[Mesa-dev] [PATCH] nv50/ir: optimmize shl(a, 0) to a

[Ilia Mirkin]

On Sat, Apr 29, 2017 at 12:46 PM, Karol Herbst <karolherbst at gmail.com> wrote:
> helps two alien isolation shaders
>
> shader-db:
> total instructions in shared programs : 4251497 -> 4251494 (-0.00%)
> total gprs used in shared programs    : 513962 -> 513962 (0.00%)
> total local used in shared programs   : 29797 -> 29797 (0.00%)
> total bytes used in shared programs   : 38960264 -> 38960232 (-0.00%)
>
>                 local        gpr       inst      bytes
>     helped           0           0           2           2
>       hurt           0           0           0           0
>
> Signed-off-by: Karol Herbst <karolherbst at gmail.com>
> ---
>  src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp b/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp
> index 015def0391..a2446e4df8 100644
> --- a/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp
> +++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp
> @@ -1284,6 +1284,11 @@ ConstantFolding::opnd(Instruction *i, ImmediateValue &imm0, int s)
>
>     case OP_SHL:
>     {
> +      if (s == 1 && imm0.isInteger(0)) {
> +         i->op = OP_MOV;
> +         i->setSrc(1, NULL);
> +         break;
> +      }
>        if (s != 1 || i->src(0).mod != Modifier(0))
>           break;

Interesting. This suggests that src(0) may have modifiers, although I
can't imagine what that'd be. Perhaps it can take a neg? In that case,
you need to fix the OP_MOV above -- should probably do it anyways,
i.e. i->op = i->src(0).mod.getOp() or something. With that, this is

Reviewed-by: Ilia Mirkin <imirkin at alum.mit.edu>

Separately, I just noticed that we don't appear to have any 0 << x or
0 >> y or EXTBF or anything like that. I doubt it comes up too often
though.

>        // try to concatenate shifts
> --
> 2.12.2
>