[Bug fortran/54667] [OOP] gimplification failure with c_f_pointer

[janus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54667

--- Comment #2 from janus at gcc dot gnu.org 2012-09-22 08:53:51 UTC ---
The question is if it is really valid. At first sight both F03 and F08 only
specify that FPTR, i.e. the second argument to C_F_POINTER, shall be a pointer
with INTENT(OUT).

However, there are additional constraints depending on the actual value of
CPTR:

"(1) If the value of CPTR is the C address of an interoperable data
entity, FPTR shall be a data pointer with type and type parame-
ters interoperable with the type of the entity. ..."

"(2) If the value of CPTR is the result of a reference to C LOC with a
noninteroperable argument X, FPTR shall be a nonpolymorphic
scalar pointer with the same type and type parameters as X. ..."


While it would be nontrivial to fully enforce these constraints by a runtime
check, I think they might effectively mean that FPTR must not be polymorphic:
In the second case this constraint is spelled out explicitly, and the first
case demands that FPTR shall be interoperable. But polymorphic objects are by
definition not interoperable.