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llvm-mirror/lib/Analysis/InstructionSimplify.cpp
Duncan Sands f68789ed87 Factorize code, no functionality change. 
llvm-svn: 118516
2010-11-09 17:25:51 +00:00

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//===- InstructionSimplify.cpp - Fold instruction operands ----------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements routines for folding instructions into simpler forms
// that do not require creating new instructions. For example, this does
// constant folding, and can handle identities like (X&0)->0.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Support/ValueHandle.h"
#include "llvm/Instructions.h"
#include "llvm/Support/PatternMatch.h"
using namespace llvm;
using namespace llvm::PatternMatch;
/// SimplifyAddInst - Given operands for an Add, see if we can
/// fold the result. If not, this returns null.
Value *llvm::SimplifyAddInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW,
const TargetData *TD) {
if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
Constant *Ops[] = { CLHS, CRHS };
return ConstantFoldInstOperands(Instruction::Add, CLHS->getType(),
Ops, 2, TD);
}
// Canonicalize the constant to the RHS.
std::swap(Op0, Op1);
}
if (Constant *Op1C = dyn_cast<Constant>(Op1)) {
// X + undef -> undef
if (isa<UndefValue>(Op1C))
return Op1C;
// X + 0 --> X
if (Op1C->isNullValue())
return Op0;
}
// FIXME: Could pull several more out of instcombine.
return 0;
}
/// SimplifyAndInst - Given operands for an And, see if we can
/// fold the result. If not, this returns null.
Value *llvm::SimplifyAndInst(Value *Op0, Value *Op1, const TargetData *TD) {
if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
Constant *Ops[] = { CLHS, CRHS };
return ConstantFoldInstOperands(Instruction::And, CLHS->getType(),
Ops, 2, TD);
}
// Canonicalize the constant to the RHS.
std::swap(Op0, Op1);
}
// X & undef -> 0
if (isa<UndefValue>(Op1))
return Constant::getNullValue(Op0->getType());
// X & X = X
if (Op0 == Op1)
return Op0;
// X & <0,0> = <0,0>
if (isa<ConstantAggregateZero>(Op1))
return Op1;
// X & <-1,-1> = X
if (ConstantVector *CP = dyn_cast<ConstantVector>(Op1))
if (CP->isAllOnesValue())
return Op0;
if (ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1)) {
// X & 0 = 0
if (Op1CI->isZero())
return Op1CI;
// X & -1 = X
if (Op1CI->isAllOnesValue())
return Op0;
}
// A & ~A = ~A & A = 0
Value *A, *B;
if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
(match(Op1, m_Not(m_Value(A))) && A == Op0))
return Constant::getNullValue(Op0->getType());
// (A | ?) & A = A
if (match(Op0, m_Or(m_Value(A), m_Value(B))) &&
(A == Op1 || B == Op1))
return Op1;
// A & (A | ?) = A
if (match(Op1, m_Or(m_Value(A), m_Value(B))) &&
(A == Op0 || B == Op0))
return Op0;
// (A & B) & A -> A & B
if (match(Op0, m_And(m_Value(A), m_Value(B))) &&
(A == Op1 || B == Op1))
return Op0;
// A & (A & B) -> A & B
if (match(Op1, m_And(m_Value(A), m_Value(B))) &&
(A == Op0 || B == Op0))
return Op1;
return 0;
}
/// SimplifyOrInst - Given operands for an Or, see if we can
/// fold the result. If not, this returns null.
Value *llvm::SimplifyOrInst(Value *Op0, Value *Op1, const TargetData *TD) {
if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
Constant *Ops[] = { CLHS, CRHS };
return ConstantFoldInstOperands(Instruction::Or, CLHS->getType(),
Ops, 2, TD);
}
// Canonicalize the constant to the RHS.
std::swap(Op0, Op1);
}
// X | undef -> -1
if (isa<UndefValue>(Op1))
return Constant::getAllOnesValue(Op0->getType());
// X | X = X
if (Op0 == Op1)
return Op0;
// X | <0,0> = X
if (isa<ConstantAggregateZero>(Op1))
return Op0;
// X | <-1,-1> = <-1,-1>
if (ConstantVector *CP = dyn_cast<ConstantVector>(Op1))
if (CP->isAllOnesValue())
return Op1;
if (ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1)) {
// X | 0 = X
if (Op1CI->isZero())
return Op0;
// X | -1 = -1
if (Op1CI->isAllOnesValue())
return Op1CI;
}
// A | ~A = ~A | A = -1
Value *A, *B;
if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
(match(Op1, m_Not(m_Value(A))) && A == Op0))
return Constant::getAllOnesValue(Op0->getType());
// (A & ?) | A = A
if (match(Op0, m_And(m_Value(A), m_Value(B))) &&
(A == Op1 || B == Op1))
return Op1;
// A | (A & ?) = A
if (match(Op1, m_And(m_Value(A), m_Value(B))) &&
(A == Op0 || B == Op0))
return Op0;
// (A | B) | A -> A | B
if (match(Op0, m_Or(m_Value(A), m_Value(B))) &&
(A == Op1 || B == Op1))
return Op0;
// A | (A | B) -> A | B
if (match(Op1, m_Or(m_Value(A), m_Value(B))) &&
(A == Op0 || B == Op0))
return Op1;
return 0;
}
static const Type *GetCompareTy(Value *Op) {
return CmpInst::makeCmpResultType(Op->getType());
}
/// ThreadCmpOverSelect - In the case of a comparison with a select instruction,
/// try to simplify the comparison by seeing whether both branches of the select
/// result in the same value. Returns the common value if so, otherwise returns
/// null.
