//
// InstructionCombining - Combine instructions to form fewer, simple
// instructions. This pass does not modify the CFG, and has a tendancy to
-// make instructions dead, so a subsequent DCE pass is useful.
+// make instructions dead, so a subsequent DIE pass is useful. This pass is
+// where algebraic simplification happens.
//
// This pass combines things like:
// %Y = add int 1, %X
//
//===----------------------------------------------------------------------===//
-#include "llvm/Transforms/Scalar/InstructionCombining.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/ConstantHandling.h"
-#include "llvm/Function.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 "../TransformInternals.h"
+#include "Support/StatisticReporter.h"
+#include <algorithm>
+static Statistic<> NumCombined("instcombine\t- Number of insts combined");
namespace {
class InstCombiner : public FunctionPass,
}
public:
+ const char *getPassName() const { return "Instruction Combining"; }
+
virtual bool runOnFunction(Function *F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
// I - Change was made, I is still valid
// otherwise - Change was made, replace I with returned instruction
//
-
+ Instruction *visitNot(UnaryOperator *I);
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);
Instruction *visitMemAccessInst(MemAccessInst *MAI);
// visitInstruction - Specify what to return for unhandled instructions...
}
+Instruction *InstCombiner::visitNot(UnaryOperator *I) {
+ if (I->use_empty()) return 0; // Don't fix dead instructions...
+
+ // not (not X) = X
+ if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(0)))
+ if (Op->getOpcode() == Instruction::Not) {
+ AddUsesToWorkList(I); // Add all modified instrs to worklist
+ I->replaceAllUsesWith(Op->getOperand(0));
+ return I;
+ }
+ return 0;
+}
+
// 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)))
- if (!I->swapOperands())
- return true;
+ 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;
+}
+
Instruction *InstCombiner::visitAdd(BinaryOperator *I) {
if (I->use_empty()) return 0; // Don't fix dead add instructions...
bool Changed = SimplifyBinOp(I);
- Value *Op1 = I->getOperand(0);
+ Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
+
+ // Eliminate 'add int %X, 0'
+ if (RHS == Constant::getNullValue(I->getType())) {
+ AddUsesToWorkList(I); // Add all modified instrs to worklist
+ I->replaceAllUsesWith(LHS);
+ return I;
+ }
+
+ // -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>(I->getOperand(1))) {
- // Eliminate 'add int %X, 0'
- if (I->getType()->isIntegral() && Op2->isNullValue()) {
- AddUsesToWorkList(I); // Add all modified instrs to worklist
- I->replaceAllUsesWith(Op1);
- return I;
- }
-
- if (BinaryOperator *IOp1 = dyn_cast<BinaryOperator>(Op1)) {
- Changed |= SimplifyBinOp(IOp1);
-
- if (IOp1->getOpcode() == Instruction::Add &&
- isa<Constant>(IOp1->getOperand(1))) {
+ 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>(IOp1->getOperand(1))) {
- I->setOperand(0, IOp1->getOperand(0));
+ if (Constant *Val = *Op2 + *cast<Constant>(ILHS->getOperand(1))) {
+ I->setOperand(0, ILHS->getOperand(0));
I->setOperand(1, Val);
return I;
}
Instruction *InstCombiner::visitSub(BinaryOperator *I) {
if (I->use_empty()) return 0; // Don't fix dead add instructions...
- bool Changed = SimplifyBinOp(I);
+ Value *Op0 = I->getOperand(0), *Op1 = I->getOperand(1);
+
+ if (Op0 == Op1) { // sub X, X -> 0
+ AddUsesToWorkList(I); // Add all modified instrs to worklist
+ I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
+ return I;
+ }
// 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>(I->getOperand(1)))
- // Calculate 0 - RHS
- if (Constant *RHS = *Constant::getNullValue(I->getType()) - *Op2) {
- return BinaryOperator::create(Instruction::Add, I->getOperand(0), RHS,
- I->getName());
- }
+ 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());
- return Changed ? I : 0;
+ // If this is a 'C = x-B', check to see if 'B = -A', so that C = 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) {
- if (I->use_empty()) return 0; // Don't fix dead add instructions...
