[Mesa-dev] [PATCH 0/2] i965: Simulate MAD opcode with gen<6

[Juha-Pekka Heikkilä]

On Tue, May 6, 2014 at 7:32 PM, Eric Anholt <eric at anholt.net> wrote:
> Juha-Pekka Heikkila <juhapekka.heikkila at gmail.com> writes:
>
>> These patches allow MAD opcode to be used with pre gen6 hardware.
>> Instead of failing on emitting MAD there will be emitted MUL and ADD
>> to simulate MAD.
>>
>> I tried this with piglit on ILK (gen5) and did not see regression.
>
> This hides the MUL and ADD from instruction scheduling, which I expect
> to make performance worse.  What was the motivation for this?

When talking about LRP with MAC there was brief comment about doing
similar for MAD. Now that you mentioned I realize this first try was
not so useful. I at first tried to go using accumulator as an attempt
to benefit one register worth here but that turned out to be
crash'n'burn, literally.

I'll look at Matt's version with LINE next for this.

/Juha-Pekka