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

[Eric Anholt]

Connor Abbott <cwabbott0 at gmail.com> writes:

> 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.

What I most object to about not calling calloc/rzalloc is that it means
you don't get to find the errors you've created until you happen to run
under valgrind, since you almost always get zero-filled contents anyway.
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