinsic::sadd_with_overflow: if (*EV.idx_begin() == 0) { // Normal result. Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1); II->replaceAllUsesWith(UndefValue::get(II->getType())); EraseInstFromFunction(*II); return BinaryOperator::CreateAdd(LHS, RHS); } break; case Intrinsic::usub_with_overflow: case Intrinsic::ssub_with_overflow: if (*EV.idx_begin() == 0) { // Normal result. Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1); II->replaceAllUsesWith(UndefValue::get(II->getType())); EraseInstFromFunction(*II); return BinaryOperator::CreateSub(LHS, RHS); } break; case Intrinsic::umul_with_overflow: case Intrinsic::smul_with_overflow: if (*EV.idx_begin() == 0) { // Normal result. Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1); II->replaceAllUsesWith(UndefValue::get(II->getType())); EraseInstFromFunction(*II); return BinaryOperator::CreateMul(LHS, RHS); } break; default: break; } } } // Can't simplify extracts from other values. Note that nested extracts are // already simplified implicitely by the above (extract ( extract (insert) ) // will be translated into extract ( insert ( extract ) ) first and then just // the value inserted, if appropriate). return 0; } /// TryToSinkInstruction - Try to move the specified instruction from its /// current block into the beginning of DestBlock, which can only happen if it's /// safe to move the instruction past all of the instructions between it and the /// end of its block. static bool TryToSinkInstruction(Instruction *I, BasicBlock *DestBlock) { assert(I->hasOneUse() && "Invariants didn't hold!"); // Cannot move control-flow-involving, volatile loads, vaarg, etc. if (isa(I) || I->mayHaveSideEffects() || isa(I)) return false; // Do not sink alloca instructions out of the entry block. if (isa(I) && I->getParent() == &DestBlock->getParent()->getEntryBlock()) return false; // We can only sink load instructions if there is nothing between the load and // the end of block that could change the value. if (I->mayReadFromMemory()) { for (BasicBlock::iterator Scan = I, E = I->getParent()->end(); Scan != E; ++Scan) if (Scan->mayWriteToMemory()) return false; } BasicBlock::iterator InsertPos = DestBlock->getFirstNonPHI(); I->moveBefore(InsertPos); ++NumSunkInst; return true; } /// AddReachableCodeToWorklist - Walk the function in depth-first order, adding /// all reachable code to the worklist. /// /// This has a couple of tricks to make the code faster and more powerful. In /// particular, we constant fold and DCE instructions as we go, to avoid adding /// them to the worklist (this significantly speeds up instcombine on code where /// many instructions are dead or constant). Additionally, if we find a branch /// whose condition is a known constant, we only visit the reachable successors. /// static bool AddReachableCodeToWorklist(BasicBlock *BB, SmallPtrSet &Visited, InstCombiner &IC, const TargetData *TD) { bool MadeIRChange = false; SmallVector Worklist; Worklist.push_back(BB); SmallVector InstrsForInstCombineWorklist; SmallPtrSet FoldedConstants; do { BB = Worklist.pop_back_val(); // We have now visited this block! If we've already been here, ignore it. if (!Visited.insert(BB)) continue; for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E; ) { Instruction *Inst = BBI++; // DCE instruction if trivially dead. if (isInstructionTriviallyDead(Inst)) { ++NumDeadInst; DEBUG(errs() << "IC: DCE: " << *Inst << '\n'); Inst->eraseFromParent(); continue; } // ConstantProp instruction if trivially constant. if (!Inst->use_empty() && isa(Inst->getOperand(0))) if (Constant *C = ConstantFoldInstruction(Inst, TD)) { DEBUG(errs() << "IC: ConstFold to: " << *C << " from: " << *Inst << '\n'); Inst->replaceAllUsesWith(C); ++NumConstProp; Inst->eraseFromParent(); continue; } if (TD) { // See if we can constant fold its operands. for (User::op_iterator i = Inst->op_begin(), e = Inst->op_end(); i != e; ++i) { ConstantExpr *CE = dyn_cast(i); if (CE == 0) continue; // If we already folded this constant, don't try again. if (!FoldedConstants.insert(CE)) continue; Constant *NewC = ConstantFoldConstantExpression(CE, TD); if (NewC && NewC != CE) { *i = NewC; MadeIRChange = true; } } } InstrsForInstCombineWorklist.push_back(Inst); } // Recursively visit successors. If this is a branch or switch on a // constant, only visit the reachable successor. TerminatorInst *TI = BB->getTerminator(); if (BranchInst *BI = dyn_cast(TI)) { if (BI->isConditional() && isa(BI->getCondition())) { bool CondVal = cast(BI->getCondition())->getZExtValue(); BasicBlock *ReachableBB = BI->getSuccessor(!CondVal); Worklist.push_back(ReachableBB); continue; } } else if (SwitchInst *SI = dyn_cast(TI)) { if (ConstantInt *Cond = dyn_cast(SI->getCondition())) { // See if this is an explicit destination. for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) if (SI->getCaseValue(i) == Cond) { BasicBlock *ReachableBB = SI->getSuccessor(i); Worklist.push_back(ReachableBB); continue; } // Otherwise it is the default destination. Worklist.push_back(SI->getSuccessor(0)); continue; } } for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) Worklist.push_back(TI->getSuccessor(i)); } while (!Worklist.empty()); // Once we've found all of the instructions to add to instcombine's worklist, // add them in reverse order. This way instcombine will visit from the top // of the function down. This