Revert "bytes: add optimized Compare for arm64"

This reverts commit bfa8b6f8ffa49b3e5796af45a2f0bf9714a37bb9.

Reason for revert: This depends on another CL which is not yet submitted.

Change-Id: I50e7594f1473c911a2079fe910849a6694ac6c07
Reviewed-on: https://go-review.googlesource.com/101496
Reviewed-by: Cherry Zhang <cherryyz@google.com>

diff --git a/src/internal/bytealg/compare_arm64.s b/src/internal/bytealg/compare_arm64.s
index 2bd38064c30b4e7bc0d2eb3894d0da40d4ef8192..9b6354715a4c490c7e33d37f3e85db11a03a8ce9 100644 (file)
--- a/src/internal/bytealg/compare_arm64.s
+++ b/src/internal/bytealg/compare_arm64.s
@@ -10,7 +10,7 @@ TEXT ·Compare(SB),NOSPLIT|NOFRAME,$0-56
        MOVD    a_len+8(FP), R0
        MOVD    b_base+24(FP), R3
        MOVD    b_len+32(FP), R1
-       MOVD    $ret+48(FP), R7
+       ADD     $56, RSP, R7
        B       cmpbody<>(SB)
 
 TEXT bytes·Compare(SB),NOSPLIT|NOFRAME,$0-56
@@ -18,7 +18,7 @@ TEXT bytes·Compare(SB),NOSPLIT|NOFRAME,$0-56
        MOVD    a_len+8(FP), R0
        MOVD    b_base+24(FP), R3
        MOVD    b_len+32(FP), R1
-       MOVD    $ret+48(FP), R7
+       ADD     $56, RSP, R7
        B       cmpbody<>(SB)
 
 TEXT runtime·cmpstring(SB),NOSPLIT|NOFRAME,$0-40
@@ -26,7 +26,7 @@ TEXT runtime·cmpstring(SB),NOSPLIT|NOFRAME,$0-40
        MOVD    a_len+8(FP), R0
        MOVD    b_base+16(FP), R3
        MOVD    b_len+24(FP), R1
-       MOVD    $ret+32(FP), R7
+       ADD     $40, RSP, R7
        B       cmpbody<>(SB)
 
 // On entry:
@@ -37,98 +37,30 @@ TEXT runtime·cmpstring(SB),NOSPLIT|NOFRAME,$0-40
 // R7 points to return value (-1/0/1 will be written here)
 //
 // On exit:
-// R4, R5, R6, R8, R9 and R10 are clobbered
+// R4, R5, and R6 are clobbered
 TEXT cmpbody<>(SB),NOSPLIT|NOFRAME,$0-0
        CMP     R2, R3
-       BEQ     samebytes         // same starting pointers; compare lengths
+       BEQ     samebytes // same starting pointers; compare lengths
        CMP     R0, R1
-       CSEL    LT, R1, R0, R6    // R6 is min(R0, R1)
+       CSEL    LT, R1, R0, R6 // R6 is min(R0, R1)
 
-       CMP     $0, R6
-       BEQ     samebytes
-       BIC     $0xf, R6, R10
-       CBZ     R10, small        // length < 16
-       ADD     R2, R10           // end of chunk16
-       // length >= 16
-chunk16_loop:
-       LDP.P   16(R2), (R4, R8)
-       LDP.P   16(R3), (R5, R9)
+       ADD     R2, R6  // R2 is current byte in a, R6 is last byte in a to compare
+loop:
+       CMP     R2, R6
+       BEQ     samebytes // all compared bytes were the same; compare lengths
+       MOVBU.P 1(R2), R4
+       MOVBU.P 1(R3), R5
        CMP     R4, R5
-       BNE     cmp
-       CMP     R8, R9
-       BNE     cmpnext
-       CMP     R10, R2
-       BNE     chunk16_loop
-       AND     $0xf, R6, R6
-       CBZ     R6, samebytes
-       SUBS    $8, R6
-       BLT     tail
-       // the length of tail > 8 bytes
-       MOVD.P  8(R2), R4
-       MOVD.P  8(R3), R5
-       CMP     R4, R5
-       BNE     cmp
-       SUB     $8, R6
-       // compare last 8 bytes
-tail:
-       MOVD    (R2)(R6), R4
-       MOVD    (R3)(R6), R5
-       CMP     R4, R5
-       BEQ     samebytes
-cmp:
-       REV     R4, R4
-       REV     R5, R5
-       CMP     R4, R5
-ret:
+       BEQ     loop
+       // bytes differed
        MOVD    $1, R4
-       CNEG    HI, R4, R4
+       CSNEG   LT, R4, R4, R4
        MOVD    R4, (R7)
        RET
-small:
-       TBZ     $3, R6, lt_8
-       MOVD    (R2), R4
-       MOVD    (R3), R5
-       CMP     R4, R5
-       BNE     cmp
-       SUBS    $8, R6
-       BEQ     samebytes
-       ADD     $8, R2
-       ADD     $8, R3
-       SUB     $8, R6
-       B       tail
-lt_8:
-       TBZ     $2, R6, lt_4
-       MOVWU   (R2), R4
-       MOVWU   (R3), R5
-       CMPW    R4, R5
-       BNE     cmp
-       SUBS    $4, R6
-       BEQ     samebytes
-       ADD     $4, R2
-       ADD     $4, R3
-lt_4:
-       TBZ     $1, R6, lt_2
-       MOVHU   (R2), R4
-       MOVHU   (R3), R5
-       CMPW    R4, R5
-       BNE     cmp
-       ADD     $2, R2
-       ADD     $2, R3
-lt_2:
-       TBZ     $0, R6, samebytes
-one:
-       MOVBU   (R2), R4
-       MOVBU   (R3), R5
-       CMPW    R4, R5
-       BNE     ret
 samebytes:
-       CMP     R1, R0
-       CSET    NE, R4
-       CNEG    LO, R4, R4
+       MOVD    $1, R4
+       CMP     R0, R1
+       CSNEG   LT, R4, R4, R4
+       CSEL    EQ, ZR, R4, R4
        MOVD    R4, (R7)
        RET
-cmpnext:
-       REV     R8, R4
-       REV     R9, R5
-       CMP     R4, R5
-       B       ret