| //===- InstructionCombining.cpp - Combine multiple instructions -----------===// |
| // |
| // 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 int 1, %X |
| // %Z = add int 1, %Y |
| // into: |
| // %Z = add int 2, %X |
| // |
| // This is a simple worklist driven algorithm. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/Transforms/Utils/BasicBlockUtils.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/ConstantHandling.h" |
| #include "llvm/iMemory.h" |
| #include "llvm/iOther.h" |
| #include "llvm/iPHINode.h" |
| #include "llvm/iOperators.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Support/InstIterator.h" |
| #include "llvm/Support/InstVisitor.h" |
| #include "Support/StatisticReporter.h" |
| #include <algorithm> |
| |
| static Statistic<> NumCombined ("instcombine\t- Number of insts combined"); |
| static Statistic<> NumConstProp("instcombine\t- Number of constant folds"); |
| static Statistic<> NumDeadInst ("instcombine\t- Number of dead inst eliminate"); |
| |
| namespace { |
| class InstCombiner : public FunctionPass, |
| public InstVisitor<InstCombiner, Instruction*> { |
| // Worklist of all of the instructions that need to be simplified. |
| std::vector<Instruction*> WorkList; |
| |
| void AddUsesToWorkList(Instruction &I) { |
| // The instruction was simplified, add all users of the instruction to |
| // the work lists because they might get more simplified now... |
| // |
| for (Value::use_iterator UI = I.use_begin(), UE = I.use_end(); |
| UI != UE; ++UI) |
| WorkList.push_back(cast<Instruction>(*UI)); |
| } |
| |
| // removeFromWorkList - remove all instances of I from the worklist. |
| void removeFromWorkList(Instruction *I); |
| public: |
| virtual bool runOnFunction(Function &F); |
| |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.preservesCFG(); |
| } |
| |
| // Visitation implementation - Implement instruction combining for different |
| // instruction types. The semantics are as follows: |
| // Return Value: |
| // null - No change was made |
| // I - Change was made, I is still valid, I may be dead though |
| // otherwise - Change was made, replace I with returned instruction |
| // |
| Instruction *visitAdd(BinaryOperator &I); |
| Instruction *visitSub(BinaryOperator &I); |
| Instruction *visitMul(BinaryOperator &I); |
| Instruction *visitDiv(BinaryOperator &I); |
| Instruction *visitRem(BinaryOperator &I); |
| Instruction *visitAnd(BinaryOperator &I); |
| Instruction *visitOr (BinaryOperator &I); |
| Instruction *visitXor(BinaryOperator &I); |
| Instruction *visitSetCondInst(BinaryOperator &I); |
| Instruction *visitShiftInst(Instruction &I); |
| Instruction *visitCastInst(CastInst &CI); |
| Instruction *visitPHINode(PHINode &PN); |
| Instruction *visitGetElementPtrInst(GetElementPtrInst &GEP); |
| |
| // visitInstruction - Specify what to return for unhandled instructions... |
| Instruction *visitInstruction(Instruction &I) { return 0; } |
| |
| // InsertNewInstBefore - insert an instruction New before instruction Old |
| // in the program. Add the new instruction to the worklist. |
| // |
| void InsertNewInstBefore(Instruction *New, Instruction &Old) { |
| assert(New && New->getParent() == 0 && |
| "New instruction already inserted into a basic block!"); |
| BasicBlock *BB = Old.getParent(); |
| BB->getInstList().insert(&Old, New); // Insert inst |
| WorkList.push_back(New); // Add to worklist |
| } |
| |
| // ReplaceInstUsesWith - This method is to be used when an instruction is |
