[llvm-dev] Condition code in DAGCombiner::visitFADDForFMACombine?

[Ryan Taylor via llvm-dev]

For this code:

  %20 = fmul reassoc nnan arcp contract float %15, %19
  %21 = fadd nnan arcp float %20, -1.000000e+00

This does not result in fused multiply-add.

it seems like the logic to contact the fmul from the fadd is different than
whether to decide to contract the fadd. I would think the logic would be
the same for each instruction in the pair.

On Tue, Aug 21, 2018 at 2:05 PM Ryan Taylor <ryta1203 at gmail.com> wrote:

> As far as being present on both, I'm not sure why that would be the case.
> If one instruction doesn't have contract or reassoc, then it should be
> allowed to be contracted or reassociated despite any other instruction
> flags.
>
> That's my interpretation of what it should mean, otherwise, you'd have to
> pair each possible combination.
>
>
>
> On Tue, Aug 21, 2018 at 11:04 AM Matt Arsenault <arsenm2 at gmail.com> wrote:
>
>>
>>
>> > 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
>
>
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