arm: Implement armv6 optimized string routines

The strcpy and strchr (and related) functions are four times faster
than the byte-by-byte default versions.

The strlen function is twice as fast for long strings and 50% faster
for short strings over the armv4 version.

7 files changed, 697 insertions, 0 deletions

diff --git a/ports/sysdeps/arm/armv6/rawmemchr.S b/ports/sysdeps/arm/armv6/rawmemchr.S
new file mode 100644
index 0000000000..7877bcf6d6
--- /dev/null
+++ b/ports/sysdeps/arm/armv6/rawmemchr.S
@@ -0,0 +1,105 @@
+/* rawmemchr -- find a byte within an unsized memory block.
+   Copyright (C) 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/>.  */
+
+#include <sysdep.h>
+
+	.syntax unified
+	.text
+
+ENTRY (__rawmemchr)
+	@ r0 = start of string
+	@ r1 = character to match
+	@ returns a pointer to the match, which must be present.
+	ldrb	r2, [r0]		@ load first byte asap
+
+	@ To cater to long strings, we want to search through a few
+	@ characters until we reach an aligned pointer.  To cater to
+	@ small strings, we don't want to start doing word operations
+	@ immediately.  The compromise is a maximum of 16 bytes less
+	@ whatever is required to end with an aligned pointer.
+	@ r3 = number of characters to search in alignment loop
+	and	r3, r0, #7
+	uxtb	r1, r1
+	rsb	r3, r3, #15		@ 16 - 1 peeled loop iteration
+	cmp	r2, r1
+	it	eq
+	bxeq	lr
+
+	@ Loop until we find ...
+1:	ldrb	r2, [r0, #1]!
+	subs	r3, r3, #1		@ ... the alignment point
+	it	ne
+	cmpne	r2, r1			@ ... or C
+	bne	1b
+
+	@ Disambiguate the exit possibilites above
+	cmp	r2, r1			@ Found C
+	it	eq
+	bxeq	lr
+	add	r0, r0, #1
+
+	@ So now we're aligned.
+	ldrd	r2, r3, [r0], #8
+	orr	r1, r1, r1, lsl #8	@ Replicate C to all bytes
+#ifdef ARCH_HAS_T2
+	movw	ip, #0x0101
+	pld	[r0, #64]
+	movt	ip, #0x0101
+#else
+	ldr	ip, =0x01010101
+	pld	[r0, #64]
+#endif
+	orr	r1, r1, r1, lsl #16
+
+	@ Loop searching for C, 8 bytes at a time.
+	@ Subtracting (unsigned saturating) from 1 means result of 1 for
+	@ any byte that was originally zero and 0 otherwise.  Therefore
+	@ we consider the lsb of each byte the "found" bit.
+2:	eor	r2, r2, r1		@ Convert C bytes to 0
+	eor	r3, r3, r1
+	uqsub8	r2, ip, r2		@ Find C
+	uqsub8	r3, ip, r3
+	pld	[r0, #128]
+	orrs	r3, r3, r2		@ Test both words for found
+	it	eq
+	ldrdeq	r2, r3, [r0], #8
+	beq	2b
+
+	@ Found something.  Disambiguate between first and second words.
+	@ Adjust r0 to point to the word containing the match.
+	@ Adjust r2 to the found bits for the word containing the match.
+	cmp	r2, #0
+	sub	r0, r0, #4
+	ite	eq
+	moveq	r2, r3
+	subne	r0, r0, #4
+
+	@ Find the bit-offset of the match within the word.  Note that the
+	@ bit result from clz will be 7 higher than "true", but we'll
+	@ immediately discard those bits converting to a byte offset.
+#ifdef __ARMEL__
+	rev	r2, r2			@ For LE, count from the little end
+#endif
+	clz	r2, r2
+	add	r0, r0, r2, lsr #3	@ Adjust the pointer to the found byte
+	bx	lr
+
+END (__rawmemchr)
+
+weak_alias (__rawmemchr, rawmemchr)
+libc_hidden_def (__rawmemchr)
diff --git a/ports/sysdeps/arm/armv6/stpcpy.S b/ports/sysdeps/arm/armv6/stpcpy.S
new file mode 100644
index 0000000000..21a4f385be
--- /dev/null
+++ b/ports/sysdeps/arm/armv6/stpcpy.S
@@ -0,0 +1 @@
+/* Defined in strcpy.S.  */
diff --git a/ports/sysdeps/arm/armv6/strchr.S b/ports/sysdeps/arm/armv6/strchr.S
new file mode 100644
index 0000000000..c856283d53
--- /dev/null
+++ b/ports/sysdeps/arm/armv6/strchr.S
@@ -0,0 +1,143 @@
+/* strchr -- find the first instance of C in a nul-terminated string.