| // found to be dead, replacable with another preexisting expression. Here |
| // we add all uses of I to the worklist, replace all uses of I with the new |
| // value, then return I, so that the inst combiner will know that I was |
| // modified. |
| // |
| Instruction *ReplaceInstUsesWith(Instruction &I, Value *V) { |
| AddUsesToWorkList(I); // Add all modified instrs to worklist |
| I.replaceAllUsesWith(V); |
| return &I; |
| } |
| }; |
| |
| RegisterOpt<InstCombiner> X("instcombine", "Combine redundant instructions"); |
| } |
| |
| |
| // Make sure that this instruction has a constant on the right hand side if it |
| // has any constant arguments. If not, fix it an return true. |
| // |
| static bool SimplifyBinOp(BinaryOperator &I) { |
| if (isa<Constant>(I.getOperand(0)) && !isa<Constant>(I.getOperand(1))) |
| return !I.swapOperands(); |
| return false; |
| } |
| |
| // dyn_castNegInst - Given a 'sub' instruction, return the RHS of the |
| // instruction if the LHS is a constant zero (which is the 'negate' form). |
| // |
| static inline Value *dyn_castNegInst(Value *V) { |
| Instruction *I = dyn_cast<Instruction>(V); |
| if (!I || I->getOpcode() != Instruction::Sub) return 0; |
| |
| if (I->getOperand(0) == Constant::getNullValue(I->getType())) |
| return I->getOperand(1); |
| return 0; |
| } |
| |
| static inline Value *dyn_castNotInst(Value *V) { |
| Instruction *I = dyn_cast<Instruction>(V); |
| if (!I || I->getOpcode() != Instruction::Xor) return 0; |
| |
| if (ConstantIntegral *CI = dyn_cast<ConstantIntegral>(I->getOperand(1))) |
| if (CI->isAllOnesValue()) |
| return I->getOperand(0); |
| return 0; |
| } |
| |
| Instruction *InstCombiner::visitAdd(BinaryOperator &I) { |
| bool Changed = SimplifyBinOp(I); |
| Value *LHS = I.getOperand(0), *RHS = I.getOperand(1); |
| |
| // Eliminate 'add int %X, 0' |
| if (RHS == Constant::getNullValue(I.getType())) |
| return ReplaceInstUsesWith(I, LHS); |
| |
| // -A + B --> B - A |
| if (Value *V = dyn_castNegInst(LHS)) |
| return BinaryOperator::create(Instruction::Sub, RHS, V); |
| |
| // A + -B --> A - B |
| if (Value *V = dyn_castNegInst(RHS)) |
| return BinaryOperator::create(Instruction::Sub, LHS, V); |
| |
| // Simplify add instructions with a constant RHS... |
| if (Constant *Op2 = dyn_cast<Constant>(RHS)) { |
| if (BinaryOperator *ILHS = dyn_cast<BinaryOperator>(LHS)) { |
| if (ILHS->getOpcode() == Instruction::Add && |
| isa<Constant>(ILHS->getOperand(1))) { |
| // Fold: |
| // %Y = add int %X, 1 |
| // %Z = add int %Y, 1 |
| // into: |
| // %Z = add int %X, 2 |
| // |
| if (Constant *Val = *Op2 + *cast<Constant>(ILHS->getOperand(1))) { |
| I.setOperand(0, ILHS->getOperand(0)); |
| I.setOperand(1, Val); |
| return &I; |
| } |
| } |
| } |
| } |
| |
| return Changed ? &I : 0; |
| } |
| |
| Instruction *InstCombiner::visitSub(BinaryOperator &I) { |
| Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); |
| |
| if (Op0 == Op1) // sub X, X -> 0 |
| return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType())); |
| |
| // If this is a subtract instruction with a constant RHS, convert it to an add |
| // instruction of a negative constant |
| // |
| if (Constant *Op2 = dyn_cast<Constant>(Op1)) |
| if (Constant *RHS = *Constant::getNullValue(I.getType()) - *Op2) // 0 - RHS |
| return BinaryOperator::create(Instruction::Add, Op0, RHS, I.getName()); |
| |
| // If this is a 'B = x-(-A)', change to B = x+A... |
| if (Value *V = dyn_castNegInst(Op1)) |
| return BinaryOperator::create(Instruction::Add, Op0, V); |
