K 10
svn:author
V 3
mjg
K 8
svn:date
V 27
2018-09-27T15:27:53.017682Z
K 7
svn:log
V 388
amd64: mostly depessimize copystr

- remove a forward branch in the common case
- replace xchg + lodsb/stosb loop with simple movs

A simple test on Intel(R) Core(TM) i7-4600U CPU @ 2.10GH copying
/foo/bar/baz in a loop goes from 295715863 ops/s to 465807408.

Further changes are pending.

Reviewed by:	kib
Approved by:	re (gjb)
Differential Revision:	https://reviews.freebsd.org/D17281

END