[Mesa-dev] [PATCH 1/2] nir/dead_cf: Don't crash on unreachable after-loop blocks

[Jason Ekstrand]

On Thu, Sep 1, 2016 at 12:41 PM, Connor Abbott <cwabbott0 at gmail.com> wrote:

> As-is, this change will make us delete trivially infinite loops (i.e.
> loops with no break statement). The most likely scenario where we get
> one of those (besides for silly Piglit tests) is a developer with an
> accidental bug in their shader. In that case, it seems kinda mean to
> then delete the entire loop and pretend like it doesn't exist. Maybe
> add something like
>
> if (!after->imm_dom)
>    return false;
>
> with a comment explaining what's going on? This would also help us
> catch other places where we don't handle infinite loops correctly that
> might've been hidden by this.
>

I wrote that patch and kicked it off to Jenkins and it passed just fine.
However, I don't know if I like it.  Matt and I were talking about this
yesterday and his suggestion was to, if they have an infinite loop, delete
the entire shader and draw pink.  That's more useful to developers than
hanging their GPU.

On Thu, Sep 1, 2016 at 3:11 PM, Jason Ekstrand <jason at jlekstrand.net> wrote:
> > Signed-off-by: Jason Ekstrand <jason at jlekstrand.net>
> > ---
> >  src/compiler/nir/nir_opt_dead_cf.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/src/compiler/nir/nir_opt_dead_cf.c
> b/src/compiler/nir/nir_opt_dead_cf.c
> > index 3551124..1490e68 100644
> > --- a/src/compiler/nir/nir_opt_dead_cf.c
> > +++ b/src/compiler/nir/nir_opt_dead_cf.c
> > @@ -205,7 +205,8 @@ loop_is_dead(nir_loop *loop)
> >     nir_metadata_require(impl, nir_metadata_live_ssa_defs |
> >                                nir_metadata_dominance);
> >
> > -   for (nir_block *cur = after->imm_dom; cur != before; cur =
> cur->imm_dom) {
> > +   for (nir_block *cur = after->imm_dom; cur && cur != before;
> > +        cur = cur->imm_dom) {
> >        nir_foreach_instr(instr, cur) {
> >           if (!nir_foreach_ssa_def(instr, def_not_live_out, after))
> >              return false;
> > --
> > 2.5.0.400.gff86faf
> >
> > _______________________________________________
> > mesa-dev mailing list
> > mesa-dev at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/mesa-dev
>
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