| |
| // Replace (x - (y - z)) with (x + (z - y)) if the (y - z) subexpression is |
| // not used by anyone else... |
| // |
| if (BinaryOperator *Op1I = dyn_cast<BinaryOperator>(Op1)) |
| if (Op1I->use_size() == 1 && Op1I->getOpcode() == Instruction::Sub) { |
| // Swap the two operands of the subexpr... |
| Value *IIOp0 = Op1I->getOperand(0), *IIOp1 = Op1I->getOperand(1); |
| Op1I->setOperand(0, IIOp1); |
| Op1I->setOperand(1, IIOp0); |
| |
| // Create the new top level add instruction... |
| return BinaryOperator::create(Instruction::Add, Op0, Op1); |
| } |
| return 0; |
| } |
| |
| Instruction *InstCombiner::visitMul(BinaryOperator &I) { |
| bool Changed = SimplifyBinOp(I); |
| Value *Op1 = I.getOperand(0); |
| |
| // Simplify mul instructions with a constant RHS... |
| if (Constant *Op2 = dyn_cast<Constant>(I.getOperand(1))) { |
| if (I.getType()->isInteger() && cast<ConstantInt>(Op2)->equalsInt(1)) |
| return ReplaceInstUsesWith(I, Op1); // Eliminate 'mul int %X, 1' |
| |
| if (I.getType()->isInteger() && cast<ConstantInt>(Op2)->equalsInt(2)) |
| // Convert 'mul int %X, 2' to 'add int %X, %X' |
| return BinaryOperator::create(Instruction::Add, Op1, Op1, I.getName()); |
| |
| if (Op2->isNullValue()) |
| return ReplaceInstUsesWith(I, Op2); // Eliminate 'mul int %X, 0' |
| } |
| |
| return Changed ? &I : 0; |
| } |
| |
| |
| Instruction *InstCombiner::visitDiv(BinaryOperator &I) { |
| // div X, 1 == X |
| if (ConstantInt *RHS = dyn_cast<ConstantInt>(I.getOperand(1))) |
| if (RHS->equalsInt(1)) |
| return ReplaceInstUsesWith(I, I.getOperand(0)); |
| return 0; |
| } |
| |
| |
| Instruction *InstCombiner::visitRem(BinaryOperator &I) { |
| // rem X, 1 == 0 |
| if (ConstantInt *RHS = dyn_cast<ConstantInt>(I.getOperand(1))) |
| if (RHS->equalsInt(1)) |
| return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType())); |
| |
| return 0; |
| } |
| |
| // isMaxValueMinusOne - return true if this is Max-1 |
| static bool isMaxValueMinusOne(const ConstantInt *C) { |
| if (const ConstantUInt *CU = dyn_cast<ConstantUInt>(C)) { |
| // Calculate -1 casted to the right type... |
| unsigned TypeBits = C->getType()->getPrimitiveSize()*8; |
| uint64_t Val = ~0ULL; // All ones |
| Val >>= 64-TypeBits; // Shift out unwanted 1 bits... |
| return CU->getValue() == Val-1; |
| } |
| |
| const ConstantSInt *CS = cast<ConstantSInt>(C); |
| |
| // Calculate 0111111111..11111 |
| unsigned TypeBits = C->getType()->getPrimitiveSize()*8; |
| int64_t Val = INT64_MAX; // All ones |
| Val >>= 64-TypeBits; // Shift out unwanted 1 bits... |
| return CS->getValue() == Val-1; |
| } |
| |
| // isMinValuePlusOne - return true if this is Min+1 |
| static bool isMinValuePlusOne(const ConstantInt *C) { |
| if (const ConstantUInt *CU = dyn_cast<ConstantUInt>(C)) |
| return CU->getValue() == 1; |
| |
| const ConstantSInt *CS = cast<ConstantSInt>(C); |
| |
| // Calculate 1111111111000000000000 |
| unsigned TypeBits = C->getType()->getPrimitiveSize()*8; |
| int64_t Val = -1; // All ones |
| Val <<= TypeBits-1; // Shift over to the right spot |
| return CS->getValue() == Val+1; |
| } |
| |
| |
| Instruction *InstCombiner::visitAnd(BinaryOperator &I) { |
| bool Changed = SimplifyBinOp(I); |
| Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); |
| |
| // and X, X = X and X, 0 == 0 |
| if (Op0 == Op1 || Op1 == Constant::getNullValue(I.getType())) |
| return ReplaceInstUsesWith(I, Op1); |
| |
| // and X, -1 == X |
| if (ConstantIntegral *RHS = dyn_cast<ConstantIntegral>(Op1)) |
