On Fri, 2017-01-06 at 12:36 +0100, Nicolai Hähnle wrote:
> On 06.01.2017 00:26, 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
>
> This will just become max(a, b), right?
Ah yes so it does. I spent so much time trying to reproduce the problem
(mostly trying trees like the first one) that I though it was doing
something more crazy than that. Makes much more sense looking at it
again with less tired eyes.
>
> The problem is that both branches are treated the same: descending
> in
> the left branch will prune the constant, and then descending the
> right
> branch will prune the constant there as well, because limits[0]
> wasn't
> updated to take the change on the left branch into account, and so
> we
> still get [3,\infty) as baserange.
>
> With your change, nothing will be done at all. That's fine as far as
> I'm
> concerned. I don't see a clean way of updating the limits on-the-fly.
>
> Thanks for the piglit test. An explanatory comment would be nice,
> but
> either way, this patch is
I'll add your explanation to the commit message.
>
> Reviewed-by: Nicolai Hähnle <nicolai.haeh...@amd.com>
>
>
Thanks :)
>
> > 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-sta...@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;
> > }
> > }
> >
>
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