internal/bytealg: optimize Equal on arm64
Currently the 16-byte loop chunk16_loop is implemented with NEON instructions LD1, VMOV and VCMEQ.
Using scalar instructions LDP and CMP to achieve this loop can reduce the number of clock cycles.
For cases where the length of strings are between 4 to 15 bytes, loading the last 8 or 4 bytes at
a time to reduce the number of comparisons.
Benchmarks:
name old time/op new time/op delta
Equal/0-8 5.51ns ± 0% 5.84ns ±14% ~ (p=0.246 n=7+8)
Equal/1-8 10.5ns ± 0% 10.5ns ± 0% ~ (all equal)
Equal/6-8 14.0ns ± 0% 12.5ns ± 0% -10.71% (p=0.000 n=8+8)
Equal/9-8 13.5ns ± 0% 12.5ns ± 0% -7.41% (p=0.000 n=8+8)
Equal/15-8 15.5ns ± 0% 12.5ns ± 0% -19.35% (p=0.000 n=8+8)
Equal/16-8 14.0ns ± 0% 13.0ns ± 0% -7.14% (p=0.000 n=8+8)
Equal/20-8 16.5ns ± 0% 16.0ns ± 0% -3.03% (p=0.000 n=8+8)
Equal/32-8 16.5ns ± 0% 15.3ns ± 0% -7.27% (p=0.000 n=8+8)
Equal/4K-8 552ns ± 0% 553ns ± 0% ~ (p=0.315 n=8+8)
Equal/4M-8 1.13ms ±23% 1.20ms ±27% ~ (p=0.442 n=8+8)
Equal/64M-8 32.9ms ± 0% 32.6ms ± 0% -1.15% (p=0.000 n=8+8)
CompareBytesEqual-8 12.0ns ± 0% 12.0ns ± 0% ~ (all equal)
Change-Id: If317ecdcc98e31883d37fd7d42b113b548c5bd2a
Reviewed-on: https://go-review.googlesource.com/112496
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
diff --git a/src/internal/bytealg/equal_arm64.s b/src/internal/bytealg/equal_arm64.s
index 30abd98..dd4840d 100644
--- a/src/internal/bytealg/equal_arm64.s
+++ b/src/internal/bytealg/equal_arm64.s
@@ -67,6 +67,7 @@
CMP R3, R4
BEQ eq
MOVD 8(R26), R5 // compiler stores size at offset 8 in the closure
+ CBZ R5, eq
MOVD R3, 8(RSP)
MOVD R4, 16(RSP)
MOVD R5, 24(RSP)
@@ -119,30 +120,41 @@
CBZ R3, tail
ADD R3, R0, R6 // end of chunks
chunk16_loop:
- VLD1.P (R0), [V0.D2]
- VLD1.P (R2), [V1.D2]
- VCMEQ V0.D2, V1.D2, V2.D2
+ LDP.P 16(R0), (R4, R5)
+ LDP.P 16(R2), (R7, R9)
+ EOR R4, R7
+ CBNZ R7, not_equal
+ EOR R5, R9
+ CBNZ R9, not_equal
CMP R0, R6
- VMOV V2.D[0], R4
- VMOV V2.D[1], R5
- CBZ R4, not_equal
- CBZ R5, not_equal
BNE chunk16_loop
AND $0xf, R1, R1
CBZ R1, equal
tail:
// special compare of tail with length < 16
TBZ $3, R1, lt_8
- MOVD.P 8(R0), R4
- MOVD.P 8(R2), R5
- CMP R4, R5
- BNE not_equal
+ MOVD (R0), R4
+ MOVD (R2), R5
+ EOR R4, R5
+ CBNZ R5, not_equal
+ SUB $8, R1, R6 // offset of the last 8 bytes
+ MOVD (R0)(R6), R4
+ MOVD (R2)(R6), R5
+ EOR R4, R5
+ CBNZ R5, not_equal
+ B equal
lt_8:
TBZ $2, R1, lt_4
- MOVWU.P 4(R0), R4
- MOVWU.P 4(R2), R5
- CMP R4, R5
- BNE not_equal
+ MOVWU (R0), R4
+ MOVWU (R2), R5
+ EOR R4, R5
+ CBNZ R5, not_equal
+ SUB $4, R1, R6 // offset of the last 4 bytes
+ MOVWU (R0)(R6), R4
+ MOVWU (R2)(R6), R5
+ EOR R4, R5
+ CBNZ R5, not_equal
+ B equal
lt_4:
TBZ $1, R1, lt_2
MOVHU.P 2(R0), R4
@@ -150,7 +162,7 @@
CMP R4, R5
BNE not_equal
lt_2:
- TBZ $0, R1, equal
+ TBZ $0, R1, equal
one:
MOVBU (R0), R4
MOVBU (R2), R5
