[FFmpeg-devel] [PATCH 2/2] lavu/float_dsp: optimise R-V V fmul_reverse & fmul_window

[Rémi Denis-Courmont]

Roll the loop to avoid slow gathers.

Before:
vector_fmul_reverse_c:       1561.7
vector_fmul_reverse_rvv_f32: 2410.2
vector_fmul_window_c:        2068.2
vector_fmul_window_rvv_f32:  1879.5

After:
vector_fmul_reverse_c:       1561.7
vector_fmul_reverse_rvv_f32:  916.2
vector_fmul_window_c:        2068.2
vector_fmul_window_rvv_f32:  1202.5
---
 libavutil/riscv/float_dsp_rvv.S | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/libavutil/riscv/float_dsp_rvv.S b/libavutil/riscv/float_dsp_rvv.S
index a2f9488249..ce5b6823d4 100644
--- a/libavutil/riscv/float_dsp_rvv.S
+++ b/libavutil/riscv/float_dsp_rvv.S
@@ -75,18 +75,19 @@ endfunc
 
 func ff_vector_fmul_window_rvv, zve32f
         // a0: dst, a1: src0, a2: src1, a3: window, a4: length
-        vsetvli    t0, zero, e16, m2, ta, ma
+        // e16/m2 and e32/m4 are possible but slower due to gather.
+        vsetvli    t0, zero, e16, m1, ta, ma
         sh2add     a2, a4, a2
         vid.v      v0
         sh3add     t3, a4, a3
         vadd.vi    v0, v0, 1
         sh3add     t0, a4, a0
 1:
-        vsetvli    t2, a4, e16, m2, ta, ma
+        vsetvli    t2, a4, e16, m1, ta, ma
         slli       t4, t2, 2
         vrsub.vx   v2, v0, t2
         sub        t3, t3, t4
-        vsetvli    zero, zero, e32, m4, ta, ma
+        vsetvli    zero, zero, e32, m2, ta, ma
         sub        a2, a2, t4
         vle32.v    v8, (t3)
         sub        t0, t0, t4
@@ -133,6 +134,7 @@ endfunc
 // TODO factor vrsub, separate last iteration?
 // (a0) = (a1) * reverse(a2) [0..a3-1]
 func ff_vector_fmul_reverse_rvv, zve32f
+        // e16/m4 and e32/m8 are possible but slower due to gather.
         vsetvli  t0, zero, e16, m4, ta, ma
         sh2add   a2, a3, a2
         vid.v    v0
-- 
2.42.0