https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108906
Bug ID: 108906
Summary: Bogus may be used uninitialized warning
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Keywords: diagnostic
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: burnus at gcc dot gnu.org
Target Milestone: ---
Split-off from on PR fortran/108621
This shows up with code generated by gfortran internally. The warning is bogus
and (rightly!) disappears when compiled with -Og, -Os, -O1 or higher:
Warning: ‘f.dim[idx.1_32].lbound’ may be used uninitialized
[-Wmaybe-uninitialized]
If I now look at the 021t.ssa dump, I see:
f.data = 0B;
...
_1 = f.data;
cfi.0.base_addr = _1;
...
_2 = cfi.0.base_addr;
if (_2 != 0B)
goto <bb 3>; [INV]
else
goto <bb 6>; [INV]
...
<bb 4> :
_3 = f.dim[idx.1_32].lbound;
...
<bb 6> :
fun (&cfi.0);
I get the same result when I use '_2 = f.data' instead, i.e. neither value
propagation works.
The basic block <bb 4> is the only place where idx.1_32 gets used - but as
f.data == NULL, we directly jump to <bb 6>. Seemingly, the range/value
propagation from 'f.data = 0' to '_2 = ' does not work.
* * *
Testcase – compile with "gfortran -Wall"; a variant is 'subroutine'
instead of 'program' but this does not have any effect, either.
program demo
use, intrinsic :: iso_c_binding, only : c_int
implicit none
interface
subroutine fun(f_p) bind(c)
import c_int
integer(c_int), pointer, intent(inout) :: f_p(:)
end subroutine
end interface
integer(c_int), pointer :: f(:)
nullify(f)
call fun(f)
end
