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intel/fs: Better handle constant sources of FS_OPCODE_PACK_HALF_2x16_SPLIT

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I noticed that a *LOT* of fragment shaders in Shadow of the Tomb Raider,
for instance, end up with a sequence of NIR like:

    vec1 32 ssa_2 = load_const (0x00000000 = 0.000000)
    ...
    vec1 32 ssa_191 = pack_half_2x16_split ssa_188, ssa_2
    vec1 32 ssa_192 = pack_half_2x16_split ssa_189, ssa_2
    vec1 32 ssa_193 = pack_half_2x16_split ssa_190, ssa_2

This results in an assembly sequence like:

    mov(8)          g28<1>UD        0x00000000UD
    mov(8)          g21<2>HF        g28<8,8,1>F
    shl(8)          g21<1>UD        g21<8,8,1>UD    0x00000010UD
    mov(8)          g21<2>HF        g25<8,8,1>F
    mov(8)          g19<2>HF        g28<8,8,1>F
    shl(8)          g19<1>UD        g19<8,8,1>UD    0x00000010UD
    mov(8)          g19<2>HF        g23<8,8,1>F
    mov(8)          g20<2>HF        g28<8,8,1>F
    shl(8)          g20<1>UD        g20<8,8,1>UD    0x00000010UD
    mov(8)          g20<2>HF        g24<8,8,1>F

After this commit, the generated assembly is:

    mov(8)          g21<1>UD        0x00000000UD
    mov(8)          g21<2>HF        g23<8,8,1>F
    mov(8)          g19<1>UD        0x00000000UD
    mov(8)          g19<2>HF        g17<8,8,1>F
    mov(8)          g20<1>UD        0x00000000UD
    mov(8)          g20<2>HF        g18<8,8,1>F

Tiger Lake, Ice Lake, Skylake, and Haswell had similar results. (Ice Lake shown)
total instructions in shared programs: 20119086 -> 20119034 (<.01%)
instructions in affected programs: 9056 -> 9004 (-0.57%)
helped: 8
HURT: 0
helped stats (abs) min: 2 max: 16 x̄: 6.50 x̃: 4
helped stats (rel) min: 0.29% max: 1.75% x̄: 1.00% x̃: 0.98%
95% mean confidence interval for instructions value: -11.01 -1.99
95% mean confidence interval for instructions %-change: -1.56% -0.44%
Instructions are helped.

total cycles in shared programs: 861019414 -> 861021044 (<.01%)
cycles in affected programs: 279862 -> 281492 (0.58%)
helped: 4
HURT: 2
helped stats (abs) min: 6 max: 936 x̄: 239.00 x̃: 7
helped stats (rel) min: 0.03% max: 8.13% x̄: 2.09% x̃: 0.09%
HURT stats (abs)   min: 18 max: 2568 x̄: 1293.00 x̃: 1293
HURT stats (rel)   min: 0.36% max: 1.14% x̄: 0.75% x̃: 0.75%
95% mean confidence interval for cycles value: -972.56 1515.89
95% mean confidence interval for cycles %-change: -4.77% 2.49%
Inconclusive result (value mean confidence interval includes 0).

Broadwell
total instructions in shared programs: 17812327 -> 17812263 (<.01%)
instructions in affected programs: 9867 -> 9803 (-0.65%)
helped: 8
HURT: 0
helped stats (abs) min: 2 max: 28 x̄: 8.00 x̃: 4
helped stats (rel) min: 0.32% max: 1.80% x̄: 1.00% x̃: 0.95%
95% mean confidence interval for instructions value: -15.46 -0.54
95% mean confidence interval for instructions %-change: -1.54% -0.47%
Instructions are helped.

total cycles in shared programs: 904768620 -> 904773291 (<.01%)
cycles in affected programs: 454799 -> 459470 (1.03%)
helped: 4
HURT: 4
helped stats (abs) min: 36 max: 586 x̄: 344.50 x̃: 378
helped stats (rel) min: 0.47% max: 4.04% x̄: 2.01% x̃: 1.77%
HURT stats (abs)   min: 1 max: 5572 x̄: 1512.25 x̃: 238
HURT stats (rel)   min: <.01% max: 2.77% x̄: 1.46% x̃: 1.53%
95% mean confidence interval for cycles value: -1122.40 2290.15
95% mean confidence interval for cycles %-change: -2.26% 1.71%
Inconclusive result (value mean confidence interval includes 0).

total spills in shared programs: 18581 -> 18579 (-0.01%)
spills in affected programs: 323 -> 321 (-0.62%)
helped: 1
HURT: 0

total fills in shared programs: 24985 -> 24981 (-0.02%)
fills in affected programs: 1348 -> 1344 (-0.30%)
helped: 1
HURT: 0

Tiger Lake, Ice Lake, and Skylake had similar results. (Ice Lake shown)
Instructions in all programs: 143585431 -> 143513657 (-0.0%)
Instructions helped: 14403

Cycles in all programs: 8439312778 -> 8439371578 (+0.0%)
Cycles helped: 10570
Cycles hurt: 3290

Gained: 146
Lost: 74

All of the lost and gained fossil-db shaders are SIMD32 fragment
shaders.  14,247 of the affected shaders are from Shadow of the Tomb
Raider.  154 are from Batman Arkham Origins, and the remaining two are
from Octopath Traveler.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15089>
This commit is contained in:
Ian Romanick 2022-02-14 14:07:18 -08:00 • committed by Marge Bot
parent 1fb4427a7a
commit b5fa43952a
2 changed files with 21 additions and 10 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

5
src/intel/compiler/brw_fs_copy_propagation.cpp
View file

@ -934,6 +934,11 @@ fs_visitor::try_constant_propagate(fs_inst *inst, acp_entry *entry)
progress = true;
break;
case FS_OPCODE_PACK_HALF_2x16_SPLIT:
inst->src[i] = val;
progress = true;
break;
default:
break;
}

26
src/intel/compiler/brw_fs_generator.cpp
View file

@ -31,6 +31,7 @@
#include "brw_fs.h"
#include "brw_cfg.h"
#include "util/mesa-sha1.h"
#include "util/half_float.h"
static enum brw_reg_file
brw_file_from_reg(fs_reg *reg)
@ -1782,17 +1783,22 @@ fs_generator::generate_pack_half_2x16_split(fs_inst *,
? BRW_REGISTER_TYPE_HF : BRW_REGISTER_TYPE_W;
struct brw_reg dst_w = spread(retype(dst, t), 2);
/* Give each 32-bit channel of dst the form below, where "." means
* unchanged.
* 0x....hhhh
*/
brw_F32TO16(p, dst_w, y);
if (y.file == IMM) {
const uint32_t hhhh0000 = _mesa_float_to_half(y.f) << 16;
brw_MOV(p, dst, brw_imm_ud(hhhh0000));
} else {
/* Give each 32-bit channel of dst the form below, where "." means
* unchanged.
* 0x....hhhh
*/
brw_F32TO16(p, dst_w, y);
/* Now the form:
* 0xhhhh0000
*/
brw_set_default_swsb(p, tgl_swsb_regdist(1));
brw_SHL(p, dst, dst, brw_imm_ud(16u));
/* Now the form:
* 0xhhhh0000
*/
brw_set_default_swsb(p, tgl_swsb_regdist(1));
brw_SHL(p, dst, dst, brw_imm_ud(16u));
}
/* And, finally the form of packHalf2x16's output:
* 0xhhhhllll