[Mesa-dev] [PATCH] nir: Add a lower_fdiv option, turn fdiv into fmul/frcp.

[Jason Ekstrand]

Reviewed-by: Jason Ekstrand <jason.ekstrand at intel.com>

On Tue, Jan 5, 2016 at 4:25 PM, Kenneth Graunke <kenneth at whitecape.org>
wrote:

> The nir_opt_algebraic rule
>
> (('fadd', ('flog2', a), ('fneg', ('flog2', b))), ('flog2', ('fdiv', a,
> b))),
>
> can produce new fdiv operations, which need to be lowered on i965,
> as we don't actually implement fdiv.  (Normally, we handle this in
> GLSL IR's lower_instructions pass, but in the above case we introduce
> an fdiv after that point.  So, make NIR do it for us.)
>
> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> Cc: mesa-stable at lists.freedesktop.org
> ---
>  src/glsl/nir/nir.h                       | 1 +
>  src/glsl/nir/nir_opt_algebraic.py        | 1 +
>  src/mesa/drivers/dri/i965/brw_shader.cpp | 1 +
>  3 files changed, 3 insertions(+)
>
> diff --git a/src/glsl/nir/nir.h b/src/glsl/nir/nir.h
> index 4286738..fed8a97 100644
> --- a/src/glsl/nir/nir.h
> +++ b/src/glsl/nir/nir.h
> @@ -1440,6 +1440,7 @@ typedef struct nir_function {
>  } nir_function;
>
>  typedef struct nir_shader_compiler_options {
> +   bool lower_fdiv;
>     bool lower_ffma;
>     bool lower_flrp;
>     bool lower_fpow;
> diff --git a/src/glsl/nir/nir_opt_algebraic.py
> b/src/glsl/nir/nir_opt_algebraic.py
> index 1fdad3d..c553de5 100644
> --- a/src/glsl/nir/nir_opt_algebraic.py
> +++ b/src/glsl/nir/nir_opt_algebraic.py
> @@ -183,6 +183,7 @@ optimizations = [
>     (('fmul', ('fexp2', a), ('fexp2', b)), ('fexp2', ('fadd', a, b))),
>     # Division and reciprocal
>     (('fdiv', 1.0, a), ('frcp', a)),
> +   (('fdiv', a, b), ('fmul', a, ('frcp', b)), 'options->lower_fdiv'),
>     (('frcp', ('frcp', a)), a),
>     (('frcp', ('fsqrt', a)), ('frsq', a)),
>     (('fsqrt', a), ('frcp', ('frsq', a)), 'options->lower_fsqrt'),
> diff --git a/src/mesa/drivers/dri/i965/brw_shader.cpp
> b/src/mesa/drivers/dri/i965/brw_shader.cpp
> index d4b6410..4bd24a7 100644
> --- a/src/mesa/drivers/dri/i965/brw_shader.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_shader.cpp
> @@ -97,6 +97,7 @@ brw_compiler_create(void *mem_ctx, const struct
> brw_device_info *devinfo)
>     nir_shader_compiler_options *nir_options =
>        rzalloc(compiler, nir_shader_compiler_options);
>     nir_options->native_integers = true;
> +   nir_options->lower_fdiv = true;
>     /* In order to help allow for better CSE at the NIR level we tell NIR
>      * to split all ffma instructions during opt_algebraic and we then
>      * re-combine them as a later step.
> --
> 2.6.4
>
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