//===- 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/Instructions.h" #include "llvm/Pass.h" #include "llvm/Constants.h" #include "llvm/ConstantHandling.h" #include "llvm/DerivedTypes.h" #include "llvm/Support/InstIterator.h" #include "llvm/Support/InstVisitor.h" #include "llvm/Support/CallSite.h" #include "Support/Statistic.h" #include namespace { Statistic<> NumCombined ("instcombine", "Number of insts combined"); Statistic<> NumConstProp("instcombine", "Number of constant folds"); Statistic<> NumDeadInst ("instcombine", "Number of dead inst eliminated"); class InstCombiner : public FunctionPass, public InstVisitor { // Worklist of all of the instructions that need to be simplified. std::vector 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(*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.setPreservesCFG(); } // 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(ShiftInst &I); Instruction *visitCastInst(CastInst &CI); Instruction *visitCallInst(CallInst &CI); Instruction *visitInvokeInst(InvokeInst &II); Instruction *visitPHINode(PHINode &PN); Instruction *visitGetElementPtrInst(GetElementPtrInst &GEP); Instruction *visitAllocationInst(AllocationInst &AI); Instruction *visitBranchInst(BranchInst &BI); // visitInstruction - Specify what to return for unhandled instructions... Instruction *visitInstruction(Instruction &I) { return 0; } private: bool transformConstExprCastCall(CallSite CS); // 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; } // SimplifyCommutative - This performs a few simplifications for commutative // operators... bool SimplifyCommutative(BinaryOperator &I); }; RegisterOpt X("instcombine", "Combine redundant instructions"); } // getComplexity: Assign a complexity or rank value to LLVM Values... // 0 -> Constant, 1 -> Other, 2 -> Argument, 2 -> Unary, 3 -> OtherInst static unsigned getComplexity(Value *V) { if (isa(V)) { if (BinaryOperator::isNeg(V) || BinaryOperator::isNot(V)) return 2; return 3; } if (isa(V)) return 2; return isa(V) ? 0 : 1; } // isOnlyUse - Return true if this instruction will be deleted if we stop using // it. static bool isOnlyUse(Value *V) { return V->use_size() == 1 || isa(V); } // SimplifyCommutative - This performs a few simplifications for 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. // // 2. Transform: (op (op V, C1), C2) ==> (op V, (op C1, C2)) // 3. Transform: (op (op V1, C1), (op V2, C2)) ==> (op (op V1, V2), (op C1,C2)) // bool InstCombiner::SimplifyCommutative(BinaryOperator &I) { bool Changed = false; if (getComplexity(I.getOperand(0)) < getComplexity(I.getOperand(1))) Changed = !I.swapOperands(); if (!I.isAssociative()) return Changed; Instruction::BinaryOps Opcode = I.getOpcode(); if (BinaryOperator *Op = dyn_cast(I.getOperand(0))) if (Op->getOpcode() == Opcode && isa(Op->getOperand(1))) { if (isa(I.getOperand(1))) { Constant *Folded = ConstantExpr::get(I.getOpcode(), cast(I.getOperand(1)), cast(Op->getOperand(1))); I.setOperand(0, Op->getOperand(0)); I.setOperand(1, Folded); return true; } else if (BinaryOperator *Op1=dyn_cast(I.getOperand(1))) if (Op1->getOpcode() == Opcode && isa(Op1->getOperand(1)) && isOnlyUse(Op) && isOnlyUse(Op1)) { Constant *C1 = cast(Op->getOperand(1)); Constant *C2 = cast(Op1->getOperand(1)); // Fold (op (op V1, C1), (op V2, C2)) ==> (op (op V1, V2), (op C1,C2)) Constant *Folded = ConstantExpr::get(I.getOpcode(), C1, C2); Instruction *New = BinaryOperator::create(Opcode, Op->getOperand(0), Op1->getOperand(0), Op1->getName(), &I); WorkList.push_back(New); I.setOperand(0, New); I.setOperand(1, Folded); return true; } } return Changed; } // dyn_castNegVal - 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_castNegVal(Value *V) { if (BinaryOperator::isNeg(V)) return BinaryOperator::getNegArgument(cast(V)); // Constants can be considered to be negated values if they can be folded... if (Constant *C = dyn_cast(V)) return ConstantExpr::get(Instruction::Sub, Constant::getNullValue(V->getType()), C); return 0; } static inline Value *dyn_castNotVal(Value *V) { if (BinaryOperator::isNot(V)) return BinaryOperator::getNotArgument(cast(V)); // Constants can be considered to be not'ed values... if (ConstantIntegral *C = dyn_cast(V)) return ConstantExpr::get(Instruction::Xor, ConstantIntegral::getAllOnesValue(C->getType()),C); return 0; } // dyn_castFoldableMul - If this value is a multiply that can be folded into // other computations (because it has a constant operand), return the // non-constant operand of the multiply. // static inline Value *dyn_castFoldableMul(Value *V) { if (V->use_size() == 1 && V->getType()->isInteger()) if (Instruction *I = dyn_cast(V)) if (I->getOpcode() == Instruction::Mul) if (isa(I->getOperand(1))) return I->getOperand(0); return 0; } // dyn_castMaskingAnd - If this value is an And instruction masking a value with // a constant, return the constant being anded with. // static inline Constant *dyn_castMaskingAnd(Value *V) { if (Instruction *I = dyn_cast(V)) if (I->getOpcode() == Instruction::And) return dyn_cast(I->getOperand(1)); // If this is a constant, it acts just like we were masking with it. return dyn_cast(V); } // Log2 - Calculate the log base 2 for the specified value if it is exactly a // power of 2. static unsigned Log2(uint64_t Val) { assert(Val > 1 && "Values 0 and 1 should be handled elsewhere!"); unsigned Count = 0; while (Val != 1) { if (Val & 1) return 0; // Multiple bits set? Val >>= 1; ++Count; } return Count; } Instruction *InstCombiner::visitAdd(BinaryOperator &I) { bool Changed = SimplifyCommutative(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_castNegVal(LHS)) return BinaryOperator::create(Instruction::Sub, RHS, V); // A + -B --> A - B if (!isa(RHS)) if (Value *V = dyn_castNegVal(RHS)) return BinaryOperator::create(Instruction::Sub, LHS, V); // X*C + X --> X * (C+1) if (dyn_castFoldableMul(LHS) == RHS) { Constant *CP1 = ConstantExpr::get(Instruction::Add, cast(cast(LHS)->getOperand(1)), ConstantInt::get(I.getType(), 1)); return BinaryOperator::create(Instruction::Mul, RHS, CP1); } // X + X*C --> X * (C+1) if (dyn_castFoldableMul(RHS) == LHS) { Constant *CP1 = ConstantExpr::get(Instruction::Add, cast(cast(RHS)->getOperand(1)), ConstantInt::get(I.getType(), 1)); return BinaryOperator::create(Instruction::Mul, LHS, CP1); } // (A & C1)+(B & C2) -> (A & C1)|(B & C2) iff C1&C2 == 0 if (Constant *C1 = dyn_castMaskingAnd(LHS)) if (Constant *C2 = dyn_castMaskingAnd(RHS)) if (ConstantExpr::get(Instruction::And, C1, C2)->isNullValue()) return BinaryOperator::create(Instruction::Or, LHS, RHS); 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 'B = x-(-A)', change to B = x+A... if (Value *V = dyn_castNegVal(Op1)) return BinaryOperator::create(Instruction::Add, Op0, V); // Replace (-1 - A) with (~A)... if (ConstantInt *C = dyn_cast(Op0)) if (C->isAllOnesValue()) return BinaryOperator::createNot(Op1); if (BinaryOperator *Op1I = dyn_cast(Op1)) if (Op1I->use_size() == 1) { // Replace (x - (y - z)) with (x + (z - y)) if the (y - z) subexpression // is not used by anyone else... // if (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); } // Replace (A - (A & B)) with (A & ~B) if this is the only use of (A&B)... // if (Op1I->getOpcode() == Instruction::And && (Op1I->getOperand(0) == Op0 || Op1I->getOperand(1) == Op0)) { Value *OtherOp = Op1I->getOperand(Op1I->getOperand(0) == Op0); Instruction *NewNot = BinaryOperator::createNot(OtherOp, "B.not", &I); return BinaryOperator::create(Instruction::And, Op0, NewNot); } // X - X*C --> X * (1-C) if (dyn_castFoldableMul(Op1I) == Op0) { Constant *CP1 = ConstantExpr::get(Instruction::Sub, ConstantInt::get(I.getType(), 1), cast(cast(Op1)->getOperand(1))); assert(CP1 && "Couldn't constant fold 1-C?"); return BinaryOperator::create(Instruction::Mul, Op0, CP1); } } // X*C - X --> X * (C-1) if (dyn_castFoldableMul(Op0) == Op1) { Constant *CP1 = ConstantExpr::get(Instruction::Sub, cast(cast(Op0)->getOperand(1)), ConstantInt::get(I.getType(), 1)); assert(CP1 && "Couldn't constant fold C - 1?"); return BinaryOperator::create(Instruction::Mul, Op1, CP1); } return 0; } Instruction *InstCombiner::visitMul(BinaryOperator &I) { bool Changed = SimplifyCommutative(I); Value *Op0 = I.getOperand(0); // Simplify mul instructions with a constant RHS... if (Constant *Op1 = dyn_cast(I.getOperand(1))) { if (ConstantInt *CI = dyn_cast(Op1)) { const Type *Ty = CI->getType(); uint64_t Val = Ty->isSigned() ? (uint64_t)cast(CI)->getValue() : cast(CI)->getValue(); switch (Val) { case 0: return ReplaceInstUsesWith(I, Op1); // Eliminate 'mul double %X, 0' case 1: return ReplaceInstUsesWith(I, Op0); // Eliminate 'mul int %X, 1' case 2: // Convert 'mul int %X, 2' to 'add int %X, %X' return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName()); } if (uint64_t C = Log2(Val)) // Replace X*(2^C) with X << C return new ShiftInst(Instruction::Shl, Op0, ConstantUInt::get(Type::UByteTy, C)); } else { ConstantFP *Op1F = cast(Op1); if (Op1F->isNullValue()) return ReplaceInstUsesWith(I, Op1); // "In IEEE floating point, x*1 is not equivalent to x for nans. However, // ANSI says we can drop signals, so we can do this anyway." (from GCC) if (Op1F->getValue() == 1.0) return ReplaceInstUsesWith(I, Op0); // Eliminate 'mul double %X, 1.0' } } if (Value *Op0v = dyn_castNegVal(Op0)) // -X * -Y = X*Y if (Value *Op1v = dyn_castNegVal(I.getOperand(1))) return BinaryOperator::create(Instruction::Mul, Op0v, Op1v); return Changed ? &I : 0; } Instruction *InstCombiner::visitDiv(BinaryOperator &I) { // div X, 1 == X if (ConstantInt *RHS = dyn_cast(I.getOperand(1))) { if (RHS->equalsInt(1)) return ReplaceInstUsesWith(I, I.getOperand(0)); // Check to see if this is an unsigned division with an exact power of 2, // if so, convert to a right shift. if (ConstantUInt *C = dyn_cast(RHS)) if (uint64_t Val = C->getValue()) // Don't break X / 0 if (uint64_t C = Log2(Val)) return new ShiftInst(Instruction::Shr, I.getOperand(0), ConstantUInt::get(Type::UByteTy, C)); } // 0 / X == 0, we don't need to preserve faults! if (ConstantInt *LHS = dyn_cast(I.getOperand(0))) if (LHS->equalsInt(0)) return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType())); return 0; } Instruction *InstCombiner::visitRem(BinaryOperator &I) { if (ConstantInt *RHS = dyn_cast(I.getOperand(1))) { if (RHS->equalsInt(1)) // X % 1 == 0 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType())); // Check