+   Copyright (C) 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/>.  */
+
+#include <sysdep.h>
+
+	.syntax unified
+	.text
+
+ENTRY (strchr)
+	@ r0 = start of string
+	@ r1 = character to match
+	@ returns NULL for no match, or a pointer to the match
+	ldrb	r2, [r0]		@ load the first byte asap
+	uxtb	r1, r1
+
+	@ To cater to long strings, we want to search through a few
+	@ characters until we reach an aligned pointer.  To cater to
+	@ small strings, we don't want to start doing word operations
+	@ immediately.  The compromise is a maximum of 16 bytes less
+	@ whatever is required to end with an aligned pointer.
+	@ r3 = number of characters to search in alignment loop
+	and	r3, r0, #7
+	rsb	r3, r3, #15		@ 16 - 1 peeled loop iteration
+	cmp	r2, r1			@ Found C?
+	it	ne
+	cmpne	r2, #0			@ Found EOS?
+	beq	99f
+
+	@ Loop until we find ...
+1:	ldrb	r2, [r0, #1]!
+	subs	r3, r3, #1		@ ... the aligment point
+	it	ne
+	cmpne	r2, r1			@ ... or the character
+	it	ne
+	cmpne	r2, #0			@ ... or EOS
+	bne	1b
+
+	@ Disambiguate the exit possibilites above
+	cmp	r2, r1			@ Found the character
+	it	ne
+	cmpne	r2, #0			@ Found EOS
+	beq	99f
+	add	r0, r0, #1
+
+	@ So now we're aligned.  Now we actually need a stack frame.
+	push	{ r4, r5, r6, r7 }
+	cfi_adjust_cfa_offset (16)
+	cfi_rel_offset (r4, 0)
+	cfi_rel_offset (r5, 4)
+	cfi_rel_offset (r6, 8)
+	cfi_rel_offset (r7, 12)
+
+	ldrd	r2, r3, [r0], #8
+	orr	r1, r1, r1, lsl #8	@ Replicate C to all bytes
+#ifdef ARCH_HAS_T2
+	movw	ip, #0x0101
+	pld	[r0, #64]
+	movt	ip, #0x0101
+#else
+	ldr	ip, =0x01010101
+	pld	[r0, #64]
+#endif
+	orr	r1, r1, r1, lsl #16
+
+	@ Loop searching for EOS or C, 8 bytes at a time.
+2:
+	@ Subtracting (unsigned saturating) from 1 means result of 1 for
+	@ any byte that was originally zero and 0 otherwise.  Therefore
+	@ we consider the lsb of each byte the "found" bit.
+	uqsub8	r4, ip, r2		@ Find EOS
+	eor	r6, r2, r1		@ Convert C bytes to 0
+	uqsub8	r5, ip, r3
+	eor	r7, r3, r1
+	uqsub8	r6, ip, r6		@ Find C
+	pld	[r0, #128]		@ Prefetch 2 lines ahead
+	uqsub8	r7, ip, r7
+	orr	r4, r4, r6		@ Combine found for EOS and C
+	orr	r5, r5, r7
+	orrs	r6, r4, r5		@ Combine the two words
+	it	eq
+	ldrdeq	r2, r3, [r0], #8
+	beq	2b
+
+	@ Found something.  Disambiguate between first and second words.
+	@ Adjust r0 to point to the word containing the match.
+	@ Adjust r2 to the contents of the word containing the match.
+	@ Adjust r4 to the found bits for the word containing the match.
+	cmp	r4, #0
+	sub	r0, r0, #4
+	itte	eq
+	moveq	r4, r5
+	moveq	r2, r3
+	subne	r0, r0, #4
+
+	@ Find the bit-offset of the match within the word.
+#if defined(__ARMEL__)
+	@ For LE, swap the found word so clz searches from the little end.
+	rev	r4, r4
+#else
+	@ For BE, byte swap the word to make it easier to extract the byte.
