[Bug c++/23383] builtin array operator new is not marked with malloc attribute

["xinliangli at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23383

--- Comment #18 from davidxl <xinliangli at gmail dot com> 2012-01-04 17:11:26 UTC ---
(In reply to comment #17)
> On Wed, 4 Jan 2012, xinliangli at gmail dot com wrote:
> 
> > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23383
> > 
> > --- Comment #16 from davidxl <xinliangli at gmail dot com> 2012-01-04 00:28:55 UTC ---
> > A related topic - aliasing property of realloc -- the malloc attribute is not
> > applied in the glibc header and the comment is like
> > 
> > /* __attribute_malloc__ is not used, because if realloc returns
> >    the same pointer that was passed to it, aliasing needs to be allowed
> >    between objects pointed by the old and new pointers.  *
> > 
> > 
> > It is true that the realloc can return an address is physically aliased with
> > the pointer passed to it -- but assuming no-alias by the compiler should cause
> > no harm -- as all code motions/CSEs across the realloc call will not be
> > possible because realloc may modify/use the memory location.
> > 
> > 
> > Any comment on this? 
> 
> The malloc attribute assumes that the contents of the memory pointed
> to by the return value is undefined, so the comment is inaccurate
> but the malloc attribute can indeed be not used.

Which part of the optimizer takes advantage of the 'undefinedness' of returned
memory?


> 
> We can explicitly handle REALLOC in the points-to code to honor the
> fact that it is not (we do not at the moment).

ok.