[Mesa-dev] [PATCH] radeonsi: enable 32-bit denormals on VI+

[Marek Olšák]

I've realized there is a small problem with this. MAD never supports
denorms, but MUL+ADD do. That can cause issues, because the compiler
assumes that MAD = MUL+ADD.

We need to use MAD for good performance, which means we should
probably never enable FP32 denorms.

Marek

On Wed, Jan 11, 2017 at 6:29 PM, Samuel Pitoiset
<samuel.pitoiset at gmail.com> wrote:
> Only VI can do 32-bit denormals at full rate while previous
> generations can do it only for 64-bit and 16-bit.
>
> This fixes some dEQP tests with the highp type qualifier.
>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99343
> Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
> ---
>  src/gallium/drivers/radeonsi/si_shader.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/src/gallium/drivers/radeonsi/si_shader.c b/src/gallium/drivers/radeonsi/si_shader.c
> index 5dfbd6603a..e9cb11883f 100644
> --- a/src/gallium/drivers/radeonsi/si_shader.c
> +++ b/src/gallium/drivers/radeonsi/si_shader.c
> @@ -6361,8 +6361,10 @@ int si_compile_llvm(struct si_screen *sscreen,
>
>         si_shader_binary_read_config(binary, conf, 0);
>
> -       /* Enable 64-bit and 16-bit denormals, because there is no performance
> -        * cost.
> +       /* Enable denormals when there is no performance cost.
> +        *
> +        * Only VI can do 32-bit denormals at full rate while previous
> +        * generations can do it only for 64-bit and 16-bit.
>          *
>          * If denormals are enabled, all floating-point output modifiers are
>          * ignored.
> @@ -6373,7 +6375,10 @@ int si_compile_llvm(struct si_screen *sscreen,
>          *   have to stop using those.
>          * - SI & CI would be very slow.
>          */
> -       conf->float_mode |= V_00B028_FP_64_DENORMS;
> +       if (sscreen->b.chip_class >= VI)
> +               conf->float_mode |= V_00B028_FP_ALL_DENORMS;
> +       else
> +               conf->float_mode |= V_00B028_FP_64_DENORMS;
>
>         FREE(binary->config);
>         FREE(binary->global_symbol_offsets);
> --
> 2.11.0
>
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