| if (RHS->isAllOnesValue()) |
| return ReplaceInstUsesWith(I, Op0); |
| |
| // and (not A), (not B) == not (or A, B) |
| if (Op0->use_size() == 1 && Op1->use_size() == 1) |
| if (Value *A = dyn_castNotInst(Op0)) |
| if (Value *B = dyn_castNotInst(Op1)) { |
| Instruction *Or = BinaryOperator::create(Instruction::Or, A, B, |
| I.getName()+".demorgan"); |
| InsertNewInstBefore(Or, I); |
| return BinaryOperator::createNot(Or, I.getName()); |
| } |
| |
| return Changed ? &I : 0; |
| } |
| |
| |
| |
| Instruction *InstCombiner::visitOr(BinaryOperator &I) { |
| bool Changed = SimplifyBinOp(I); |
| Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); |
| |
| // or X, X = X or X, 0 == X |
| if (Op0 == Op1 || Op1 == Constant::getNullValue(I.getType())) |
| return ReplaceInstUsesWith(I, Op0); |
| |
| // or X, -1 == -1 |
| if (ConstantIntegral *RHS = dyn_cast<ConstantIntegral>(Op1)) |
| if (RHS->isAllOnesValue()) |
| return ReplaceInstUsesWith(I, Op1); |
| |
| return Changed ? &I : 0; |
| } |
| |
| |
| |
| Instruction *InstCombiner::visitXor(BinaryOperator &I) { |
| bool Changed = SimplifyBinOp(I); |
| Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); |
| |
| // xor X, X = 0 |
| if (Op0 == Op1) |
| return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType())); |
| |
| if (ConstantIntegral *Op1C = dyn_cast<ConstantIntegral>(Op1)) { |
| // xor X, 0 == X |
| if (Op1C->isNullValue()) |
| return ReplaceInstUsesWith(I, Op0); |
| |
| // Is this a "NOT" instruction? |
| if (Op1C->isAllOnesValue()) { |
| // xor (xor X, -1), -1 = not (not X) = X |
| if (Value *X = dyn_castNotInst(Op0)) |
| return ReplaceInstUsesWith(I, X); |
| |
| // xor (setcc A, B), true = not (setcc A, B) = setncc A, B |
| if (SetCondInst *SCI = dyn_cast<SetCondInst>(Op0)) |
| if (SCI->use_size() == 1) |
| return new SetCondInst(SCI->getInverseCondition(), |
| SCI->getOperand(0), SCI->getOperand(1)); |
| } |
| } |
| |
| return Changed ? &I : 0; |
| } |
| |
| // AddOne, SubOne - Add or subtract a constant one from an integer constant... |
| static Constant *AddOne(ConstantInt *C) { |
| Constant *Result = *C + *ConstantInt::get(C->getType(), 1); |
| assert(Result && "Constant folding integer addition failed!"); |
| return Result; |
| } |
| static Constant *SubOne(ConstantInt *C) { |
| Constant *Result = *C - *ConstantInt::get(C->getType(), 1); |
| assert(Result && "Constant folding integer addition failed!"); |
| return Result; |
| } |
| |
| // isTrueWhenEqual - Return true if the specified setcondinst instruction is |
| // true when both operands are equal... |
| // |
| static bool isTrueWhenEqual(Instruction &I) { |
| return I.getOpcode() == Instruction::SetEQ || |
| I.getOpcode() == Instruction::SetGE || |
| I.getOpcode() == Instruction::SetLE; |
| } |
| |
| Instruction *InstCombiner::visitSetCondInst(BinaryOperator &I) { |
| bool Changed = SimplifyBinOp(I); |
| Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); |
| const Type *Ty = Op0->getType(); |
| |
| // setcc X, X |
| if (Op0 == Op1) |
| return ReplaceInstUsesWith(I, ConstantBool::get(isTrueWhenEqual(I))); |
| |
| // setcc <global*>, 0 - Global value addresses are never null! |
| if (isa<GlobalValue>(Op0) && isa<ConstantPointerNull>(Op1)) |
| return ReplaceInstUsesWith(I, ConstantBool::get(!isTrueWhenEqual(I))); |
| |
| // setcc's with boolean values can always be turned into bitwise operations |
| if (Ty == Type::BoolTy) { |
| // If this is <, >, or !=, we can change this into a simple xor instruction |
