[Mesa-dev] [PATCH] glsl: Ignore redundant prototypes after a function's been defined.

[Chad Versace]

On 04/30/2013 01:52 AM, Kenneth Graunke wrote:
> Consider the following shader:
>
>      vec4 f(vec4 v) { return v; }
>      vec4 f(vec4 v);
>
> The prototype exactly matches the signature of the earlier definition,
> so there's absolutely no point in it.  However, it doesn't appear to
> be illegal.  The GLSL 4.30 specification offers two relevant quotes:
>
> "If a function name is declared twice with the same parameter types,
>   then the return types and all qualifiers must also match, and it is the
>   same function being declared."
>
> "User-defined functions can have multiple declarations, but only one
>   definition."
>
> In this case the same function was declared twice, and there's only one
> definition, which fits both pieces of text.  There doesn't appear to be
> any text saying late prototypes are illegal, so presumably it's valid.
>
> Unfortunately, it currently triggers an assertion failure:
> ir_dereference_variable @ <p1> specifies undeclared variable `v' @ <p2>
>
> When we process the second line, we look for an existing exact match so
> we can enforce the one-definition rule.  We then leave sig set to that
> existing function, and hit sig->replace_parameters(&hir_parameters),
> unfortunately nuking our existing definition's parameters (which have
> actual dereferences) with the prototype's bogus unused parameters.
>
> Simply bailing out and ignoring such late prototypes is the safest
> thing to do.
>
> Fixes Piglit's late-proto.vert as well as 3DMark/Ice Storm for Android.
>
> NOTE: This is a candidate for stable branches.
> Cc: Tapani Pälli <tapani.palli at intel.com>
> Cc: Ian Romanick <idr at freedesktop.org>
> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>

Reviewed-by: Chad Versace <chad.versace at linux.intel.com>