llvm-6502/lib/Transforms/Scalar/InstructionCombining.cpp
2002-05-23 17:11:38 +00:00

579 lines
19 KiB
C++

//===- InstructionCombining.cpp - Combine multiple instructions -------------=//
//
// 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 DIE pass is useful. 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/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");
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));
}
public:
const char *getPassName() const { return "Instruction Combining"; }
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
// 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 *visitInstruction(Instruction *I) { return 0; }
};
}
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)))
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 *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>(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) {
if (I->use_empty()) return 0; // Don't fix dead add instructions...
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>(Op1))
if (Constant *RHS = *Constant::getNullValue(I->getType()) - *Op2) // 0 - RHS
return BinaryOperator::create(Instruction::Add, Op0, RHS, I->getName());
// 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 instructions...
bool Changed = SimplifyBinOp(I);
Value *Op1 = I->getOperand(0);
// Simplify add instructions with a constant RHS...
if (Constant *Op2 = dyn_cast<Constant>(I->getOperand(1))) {
if (I->getType()->isIntegral() && cast<ConstantInt>(Op2)->equalsInt(1)){
// Eliminate 'mul int %X, 1'
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;
}
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
//
Instruction *InstCombiner::visitMemAccessInst(MemAccessInst *MAI) {
GetElementPtrInst *Src =
dyn_cast<GetElementPtrInst>(MAI->getPointerOperand());
if (!Src) return 0;
std::vector<Value *> Indices;
// Only special case we have to watch out for is pointer arithmetic on the
// 0th index of MAI.
unsigned FirstIdx = MAI->getFirstIndexOperandNumber();
if (FirstIdx == MAI->getNumOperands() ||
(FirstIdx == MAI->getNumOperands()-1 &&
MAI->getOperand(FirstIdx) == ConstantUInt::get(Type::UIntTy, 0))) {
// Replace the index list on this MAI with the index on the getelementptr
Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end());
} else if (*MAI->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(), MAI->idx_begin()+1, MAI->idx_end());
}
if (Indices.empty()) return 0; // Can't do the fold?
switch (MAI->getOpcode()) {
case Instruction::GetElementPtr:
return new GetElementPtrInst(Src->getOperand(0), Indices, MAI->getName());
case Instruction::Load:
return new LoadInst(Src->getOperand(0), Indices, MAI->getName());
case Instruction::Store:
return new StoreInst(MAI->getOperand(0), Src->getOperand(0), Indices);
default:
assert(0 && "Unknown memaccessinst!");
break;
}
abort();
return 0;
}
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();
// 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) {
// 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);
Changed = true;
}
}
return Changed;
}
Pass *createInstructionCombiningPass() {
return new InstCombiner();
}