memcpy() optomization issue

[Paul Forgey <paulf at aphrodite dot com>]

I guess this could be considered either a bug or a feature, but the
circumstance surrounding it is curious.

Using gnu-as (binutils 2.9.1) and egcs-2.91.60, there is a very wierd
gotcha with memcpy() optomizations on -O2.

Consider a pointer to structure assigned to a non-aligned memory space. A
memcpy() of 4 bytes will optomize to an assignment (as I would expect; how
is the compiler to know the structure isn't pointing to an aligned
address?).  On Solaris 2.6 and Hpux 10.20, both of which are non-intel
architectures which care about alignment, this causes an obvious problem.

The wierd thing is this doesn't happen if -pipe isn't used as a compiler
option.  That is, -O2 -pipe causes an aligment execption, while -O2
doesn't, however both versions compile to the same assembly output, as far
as I can tell.  This to me is wierd.

This does have an obious workaround; in my case I wrote a copy4()
function which performs the copy without using memcpy().

But given that a programmer will use a memcpy() of 4 bytes explicitly to
NOT cause an alignment exepction, is this really a sensible optomization?