Invalid GLSL produced from valid SPIRV

[MartynJacques-Arm]

Decompiling valid SPIRV results in invalid GLSL.

$ spirv-cross --stage comp --version 460 --vulkan-semantics lumen.spirv --output out.glsl

$ glslangValidator -g -V -S comp --target-env spirv1.6 out.glsl 
out.glsl
ERROR: out.glsl:317: 'ShadowTraces' : undeclared identifier 
ERROR: out.glsl:317: '_m0' : unknown swizzle selection 
ERROR: out.glsl:317: '_m0' : unknown swizzle selection 
ERROR: out.glsl:317: '_m0' : unknown swizzle selection 
ERROR: out.glsl:317: '=' :  cannot convert from ' temp float' to ' temp highp uint'
ERROR: out.glsl:317: '' : compilation terminated 
ERROR: 6 compilation errors.  No code generated.


SPIR-V is not generated for failed compile or link

Tested on

$ ./glslangValidator --version                                                               
Glslang Version: 11:15.0.0
ESSL Version: OpenGL ES GLSL 3.20 glslang Khronos. 15.0.0
GLSL Version: 4.60 glslang Khronos. 15.0.0
SPIR-V Version 0x00010600, Revision 1
GLSL.std.450 Version 100, Revision 1
Khronos Tool ID 8
SPIR-V Generator Version 11
GL_KHR_vulkan_glsl version 100
ARB_GL_gl_spirv version 100

$ ./spirv-cross --version                                                                                    
Git commit: vulkan-sdk-1.3.296.0-10-g36e54568 Timestamp: 2024-10-14T16:18:23

lumen_spirv.txt
out_glsl.txt

[HansKristian-Work]

lumen_spirv.txt is not SPIR-V, it seems to be a dump from RenderDoc's SPIR-V disassembler. Please add proper SPIR-V.

[MartynJacques-Arm]

Apologies, here it is with a .txt appended to allow upload, rawspirv.txt

Let me know if you need anything else

[HansKristian-Work]

Fixed it partially, but I believe this shader is invalid:

ERROR: /tmp/test.comp:4525: 'type_StructuredBuffer_FHitGroupRootConstants' : cannot be used (maybe an instance name is needed) 
ERROR: /tmp/test.comp:4525: 'type_StructuredBuffer_FHitGroupRootConstants' : undeclared identifier 
ERROR: /tmp/test.comp:4525: '' : compilation terminated 
ERROR: 3 compilation errors.  No code generated.

In SPIR-V, this is

       %3816 = OpVariable %_ptr_Function__ptr_StorageBuffer_type_StructuredBuffer_FHitGroupRootConstants Function

This is a pointer to pointer situation which requires VariablePointer support. The SPIR-V does not declare this capability, and GLSL cannot support this due to lack of pointer support. This seems like a validation hole in spirv-val.

However, this is also an optimization hole, since %3816 is only written to, so all this code can be dead-code eliminated, but spirv-cross will not do this. It is unsupported SPIR-V for GLSL.