[Mesa-dev] [PATCH 6/6] i965/fs: don't copy propagate if the instruction writes to more than two adjacent GRFs

[Samuel Iglesias Gonsálvez]

On 08/07/16 04:49, Francisco Jerez wrote:
> Samuel Iglesias Gonsálvez <siglesias at igalia.com> writes:
> 
>> This is not allowed by the HW and copy propagation can hide this issue to
>> lower_simd_width pass, which is going to fix it.
>>
>> Signed-off-by: Samuel Iglesias Gonsálvez <siglesias at igalia.com>
>> ---
>>  src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
>> index 438f681..c7f7628 100644
>> --- a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
>> +++ b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
>> @@ -752,6 +752,7 @@ can_propagate_from(fs_inst *inst)
>>              inst->src[0].file == UNIFORM ||
>>              inst->src[0].file == IMM) &&
>>             inst->src[0].type == inst->dst.type &&
>> +           inst->regs_written <= 2 &&
> 
> This doesn't look right to me, why should copy propagation care whether
> the SIMD width of a MOV instruction it's going to propagate away is
> allowed by the hardware or not?  The "illegal" copy instruction is
> already there anyway, and preventing copy propagation from doing its job
> in that case can only increase the likelihood that the unsupported
> instruction will remain in the program which implies more work for the
> SIMD lowering pass at a later point.
> 

Right, I understood wrongly the issue. Today I found what was going-on
and I will send a patch as part of the v2 of the series.

Please ignore this patch.

Thanks,

Sam


>>             !inst->is_partial_write());
>>  }
>>  
>> -- 
>> 2.7.4
>>
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>> mesa-dev at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev

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