K 10
svn:author
V 3
mjg
K 8
svn:date
V 27
2018-09-16T19:28:27.096635Z
K 7
svn:log
V 265
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)

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