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Enhance analysis of srem.

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Remove dead code analyzing urem. 'urem' of power-of-2 is canonicalized to an
'and' instruction.

llvm-svn: 53506
This commit is contained in:
Nick Lewycky 2008-07-12 05:04:38 +00:00
parent c69b53dff9
commit 3fb5816774
2 changed files with 12 additions and 15 deletions
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18
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -1254,6 +1254,9 @@ bool InstCombiner::SimplifyDemandedBits(Value *V, APInt DemandedMask,
if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
APInt RA = Rem->getValue();
if (RA.isPowerOf2() || (-RA).isPowerOf2()) {
if (DemandedMask.ule(RA)) // srem won't affect demanded bits
return UpdateValueUsesWith(I, I->getOperand(0));
APInt LowBits = RA.isStrictlyPositive() ? (RA - 1) : ~RA;
APInt Mask2 = LowBits | APInt::getSignBit(BitWidth);
if (SimplifyDemandedBits(I->getOperand(0), Mask2,
@ -1273,21 +1276,6 @@ bool InstCombiner::SimplifyDemandedBits(Value *V, APInt DemandedMask,
}
break;
case Instruction::URem: {
if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
APInt RA = Rem->getValue();
if (RA.isPowerOf2()) {
APInt LowBits = (RA - 1);
APInt Mask2 = LowBits & DemandedMask;
KnownZero |= ~LowBits & DemandedMask;
if (SimplifyDemandedBits(I->getOperand(0), Mask2,
KnownZero, KnownOne, Depth+1))
return true;
assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
break;
}
}
APInt KnownZero2(BitWidth, 0), KnownOne2(BitWidth, 0);
APInt AllOnes = APInt::getAllOnesValue(BitWidth);
if (SimplifyDemandedBits(I->getOperand(0), AllOnes,

9
test/Transforms/InstCombine/2008-07-11-RemAnd.ll Normal file
View File

@ -0,0 +1,9 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep rem
; PR2330
define i32 @a(i32 %b) nounwind {
entry:
srem i32 %b, 8 ; <i32>:0 [#uses=1]
and i32 %0, 1 ; <i32>:1 [#uses=1]
ret i32 %1
}