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lavc/aacpsdsp: use LMUL=2 and amortise strides 

The input is laid out in 16 segments, of which 13 actually need to be
loaded. There are no really efficient ways to deal with this:
1) If we load 8 segments wit unit stride, then narrow to 16 segments with
   right shifts, we can only get one half-size vector per segment, or just 2
   elements per vector (EMUL=1/2) - at least with 128-bit vectors.
   This ends up unsurprisingly about as fas as the C code.
2) The current approach is to load with strides. We keep that approach,
   but improve it using three 4-segmented loads instead of 12 single-segment
   loads. This divides the number of distinct loaded addresses by 4.
3) A potential third approach would be to avoid segmentation altogether
   and splat the scalar coefficient into vectors. Then we can use a
   unit-stride and maximum EMUL. But the downside then is that we have to
   multiply the 3 (of 16) unused segments with zero as part of the
   multiply-accumulate operations.

In addition, we also reuse vectors mid-loop so as to increase the EMUL
from 1 to 2, which also improves performance a little bit.

Oeverall the gains are quite small with the device under test, as it does
not deal with segmented loads very well. But at least the code is tidier,
and should enjoy bigger speed-ups on better hardware implementation.

Before:
ps_hybrid_analysis_c:       1819.2
ps_hybrid_analysis_rvv_f32: 1037.0 (before)
ps_hybrid_analysis_rvv_f32:  990.0 (after)
This commit is contained in:
Rémi Denis-Courmont 2023-11-19 17:50:49 +02:00
parent b88d4058f9
commit 0183c2c830
1 changed files with 20 additions and 41 deletions
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61
libavcodec/riscv/aacpsdsp_rvv.S
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@ -85,63 +85,42 @@ NOHWD fsw fs\n, (4 * \n)(sp)
flw fs4, (4 * ((6 * 2) + 0))(a1)
flw fs5, (4 * ((6 * 2) + 1))(a1)
add a2, a2, 6 * 2 * 4 // point to filter[i][6][0]
add t2, a2, 6 * 2 * 4 // point to filter[i][6][0]
li t4, 8 * 2 * 4 // filter byte stride
slli a3, a3, 3 // output byte stride
1:
.macro filter, vs0, vs1, fo0, fo1, fo2, fo3
vfmacc.vf v8, \fo0, \vs0
vfmacc.vf v9, \fo2, \vs0
vfmacc.vf v10, \fo2, \vs0
vfnmsac.vf v8, \fo1, \vs1
vfmacc.vf v9, \fo3, \vs1
vfmacc.vf v10, \fo3, \vs1
.endm
vsetvli t0, a4, e32, m1, ta, ma
vsetvli t0, a4, e32, m2, ta, ma
/*
* The filter (a2) has 16 segments, of which 13 need to be extracted.
* R-V V supports only up to 8 segments, so unrolling is unavoidable.
*/
addi t1, a2, -48
vlse32.v v22, (a2), t4
addi t2, a2, -44
vlse32.v v16, (t1), t4
addi t1, a2, -40
vfmul.vf v8, v22, fs4
vlse32.v v24, (t2), t4
addi t2, a2, -36
vfmul.vf v9, v22, fs5
vlse32.v v17, (t1), t4
addi t1, a2, -32
vlse32.v v25, (t2), t4
addi t2, a2, -28
filter v16, v24, ft0, ft1, ft2, ft3
vlse32.v v18, (t1), t4
addi t1, a2, -24
vlse32.v v26, (t2), t4
addi t2, a2, -20
filter v17, v25, ft4, ft5, ft6, ft7
vlse32.v v19, (t1), t4
addi t1, a2, -16
vlse32.v v27, (t2), t4
addi t2, a2, -12
filter v18, v26, ft8, ft9, ft10, ft11
vlse32.v v20, (t1), t4
addi t1, a2, -8
vlse32.v v28, (t2), t4
addi t2, a2, -4
filter v19, v27, fa0, fa1, fa2, fa3
vlse32.v v21, (t1), t4
addi t1, a2, 16
vfmul.vf v8, v28, fs4
vlsseg4e32.v v16, (a2), t4
vfmul.vf v10, v28, fs5
filter v16, v18, ft0, ft1, ft2, ft3
vlsseg4e32.v v24, (t1), t4
filter v20, v22, ft4, ft5, ft6, ft7
addi t1, a2, 32
filter v24, v26, ft8, ft9, ft10, ft11
vlsseg4e32.v v16, (t1), t4
sub a4, a4, t0
vlse32.v v29, (t2), t4
filter v28, v30, fa0, fa1, fa2, fa3
slli t1, t0, 3 + 1 + 2 // ctz(8 * 2 * 4)
add a2, a2, t1
filter v20, v28, fa4, fa5, fa6, fa7
filter v21, v29, fs0, fs1, fs2, fs3
add t2, a0, 4
vsse32.v v8, (a0), a3
filter v16, v18, fa4, fa5, fa6, fa7
mul t0, t0, a3
vsse32.v v9, (t2), a3
filter v20, v22, fs0, fs1, fs2, fs3
add a2, a2, t1
add t2, t2, t1
vssseg2e32.v v8, (a0), a3
add a0, a0, t0
bnez a4, 1b