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Add an instcombine for constructs like a | -(b != c); a select is more

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canonical, and generally leads to better code.  Found while looking at
an article about saturating arithmetic.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129545 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eli Friedman 2011-04-14 22:41:27 +00:00
parent f6832bbda0
commit 3ec01b7dac
2 changed files with 27 additions and 1 deletions
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9
lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
View File

@ -2003,7 +2003,14 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
}
}
}
// or(sext(A), B) -> A ? -1 : B where A is an i1
// or(A, sext(B)) -> B ? -1 : A where B is an i1
if (match(Op0, m_SExt(m_Value(A))) && A->getType()->isIntegerTy(1))
return SelectInst::Create(A, ConstantInt::getSigned(I.getType(), -1), Op1);
if (match(Op1, m_SExt(m_Value(A))) && A->getType()->isIntegerTy(1))
return SelectInst::Create(A, ConstantInt::getSigned(I.getType(), -1), Op0);
// Note: If we've gotten to the point of visiting the outer OR, then the
// inner one couldn't be simplified. If it was a constant, then it won't
// be simplified by a later pass either, so we try swapping the inner/outer

19
test/Transforms/InstCombine/or.ll
View File

@ -390,3 +390,22 @@ define i1 @test36(i32 %x) {
; CHECK-NEXT: ret i1
}
define i32 @test37(i32* %xp, i32 %y) {
; CHECK: @test37
; CHECK: select i1 %tobool, i32 -1, i32 %x
%tobool = icmp ne i32 %y, 0
%sext = sext i1 %tobool to i32
%x = load i32* %xp
%or = or i32 %sext, %x
ret i32 %or
}
define i32 @test38(i32* %xp, i32 %y) {
; CHECK: @test38
; CHECK: select i1 %tobool, i32 -1, i32 %x
%tobool = icmp ne i32 %y, 0
%sext = sext i1 %tobool to i32
%x = load i32* %xp
%or = or i32 %x, %sext
ret i32 %or
}