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Move MaskedValueIsZero up.

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Match a bunch of idioms for sign extensions, implementing InstCombine/signext.ll


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@23428 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2005-09-24 23:43:33 +00:00
parent 8a11da021b
commit 5931c54e85
1 changed files with 146 additions and 77 deletions
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223
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -385,6 +385,82 @@ static ConstantInt *SubOne(ConstantInt *C) {
ConstantInt::get(C->getType(), 1)));
}
/// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
/// this predicate to simplify operations downstream. V and Mask are known to
/// be the same type.
static bool MaskedValueIsZero(Value *V, ConstantIntegral *Mask) {
// Note, we cannot consider 'undef' to be "IsZero" here. The problem is that
// we cannot optimize based on the assumption that it is zero without changing
// to to an explicit zero. If we don't change it to zero, other code could
// optimized based on the contradictory assumption that it is non-zero.
// Because instcombine aggressively folds operations with undef args anyway,
// this won't lose us code quality.
if (Mask->isNullValue())
return true;
if (ConstantIntegral *CI = dyn_cast<ConstantIntegral>(V))
return ConstantExpr::getAnd(CI, Mask)->isNullValue();
if (Instruction *I = dyn_cast<Instruction>(V)) {
switch (I->getOpcode()) {
case Instruction::And:
// (X & C1) & C2 == 0 iff C1 & C2 == 0.
if (ConstantIntegral *CI = dyn_cast<ConstantIntegral>(I->getOperand(1)))
if (ConstantExpr::getAnd(CI, Mask)->isNullValue())
return true;
break;
case Instruction::Or:
// If the LHS and the RHS are MaskedValueIsZero, the result is also zero.
return MaskedValueIsZero(I->getOperand(1), Mask) &&
MaskedValueIsZero(I->getOperand(0), Mask);
case Instruction::Select:
// If the T and F values are MaskedValueIsZero, the result is also zero.
return MaskedValueIsZero(I->getOperand(2), Mask) &&
MaskedValueIsZero(I->getOperand(1), Mask);
case Instruction::Cast: {
const Type *SrcTy = I->getOperand(0)->getType();
if (SrcTy == Type::BoolTy)
return (Mask->getRawValue() & 1) == 0;
if (SrcTy->isInteger()) {
// (cast <ty> X to int) & C2 == 0 iff <ty> could not have contained C2.
if (SrcTy->isUnsigned() && // Only handle zero ext.
ConstantExpr::getCast(Mask, SrcTy)->isNullValue())
return true;
// If this is a noop cast, recurse.
if ((SrcTy->isSigned() && SrcTy->getUnsignedVersion() == I->getType())||
SrcTy->getSignedVersion() == I->getType()) {
Constant *NewMask =
ConstantExpr::getCast(Mask, I->getOperand(0)->getType());
return MaskedValueIsZero(I->getOperand(0),
cast<ConstantIntegral>(NewMask));
}
}
break;
}
case Instruction::Shl:
// (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0
if (ConstantUInt *SA = dyn_cast<ConstantUInt>(I->getOperand(1)))
return MaskedValueIsZero(I->getOperand(0),
cast<ConstantIntegral>(ConstantExpr::getUShr(Mask, SA)));
break;
case Instruction::Shr:
// (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
if (ConstantUInt *SA = dyn_cast<ConstantUInt>(I->getOperand(1)))
if (I->getType()->isUnsigned()) {
Constant *C1 = ConstantIntegral::getAllOnesValue(I->getType());
C1 = ConstantExpr::getShr(C1, SA);
C1 = ConstantExpr::getAnd(C1, Mask);
if (C1->isNullValue())
return true;
}
break;
}
}
return false;
}
// isTrueWhenEqual - Return true if the specified setcondinst instruction is
// true when both operands are equal...
//
@ -627,6 +703,58 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
if (isa<PHINode>(LHS))
if (Instruction *NV = FoldOpIntoPhi(I))
return NV;
ConstantInt *XorRHS;
Value *XorLHS;
if (match(LHS, m_Xor(m_Value(XorLHS), m_ConstantInt(XorRHS)))) {
unsigned TySizeBits = I.getType()->getPrimitiveSizeInBits();
int64_t RHSSExt = cast<ConstantInt>(RHSC)->getSExtValue();
uint64_t RHSZExt = cast<ConstantInt>(RHSC)->getZExtValue();
uint64_t C0080Val = 1ULL << 31;
int64_t CFF80Val = -C0080Val;
unsigned Size = 32;
do {
if (TySizeBits > Size) {
bool Found = false;
// If we have ADD(XOR(AND(X, 0xFF), 0x80), 0xF..F80), it's a sext.
// If we have ADD(XOR(AND(X, 0xFF), 0xF..F80), 0x80), it's a sext.
if (RHSSExt == CFF80Val) {
if (XorRHS->getZExtValue() == C0080Val)
Found = true;
} else if (RHSZExt == C0080Val) {
if (XorRHS->getSExtValue() == CFF80Val)
Found = true;
}
if (Found) {
// This is a sign extend if the top bits are known zero.