static Value *ThreadCmpOverSelect(CmpInst::Predicate Pred, Value *LHS,
Value *RHS, const TargetData *TD) {
// Make sure the select is on the LHS.
if (!isa<SelectInst>(LHS)) {
std::swap(LHS, RHS);
Pred = CmpInst::getSwappedPredicate(Pred);
}
assert(isa<SelectInst>(LHS) && "Not comparing with a select instruction!");
SelectInst *SI = cast<SelectInst>(LHS);
// Now that we have "cmp select(cond, TV, FV), RHS", analyse it.
// Does "cmp TV, RHS" simplify?
if (Value *TCmp = SimplifyCmpInst(Pred, SI->getTrueValue(), RHS, TD))
// It does! Does "cmp FV, RHS" simplify?
if (Value *FCmp = SimplifyCmpInst(Pred, SI->getFalseValue(), RHS, TD))
// It does! If they simplified to the same value, then use it as the
// result of the original comparison.
if (TCmp == FCmp)
return TCmp;
return 0;
}
/// SimplifyICmpInst - Given operands for an ICmpInst, see if we can
/// fold the result. If not, this returns null.
Value *llvm::SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
const TargetData *TD) {
CmpInst::Predicate Pred = (CmpInst::Predicate)Predicate;
assert(CmpInst::isIntPredicate(Pred) && "Not an integer compare!");
if (Constant *CLHS = dyn_cast<Constant>(LHS)) {
if (Constant *CRHS = dyn_cast<Constant>(RHS))
return ConstantFoldCompareInstOperands(Pred, CLHS, CRHS, TD);
// If we have a constant, make sure it is on the RHS.
std::swap(LHS, RHS);
Pred = CmpInst::getSwappedPredicate(Pred);
}
// ITy - This is the return type of the compare we're considering.
const Type *ITy = GetCompareTy(LHS);
// icmp X, X -> true/false
// X icmp undef -> true/false. For example, icmp ugt %X, undef -> false
// because X could be 0.
if (LHS == RHS || isa<UndefValue>(RHS))
return ConstantInt::get(ITy, CmpInst::isTrueWhenEqual(Pred));
// icmp <global/alloca*/null>, <global/alloca*/null> - Global/Stack value
// addresses never equal each other! We already know that Op0 != Op1.
if ((isa<GlobalValue>(LHS) || isa<AllocaInst>(LHS) ||
isa<ConstantPointerNull>(LHS)) &&
(isa<GlobalValue>(RHS) || isa<AllocaInst>(RHS) ||
isa<ConstantPointerNull>(RHS)))
return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
// See if we are doing a comparison with a constant.
if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) {
// If we have an icmp le or icmp ge instruction, turn it into the
// appropriate icmp lt or icmp gt instruction. This allows us to rely on
// them being folded in the code below.
switch (Pred) {
default: break;
case ICmpInst::ICMP_ULE:
if (CI->isMaxValue(false)) // A <=u MAX -> TRUE
return ConstantInt::getTrue(CI->getContext());
break;
case ICmpInst::ICMP_SLE:
if (CI->isMaxValue(true)) // A <=s MAX -> TRUE
return ConstantInt::getTrue(CI->getContext());
break;
case ICmpInst::ICMP_UGE:
if (CI->isMinValue(false)) // A >=u MIN -> TRUE
return ConstantInt::getTrue(CI->getContext());
break;
case ICmpInst::ICMP_SGE:
if (CI->isMinValue(true)) // A >=s MIN -> TRUE
return ConstantInt::getTrue(CI->getContext());
break;
}
}
// If the comparison is with the result of a select instruction, check whether
// comparing with either branch of the select always yields the same value.
if (isa<SelectInst>(LHS) || isa<SelectInst>(RHS))
if (Value *V = ThreadCmpOverSelect(Pred, LHS, RHS, TD))
return V;
return 0;
}
/// SimplifyFCmpInst - Given operands for an FCmpInst, see if we can
/// fold the result. If not, this returns null.
