float comparison to double 'zero' constant can just be a float 'zero.'
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
diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index d2faab5..26432d2 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2837,10 +2837,13 @@
APFloat F = RHSF->getValueAPF();
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 &&
- F.compare(APFloat::getSmallestNormalized(*Sem)) !=
- APFloat::cmpLessThan)
+ ((F.compare(APFloat::getSmallestNormalized(*Sem)) !=
+ APFloat::cmpLessThan) || F.isZero()))
+
return new FCmpInst(I.getPredicate(), LHSExt->getOperand(0),
ConstantFP::get(RHSC->getContext(), F));
break;