to see if this is an unsigned remainder with an exact power of 2, // if so, convert to a bitwise and. if (ConstantUInt *C = dyn_cast(RHS)) if (uint64_t Val = C->getValue()) // Don't break X % 0 (divide by zero) if (Log2(Val)) return BinaryOperator::create(Instruction::And, I.getOperand(0), ConstantUInt::get(I.getType(), Val-1)); } // 0 % X == 0, we don't need to preserve faults! if (ConstantInt *LHS = dyn_cast(I.getOperand(0))) if (LHS->equalsInt(0)) 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(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(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(C)) return CU->getValue() == 1; const ConstantSInt *CS = cast(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 = SimplifyCommutative(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(Op1)) if (RHS->isAllOnesValue()) return ReplaceInstUsesWith(I, Op0); Value *Op0NotVal = dyn_castNotVal(Op0); Value *Op1NotVal = dyn_castNotVal(Op1); // (~A & ~B) == (~(A | B)) - Demorgan's Law if (Op0NotVal && Op1NotVal && isOnlyUse(Op0) && isOnlyUse(Op1)) { Instruction *Or = BinaryOperator::create(Instruction::Or, Op0NotVal, Op1NotVal,I.getName()+".demorgan", &I); WorkList.push_back(Or); return BinaryOperator::createNot(Or); } if (Op0NotVal == Op1 || Op1NotVal == Op0) // A & ~A == ~A & A == 0 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType())); return Changed ? &I : 0; } Instruction *InstCombiner::visitOr(BinaryOperator &I) { bool Changed = SimplifyCommutative(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(Op1)) if (RHS->isAllOnesValue()) return ReplaceInstUsesWith(I, Op1); Value *Op0NotVal = dyn_castNotVal(Op0); Value *Op1NotVal = dyn_castNotVal(Op1); if (Op1 == Op0NotVal) // ~A | A == -1 return ReplaceInstUsesWith(I, ConstantIntegral::getAllOnesValue(I.getType())); if (Op0 == Op1NotVal) // A | ~A == -1 return ReplaceInstUsesWith(I, ConstantIntegral::getAllOnesValue(I.getType())); // (~A | ~B) == (~(A & B)) - Demorgan's Law if (Op0NotVal && Op1NotVal && isOnlyUse(Op0) && isOnlyUse(Op1)) { Instruction *And = BinaryOperator::create(Instruction::And, Op0NotVal, Op1NotVal,I.getName()+".demorgan", &I); WorkList.push_back(And); return BinaryOperator::createNot(And); } return Changed ? &I : 0; } Instruction *InstCombiner::visitXor(BinaryOperator &I) { bool Changed = SimplifyCommutative(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(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_castNotVal(Op0)) return ReplaceInstUsesWith(I, X); // xor (setcc A, B), true = not (setcc A, B) = setncc A, B if (SetCondInst *SCI = dyn_cast(Op0)) if (SCI->use_size() == 1) return new SetCondInst(SCI->getInverseCondition(), SCI->getOperand(0), SCI->getOperand(1)); } } if (Value *X = dyn_castNotVal(Op0)) // ~A ^ A == -1 if (X == Op1) return ReplaceInstUsesWith(I, ConstantIntegral::getAllOnesValue(I.getType())); if (Value *X = dyn_castNotVal(Op1)) // A ^ ~A == -1 if (X == Op0) return ReplaceInstUsesWith(I, ConstantIntegral::getAllOnesValue(I.getType())); if (Instruction *Op1I = dyn_cast(Op1)) if (Op1I->getOpcode() == Instruction::Or) if (Op1I->getOperand(0) == Op0) { // B^(B|A) == (A|B)^B cast(Op1I)->swapOperands(); I.swapOperands(); std::swap(Op0, Op1); } else if (Op1I->getOperand(1) == Op0) { // B^(A|B) == (A|B)^B I.swapOperands(); std::swap(Op0, Op1); } if (Instruction *Op0I = dyn_cast(Op0)) if (Op0I->getOpcode() == Instruction::Or && Op0I->use_size() == 1) { if (Op0I->getOperand(0) == Op1) // (B|A)^B == (A|B)^B