------- Comment #10 from rguenth at gcc dot gnu dot org 2010-05-18 14:58
-------
(In reply to comment #9)
> But the standard says in [basic.types] that "For any trivially copyable type
> T,
> if two pointers to T point to distinct T objects obj1 and obj2, where neither
> obj1 nor obj2 is a base-class subobject, if the underlying bytes (1.7) making
> up obj1 are copied into obj2,40 obj2 shall subsequently hold the same value as
> obj1."
Yep. But an assignment is not a byte-copy and exactly the assignment is
what invokes the undefined behavior (not the subsequent access).
So,
struct X
{
char data[ sizeof( float ) ];
};
int main()
{
X x1;
new( &x1.data ) float( 3.14f );
X x2 = x1;
GCC sees this as reading the float object you made live in x1.data via
an lvalue of type X and thus decides that the float object is unused
and removes it.
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rguenth at gcc dot gnu dot
| |org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44164
