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http://sourceware.org/ml/libc-alpha/2013-08/msg00105.html Like strnlen, memchr and memrchr had a number of defects fixed by this patch as well as adding little-endian support. The first one I noticed was that the entry to the main loop needlessly checked for "are we done yet?" when we know the size is large enough that we can't be done. The second defect I noticed was that the main loop count was wrong, which in turn meant that the small loop needed to handle an extra word. Thirdly, there is nothing to say that the string can't wrap around zero, except of course that we'd normally hit a segfault on trying to read from address zero. Fixing that simplified a number of places: - /* Are we done already? */ - addi r9,r8,8 - cmpld r9,r7 - bge L(null) becomes + cmpld r8,r7 + beqlr However, the exit gets an extra test because I test for being on the last word then if so whether the byte offset is less than the end. Overall, the change is a win. Lastly, memrchr used the wrong cache hint. * sysdeps/powerpc/powerpc64/power7/memchr.S: Replace rlwimi with insrdi. Make better use of reg selection to speed exit slightly. Schedule entry path a little better. Remove useless "are we done" checks on entry to main loop. Handle wrapping around zero address. Correct main loop count. Handle single left-over word from main loop inline rather than by using loop_small. Remove extra word case in loop_small caused by wrong loop count. Add little-endian support. * sysdeps/powerpc/powerpc32/power7/memchr.S: Likewise. * sysdeps/powerpc/powerpc64/power7/memrchr.S: Likewise. Use proper cache hint. * sysdeps/powerpc/powerpc32/power7/memrchr.S: Likewise. * sysdeps/powerpc/powerpc64/power7/rawmemchr.S: Add little-endian support. Avoid rlwimi. * sysdeps/powerpc/powerpc32/power7/rawmemchr.S: Likewise.
197 lines
4.7 KiB
ArmAsm
197 lines
4.7 KiB
ArmAsm
/* Optimized memrchr implementation for PowerPC32/POWER7 using cmpb insn.
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Copyright (C) 2010-2013 Free Software Foundation, Inc.
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Contributed by Luis Machado <luisgpm@br.ibm.com>.
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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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/* int [r3] memrchr (char *s [r3], int byte [r4], int size [r5]) */
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.machine power7
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ENTRY (__memrchr)
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CALL_MCOUNT
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add r7,r3,r5 /* Calculate the last acceptable address. */
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neg r0,r7
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addi r7,r7,-1
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mr r10,r3
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clrrwi r6,r7,7
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li r9,3<<5
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dcbt r9,r6,16 /* Stream hint, decreasing addresses. */
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/* Replicate BYTE to word. */
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rldimi r4,r4,8,48
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rldimi r4,r4,16,32
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li r6,-4
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li r9,-1
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rlwinm r0,r0,3,27,28 /* Calculate padding. */
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clrrwi r8,r7,2
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srw r9,r9,r0
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cmplwi r5,16
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clrrwi r0,r10,2
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ble L(small_range)
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#ifdef __LITTLE_ENDIAN__
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lwzx r12,0,r8
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#else
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lwbrx r12,0,r8 /* Load reversed word from memory. */
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#endif
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cmpb r3,r12,r4 /* Check for BYTE in WORD1. */
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and r3,r3,r9
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cmplwi cr7,r3,0 /* If r3 == 0, no BYTEs have been found. */
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bne cr7,L(done)
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mtcrf 0x01,r8
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/* Are we now aligned to a doubleword boundary? If so, skip to
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the main loop. Otherwise, go through the alignment code. */
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bf 29,L(loop_setup)
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/* Handle WORD2 of pair. */
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#ifdef __LITTLE_ENDIAN__
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lwzx r12,r8,r6
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#else
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lwbrx r12,r8,r6
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#endif
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addi r8,r8,-4
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cmpb r3,r12,r4
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cmplwi cr7,r3,0
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bne cr7,L(done)
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L(loop_setup):
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/* The last word we want to read in the loop below is the one
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containing the first byte of the string, ie. the word at
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s & ~3, or r0. The first word read is at r8 - 4, we
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read 2 * cnt words, so the last word read will be at
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r8 - 4 - 8 * cnt + 4. Solving for cnt gives
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cnt = (r8 - r0) / 8 */
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sub r5,r8,r0
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addi r8,r8,-4
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srwi r9,r5,3 /* Number of loop iterations. */
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mtctr r9 /* Setup the counter. */
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/* Main loop to look for BYTE backwards in the string.
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FIXME: Investigate whether 32 byte align helps with this
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9 instruction loop. */
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.align 5
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L(loop):
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/* Load two words, compare and merge in a
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single register for speed. This is an attempt
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to speed up the byte-checking process for bigger strings. */
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#ifdef __LITTLE_ENDIAN__
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lwzx r12,0,r8
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lwzx r11,r8,r6
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#else
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lwbrx r12,0,r8
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lwbrx r11,r8,r6
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#endif
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cmpb r3,r12,r4
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cmpb r9,r11,r4
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or r5,r9,r3 /* Merge everything in one word. */
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cmplwi cr7,r5,0
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bne cr7,L(found)
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addi r8,r8,-8
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bdnz L(loop)
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/* We may have one more word to read. */
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cmplw r8,r0
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bnelr
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#ifdef __LITTLE_ENDIAN__
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lwzx r12,0,r8
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#else
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lwbrx r12,0,r8
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#endif
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cmpb r3,r12,r4
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cmplwi cr7,r3,0
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bne cr7,L(done)
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blr
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.align 4
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L(found):
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/* OK, one (or both) of the words contains BYTE. Check
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the first word. */
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cmplwi cr6,r3,0
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bne cr6,L(done)
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/* BYTE must be in the second word. Adjust the address
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again and move the result of cmpb to r3 so we can calculate the
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pointer. */
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mr r3,r9
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addi r8,r8,-4
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/* r3 has the output of the cmpb instruction, that is, it contains
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0xff in the same position as BYTE in the original
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word from the string. Use that to calculate the pointer.
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We need to make sure BYTE is *before* the end of the
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range. */
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L(done):
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cntlzw r9,r3 /* Count leading zeros before the match. */
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cmplw r8,r0 /* Are we on the last word? */
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srwi r6,r9,3 /* Convert leading zeros to bytes. */
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addi r0,r6,-3
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sub r3,r8,r0
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cmplw cr7,r3,r10
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bnelr
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bgelr cr7
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li r3,0
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blr
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.align 4
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L(null):
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li r3,0
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blr
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/* Deals with size <= 16. */
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.align 4
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L(small_range):
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cmplwi r5,0
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beq L(null)
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#ifdef __LITTLE_ENDIAN__
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lwzx r12,0,r8
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#else
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lwbrx r12,0,r8 /* Load reversed word from memory. */
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#endif
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cmpb r3,r12,r4 /* Check for BYTE in WORD1. */
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and r3,r3,r9
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cmplwi cr7,r3,0
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bne cr7,L(done)
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/* Are we done already? */
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cmplw r8,r0
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addi r8,r8,-4
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beqlr
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.align 5
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L(loop_small):
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#ifdef __LITTLE_ENDIAN__
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lwzx r12,0,r8
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#else
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lwbrx r12,0,r8
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#endif
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cmpb r3,r12,r4
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cmplw r8,r0
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cmplwi cr7,r3,0
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bne cr7,L(done)
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addi r8,r8,-4
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bne L(loop_small)
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blr
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END (__memrchr)
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weak_alias (__memrchr, memrchr)
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libc_hidden_builtin_def (memrchr)
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