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

[Iago Toral]

Hi Tim,

it's been a while, so off the top of my head I don't have any
particular suggestions or the capacity to tell whether your fix is
correct or not :-/.

I'll try to spend some time re-acquainting myself with that code on
Monday and see if I can see what is going on here.

Iago

On Fri, 2017-01-06 at 22:08 +1100, Timothy Arceri wrote:
> 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;
> >           }
> >        }