https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101641
--- Comment #5 from Martin Uecker <muecker at gwdg dot de> ---
(In reply to Richard Biener from comment #3)
>
> What we know from the union read is that the dynamic type is either the
> union type (so the read can pun) or the dynamic type is the union member
> type (then the read cannot pun). 6.5/7 allows accesses using
> "an aggregate or union type that includes [a type compatible with the
> effective
> type of the object]". Though the 'aggregate' case appears quite odd to me,
> does it really allow 'int i; struct { float f; int i; } *p = &i; float x =
> p->f;'?
I do not think this is meant to work as the
read is using an lvalue of type float and
that is not covered by the rules.
I believe that the aggregate case is meant for
the case where sub objects are modified as part of
struct/union assignment (i.e. when the lvalue used
for the access is of struct/union type).
But the rules could be interpreted to allow:
int i; struct { float f; int i; } *p = &i;
int j = p->i;
which I think should not be allowed.
