[Mesa-dev] [PATCH 7/9] nir/peephole_ffma: Be less agressive about fusing multiply-adds

[Matt Turner]

On Mon, Mar 23, 2015 at 8:13 PM, Jason Ekstrand <jason at jlekstrand.net> wrote:
> shader-db results for fragment shaders on Haswell:
> total instructions in shared programs: 4395688 -> 4389623 (-0.14%)
> instructions in affected programs:     355876 -> 349811 (-1.70%)
> helped:                                1455
> HURT:                                  14
> GAINED:                                5
> LOST:                                  0
> ---

Subject: s/agressive/aggressive/

>  src/glsl/nir/nir_opt_peephole_ffma.c | 41 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 41 insertions(+)
>
> diff --git a/src/glsl/nir/nir_opt_peephole_ffma.c b/src/glsl/nir/nir_opt_peephole_ffma.c
> index 4674505..b875bb6 100644
> --- a/src/glsl/nir/nir_opt_peephole_ffma.c
> +++ b/src/glsl/nir/nir_opt_peephole_ffma.c
> @@ -38,6 +38,41 @@ struct peephole_ffma_state {
>     bool progress;
>  };
>
> +static inline bool

No point in inline. The compiler will see it's only used in one place
and make an appropriate decision.

> +are_all_uses_fadd(nir_ssa_def *def)
> +{
> +   if (def->if_uses->entries > 0)
> +      return false;
> +
> +   struct set_entry *use_iter;
> +   set_foreach(def->uses, use_iter) {
> +      nir_instr *use_instr = (nir_instr *)use_iter->key;
> +
> +      if (use_instr->type != nir_instr_type_alu)
> +         return false;
> +
> +      nir_alu_instr *use_alu = nir_instr_as_alu(use_instr);
> +      switch (use_alu->op) {
> +      case nir_op_fadd:
> +         break; /* This one's ok */
> +
> +      case nir_op_imov:
> +      case nir_op_fmov:
> +      case nir_op_fneg:
> +      case nir_op_fabs:
> +         assert(use_alu->dest.dest.is_ssa);
> +         if (!are_all_uses_fadd(&use_alu->dest.dest.ssa))
> +            return false;
> +         break;
> +
> +      default:
> +         return false;
> +      }
> +   }
> +
> +   return true;
> +}
> +
>  static inline nir_alu_instr *
>  get_mul_for_src(nir_alu_src *src, uint8_t swizzle[4], bool *negate, bool *abs)
>  {
> @@ -66,6 +101,12 @@ get_mul_for_src(nir_alu_src *src, uint8_t swizzle[4], bool *negate, bool *abs)
>        break;
>
>     case nir_op_fmul:
> +      /* Only absorbe a fmul into a ffma if the fmul is is only used in fadd

typo: absorb
> +       * operations.  This prevents us from being too agressive with our

typo: aggressive

> +       * fusing which can actually lead to more instructions.
> +       */
> +      if (!are_all_uses_fadd(&alu->dest.dest.ssa))
> +         return NULL;
>        break;
>
>     default:
> --
> 2.3.3