https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108889
Paul Thomas <pault at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |pault at gcc dot gnu.org
--- Comment #5 from Paul Thomas <pault at gcc dot gnu.org> ---
(In reply to Tobias Burnus from comment #0)
> The following testcase shows the following -Wall warnings:
>
> Warning: ‘reference.offset’ is used uninitialized [-Wuninitialized]
> Warning: ‘reference.dim[0].lbound’ is used uninitialized [-Wuninitialized]
> Warning: ‘reference.dim[0].ubound’ may be used uninitialized
> [-Wmaybe-uninitialized]
>
> The warning (but not the issue) is new since GCC 12. The dump shows:
>
> D.4310 = reference.offset;
> D.4311 = reference.dim[0].lbound;
> D.4312 = reference.dim[0].ubound;
>
> D.4313 = D.4311 - D.4307; // D.4307 = single.var.dim[0].lbound
>
> But all expressions are actually re-evaluated later:
> D.4317 = (real(kind=4)[0:] * restrict) reference.data == 0B;
> if (D.4317) goto L.4;
> ...
> L.4:;
> ...
> reference.dim[0].lbound = single.var.dim...
> reference.offset = -NON_LVALUE_EXPR <reference.dim[0].lbound>;
> D.4310 = reference.offset;
> D.4313 = reference.dim[0].lbound - D.4307;
> ...
> L.5:; /// If the shape was correct, there is a jump to here / L.5
> while (1)
> {
> if (S.2 > D.4308) goto L.6;
> (*D.4309)[(S.2 + D.4313) + D.4310] = (*D.4305)[S.2 + D.4306];
>
> Thus, D.4313 + D.4310 needs to be evaluated in the no-(re)alloc case and in
> the needs-to-be allocated case.
>
>
> Thus, the produced code is fine at the end – even though there was
> uninitialized memory in between. — But this should be fixed, also to silence
> the warning.
>
> * * *
>
> ! Testcase: Compile with -Wall
>
> program main
> implicit none
>
> type :: struct
> real, allocatable :: var(:)
> end type struct
>
> type(struct) :: single
> real, allocatable :: reference(:)
>
> single%var = [1,2,3,4,5]
> reference = single%var
>
> if (size(reference) /= size(single%var)) stop 1
> if (lbound(reference, 1) /= 1) stop 3
> if (any (reference /= single%var)) stop 3
> end
The offending temporaries are emerging out of the scalarizer, rather than
gfc_alloc_allocatable_for_assignment, and are used for the saved_offset and
deltas. These are set in gfc_alloc_allocatable_for_assignment at lines
11378-11392, which is why the temporaries pop up again.
I'm thinking about it :-)
Cheers
Paul
