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111 lines
3.1 KiB
ArmAsm
111 lines
3.1 KiB
ArmAsm
/* Copyright (C) 1996-2020 Free Software Foundation, Inc.
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Contributed by Richard Henderson (rth@tamu.edu)
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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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<https://www.gnu.org/licenses/>. */
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/* Fill a block of memory with zeros. Optimized for the Alpha architecture:
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- memory accessed as aligned quadwords only
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- destination memory not read unless needed for good cache behaviour
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- basic blocks arranged to optimize branch prediction for full-quadword
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aligned memory blocks.
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- partial head and tail quadwords constructed with byte-mask instructions
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This is generally scheduled for the EV5 (got to look out for my own
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interests :-), but with EV4 needs in mind. There *should* be no more
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stalls for the EV4 than there are for the EV5.
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*/
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#include <sysdep.h>
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.set noat
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.set noreorder
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.text
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.type __bzero, @function
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.globl __bzero
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.usepv __bzero, USEPV_PROF
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cfi_startproc
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/* On entry to this basic block:
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t3 == loop counter
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t4 == bytes in partial final word
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a0 == possibly misaligned destination pointer */
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.align 3
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bzero_loop:
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beq t3, $tail #
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blbc t3, 0f # skip single store if count even
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stq_u zero, 0(a0) # e0 : store one word
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subq t3, 1, t3 # .. e1 :
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addq a0, 8, a0 # e0 :
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beq t3, $tail # .. e1 :
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0: stq_u zero, 0(a0) # e0 : store two words
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subq t3, 2, t3 # .. e1 :
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stq_u zero, 8(a0) # e0 :
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addq a0, 16, a0 # .. e1 :
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bne t3, 0b # e1 :
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$tail: bne t4, 1f # is there a tail to do?
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ret # no
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1: ldq_u t0, 0(a0) # yes, load original data
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mskqh t0, t4, t0 #
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stq_u t0, 0(a0) #
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ret #
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__bzero:
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#ifdef PROF
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ldgp gp, 0(pv)
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lda AT, _mcount
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jsr AT, (AT), _mcount
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#endif
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mov a0, v0 # e0 : move return value in place
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beq a1, $done # .. e1 : early exit for zero-length store
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and a0, 7, t1 # e0 :
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addq a1, t1, a1 # e1 : add dest misalignment to count
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srl a1, 3, t3 # e0 : loop = count >> 3
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and a1, 7, t4 # .. e1 : find number of bytes in tail
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unop # :
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beq t1, bzero_loop # e1 : aligned head, jump right in
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ldq_u t0, 0(a0) # e0 : load original data to mask into
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cmpult a1, 8, t2 # .. e1 : is this a sub-word set?
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bne t2, $oneq # e1 :
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mskql t0, a0, t0 # e0 : we span words. finish this partial
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subq t3, 1, t3 # e0 :
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addq a0, 8, a0 # .. e1 :
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stq_u t0, -8(a0) # e0 :
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br bzero_loop # .. e1 :
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.align 3
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$oneq:
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mskql t0, a0, t2 # e0 :
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mskqh t0, a1, t3 # e0 :
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or t2, t3, t0 # e1 :
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stq_u t0, 0(a0) # e0 :
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$done: ret
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cfi_endproc
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weak_alias (__bzero, bzero)
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