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Consider the case where xor by -1 and xor by 128 have been combined already to 

produce an xor by 127.

llvm-svn: 54906
This commit is contained in:
Nick Lewycky 2008-08-17 19:58:24 +00:00
parent f37daa50da
commit 53b44029d6
2 changed files with 42 additions and 1 deletions
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24
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -5503,8 +5503,8 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
return new ICmpInst(I.getPredicate(), Op0I->getOperand(0),
Op1I->getOperand(0));
} else {
// icmp u/s (a ^ signbit), (b ^ signbit) --> icmp s/u a, b
if (ConstantInt *CI = dyn_cast<ConstantInt>(Op0I->getOperand(1))) {
// icmp u/s (a ^ signbit), (b ^ signbit) --> icmp s/u a, b
if (CI->getValue().isSignBit()) {
ICmpInst::Predicate Pred = I.isSignedPredicate()
? I.getUnsignedPredicate()
@ -5512,6 +5512,17 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
return new ICmpInst(Pred, Op0I->getOperand(0),
Op1I->getOperand(0));
}
// icmp u/s (a ^ ~signbit), (b ^ ~signbit) --> icmp s/u b, a
if ((~CI->getValue()).isSignBit()) {
ICmpInst::Predicate Pred = I.isSignedPredicate()
? I.getUnsignedPredicate()
: I.getSignedPredicate();
Pred = I.getSwappedPredicate(Pred);
return new ICmpInst(Pred, Op0I->getOperand(0),
Op1I->getOperand(0));
}
}
}
break;
@ -5818,6 +5829,17 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
return new ICmpInst(Pred, LHSI->getOperand(0),
ConstantInt::get(RHSV ^ SignBit));
}
// (icmp u/s (xor A ~SignBit), C) -> (icmp ~s/u A, (xor C ~SignBit))
if (!ICI.isEquality() && (~XorCST->getValue()).isSignBit()) {
const APInt &NotSignBit = XorCST->getValue();
ICmpInst::Predicate Pred = ICI.isSignedPredicate()
? ICI.getUnsignedPredicate()
: ICI.getSignedPredicate();
Pred = ICI.getSwappedPredicate(Pred);
return new ICmpInst(Pred, LHSI->getOperand(0),
ConstantInt::get(RHSV ^ NotSignBit));
}
}
break;
case Instruction::And: // (icmp pred (and X, AndCST), RHS)

19
llvm/test/Transforms/InstCombine/2008-08-17-ICmpXorSignbit.ll
View File

@ -20,3 +20,22 @@ define i1 @test3(i8 %x) {
ret i1 %tmp
}
define i1 @test4(i8 %x, i8 %y) {
%X = xor i8 %x, 127
%Y = xor i8 %y, 127
%tmp = icmp slt i8 %X, %Y
ret i1 %tmp
}
define i1 @test5(i8 %x, i8 %y) {
%X = xor i8 %x, 127
%Y = xor i8 %y, 127
%tmp = icmp ult i8 %X, %Y
ret i1 %tmp
}
define i1 @test6(i8 %x) {
%X = xor i8 %x, 127
%tmp = icmp uge i8 %X, 15
ret i1 %tmp
}