| if (!isTrueWhenEqual(I)) |
| return BinaryOperator::create(Instruction::Xor, Op0, Op1, I.getName()); |
| |
| // Otherwise we need to make a temporary intermediate instruction and insert |
| // it into the instruction stream. This is what we are after: |
| // |
| // seteq bool %A, %B -> ~(A^B) |
| // setle bool %A, %B -> ~A | B |
| // setge bool %A, %B -> A | ~B |
| // |
| if (I.getOpcode() == Instruction::SetEQ) { // seteq case |
| Instruction *Xor = BinaryOperator::create(Instruction::Xor, Op0, Op1, |
| I.getName()+"tmp"); |
| InsertNewInstBefore(Xor, I); |
| return BinaryOperator::createNot(Xor, I.getName()); |
| } |
| |
| // Handle the setXe cases... |
| assert(I.getOpcode() == Instruction::SetGE || |
| I.getOpcode() == Instruction::SetLE); |
| |
| if (I.getOpcode() == Instruction::SetGE) |
| std::swap(Op0, Op1); // Change setge -> setle |
| |
| // Now we just have the SetLE case. |
| Instruction *Not = BinaryOperator::createNot(Op0, I.getName()+"tmp"); |
| InsertNewInstBefore(Not, I); |
| return BinaryOperator::create(Instruction::Or, Not, Op1, I.getName()); |
| } |
| |
| // Check to see if we are doing one of many comparisons against constant |
| // integers at the end of their ranges... |
| // |
| if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) { |
| // Check to see if we are comparing against the minimum or maximum value... |
| if (CI->isMinValue()) { |
| if (I.getOpcode() == Instruction::SetLT) // A < MIN -> FALSE |
| return ReplaceInstUsesWith(I, ConstantBool::False); |
| if (I.getOpcode() == Instruction::SetGE) // A >= MIN -> TRUE |
| return ReplaceInstUsesWith(I, ConstantBool::True); |
| if (I.getOpcode() == Instruction::SetLE) // A <= MIN -> A == MIN |
| return BinaryOperator::create(Instruction::SetEQ, Op0,Op1, I.getName()); |
| if (I.getOpcode() == Instruction::SetGT) // A > MIN -> A != MIN |
| return BinaryOperator::create(Instruction::SetNE, Op0,Op1, I.getName()); |
| |
| } else if (CI->isMaxValue()) { |
| if (I.getOpcode() == Instruction::SetGT) // A > MAX -> FALSE |
| return ReplaceInstUsesWith(I, ConstantBool::False); |
| if (I.getOpcode() == Instruction::SetLE) // A <= MAX -> TRUE |
| return ReplaceInstUsesWith(I, ConstantBool::True); |
| if (I.getOpcode() == Instruction::SetGE) // A >= MAX -> A == MAX |
| return BinaryOperator::create(Instruction::SetEQ, Op0,Op1, I.getName()); |
| if (I.getOpcode() == Instruction::SetLT) // A < MAX -> A != MAX |
| return BinaryOperator::create(Instruction::SetNE, Op0,Op1, I.getName()); |
| |
| // Comparing against a value really close to min or max? |
| } else if (isMinValuePlusOne(CI)) { |
| if (I.getOpcode() == Instruction::SetLT) // A < MIN+1 -> A == MIN |
| return BinaryOperator::create(Instruction::SetEQ, Op0, |
| SubOne(CI), I.getName()); |
| if (I.getOpcode() == Instruction::SetGE) // A >= MIN-1 -> A != MIN |
| return BinaryOperator::create(Instruction::SetNE, Op0, |
| SubOne(CI), I.getName()); |
| |
| } else if (isMaxValueMinusOne(CI)) { |
| if (I.getOpcode() == Instruction::SetGT) // A > MAX-1 -> A == MAX |
| return BinaryOperator::create(Instruction::SetEQ, Op0, |
| AddOne(CI), I.getName()); |
| if (I.getOpcode() == Instruction::SetLE) // A <= MAX-1 -> A != MAX |
| return BinaryOperator::create(Instruction::SetNE, Op0, |
| AddOne(CI), I.getName()); |
| } |
| } |
| |
| return Changed ? &I : 0; |
| } |
| |
| |
| |
| Instruction *InstCombiner::visitShiftInst(Instruction &I) { |
| assert(I.getOperand(1)->getType() == Type::UByteTy); |
| Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); |