cast(Op0I)->swapOperands(); if (Op0I->getOperand(1) == Op1) { // (A|B)^B == A & ~B Value *NotB = BinaryOperator::createNot(Op1, Op1->getName()+".not", &I); WorkList.push_back(cast(NotB)); return BinaryOperator::create(Instruction::And, Op0I->getOperand(0), NotB); } } // (A & C1)^(B & C2) -> (A & C1)|(B & C2) iff C1^C2 == 0 if (Constant *C1 = dyn_castMaskingAnd(Op0)) if (Constant *C2 = dyn_castMaskingAnd(Op1)) if (ConstantExpr::get(Instruction::And, C1, C2)->isNullValue()) return BinaryOperator::create(Instruction::Or, Op0, Op1); return Changed ? &I : 0; } // AddOne, SubOne - Add or subtract a constant one from an integer constant... static Constant *AddOne(ConstantInt *C) { Constant *Result = ConstantExpr::get(Instruction::Add, C, ConstantInt::get(C->getType(), 1)); assert(Result && "Constant folding integer addition failed!"); return Result; } static Constant *SubOne(ConstantInt *C) { Constant *Result = ConstantExpr::get(Instruction::Sub, 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 = SimplifyCommutative(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 , 0 - Global value addresses are never null! if (isa(Op0) && isa(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(Op1)) { if (CI->isNullValue()) { if (I.getOpcode() == Instruction::SetNE) return new CastInst(Op0, Type::BoolTy, I.getName()); else if (I.getOpcode() == Instruction::SetEQ) { // seteq X, 0 -> not (cast X to bool) Instruction *Val = new CastInst(Op0, Type::BoolTy, I.getName()+".not"); InsertNewInstBefore(Val, I); return BinaryOperator::createNot(Val, I.getName()); } } // 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(ShiftInst &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); // If this is a shift of a shift, see if we can fold the two together... if (ShiftInst *Op0SI = dyn_cast(Op0)) { if (isa(Op1) && isa(Op0SI->getOperand(1))) { ConstantUInt *ShiftAmt1C = cast(Op0SI->getOperand(1)); unsigned ShiftAmt1 = ShiftAmt1C->getValue(); unsigned ShiftAmt2 = cast(Op1)->getValue(); // Check for (A << c1) << c2 and (A >> c1) >> c2 if (I.getOpcode() == Op0SI->getOpcode()) { unsigned Amt = ShiftAmt1+ShiftAmt2; // Fold into one big shift... return new ShiftInst(I.getOpcode(), Op0SI->getOperand(0), ConstantUInt::get(Type::UByteTy, Amt)); } if (I.getType()->isUnsigned()) { // Check for (A << c1) >> c2 or visaversa // Calculate bitmask for what gets shifted off the edge... Constant *C = ConstantIntegral::getAllOnesValue(I.getType()); if (I.getOpcode() == Instruction::Shr) C = ConstantExpr::getShift(Instruction::Shr, C, ShiftAmt1C); else C = ConstantExpr::getShift(Instruction::Shl, C, ShiftAmt1C); Instruction *Mask = BinaryOperator::create(Instruction::And, Op0SI->getOperand(0), C, Op0SI->getOperand(0)->getName()+".mask",&I); WorkList.push_back(Mask); // Figure out what flavor of shift we should use... if (ShiftAmt1 == ShiftAmt2) return ReplaceInstUsesWith(I, Mask); // (A << c) >> c === A & c2 else if (ShiftAmt1 < ShiftAmt2) { return new ShiftInst(I.getOpcode(), Mask, ConstantUInt::get(Type::UByteTy, ShiftAmt2-ShiftAmt1)); } else { return new ShiftInst(Op0SI->getOpcode(), Mask, ConstantUInt::get(Type::UByteTy, ShiftAmt1-ShiftAmt2)); } } } } // 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(Op1)) { unsigned TypeBits = Op0->getType()->getPrimitiveSize()*8; if (CUI->getValue() >= TypeBits && (!Op0->getType()->isSigned() || I.getOpcode() == Instruction::Shl)) return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType())); // Check