Re: [Patch] Replace MIPS strcmp.c with assembly language version.

[Jeff Johnston <jjohnstn at redhat dot com>]

I noticed that the glibc version has an LGPL license.  Where did you get this version
from with the BSD-style license?

I also assume this is noticeably better
than the much smaller NetBSD version of MIPS strcmp.S I found on the net: 

http://cvsweb.netbsd.org/bsdweb.cgi/src/common/lib/libc/arch/mips/string/strcmp.S?rev=1.2&content-type=text/x-cvsweb-markup&only_with_tag=MAIN

-- Jeff J.

----- Original Message -----
From: "Steve Ellcey" <sellcey@mips.com>
To: newlib@sourceware.org
Cc: c@mips.com
Sent: Thursday, October 2, 2014 4:49:50 PM
Subject: [Patch] Replace MIPS strcmp.c with assembly language version.


I would like to replace the MIPS C strcmp.c with an assembly language
version that is a bit faster.  Both versions load 4 bytes at a time on
aligned strings but the assembly version has the advantage of being
scheduled by hand and having some loop unrolling to be a bit faster.
This version is already checked in to glibc.  It has been tested by
hand and by running the GCC testsuite.

OK for checkin?

Steve Ellcey
sellcey@mips.com


2014-10-02  Steve Ellcey  <sellcey@mips.com>

	* newlib/libc/machine/mips/strcmp.c: Remove.
	* newlib/libc/machine/mips/strcmp.S: New.
	* newlib/libc/machine/mips/Makefile.am (lib_a_SOURCES):
	Replace strcmp.c with strcmp.S
	* newlib/libc/machine/mips/Makefile.in: Regenerate.


diff --git a/newlib/libc/machine/mips/Makefile.am b/newlib/libc/machine/mips/Makefile.am
index 46b4cc3..1695b18 100644
--- a/newlib/libc/machine/mips/Makefile.am
+++ b/newlib/libc/machine/mips/Makefile.am
@@ -8,7 +8,7 @@ AM_CCASFLAGS = $(INCLUDES)
 
 noinst_LIBRARIES = lib.a
 
-lib_a_SOURCES = setjmp.S strlen.c strcmp.c strncpy.c memset.S memcpy.S
+lib_a_SOURCES = setjmp.S strlen.c strcmp.S strncpy.c memset.S memcpy.S
 lib_a_CCASFLAGS=$(AM_CCASFLAGS) -D_COMPILING_NEWLIB
 lib_a_CFLAGS=$(AM_CFLAGS) -D_COMPILING_NEWLIB
 
