[Mesa-dev] [PATCH v2] nir: Implement optional b2f->iand lowering

[Christian Gmeiner]

Am Mi., 2. Mai 2018 um 09:50 Uhr schrieb Alyssa Rosenzweig <
alyssa at rosenzweig.io>:

> This pass is required by the Midgard compiler; our instruction set uses
> NIR-style booleans (~0 for true) but lacks a dedicated b2f instruction.
> Normally, this lowering pass would be implemented in a backend-specific
> algebraic pass, but this conflicts with the existing iand->b2f pass in
> nir_opt_algebraic.py, hanging the compiler. This patch thus makes the
> existing pass optional (default on -- all other backends should remain
> unaffected), adding an optional pass for lowering the opposite
> direction.

> v2: Defer lowering until late algebraic optimisations to allow
> optimising the b2f instruction itself.

> Signed-off-by: Alyssa Rosenzweig <alyssa at rosenzweig.io>

LGTM - will push it for you that it don't get lost.

Reviewed-by: Christian Gmeiner <christian.gmeiner at gmail.com>

> ---
>   src/compiler/nir/nir.h                | 3 +++
>   src/compiler/nir/nir_opt_algebraic.py | 5 ++++-
>   2 files changed, 7 insertions(+), 1 deletion(-)

> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
> index 5b28c727c8..fe0887865c 100644
> --- a/src/compiler/nir/nir.h
> +++ b/src/compiler/nir/nir.h
> @@ -1862,6 +1862,9 @@ typedef struct nir_shader_compiler_options {
>      /** enables rules to lower idiv by power-of-two: */
>      bool lower_idiv;

> +   /* lower b2f to iand */
> +   bool lower_b2f;
> +
>      /* Does the native fdot instruction replicate its result for four
>       * components?  If so, then opt_algebraic_late will turn all fdotN
>       * instructions into fdot_replicatedN instructions.
> diff --git a/src/compiler/nir/nir_opt_algebraic.py
b/src/compiler/nir/nir_opt_algebraic.py
> index c9575e6be4..99b5e57f30 100644
> --- a/src/compiler/nir/nir_opt_algebraic.py
> +++ b/src/compiler/nir/nir_opt_algebraic.py
> @@ -318,7 +318,7 @@ optimizations = [
>      (('imul', ('b2i', a), ('b2i', b)), ('b2i', ('iand', a, b))),
>      (('fmul', ('b2f', a), ('b2f', b)), ('b2f', ('iand', a, b))),
>      (('fsat', ('fadd', ('b2f', a), ('b2f', b))), ('b2f', ('ior', a, b))),
> -   (('iand', 'a at bool', 1.0), ('b2f', a)),
> +   (('iand', 'a at bool', 1.0), ('b2f', a), '!options->lower_b2f'),
>      # True/False are ~0 and 0 in NIR.  b2i of True is 1, and -1 is ~0
(True).
>      (('ineg', ('b2i at 32', a)), a),
>      (('flt', ('fneg', ('b2f', a)), 0), a), # Generated by TGSI KILL_IF.
> @@ -721,6 +721,9 @@ late_optimizations = [
>      # we do these late so that we don't get in the way of creating ffmas
>      (('fmin', ('fadd(is_used_once)', '#c', a), ('fadd(is_used_once)',
'#c', b)), ('fadd', c, ('fmin', a, b))),
>      (('fmax', ('fadd(is_used_once)', '#c', a), ('fadd(is_used_once)',
'#c', b)), ('fadd', c, ('fmax', a, b))),
> +
> +   # Lowered for backends without a dedicated b2f instruction
> +   (('b2f at 32', a), ('iand', a, 1.0), 'options->lower_b2f'),
>   ]

>   print nir_algebraic.AlgebraicPass("nir_opt_algebraic",
optimizations).render()
> --
> 2.16.1

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-- 
greets
--
Christian Gmeiner, MSc

https://christian-gmeiner.info