[Mesa-dev] [PATCH] nir: add flt comparision simplification

[Timothy Arceri]

Actually I might just try moving this to the late block as the reason
for 'is_not_used_by_conditional' is to stop getting in the way of
ffmas.

On Fri, 2017-01-13 at 08:29 +1100, Timothy Arceri wrote:
> Didn't turn out as useful as I'd hoped, but it will help alot more on
> i965 by reducing regressions when we drop
> brw_do_channel_expressions()
> and brw_do_vector_splitting().
> 
> I'm not sure how much sense 'is_not_used_by_conditional' makes on
> platforms other than i965 but since this is a new opt it at least
> won't do any harm.
> 
> shader-db BDW:
> 
> total instructions in shared programs: 13060410 -> 13060242 (-0.00%)
> instructions in affected programs: 44880 -> 44712 (-0.37%)
> helped: 86
> HURT: 0
> 
> total cycles in shared programs: 256585692 -> 256584248 (-0.00%)
> cycles in affected programs: 8060766 -> 8059322 (-0.02%)
> helped: 177
> HURT: 33
> ---
>  src/compiler/nir/nir_opt_algebraic.py |  4 ++++
>  src/compiler/nir/nir_search_helpers.h | 15 +++++++++++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/src/compiler/nir/nir_opt_algebraic.py
> b/src/compiler/nir/nir_opt_algebraic.py
> index 3c8318c..59f9e43 100644
> --- a/src/compiler/nir/nir_opt_algebraic.py
> +++ b/src/compiler/nir/nir_opt_algebraic.py
> @@ -159,6 +159,10 @@ optimizations = [
>     # a != 0.0
>     (('flt', 0.0, ('fabs', a)), ('fne', a, 0.0)),
>  
> +   # ignore this opt when the result is used by a bcsel or if so we
> can make
> +   # use of conditional modifiers on supported hardware.
> +   (('flt(is_not_used_by_conditional)', ('fadd(is_used_once)', a,
> ('fneg', b)), 0.0), ('flt', a, b)),
> +
>     (('fge', ('fneg', ('fabs', a)), 0.0), ('feq', a, 0.0)),
>     (('bcsel', ('flt', b, a), b, a), ('fmin', a, b)),
>     (('bcsel', ('flt', a, b), b, a), ('fmax', a, b)),
> diff --git a/src/compiler/nir/nir_search_helpers.h
> b/src/compiler/nir/nir_search_helpers.h
> index ddaff52..05bd317 100644
> --- a/src/compiler/nir/nir_search_helpers.h
> +++ b/src/compiler/nir/nir_search_helpers.h
> @@ -158,4 +158,19 @@ is_not_used_by_if(nir_alu_instr *instr)
>     return list_empty(&instr->dest.dest.ssa.if_uses);
>  }
>  
> +static inline bool
> +is_not_used_by_conditional(nir_alu_instr *instr)
> +{
> +   if (!is_not_used_by_if(instr))
> +      return false;
> +
> +   nir_foreach_use(use, &instr->dest.dest.ssa) {
> +      if (use->parent_instr->type == nir_instr_type_alu &&
> +          nir_instr_as_alu(use->parent_instr)->op == nir_op_bcsel)
> +         return false;
> +   }
> +
> +   return true;
> +}
> +
>  #endif /* _NIR_SEARCH_ */