[Mesa-dev] [PATCH] glsl: Trigger precision mismatch error only if both symbols are used

[Ian Romanick]

On 09/25/2017 02:53 AM, Tomasz Figa wrote:
> Commit 259fc505454ea6a67aeacf6cdebf1398d9947759 added linker error for
> mismatching uniform precision, as required by GLES specification and
> conformance test-suite.
> 
> Several Android applications, including Forge of Empires, have shaders
> which violate this rule, on a dead varying that will be eliminated.
> The problem affects a big number of applications using Cocos2D engine
> and other GLES implementations accept this, so work around the problem
> by erroring out only if both symbols are actually referenced in the
> code, which is the only case when the mismatch can cause incorrect
> behavior.

I think this change will cause failures in the CTS... but, there's a
Khronos bug about this issue, and I think some of the rules are going to
get relaxed.  I'd like to wait until that gets sorted before we start
changing how our linker applies the rules.

> Based on Kenneth Graunke's patch from Bugzilla, reworked from a drirc
> option that completely bypasses the check into an incoditional check

                                                    unconditional

> that triggers either an error or warning, respectively if both
> declarations are further referenced by the code or not.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97532
> Signed-off-by: Tomasz Figa <tfiga at chromium.org>
> ---
>  src/compiler/glsl/linker.cpp | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/src/compiler/glsl/linker.cpp b/src/compiler/glsl/linker.cpp
> index f352c5385ca..1c534ea1a3b 100644
> --- a/src/compiler/glsl/linker.cpp
> +++ b/src/compiler/glsl/linker.cpp
> @@ -1121,10 +1121,16 @@ cross_validate_globals(struct gl_shader_program *prog,
>           if (prog->IsES && (prog->data->Version != 310 ||
>           

Does just removing the "prog->data->Version != 310" clause also fix the
problem?

                   !var->get_interface_type()) &&
>               existing->data.precision != var->data.precision) {
> -            linker_error(prog, "declarations for %s `%s` have "
> -                         "mismatching precision qualifiers\n",
> -                         mode_string(var), var->name);
> -            return;
> +            if (existing->data.used && var->data.used) {
> +               linker_error(prog, "declarations for %s `%s` have "
> +                            "mismatching precision qualifiers\n",
> +                            mode_string(var), var->name);
> +               return;
> +            } else {
> +               linker_warning(prog, "declarations for %s `%s` have "
> +                              "mismatching precision qualifiers\n",
> +                              mode_string(var), var->name);
> +            }
>           }
>        } else
>           variables->add_variable(var);
>