[Mesa-dev] [PATCH 3/5] glsl: fall back to inexact function-match

[Ilia Mirkin]

I had to do a double (or triple) take on this logic as well. Part of
the subtlety is that the fallback only applies for ES when there's a
match but no exact match. Probably good to mention this.
On Wed, Oct 31, 2018 at 11:13 AM Erik Faye-Lund
<erik.faye-lund at collabora.com> wrote:
>
> On Wed, 2018-10-31 at 15:46 +0200, Tapani Pälli wrote:
> >
> > On 10/30/18 7:11 PM, Erik Faye-Lund wrote:
> > > In GLES, we currently either need an exact match with a local
> > > function,
> > > or an exact match with a builtin.
> > >
> > > However, if we add support for implicit conversions for GLES
> > > shaders,
> > > we also need to fall back to a non-exact match in the case where
> > > there
> > > were no builtin match either.
> > >
> > > Luckily, we already have a variable ready with this, so let's just
> > > return it if the builtin-search failed.
> > >
> > > Signed-off-by: Erik Faye-Lund <erik.faye-lund at collabora.com>
> > > ---
> > >   src/compiler/glsl/ast_function.cpp | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/src/compiler/glsl/ast_function.cpp
> > > b/src/compiler/glsl/ast_function.cpp
> > > index 1fa3f7561ae..50fd8bc5f5d 100644
> > > --- a/src/compiler/glsl/ast_function.cpp
> > > +++ b/src/compiler/glsl/ast_function.cpp
> > > @@ -667,7 +667,7 @@ match_function_by_name(const char *name,
> > >      /* Local shader has no exact candidates; check the built-ins.
> > > */
> > >      _mesa_glsl_initialize_builtin_functions();
> > >      sig = _mesa_glsl_find_builtin_function(state, name,
> > > actual_parameters);
> > > -   return sig;
> > > +   return sig ? sig : local_sig;
> >
> > I think this would deserve a comment about 'local_sig', it did not
> > seem
> > obvious ... maybe something like:
> >
> > /* Variable local_sig contains the result from
> > choose_best_inexact_overload(). */
> >
>
> Yeah, good point. I've changed it to this, which feels like it explains
> the point without spoon-feeding the reader too much... How does that
> sound?
>
> ---8<---
> diff --git a/src/compiler/glsl/ast_function.cpp
> b/src/compiler/glsl/ast_function.cpp
> index 1fa3f7561ae..6aa30400060 100644
> --- a/src/compiler/glsl/ast_function.cpp
> +++ b/src/compiler/glsl/ast_function.cpp
> @@ -667,7 +667,11 @@ match_function_by_name(const char *name,
>     /* Local shader has no exact candidates; check the built-ins. */
>     _mesa_glsl_initialize_builtin_functions();
>     sig = _mesa_glsl_find_builtin_function(state, name,
> actual_parameters);
> -   return sig;
> +
> +   /* if _mesa_glsl_find_builtin_function failed, fall back to the
> result
> +    * of choose_best_inexact_overload() instead
> +    */
> +   return sig ? sig : local_sig;
>  }
>
>  static ir_function_signature *
> ---8<---
>
>
> > >   }
> > >
> > >   static ir_function_signature *
> > >
> >
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