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[AArch64] Improve integer memcpy
Further optimize integer memcpy. Small cases now include copies up to 32 bytes. 64-128 byte copies are split into two cases to improve performance of 64-96 byte copies. Comments have been rewritten.
This commit is contained in:
Wilco Dijkstra
parent
15ab195229
commit
7000651327
@ -33,11 +33,11 @@
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#define A_l x6
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#define A_lw w6
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#define A_h x7
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#define A_hw w7
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#define B_l x8
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#define B_lw w8
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#define B_h x9
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#define C_l x10
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#define C_lw w10
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#define C_h x11
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#define D_l x12
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#define D_h x13
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@ -51,16 +51,6 @@
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#define H_h srcend
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#define tmp1 x14
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/* Copies are split into 3 main cases: small copies of up to 32 bytes,
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medium copies of 33..128 bytes which are fully unrolled. Large copies
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of more than 128 bytes align the destination and use an unrolled loop
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processing 64 bytes per iteration.
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In order to share code with memmove, small and medium copies read all
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data before writing, allowing any kind of overlap. So small, medium
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and large backwards memmoves are handled by falling through into memcpy.
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Overlapping large forward memmoves use a loop that copies backwards.
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*/
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#ifndef MEMMOVE
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# define MEMMOVE memmove
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#endif
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@ -68,35 +58,76 @@
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# define MEMCPY memcpy
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#endif
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ENTRY_ALIGN (MEMMOVE, 6)
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/* This implementation supports both memcpy and memmove and shares most code.
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It uses unaligned accesses and branchless sequences to keep the code small,
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simple and improve performance.
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Copies are split into 3 main cases: small copies of up to 32 bytes, medium
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copies of up to 128 bytes, and large copies. The overhead of the overlap
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check in memmove is negligible since it is only required for large copies.
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Large copies use a software pipelined loop processing 64 bytes per
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iteration. The destination pointer is 16-byte aligned to minimize
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unaligned accesses. The loop tail is handled by always copying 64 bytes
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from the end.
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*/
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ENTRY_ALIGN (MEMCPY, 6)
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DELOUSE (0)
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DELOUSE (1)
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DELOUSE (2)
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sub tmp1, dstin, src
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cmp count, 128
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ccmp tmp1, count, 2, hi
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b.lo L(move_long)
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/* Common case falls through into memcpy. */
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END (MEMMOVE)
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libc_hidden_builtin_def (MEMMOVE)
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ENTRY (MEMCPY)
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DELOUSE (0)
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DELOUSE (1)
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DELOUSE (2)
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prfm PLDL1KEEP, [src]
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add srcend, src, count
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add dstend, dstin, count
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cmp count, 32
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b.ls L(copy32)
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cmp count, 128
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b.hi L(copy_long)
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cmp count, 32
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b.hi L(copy32_128)
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/* Small copies: 0..32 bytes. */
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cmp count, 16
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b.lo L(copy16)
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ldp A_l, A_h, [src]
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ldp D_l, D_h, [srcend, -16]
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stp A_l, A_h, [dstin]
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stp D_l, D_h, [dstend, -16]
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ret
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/* Copy 8-15 bytes. */
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L(copy16):
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tbz count, 3, L(copy8)
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ldr A_l, [src]
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ldr A_h, [srcend, -8]
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str A_l, [dstin]
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str A_h, [dstend, -8]
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ret
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.p2align 3
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/* Copy 4-7 bytes. */
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L(copy8):
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tbz count, 2, L(copy4)
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ldr A_lw, [src]
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ldr B_lw, [srcend, -4]
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str A_lw, [dstin]
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str B_lw, [dstend, -4]
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ret
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/* Copy 0..3 bytes using a branchless sequence. */
