[Piglit] [PATCH] glsl: update assumption in array out of bounds test

[Nicolai Hähnle]

On 03.04.2017 02:01, Timothy Arceri wrote:
>
>
> On 31/03/17 17:30, Nicolai Hähnle wrote:
>> On 31.03.2017 01:53, Timothy Arceri wrote:
>>> Section 5.7 of the GLSL 4.5 spec says:
>>>
>>>    "Behavior is undefined if a shader subscripts an array with an
>>>    index less than 0 or greater than or equal to the size the array
>>>    was declared with."
>>>
>>> So we cannot be sure which path the shader will take. Update the
>>> test so that both branches end in the same result.
>>>
>>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96684
>>> ---
>>>  tests/shaders/glsl-array-bounds-01.shader_test | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/tests/shaders/glsl-array-bounds-01.shader_test
>>> b/tests/shaders/glsl-array-bounds-01.shader_test
>>> index 2e7c762..a06fef7 100644
>>> --- a/tests/shaders/glsl-array-bounds-01.shader_test
>>> +++ b/tests/shaders/glsl-array-bounds-01.shader_test
>>> @@ -15,21 +15,21 @@ void main()
>>>   */
>>>  #version 120
>>>
>>>  float array[] = float [] (1.0, 2.0, 3.0, 4.0);
>>>
>>>  void main()
>>>  {
>>>     int idx = 20;
>>>
>>>     if (array[idx] == 5.0)
>>> -      gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
>>> +      gl_FragColor = vec4(0.0, 1.0, 0.0, 1.0);
>>>     else
>>>        gl_FragColor = vec4(0.0, 1.0, 0.0, 1.0);
>>>  }
>>
>> I'm a bit concerned that an optimizer will do tail-merging followed by
>> eliminating the load. Maybe do something silly like
>>
>> float tmp = array[idx];
>>
>> gl_FragColor = vec4(0.0, 1.0 + abs(tmp), 0.0, 1.0);
>>
>> instead? Then the compiler can't optimize the load away, because the
>> shader has to work with un-clamped floating point framebuffers.
>>
>> On second thought, what about NaNs?
>
> Well we are testing undefined behavior, the correct thing might be to
> just delete the test?

That's a good point. Though robust buffer access changes this, so that 
only the returned value is undefined. So instead of deleting the test, 
it should probably be modified / moved to become a test for robust 
buffer access.

Cheers,
Nicolai

>
>
>
>>
>> Cheers,
>> Nicolai
>>
>>>
>>>  [test]
>>>  clear color 0.0 0.0 0.0 0.0
>>>  clear
>>>  ortho
>>>  draw rect 10 10 10 10
>>>  probe rgb 15 15 0.0 1.0 0.0
>>>
>>
>>


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