1 files changed, 113 insertions, 0 deletions
diff --git a/sysdeps/alpha/bzero.S b/sysdeps/alpha/bzero.S
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+/* Copyright (C) 1996 Free Software Foundation, Inc.
+   Contributed by Richard Henderson (rth@tamu.edu)
+
+This file is part of the GNU C Library.
+
+The GNU C Library is free software; you can redistribute it and/or
+modify it under the terms of the GNU Library General Public License as
+published by the Free Software Foundation; either version 2 of the
+License, or (at your option) any later version.
+
+The GNU C Library is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+Library General Public License for more details.
+
+You should have received a copy of the GNU Library General Public
+License along with the GNU C Library; see the file COPYING.LIB.  If
+not, write to the Free Software Foundation, Inc., 675 Mass Ave,
+Cambridge, MA 02139, USA.  */
+
+/* Fill a block of memory with zeros.  Optimized for the Alpha architecture:
+
+   - memory accessed as aligned quadwords only
+   - destination memory not read unless needed for good cache behaviour
+   - basic blocks arranged to optimize branch prediction for full-quadword
+     aligned memory blocks.
+   - partial head and tail quadwords constructed with byte-mask instructions
+
+   This is generally scheduled for the EV5 (got to look out for my own
+   interests :-), but with EV4 needs in mind.  There *should* be no more
+   stalls for the EV4 than there are for the EV5.
+*/
+
+
+#include <sysdep.h>
+
+	.set noat
+	.set noreorder
+
+	.text
+
+/* There is a problem with either gdb (as of 4.16) or gas (as of 2.7) that
+   doesn't like putting the entry point for a procedure somewhere in the
+   middle of the procedure descriptor.  Work around this by putting the main
+   loop in its own procedure descriptor.  */
+
+	/* On entry to this basic block:
+	   t3 == loop counter
+	   t4 == bytes in partial final word
+	   a0 == possibly misaligned destination pointer  */
+
+	.ent bzero_loop
+	.align 3
+bzero_loop:
+	.frame sp, 0, ra, 0
+	.prologue 0
+
+	beq	t3, $tail	#
+	blbc	t3, 0f		# skip single store if count even
+
+	stq_u	zero, 0(a0)	# e0    : store one word
+	subq	t3, 1, t3	# .. e1 :
+	addq	a0, 8, a0	# e0    :
+	beq	t3, $tail	# .. e1 :
+
+0:	stq_u	zero, 0(a0)	# e0    : store two words
+	subq	t3, 2, t3	# .. e1 :
+	stq_u	zero, 8(a0)	# e0    :
+	addq	a0, 16, a0	# .. e1 :
+	bne	t3, 0b		# e1    :
+
+$tail:	bne	t4, 1f		# is there a tail to do?
+	ret			# no
+
+1:	ldq_u	t0, 0(a0)	# yes, load original data
+	mskqh	t0, t4, t0	#
+	stq_u	t0, 0(a0)	#
+	ret			#
+
+	.end bzero_loop
+
+ENTRY(bzero)
+	.prologue 0
+
+	mov	a0, v0		# e0    : move return value in place
+	beq	a1, $done	# .. e1 : early exit for zero-length store
+	and	a0, 7, t1	# e0    :
+	addq	a1, t1, a1	# e1    : add dest misalignment to count
+	srl	a1, 3, t3	# e0    : loop = count >> 3
+	and	a1, 7, t4	# .. e1 : find number of bytes in tail
+	unop			#       :
+	beq	t1, bzero_loop	# e1    : aligned head, jump right in
+
+	ldq_u	t0, 0(a0)	# e0    : load original data to mask into
+	cmpult	a1, 8, t2	# .. e1 : is this a sub-word set?
+	bne	t2, $oneq	# e1    :
+
+	mskql	t0, a0, t0	# e0    : we span words.  finish this partial
+	subq	t3, 1, t3	# e0    :
+	addq	a0, 8, a0	# .. e1 :
+	stq_u	t0, -8(a0)	# e0    :
+	br 	bzero_loop	# .. e1 :
+
+	.align 3
+$oneq:
+	mskql	t0, a0, t2	# e0    :
+	mskqh	t0, a1, t3	# e0    :
+	or	t2, t3, t0	# e1    :
+	stq_u	t0, 0(a0)	# e0    :
+
+$done:	ret
+
+	END(bzero)