[llvm] r222040 - InstCombine: Fix infinite loop caused by visitFPTrunc

[David Majnemer]

Sure, feel free to revert.

On Mon, Nov 17, 2014 at 4:17 PM, Manman Ren <mren at apple.com> wrote:

>
> Hi David,
>
> I think this breaks the public stage2 builedbot:
> http://lab.llvm.org:8080/green/job/clang-Rlto_master/298/
>
> r222039 builds fine, but r222040 does not, from my local debugging.
>
> Can we revert this commit and see if the bot becomes green?
>
> Thanks,
> Manman
>
> > On Nov 14, 2014, at 1:21 PM, David Majnemer <david.majnemer at gmail.com>
> wrote:
> >
> > Author: majnemer
> > Date: Fri Nov 14 15:21:15 2014
> > New Revision: 222040
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=222040&view=rev
> > Log:
> > InstCombine: Fix infinite loop caused by visitFPTrunc
> >
> > We would attempt to replace a fptrunc of an frem with an identical
> > fptrunc.  This would cause the new fptrunc to be added to the worklist.
> > Of course, this results in an infinite loop because we will keep
> > visiting the newly created fptruncs.
> >
> > This fixes PR21576.
> >
> > Modified:
> >    llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
> >    llvm/trunk/test/Transforms/InstCombine/fpcast.ll
> >
> > Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
> > URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp?rev=222040&r1=222039&r2=222040&view=diff
> >
> ==============================================================================
> > --- llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp (original)
> > +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp Fri Nov
> 14 15:21:15 2014
> > @@ -1269,14 +1269,17 @@ Instruction *InstCombiner::visitFPTrunc(
> >         // type of OpI doesn't enter into things at all.  We simply
> evaluate
> >         // in whichever source type is larger, then convert to the
> >         // destination type.
> > +        Value *NewLHS = LHSOrig, *NewRHS = RHSOrig;
> >         if (LHSWidth < SrcWidth)
> > -          LHSOrig = Builder->CreateFPExt(LHSOrig, RHSOrig->getType());
> > +          NewLHS = Builder->CreateFPExt(NewLHS, RHSOrig->getType());
> >         else if (RHSWidth <= SrcWidth)
> > -          RHSOrig = Builder->CreateFPExt(RHSOrig, LHSOrig->getType());
> > -        Value *ExactResult = Builder->CreateFRem(LHSOrig, RHSOrig);
> > -        if (Instruction *RI = dyn_cast<Instruction>(ExactResult))
> > -          RI->copyFastMathFlags(OpI);
> > -        return CastInst::CreateFPCast(ExactResult, CI.getType());
> > +          NewRHS = Builder->CreateFPExt(NewRHS, LHSOrig->getType());
> > +        if (NewLHS != LHSOrig || NewRHS != RHSOrig) {
> > +          Value *ExactResult = Builder->CreateFRem(NewLHS, NewRHS);
> > +          if (Instruction *RI = dyn_cast<Instruction>(ExactResult))
> > +            RI->copyFastMathFlags(OpI);
> > +          return CastInst::CreateFPCast(ExactResult, CI.getType());
> > +        }
> >     }
> >
> >     // (fptrunc (fneg x)) -> (fneg (fptrunc x))
> >
> > Modified: llvm/trunk/test/Transforms/InstCombine/fpcast.ll
> > URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/fpcast.ll?rev=222040&r1=222039&r2=222040&view=diff
> >
> ==============================================================================
> > --- llvm/trunk/test/Transforms/InstCombine/fpcast.ll (original)
> > +++ llvm/trunk/test/Transforms/InstCombine/fpcast.ll Fri Nov 14 15:21:15
> 2014
> > @@ -53,3 +53,13 @@ define half @test5(float %a, float %b, f
> > }
> >
> > declare float @llvm.fabs.f32(float) nounwind readonly
> > +
> > +define <1 x float> @test6(<1 x double> %V) {
> > +  %frem = frem <1 x double> %V, %V
> > +  %trunc = fptrunc <1 x double> %frem to <1 x float>
> > +  ret <1 x float> %trunc
> > +; CHECK-LABEL: @test6
> > +; CHECK-NEXT: %[[frem:.*]]  = frem <1 x double> %V, %V
> > +; CHECK-NEXT: %[[trunc:.*]] = fptrunc <1 x double> %[[frem]] to <1 x
> float>
> > +; CHECK-NEXT: ret <1 x float> %trunc
> > +}
> >
> >
> > _______________________________________________
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>
>
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