Re: [PATCH,i386] fma,fma4 and xop flags

[Uros Bizjak <ubizjak at gmail dot com>]

On Thu, Aug 16, 2012 at 1:43 PM, Gopalasubramanian, Ganesh
<Ganesh.Gopalasubramanian@amd.com> wrote:
>> This won't work, since we have to prefer FMA3 also in case when only "-mfma -mfma4" without -mtune=XX is used.
>> We can add TARGET_FMA_BOTH though, but I doubt there will ever be target that implements both insn sets without preferences.
>
> Preferring FMA3 over FMA4 might not do good always. For instance, with increased register pressure FMA3 can be used.
> But, when we have more registers at our disposal, fma4 if used might do good by avoiding extra reload.
> IMO, when preference of FMA instructions is adjudged by register pressure,  we may need some functionality to support that.
>
> So, ideally for bdver2, we like to have both fma and fma4 getting generated with options "-mfma -mfma4".

Yes, now it can also work that way. Current insn generation can be
trivially changed now, just change "fma4" condition for "enabled"
attribute in i386.md.

I will wait for your recommendation.

Uros.