jives well with the way that it adds all uses // of instructions to the worklist after doing a transformation, thus avoiding // some N^2 behavior in pathological cases. IC.Worklist.AddInitialGroup(&InstrsForInstCombineWorklist[0], InstrsForInstCombineWorklist.size()); return MadeIRChange; } bool InstCombiner::DoOneIteration(Function &F, unsigned Iteration) { MadeIRChange = false; DEBUG(errs() << "\n\nINSTCOMBINE ITERATION #" << Iteration << " on " << F.getNameStr() << "\n"); { // Do a depth-first traversal of the function, populate the worklist with // the reachable instructions. Ignore blocks that are not reachable. Keep // track of which blocks we visit. SmallPtrSet Visited; MadeIRChange |= AddReachableCodeToWorklist(F.begin(), Visited, *this, TD); // Do a quick scan over the function. If we find any blocks that are // unreachable, remove any instructions inside of them. This prevents // the instcombine code from having to deal with some bad special cases. for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) if (!Visited.count(BB)) { Instruction *Term = BB->getTerminator(); while (Term != BB->begin()) { // Remove instrs bottom-up BasicBlock::iterator I = Term; --I; DEBUG(errs() << "IC: DCE: " << *I << '\n'); // A debug intrinsic shouldn't force another iteration if we weren't // going to do one without it. if (!isa(I)) { ++NumDeadInst; MadeIRChange = true; } // If I is not void type then replaceAllUsesWith undef. // This allows ValueHandlers and custom metadata to adjust itself. if (!I->getType()->isVoidTy()) I->replaceAllUsesWith(UndefValue::get(I->getType())); I->eraseFromParent(); } } } while (!Worklist.isEmpty()) { Instruction *I = Worklist.RemoveOne(); if (I == 0) continue; // skip null values. // Check to see if we can DCE the instruction. if (isInstructionTriviallyDead(I)) { DEBUG(errs() << "IC: DCE: " << *I << '\n'); EraseInstFromFunction(*I); ++NumDeadInst; MadeIRChange = true; continue; } // Instruction isn't dead, see if we can constant propagate it. if (!I->use_empty() && isa(I->getOperand(0))) if (Constant *C = ConstantFoldInstruction(I, TD)) { DEBUG(errs() << "IC: ConstFold to: " << *C << " from: " << *I << '\n'); // Add operands to the worklist. ReplaceInstUsesWith(*I, C); ++NumConstProp; EraseInstFromFunction(*I); MadeIRChange = true; continue; } // See if we can trivially sink this instruction to a successor basic block. if (I->hasOneUse()) { BasicBlock *BB = I->getParent(); Instruction *UserInst = cast(I->use_back()); BasicBlock *UserParent; // Get the block the use occurs in. if (PHINode *PN = dyn_cast(UserInst)) UserParent = PN->getIncomingBlock(I->use_begin().getUse()); else UserParent = UserInst->getParent(); if (UserParent != BB) { bool UserIsSuccessor = false; // See if the user is one of our successors. for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) if (*SI == UserParent) { UserIsSuccessor = true; break; } // If the user is one of our immediate successors, and if that successor // only has us as a predecessors (we'd have to split the critical edge // otherwise), we can keep going. if (UserIsSuccessor && UserParent->getSinglePredecessor()) // Okay, the CFG is simple enough, try to sink this instruction. MadeIRChange |= TryToSinkInstruction(I, UserParent); } } // Now that we have an instruction, try combining it to simplify it. Builder->SetInsertPoint(I->getParent(), I); #ifndef NDEBUG std::string OrigI; #endif DEBUG(raw_string_ostream SS(OrigI); I->print(SS); OrigI = SS.str();); DEBUG(errs() << "IC: Visiting: " << OrigI << '\n'); if (Instruction *Result = visit(*I)) { ++NumCombined; // Should we replace the old instruction with a new one? if (Result != I) { DEBUG(errs() << "IC: Old = " << *I << '\n' << " New = " << *Result << '\n'); // Everything uses the new instruction now. I->replaceAllUsesWith(Result); // Push the new instruction and any users onto the worklist. Worklist.Add(Result); Worklist.AddUsersToWorkList(*Result); // Move the name to the new instruction first. Result->takeName(I); // Insert the new instruction into the basic block... BasicBlock *InstParent = I->getParent(); BasicBlock::iterator InsertPos = I; if (!isa(Result)) // If combining a PHI, don't insert while (isa(InsertPos)) // middle of a block of PHIs. ++InsertPos; InstParent->getInstList().insert(InsertPos, Result); EraseInstFromFunction(*I); } else { #ifndef NDEBUG DEBUG(errs() << "IC: Mod = " << OrigI << '\n' << " New = " << *I << '\n'); #endif // If the instruction was modified, it's possible that it is now dead. // if so, remove it. if (isInstructionTriviallyDead(I)) { EraseInstFromFunction(*I); } else { Worklist.Add(I); Worklist.AddUsersToWorkList(*I); } } MadeIRChange = true; } } Worklist.Zap(); return MadeIRChange; } bool InstCombiner::runOnFunction(Function &F) { MustPreserveLCSSA = mustPreserveAnalysisID(LCSSAID); TD = getAnalysisIfAvailable(); /// Builder - This is an IRBuilder that automatically inserts new /// instructions into the worklist when they are created. IRBuilder TheBuilder(F.getContext(), TargetFolder(TD), InstCombineIRInserter(Worklist)); Builder = &TheBuilder; bool EverMadeChange = false; // Iterate while there is work to do. unsigned Iteration = 0; while (DoOneIteration(F, Iteration++)) EverMadeChange = true; Builder = 0; return EverMadeChange; } FunctionPass *llvm::createInstructionCombiningPass() { return new InstCombiner(); }