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Remove a instcombine transform that (no longer?) makes sense:

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// C - zext(bool) -> bool ? C - 1 : C
    if (ZExtInst *ZI = dyn_cast<ZExtInst>(Op1))
      if (ZI->getSrcTy()->isIntegerTy(1))
        return SelectInst::Create(ZI->getOperand(0), SubOne(C), C);

This ends up forming sext i1 instructions that codegen to terrible code. e.g.
int blah(_Bool x, _Bool y) {
  return (x - y) + 1;
}
=>
        movzbl  %dil, %eax
        movzbl  %sil, %ecx
        shll    $31, %ecx
        sarl    $31, %ecx
        leal    1(%rax,%rcx), %eax
        ret


Without the rule, llvm now generates:
        movzbl  %sil, %ecx
        movzbl  %dil, %eax
        incl    %eax
        subl    %ecx, %eax
        ret

It also helps with ARM (and pretty much any target that doesn't have a sext i1 :-).

The transformation was done as part of Eli's r75531. He has given the ok to
remove it.

rdar://11748024


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159230 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng
2012-06-26 22:03:13 +00:00
parent 4750c1d804
commit bbbe413846
3 changed files with 16 additions and 33 deletions
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5
lib/Transforms/InstCombine/InstCombineAddSub.cpp
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@@ -544,11 +544,6 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
if (Instruction *R = FoldOpIntoSelect(I, SI))
return R;
// C - zext(bool) -> bool ? C - 1 : C
if (ZExtInst *ZI = dyn_cast<ZExtInst>(Op1))
if (ZI->getSrcTy()->isIntegerTy(1))
return SelectInst::Create(ZI->getOperand(0), SubOne(C), C);
// C-(X+C2) --> (C-C2)-X
ConstantInt *C2;
if (match(Op1, m_Add(m_Value(X), m_ConstantInt(C2))))