AArch64: Implement optimized memset.

1 files changed, 229 insertions, 0 deletions

diff --git a/ports/sysdeps/aarch64/memset.S b/ports/sysdeps/aarch64/memset.S
new file mode 100644
index 0000000000..f96f6a6bab
--- /dev/null
+++ b/ports/sysdeps/aarch64/memset.S
@@ -0,0 +1,229 @@
+/* Copyright (C) 2012-2013 Free Software Foundation, Inc.
+
+   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 Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library.  If not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* Assumptions:
+ *
+ * ARMv8-a, AArch64
+ * Unaligned accesses
+ *
+ */
+
+#include <sysdep.h>
+
+/* By default we assume that the DC instruction can be used to zero
+   data blocks more efficiently.  In some circumstances this might be
+   unsafe, for example in an asymmetric multiprocessor environment with
+   different DC clear lengths (neither the upper nor lower lengths are
+   safe to use).  The feature can be disabled by defining DONT_USE_DC.
+
+   If code may be run in a virtualized environment, then define
+   MAYBE_VIRT.  This will cause the code to cache the system register
+   values rather than re-reading them each call.  */
+
+#define dstin		x0
+#define val		w1
+#define count		x2
+#define tmp1		x3
+#define tmp1w		w3
+#define tmp2		x4
+#define tmp2w		w4
+#define zva_len_x	x5
+#define zva_len		w5
+#define zva_bits_x	x6
+
+#define A_l		x7
+#define A_lw		w7
+#define dst		x8
+#define tmp3w		w9
+
+ENTRY_ALIGN (__memset, 6)
+
+	mov	dst, dstin		/* Preserve return value.  */
+	ands	A_lw, val, #255
+#ifndef DONT_USE_DC
+	b.eq	L(zero_mem)
+#endif
+	orr	A_lw, A_lw, A_lw, lsl #8
+	orr	A_lw, A_lw, A_lw, lsl #16
+	orr	A_l, A_l, A_l, lsl #32
+L(tail_maybe_long):
+	cmp	count, #64
+	b.ge	L(not_short)
+L(tail_maybe_tiny):
+	cmp	count, #15
+	b.le	L(tail15tiny)
+L(tail63):
+	ands	tmp1, count, #0x30
+	b.eq	L(tail15)
+	add	dst, dst, tmp1
+	cmp	tmp1w, #0x20
+	b.eq	1f
+	b.lt	2f
+	stp	A_l, A_l, [dst, #-48]
+1:
+	stp	A_l, A_l, [dst, #-32]
+2:
+	stp	A_l, A_l, [dst, #-16]
+
+L(tail15):
+	and	count, count, #15
+	add	dst, dst, count
+	stp	A_l, A_l, [dst, #-16]	/* Repeat some/all of last store. */
+	RET
+
+L(tail15tiny):
+	/* Set up to 15 bytes.  Does not assume earlier memory
+	   being set.  */
+	tbz	count, #3, 1f
+	str	A_l, [dst], #8
+1:
+	tbz	count, #2, 1f
+	str	A_lw, [dst], #4
+1:
+	tbz	count, #1, 1f
+	strh	A_lw, [dst], #2
+1:
+	tbz	count, #0, 1f
+	strb	A_lw, [dst]
+1:
+	RET
+
+	/* Critical loop.  Start at a new cache line boundary.  Assuming
+	 * 64 bytes per line, this ensures the entire loop is in one line.  */
+	.p2align 6
+L(not_short):
+	neg	tmp2, dst
+	ands	tmp2, tmp2, #15
+	b.eq	2f
+	/* Bring DST to 128-bit (16-byte) alignment.  We know that there's
+	 * more than that to set, so we simply store 16 bytes and advance by
+	 * the amount required to reach alignment.  */
+	sub	count, count, tmp2
+	stp	A_l, A_l, [dst]
+	add	dst, dst, tmp2
+	/* There may be less than 63 bytes to go now.  */
+	cmp	count, #63
+	b.le	L(tail63)
+2:
+	sub	dst, dst, #16		/* Pre-bias.  */
+	sub	count, count, #64
+1:
+	stp	A_l, A_l, [dst, #16]
+	stp	A_l, A_l, [dst, #32]
+	stp	A_l, A_l, [dst, #48]
+	stp	A_l, A_l, [dst, #64]!
