[Mesa-dev] [PATCH] glsl: fix opt_minmax redundancy checks against baserange

[Timothy Arceri]

Hi Iago/Petri,

Just Ccing you guys in case you have a better solution (I know its been
a while since this was written).

This is causing incorrect shaders in at least Serious Sam 3 possibly
others. I've sent some piglit tests to reproduce it to the piglit list.

Thanks,
Tim

On Fri, 2017-01-06 at 10:26 +1100, Timothy Arceri wrote:
> Marking operations as redundant if they are equal to the base
> range is fine when the tree structure is something like this:
> 
>         max
>       /     \
>      max     b
>     /   \
>    3    max
>        /   \
>       3     a
> 
> But the opt falls apart with a tree like this:
> 
>         max
>      /       \
>     max     max
>    /   \   /   \
>   3    a   b    3
> 
> I'm not 100% sure what is going wrong as a tree like:
> 
>         max
>      /       \
>     max     max
>    /   \   /   \
>   3    a   b    4
> 
> Will remove the right hand side max just fine. But not marking
> limits that equal the base range seems to fix the problem.
> 
> NIR algebraic opt will clean up the first tree for anyway, hopefully
> other backends are smart enough to do this also.
> 
> Cc: "13.0" <mesa-stable at lists.freedesktop.org>
> ---
>  src/compiler/glsl/opt_minmax.cpp | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/src/compiler/glsl/opt_minmax.cpp
> b/src/compiler/glsl/opt_minmax.cpp
> index 29482ee..9f64db9 100644
> --- a/src/compiler/glsl/opt_minmax.cpp
> +++ b/src/compiler/glsl/opt_minmax.cpp
> @@ -355,7 +355,7 @@ ir_minmax_visitor::prune_expression(ir_expression
> *expr, minmax_range baserange)
>            */
>           if (!is_redundant && limits[i].low && baserange.high) {
>              cr = compare_components(limits[i].low, baserange.high);
> -            if (cr >= EQUAL && cr != MIXED)
> +            if (cr > EQUAL && cr != MIXED)
>                 is_redundant = true;
>           }
>        } else {
> @@ -373,7 +373,7 @@ ir_minmax_visitor::prune_expression(ir_expression
> *expr, minmax_range baserange)
>            */
>           if (!is_redundant && limits[i].high && baserange.low) {
>              cr = compare_components(limits[i].high, baserange.low);
> -            if (cr <= EQUAL)
> +            if (cr < EQUAL)
>                 is_redundant = true;
>           }
>        }