+ if (I->use_empty()) return 0; // Don't fix dead instructions...
bool Changed = SimplifyBinOp(I);
Value *Op1 = I->getOperand(0);
AddUsesToWorkList(I); // Add all modified instrs to worklist
I->replaceAllUsesWith(Op1);
return I;
+
+ } else if (I->getType()->isIntegral() &&
+ cast<ConstantInt>(Op2)->equalsInt(2)) {
+ // Convert 'mul int %X, 2' to 'add int %X, %X'
+ return BinaryOperator::create(Instruction::Add, Op1, Op1, I->getName());
+
+ } else if (Op2->isNullValue()) {
+ // Eliminate 'mul int %X, 0'
+ AddUsesToWorkList(I); // Add all modified instrs to worklist
+ I->replaceAllUsesWith(Op2); // Set this value to zero directly
+ return I;
+ }
+ }
+
+ return Changed ? I : 0;
+}
+
+
+Instruction *InstCombiner::visitDiv(BinaryOperator *I) {
+ if (I->use_empty()) return 0; // Don't fix dead instructions...
+
+ // div X, 1 == X
+ if (ConstantInt *RHS = dyn_cast<ConstantInt>(I->getOperand(1)))
+ if (RHS->equalsInt(1)) {
+ AddUsesToWorkList(I); // Add all modified instrs to worklist
+ I->replaceAllUsesWith(I->getOperand(0));
+ return I;
+ }
+ return 0;
+}
+
+
+Instruction *InstCombiner::visitRem(BinaryOperator *I) {
+ if (I->use_empty()) return 0; // Don't fix dead instructions...
+
+ // rem X, 1 == 0
+ if (ConstantInt *RHS = dyn_cast<ConstantInt>(I->getOperand(1)))
+ if (RHS->equalsInt(1)) {
+ AddUsesToWorkList(I); // Add all modified instrs to worklist
+ I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
+ return I;
+ }
+ return 0;
+}
+
+static Constant *getMaxValue(const Type *Ty) {
+ assert(Ty == Type::BoolTy || Ty->isIntegral());
+ if (Ty == Type::BoolTy)
+ return ConstantBool::True;
+
+ if (Ty->isSigned())
+ return ConstantSInt::get(Ty, -1);
+ else if (Ty->isUnsigned()) {
+ // Calculate -1 casted to the right type...
+ unsigned TypeBits = Ty->getPrimitiveSize()*8;
+ uint64_t Val = (uint64_t)-1LL; // All ones
+ Val >>= 64-TypeBits; // Shift out unwanted 1 bits...
+ return ConstantUInt::get(Ty, Val);
+ }
+ return 0;
+}
+
+
+Instruction *InstCombiner::visitAnd(BinaryOperator *I) {
+ if (I->use_empty()) return 0; // Don't fix dead instructions...
+ 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())) {
+ AddUsesToWorkList(I); // Add all modified instrs to worklist
+ I->replaceAllUsesWith(Op1);
+ return I;
+ }
+
+ // and X, -1 == X
+ if (Constant *RHS = dyn_cast<Constant>(Op1))
+ if (RHS == getMaxValue(I->getType())) {
+ AddUsesToWorkList(I); // Add all modified instrs to worklist
+ I->replaceAllUsesWith(Op0);
+ return I;
+ }
+
+ return Changed ? I : 0;
+}
+
+
+
+Instruction *InstCombiner::visitOr(BinaryOperator *I) {
+ if (I->use_empty()) return 0; // Don't fix dead instructions...
+ 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())) {
+ AddUsesToWorkList(I); // Add all modified instrs to worklist
+ I->replaceAllUsesWith(Op0);
+ return I;
+ }
+
+ // or X, -1 == -1
+ if (Constant *RHS = dyn_cast<Constant>(Op1))
+ if (RHS == getMaxValue(I->getType())) {
+ AddUsesToWorkList(I); // Add all modified instrs to worklist
+ I->replaceAllUsesWith(Op1);
+ return I;
}
+
+ return Changed ? I : 0;
+}
+
+
+
+Instruction *InstCombiner::visitXor(BinaryOperator *I) {
+ if (I->use_empty()) return 0; // Don't fix dead instructions...
+ bool Changed = SimplifyBinOp(I);
+ Value *Op0 = I->getOperand(0), *Op1 = I->getOperand(1);
+
+ // xor X, X = 0
+ if (Op0 == Op1) {
+ AddUsesToWorkList(I); // Add all modified instrs to worklist
+ I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
+ return I;
+ }
+
+ // xor X, 0 == X
+ if (Op1 == Constant::getNullValue(I->getType())) {
+ AddUsesToWorkList(I); // Add all modified instrs to worklist
+ I->replaceAllUsesWith(Op0);
+ return I;
+ }
+
+ return Changed ? I : 0;
+}
+
+// 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) {
+ if (I->use_empty()) return 0; // Don't fix dead instructions...