to see if we are shifting left by 1. If so, turn it into an add // instruction. if (I.getOpcode() == Instruction::Shl && CUI->equalsInt(1)) // Convert 'shl int %X, 1' to 'add int %X, %X' return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName()); } // shr int -1, X = -1 (for any arithmetic shift rights of ~0) if (ConstantSInt *CSI = dyn_cast(Op0)) if (I.getOpcode() == Instruction::Shr && CSI->isAllOnesValue()) return ReplaceInstUsesWith(I, CSI); 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->isLosslesslyConvertibleTo(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; // Cases where the source and destination type are the same, but the middle // type is bigger are noops. // if (SrcSize == DstSize && MidSize > SrcSize) 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(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!"); uint64_t AndValue = (1ULL << CSrc->getType()->getPrimitiveSize()*8)-1; Constant *AndOp = ConstantUInt::get(CI.getType(), AndValue); return BinaryOperator::create(Instruction::And, CSrc->getOperand(0), AndOp); } } // If casting the result of a getelementptr instruction with no offset, turn // this into a cast of the original pointer! // if (GetElementPtrInst *GEP = dyn_cast(CI.getOperand(0))) { bool AllZeroOperands = true; for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i) if (!isa(GEP->getOperand(i)) || !cast(GEP->getOperand(i))->isNullValue()) { AllZeroOperands = false; break; } if (AllZeroOperands) { CI.setOperand(0, GEP->getOperand(0)); return &CI; } } return 0; } // CallInst simplification // Instruction *InstCombiner::visitCallInst(CallInst &CI) { if (transformConstExprCastCall(&CI)) return 0; return 0; } // InvokeInst simplification // Instruction *InstCombiner::visitInvokeInst(InvokeInst &II) { if (transformConstExprCastCall(&II)) return 0; return 0; } // getPromotedType - Return the specified type promoted as it would be to pass // though a va_arg area... static const Type *getPromotedType(const Type *Ty) { switch (Ty->getPrimitiveID()) { case Type::SByteTyID: case Type::ShortTyID: return Type::IntTy; case Type::UByteTyID: case Type::UShortTyID: return Type::UIntTy; case Type::FloatTyID: return Type::DoubleTy; default: return Ty; } } // transformConstExprCastCall - If the callee is a constexpr cast of a function, // attempt to move the cast to the arguments of the call/invoke. // bool InstCombiner::transformConstExprCastCall(CallSite CS) { if (!isa(CS.getCalledValue())) return false; ConstantExpr *CE = cast(CS.getCalledValue()); if (CE->getOpcode() != Instruction::Cast || !isa(CE->getOperand(0))) return false; ConstantPointerRef *CPR = cast(CE->getOperand(0)); if (!isa(CPR->getValue())) return false; Function *Callee = cast(CPR->getValue()); Instruction *Caller = CS.getInstruction(); // Okay, this is a cast from a function to a different type. Unless doing so // would cause a type conversion of one of our arguments, change this call to // be a direct call with arguments casted to the appropriate types. // const FunctionType *FT = Callee->getFunctionType(); const Type *OldRetTy = Caller->getType(); if (Callee->isExternal() && !OldRetTy->isLosslesslyConvertibleTo(FT->getReturnType())) return false; // Cannot transform this return value... unsigned NumActualArgs = unsigned(CS.arg_end()-CS.arg_begin()); unsigned NumCommonArgs = std::min(FT->getNumParams(), NumActualArgs); CallSite::arg_iterator AI = CS.arg_begin(); for (unsigned i = 0, e = NumCommonArgs; i != e; ++i, ++AI) { const Type *ParamTy = FT->getParamType(i); bool isConvertible = (*AI)->getType()->isLosslesslyConvertibleTo(ParamTy); if (Callee->isExternal() && !isConvertible) return false; } if (FT->getNumParams() < NumActualArgs && !FT->isVarArg() && Callee->isExternal()) return false; // Do not delete arguments unless we have a function body... // Okay, we decided that this is a safe thing to do: go ahead and start // inserting cast instructions as necessary... std::vector Args; Args.reserve(NumActualArgs); AI = CS.arg_begin(); for (unsigned i = 0; i != NumCommonArgs; ++i, ++AI) { const Type *ParamTy = FT->getParamType(i); if ((*AI)->getType() == ParamTy) { Args.push_back(*AI); } else { Instruction *Cast = new CastInst(*AI, ParamTy, "tmp"); InsertNewInstBefore(Cast, *Caller); Args.push_back(Cast); } } // If the function takes more arguments than the call was taking, add them // now... for (unsigned i = NumCommonArgs; i != FT->getNumParams(); ++i) Args.push_back(Constant::getNullValue(FT->getParamType(i))); // If we are removing arguments to the function, emit an obnoxious warning... if (FT->getNumParams() < NumActualArgs) if (!FT->isVarArg()) { std::cerr << "WARNING: While resolving call to function '" << Callee->getName() << "' arguments were dropped!\n"; } else { // Add all of the arguments in their promoted form to the arg list... for (unsigned i = FT->getNumParams(); i != NumActualArgs; ++i, ++AI) { const Type *PTy = getPromotedType((*AI)->getType()); if (PTy != (*AI)->getType()) { // Must promote to pass through va_arg area! Instruction *Cast = new CastInst(*AI, PTy, "tmp"); InsertNewInstBefore(Cast, *Caller); Args.push_back(Cast); } else { Args.push_back(*AI); } } } if (FT->getReturnType() == Type::VoidTy) Caller->setName(""); // Void type should not have a name... Instruction *NC; if (InvokeInst *II = dyn_cast(Caller)) { NC = new InvokeInst(Callee, II->getNormalDest(), II->getExceptionalDest(), Args, Caller->getName(), Caller); } else { NC = new CallInst(Callee, Args, Caller->getName(), Caller); } // Insert a cast of the return type as necessary... Value *NV = NC; if (Caller->getType() != NV->getType() && !Caller->use_empty()) { if (NV->getType() != Type::VoidTy) { NV = NC = new CastInst(NC, Caller->getType(), "tmp"); InsertNewInstBefore(NC, *Caller); AddUsesToWorkList(*Caller); } else { NV = Constant::getNullValue(Caller->getType()); } } if (Caller->getType() != Type::VoidTy && !Caller->use_empty()) Caller->replaceAllUsesWith(NV); Caller->getParent()->getInstList().erase(Caller); removeFromWorkList(Caller); return true; } // PHINode simplification // Instruction *InstCombiner::visitPHINode(PHINode &PN) { // If the PHI node only has one incoming value, eliminate the PHI node... 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, long 0' or 'getelementptr %P' // If so, eliminate the noop. if ((GEP.getNumOperands() == 2 && GEP.getOperand(1) == Constant::getNullValue(Type::LongTy)) || 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(GEP.getOperand(0))) { std::vector Indices; // Can we combine the two pointer arithmetics offsets? if (Src->getNumOperands() == 2 && isa(Src->getOperand(1)) && isa(GEP.getOperand(1))) { // Replace: gep (gep %P, long C1), long C2, ... // With: gep %P, long (C1+C2), ... Value *Sum = ConstantExpr::get(Instruction::Add, cast(Src->getOperand(1)), cast(GEP.getOperand(1))); assert(Sum && "Constant folding of longs