spirv-opt: OpAccessChain without indices is not supported

[Vasniktel]

The following SPIR-V passes spirv-val's checks

               OpCapability Shader
          %1 = OpExtInstImport "GLSL.std.450"
               OpMemoryModel Logical GLSL450
               OpEntryPoint Fragment %4 "main"
               OpExecutionMode %4 OriginUpperLeft
               OpSource ESSL 310
          %2 = OpTypeVoid
          %3 = OpTypeFunction %2
          %6 = OpTypeBool
          %7 = OpTypePointer Function %6
          %4 = OpFunction %2 None %3
          %5 = OpLabel
         %10 = OpVariable %7 Function
         %11 = OpAccessChain %7 %10
               OpReturn
               OpFunctionEnd

In this code, the Base operand of the OpAccessChain is not a pointer to a composite. Also, indices operands are missing. The same issue arises with OpInBoundsAccessChain.

[Vasniktel]

@alan-baker @s-perron ping

[s-perron]

@alan-baker Where did the spec come done on the legality of this? I remember we had discussions about it because some optimizations assume at least one index. However, I forget the result.

[alan-baker]

It was left as valid because there are a reasonable number of code generators that generate this case.

[Vasniktel]

spirv-opt doesn't support this case, though. This SPIR-V

               OpCapability Shader
          %1 = OpExtInstImport "GLSL.std.450"
               OpMemoryModel Logical GLSL450
               OpEntryPoint Fragment %4 "main"
               OpExecutionMode %4 OriginUpperLeft
               OpSource ESSL 310
          %2 = OpTypeVoid
          %3 = OpTypeFunction %2
          %6 = OpTypeBool
          %7 = OpTypePointer Function %6
          %4 = OpFunction %2 None %3
          %5 = OpLabel
         %10 = OpVariable %7 Function
         %11 = OpAccessChain %7 %10
         %12 = OpLoad %6 %11
               OpReturn
               OpFunctionEnd

produces an error

error: line 16: Expected at least one index to OpCompositeExtract, zero found
%12 = OpCompositeExtract %bool %13

error: line 0: Validation failed after pass convert-local-access-chains

when executed with the following command spirv-opt <attached file> -o out.spv --validate-after-all --convert-local-access-chains. This can be reproduced on 28f32ca.

Compiled shader is in the attached file .

[paulthomson]

In an internal discussion, it was suggested that the pointer operand must point to a composite (as implied by the spec). Thus, this can be regarded as a spirv-val bug.

And 0 indices is fine, so this can be classed as a spirv-opt bug.