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)
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