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InstCombine: (X ^ signbit) + C -> X + (signbit ^ C)

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181249 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2013-05-06 21:21:31 +00:00
parent e305e03d6f
commit 8ec23cb07e
2 changed files with 15 additions and 0 deletions
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5
lib/Transforms/InstCombine/InstCombineAddSub.cpp
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@ -974,6 +974,11 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
return BinaryOperator::CreateSub(ConstantExpr::getAdd(XorRHS, CI),
XorLHS);
}
// (X + signbit) + C could have gotten canonicalized to (X ^ signbit) + C,
// transform them into (X + (signbit ^ C))
if (XorRHS->getValue().isSignBit())
return BinaryOperator::CreateAdd(XorLHS,
ConstantExpr::getXor(XorRHS, CI));
}
}

10
test/Transforms/InstCombine/sub-xor.ll
View File

@ -35,3 +35,13 @@ define i32 @test3(i32 %x) nounwind {
; CHECK-NEXT: sub i32 73, %and
; CHECK-NEXT: ret
}
define i32 @test4(i32 %x) nounwind {
%sub = xor i32 %x, 2147483648
%add = add i32 %sub, 42
ret i32 %add
; CHECK: @test4
; CHECK-NEXT: add i32 %x, -2147483606
; CHECK-NEXT: ret
}