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remove some more dead special case code

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26135 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-02-12 08:07:37 +00:00
parent f8c36f502b
commit 8d6bbdbbcb
1 changed files with 8 additions and 35 deletions
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43
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -3940,7 +3940,7 @@ Instruction *InstCombiner::visitShiftInst(ShiftInst &I) {
if (Op1 == Constant::getNullValue(Type::UByteTy) ||
Op0 == Constant::getNullValue(Op0->getType()))
return ReplaceInstUsesWith(I, Op0);
if (isa<UndefValue>(Op0)) { // undef >>s X -> undef
if (!isLeftShift && I.getType()->isSigned())
return ReplaceInstUsesWith(I, Op0);
@ -3989,6 +3989,13 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantUInt *Op1,
bool isSignedShift = Op0->getType()->isSigned();
bool isUnsignedShift = !isSignedShift;
// See if we can simplify any instructions used by the instruction whose sole
// purpose is to compute bits we don't care about.
uint64_t KnownZero, KnownOne;
if (SimplifyDemandedBits(&I, I.getType()->getIntegralTypeMask(),
KnownZero, KnownOne))
return &I;
// shl uint X, 32 = 0 and shr ubyte Y, 9 = 0, ... just don't eliminate shr
// of a signed value.
//
@ -4018,40 +4025,6 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantUInt *Op1,
return NV;
if (Op0->hasOneUse()) {
// If this is a SHL of a sign-extending cast, see if we can turn the input
// into a zero extending cast (a simple strength reduction).
if (CastInst *CI = dyn_cast<CastInst>(Op0)) {
const Type *SrcTy = CI->getOperand(0)->getType();
if (isLeftShift && SrcTy->isInteger() && SrcTy->isSigned() &&
SrcTy->getPrimitiveSizeInBits() <
CI->getType()->getPrimitiveSizeInBits()) {
// We can change it to a zero extension if we are shifting out all of
// the sign extended bits. To check this, form a mask of all of the
// sign extend bits, then shift them left and see if we have anything
// left.
Constant *Mask = ConstantIntegral::getAllOnesValue(SrcTy); // 1111
Mask = ConstantExpr::getZeroExtend(Mask, CI->getType()); // 00001111
Mask = ConstantExpr::getNot(Mask); // 1's in the sign bits: 11110000
if (ConstantExpr::getShl(Mask, Op1)->isNullValue()) {
// If the shift is nuking all of the sign bits, change this to a
// zero extension cast. To do this, cast the cast input to
// unsigned, then to the requested size.
Value *CastOp = CI->getOperand(0);
Instruction *NC =
new CastInst(CastOp, CastOp->getType()->getUnsignedVersion(),
CI->getName()+".uns");
NC = InsertNewInstBefore(NC, I);
// Finally, insert a replacement for CI.
NC = new CastInst(NC, CI->getType(), CI->getName());
CI->setName("");
NC = InsertNewInstBefore(NC, I);
WorkList.push_back(CI); // Delete CI later.
I.setOperand(0, NC);
return &I; // The SHL operand was modified.
}
}
}
if (BinaryOperator *Op0BO = dyn_cast<BinaryOperator>(Op0)) {
// Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C)
Value *V1, *V2;