[Mesa-dev] [PATCH 1/3] nir: Add support for CSE on textures.

[Connor Abbott]

On Wed, Feb 11, 2015 at 2:36 PM, Eric Anholt <eric at anholt.net> wrote:
> Connor Abbott <cwabbott0 at gmail.com> writes:
>
>> On Tue, Feb 10, 2015 at 1:32 PM, Eric Anholt <eric at anholt.net> wrote:
>>> Connor Abbott <cwabbott0 at gmail.com> writes:
>>>
>>>> On Sat, Feb 7, 2015 at 12:16 AM, Eric Anholt <eric at anholt.net> wrote:
>>>>> NIR instruction count results on i965:
>>>>> total instructions in shared programs: 1261954 -> 1261937 (-0.00%)
>>>>> instructions in affected programs:     455 -> 438 (-3.74%)
>>>>>
>>>>> One in yofrankie, two in tropics.  Apparently i965 had also optimized all
>>>>> of these out anyway.
>>>>> ---
>>>>>  src/glsl/nir/nir_opt_cse.c | 43 +++++++++++++++++++++++++++++++++++++++----
>>>>>  1 file changed, 39 insertions(+), 4 deletions(-)
>>>>>
>>>>> diff --git a/src/glsl/nir/nir_opt_cse.c b/src/glsl/nir/nir_opt_cse.c
>>>>> index b3e9c0d..55dc083 100644
>>>>> --- a/src/glsl/nir/nir_opt_cse.c
>>>>> +++ b/src/glsl/nir/nir_opt_cse.c
>>>>> @@ -80,8 +80,41 @@ nir_instrs_equal(nir_instr *instr1, nir_instr *instr2)
>>>>>        }
>>>>>        return true;
>>>>>     }
>>>>> -   case nir_instr_type_tex:
>>>>> -      return false;
>>>>> +   case nir_instr_type_tex: {
>>>>> +      nir_tex_instr *tex1 = nir_instr_as_tex(instr1);
>>>>> +      nir_tex_instr *tex2 = nir_instr_as_tex(instr2);
>>>>> +
>>>>> +      if (tex1->op != tex2->op)
>>>>> +         return false;
>>>>> +
>>>>> +      if (tex1->num_srcs != tex2->num_srcs)
>>>>> +         return false;
>>>>> +      for (unsigned i = 0; i < tex1->num_srcs; i++) {
>>>>> +         if (tex1->src[i].src_type != tex2->src[i].src_type ||
>>>>> +             !nir_srcs_equal(tex1->src[i].src, tex2->src[i].src)) {
>>>>> +            return false;
>>>>> +         }
>>>>> +      }
>>>>> +
>>>>> +      if (tex1->coord_components != tex2->coord_components ||
>>>>> +          tex1->sampler_dim != tex2->sampler_dim ||
>>>>> +          tex1->is_array != tex2->is_array ||
>>>>> +          tex1->is_shadow != tex2->is_shadow ||
>>>>> +          tex1->is_new_style_shadow != tex2->is_new_style_shadow ||
>>>>> +          memcmp(tex1->const_offset, tex2->const_offset,
>>>>> +                 sizeof(tex1->const_offset)) != 0 ||
>>>>> +          tex1->component != tex2->component ||
>>>>> +         tex1->sampler_index != tex2->sampler_index ||
>>>>> +         tex1->sampler_array_size != tex2->sampler_array_size) {
>>>>
>>>> I think some of these fields are sometimes unused, so you need to
>>>> split them out and not check them if they're unused. For example,
>>>> is_new_style_shadow is only used when is_shadow is true, and component
>>>> isn't used if we're not doing a textureGather (?) op -- I don't
>>>> remember all the details. That, or we have to have a defined value for
>>>> these fields when they're unused and document that somewhere.
>>>
>>> Oh god, we don't zero-allocate structures.  This is going to be awful.
>>
>> No, with valgrind it's actually better... you get an error if you
>> don't know what you're doing rather than silently having it ignored.
>> These days, zero-allocating structures by default doesn't make much
>> sense any more.
>
> So, why should nir.c not be zero-filling those fields, when we zero fill
> the nir_dests and nir_srcs and and tex->sampler and tex->sampler_index
> and deref->base_offset?

because in 99% of cases, that's what we want. To be clear, I'm not
against initializing stuff to some default value when it makes sense,
and in this case I'm fine with initializing all the sometimes-used
things to 0 and ensuring that they stay 0 to make comparing
tex_instr's less of a PITA. But I don't think we should be blindly
calling calloc()/rzalloc() on everything; if there's some field the
caller has to set, and there's no default value that 99% of callers
will want, don't set it and then let valgrind find any errors (or,
even better, pass it as a parameter to the constructor). And yes,
there are probably a few places where we initialize stuff when it's
not necessary -- that's a mistake on my part.