get_current is __pure__, maybe __const__ even

[Albert Cahalan <albert@users.sf.net>]

Andi Kleen writes:

> Please CSE "current" manually. It generates
> much better code on some architectures
> because the compiler cannot do it for you.

This looks fixable.

At the very least, __attribute__((__pure__))
will apply to your get_current function.

I think __attribute__((__const__)) will too,
even though it's technically against the
documentation. While you do indeed read from
memory, you don't read from memory that could
be seen as changing. Nothing done during the
lifetime of a task will change "current" as
viewed from within that task.