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L(copy4):
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cbz count, L(copy0)
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lsr tmp1, count, 1
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ldrb A_lw, [src]
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ldrb C_lw, [srcend, -1]
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ldrb B_lw, [src, tmp1]
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strb A_lw, [dstin]
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strb B_lw, [dstin, tmp1]
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strb C_lw, [dstend, -1]
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L(copy0):
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ret
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.p2align 4
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/* Medium copies: 33..128 bytes. */
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L(copy32_128):
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ldp A_l, A_h, [src]
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ldp B_l, B_h, [src, 16]
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ldp C_l, C_h, [srcend, -32]
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@ -110,76 +141,32 @@ ENTRY (MEMCPY)
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ret
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.p2align 4
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/* Small copies: 0..32 bytes. */
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L(copy32):
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/* 16-32 bytes. */
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cmp count, 16
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b.lo 1f
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ldp A_l, A_h, [src]
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ldp B_l, B_h, [srcend, -16]
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stp A_l, A_h, [dstin]
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stp B_l, B_h, [dstend, -16]
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ret
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.p2align 4
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1:
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/* 8-15 bytes. */
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tbz count, 3, 1f
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ldr A_l, [src]
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ldr A_h, [srcend, -8]
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str A_l, [dstin]
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str A_h, [dstend, -8]
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ret
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.p2align 4
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1:
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/* 4-7 bytes. */
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tbz count, 2, 1f
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ldr A_lw, [src]
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ldr A_hw, [srcend, -4]
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str A_lw, [dstin]
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str A_hw, [dstend, -4]
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ret
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/* Copy 0..3 bytes. Use a branchless sequence that copies the same
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byte 3 times if count==1, or the 2nd byte twice if count==2. */
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1:
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cbz count, 2f
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lsr tmp1, count, 1
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ldrb A_lw, [src]
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ldrb A_hw, [srcend, -1]
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ldrb B_lw, [src, tmp1]
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strb A_lw, [dstin]
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strb B_lw, [dstin, tmp1]
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strb A_hw, [dstend, -1]
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2: ret
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.p2align 4
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/* Copy 65..128 bytes. Copy 64 bytes from the start and
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64 bytes from the end. */
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/* Copy 65..128 bytes. */
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L(copy128):
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ldp E_l, E_h, [src, 32]
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ldp F_l, F_h, [src, 48]
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cmp count, 96
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b.ls L(copy96)
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ldp G_l, G_h, [srcend, -64]
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ldp H_l, H_h, [srcend, -48]
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stp G_l, G_h, [dstend, -64]
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stp H_l, H_h, [dstend, -48]
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L(copy96):
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stp A_l, A_h, [dstin]
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stp B_l, B_h, [dstin, 16]
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stp E_l, E_h, [dstin, 32]
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stp F_l, F_h, [dstin, 48]
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stp G_l, G_h, [dstend, -64]
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stp H_l, H_h, [dstend, -48]
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stp C_l, C_h, [dstend, -32]
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stp D_l, D_h, [dstend, -16]
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ret
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/* Align DST to 16 byte alignment so that we don't cross cache line
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boundaries on both loads and stores. There are at least 128 bytes
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to copy, so copy 16 bytes unaligned and then align. The loop
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copies 64 bytes per iteration and prefetches one iteration ahead. */
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.p2align 4
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/* Copy more than 128 bytes. */
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L(copy_long):
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/* Copy 16 bytes and then align dst to 16-byte alignment. */
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ldp D_l, D_h, [src]
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and tmp1, dstin, 15
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bic dst, dstin, 15
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ldp D_l, D_h, [src]
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sub src, src, tmp1
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add count, count, tmp1 /* Count is now 16 too large. */
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ldp A_l, A_h, [src, 16]
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@ -188,7 +175,8 @@ L(copy_long):
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ldp C_l, C_h, [src, 48]
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ldp D_l, D_h, [src, 64]!
