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InstCombine: Shrink "fcmp (fpext x), C" to "fcmp x, C" if C can be losslessly converted to the type of x.

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Fixes PR9592.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128625 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2011-03-31 10:12:07 +00:00
parent cd0274ca18
commit b194bdc03b
2 changed files with 57 additions and 0 deletions
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34
lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -2762,6 +2762,40 @@ Instruction *InstCombiner::visitFCmpInst(FCmpInst &I) {
if (Constant *RHSC = dyn_cast<Constant>(Op1)) {
if (Instruction *LHSI = dyn_cast<Instruction>(Op0))
switch (LHSI->getOpcode()) {
case Instruction::FPExt: {
// fcmp (fpext x), C -> fcmp x, (fptrunc C) if fptrunc is lossless
FPExtInst *LHSExt = cast<FPExtInst>(LHSI);
ConstantFP *RHSF = dyn_cast<ConstantFP>(RHSC);
if (!RHSF)
break;
const fltSemantics *Sem;
// FIXME: This shouldn't be here.
if (LHSExt->getSrcTy()->isFloatTy())
Sem = &APFloat::IEEEsingle;
else if (LHSExt->getSrcTy()->isDoubleTy())
Sem = &APFloat::IEEEdouble;
else if (LHSExt->getSrcTy()->isFP128Ty())
Sem = &APFloat::IEEEquad;
else if (LHSExt->getSrcTy()->isX86_FP80Ty())
Sem = &APFloat::x87DoubleExtended;
else if (LHSExt->getSrcTy()->isPPC_FP128Ty())
Sem = &APFloat::PPCDoubleDouble;
else
break;
bool Lossy;
APFloat F = RHSF->getValueAPF();
F.convert(*Sem, APFloat::rmNearestTiesToEven, &Lossy);
// Avoid lossy conversions and denormals.
if (!Lossy &&
F.compare(APFloat::getSmallestNormalized(*Sem)) !=
APFloat::cmpLessThan)
return new FCmpInst(I.getPredicate(), LHSExt->getOperand(0),
ConstantFP::get(RHSC->getContext(), F));
break;
}
case Instruction::PHI:
// Only fold fcmp into the PHI if the phi and fcmp are in the same
// block. If in the same block, we're encouraging jump threading. If

23
test/Transforms/InstCombine/fcmp.ll
View File

@ -9,3 +9,26 @@ define i1 @test1(float %x, float %y) nounwind {
; CHECK-NEXT: fcmp ogt float %x, %y
}
define i1 @test2(float %a) nounwind {
%ext = fpext float %a to double
%cmp = fcmp ogt double %ext, 1.000000e+00
ret i1 %cmp
; CHECK: @test2
; CHECK-NEXT: fcmp ogt float %a, 1.0
}
define i1 @test3(float %a) nounwind {
%ext = fpext float %a to double
%cmp = fcmp ogt double %ext, 0x3FF0000000000001 ; more precision than float.
ret i1 %cmp
; CHECK: @test3
; CHECK-NEXT: fpext float %a to double
}
define i1 @test4(float %a) nounwind {
%ext = fpext float %a to double
%cmp = fcmp ogt double %ext, 0x36A0000000000000 ; denormal in float.
ret i1 %cmp
; CHECK: @test4
; CHECK-NEXT: fpext float %a to double
}