[ARM] Factor out the thumb2 -Os implementation.

The patch moves the inline ASM thumb2 -Os implementation out into its
own .S file.

Tested by building newlib and comparing libc.a binaries before and
after for all permutations of:

      Architectures:
        armv4 armv4t armv5 armv5t armv5te armv6 armv6j armv6k
        armv6z armv6kz armv6t2 armv6-m armv6s-m armv7 armv7-a
        armv7ve armv7-r armv7-m armv7e-m armv8-a iwmmxt iwmmxt2

      ISAs:
        thumb arm

      Optimization Levels:
        Os O2

      Excluding:
        armv6s-m -mthumb
        armv6-m -mthumb

        armv6zk -mthumb
        armv6z -mthumb
        armv6k -mthumb
        armv6j -mthumb

newlib/ChangeLog

@@ -1,3 +1,9 @@
+2015-11-23  Marcus Shawcroft  <marcus.shawcroft@arm.com>
+
+	* libc/machine/arm/strlen-stub.c: Move T2 -O2 implementation to...
+	* libc/machine/arm/strlen-thumb2-Os.S: New file.
+	* libc/machine/arm/strlen.S: Include strlen-thumb2-Os.S.
+
 2015-11-21  Corinna Vinschen  <corinna@vinschen.de>
 
 	* libc/stdlib/strtodg.c: Define USE_LOCALE.

newlib/libc/machine/arm/strlen-stub.c

@@ -36,18 +36,8 @@
 /* Implemented in strlen.S.  */
 
 #else
-size_t
+/* Implemented in strlen.S.  */
-strlen (const char* str)
+
-{
-  int scratch;
-  const char* end;
-  asm ("1:\n\t"
-       "ldrb	%1, [%0], #1\n\t"
-       "cmp	%1, #0\n\t"
-       "bne	1b"
-       : "=&r" (end), "=&r" (scratch) : "0" (str) : "memory", "cc");
-  return end - str - 1;
-}
 #endif
 
 #else /* defined __OPTIMIZE_SIZE__ || defined PREFER_SIZE_OVER_SPEED */

newlib/libc/machine/arm/strlen-thumb2-Os.S

@@ -0,0 +1,54 @@
+/* Copyright (c) 2015 ARM Ltd.
+   All rights reserved.
+
+   Redistribution and use in source and binary forms, with or without
+   modification, are permitted provided that the following conditions are met:
+       * Redistributions of source code must retain the above copyright
+	 notice, this list of conditions and the following disclaimer.
+       * Redistributions in binary form must reproduce the above copyright
+	 notice, this list of conditions and the following disclaimer in the
+	 documentation and/or other materials provided with the distribution.
+       * Neither the name of the Linaro nor the
+	 names of its contributors may be used to endorse or promote products
+	 derived from this software without specific prior written permission.
+
+   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+   A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT
+   HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.  */
+
+#include "acle-compat.h"
+
+	.macro def_fn f p2align=0
+	.text
+	.p2align \p2align
+	.global \f
+	.type \f, %function
+\f:
+	.endm
+
+#if __ARM_ARCH_ISA_THUMB >= 2 && __ARM_ARCH >= 7
+	.arch   armv7
+#else
+	.arch	armv6t2
+#endif
+	.eabi_attribute Tag_ARM_ISA_use, 0
+	.thumb
+	.syntax unified
+
+def_fn	strlen p2align=1
+	mov     r3, r0
+1:	ldrb.w  r2, [r3], #1
+	cmp     r2, #0
+	bne	1b
+	subs    r0, r3, r0
+	subs    r0, #1
+	bx      lr
+	.size	strlen, . - strlen

newlib/libc/machine/arm/strlen.S

@@ -31,7 +31,7 @@
 #include "strlen-thumb1-Os.S"
 
 #else
-  /* Implemented in strlen-stub.c.  */
+#include "strlen-thumb2-Os.S"
 
 #endif