svn commit: r338700 - head/sys/amd64/amd64

[Mateusz Guzik]

Author: mjg
Date: Sun Sep 16 19:28:27 2018
New Revision: 338700
URL: https://svnweb.freebsd.org/changeset/base/338700

Log:
  amd64: tidy up kernel memmove
  
  There is no need to use %rax for temporary values and avoiding doing
  so shortens the func.
  Handle the explicit 'check for tail' depessimisization for backwards copying.
  
  This reduces the diff against userspace.
  
  Approved by:	re (kib)

Modified:
  head/sys/amd64/amd64/support.S

Modified: head/sys/amd64/amd64/support.S
==============================================================================
--- head/sys/amd64/amd64/support.S	Sun Sep 16 18:36:42 2018	(r338699)
+++ head/sys/amd64/amd64/support.S	Sun Sep 16 19:28:27 2018	(r338700)
@@ -108,12 +108,12 @@ END(sse2_pagezero)
  */
 ENTRY(memmove_std)
 	PUSH_FRAME_POINTER
-	movq	%rdi,%r9
+	movq	%rdi,%rax
 	movq	%rdx,%rcx
 
-	movq	%rdi,%rax
-	subq	%rsi,%rax
-	cmpq	%rcx,%rax			/* overlapping && src < dst? */
+	movq	%rdi,%r8
+	subq	%rsi,%r8
+	cmpq	%rcx,%r8			/* overlapping && src < dst? */
 	jb	1f
 
 	shrq	$3,%rcx				/* copy by 64-bit words */
@@ -128,7 +128,6 @@ ENTRY(memmove_std)
 2:
 	rep
 	movsb
-	movq	%r9,%rax
 	POP_FRAME_POINTER
 	ret
 
@@ -140,8 +139,10 @@ ENTRY(memmove_std)
 	decq	%rsi
 	andq	$7,%rcx				/* any fractional bytes? */
 	std
+	jne	3f
 	rep
 	movsb
+3:
 	movq	%rdx,%rcx			/* copy remainder by 32-bit words */
 	shrq	$3,%rcx
 	subq	$7,%rsi
@@ -149,24 +150,22 @@ ENTRY(memmove_std)
 	rep
 	movsq
 	cld
-	movq	%r9,%rax
 	POP_FRAME_POINTER
 	ret
 END(memmove_std)
 
 ENTRY(memmove_erms)
 	PUSH_FRAME_POINTER
-	movq	%rdi,%r9
+	movq	%rdi,%rax
 	movq	%rdx,%rcx
 
-	movq	%rdi,%rax
-	subq	%rsi,%rax
-	cmpq	%rcx,%rax			/* overlapping && src < dst? */
+	movq	%rdi,%r8
+	subq	%rsi,%r8
+	cmpq	%rcx,%r8			/* overlapping && src < dst? */
 	jb	1f
 
 	rep
 	movsb
-	movq	%r9,%rax
 	POP_FRAME_POINTER
 	ret
 
@@ -179,7 +178,6 @@ ENTRY(memmove_erms)
 	rep
 	movsb
 	cld
-	movq	%r9,%rax
 	POP_FRAME_POINTER
 	ret
 END(memmove_erms)