------- Comment #22 from fpbeekhof at gmail dot com 2009-03-18 09:56 -------
Subject: Re: generated memcpy causes trouble in assignment
jakub at gcc dot gnu dot org wrote:
> ------- Comment #20 from jakub at gcc dot gnu dot org 2009-03-18 09:10
> -------
> So let's use memmove on alpha and let targets with sane memcpy not suffer just
> because of one dead architecture.
1) sane memcpy, by the standard, is unsafe.
2) alpha was just an example, I vaguely remember that similar problems
were found on x86 with certain mmx instructions, but don't remember the
details.
A better approach is to use memmove by default, and memcpy when you can
prove that it's safe; rather than assuming that a "non-dead"
architecture extends the standard.
Alternatively, the following should be safe too, in accordance with
comment #21:
Foo &operator=(const Foo &rhs)
{
if (this != &rhs)
memcpy(this, &rhs, sizeof(Foo));
}
But that introduces a branch instruction.
Another safe alternative is to do what is described in comment #12.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39480
