internal/bytealg: optimize IndexString on arm64

This CL adjusts the order of the branch instructions of the
code to make it easier for the LIKELY branch to happen.

Benchmarks:
name                            old time/op    new time/op    delta
pkg:strings goos:linux goarch:arm64
IndexHard2-8                      2.17ms ± 1%    1.23ms ± 0%  -43.34%  (p=0.008 n=5+5)
CountHard2-8                      2.13ms ± 1%    1.21ms ± 2%  -43.31%  (p=0.008 n=5+5)

pkg:bytes goos:linux goarch:arm64
IndexRune/4M-8                     661µs ±22%     513µs ± 0%  -22.32%  (p=0.008 n=5+5)
IndexEasy/4M-8                     672µs ±23%     513µs ± 0%  -23.71%  (p=0.016 n=5+4)

Change-Id: Ib96f095edf77747edc8a971e79f5c1428e5808ce
Reviewed-on: https://go-review.googlesource.com/109015
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/internal/bytealg/index_arm64.s b/src/internal/bytealg/index_arm64.s
index 6c93ef3ce8332fba930ddd7a267beacd9ac151d4..02eb658fd0487d3b0fb6658a07c2f9d703ba258a 100644 (file)
--- a/src/internal/bytealg/index_arm64.s
+++ b/src/internal/bytealg/index_arm64.s
@@ -41,12 +41,12 @@ len_8:
        MOVD    (R2), R5
 loop_8:
        // R6 contains substring for comparison
+       CMP     R4, R0
+       BHI     not_found
        MOVD.P  1(R0), R6
        CMP     R5, R6
-       BEQ     found
-       CMP     R4, R0
-       BLS     loop_8
-       JMP     not_found
+       BNE     loop_8
+       B       found
 len_2_7:
        TBZ     $2, R3, len_2_3
        TBZ     $1, R3, len_4_5
@@ -57,31 +57,29 @@ len_7:
        // 1-byte overlap with R5
        MOVWU   3(R2), R6
 loop_7:
+       CMP     R4, R0
+       BHI     not_found
        MOVWU.P 1(R0), R3
        CMP     R5, R3
-       BNE     not_equal_7
+       BNE     loop_7
        MOVWU   2(R0), R3
        CMP     R6, R3
-       BEQ     found
-not_equal_7:
-       CMP     R4, R0
-       BLS     loop_7
-       JMP     not_found
+       BNE     loop_7
+       B       found
 len_6:
        // R5 and R6 contain 6-byte sep
        MOVWU   (R2), R5
        MOVHU   4(R2), R6
 loop_6:
+       CMP     R4, R0
+       BHI     not_found
        MOVWU.P 1(R0), R3
        CMP     R5, R3
-       BNE     not_equal_6
+       BNE     loop_6
        MOVHU   3(R0), R3
        CMP     R6, R3
-       BEQ     found
-not_equal_6:
-       CMP     R4, R0
-       BLS     loop_6
-       JMP     not_found
+       BNE     loop_6
+       B       found
 len_4_5:
        TBZ     $0, R3, len_4
 len_5:
@@ -89,26 +87,25 @@ len_5:
        MOVWU   (R2), R5
        MOVBU   4(R2), R7
 loop_5:
+       CMP     R4, R0
+       BHI     not_found
        MOVWU.P 1(R0), R3
        CMP     R5, R3
-       BNE     not_equal_5
+       BNE     loop_5
        MOVBU   3(R0), R3
        CMP     R7, R3
-       BEQ     found
-not_equal_5:
-       CMP     R4, R0
-       BLS     loop_5
-       JMP     not_found
+       BNE     loop_5
+       B       found
 len_4:
        // R5 contains 4-byte sep
        MOVWU   (R2), R5
 loop_4:
+       CMP     R4, R0
+       BHI     not_found
        MOVWU.P 1(R0), R6
        CMP     R5, R6
-       BEQ     found
-       CMP     R4, R0
-       BLS     loop_4
-       JMP     not_found
+       BNE     loop_4
+       B       found
 len_2_3:
        TBZ     $0, R3, len_2
 len_3:
@@ -116,30 +113,29 @@ len_3:
        MOVHU   (R2), R6
        MOVBU   2(R2), R7
 loop_3:
+       CMP     R4, R0
+       BHI     not_found
        MOVHU.P 1(R0), R3
        CMP     R6, R3
-       BNE     not_equal_3
+       BNE     loop_3
        MOVBU   1(R0), R3
        CMP     R7, R3
-       BEQ     found
-not_equal_3:
-       CMP     R4, R0
-       BLS     loop_3
-       JMP     not_found
+       BNE     loop_3
+       B       found
 len_2:
        // R5 contains 2-byte sep
        MOVHU   (R2), R5
 loop_2:
+       CMP     R4, R0
+       BHI     not_found
        MOVHU.P 1(R0), R6
        CMP     R5, R6
-       BEQ     found
-       CMP     R4, R0
-       BLS     loop_2
-not_found:
-       MOVD    $-1, R0
-       MOVD    R0, (R9)
-       RET
+       BNE     loop_2
 found:
        SUB     R8, R0, R0
        MOVD    R0, (R9)
        RET
+not_found:
+       MOVD    $-1, R0
+       MOVD    R0, (R9)
+       RET