| |
| // shl X, 0 == X and shr X, 0 == X |
| // shl 0, X == 0 and shr 0, X == 0 |
| if (Op1 == Constant::getNullValue(Type::UByteTy) || |
| Op0 == Constant::getNullValue(Op0->getType())) |
| return ReplaceInstUsesWith(I, Op0); |
| |
| // shl uint X, 32 = 0 and shr ubyte Y, 9 = 0, ... just don't eliminate shr of |
| // a signed value. |
| // |
| if (ConstantUInt *CUI = dyn_cast<ConstantUInt>(Op1)) { |
| unsigned TypeBits = Op0->getType()->getPrimitiveSize()*8; |
| if (CUI->getValue() >= TypeBits && |
| !(Op0->getType()->isSigned() && I.getOpcode() == Instruction::Shr)) |
| return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType())); |
| } |
| return 0; |
| } |
| |
| |
| // isEliminableCastOfCast - Return true if it is valid to eliminate the CI |
| // instruction. |
| // |
| static inline bool isEliminableCastOfCast(const CastInst &CI, |
| const CastInst *CSrc) { |
| assert(CI.getOperand(0) == CSrc); |
| const Type *SrcTy = CSrc->getOperand(0)->getType(); |
| const Type *MidTy = CSrc->getType(); |
| const Type *DstTy = CI.getType(); |
| |
| // It is legal to eliminate the instruction if casting A->B->A if the sizes |
| // are identical and the bits don't get reinterpreted (for example |
| // int->float->int would not be allowed) |
| if (SrcTy == DstTy && SrcTy->isLosslesslyConvertableTo(MidTy)) |
| return true; |
| |
| // Allow free casting and conversion of sizes as long as the sign doesn't |
| // change... |
| if (SrcTy->isIntegral() && MidTy->isIntegral() && DstTy->isIntegral()) { |
| unsigned SrcSize = SrcTy->getPrimitiveSize(); |
| unsigned MidSize = MidTy->getPrimitiveSize(); |
| unsigned DstSize = DstTy->getPrimitiveSize(); |
| |
| // Cases where we are monotonically decreasing the size of the type are |
| // always ok, regardless of what sign changes are going on. |
| // |
| if (SrcSize >= MidSize && MidSize >= DstSize) |
| return true; |
| |
| // If we are monotonically growing, things are more complex. |
| // |
| if (SrcSize <= MidSize && MidSize <= DstSize) { |
| // We have eight combinations of signedness to worry about. Here's the |
| // table: |
| static const int SignTable[8] = { |
| // CODE, SrcSigned, MidSigned, DstSigned, Comment |
| 1, // U U U Always ok |
| 1, // U U S Always ok |
| 3, // U S U Ok iff SrcSize != MidSize |
| 3, // U S S Ok iff SrcSize != MidSize |
| 0, // S U U Never ok |
| 2, // S U S Ok iff MidSize == DstSize |
| 1, // S S U Always ok |
| 1, // S S S Always ok |
| }; |
| |
| // Choose an action based on the current entry of the signtable that this |
| // cast of cast refers to... |
| unsigned Row = SrcTy->isSigned()*4+MidTy->isSigned()*2+DstTy->isSigned(); |
| switch (SignTable[Row]) { |
| case 0: return false; // Never ok |
| case 1: return true; // Always ok |
| case 2: return MidSize == DstSize; // Ok iff MidSize == DstSize |
| case 3: // Ok iff SrcSize != MidSize |
| return SrcSize != MidSize || SrcTy == Type::BoolTy; |
| default: assert(0 && "Bad entry in sign table!"); |
| } |
| } |
| } |
| |
| // Otherwise, we cannot succeed. Specifically we do not want to allow things |
| // like: short -> ushort -> uint, because this can create wrong results if |
| // the input short is negative! |
| // |
| return false; |
| } |
| |
| |
| // CastInst simplification |
| // |
| Instruction *InstCombiner::visitCastInst(CastInst &CI) { |
| // If the user is casting a value to the same type, eliminate this cast |
| // instruction... |
| if (CI.getType() == CI.getOperand(0)->getType()) |