+	subs	count, count, #64
+	b.ge	1b
+	tst	count, #0x3f
+	add	dst, dst, #16
+	b.ne	L(tail63)
+	RET
+
+#ifndef DONT_USE_DC
+	/* For zeroing memory, check to see if we can use the ZVA feature to
+	 * zero entire 'cache' lines.  */
+L(zero_mem):
+	mov	A_l, #0
+	cmp	count, #63
+	b.le	L(tail_maybe_tiny)
+	neg	tmp2, dst
+	ands	tmp2, tmp2, #15
+	b.eq	1f
+	sub	count, count, tmp2
+	stp	A_l, A_l, [dst]
+	add	dst, dst, tmp2
+	cmp	count, #63
+	b.le	L(tail63)
+1:
+	/* For zeroing small amounts of memory, it's not worth setting up
+	 * the line-clear code.  */
+	cmp	count, #128
+	b.lt	L(not_short)
+#ifdef MAYBE_VIRT
+	/* For efficiency when virtualized, we cache the ZVA capability.  */
+	adrp	tmp2, L(cache_clear)
+	ldr	zva_len, [tmp2, #:lo12:L(cache_clear)]
+	tbnz	zva_len, #31, L(not_short)
+	cbnz	zva_len, L(zero_by_line)
+	mrs	tmp1, dczid_el0
+	tbz	tmp1, #4, 1f
+	/* ZVA not available.  Remember this for next time.  */
+	mov	zva_len, #~0
+	str	zva_len, [tmp2, #:lo12:L(cache_clear)]
+	b	L(not_short)
+1:
+	mov	tmp3w, #4
+	and	zva_len, tmp1w, #15	/* Safety: other bits reserved.  */
+	lsl	zva_len, tmp3w, zva_len
+	str	zva_len, [tmp2, #:lo12:L(cache_clear)]
+#else
+	mrs	tmp1, dczid_el0
+	tbnz	tmp1, #4, L(not_short)
+	mov	tmp3w, #4
+	and	zva_len, tmp1w, #15	/* Safety: other bits reserved.  */
+	lsl	zva_len, tmp3w, zva_len
+#endif
+
+L(zero_by_line):
+	/* Compute how far we need to go to become suitably aligned.  We're
+	 * already at quad-word alignment.  */
+	cmp	count, zva_len_x
+	b.lt	L(not_short)		/* Not enough to reach alignment.  */
+	sub	zva_bits_x, zva_len_x, #1
+	neg	tmp2, dst
+	ands	tmp2, tmp2, zva_bits_x
+	b.eq	1f			/* Already aligned.  */
+	/* Not aligned, check that there's enough to copy after alignment.  */
+	sub	tmp1, count, tmp2
+	cmp	tmp1, #64
+	ccmp	tmp1, zva_len_x, #8, ge	/* NZCV=0b1000 */
+	b.lt	L(not_short)
+	/* We know that there's at least 64 bytes to zero and that it's safe
+	 * to overrun by 64 bytes.  */
+	mov	count, tmp1
+2:
+	stp	A_l, A_l, [dst]
+	stp	A_l, A_l, [dst, #16]
+	stp	A_l, A_l, [dst, #32]
+	subs	tmp2, tmp2, #64
+	stp	A_l, A_l, [dst, #48]
+	add	dst, dst, #64
+	b.ge	2b
+	/* We've overrun a bit, so adjust dst downwards.  */
+	add	dst, dst, tmp2
+1:
+	sub	count, count, zva_len_x
+3:
+	dc	zva, dst
+	add	dst, dst, zva_len_x
+	subs	count, count, zva_len_x
+	b.ge	3b
+	ands	count, count, zva_bits_x
+	b.ne	L(tail_maybe_long)
+	RET
+#ifdef MAYBE_VIRT
+	.bss
+	.p2align 2
+L(cache_clear):
+	.space 4
+#endif
+#endif /* DONT_USE_DC */
+
+END (__memset)
+weak_alias (__memset, memset)
+libc_hidden_builtin_def (memset)