https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93745
--- Comment #11 from Martin Sebor <msebor at gcc dot gnu.org> ---
Regarding the DECL_FIXED_DYNAMIC_TYPE flag: it seems like in C every DECL would
have it set, but in C++ none could (because placement new can change the
dynamic type of decls), and so GCC would not be able to optimize the example in
that language even though there the read via *p means that p cannot alias d.
If what's keeping GCC from optimizing the code is the fact that the middle-end
doesn't distinguish placement new from plain assignment, i.e., that it can't
tell that the original source didn't look like this:
double d;
void f (long *p)
{
long i = *p;
new (&d) double (3);
*p = i;
}
wouldn't the solution be to keep placement new around in some form and teach
the middle-end how to work with it?