+ bool Changed = SimplifyBinOp(I);
+
+ // setcc X, X
+ if (I->getOperand(0) == I->getOperand(1)) {
+ AddUsesToWorkList(I); // Add all modified instrs to worklist
+ I->replaceAllUsesWith(ConstantBool::get(isTrueWhenEqual(I)));
+ return I;
+ }
+
+ // setcc <global*>, 0 - Global value addresses are never null!
+ if (isa<GlobalValue>(I->getOperand(0)) &&
+ isa<ConstantPointerNull>(I->getOperand(1))) {
+ AddUsesToWorkList(I); // Add all modified instrs to worklist
+ I->replaceAllUsesWith(ConstantBool::get(!isTrueWhenEqual(I)));
+ return I;
}
return Changed ? I : 0;
}
-// CastInst simplification - If the user is casting a value to the same type,
-// eliminate this cast instruction...
+
+Instruction *InstCombiner::visitShiftInst(Instruction *I) {
+ if (I->use_empty()) return 0; // Don't fix dead instructions...
+ 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())) {
+ AddUsesToWorkList(I); // Add all modified instrs to worklist
+ I->replaceAllUsesWith(Op0);
+ return I;
+ }
+
+ // shl int X, 32 = 0 and shr sbyte 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)) {
+ AddUsesToWorkList(I); // Add all modified instrs to worklist
+ I->replaceAllUsesWith(Constant::getNullValue(Op0->getType()));
+ return I;
+ }
+ }
+ 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 (SrcTy == DstTy) return true;
+
+ // Allow free casting and conversion of sizes as long as the sign doesn't
+ // change...
+ if (SrcTy->isSigned() == MidTy->isSigned() &&
+ MidTy->isSigned() == DstTy->isSigned())
+ return true;
+
+ // 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 (CI->use_empty()) return 0; // Don't fix dead instructions...
+
+ // If the user is casting a value to the same type, eliminate this cast
+ // instruction...
if (CI->getType() == CI->getOperand(0)->getType() && !CI->use_empty()) {
AddUsesToWorkList(CI); // Add all modified instrs to worklist
CI->replaceAllUsesWith(CI->getOperand(0));
return CI;
}
+
+
+ // 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;
+ }
+
+ return 0;
+}
+
+
+// PHINode simplification
+//
+Instruction *InstCombiner::visitPHINode(PHINode *PN) {
+ if (PN->use_empty()) return 0; // Don't fix dead instructions...
+
+ // If the PHI node only has one incoming value, eliminate the PHI node...
+ if (PN->getNumIncomingValues() == 1) {
+ AddUsesToWorkList(PN); // Add all modified instrs to worklist
+ PN->replaceAllUsesWith(PN->getIncomingValue(0));
+ return PN;
+ }
+
return 0;
}
+
+Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst *GEP) {
+ // Is it getelementptr %P, uint 0
+ // If so, elminate the noop.
+ if (GEP->getNumOperands() == 2 && !GEP->use_empty() &&
+ GEP->getOperand(1) == Constant::getNullValue(Type::UIntTy)) {
+ AddUsesToWorkList(GEP); // Add all modified instrs to worklist
+ GEP->replaceAllUsesWith(GEP->getOperand(0));
+ return GEP;
+ }
+
+ return visitMemAccessInst(GEP);
+}
+
+
// Combine Indices - If the source pointer to this mem access instruction is a
// getelementptr instruction, combine the indices of the GEP into this
// instruction
// Now that we have an instruction, try combining it to simplify it...
Instruction *Result = visit(I);
if (Result) {
+ ++NumCombined;
// Should we replace the old instruction with a new one?
- if (Result != I)
+ 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.
+ std::vector<Instruction*>::iterator It = std::find(WorkList.begin(),
+ WorkList.end(), I);
+ while (It != WorkList.end()) {
+ It = WorkList.erase(It);
+ It = std::find(It, WorkList.end(), I);
+ }
+
ReplaceInstWithInst(I, Result);
+ }
WorkList.push_back(Result);
AddUsesToWorkList(Result);
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