[Mesa-dev] [Freedreno] [PATCH] freedreno/ir3: Make imageStore use num components from image format

[Eduardo Lima Mitev]

On 12/18/18 2:31 PM, Rob Clark wrote:
> On Mon, Dec 17, 2018 at 3:41 PM Eduardo Lima Mitev <elima at igalia.com> wrote:
>>
>> emit_intrinsic_store_image() is always using 4 components when
>> collecting registers for the value. When image has less than
>> 4 components (e.g, r32f, r32i, r32ui) this results in extra mov
>> instructions.
>>
>> This patch uses the actual number of components from the image format.
>>
>> For example, in a shader like:
>>
>> layout (r32f, binding=0) writeonly uniform imageBuffer u_image;
>> ...
>> void main(void) {
>>    ...
>>    imageStore (u_image, some_offset, vec4(1.0));
>>    ...
>> }
>>
>> instruction count is reduced in at least 3 instructions (note image
>> format is r32f, 1 component only).
>>
>> This obviously reduces register pressure as well.
>> ---
>>  src/freedreno/ir3/ir3_compiler_nir.c | 34 ++++++++++++++++++++++++++--
>>  1 file changed, 32 insertions(+), 2 deletions(-)
>>
>> diff --git a/src/freedreno/ir3/ir3_compiler_nir.c b/src/freedreno/ir3/ir3_compiler_nir.c
>> index 85f14f354d2..cc00602c249 100644
>> --- a/src/freedreno/ir3/ir3_compiler_nir.c
>> +++ b/src/freedreno/ir3/ir3_compiler_nir.c
>> @@ -1251,6 +1251,35 @@ emit_intrinsic_load_image(struct ir3_context *ctx, nir_intrinsic_instr *intr,
>>         ir3_split_dest(b, dst, sam, 0, 4);
>>  }
>>
>> +/* Get the number of components of the different image formats supported
>> + * by the GLES 3.1 spec.
>> + */
>> +static unsigned
>> +get_num_components_for_glformat(GLuint format)
>> +{
>> +       switch (format) {
>> +       case GL_R32F:
>> +       case GL_R32I:
>> +       case GL_R32UI:
>> +               return 1;
>> +
>> +       case GL_RGBA32F:
>> +       case GL_RGBA16F:
>> +       case GL_RGBA8:
>> +       case GL_RGBA8_SNORM:
>> +       case GL_RGBA32I:
>> +       case GL_RGBA16I:
>> +       case GL_RGBA8I:
>> +       case GL_RGBA32UI:
>> +       case GL_RGBA16UI:
>> +       case GL_RGBA8UI:
>> +               return 4;
>> +
>> +       default:
>> +               assert(!"Unsupported GL format for image");
> 
> One thought, default could still return 4, at least for release
> builds.. that should always be a safe fallback.  But I suppose
> addition of new formats maybe doesn't happen so much.
>

All things considered I think is better to make 4 components the
default. After all, we should not be in the business of validating
internal state at this point. And the worse case is we emit a few
unnecessary instructions.

>
> (There is no glsl_types helper for this?)
> 

I couldn't find any helper :(. There is glsl_get_components() but it
expects a glsl_type, and we have a GLformat enum. Also, this is only a
subset of GL formats that can be image textures.

> If we do have an assert, compile_assert() or ir3_context_error() would
> be nice, since (at least for debug builds) should print out the nir
> annotated w/ location of error, which I find convenient for debugging.
> 

Doesn't apply now that I've chosen to remove the assert, but I have
taken note!

Thanks,

Eduardo

> BR,
> -R
> 
> 
>> +       }
>> +}
>> +
>>  /* src[] = { deref, coord, sample_index, value }. const_index[] = {} */
>>  static void
>>  emit_intrinsic_store_image(struct ir3_context *ctx, nir_intrinsic_instr *intr)
>> @@ -1262,6 +1291,7 @@ emit_intrinsic_store_image(struct ir3_context *ctx, nir_intrinsic_instr *intr)
>>         struct ir3_instruction * const *coords = ir3_get_src(ctx, &intr->src[1]);
>>         unsigned ncoords = get_image_coords(var, NULL);
>>         unsigned tex_idx = get_image_slot(ctx, nir_src_as_deref(intr->src[0]));
>> +       unsigned ncomp = get_num_components_for_glformat(var->data.image.format);
>>
>>         /* src0 is value
>>          * src1 is coords
>> @@ -1276,10 +1306,10 @@ emit_intrinsic_store_image(struct ir3_context *ctx, nir_intrinsic_instr *intr)
>>          */
>>
>>         stib = ir3_STIB(b, create_immed(b, tex_idx), 0,
>> -                       ir3_create_collect(ctx, value, 4), 0,
>> +                       ir3_create_collect(ctx, value, ncomp), 0,
>>                         ir3_create_collect(ctx, coords, ncoords), 0,
>>                         offset, 0);
>> -       stib->cat6.iim_val = 4;
>> +       stib->cat6.iim_val = ncomp;
>>         stib->cat6.d = ncoords;
>>         stib->cat6.type = get_image_type(var);
>>         stib->cat6.typed = true;
>> --
>> 2.19.2
>>
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