[CTS] SPIR-V Validation failure, "Expected Image Operand ConstOffset to be a const object"

[jkwak-work]

Three CTS tests are occasionally causing the crash of deqp-vk.exe.

dEQP-VK.glsl.texture_gather.offset.implementation_offset.2d.rgba8.size_pot.clamp_to_edge_repeat
dEQP-VK.glsl.texture_gather.offset.implementation_offset.2d.rgba8.size_pot.mirrored_repeat_clamp_to_edge
dEQP-VK.glsl.texture_gather.offset.implementation_offset.2d.rgba8.size_pot.repeat_mirrored_repeat

When the validation is enabled, those tests fail with the following message,

Expected Image Operand ConstOffset to be a const objec

A simple repro is following,

#extension GL_EXT_gpu_shader5 : require

layout (location = 0) out mediump vec4 o_color;

layout (location = 0) in highp vec2 v_texCoord;

layout (binding = 0) uniform highp sampler2D u_sampler;
layout (binding = 1) uniform offset { highp ivec2 u_offset; };

void main(void)
{
                o_color = textureGatherOffset(u_sampler, v_texCoord, u_offset);
}

When the shader above is stored as test.slang, observe the validation error with the following command,

$ slangc.exe -target spirv -entry main -stage fragment -allow-glsl test.slang

error: line 53: Expected Image Operand ConstOffset to be a const object
  %29 = OpImageGather %v4float %24 %27 %int_0 ConstOffset %21

(0): internal error 99999: Validation of generated SPIR-V failed. SPIRV generated:
; SPIR-V
; Version: 1.5
; Generator: Khronos; 40
; Bound: 37
; Schema: 0
               OpCapability Shader
               OpMemoryModel Logical GLSL450
               OpEntryPoint Fragment %main "main" %11 %offset %u_sampler %31 %entryPointParam_main_o_color %v_texCoord
               OpExecutionMode %main OriginUpperLeft

               ; Debug Information
               OpSource Slang 1
               OpName %v_texCoord "v_texCoord"  ; id %9
               OpName %SLANG_ParameterGroup_offset_std140 "SLANG_ParameterGroup_offset_std140"  ; id %13
               OpMemberName %SLANG_ParameterGroup_offset_std140 0 "u_offset"
               OpName %offset "offset"  ; id %17
               OpName %u_sampler "u_sampler"  ; id %26
               OpName %entryPointParam_main_o_color "entryPointParam_main.o_color"  ; id %34
               OpName %main "main"  ; id %2

               ; Annotations
               OpDecorate %v_texCoord Location 0
               OpDecorate %SLANG_ParameterGroup_offset_std140 Block
               OpMemberDecorate %SLANG_ParameterGroup_offset_std140 0 Offset 0
               OpDecorate %offset Binding 1
               OpDecorate %offset DescriptorSet 0
               OpDecorate %u_sampler Binding 0
               OpDecorate %u_sampler DescriptorSet 0
               OpDecorate %entryPointParam_main_o_color Location 0

               ; Types, variables and constants
       %void = OpTypeVoid
          %3 = OpTypeFunction %void
      %float = OpTypeFloat 32
    %v2float = OpTypeVector %float 2
%_ptr_Input_v2float = OpTypePointer Input %v2float
%_ptr_Private_v2float = OpTypePointer Private %v2float
        %int = OpTypeInt 32 1
      %v2int = OpTypeVector %int 2
%SLANG_ParameterGroup_offset_std140 = OpTypeStruct %v2int
%_ptr_Uniform_SLANG_ParameterGroup_offset_std140 = OpTypePointer Uniform %SLANG_ParameterGroup_offset_std140
      %int_0 = OpConstant %int 0
%_ptr_Uniform_v2int = OpTypePointer Uniform %v2int
         %22 = OpTypeImage %float 2D 2 0 0 1 Unknown
         %23 = OpTypeSampledImage %22
%_ptr_UniformConstant_23 = OpTypePointer UniformConstant %23
    %v4float = OpTypeVector %float 4
%_ptr_Private_v4float = OpTypePointer Private %v4float
%_ptr_Output_v4float = OpTypePointer Output %v4float
 %v_texCoord = OpVariable %_ptr_Input_v2float Input
         %11 = OpVariable %_ptr_Private_v2float Private
     %offset = OpVariable %_ptr_Uniform_SLANG_ParameterGroup_offset_std140 Uniform
  %u_sampler = OpVariable %_ptr_UniformConstant_23 UniformConstant
         %31 = OpVariable %_ptr_Private_v4float Private
%entryPointParam_main_o_color = OpVariable %_ptr_Output_v4float Output

               ; Function main
       %main = OpFunction %void None %3
          %4 = OpLabel
          %7 = OpLoad %v2float %v_texCoord
               OpStore %11 %7
         %20 = OpAccessChain %_ptr_Uniform_v2int %offset %int_0
         %21 = OpLoad %v2int %20
         %24 = OpLoad %23 %u_sampler
         %27 = OpLoad %v2float %v_texCoord
         %29 = OpImageGather %v4float %24 %27 %int_0 ConstOffset %21
               OpStore %31 %29
               OpStore %entryPointParam_main_o_color %29
               OpReturn
               OpFunctionEnd

[jkwak-work]

Due to this problem, the following tests are currently disabled for the nightly CTS test.

dEQP-VK.glsl.texture_gather.offset.implementation_offset.2d.rgba8.size_pot.clamp_to_edge_repeat
dEQP-VK.glsl.texture_gather.offset.implementation_offset.2d.rgba8.size_pot.mirrored_repeat_clamp_to_edge
dEQP-VK.glsl.texture_gather.offset.implementation_offset.2d.rgba8.size_pot.repeat_mirrored_repeat

Once the problem is resolved, we should re-enabled them back.

[jkwak-work]

I think the problem is on the fact that ConstOffset is used when it should be just Offset

[csyonghe]

seems like should be easy to fix.

[jkwak-work]

I found it interesting that all of the offset variants of GLSL textureXXX functions require the offset value to be a compile-time constant value except for textureGatherOffset().

The GLSL spec says,

(textureGatherOffset) Perform a texture gather operation as in
textureGather by offset as described in
textureOffset except that the offset can be
variable (non constant)

When textureGatherOffset is converted to SPIR-V code, it uses OpImageGather instruction with Offset option.
In this case, it has to use ImageGatherExtended capability.

Note that OpImageGather is also available with ConstOffset option if the offset value is known at the compile-time.
In this case, it doesn't need ImageGatherExtended capability.

[jkwak-work]

A note for myself here.
Once the fix is merged, I need to re-enable three tests on the nightly CTS test that was disabled by shader-slang/VK-GL-CTS#7

dEQP-VK.glsl.texture_gather.offset.implementation_offset.2d.rgba8.size_pot.clamp_to_edge_repeat
dEQP-VK.glsl.texture_gather.offset.implementation_offset.2d.rgba8.size_pot.mirrored_repeat_clamp_to_edge
dEQP-VK.glsl.texture_gather.offset.implementation_offset.2d.rgba8.size_pot.repeat_mirrored_repeat