http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53726
H.J. Lu <hjl.tools at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|WAITING |RESOLVED
Resolution| |WORKSFORME
--- Comment #21 from H.J. Lu <hjl.tools at gmail dot com> 2012-06-21 12:55:33
UTC ---
(In reply to comment #18)
> > string/memory functions in libc can be much faster than the ones generated
> > by GCC unless the size is very small, PR 43052.
>
> Yes. The question is what is "very small" and how can we possibly
> detect "very small". For this testcase we can derive an upper bound
> of the size, which is 8, but the size is not constant. I think unless
> we know we can expand the variable-size memcpy with, say, three
> CPU instructions inline there is no reason to not call memcpy.
It is OK to call memcpy if the size isn't constant.
>
> Which would leave us to inline expanding the case of at most 2 byte
> memcpy. Of course currently there is no way to record an upper
> bound for the size (we do not retain value-range information - but
> we of course should).
It is nice to have. We can open another bug for this.