failed!?"); GEP.setOperand(0, Src->getOperand(0)); GEP.setOperand(1, Sum); AddUsesToWorkList(*Src); // Reduce use count of Src return &GEP; } else if (Src->getNumOperands() == 2) { // Replace: gep (gep %P, long B), long A, ... // With: T = long A+B; gep %P, T, ... // Value *Sum = BinaryOperator::create(Instruction::Add, Src->getOperand(1), GEP.getOperand(1), Src->getName()+".sum", &GEP); GEP.setOperand(0, Src->getOperand(0)); GEP.setOperand(1, Sum); WorkList.push_back(cast(Sum)); return &GEP; } else if (*GEP.idx_begin() == Constant::getNullValue(Type::LongTy) && Src->getNumOperands() != 1) { // 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()); } else if (Src->getOperand(Src->getNumOperands()-1) == Constant::getNullValue(Type::LongTy)) { // If the src gep ends with a constant array index, merge this get into // it, even if we have a non-zero array index. Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end()-1); Indices.insert(Indices.end(), GEP.idx_begin(), GEP.idx_end()); } if (!Indices.empty()) return new GetElementPtrInst(Src->getOperand(0), Indices, GEP.getName()); } else if (GlobalValue *GV = dyn_cast(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 Indices; User::op_iterator I = GEP.idx_begin(), E = GEP.idx_end(); for (; I != E && isa(*I); ++I) Indices.push_back(cast(*I)); if (I == E) { // If they are all constants... Constant *CE = ConstantExpr::getGetElementPtr(ConstantPointerRef::get(GV), Indices); // Replace all uses of the GEP with the new constexpr... return ReplaceInstUsesWith(GEP, CE); } } return 0; } Instruction *InstCombiner::visitAllocationInst(AllocationInst &AI) { // Convert: malloc Ty, C - where C is a constant != 1 into: malloc [C x Ty], 1 if (AI.isArrayAllocation()) // Check C != 1 if (const ConstantUInt *C = dyn_cast(AI.getArraySize())) { const Type *NewTy = ArrayType::get(AI.getAllocatedType(), C->getValue()); AllocationInst *New = 0; // Create and insert the replacement instruction... if (isa(AI)) New = new MallocInst(NewTy, 0, AI.getName(), &AI); else { assert(isa(AI) && "Unknown type of allocation inst!"); New = new AllocaInst(NewTy, 0, AI.getName(), &AI); } // Scan to the end of the allocation instructions, to skip over a block of // allocas if possible... // BasicBlock::iterator It = New; while (isa(*It)) ++It; // Now that I is pointing to the first non-allocation-inst in the block, // insert our getelementptr instruction... // std::vector Idx(2, Constant::getNullValue(Type::LongTy)); Value *V = new GetElementPtrInst(New, Idx, New->getName()+".sub", It); // Now make everything use the getelementptr instead of the original // allocation. ReplaceInstUsesWith(AI, V); return &AI; } return 0; } Instruction *InstCombiner::visitBranchInst(BranchInst &BI) { // Change br (not X), label True, label False to: br X, label False, True if (BI.isConditional() && !isa(BI.getCondition())) if (Value *V = dyn_castNotVal(BI.getCondition())) { BasicBlock *TrueDest = BI.getSuccessor(0); BasicBlock *FalseDest = BI.getSuccessor(1); // Swap Destinations and condition... BI.setCondition(V); BI.setSuccessor(0, FalseDest); BI.setSuccessor(1, TrueDest); return &BI; } 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 ConstantPropagate 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(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 propagate 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(I->getOperand(i))) WorkList.push_back(Op); ReplaceInstUsesWith(*I, 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(); }