llvm dev - Aug 2018 - Condition code in DAGCombiner::visitFADDForFMACombine?

> On Aug 21, 2018, at 17:08, Ryan Taylor via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> So I have a test case where:
> 
> %20 = fmul nnan arcp float %15, %19
> %21 = fadd reassoc nnan arcp contract float %20, -1.000000e+00
> 
> is being contracted in DAG to fmad. Is this correct since the fmul has no
reassoc or contract fast math flag?
> 
> Thanks.

fmad is defined as the exact same result as the separate fmul + fadd, unlike fma
so this is OK

-Matt

Matt,
I'm sorry, actually it's fma not fmad.

In the post-legalizer DAG combine for the given code it's producing fma not
fmad. That doens't seem correct.

On Tue, Aug 21, 2018 at 10:11 AM Matt Arsenault <arsenm2 at gmail.com>
wrote:
>
>
> > On Aug 21, 2018, at 17:08, Ryan Taylor via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >
> > So I have a test case where:
> >
> > %20 = fmul nnan arcp float %15, %19
> > %21 = fadd reassoc nnan arcp contract float %20, -1.000000e+00
> >
> > is being contracted in DAG to fmad. Is this correct since the fmul has
> no reassoc or contract fast math flag?
> >
> > Thanks.
>
>
> fmad is defined as the exact same result as the separate fmul + fadd,
> unlike fma so this is OK
>
> -Matt
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> On Aug 21, 2018, at 17:57, Ryan Taylor <ryta1203 at gmail.com> wrote:
> 
> Matt,
> I'm sorry, actually it's fma not fmad.
> 
> In the post-legalizer DAG combine for the given code it's producing fma
not fmad. That doens't seem correct.
> 
The contract is on the fadd. I’m not really sure what the rule is supposed to be
for contract between the nodes. The LangRef doesn’t clarify on this. I would
assume it would need to be present on both?

-Matt