https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107411
--- Comment #6 from qinzhao at gcc dot gnu.org ---
(In reply to Richard Biener from comment #2)
>
> The gimplifier instead of
>
> _1 = t ();
> D.2389 = _1;
> e = &D.2389;
> _2 = *e;
> f (_2);
>
> produces
>
> _1 = .DEFERRED_INIT (4, 2, &"D.2389"[0]);
> D.2389 = _1;
> e = .DEFERRED_INIT (8, 2, &"e"[0]);
> _2 = t ();
> D.2389 = _2;
> e = &D.2389;
> _3 = *e;
> f (_3);
>
> which is odd and sub-optimal at least. Doing such things makes us rely
> on DSE to elide the uninit "inits".
actually, this is because, The simplifier sees the following IR from FE
(.original)
const int D.2768;
const int & e;
<<cleanup_point <<< Unknown tree: expr_stmt
(void) (e = D.2768 = t ();, (const int &) &D.2768;) >>>>>;
<<cleanup_point <<< Unknown tree: expr_stmt
f ((int) *e) >>>>>;
}
i.e, it sees two DECL_EXPR "D.2768" and "e" without any initialization first,
and then see the "CLEANUP_POINT_EXPR" which include the initializations to "e"
and "D.2768". since it doesn't see any connections between these two DECL_EXPRs
and the initializations inside "CLEANUP_POINT_EXPR", it just treats the two
DECL_EXPRs as not initialized, therefore add the .DEFERED_INIT to them.
the best approach to resolve this issue is:
if there is any connection between DECL_EXPR "D.2768","e" and their
initializations inside "CLEANUP_POINT_EXPR" that can be checked from IR, then
during "gimplify_decl_expr", we can avoid generating .DEFERRED_INIT to them;
my question is: in the current IR from C++ FE, is there any bit I can check to
make sure that the DECL_EXPR "D.2768" and "e" already have initialization
inside "CLEANUP_POINT_EXPR"?