+	rev	r2, r2
+#endif
+	@ We're counting 0x01 (not 0x80), so the bit offset is 7 too high.
+	clz	r3, r4
+	sub	r3, r3, #7
+	lsr	r2, r2, r3		@ Shift down found byte
+	uxtb	r1, r1			@ Undo replication of C
+	uxtb	r2, r2			@ Extract found byte
+	add	r0, r0, r3, lsr #3	@ Adjust the pointer to the found byte
+
+	pop	{ r4, r5, r6, r7 }
+	cfi_adjust_cfa_offset (-16)
+	cfi_restore (r4)
+	cfi_restore (r5)
+	cfi_restore (r6)
+	cfi_restore (r7)
+
+	@ Disambiguate between EOS and C.
+99:
+	cmp	r2, r1
+	it	ne
+	movne	r0, #0			@ Found EOS, return NULL
+	bx	lr
+
+END (strchr)
+
+weak_alias (strchr, index)
+libc_hidden_builtin_def (strchr)
diff --git a/ports/sysdeps/arm/armv6/strcpy.S b/ports/sysdeps/arm/armv6/strcpy.S
new file mode 100644
index 0000000000..41f6443319
--- /dev/null
+++ b/ports/sysdeps/arm/armv6/strcpy.S
@@ -0,0 +1,218 @@
+/* strcpy -- copy a nul-terminated string.
+   Copyright (C) 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/>.  */
+
+#include <sysdep.h>
+
+/* Endian independent macros for shifting bytes within registers.  */
+#ifdef __ARMEB__
+#define lsh_gt		lsr
+#define lsh_ls		lsl
+#else
+#define lsh_gt		lsl
+#define lsh_ls		lsr
+#endif
+
+	.syntax unified
+	.text
+
+ENTRY (__stpcpy)
+	@ Signal stpcpy with NULL in IP.
+	mov	ip, #0
+	b	0f
+END (__stpcpy)
+
+weak_alias (__stpcpy, stpcpy)
+libc_hidden_def (__stpcpy)
+libc_hidden_builtin_def (stpcpy)
+
+ENTRY (strcpy)
+	@ Signal strcpy with DEST in IP.
+	mov	ip, r0
+0:
+	pld	[r0]
+	pld	[r1]
+
+	@ To cater to long strings, we want 8 byte alignment in the source.
+	@ To cater to small strings, we don't want to start that right away.
+	@ Loop up to 16 times, less whatever it takes to reach alignment.
+	and	r3, r1, #7
+	rsb	r3, r3, #16
+
+	@ Loop until we find ...
+1:	ldrb	r2, [r1], #1
+	subs	r3, r3, #1		@ ... the alignment point
+	strb	r2, [r0], #1
+	it	ne
+	cmpne	r2, #0			@ ... or EOS
+	bne	1b
+
+	@ Disambiguate the exit possibilites above
+	cmp	r2, #0			@ Found EOS
+	beq	.Lreturn
+
+	@ Load the next two words asap
+	ldrd	r2, r3, [r1], #8
+	pld	[r0, #64]
+	pld	[r1, #64]
+
+	@ For longer strings, we actaully need a stack frame.
+	push	{ r4, r5, r6, r7 }
+	cfi_adjust_cfa_offset (16)
+	cfi_rel_offset (r4, 0)
+	cfi_rel_offset (r5, 4)
+	cfi_rel_offset (r6, 8)
+	cfi_rel_offset (r7, 12)
+
+	@ Subtracting (unsigned saturating) from 1 for any byte means result
+	@ of 1 for any byte that was originally zero and 0 otherwise.
+	@ Therefore we consider the lsb of each byte the "found" bit.
+#ifdef ARCH_HAS_T2
+	movw	r7, #0x0101
+	tst	r0, #3			@ Test alignment of DEST
+	movt	r7, #0x0101
+#else
+	ldr	ip, =0x01010101
+	tst	r0, #3
+#endif
+	bne	.Lunaligned
+
+	@ So now source (r1) is aligned to 8, and dest (r0) is aligned to 4.
+	@ Loop, reading 8 bytes at a time, searching for EOS.
+	.balign	16
+2:	uqsub8	r4, r7, r2		@ Find EOS
+	uqsub8	r5, r7, r3
+	pld	[r1, #128]
+	cmp	r4, #0			@ EOS in first word?
