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

[Samuel Pitoiset]

On 01/11/2017 07:49 PM, Marek Olšák wrote:
> 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.

Yeah, this is explained in the code also, but according to your comment 
on Bugzilla, I thought VI+ was not affected by that...

>
> 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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