[Mesa-dev] [PATCH] nir/spirv: short-circuit when conditional branch contains end block

[Juan A. Suarez Romero]

On Thu, 2019-03-14 at 11:25 -0500, Jason Ekstrand wrote:
> Looking at this a bit more, I'm not sure that just short-circuiting actually covers all the cases.  Unfortunately, we don't know what all the cases are because the SPIR-V spec doesn't say.  I'm trying to work towards fixing that right now.
> 
> 

Did you have time to check this?
	J.A.
> --Jason
> 
> 
> On Wed, Mar 6, 2019 at 5:25 AM Juan A. Suarez Romero <jasuarez at igalia.com> wrote:
> > This fixes the case when the SPIR-V code has two nested conditional
> > 
> > branches, but only one selection merge:
> > 
> > 
> > 
> > [...]
> > 
> > %1 = OpLabel
> > 
> >      OpSelectionMerge %2 None
> > 
> >      OpBranchConditional %3 %4 %2
> > 
> > %4 = OpLabel
> > 
> >      OpBranchConditional %3 %5 %2
> > 
> > %5 = OpLabel
> > 
> >      OpBranch %2
> > 
> > %2 = OpLabel
> > 
> > [...]
> > 
> > 
> > 
> > In the second OpBranchConditional, as the else-part is the end
> > 
> > block (started in the first OpBranchConditional) we can just follow the
> > 
> > then-part.
> > 
> > 
> > 
> > This fixes dEQP-VK.vkrunner.controlflow.2-obc-triangle-triangle
> > 
> > 
> > 
> > CC: Jason Ekstrand <jason at jlekstrand.net>
> > 
> > ---
> > 
> >  src/compiler/spirv/vtn_cfg.c | 11 ++++++++++-
> > 
> >  1 file changed, 10 insertions(+), 1 deletion(-)
> > 
> > 
> > 
> > diff --git a/src/compiler/spirv/vtn_cfg.c b/src/compiler/spirv/vtn_cfg.c
> > 
> > index 7868eeb60bc..f749118efbe 100644
> > 
> > --- a/src/compiler/spirv/vtn_cfg.c
> > 
> > +++ b/src/compiler/spirv/vtn_cfg.c
> > 
> > @@ -605,7 +605,16 @@ vtn_cfg_walk_blocks(struct vtn_builder *b, struct list_head *cf_list,
> > 
> >              }
> > 
> >           } else if (if_stmt->then_type == vtn_branch_type_none &&
> > 
> >                      if_stmt->else_type == vtn_branch_type_none) {
> > 
> > -            /* Neither side of the if is something we can short-circuit. */
> > 
> > +            /* Neither side of the if is something we can short-circuit,
> > 
> > +             * unless one of the blocks is the end block. */
> > 
> > +            if (then_block == end) {
> > 
> > +               block = else_block;
> > 
> > +               continue;
> > 
> > +            } else if (else_block == end) {
> > 
> > +               block = then_block;
> > 
> > +               continue;
> > 
> > +            }
> > 
> > +
> > 
> >              vtn_assert((*block->merge & SpvOpCodeMask) == SpvOpSelectionMerge);
> > 
> >              struct vtn_block *merge_block =
> > 
> >                 vtn_value(b, block->merge[1], vtn_value_type_block)->block;
> > 
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