On 09/23/2015 07:18 AM, Jason Ekstrand wrote:
>
> On Sep 22, 2015 10:01 PM, "Jason Ekstrand" <ja...@jlekstrand.net
> <mailto:ja...@jlekstrand.net>> wrote:
>>
>> It's possible that, if a vecN operation is involved in a phi node, that we
>> could end up moving from a register to itself. If swizzling is involved,
>> we need to emit the move but. However, if there is no swizzling, then the
>> mov is a no-op and we might as well not bother emitting it.
>>
>> Shader-db results on Haswell:
>>
>> total instructions in shared programs: 6262536 -> 6259558 (-0.05%)
>> instructions in affected programs: 184780 -> 181802 (-1.61%)
>> helped: 838
>> HURT: 0
>
> By the way, I have absolutely no idea why this helps more than Matt's
> patch to delete these in register coalesce.
>
Also in HSW, and with current master, I get this:
total instructions in shared programs: 6260467 -> 6259804 (-0.01%)
instructions in affected programs: 84738 -> 84075 (-0.78%)
helped: 375
HURT: 0
Something must have overlapped improvements in the mean, likely
Alejandro's register coalescing modifiers patch.
The two patches are:
Reviewed-by: Eduardo Lima Mitev <el...@igalia.com>
>> ---
>> src/glsl/nir/nir_lower_vec_to_movs.c | 19 ++++++++++++++++++-
>> 1 file changed, 18 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/glsl/nir/nir_lower_vec_to_movs.c
> b/src/glsl/nir/nir_lower_vec_to_movs.c
>> index 287f2bf..2039891 100644
>> --- a/src/glsl/nir/nir_lower_vec_to_movs.c
>> +++ b/src/glsl/nir/nir_lower_vec_to_movs.c
>> @@ -83,7 +83,24 @@ insert_mov(nir_alu_instr *vec, unsigned start_idx,
> nir_shader *shader)
>> }
>> }
>>
>> - nir_instr_insert_before(&vec->instr, &mov->instr);
>> + /* In some situations (if the vecN is involved in a phi-web), we
> can end
>> + * up with a mov from a register to itself. Some of those
> channels may end
>> + * up doing nothing and there's no reason to have them as part of
> the mov.
>> + */
>> + if (src_matches_dest_reg(&mov->dest.dest, &mov->src[0].src) &&
>> + !mov->src[0].abs && !mov->src[0].negate) {
>> + for (unsigned i = 0; i < 4; i++) {
>> + if (mov->src[0].swizzle[i] == i)
>> + mov->dest.write_mask &= ~(1 << i);
>> + }
>> + }
>> +
>> + /* Only emit the instruction if it actually does something */
>> + if (mov->dest.write_mask) {
>> + nir_instr_insert_before(&vec->instr, &mov->instr);
>> + } else {
>> + ralloc_free(mov);
>> + }
>>
>> return mov->dest.write_mask;
>> }
>> --
>> 2.5.0.400.gff86faf
>>
>
>
>
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