[Mesa-dev] [PATCH] spirv: Relax the validation conditions of OpSelect

[Jason Ekstrand]

It turns out there's already a glslang bug for this and it was closed in
March:

https://github.com/KhronosGroup/glslang/issues/809

Unfortunately, there are applications shipping with these shaders so
failure isn't really an option.

--Jason

On Thu, Dec 14, 2017 at 7:56 PM, Jason Ekstrand <jason at jlekstrand.net>
wrote:

> The Talos Principle contains shaders with an OpSelect between two
> vectors where the condition is a scalar boolean.  This is technically
> against the spec bout nir_builder gracefully handles it by splatting
> out the condition to all the channels.  So long as the condition is a
> boolean, just emit a warning instead of failing.
>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104246
> ---
>  src/compiler/spirv/spirv_to_nir.c | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/src/compiler/spirv/spirv_to_nir.c
> b/src/compiler/spirv/spirv_to_nir.c
> index 0493dd3..f0476b2 100644
> --- a/src/compiler/spirv/spirv_to_nir.c
> +++ b/src/compiler/spirv/spirv_to_nir.c
> @@ -3511,10 +3511,20 @@ vtn_handle_body_instruction(struct vtn_builder
> *b, SpvOp opcode,
>           vtn_fail("Result type of OpSelect must be a scalar, vector, or
> pointer");
>        }
>
> -      vtn_fail_if(sel_val->type->type != sel_type,
> -                  "Condition type of OpSelect must be a scalar or vector
> of "
> -                  "Boolean type. It must have the same number of
> components "
> -                  "as Result Type");
> +      if (unlikely(sel_val->type->type != sel_type)) {
> +         if (sel_val->type->type == glsl_bool_type()) {
> +            /* This case is illegal but some versions of GLSLang produce
> it.
> +             * That's fine, nir_builder will just splat the condition out
> +             * which is most likely what the client wanted anyway.
> +             */
> +            vtn_warn("Condition type of OpSelect must have the same
> number "
> +                     "of components as Result Type");
> +         } else {
> +            vtn_fail("Condition type of OpSelect must be a scalar or
> vector "
> +                     "of Boolean type. It must have the same number of "
> +                     "components as Result Type");
> +         }
> +      }
>
>        vtn_fail_if(obj1_val->type != res_val->type ||
>                    obj2_val->type != res_val->type,
> --
> 2.5.0.400.gff86faf
>
>
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