+	pld	[r0, #128]
+	bne	3f
+	str	r2, [r0], #4
+	cmp	r5, #0			@ EOS in second word?
+	bne	4f
+	str	r3, [r0], #4
+	ldrd	r2, r3, [r1], #8
+	b	2b
+
+3:	sub	r1, r1, #4		@ backup to first word
+4:	sub	r1, r1, #4		@ backup to second word
+
+	@ ... then finish up any tail a byte at a time.
+	@ Note that we generally back up and re-read source bytes,
+	@ but we'll not re-write dest bytes.
+.Lbyte_loop:
+	ldrb	r2, [r1], #1
+	cmp	r2, #0
+	strb	r2, [r0], #1
+	bne	.Lbyte_loop
+
+	pop	{ r4, r5, r6, r7 }
+	cfi_remember_state
+	cfi_adjust_cfa_offset (-16)
+	cfi_restore (r4)
+	cfi_restore (r5)
+	cfi_restore (r6)
+	cfi_restore (r7)
+
+.Lreturn:
+	cmp	ip, #0			@ Was this strcpy or stpcpy?
+	ite	eq
+	subeq	r0, r0, #1		@ stpcpy: undo post-inc from store
+	movne	r0, ip			@ strcpy: return original dest
+	bx	lr
+
+.Lunaligned:
+	cfi_restore_state
+	@ Here, source is aligned to 8, but the destination is not word
+	@ aligned.  Therefore we have to shift the data in order to be
+	@ able to perform aligned word stores.
+
+	@ Find out which misalignment we're dealing with.
+	tst	r0, #1
+	beq	.Lunaligned2
+	tst	r0, #2
+	bne	.Lunaligned3
+	@ Fallthru to .Lunaligned1.
+
+.macro unaligned_copy	unalign
+	@ Prologue to unaligned loop.  Seed shifted non-zero bytes.
+	uqsub8	r4, r7, r2		@ Find EOS
+	uqsub8	r5, r7, r3
+	mvns	r4, r4			@ EOS in first word?
+	it	ne
+	subne	r1, r1, #8
+	bne	.Lbyte_loop
+#ifdef __ARMEB__
+	rev	r2, r2			@ Byte stores below need LE data
+#endif
+	@ Store a few bytes from the first word.
+	@ At the same time we align r0 and shift out bytes from r2.
+.rept	4-\unalign
+	strb	r2, [r0], #1
+	lsr	r2, r2, #8
+.endr
+#ifdef __ARMEB__
+	rev	r2, r2			@ Undo previous rev
+#endif
+	@ Rotated unaligned copy loop.  The tail of the prologue is
+	@ shared with the loop itself.
+	.balign 8
+1:	mvns	r5, r5			@ EOS in second word?
+	bne	4f
+	@ Combine first and second words
+	orr	r2, r2, r3, lsh_gt #(\unalign*8)
+	@ Save leftover bytes from the two words
+	lsh_ls	r6, r3, #((4-\unalign)*8)
+	str	r2, [r0], #4
+	@ The "real" start of the unaligned copy loop.
+	ldrd	r2, r3, [r1], #8	@ Load 8 more bytes
+	uqsub8	r4, r7, r2		@ Find EOS
+	pld	[r1, #128]
+	uqsub8	r5, r7, r3
+	pld	[r0, #128]
+	mvns	r4, r4			@ EOS in first word?
+	bne	3f
+	@ Combine the leftover and the first word
+	orr	r6, r6, r2, lsh_gt #(\unalign*8)
+	@ Discard used bytes from the first word.
+	lsh_ls	r2, r2, #((4-\unalign)*8)
+	str	r6, [r0], #4
+	b	1b
+	@ Found EOS in one of the words; adjust backward
+3:	sub	r1, r1, #4
+	mov	r2, r6
+4:	sub	r1, r1, #4
+	@ And store the remaining bytes from the leftover
+#ifdef __ARMEB__
+	rev	r2, r2
+#endif
+.rept	\unalign
+	strb	r2, [r0], #1
+	lsr	r2, r2, #8
+.endr
+	b	.Lbyte_loop
+.endm
+
+.Lunaligned1:
+	unaligned_copy	1
+.Lunaligned2:
+	unaligned_copy	2
+.Lunaligned3:
+	unaligned_copy	3
+
+END (strcpy)
+
+libc_hidden_builtin_def (strcpy)
diff --git a/ports/sysdeps/arm/armv6/strlen.S b/ports/sysdeps/arm/armv6/strlen.S
new file mode 100644
index 0000000000..a53d41418a
--- /dev/null
+++ b/ports/sysdeps/arm/armv6/strlen.S
@@ -0,0 +1,99 @@
+/* strlen -- find the length of a nul-terminated string.
