Issue with RelaxedPrecision and OpCompositeConstruct

[mbechard]

I have the following shader:

                              Capability Shader
                              Capability Sampled1D
               1:             ExtInstImport  "GLSL.std.450"
                              MemoryModel Logical GLSL450
                              EntryPoint Fragment 4  "main" 9
                              ExecutionMode 4 OriginUpperLeft
                              Source GLSL 430
                              SourceExtension  "GL_EXT_nonuniform_qualifier"
                              SourceExtension  "GL_GOOGLE_cpp_style_line_directive"
                              SourceExtension  "GL_GOOGLE_include_directive"
                              Name 4  "main"
                              Name 9  "fragColor"
                              Name 11  "gl_DefaultUniformBlock"
                              MemberName 11(gl_DefaultUniformBlock) 0  "uTDPass"
                              MemberName 11(gl_DefaultUniformBlock) 1  "uTDCurrentDepth"
                              MemberName 11(gl_DefaultUniformBlock) 2  "exampleUniform"
                              Name 13  ""
                              Decorate 9(fragColor) RelaxedPrecision
                              Decorate 9(fragColor) Location 0
                              MemberDecorate 11(gl_DefaultUniformBlock) 0 Offset 0
                              MemberDecorate 11(gl_DefaultUniformBlock) 1 Offset 4
                              MemberDecorate 11(gl_DefaultUniformBlock) 2 RelaxedPrecision
                              MemberDecorate 11(gl_DefaultUniformBlock) 2 Offset 8
                              Decorate 11(gl_DefaultUniformBlock) Block
                              Decorate 17 RelaxedPrecision
                              Decorate 18 RelaxedPrecision
               2:             TypeVoid
               3:             TypeFunction 2
               6:             TypeFloat 32
               7:             TypeVector 6(float) 4
               8:             TypePointer Output 7(fvec4)
    9(fragColor):      8(ptr) Variable Output
              10:             TypeInt 32 1
11(gl_DefaultUniformBlock):             TypeStruct 10(int) 10(int) 6(float)
              12:             TypePointer PushConstant 11(gl_DefaultUniformBlock)
              13:     12(ptr) Variable PushConstant
              14:     10(int) Constant 2
              15:             TypePointer PushConstant 6(float)
         4(main):           2 Function None 3
               5:             Label
              16:     15(ptr) AccessChain 13 14
              17:    6(float) Load 16
              18:    7(fvec4) CompositeConstruct 17 17 17 17
                              Store 9(fragColor) 18
                              Return
                              FunctionEnd

Reflection fails since it's trying to reflect the RelaxedPrecision on result_id 18, however ParseNodes() does not assign the result_id to OpCompositeConstruct nodes. Isn't OpCompositeConstruct a load/store operation, and should be treated as such? The SPIR-V is coming out of GLSLang, and passes the SPIR-V validator.

Thanks

[mbechard]

Also, shouldn't it also be handled for the arithmetic operators such as FSub, along with handling ExtInst cases, since most (all?) of the GLSL instruction extensions could also be decorated with RelaxedPrecision?

[mbechard]

Sorry for the bump on this, any thoughts? I'd be happy to submit a patch if my understanding is correct.

[shangjiaxuan]

Sorry for the bump on this, any thoughts? I'd be happy to submit a patch if my understanding is correct.

It seems spirv-reflect doesn't recognize the OpCompositeConstruct op code, and falls through to default, skipping the instruction. Decoration parsing seems to already have relaxed precision flag in the node.

My understanding is that you are right.

[chaoticbob]

Sorry for the late response. Support for RelaxPrecision initially wasn't prioritized because there wasn't a production case. I'll take a look using your shader as an example. If you're able to share more complex cases, it would be helpful.

[mbechard]

Thanks for taking a look, I don't have a more complex example right now. I think the tricky part would be covering all of the possible cases. I wonder if anything that be pulled from the SPIR-V validator, since it knows to check for instructions where Relaxed Precision is legal and not.

[chaoticbob]

Sorry again for the late response. It looks likeI had missed something you said earlier. If you're still willing to submit a patch - I'd love to take a look.