| return ReplaceInstUsesWith(CI, CI.getOperand(0)); |
| |
| // If casting the result of another cast instruction, try to eliminate this |
| // one! |
| // |
| if (CastInst *CSrc = dyn_cast<CastInst>(CI.getOperand(0))) { |
| if (isEliminableCastOfCast(CI, CSrc)) { |
| // This instruction now refers directly to the cast's src operand. This |
| // has a good chance of making CSrc dead. |
| CI.setOperand(0, CSrc->getOperand(0)); |
| return &CI; |
| } |
| |
| // If this is an A->B->A cast, and we are dealing with integral types, try |
| // to convert this into a logical 'and' instruction. |
| // |
| if (CSrc->getOperand(0)->getType() == CI.getType() && |
| CI.getType()->isInteger() && CSrc->getType()->isInteger() && |
| CI.getType()->isUnsigned() && CSrc->getType()->isUnsigned() && |
| CSrc->getType()->getPrimitiveSize() < CI.getType()->getPrimitiveSize()){ |
| assert(CSrc->getType() != Type::ULongTy && |
| "Cannot have type bigger than ulong!"); |
| unsigned AndValue = (1U << CSrc->getType()->getPrimitiveSize()*8)-1; |
| Constant *AndOp = ConstantUInt::get(CI.getType(), AndValue); |
| return BinaryOperator::create(Instruction::And, CSrc->getOperand(0), |
| AndOp); |
| } |
| } |
| |
| return 0; |
| } |
| |
| |
| // PHINode simplification |
| // |
| Instruction *InstCombiner::visitPHINode(PHINode &PN) { |
| // If the PHI node only has one incoming value, eliminate the PHI node... |
| if (PN.getNumIncomingValues() == 0) |
| return ReplaceInstUsesWith(PN, Constant::getNullValue(PN.getType())); |
| if (PN.getNumIncomingValues() == 1) |
| return ReplaceInstUsesWith(PN, PN.getIncomingValue(0)); |
| |
| // Otherwise if all of the incoming values are the same for the PHI, replace |
| // the PHI node with the incoming value. |
| // |
| Value *InVal = 0; |
| for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) |
| if (PN.getIncomingValue(i) != &PN) // Not the PHI node itself... |
| if (InVal && PN.getIncomingValue(i) != InVal) |
| return 0; // Not the same, bail out. |
| else |
| InVal = PN.getIncomingValue(i); |
| |
| // The only case that could cause InVal to be null is if we have a PHI node |
| // that only has entries for itself. In this case, there is no entry into the |
| // loop, so kill the PHI. |
| // |
| if (InVal == 0) InVal = Constant::getNullValue(PN.getType()); |
| |
| // All of the incoming values are the same, replace the PHI node now. |
| return ReplaceInstUsesWith(PN, InVal); |
| } |
| |
| |
| Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) { |
| // Is it 'getelementptr %P, uint 0' or 'getelementptr %P' |
| // If so, eliminate the noop. |
| if ((GEP.getNumOperands() == 2 && |
| GEP.getOperand(1) == Constant::getNullValue(Type::UIntTy)) || |
| GEP.getNumOperands() == 1) |
| return ReplaceInstUsesWith(GEP, GEP.getOperand(0)); |
| |
| // 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 (GetElementPtrInst *Src = dyn_cast<GetElementPtrInst>(GEP.getOperand(0))) { |
| std::vector<Value *> Indices; |
| |
| // Can we combine the two pointer arithmetics offsets? |
| if (Src->getNumOperands() == 2 && isa<Constant>(Src->getOperand(1)) && |
| isa<Constant>(GEP.getOperand(1))) { |
| // Replace the index list on this GEP with the index on the getelementptr |
| Indices.insert(Indices.end(), GEP.idx_begin(), GEP.idx_end()); |
| Indices[0] = *cast<Constant>(Src->getOperand(1)) + |
| *cast<Constant>(GEP.getOperand(1)); |
| assert(Indices[0] != 0 && "Constant folding of uint's failed!?"); |
| |
| } else if (*GEP.idx_begin() == ConstantUInt::get(Type::UIntTy, 0)) { |