+   Copyright (C) 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/>.  */
+
+#include <sysdep.h>
+
+	.syntax unified
+	.text
+
+ENTRY (strlen)
+	@ r0 = start of string
+	ldrb	r2, [r0]		@ load the first byte asap
+
+	@ To cater to long strings, we want to search through a few
+	@ characters until we reach an aligned pointer.  To cater to
+	@ small strings, we don't want to start doing word operations
+	@ immediately.  The compromise is a maximum of 16 bytes less
+	@ whatever is required to end with an aligned pointer.
+	@ r3 = number of characters to search in alignment loop
+	and	r3, r0, #7
+	mov	r1, r0			@ Save the input pointer
+	rsb	r3, r3, #15		@ 16 - 1 peeled loop iteration
+	cmp	r2, #0
+	beq	99f
+
+	@ Loop until we find ...
+1:	ldrb	r2, [r0, #1]!
+	subs	r3, r3, #1		@ ... the aligment point
+	it	ne
+	cmpne	r2, #0			@ ... or EOS
+	bne	1b
+
+	@ Disambiguate the exit possibilites above
+	cmp	r2, #0			@ Found EOS
+	beq	99f
+	add	r0, r0, #1
+
+	@ So now we're aligned.
+	ldrd	r2, r3, [r0], #8
+#ifdef ARCH_HAS_T2
+	movw	ip, #0x0101
+	pld	[r0, #64]
+	movt	ip, #0x0101
+#else
+	ldr	ip, =0x01010101
+	pld	[r0, #64]
+#endif
+
+	@ Loop searching for EOS, 8 bytes at a time.
+	@ Subtracting (unsigned saturating) from 1 for any byte means that
+	@ we get 1 for any byte that was originally zero and 0 otherwise.
+	@ Therefore we consider the lsb of each byte the "found" bit.
+	.balign	16
+2:	uqsub8	r2, ip, r2		@ Find EOS
+	uqsub8	r3, ip, r3
+	pld	[r0, #128]		@ Prefetch 2 lines ahead
+	orrs	r3, r3, r2		@ Combine the two words
+	it	eq
+	ldrdeq	r2, r3, [r0], #8
+	beq	2b
+
+	@ Found something.  Disambiguate between first and second words.
+	@ Adjust r0 to point to the word containing the match.
+	@ Adjust r2 to the found bits for the word containing the match.
+	cmp	r2, #0
+	sub	r0, r0, #4
+	ite	eq
+	moveq	r2, r3
+	subne	r0, r0, #4
+
+	@ Find the bit-offset of the match within the word.  Note that the
+	@ bit result from clz will be 7 higher than "true", but we'll
+	@ immediately discard those bits converting to a byte offset.
+#ifdef __ARMEL__
+	rev	r2, r2			@ For LE, count from the little end
+#endif
+	clz	r2, r2
+	add	r0, r0, r2, lsr #3	@ Adjust the pointer to the found byte
+99:
+	sub	r0, r0, r1		@ Subtract input to compute length
+	bx	lr
+
+END (strlen)
+
+libc_hidden_builtin_def (strlen)
diff --git a/ports/sysdeps/arm/armv6/strrchr.S b/ports/sysdeps/arm/armv6/strrchr.S
new file mode 100644
index 0000000000..ddd4f7fc06
--- /dev/null
+++ b/ports/sysdeps/arm/armv6/strrchr.S
@@ -0,0 +1,129 @@
+/* strrchr -- find the last occurence of C in a nul-terminated string
+   Copyright (C) 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/>.  */
+
+#include <sysdep.h>
+
+	.syntax unified
+	.text
+
+ENTRY (strrchr)
+	@ r0 = start of string
+	@ r1 = character to match
+	@ returns NULL for no match, or a pointer to the match
+
+	mov	r3, r0
+	mov	r0, #0
+	uxtb	r1, r1
+
+	@ Loop a few times until we're aligned.
