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float comparison to double 'zero' constant can just be a float 'zero.'

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InstCombine was incorrectly considering the conversion of the constant
zero to be unsafe.

We want to transform:
define float @bar(float %x) nounwind readnone optsize ssp {
  %conv = fpext float %x to double
  %cmp = fcmp olt double %conv, 0.000000e+00
  %conv1 = zext i1 %cmp to i32
  %conv2 = sitofp i32 %conv1 to float
  ret float %conv2
}

Into:
define float @bar(float %x) nounwind readnone optsize ssp {
  %cmp = fcmp olt float %x, 0.000000e+00   ; <---- This
  %conv1 = zext i1 %cmp to i32
  %conv2 = sitofp i32 %conv1 to float
  ret float %conv2
}


rdar://10215914


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@140869 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jim Grosbach 2011-09-30 18:45:50 +00:00
parent d98f838284
commit cbf676b3ba
2 changed files with 17 additions and 3 deletions
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9
lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -2837,10 +2837,13 @@ Instruction *InstCombiner::visitFCmpInst(FCmpInst &I) {
APFloat F = RHSF->getValueAPF(); APFloat F = RHSF->getValueAPF();
F.convert(*Sem, APFloat::rmNearestTiesToEven, &Lossy); F.convert(*Sem, APFloat::rmNearestTiesToEven, &Lossy);
// Avoid lossy conversions and denormals. // Avoid lossy conversions and denormals. Zero is a special case
// that's OK to convert.
F.clearSign();
if (!Lossy && if (!Lossy &&
F.compare(APFloat::getSmallestNormalized(*Sem)) != ((F.compare(APFloat::getSmallestNormalized(*Sem)) !=
APFloat::cmpLessThan) APFloat::cmpLessThan) || F.isZero()))
return new FCmpInst(I.getPredicate(), LHSExt->getOperand(0), return new FCmpInst(I.getPredicate(), LHSExt->getOperand(0),
ConstantFP::get(RHSC->getContext(), F)); ConstantFP::get(RHSC->getContext(), F));
break; break;

11
test/Transforms/InstCombine/fcmp.ll
View File

@ -58,3 +58,14 @@ define i1 @test7(float %x) nounwind readnone ssp noredzone {
; CHECK: @test7 ; CHECK: @test7
; CHECK-NEXT: fpext float %x to ppc_fp128 ; CHECK-NEXT: fpext float %x to ppc_fp128
} }
define float @test8(float %x) nounwind readnone optsize ssp {
%conv = fpext float %x to double
%cmp = fcmp olt double %conv, 0.000000e+00
%conv1 = zext i1 %cmp to i32
%conv2 = sitofp i32 %conv1 to float
ret float %conv2
; Float comparison to zero shouldn't cast to double.
; CHECK: @test8
; CHECK-NEXT: fcmp olt float %x, 0.000000e+00
}