[Mesa-dev] [PATCH] nir: allow stitching of non-empty block

[Juan A. Suarez Romero]

On Sat, 2019-01-26 at 08:37 -0800, Jason Ekstrand wrote:
> This makes me a bit nervous. I'll have to look at it in more detail.
> 

Did you have time to take a look at this?


	J.A.

> On January 25, 2019 09:37:52 "Juan A. Suarez Romero" <jasuarez at igalia.com> 
> wrote:
> 
> > When stitching two blocks A and B, where A's last instruction is a jump,
> > it is not required that B is empty; it can be plainly removed.
> > 
> > This can happen in a situation like this:
> > 
> > vec1 1 ssa_1 = load_const (true)
> > vec1 1 ssa_2 = load_const (false)
> > block block_1:
> > [...]
> > loop {
> >  vec1 ssa_3 = phi block_1: ssa_2, block_4: ssa_1
> >  if ssa_3 {
> >    block block_2:
> >    [...]
> >    break
> >  } else {
> >    block block_3:
> >  }
> >  vec1 ssa_4 = <alu operation>
> >  if ssa_4 {
> >    block block_4:
> >    continue
> >  } else {
> >    block block_5:
> >  }
> >  block block_6:
> >  [...]
> > }
> > 
> > And opt_peel_loop_initial_if is applied. In this case, we would be
> > ending up stitching block_2 (which finalizes with a jump) with
> > block_4, which is not empty.
> > 
> > CC: Jason Ekstrand <jason at jlekstrand.net>
> > ---
> > src/compiler/nir/nir_control_flow.c | 1 -
> > 1 file changed, 1 deletion(-)
> > 
> > diff --git a/src/compiler/nir/nir_control_flow.c 
> > b/src/compiler/nir/nir_control_flow.c
> > index ddba2e55b45..27508f230d6 100644
> > --- a/src/compiler/nir/nir_control_flow.c
> > +++ b/src/compiler/nir/nir_control_flow.c
> > @@ -550,7 +550,6 @@ stitch_blocks(nir_block *before, nir_block *after)
> >     */
> > 
> >    if (nir_block_ends_in_jump(before)) {
> > -      assert(exec_list_is_empty(&after->instr_list));
> >       if (after->successors[0])
> >          remove_phi_src(after->successors[0], after);
> >       if (after->successors[1])
> > --
> > 2.20.1
> 
> 
>