/*
* memcpy - copy memory area
*
* Copyright (c) 2019-2023, Arm Limited.
* SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
*/
/* Assumptions:
*
* ARMv8-a, AArch64, Advanced SIMD, unaligned accesses.
*
*/
#include "asmdefs.h"
#define dstin x0
#define src x1
#define count x2
#define dst x3
#define srcend x4
#define dstend x5
#define A_l x6
#define A_lw w6
#define A_h x7
#define B_l x8
#define B_lw w8
#define B_h x9
#define C_lw w10
#define tmp1 x14
#define A_q q0
#define B_q q1
#define C_q q2
#define D_q q3
#define E_q q4
#define F_q q5
#define G_q q6
#define H_q q7
/* This implementation handles overlaps and supports both memcpy and memmove
from a single entry point. It uses unaligned accesses and branchless
sequences to keep the code small, simple and improve performance.
Copies are split into 3 main cases: small copies of up to 32 bytes, medium
copies of up to 128 bytes, and large copies. The overhead of the overlap
check is negligible since it is only required for large copies.
Large copies use a software pipelined loop processing 64 bytes per iteration.
The source pointer is 16-byte aligned to minimize unaligned accesses.
The loop tail is handled by always copying 64 bytes from the end.
*/
ENTRY_ALIAS (__folly_memmove_aarch64_simd)
ENTRY (__folly_memcpy_aarch64_simd)
PTR_ARG (0)
PTR_ARG (1)
SIZE_ARG (2)
add srcend, src, count
cmp count, 128
b.hi L(copy_long)
add dstend, dstin, count
cmp count, 32
b.hi L(copy32_128)
nop
/* Small copies: 0..32 bytes. */
cmp count, 16
b.lo L(copy16)
ldr A_q, [src]
ldr B_q, [srcend, -16]
str A_q, [dstin]
str B_q, [dstend, -16]
ret
.p2align 4
/* Medium copies: 33..128 bytes. */
L(copy32_128):
ldp A_q, B_q, [src]
ldp C_q, D_q, [srcend, -32]
cmp count, 64
b.hi L(copy128)
stp A_q, B_q, [dstin]
stp C_q, D_q, [dstend, -32]
ret
.p2align 4
/* Copy 8-15 bytes. */
L(copy16):
tbz count, 3, L(copy8)
ldr A_l, [src]
ldr A_h, [srcend, -8]
str A_l, [dstin]
str A_h, [dstend, -8]
ret
/* Copy 4-7 bytes. */
L(copy8):
tbz count, 2, L(copy4)
ldr A_lw, [src]
ldr B_lw, [srcend, -4]
str A_lw, [dstin]
str B_lw, [dstend, -4]
ret
/* Copy 65..128 bytes. */
L(copy128):
ldp E_q, F_q, [src, 32]
cmp count, 96
b.ls L(copy96)
ldp G_q, H_q, [srcend, -64]
stp G_q, H_q, [dstend, -64]
L(copy96):
stp A_q, B_q, [dstin]
stp E_q, F_q, [dstin, 32]
stp C_q, D_q, [dstend, -32]
ret
/* Copy 0..3 bytes using a branchless sequence. */
L(copy4):
cbz count, L(copy0)
lsr tmp1, count, 1
ldrb A_lw, [src]
ldrb C_lw, [srcend, -1]
ldrb B_lw, [src, tmp1]
strb A_lw, [dstin]
strb B_lw, [dstin, tmp1]
strb C_lw, [dstend, -1]
L(copy0):
ret
.p2align 3
/* Copy more than 128 bytes. */
L(copy_long):
add dstend, dstin, count
/* Use backwards copy if there is an overlap. */
sub tmp1, dstin, src
cmp tmp1, count
b.lo L(copy_long_backwards)
/* Copy 16 bytes and then align src to 16-byte alignment. */
ldr D_q, [src]
and tmp1, src, 15
bic src, src, 15
sub dst, dstin, tmp1
add count, count, tmp1 /* Count is now 16 too large. */
ldp A_q, B_q, [src, 16]
str D_q, [dstin]
ldp C_q, D_q, [src, 48]
subs count, count, 128 + 16 /* Test and readjust count. */
b.ls L(copy64_from_end)
L(loop64):
stp A_q, B_q, [dst, 16]
ldp A_q, B_q, [src, 80]
stp C_q, D_q, [dst, 48]
ldp C_q, D_q, [src, 112]
add src, src, 64
add dst, dst, 64
subs count, count, 64
b.hi L(loop64)
/* Write the last iteration and copy 64 bytes from the end. */
L(copy64_from_end):
ldp E_q, F_q, [srcend, -64]
stp A_q, B_q, [dst, 16]
ldp A_q, B_q, [srcend, -32]
stp C_q, D_q, [dst, 48]
stp E_q, F_q, [dstend, -64]
stp A_q, B_q, [dstend, -32]
ret
.p2align 4
nop
/* Large backwards copy for overlapping copies.
Copy 16 bytes and then align srcend to 16-byte alignment. */
L(copy_long_backwards):
cbz tmp1, L(copy0)
ldr D_q, [srcend, -16]
and tmp1, srcend, 15
bic srcend, srcend, 15
sub count, count, tmp1
ldp A_q, B_q, [srcend, -32]
str D_q, [dstend, -16]
ldp C_q, D_q, [srcend, -64]
sub dstend, dstend, tmp1
subs count, count, 128
b.ls L(copy64_from_start)
L(loop64_backwards):
str B_q, [dstend, -16]
str A_q, [dstend, -32]
ldp A_q, B_q, [srcend, -96]
str D_q, [dstend, -48]
str C_q, [dstend, -64]!
ldp C_q, D_q, [srcend, -128]
sub srcend, srcend, 64
subs count, count, 64
b.hi L(loop64_backwards)
/* Write the last iteration and copy 64 bytes from the start. */
L(copy64_from_start):
ldp E_q, F_q, [src, 32]
stp A_q, B_q, [dstend, -32]
ldp A_q, B_q, [src]
stp C_q, D_q, [dstend, -64]
stp E_q, F_q, [dstin, 32]
stp A_q, B_q, [dstin]
ret
END (__folly_memcpy_aarch64_simd)
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