| // Otherwise we can do the fold if the first index of the GEP is a zero |
| Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end()); |
| Indices.insert(Indices.end(), GEP.idx_begin()+1, GEP.idx_end()); |
| } |
| |
| if (!Indices.empty()) |
| return new GetElementPtrInst(Src->getOperand(0), Indices, GEP.getName()); |
| |
| } else if (GlobalValue *GV = dyn_cast<GlobalValue>(GEP.getOperand(0))) { |
| // GEP of global variable. If all of the indices for this GEP are |
| // constants, we can promote this to a constexpr instead of an instruction. |
| |
| // Scan for nonconstants... |
| std::vector<Constant*> Indices; |
| User::op_iterator I = GEP.idx_begin(), E = GEP.idx_end(); |
| for (; I != E && isa<Constant>(*I); ++I) |
| Indices.push_back(cast<Constant>(*I)); |
| |
| if (I == E) { // If they are all constants... |
| ConstantExpr *CE = |
| ConstantExpr::getGetElementPtr(ConstantPointerRef::get(GV), Indices); |
| |
| // Replace all uses of the GEP with the new constexpr... |
| return ReplaceInstUsesWith(GEP, CE); |
| } |
| } |
| |
| return 0; |
| } |
| |
| |
| void InstCombiner::removeFromWorkList(Instruction *I) { |
| WorkList.erase(std::remove(WorkList.begin(), WorkList.end(), I), |
| WorkList.end()); |
| } |
| |
| bool InstCombiner::runOnFunction(Function &F) { |
| bool Changed = false; |
| |
| WorkList.insert(WorkList.end(), inst_begin(F), inst_end(F)); |
| |
| while (!WorkList.empty()) { |
| Instruction *I = WorkList.back(); // Get an instruction from the worklist |
| WorkList.pop_back(); |
| |
| // Check to see if we can DCE or ConstantPropogate the instruction... |
| // Check to see if we can DIE the instruction... |
| if (isInstructionTriviallyDead(I)) { |
| // Add operands to the worklist... |
| for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) |
| if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i))) |
| WorkList.push_back(Op); |
| |
| ++NumDeadInst; |
| BasicBlock::iterator BBI = I; |
| if (dceInstruction(BBI)) { |
| removeFromWorkList(I); |
| continue; |
| } |
| } |
| |
| // Instruction isn't dead, see if we can constant propogate it... |
| if (Constant *C = ConstantFoldInstruction(I)) { |
| // Add operands to the worklist... |
| for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) |
| if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i))) |
| WorkList.push_back(Op); |
| I->replaceAllUsesWith(C); |
| ++NumConstProp; |
| BasicBlock::iterator BBI = I; |
| if (dceInstruction(BBI)) { |
| removeFromWorkList(I); |
| continue; |
| } |
| } |
| |
| // Now that we have an instruction, try combining it to simplify it... |
| if (Instruction *Result = visit(*I)) { |
| ++NumCombined; |
| // Should we replace the old instruction with a new one? |
| if (Result != I) { |
| // Instructions can end up on the worklist more than once. Make sure |
| // we do not process an instruction that has been deleted. |
| removeFromWorkList(I); |
| ReplaceInstWithInst(I, Result); |
| } else { |
| BasicBlock::iterator II = I; |
| |
| // If the instruction was modified, it's possible that it is now dead. |
| // if so, remove it. |
| if (dceInstruction(II)) { |
| // Instructions may end up in the worklist more than once. Erase them |
| // all. |
| removeFromWorkList(I); |
| Result = 0; |
| } |
| } |
| |
| if (Result) { |
| WorkList.push_back(Result); |
| AddUsesToWorkList(*Result); |
| } |
| Changed = true; |
| } |
| } |
| |
| return Changed; |
| } |
| |
| Pass *createInstructionCombiningPass() { |
| return new InstCombiner(); |
| } |