[Piglit] [PATCH] Add glsl-array-bounds-13.shader_test tests

[Nicolai Hähnle]

On 11.08.2016 07:56, Tapani Pälli wrote:
> Hi;
>
> On 08/10/2016 09:34 PM, Nicolai Hähnle wrote:
>> From: Nicolai Hähnle <nicolai.haehnle at amd.com>
>>
>> Compared to the other array bounds tests, this one exercises a larger
>> array
>> size.
>>
>> The motivation is for Radeon, where arrays can be lowered either into the
>> register file or into "real" memory. The larger array in this test
>> will be
>> sure to hit real memory.
>> ---
>>  tests/shaders/glsl-array-bounds-13.shader_test | 33
>> ++++++++++++++++++++++++++
>>  1 file changed, 33 insertions(+)
>>  create mode 100644 tests/shaders/glsl-array-bounds-13.shader_test
>>
>> diff --git a/tests/shaders/glsl-array-bounds-13.shader_test
>> b/tests/shaders/glsl-array-bounds-13.shader_test
>> new file mode 100644
>> index 0000000..95aa550
>> --- /dev/null
>> +++ b/tests/shaders/glsl-array-bounds-13.shader_test
>> @@ -0,0 +1,33 @@
>> +[require]
>> +GLSL >= 1.20
>> +
>> +[vertex shader passthrough]
>> +
>> +[fragment shader]
>> +/* Verify that out-of-bounds access to an array does not result in
>> any sort of
>> + * program interruption.
>> + *
>> + * This test case uses a larger array, to cover drivers that have
>> different
>> + * lowering paths for different array sizes.
>> + *
>> + * In this test case the array index will not be constant folded.
>> + */
>> +#version 120
>> +
>> +uniform int idx;
>> +float array[32];
>> +
>> +void main()
>> +{
>> +   /* Ensure that there can be no constant folding due to undefined
>> values. */
>> +   array[0] = 0.0;
>> +   array[1] = 1.0;
>> +   gl_FragColor = vec4(0.0, 1.0, 0.0, array[idx]);
>> +}
>> +
>> +[test]
>> +uniform int idx -2
>
> According to GLSL 1.20 specs (and up to 4.50 spec):
>
> 'Undefined behavior results from indexing an array with a non-constant
> expression that’s greater than or equal to the array’s size or less than
> 0."
>
> Having said that, we seem to have many similar tests so I guess it's
> fine to assume some output from the shader, just wanted to prompt that
> perhaps we are testing something that is undefined here?

I think you're right in theory. Undefined behavior might mean that the 
pixel shader gets terminated without writing anything to the 
framebuffer, though it definitely isn't allowed to mean program 
termination or hangs.

In practice, given that nobody has complained about these tests in the 
past, the UB seems to be limited to undefined data results in all 
implementations... if anybody ever complains, we might have to remove 
the probe checks from the test script.

> Reviewed-by: Tapani Pälli <tapani.palli at intel.com>

Thanks!

Nicolai


>> +clear color 0.0 0.0 0.0 0.0
>> +clear
>> +draw rect -1 -1 2 2
>> +probe all rgb 0.0 1.0 0.0
>
> // Tapani