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radeonsi: fuse or lower ffma optimally on all chips

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LLVM is going to support the legacy instructions soon.

This change switches FMA to MAD for gfx10.

54793 shaders in 33659 tests
Totals:
SGPRS: 2632554 -> 2629570 (-0.11 %)
VGPRS: 1536364 -> 1535312 (-0.07 %)
Spilled SGPRs: 3602 -> 3562 (-1.11 %)
Spilled VGPRs: 44 -> 40 (-9.09 %)
Private memory VGPRs: 256 -> 256 (0.00 %)
Scratch size: 312 -> 308 (-1.28 %) dwords per thread
Code Size: 55422660 -> 55345408 (-0.14 %) bytes
Max Waves: 963983 -> 964200 (0.02 %)

Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6756>
This commit is contained in:
Marek Olšák 2020-09-16 22:06:22 -04:00 • committed by Marge Bot
parent 771aad3027
commit f1284505f0
2 changed files with 21 additions and 13 deletions
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2
src/amd/llvm/ac_nir_to_llvm.c
View file

@ -862,7 +862,7 @@ static void visit_alu(struct ac_nir_context *ctx, const nir_alu_instr *instr)
break;
case nir_op_ffma:
/* FMA is slow on gfx6-8, so it shouldn't be used. */
assert(ctx->ac.chip_class >= GFX9);
assert(instr->dest.dest.ssa.bit_size != 32 || ctx->ac.chip_class >= GFX9);
result = emit_intrin_3f_param(&ctx->ac, "llvm.fma", ac_to_float_type(&ctx->ac, def_type),
src[0], src[1], src[2]);
break;

32
src/gallium/drivers/radeonsi/si_get.c
View file

@ -937,20 +937,28 @@ void si_init_screen_get_functions(struct si_screen *sscreen)
.lower_bitfield_insert_to_bitfield_select = true,
.lower_bitfield_extract = true,
.lower_sub = true,
/* gfx6-8: use MAD (FMA is 4x slower)
* gfx9-10: either is OK (MAD and FMA have the same performance)
* gfx10.3: use FMA (MAD doesn't exist, separate MUL+ADD are 2x slower)
/* |---------------------------------- Performance & Availability --------------------------------|
* |MAD/MAC/MADAK/MADMK|MAD_LEGACY|MAC_LEGACY| FMA |FMAC/FMAAK/FMAMK|FMA_LEGACY|PK_FMA_F16,|Best choice
* Arch | F32,F16,F64 | F32,F16 | F32,F16 |F32,F16,F64 | F32,F16 | F32,F16 |PK_FMAC_F16|F16,F32,F64
* ------------------------------------------------------------------------------------------------------------------
* gfx6,7 | 1 , - , - | 1 , - | 1 , - |1/4, - ,1/16| - , - | - , - | - , - | - ,MAD,FMA
* gfx8 | 1 , 1 , - | 1 , - | - , - |1/4, 1 ,1/16| - , - | - , - | - , - |MAD,MAD,FMA
* gfx9 | 1 , 1 , - | 1 , - | 1 , - | 1 , 1 ,1/16| - , - | - , 1 | 2 , - |FMA,MAD,FMA
* gfx10 | 1 , 1 , - | 1 , - | 1 , - | 1 , 1 ,1/16| 1 , 1 | - , - | 2 , 2 |FMA,MAD,FMA
* gfx10.3| - , - , - | - , - | - , - | 1 , 1 ,1/16| 1 , 1 | 1 , - | 2 , 2 | all FMA
*
* FMA has no advantage on gfx9-10 and MAD allows more algebraic optimizations.
* Keep FMA enabled on gfx10 to test it, which helps us validate correctness
* for gfx10.3 on gfx10.
* Tahiti, Hawaii, Carrizo, Vega20: FMA_F32 is full rate, FMA_F64 is 1/4
*
* gfx8 prefers MAD for F16 because of MAC/MADAK/MADMK.
* gfx9 and newer prefer FMA for F16 because of the packed instruction.
* gfx10 and older prefer MAD for F32 because of the legacy instruction.
*/
.lower_ffma16 = sscreen->info.chip_class <= GFX9,
.lower_ffma32 = sscreen->info.chip_class <= GFX9,
.lower_ffma64 = sscreen->info.chip_class <= GFX9,
.fuse_ffma16 = sscreen->info.chip_class >= GFX10,
.fuse_ffma32 = sscreen->info.chip_class >= GFX10,
.fuse_ffma64 = sscreen->info.chip_class >= GFX10,
.lower_ffma16 = sscreen->info.chip_class < GFX9,
.lower_ffma32 = sscreen->info.chip_class < GFX10_3,
.lower_ffma64 = false,
.fuse_ffma16 = sscreen->info.chip_class >= GFX9,
.fuse_ffma32 = sscreen->info.chip_class >= GFX10_3,
.fuse_ffma64 = true,
.lower_fmod = true,
.lower_pack_snorm_4x8 = true,
.lower_pack_unorm_4x8 = true,