+	tst	r3, #7
+	beq	2f
+1:	ldrb	r2, [r3], #1
+	cmp	r2, r1			@ Find the character
+	it	eq
+	subeq	r0, r3, #1
+	cmp	r2, #0			@ Find EOS
+	it	eq
+	bxeq	lr
+	tst	r3, #7			@ Find the aligment point
+	bne	1b
+
+	@ So now we're aligned.  Now we actually need a stack frame.
+2:	push	{ r4, r5, r6, r7 }
+	cfi_adjust_cfa_offset (16)
+	cfi_rel_offset (r4, 0)
+	cfi_rel_offset (r5, 4)
+	cfi_rel_offset (r6, 8)
+	cfi_rel_offset (r7, 12)
+
+	orr	r1, r1, r1, lsl #8	@ Replicate C to all bytes
+#ifdef ARCH_HAS_T2
+	movw	ip, #0x0101
+	movt	ip, #0x0101
+#else
+	ldr	ip, =0x01010101
+#endif
+	orr	r1, r1, r1, lsl #16
+	mov	r2, #0			@ No found bits yet
+
+	@ Loop searching for EOS and C, 8 bytes at a time.
+	@ Any time we find a match in a word, we copy the address of
+	@ the word to r0, and the found bits to r2.
+3:	ldrd	r4, r5, [r3], #8
+	@ Subtracting (unsigned saturating) from 1 means result of 1 for
+	@ any byte that was originally zero and 0 otherwise.  Therefore
+	@ we consider the lsb of each byte the "found" bit.
+	uqsub8	r6, ip, r4		@ Find EOS
+	uqsub8	r7, ip, r5
+	eor	r4, r4, r1		@ Convert C bytes to 0
+	eor	r5, r5, r1
+	uqsub8	r4, ip, r4		@ Find C
+	uqsub8	r5, ip, r5
+	cmp	r6, #0			@ Found EOS, first word
+	bne	4f
+	cmp	r4, #0			@ Handle C, first word
+	itt	ne
+	subne	r0, r3, #8
+	movne	r2, r4
+	cmp	r7, #0			@ Found EOS, second word
+	bne	5f
+	cmp	r5, #0			@ Handle C, second word
+	itt	ne
+	subne	r0, r3, #4
+	movne	r2, r5
+	b	3b
+
+	@ Found EOS in second word; fold to first word.
+5:	add	r3, r3, #4		@ Dec pointer to 2nd word, with below
+	mov	r4, r5			@ Overwrite first word C found
+	mov	r6, r7			@ Overwrite first word EOS found
+
+	@ Found EOS.  Zap found C after EOS.
+4:	sub	r3, r3, #8		@ Decrement pointer to first word
+#ifdef __ARMEB__
+	@ Byte swap to be congruent with LE, which is easier from here on.
+	rev	r6, r6			@ Byte swap found EOS,
+	rev	r4, r4			@ ... this found C
+	rev	r2, r2			@ ... prev found C
+#endif
+	sub	r7, r6, #1		@ Toggle EOS lsb and below
+	eor	r6, r6, r7		@ All bits below and including lsb
+	ands	r4, r4, r6		@ Zap C above EOS
+	itt	ne
+	movne	r2, r4			@ Copy to result, if still non-zero
+	movne	r0, r3
+
+	pop	{ r4, r5, r6, r7 }
+	cfi_adjust_cfa_offset (-16)
+	cfi_restore (r4)
+	cfi_restore (r5)
+	cfi_restore (r6)
+	cfi_restore (r7)
+
+	@ Adjust the result pointer if we found a word containing C.
+	cmp	r2, #0
+	clz	r2, r2			@ Find the bit offset of the last C
+	itt	ne
+	rsbne	r2, r2, #32		@ Convert to a count from the right
+	addne	r0, r0, r2, lsr #3	@ Convert to byte offset and add.
+	bx	lr
+
+END (strrchr)
+
+weak_alias (strrchr, rindex)
+libc_hidden_builtin_def (strrchr)
diff --git a/ports/sysdeps/arm/armv6t2/Implies b/ports/sysdeps/arm/armv6t2/Implies
new file mode 100644
index 0000000000..20a87fc8a5
--- /dev/null
+++ b/ports/sysdeps/arm/armv6t2/Implies
@@ -0,0 +1,2 @@
+# We can do everything that 6 can
+arm/armv6