Invalid SPIR-V produced when gl_ObjectToWorldEXT and gl_ObjectToWorld3x4EXT used in the same shader

[andfau-arm]

Consider the following intersection shader:

#version 460
#extension GL_EXT_ray_tracing : require

void main()
{
    mat4x3 foo = gl_ObjectToWorldEXT;
    mat3x4 bar = gl_ObjectToWorld3x4EXT;
}

There is no "3x4" version of the SPIR-V built-in, so glslang maps both of these built-ins to ObjectToWorldKHR and inserts a transpose.

However, if you use both of these in the same shader, you will get two variables decorated with the same BuiltIn:

                              Decorate 12(gl_ObjectToWorldEXT) BuiltIn ObjectToWorldKHR
                              Decorate 18(gl_ObjectToWorld3x4EXT) BuiltIn ObjectToWorldKHR
               2:             TypeVoid
               3:             TypeFunction 2
               6:             TypeFloat 32
               7:             TypeVector 6(float) 3
               8:             TypeMatrix 7(fvec3) 4
               9:             TypePointer Function 8
              11:             TypePointer Input 8
12(gl_ObjectToWorldEXT):     11(ptr) Variable Input
              14:             TypeVector 6(float) 4
              15:             TypeMatrix 14(fvec4) 3
              16:             TypePointer Function 15
18(gl_ObjectToWorld3x4EXT):     11(ptr) Variable Input
         4(main):           2 Function None 3
               5:             Label
         10(foo):      9(ptr) Variable Function
         17(bar):     16(ptr) Variable Function
              13:           8 Load 12(gl_ObjectToWorldEXT)
                              Store 10(foo) 13
              19:           8 Load 18(gl_ObjectToWorld3x4EXT)
              20:          15 Transpose 19

This is not permitted by the SPIR-V specification:

For all the declarations of all the global variables and constants statically referenced by the entry-point’s call tree, within any specific storage class it is invalid to decorate with a specific BuiltIn more than once.

The same issue exists for the pair of gl_WorldToObjectEXT and gl_WorldToObject3x4EXT.

This issue is similar to #2910 but is not as easy to fix because the built-ins are not perfect aliases.

[andfau-arm]

Incidentally, spirv-val doesn't seem to catch this case. That could be a potential improvement to the validator.

[greg-lunarg]

@dgkoch This code appears to be yours. Can you please fix?

[dgkoch]

@greg-lunarg I contributed the code, but it was written by someone else, who is likely not available at this point.
I don't think I know enough about the compiler internals to be able to fix this myself.

[andfau-arm]

@greg-lunarg If you haven't started on this yet: we (Arm) will try to write a patch at some point.

[greg-lunarg]

OK. I will wait for your patch.

[andfau-arm]

Here is the patch: #2955