spirv-val over-validation on private variable decoration

[kaizhangNV]

I have a spirv code like this:

OpDecorate %_arr_int_int_6 ArrayStride 4
......

; Types, variables and constants
......
%_ptr_Function__arr_int_int_6 = OpTypePointer Function %_arr_int_int_6
......
; Function main
%main = OpFunction %void None %3
%4 = OpLabel
%11 = OpVariable %_ptr_Function__arr_int_int_6 Function

and spirv-val tools complains about

error: line 36: [VUID-StandaloneSpirv-None-10684] Invalid explicit layout decorations on type for operand '10[%_ptr_Function__arr_int_int_6]'
  %11 = OpVariable %_ptr_Function__arr_int_int_6 Function

it turns out that we should not specify the explicit layout decoration for type _arr_int_int_6, as it passes spirv-val if I delete this line

OpDecorate %_arr_int_int_6 ArrayStride 4

However, after reading this rule VUID-StandaloneSpirv-None-10684 couple of times, it looks like the rule should only be used on shader interface, instead of private variable (Function storage class).

So I'm wondering if this is spirv-val issue that it over-validates, or I misunderstood something?

[alan-baker]

That VU points to the shader interfaces chapter says:

This chapter describes valid uses for a set of SPIR-V decorations. Any other use of one of these decorations is invalid, with the exception that, when using SPIR-V versions 1.4 and earlier: Block, BufferBlock, Offset, ArrayStride, and MatrixStride can also decorate types and type members used by variables in the Private and Function storage classes.

So if you generate SPIR-V 1.4 or earlier the decoration is permitted. In SPIR-V 1.5 or later, it is not allowed. Generally speaking array stride is only allowed on storage classes that are explicitly laid out, which Private is not. The 1.4 or earlier blurb was to accommodate tooling that already existed and gave time to adjust.

[kaizhangNV]

Thanks, that makes sense.