Value *llvm::SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
const TargetData *TD) {
CmpInst::Predicate Pred = (CmpInst::Predicate)Predicate;
assert(CmpInst::isFPPredicate(Pred) && "Not an FP compare!");
if (Constant *CLHS = dyn_cast<Constant>(LHS)) {
if (Constant *CRHS = dyn_cast<Constant>(RHS))
return ConstantFoldCompareInstOperands(Pred, CLHS, CRHS, TD);
// If we have a constant, make sure it is on the RHS.
std::swap(LHS, RHS);
Pred = CmpInst::getSwappedPredicate(Pred);
}
// Fold trivial predicates.
if (Pred == FCmpInst::FCMP_FALSE)
return ConstantInt::get(GetCompareTy(LHS), 0);
if (Pred == FCmpInst::FCMP_TRUE)
return ConstantInt::get(GetCompareTy(LHS), 1);
if (isa<UndefValue>(RHS)) // fcmp pred X, undef -> undef
return UndefValue::get(GetCompareTy(LHS));
// fcmp x,x -> true/false. Not all compares are foldable.
if (LHS == RHS) {
if (CmpInst::isTrueWhenEqual(Pred))
return ConstantInt::get(GetCompareTy(LHS), 1);
if (CmpInst::isFalseWhenEqual(Pred))
return ConstantInt::get(GetCompareTy(LHS), 0);
}
// Handle fcmp with constant RHS
if (Constant *RHSC = dyn_cast<Constant>(RHS)) {
// If the constant is a nan, see if we can fold the comparison based on it.
if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHSC)) {
if (CFP->getValueAPF().isNaN()) {
if (FCmpInst::isOrdered(Pred)) // True "if ordered and foo"
return ConstantInt::getFalse(CFP->getContext());
assert(FCmpInst::isUnordered(Pred) &&
"Comparison must be either ordered or unordered!");
// True if unordered.
return ConstantInt::getTrue(CFP->getContext());
}
// Check whether the constant is an infinity.
if (CFP->getValueAPF().isInfinity()) {
if (CFP->getValueAPF().isNegative()) {
switch (Pred) {
case FCmpInst::FCMP_OLT:
// No value is ordered and less than negative infinity.
return ConstantInt::getFalse(CFP->getContext());
case FCmpInst::FCMP_UGE:
// All values are unordered with or at least negative infinity.
return ConstantInt::getTrue(CFP->getContext());
default:
break;
}
} else {
switch (Pred) {
case FCmpInst::FCMP_OGT:
// No value is ordered and greater than infinity.
return ConstantInt::getFalse(CFP->getContext());
case FCmpInst::FCMP_ULE:
// All values are unordered with and at most infinity.
return ConstantInt::getTrue(CFP->getContext());
default:
break;
}
}
}
}
}
// If the comparison is with the result of a select instruction, check whether
// comparing with either branch of the select always yields the same value.
if (isa<SelectInst>(LHS) || isa<SelectInst>(RHS))
if (Value *V = ThreadCmpOverSelect(Pred, LHS, RHS, TD))
return V;
return 0;
}
/// SimplifySelectInst - Given operands for a SelectInst, see if we can fold
/// the result. If not, this returns null.
Value *llvm::SimplifySelectInst(Value *CondVal, Value *TrueVal, Value *FalseVal,
const TargetData *TD) {
// select true, X, Y -> X
// select false, X, Y -> Y
if (ConstantInt *CB = dyn_cast<ConstantInt>(CondVal))
return CB->getZExtValue() ? TrueVal : FalseVal;
// select C, X, X -> X
if (TrueVal == FalseVal)
return TrueVal;
if (isa<UndefValue>(TrueVal)) // select C, undef, X -> X
return FalseVal;
if (isa<UndefValue>(FalseVal)) // select C, X, undef -> X
return TrueVal;
if (isa<UndefValue>(CondVal)) { // select undef, X, Y -> X or Y
if (isa<Constant>(TrueVal))
return TrueVal;
return FalseVal;
}
return 0;
}
/// SimplifyGEPInst - Given operands for an GetElementPtrInst, see if we can
/// fold the result. If not, this returns null.
Value *llvm::SimplifyGEPInst(Value *const *Ops, unsigned NumOps,
const TargetData *TD) {
// getelementptr P -> P.
if (NumOps == 1)
return Ops[0];
// TODO.
//if (isa<UndefValue>(Ops[0]))
// return UndefValue::get(GEP.getType());
// getelementptr P, 0 -> P.
if (NumOps == 2)
if (ConstantInt *C = dyn_cast<ConstantInt>(Ops[1]))
if (C->isZero())
return Ops[0];
// Check to see if this is constant foldable.
for (unsigned i = 0; i != NumOps; ++i)
if (!isa<Constant>(Ops[i]))
return 0;
return ConstantExpr::getGetElementPtr(cast<Constant>(Ops[0]),
(Constant *const*)Ops+1, NumOps-1);
}
//=== Helper functions for higher up the class hierarchy.
