[Mesa-dev] [PATCH] nv50/ir: replace the right def in global cse

[Ilia Mirkin]

Actually this is still a little bogus... We'd have to ensure that
*all* of the defs are used in this bb or later. I'll try to come up
with something that still maintains some of the potential benefit but
is correct.

On Mon, Jan 11, 2016 at 10:06 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> GlobalCSE looks for phi nodes with identically-defined sources, and
> replaces them with one of the (identical) instructions.
>
> However the defining instruction might have multiple defs, so we have to
> replace the one that the original phi node was pointing at.
>
> Observed when playing around with st_glsl_to_tgsi optimization settings,
> this produced a shader where a texture op was being propagated. We would
> always end up setting its first def instead of the one the phi node was
> pointing at.
>
> Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
> ---
>  .../drivers/nouveau/codegen/nv50_ir_peephole.cpp    | 21 +++++++++++++--------
>  1 file changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp b/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp
> index 24caf18..aa56078 100644
> --- a/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp
> +++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp
> @@ -3028,7 +3028,7 @@ bool
>  GlobalCSE::visit(BasicBlock *bb)
>  {
>     Instruction *phi, *next, *ik;
> -   int s;
> +   int s, d;
>
>     // TODO: maybe do this with OP_UNION, too
>
> @@ -3048,13 +3048,18 @@ GlobalCSE::visit(BasicBlock *bb)
>        }
>        if (!phi->srcExists(s)) {
>           Instruction *entry = bb->getEntry();
> -         ik->bb->remove(ik);
> -         if (!entry || entry->op != OP_JOIN)
> -            bb->insertHead(ik);
> -         else
> -            bb->insertAfter(entry, ik);
> -         ik->setDef(0, phi->getDef(0));
> -         delete_Instruction(prog, phi);
> +         for (d = 0; ik->defExists(d); ++d)
> +            if (ik->getDef(d) == phi->getSrc(0))
> +               break;
> +         if (ik->defExists(d)) {
> +            ik->bb->remove(ik);
> +            if (!entry || entry->op != OP_JOIN)
> +               bb->insertHead(ik);
> +            else
> +               bb->insertAfter(entry, ik);
> +            ik->setDef(d, phi->getDef(0));
> +            delete_Instruction(prog, phi);
> +         }
>        }
>     }
>
> --
> 2.4.10
>