[Mesa-dev] [PATCH] ac/nir: use llvm fma intrinsic if nir instruction is exact.

[Connor Abbott]

Why? While it might technically be legal, always generating an unfused
mul+add when the user explicitly requested fma() seems harsh...

On Thu, Oct 5, 2017 at 9:32 PM, Marek Olšák <maraeo at gmail.com> wrote:
> FYI, if we switch radeonsi to NIR, we are going to disable fma
> completely, exact or not.
>
> Marek
>
> On Wed, Oct 4, 2017 at 10:04 PM, Dave Airlie <airlied at gmail.com> wrote:
>> From: Dave Airlie <airlied at redhat.com>
>>
>> As pointed out by Connor we still need to use fma if nir wants
>> exact (precise) behaviour.
>>
>> Signed-off-by: Dave Airlie <airlied at redhat.com>
>> ---
>>  src/amd/common/ac_nir_to_llvm.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/src/amd/common/ac_nir_to_llvm.c b/src/amd/common/ac_nir_to_llvm.c
>> index 11ba487..38a2bbe 100644
>> --- a/src/amd/common/ac_nir_to_llvm.c
>> +++ b/src/amd/common/ac_nir_to_llvm.c
>> @@ -1707,7 +1707,7 @@ static void visit_alu(struct ac_nir_context *ctx, const nir_alu_instr *instr)
>>                                                       result);
>>                 break;
>>         case nir_op_ffma:
>> -               result = emit_intrin_3f_param(&ctx->ac, "llvm.fmuladd",
>> +               result = emit_intrin_3f_param(&ctx->ac, instr->exact ? "llvm.fma" : "llvm.fmuladd",
>>                                               ac_to_float_type(&ctx->ac, def_type), src[0], src[1], src[2]);
>>                 break;
>>         case nir_op_ibitfield_extract:
>> --
>> 2.9.5
>>
>> _______________________________________________
>> mesa-dev mailing list
>> mesa-dev at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
> _______________________________________________
> mesa-dev mailing list
> mesa-dev at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/mesa-dev