[PATCH RESEND] x86/asm/32: Modernize _memcpy()

[Uros Bizjak <ubizjak@gmail.com>]

Use inout "+" constraint modifier where appropriate, declare
temporary variables as unsigned long and rewrite parts of assembly
in plain C. The memcpy() function shrinks by 10 bytes, from:

00e778d0 <memcpy>:
  e778d0:	55                   	push   %ebp
  e778d1:	89 e5                	mov    %esp,%ebp
  e778d3:	83 ec 0c             	sub    $0xc,%esp
  e778d6:	89 5d f4             	mov    %ebx,-0xc(%ebp)
  e778d9:	89 c3                	mov    %eax,%ebx
  e778db:	89 c8                	mov    %ecx,%eax
  e778dd:	89 75 f8             	mov    %esi,-0x8(%ebp)
  e778e0:	c1 e9 02             	shr    $0x2,%ecx
  e778e3:	89 d6                	mov    %edx,%esi
  e778e5:	89 7d fc             	mov    %edi,-0x4(%ebp)
  e778e8:	89 df                	mov    %ebx,%edi
  e778ea:	f3 a5                	rep movsl %ds:(%esi),%es:(%edi)
  e778ec:	89 c1                	mov    %eax,%ecx
  e778ee:	83 e1 03             	and    $0x3,%ecx
  e778f1:	74 02                	je     e778f5 <memcpy+0x25>
  e778f3:	f3 a4                	rep movsb %ds:(%esi),%es:(%edi)
  e778f5:	8b 75 f8             	mov    -0x8(%ebp),%esi
  e778f8:	89 d8                	mov    %ebx,%eax
  e778fa:	8b 5d f4             	mov    -0xc(%ebp),%ebx
  e778fd:	8b 7d fc             	mov    -0x4(%ebp),%edi
  e77900:	89 ec                	mov    %ebp,%esp
  e77902:	5d                   	pop    %ebp
  e77903:	c3                   	ret

to:

00e778b0 <memcpy>:
  e778b0:	55                   	push   %ebp
  e778b1:	89 e5                	mov    %esp,%ebp
  e778b3:	83 ec 08             	sub    $0x8,%esp
  e778b6:	89 75 f8             	mov    %esi,-0x8(%ebp)
  e778b9:	89 d6                	mov    %edx,%esi
  e778bb:	89 ca                	mov    %ecx,%edx
  e778bd:	89 7d fc             	mov    %edi,-0x4(%ebp)
  e778c0:	c1 e9 02             	shr    $0x2,%ecx
  e778c3:	89 c7                	mov    %eax,%edi
  e778c5:	f3 a5                	rep movsl %ds:(%esi),%es:(%edi)
  e778c7:	83 e2 03             	and    $0x3,%edx
  e778ca:	74 04                	je     e778d0 <memcpy+0x20>
  e778cc:	89 d1                	mov    %edx,%ecx
  e778ce:	f3 a4                	rep movsb %ds:(%esi),%es:(%edi)
  e778d0:	8b 75 f8             	mov    -0x8(%ebp),%esi
  e778d3:	8b 7d fc             	mov    -0x4(%ebp),%edi
  e778d6:	89 ec                	mov    %ebp,%esp
  e778d8:	5d                   	pop    %ebp
  e778d9:	c3                   	ret

due to a better register allocation, avoiding the call-saved
%ebx register.

No functional changes intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
---
 arch/x86/include/asm/string_32.h | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/string_32.h b/arch/x86/include/asm/string_32.h
index e9cce169bb4c..16cdda93e437 100644
--- a/arch/x86/include/asm/string_32.h
+++ b/arch/x86/include/asm/string_32.h
@@ -32,16 +32,18 @@ extern size_t strlen(const char *s);
 
 static __always_inline void *__memcpy(void *to, const void *from, size_t n)
 {
-	int d0, d1, d2;
-	asm volatile("rep movsl\n\t"
-		     "movl %4,%%ecx\n\t"
-		     "andl $3,%%ecx\n\t"
-		     "jz 1f\n\t"
-		     "rep movsb\n\t"
-		     "1:"
-		     : "=&c" (d0), "=&D" (d1), "=&S" (d2)
-		     : "0" (n / 4), "g" (n), "1" ((long)to), "2" ((long)from)
-		     : "memory");
+	unsigned long esi = (unsigned long)from;
+	unsigned long edi = (unsigned long)to;
+	unsigned long ecx = n >> 2;
+
+	asm volatile("rep movsl"
+		     : "+D" (edi), "+S" (esi), "+c" (ecx)
+		     : : "memory");
+	ecx = n & 3;
+	if (ecx)
+		asm volatile("rep movsb"
+			     : "+D" (edi), "+S" (esi), "+c" (ecx)
+			     : : "memory");
 	return to;
 }
 
-- 
2.52.0