[src/trunk]: src/common/lib/libc/arch/x86_64/string Rewrite bcmp() & memcmp()...

[ad <ad%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/05c044eaed0e
branches:  trunk
changeset: 467150:05c044eaed0e
user:      ad <ad%NetBSD.org@localhost>
date:      Wed Jan 15 10:56:49 2020 +0000

description:
Rewrite bcmp() & memcmp() to not use REP CMPS.  Seems about 5-10x faster for
small strings on modern hardware.

diffstat:

 common/lib/libc/arch/x86_64/string/bcmp.S   |  77 ++++++++++++++++++++-----
 common/lib/libc/arch/x86_64/string/memcmp.S |  86 ++++++++++++++++++++--------
 2 files changed, 121 insertions(+), 42 deletions(-)

diffs (191 lines):

diff -r 4c7d5f2def7f -r 05c044eaed0e common/lib/libc/arch/x86_64/string/bcmp.S
--- a/common/lib/libc/arch/x86_64/string/bcmp.S Wed Jan 15 10:25:47 2020 +0000
+++ b/common/lib/libc/arch/x86_64/string/bcmp.S Wed Jan 15 10:56:49 2020 +0000
@@ -1,24 +1,67 @@
+/*     $NetBSD: bcmp.S,v 1.4 2020/01/15 10:56:49 ad Exp $      */
+
+/*-
+ * Copyright (c) 2020 The NetBSD Foundation, Inc.
+ * All rights reserved.
+ *
+ * This code is derived from software contributed to The NetBSD Foundation
+ * by Andrew Doran.
+ *
+ * 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.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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 <machine/asm.h>
 
 #if defined(LIBC_SCCS)
-       RCSID("$NetBSD: bcmp.S,v 1.3 2014/03/22 19:16:34 jakllsch Exp $")
+       RCSID("$NetBSD: bcmp.S,v 1.4 2020/01/15 10:56:49 ad Exp $")
 #endif
 
 ENTRY(bcmp)
-       xorl    %eax,%eax               /* clear return value */
-
-       movq    %rdx,%rcx               /* compare by words */
-       shrq    $3,%rcx
-       repe
-       cmpsq
-       jne     L1
-
-       movq    %rdx,%rcx               /* compare remainder by bytes */
-       andq    $7,%rcx
-       repe
-       cmpsb
-       je      L2
-
-L1:    incl    %eax
-L2:    ret
+       movq    %rdx, %rcx      /* compare by longs, equality only */
+       shrq    $3, %rcx
+       jz      2f
+1:
+       movq    (%rdi), %rax
+       cmpq    %rax, (%rsi)
+       jne     5f
+       decq    %rcx
+       leaq    8(%rdi), %rdi
+       leaq    8(%rsi), %rsi
+       jnz     1b
+2:
+       andl    $7, %edx
+       jz      4f
+3:
+       movb    (%rdi), %al     /* compare by chars, equality only */
+       cmpb    %al, (%rsi)
+       jne     5f
+       decl    %edx
+       leaq    1(%rdi), %rdi
+       leaq    1(%rsi), %rsi
+       jnz     3b
+4:
+       xorl    %eax, %eax
+       ret
+5:
+       movl    $1, %eax
+       ret
 END(bcmp)
diff -r 4c7d5f2def7f -r 05c044eaed0e common/lib/libc/arch/x86_64/string/memcmp.S
--- a/common/lib/libc/arch/x86_64/string/memcmp.S       Wed Jan 15 10:25:47 2020 +0000
+++ b/common/lib/libc/arch/x86_64/string/memcmp.S       Wed Jan 15 10:56:49 2020 +0000
@@ -1,3 +1,34 @@
+/*     $NetBSD: memcmp.S,v 1.4 2020/01/15 10:56:49 ad Exp $    */
+
+/*-
+ * Copyright (c) 2020 The NetBSD Foundation, Inc.
+ * All rights reserved.
+ *
+ * This code is derived from software contributed to The NetBSD Foundation
+ * by Andrew Doran.
+ *
+ * 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.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
+ */
+
 /*
  * Written by J.T. Conklin <jtc%NetBSD.org@localhost>.
  * Public domain.
@@ -7,34 +38,39 @@
 #include <machine/asm.h>
 
 #if defined(LIBC_SCCS)
-       RCSID("$NetBSD: memcmp.S,v 1.3 2014/03/22 19:16:34 jakllsch Exp $")
+       RCSID("$NetBSD: memcmp.S,v 1.4 2020/01/15 10:56:49 ad Exp $")
 #endif
 
 ENTRY(memcmp)
-       movq    %rdx,%rcx               /* compare by longs */
-       shrq    $3,%rcx
-       repe
-       cmpsq
-       jne     L5                      /* do we match so far? */
-
-       movq    %rdx,%rcx               /* compare remainder by bytes */
-       andq    $7,%rcx
-       repe
-       cmpsb
-       jne     L6                      /* do we match? */
-
-       xorl    %eax,%eax               /* we match, return zero        */
+       movq    %rdx, %rcx      /* compare by longs, equality only */
+       shrq    $3, %rcx
+       jz      2f
+1:
+       movq    (%rdi), %rax
+       cmpq    %rax, (%rsi)
+       jne     6f
+       decq    %rcx
+       leaq    8(%rdi), %rdi
+       leaq    8(%rsi), %rsi
+       jnz     1b
+2:
+       andl    $7, %edx
+       jz      5f
+3:
+       movb    (%rdi), %al     /* compare by chars, find difference */
+       subb    (%rsi), %al
+       jne     4f
+       decl    %edx
+       leaq    1(%rdi), %rdi
+       leaq    1(%rsi), %rsi
+       jnz     3b
+4:
+       movsbl  %al, %eax
        ret
-
-L5:    movl    $8,%ecx                 /* We know that one of the next */
-       subq    %rcx,%rdi               /* eight pairs of bytes do not  */
-       subq    %rcx,%rsi               /* match.                       */
-       repe
-       cmpsb
-L6:    xorl    %eax,%eax               /* Perform unsigned comparison  */
-       movb    -1(%rdi),%al
-       xorl    %edx,%edx
-       movb    -1(%rsi),%dl
-       subl    %edx,%eax
+5:
+       xorl    %eax, %eax
        ret
+6:
+       movl    $8, %edx
+       jmp     3b
 END(memcmp)