[Mesa-dev] odd translation from glsl to tgsi for ir_unop_any_nequal

[Ilia Mirkin]

On Wed, May 7, 2014 at 10:55 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> On Wed, May 7, 2014 at 8:38 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>> So... this shader (from
>> generated_tests/spec/glsl-1.10/execution/built-in-functions/fs-op-eq-mat2-mat2.shader_test):
>>
>> uniform mat2 arg0;
>> uniform mat2 arg1;
>>
>> void main()
>> {
>>   bool result = (arg0 == arg1);
>>   gl_FragColor = vec4(result, 0.0, 0.0, 0.0);
>> }
>>
>> Which becomes the following IR:
>>
>> (
>> (declare (shader_out ) vec4 gl_FragColor)
>> (declare (temporary ) vec4 gl_FragColor)
>> (declare (uniform ) mat2 arg0)
>> (declare (uniform ) mat2 arg1)
>> (function main
>>   (signature void
>>     (parameters
>>     )
>>     (
>>       (declare (temporary ) vec4 vec_ctor)
>>       (assign  (yzw) (var_ref vec_ctor)  (constant vec3 (0.0 0.0 0.0)) )
>>       (declare (temporary ) bvec2 mat_cmp_bvec)
>>       (assign  (x) (var_ref mat_cmp_bvec)  (expression bool any_nequal
>> (array_ref (var_ref arg1) (constant int (0)) ) (array_ref (var_ref
>> arg0) (constant int (0)) ) ) )
>>       (assign  (y) (var_ref mat_cmp_bvec)  (expression bool any_nequal
>> (array_ref (var_ref arg1) (constant int (1)) ) (array_ref (var_ref
>> arg0) (constant int (1)) ) ) )
>>       (assign  (x) (var_ref vec_ctor)  (expression float b2f
>> (expression bool ! (expression bool any (var_ref mat_cmp_bvec) ) ) ) )
>>       (assign  (xyzw) (var_ref gl_FragColor)  (var_ref vec_ctor) )
>>       (assign  (xyzw) (var_ref gl_FragColor at 4)  (var_ref gl_FragColor) )
>>     ))
>>
>> )
>>
>>
>> When converted to TGS becomes:
>>
>> FRAG
>> PROPERTY FS_COLOR0_WRITES_ALL_CBUFS 1
>> DCL OUT[0], COLOR
>> DCL CONST[0..3]
>> DCL TEMP[0..2], LOCAL
>> IMM[0] FLT32 {    0.0000,     1.0000,     0.0000,     0.0000}
>> IMM[1] INT32 {0, 0, 0, 0}
>>   0: MOV TEMP[0].yzw, IMM[0].xxxx
>>   1: FSNE TEMP[1].xy, CONST[2].xyyy, CONST[0].xyyy
>>   2: OR TEMP[1].x, TEMP[1].xxxx, TEMP[1].yyyy
>>   3: FSNE TEMP[2].xy, CONST[3].xyyy, CONST[1].xyyy
>>   4: OR TEMP[2].x, TEMP[2].xxxx, TEMP[2].yyyy
>>   5: MOV TEMP[1].y, TEMP[2].xxxx
>>   6: DP2 TEMP[1].x, TEMP[1].xyyy, TEMP[1].xyyy
>>   7: USNE TEMP[1].x, TEMP[1].xxxx, IMM[1].xxxx
>>   8: NOT TEMP[1].x, TEMP[1].xxxx
>>   9: AND TEMP[0].x, TEMP[1].xxxx, IMM[0].yyyy
>>  10: MOV OUT[0], TEMP[0]
>>  11: END
>>
>> Note that FSNE/OR are used, implying that the integer version of these
>> is expected. However then it goes on to use DP2, which, as I
>> understand, does a floating point multiply + add. Now, this _happens_
>> to work out, since the integer representations of float 0 and int 0
>> are the same, and those are really the only possilibities we care
>> about.
>>
>> However this seems really dodgy... wouldn't it be clearer to use
>> either SNE + OR (which would still work!) + DP2, or alternatively AND
>> them all together instead of SNE/DP2? This seems to come in via
>> ir_unop_any_nequal. IMO the latter would be better since it keeps
>
> Erm, sorry -- the email subject and this sentence isn't _quite_
> accurate. That should be ir_unop_any. ir_binop_any_nequal is what
> generates the FSNE/OR' combos. But everything else still holds :)
>
>> things in integer space, and presumably AND's are cheaper than
>> fmul/fadd.
>>
>> I noticed this because nouveau's codegen logic isn't able to optimize
>> this intelligently and I was trying to figure out why.
>>
>> Thoughts?

I sent a patch that implements a native integers version of
ir_unop_any: http://patchwork.freedesktop.org/patch/25569/

>From the overall symmetry of things, it seems like this was just
forgotten whenever native integer support was added. All the other
any_equal/etc have if (native_integers) do OR+etc else DP2 + etc.

  -ilia