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[AArch64] Add optimized strchr.
Implementation of strchr for AArch64. Speedups taken from micro-bench show the improvements relative to the standard C code. The use of LD1 means we have identical code for both big- and little-endian systems.
This commit is contained in:
Richard Earnshaw
Marcus Shawcroft
parent
4ba7a00fe3
commit
f940b96522
@ -1,3 +1,7 @@
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2014-06-19 Richard Earnshaw <rearnsha@arm.com>
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* sysdeps/aarch64/strchr.S: New file.
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2014-06-18 Joseph Myers <joseph@codesourcery.com>
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[BZ #17022]
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2
NEWS
2
NEWS
@ -22,6 +22,8 @@ Version 2.20
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16967, 16977, 16978, 16984, 16990, 16996, 17009, 17022, 17031, 17042,
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17048, 17058, 17062.
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* Optimized strchr implementation for AArch64. Contributed by ARM Ltd.
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* The minimum Linux kernel version that this version of the GNU C Library
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can be used with is 2.6.32.
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138
sysdeps/aarch64/strchr.S
Normal file
138
sysdeps/aarch64/strchr.S
Normal file
@ -0,0 +1,138 @@
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/* strchr - find a character in a string
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Copyright (C) 2014 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library. If not, see
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<http://www.gnu.org/licenses/>. */
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#include <sysdep.h>
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/* Assumptions:
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*
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* ARMv8-a, AArch64
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*/
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/* Arguments and results. */
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#define srcin x0
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#define chrin w1
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#define result x0
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#define src x2
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#define tmp1 x3
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#define wtmp2 w4
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#define tmp3 x5
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#define vrepchr v0
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#define vdata1 v1
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#define vdata2 v2
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#define vhas_nul1 v3
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#define vhas_nul2 v4
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#define vhas_chr1 v5
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#define vhas_chr2 v6
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#define vrepmask_0 v7
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#define vrepmask_c v16
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#define vend1 v17
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#define vend2 v18
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/* Core algorithm.
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For each 32-byte hunk we calculate a 64-bit syndrome value, with
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two bits per byte (LSB is always in bits 0 and 1, for both big
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and little-endian systems). Bit 0 is set iff the relevant byte
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matched the requested character. Bit 1 is set iff the
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relevant byte matched the NUL end of string (we trigger off bit0
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for the special case of looking for NUL). Since the bits
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in the syndrome reflect exactly the order in which things occur
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in the original string a count_trailing_zeros() operation will
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identify exactly which byte is causing the termination, and why. */
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/* Locals and temporaries. */
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ENTRY (strchr)
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mov wtmp2, #0x0401
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movk wtmp2, #0x4010, lsl #16
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dup vrepchr.16b, chrin
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bic src, srcin, #31
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dup vrepmask_c.4s, wtmp2
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ands tmp1, srcin, #31
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add vrepmask_0.4s, vrepmask_c.4s, vrepmask_c.4s // lsl #1
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b.eq L(loop)
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/* Input string is not 32-byte aligned. Rather than forcing
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the padding bytes to a safe value, we calculate the syndrome
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for all the bytes, but then mask off those bits of the
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syndrome that are related to the padding. */
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ld1 {vdata1.16b, vdata2.16b}, [src], #32
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neg tmp1, tmp1
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cmeq vhas_nul1.16b, vdata1.16b, #0
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cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b
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cmeq vhas_nul2.16b, vdata2.16b, #0
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cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b
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and vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b
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and vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b
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and vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b
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and vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b
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orr vend1.16b, vhas_nul1.16b, vhas_chr1.16b
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orr vend2.16b, vhas_nul2.16b, vhas_chr2.16b
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lsl tmp1, tmp1, #1
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addp vend1.16b, vend1.16b, vend2.16b // 256->128
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mov tmp3, #~0
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addp vend1.16b, vend1.16b, vend2.16b // 128->64
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lsr tmp1, tmp3, tmp1
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mov tmp3, vend1.2d[0]
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bic tmp1, tmp3, tmp1 // Mask padding bits.
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cbnz tmp1, L(tail)
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L(loop):
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ld1 {vdata1.16b, vdata2.16b}, [src], #32
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cmeq vhas_nul1.16b, vdata1.16b, #0
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cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b
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cmeq vhas_nul2.16b, vdata2.16b, #0
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cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b
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/* Use a fast check for the termination condition. */
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orr vend1.16b, vhas_nul1.16b, vhas_chr1.16b
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orr vend2.16b, vhas_nul2.16b, vhas_chr2.16b
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orr vend1.16b, vend1.16b, vend2.16b
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addp vend1.2d, vend1.2d, vend1.2d
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mov tmp1, vend1.2d[0]
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cbz tmp1, L(loop)
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/* Termination condition found. Now need to establish exactly why
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we terminated. */
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and vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b
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and vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b
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and vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b
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and vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b
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orr vend1.16b, vhas_nul1.16b, vhas_chr1.16b
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orr vend2.16b, vhas_nul2.16b, vhas_chr2.16b
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addp vend1.16b, vend1.16b, vend2.16b // 256->128
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addp vend1.16b, vend1.16b, vend2.16b // 128->64
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mov tmp1, vend1.2d[0]
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L(tail):
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sub src, src, #32
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rbit tmp1, tmp1
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clz tmp1, tmp1
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/* Tmp1 is even if the target charager was found first. Otherwise
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we've found the end of string and we weren't looking for NUL. */
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tst tmp1, #1
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add result, src, tmp1, lsr #1
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csel result, result, xzr, eq
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ret
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END (strchr)
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libc_hidden_builtin_def (strchr)
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weak_alias (strchr, index)
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