/// SimplifyBinOp - Given operands for a BinaryOperator, see if we can
/// fold the result. If not, this returns null.
Value *llvm::SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS,
const TargetData *TD) {
switch (Opcode) {
case Instruction::And: return SimplifyAndInst(LHS, RHS, TD);
case Instruction::Or: return SimplifyOrInst(LHS, RHS, TD);
default:
if (Constant *CLHS = dyn_cast<Constant>(LHS))
if (Constant *CRHS = dyn_cast<Constant>(RHS)) {
Constant *COps[] = {CLHS, CRHS};
return ConstantFoldInstOperands(Opcode, LHS->getType(), COps, 2, TD);
}
return 0;
}
}
/// SimplifyCmpInst - Given operands for a CmpInst, see if we can
/// fold the result.
Value *llvm::SimplifyCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
const TargetData *TD) {
if (CmpInst::isIntPredicate((CmpInst::Predicate)Predicate))
return SimplifyICmpInst(Predicate, LHS, RHS, TD);
return SimplifyFCmpInst(Predicate, LHS, RHS, TD);
}
/// SimplifyInstruction - See if we can compute a simplified version of this
/// instruction. If not, this returns null.
Value *llvm::SimplifyInstruction(Instruction *I, const TargetData *TD) {
switch (I->getOpcode()) {
default:
return ConstantFoldInstruction(I, TD);
case Instruction::Add:
return SimplifyAddInst(I->getOperand(0), I->getOperand(1),
cast<BinaryOperator>(I)->hasNoSignedWrap(),
cast<BinaryOperator>(I)->hasNoUnsignedWrap(), TD);
case Instruction::And:
return SimplifyAndInst(I->getOperand(0), I->getOperand(1), TD);
case Instruction::Or:
return SimplifyOrInst(I->getOperand(0), I->getOperand(1), TD);
case Instruction::ICmp:
return SimplifyICmpInst(cast<ICmpInst>(I)->getPredicate(),
I->getOperand(0), I->getOperand(1), TD);
case Instruction::FCmp:
return SimplifyFCmpInst(cast<FCmpInst>(I)->getPredicate(),
I->getOperand(0), I->getOperand(1), TD);
case Instruction::Select:
return SimplifySelectInst(I->getOperand(0), I->getOperand(1),
I->getOperand(2), TD);
case Instruction::GetElementPtr: {
SmallVector<Value*, 8> Ops(I->op_begin(), I->op_end());
return SimplifyGEPInst(&Ops[0], Ops.size(), TD);
}
}
}
/// ReplaceAndSimplifyAllUses - Perform From->replaceAllUsesWith(To) and then
/// delete the From instruction. In addition to a basic RAUW, this does a
/// recursive simplification of the newly formed instructions. This catches
/// things where one simplification exposes other opportunities. This only
/// simplifies and deletes scalar operations, it does not change the CFG.
///
void llvm::ReplaceAndSimplifyAllUses(Instruction *From, Value *To,
const TargetData *TD) {
assert(From != To && "ReplaceAndSimplifyAllUses(X,X) is not valid!");
// FromHandle/ToHandle - This keeps a WeakVH on the from/to values so that
// we can know if it gets deleted out from under us or replaced in a
// recursive simplification.
WeakVH FromHandle(From);
WeakVH ToHandle(To);
while (!From->use_empty()) {
// Update the instruction to use the new value.
Use &TheUse = From->use_begin().getUse();
Instruction *User = cast<Instruction>(TheUse.getUser());
TheUse = To;
// Check to see if the instruction can be folded due to the operand
// replacement. For example changing (or X, Y) into (or X, -1) can replace
// the 'or' with -1.
Value *SimplifiedVal;
{
// Sanity check to make sure 'User' doesn't dangle across
// SimplifyInstruction.
AssertingVH<> UserHandle(User);
SimplifiedVal = SimplifyInstruction(User, TD);
if (SimplifiedVal == 0) continue;
}
// Recursively simplify this user to the new value.
ReplaceAndSimplifyAllUses(User, SimplifiedVal, TD);
From = dyn_cast_or_null<Instruction>((Value*)FromHandle);
To = ToHandle;
assert(ToHandle && "To value deleted by recursive simplification?");
// If the recursive simplification ended up revisiting and deleting
// 'From' then we're done.
if (From == 0)
return;
}
// If 'From' has value handles referring to it, do a real RAUW to update them.
From->replaceAllUsesWith(To);
From->eraseFromParent();
}
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