[Mesa-dev] [PATCH 6/7] nir: Teach nir_opt_algebraic about adding and subtracting the same thing

[Matt Turner]

On Tue, Dec 15, 2015 at 1:16 AM, Eduardo Lima Mitev <elima at igalia.com> wrote:
> On 12/15/2015 09:28 AM, Kristian Høgsberg Kristensen wrote:
>> This optimizes a + b - b to just a. Modest shader-db results (BDW):
>>
>>   total instructions in shared programs: 7842452 -> 7841862 (-0.01%)
>>   instructions in affected programs:     61938 -> 61348 (-0.95%)
>>   total loops in shared programs:        2131 -> 2131 (0.00%)
>>   helped:                                263
>>   HURT:                                  0
>>   GAINED:                                0
>>   LOST:                                  0
>>
>
> In HSW, I get these shader-db results:
>
> total instructions in shared programs: 6257265 -> 6256788 (-0.01%)
> instructions in affected programs: 46601 -> 46124 (-1.02%)
> helped: 218
> HURT: 0
>
> total cycles in shared programs: 56010026 -> 56007760 (-0.00%)
> cycles in affected programs: 1048392 -> 1046126 (-0.22%)
> helped: 199
> HURT: 154
>
> total loops in shared programs: 1979 -> 1979 (0.00%)
> loops in affected programs: 0 -> 0
> helped: 0
> HURT: 0
>
> LOST:   0
> GAINED: 0
>
>
> I wonder where those cycle HURTs come from. In any case, the net result
> is positive.

I haven't confirmed, but I've seen cases that seem like the cycle
counts are wrong.