Constant *Mask = ConstantInt::getAllOnesValue(XorLHS->getType());
Mask = ConstantExpr::getShl(Mask,
ConstantInt::get(Type::UByteTy, 64-TySizeBits-Size));
if (!MaskedValueIsZero(XorLHS, cast<ConstantInt>(Mask)))
Size = 0; // Not a sign ext, but can't be any others either.
goto FoundSExt;
}
}
Size >>= 1;
C0080Val >>= Size;
CFF80Val >>= Size;
} while (Size >= 8);
FoundSExt:
const Type *MiddleType = 0;
switch (Size) {
default: break;
case 32: MiddleType = Type::IntTy; break;
case 16: MiddleType = Type::ShortTy; break;
case 8: MiddleType = Type::SByteTy; break;
}
if (MiddleType) {
Instruction *NewTrunc = new CastInst(XorLHS, MiddleType, "sext");
InsertNewInstBefore(NewTrunc, I);
return new CastInst(NewTrunc, I.getType());
}
}
}
// X + X --> X << 1
@ -1317,83 +1445,6 @@ struct FoldSetCCLogical {
}
};
/// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
/// this predicate to simplify operations downstream. V and Mask are known to
/// be the same type.
static bool MaskedValueIsZero(Value *V, ConstantIntegral *Mask) {
// Note, we cannot consider 'undef' to be "IsZero" here. The problem is that
// we cannot optimize based on the assumption that it is zero without changing
// to to an explicit zero. If we don't change it to zero, other code could
// optimized based on the contradictory assumption that it is non-zero.
// Because instcombine aggressively folds operations with undef args anyway,
// this won't lose us code quality.
if (Mask->isNullValue())
return true;
if (ConstantIntegral *CI = dyn_cast<ConstantIntegral>(V))
return ConstantExpr::getAnd(CI, Mask)->isNullValue();
if (Instruction *I = dyn_cast<Instruction>(V)) {
switch (I->getOpcode()) {
case Instruction::And:
// (X & C1) & C2 == 0 iff C1 & C2 == 0.
if (ConstantIntegral *CI = dyn_cast<ConstantIntegral>(I->getOperand(1)))
if (ConstantExpr::getAnd(CI, Mask)->isNullValue())
return true;
break;
case Instruction::Or:
// If the LHS and the RHS are MaskedValueIsZero, the result is also zero.
return MaskedValueIsZero(I->getOperand(1), Mask) &&
MaskedValueIsZero(I->getOperand(0), Mask);
case Instruction::Select:
// If the T and F values are MaskedValueIsZero, the result is also zero.
return MaskedValueIsZero(I->getOperand(2), Mask) &&
MaskedValueIsZero(I->getOperand(1), Mask);
case Instruction::Cast: {
const Type *SrcTy = I->getOperand(0)->getType();
if (SrcTy == Type::BoolTy)
return (Mask->getRawValue() & 1) == 0;
if (SrcTy->isInteger()) {
// (cast <ty> X to int) & C2 == 0 iff <ty> could not have contained C2.
if (SrcTy->isUnsigned() && // Only handle zero ext.
ConstantExpr::getCast(Mask, SrcTy)->isNullValue())
return true;
// If this is a noop cast, recurse.
if ((SrcTy->isSigned() && SrcTy->getUnsignedVersion() == I->getType())||
SrcTy->getSignedVersion() == I->getType()) {
Constant *NewMask =
ConstantExpr::getCast(Mask, I->getOperand(0)->getType());
return MaskedValueIsZero(I->getOperand(0),
cast<ConstantIntegral>(NewMask));
}
}
break;
}
case Instruction::Shl:
// (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0
if (ConstantUInt *SA = dyn_cast<ConstantUInt>(I->getOperand(1)))
return MaskedValueIsZero(I->getOperand(0),
cast<ConstantIntegral>(ConstantExpr::getUShr(Mask, SA)));
break;
case Instruction::Shr:
// (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
if (ConstantUInt *SA = dyn_cast<ConstantUInt>(I->getOperand(1)))
if (I->getType()->isUnsigned()) {
Constant *C1 = ConstantIntegral::getAllOnesValue(I->getType());
C1 = ConstantExpr::getShr(C1, SA);
C1 = ConstantExpr::getAnd(C1, Mask);
if (C1->isNullValue())
return true;
}
break;
}
}
return false;
}
// OptAndOp - This handles expressions of the form ((val OP C1) & C2). Where
// the Op parameter is 'OP', OpRHS is 'C1', and AndRHS is 'C2'. Op is
// guaranteed to be either a shift instruction or a binary operator.
@ -3566,6 +3617,24 @@ Instruction *InstCombiner::visitShiftInst(ShiftInst &I) {
return new ShiftInst(Op0SI->getOpcode(), Mask,
ConstantUInt::get(Type::UByteTy, ShiftAmt1-ShiftAmt2));
}
} else {
// We can handle signed (X << C1) >> C2 if it's a sign extend. In
// this case, C1 == C2 and C1 is 8, 16, or 32.
if (ShiftAmt1 == ShiftAmt2) {
const Type *SExtType = 0;
switch (ShiftAmt1) {
case 8 : SExtType = Type::SByteTy; break;
case 16: SExtType = Type::ShortTy; break;
case 32: SExtType = Type::IntTy; break;
}
if (SExtType) {
Instruction *NewTrunc = new CastInst(Op0SI->getOperand(0),
SExtType, "sext");
InsertNewInstBefore(NewTrunc, I);
return new CastInst(NewTrunc, I.getType());
}
}
}
}
}