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From: "burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug fortran/98904] valgrind error in gfc_trans_assignment_1 during
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Date: Wed, 03 Feb 2021 14:56:13 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98904

--- Comment #11 from Tobias Burnus <burnus at gcc dot gnu.org> ---
(In reply to David Binderman from comment #10)
> lhs_caf_attr.codimension is uninitialised.

It is clear that lhs_caf_attr is uninitialized
- if and only if flag_coarray !=3D GFC_FCOARRAY_LIB

It might be that some code optimizes converts

  if (flag_coarray =3D=3D GFC_FCOARRAY_LIB && lhs_caf_attr.codimension)

to

  if (flag_coarray =3D=3D GFC_FCOARRAY_LIB & lhs_caf_attr.codimension)

to speed up =E2=80=93 relying that lhs_caf_attr.codimension accesses valid =
memory
(which may be uninitialized). The replacement would work correctly anywhere
where accessing uninitialized memory works. As: if flag_coarray =3D=3D
GFC_FCOARRAY_LIB is 0, the value of lhs_caf_attr.codimension does not matte=
r =E2=80=93
and if it is not 0, lhs_caf_attr.codimension is properly initialized.

It might be that the either the middle end of GCC does this optimization or
that valgrind does this internally.

In any case, the Fortran-compiler part is perfectly valid C/C++.=