[Mesa-dev] [Nouveau] [PATCH] nvc0/ir: propagate immediates to CALL input MOVs

[Ilia Mirkin]

On Sat, Aug 12, 2017 at 3:33 PM, Tobias Klausmann
<tobias.johannes.klausmann at mni.thm.de> wrote:
> On using builtin functions we have to move the input to registers $0 and $1, if
> one of the input value is an immediate, we fail to propagate the immediate:
>
> ...
> mov u32 $r477 0x00000003 (0)
> ...
> mov u32 $r0 %r473 (0)
> mov u32 $r1 $r477 (0)
> call abs BUILTIN:0 (0)
> mov u32 %r495 $r1 (0)
> ...
>
> With this patch the immediate is propagated, potentially causing the first MOV
> to be superfluous, which we'd remove in that case:
>
> ...
>
> mov u32 $r0 %r473 (0)
> mov u32 $r1 0x00000003 (0)
> call abs BUILTIN:0 (0)
> mov u32 %r495 $r1 (0)
> ...
>
> Shaderdb stats:
> total instructions in shared programs : 4893460 -> 4893324 (-0.00%)
> total gprs used in shared programs    : 582972 -> 582881 (-0.02%)
> total local used in shared programs   : 17960 -> 17960 (0.00%)
>
>                 local        gpr       inst      bytes
>     helped           0          91         112         112
>       hurt           0           0           0           0
>
> Signed-off-by: Tobias Klausmann <tobias.johannes.klausmann at mni.thm.de>
> ---
>  .../nouveau/codegen/nv50_ir_lowering_nvc0.cpp       | 21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp b/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
> index c8f0701572..861d08af24 100644
> --- a/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
> +++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
> @@ -47,8 +47,25 @@ NVC0LegalizeSSA::handleDIV(Instruction *i)
>     int builtin;
>
>     bld.setPosition(i, false);
> -   bld.mkMovToReg(0, i->getSrc(0));
> -   bld.mkMovToReg(1, i->getSrc(1));
> +
> +   // Generate movs to the input regs for the call we want to generate
> +   for (int s = 0; i->srcExists(s); ++s) {
> +      Instruction *ld = i->getSrc(s)->getInsn();
> +      ImmediateValue imm;
> +      // check if we are moving an immediate, propagate it in that case
> +      if (!ld || ld->fixed || (ld->op != OP_LOAD && ld->op != OP_MOV) ||
> +            !ld->src(0).getImmediate(imm))

At this point you don't even have to use getImmediate - you can just
look at ld->src(0).getFile() == FILE_IMMEDIATE.

Normally you'd just do i->src(s).getImmediate(imm) and moved on with
life. But you kinda need the ld here, which is annoying. Perhaps you
can just drop the manual deletion of the op here... which would let
you do the much simpler thing. Can you see if there's any effect from
that?

> +         bld.mkMovToReg(s, i->getSrc(s));
> +      else {
> +         bld.mkMovToReg(s, ld->getSrc(0));
> +         // Clear the src, to make code elimination possible here before we
> +         // delete the instruction i later
> +         i->setSrc(s, NULL);

i gets deleted later on. move the deletion of ld after that happens?

> +         if (ld->getDef(0)->refCount() == 0)

ld->isDead()

> +            delete_Instruction(prog, ld);
> +      }
> +   }
> +
>     switch (i->dType) {
>     case TYPE_U32: builtin = NVC0_BUILTIN_DIV_U32; break;
>     case TYPE_S32: builtin = NVC0_BUILTIN_DIV_S32; break;
> --
> 2.14.0
>
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