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subs count, count, 128 + 16 /* Test and readjust count. */
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b.ls L(last64)
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b.ls L(copy64_from_end)
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L(loop64):
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stp A_l, A_h, [dst, 16]
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ldp A_l, A_h, [src, 16]
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@ -201,10 +189,8 @@ L(loop64):
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subs count, count, 64
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b.hi L(loop64)
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/* Write the last full set of 64 bytes. The remainder is at most 64
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bytes, so it is safe to always copy 64 bytes from the end even if
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there is just 1 byte left. */
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L(last64):
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/* Write the last iteration and copy 64 bytes from the end. */
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L(copy64_from_end):
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ldp E_l, E_h, [srcend, -64]
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stp A_l, A_h, [dst, 16]
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ldp A_l, A_h, [srcend, -48]
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@ -219,20 +205,42 @@ L(last64):
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stp C_l, C_h, [dstend, -16]
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ret
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.p2align 4
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L(move_long):
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cbz tmp1, 3f
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END (MEMCPY)
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libc_hidden_builtin_def (MEMCPY)
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ENTRY_ALIGN (MEMMOVE, 4)
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DELOUSE (0)
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DELOUSE (1)
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DELOUSE (2)
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add srcend, src, count
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add dstend, dstin, count
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cmp count, 128
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b.hi L(move_long)
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cmp count, 32
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b.hi L(copy32_128)
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/* Align dstend to 16 byte alignment so that we don't cross cache line
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boundaries on both loads and stores. There are at least 128 bytes
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to copy, so copy 16 bytes unaligned and then align. The loop
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copies 64 bytes per iteration and prefetches one iteration ahead. */
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and tmp1, dstend, 15
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/* Small copies: 0..32 bytes. */
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cmp count, 16
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b.lo L(copy16)
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ldp A_l, A_h, [src]
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ldp D_l, D_h, [srcend, -16]
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stp A_l, A_h, [dstin]
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stp D_l, D_h, [dstend, -16]
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ret
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.p2align 4
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L(move_long):
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/* Only use backward copy if there is an overlap. */
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sub tmp1, dstin, src
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cbz tmp1, L(copy0)
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cmp tmp1, count
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b.hs L(copy_long)
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/* Large backwards copy for overlapping copies.
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Copy 16 bytes and then align dst to 16-byte alignment. */
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ldp D_l, D_h, [srcend, -16]
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and tmp1, dstend, 15
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sub srcend, srcend, tmp1
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sub count, count, tmp1
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ldp A_l, A_h, [srcend, -16]
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@ -242,10 +250,9 @@ L(move_long):
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ldp D_l, D_h, [srcend, -64]!
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sub dstend, dstend, tmp1
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subs count, count, 128
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b.ls 2f
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b.ls L(copy64_from_start)
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nop
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1:
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L(loop64_backwards):
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stp A_l, A_h, [dstend, -16]
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ldp A_l, A_h, [srcend, -16]
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stp B_l, B_h, [dstend, -32]
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@ -255,12 +262,10 @@ L(move_long):
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stp D_l, D_h, [dstend, -64]!
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ldp D_l, D_h, [srcend, -64]!
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subs count, count, 64
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b.hi 1b
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b.hi L(loop64_backwards)
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/* Write the last full set of 64 bytes. The remainder is at most 64
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bytes, so it is safe to always copy 64 bytes from the start even if
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there is just 1 byte left. */
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2:
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/* Write the last iteration and copy 64 bytes from the start. */
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L(copy64_from_start):
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ldp G_l, G_h, [src, 48]
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stp A_l, A_h, [dstend, -16]
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ldp A_l, A_h, [src, 32]
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@ -273,7 +278,7 @@ L(move_long):
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stp A_l, A_h, [dstin, 32]
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stp B_l, B_h, [dstin, 16]
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stp C_l, C_h, [dstin]
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3: ret
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ret
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END (MEMCPY)
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libc_hidden_builtin_def (MEMCPY)
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END (MEMMOVE)
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libc_hidden_builtin_def (MEMMOVE)
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