SPIRV-Cross/shaders-msl-no-opt/vert/unused-subgroup-builtin.msl22.vert

#version 450
#extension GL_KHR_shader_subgroup_ballot : require

void main()
{
	gl_SubgroupEqMask;
}
spirv_msl: Don't add fixup hooks for builtin variables if they're unused. This is necessary to avoid invalid output because of how implicit dependencies on builtins work. For example, the fixup for `BuiltInSubgroupEqMask` initializes the variable based on `builtin_subgroup_invocation_id_id`, a field storing the ID for a variable with decoration `BuiltInSubgroupLocalInvocationId`. This could be either a variable that already exists in the input (spirv_msl.cpp:300) or, if necessary, a newly created one (spirv_msl.cpp:621). In both cases, though, `builtin_subgroup_invocation_id_id` is only set under the condition `need_subgroup_mask \|\| needs_subgroup_invocation_id`. `need_subgroup_mask` is true if any of the `BuiltInSubgroupXXMask` are set in `active_input_builtins`. Normally, if the program contains `BuiltInSubgroupEqMask`, `Compiler::ActiveBuiltinHandler` will set it in `active_input_builtins`. But this only happens if the variable is actually used, whereas `fix_up_shader_inputs_outputs` loops over all variables in the program regardless of whether they're used. If `BuiltInSubgroupEqMask` is not used, `builtin_subgroup_invocation_id_id` is never set, but before this patch the fixup hook would try to use it anyway, producing MSL that references a nonexistent variable named `_0`. Avoid this by changing `fix_up_shader_inputs_outputs` to skip builtins which are not set in `active_input_builtins` or `active_output_builtins`. And add a test case. 2020-11-25 17:43:01 +00:00			`#version 450`
			`#extension GL_KHR_shader_subgroup_ballot : require`

			`void main()`
			`{`
			`gl_SubgroupEqMask;`
			`}`