On Fri, 2019-02-08 at 15:39 -0600, Jason Ekstrand wrote:
> I had a chat with Caio about this and I'm skeptical. In general, users of
> the CF manipulation code shouldn't be stitching two blocks together where the
> first contains a jump and the second is non-empty. If the caller knows that
> this case is ok, then they can check for it and empty out the one block
> before stitching. Also, I'm not really seeing how peel_initial_if would hit
> this case from your example.
>
I'll re-check again, as with the last changes in Mesa the problem moved to a
different place.
J.A.
> --Jason
>
>
> On Fri, Jan 25, 2019 at 11:37 AM Juan A. Suarez Romero <jasua...@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 <ja...@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])
> >
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