diff --git a/newlib/libc/machine/mips/strcmp.S b/newlib/libc/machine/mips/strcmp.S
new file mode 100644
index 0000000..b1d757e
--- /dev/null
+++ b/newlib/libc/machine/mips/strcmp.S
@@ -0,0 +1,261 @@
+/*
+ * Copyright (c) 2014
+ *      Imagination Technologies Limited.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. 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.
+ * 3. Neither the name of the MIPS Technologies, Inc., 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 IMAGINATION TECHNOLOGIES LIMITED ``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 IMAGINATION TECHNOLOGIES LIMITED 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.
+ */
+
+#ifdef ANDROID_CHANGES
+# include "machine/asm.h"
+# include "machine/regdef.h"
+#elif _LIBC
+# include <sysdep.h>
+# include <regdef.h>
+# include <sys/asm.h>
+#elif _COMPILING_NEWLIB
+# include "machine/asm.h"
+# include "machine/regdef.h"
+#else
+# include <regdef.h>
+# include <sys/asm.h>
+#endif
+
+/* Technically strcmp should not read past the end of the strings being
+   compared.  We will read a full word that may contain excess bits beyond
+   the NULL string terminator but unless ENABLE_READAHEAD is set, we will not
+   read the next word after the end of string.  Setting ENABLE_READAHEAD will
+   improve performance but is technically illegal based on the definition of
+   strcmp.  */
+#ifdef ENABLE_READAHEAD
+# define DELAY_READ
+#else
+# define DELAY_READ nop
+#endif
+
+/* Testing on a little endian machine showed using CLZ was a
+   performance loss, so we are not turning it on by default.  */
+#if defined(ENABLE_CLZ) && (__mips_isa_rev > 1)
+# define USE_CLZ
+#endif
+
+/* Some asm.h files do not have the L macro definition.  */
+#ifndef L
+# if _MIPS_SIM == _ABIO32
+#  define L(label) $L ## label
+# else
+#  define L(label) .L ## label
+# endif
+#endif
+
+/* Some asm.h files do not have the PTR_ADDIU macro definition.  */
+#ifndef PTR_ADDIU
+# ifdef USE_DOUBLE
+#  define PTR_ADDIU       daddiu
+# else
+#  define PTR_ADDIU       addiu
+# endif
+#endif
+
+/* Allow the routine to be named something else if desired.  */
+#ifndef STRCMP_NAME
+# define STRCMP_NAME strcmp
+#endif
+
+#ifdef ANDROID_CHANGES
+LEAF(STRCMP_NAME, 0)
+#else
+LEAF(STRCMP_NAME)
+#endif
+	.set	nomips16
+	.set	noreorder
+
+	or	t0, a0, a1
+	andi	t0,0x3
+	bne	t0, zero, L(byteloop)
+
+/* Both strings are 4 byte aligned at this point.  */
+
+	lui	t8, 0x0101
+	ori	t8, t8, 0x0101
+	lui	t9, 0x7f7f
+	ori	t9, 0x7f7f
+
+#define STRCMP32(OFFSET) \
+	lw	v0, OFFSET(a0); \
+	lw	v1, OFFSET(a1); \
+	subu	t0, v0, t8; \
+	bne	v0, v1, L(worddiff); \
+	nor	t1, v0, t9; \
+	and	t0, t0, t1; \
+	bne	t0, zero, L(returnzero)
+
+L(wordloop):
+	STRCMP32(0)
+	DELAY_READ
+	STRCMP32(4)
+	DELAY_READ
+	STRCMP32(8)
+	DELAY_READ
+	STRCMP32(12)
+	DELAY_READ
+	STRCMP32(16)
+	DELAY_READ
+	STRCMP32(20)
+	DELAY_READ
+	STRCMP32(24)
+	DELAY_READ
+	STRCMP32(28)
+	PTR_ADDIU a0, a0, 32
+	b	L(wordloop)
+	PTR_ADDIU a1, a1, 32
+
+L(returnzero):
+	j	ra
+	move	v0, zero
+
+L(worddiff):
+#ifdef USE_CLZ
+	subu	t0, v0, t8
+	nor	t1, v0, t9
+	and	t1, t0, t1
+	xor	t0, v0, v1
+	or	t0, t0, t1
+# if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+	wsbh	t0, t0
+	rotr	t0, t0, 16
+# endif
+	clz	t1, t0
+	and	t1, 0xf8
+# if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+	neg	t1
+	addu	t1, 24
+# endif
+	rotrv	v0, v0, t1
+	rotrv	v1, v1, t1
+	and	v0, v0, 0xff
+	and	v1, v1, 0xff
+	j	ra
+	subu	v0, v0, v1
+#else /* USE_CLZ */
+# if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+	andi	t0, v0, 0xff
+	beq	t0, zero, L(wexit01)
+	andi	t1, v1, 0xff
+	bne	t0, t1, L(wexit01)
+
+	srl	t8, v0, 8
+	srl	t9, v1, 8
+	andi	t8, t8, 0xff
+	beq	t8, zero, L(wexit89)
+	andi	t9, t9, 0xff
+	bne	t8, t9, L(wexit89)
+
+	srl	t0, v0, 16
+	srl	t1, v1, 16
+	andi	t0, t0, 0xff
+	beq	t0, zero, L(wexit01)
+	andi	t1, t1, 0xff
+	bne	t0, t1, L(wexit01)
+
+	srl	t8, v0, 24
+	srl	t9, v1, 24
+# else /* __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ */
+	srl	t0, v0, 24
+	beq	t0, zero, L(wexit01)
+	srl	t1, v1, 24
+	bne	t0, t1, L(wexit01)
+
+	srl	t8, v0, 16
+	srl	t9, v1, 16
+	andi	t8, t8, 0xff
+	beq	t8, zero, L(wexit89)
+	andi	t9, t9, 0xff
+	bne	t8, t9, L(wexit89)
+
+	srl	t0, v0, 8
+	srl	t1, v1, 8
+	andi	t0, t0, 0xff
+	beq	t0, zero, L(wexit01)
+	andi	t1, t1, 0xff
+	bne	t0, t1, L(wexit01)
+
+	andi	t8, v0, 0xff
+	andi	t9, v1, 0xff
+# endif /* __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ */
+
+L(wexit89):
+	j	ra
+	subu	v0, t8, t9
+L(wexit01):
+	j	ra
+	subu	v0, t0, t1
+#endif /* USE_CLZ */
+
+/* It might seem better to do the 'beq' instruction between the two 'lbu'
+   instructions so that the nop is not needed but testing showed that this
+   code is actually faster (based on glibc strcmp test).  */
+#define BYTECMP01(OFFSET) \
+	lbu	v0, OFFSET(a0); \
+	lbu	v1, OFFSET(a1); \
+	beq	v0, zero, L(bexit01); \
+	nop; \
+	bne	v0, v1, L(bexit01)
+
+#define BYTECMP89(OFFSET) \
+	lbu	t8, OFFSET(a0); \
+	lbu	t9, OFFSET(a1); \
+	beq	t8, zero, L(bexit89); \
+	nop;	\
+	bne	t8, t9, L(bexit89)
+
+L(byteloop):
+	BYTECMP01(0)
+	BYTECMP89(1)
+	BYTECMP01(2)
+	BYTECMP89(3)
+	BYTECMP01(4)
+	BYTECMP89(5)
+	BYTECMP01(6)
+	BYTECMP89(7)
+	PTR_ADDIU a0, a0, 8
+	b	L(byteloop)
+	PTR_ADDIU a1, a1, 8
+
+L(bexit01):
+	j	ra
+	subu	v0, v0, v1
+L(bexit89):
+	j	ra
+	subu	v0, t8, t9
+
+	.set	at
+	.set	reorder
+
+END(STRCMP_NAME)
+#ifndef ANDROID_CHANGES
+# ifdef _LIBC
+libc_hidden_builtin_def (STRCMP_NAME)
+# endif
+#endif