https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86330
Bug ID: 86330
Summary: False positive warnings about uninitialized
offset/lbound/ubound when allocating on assignment
Product: gcc
Version: 8.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: tomastrnka at gmx dot com
Target Milestone: ---
The following testcase generates false positive warnings because "x" is
unallocated before assignment:
program realloc_uninitialized
implicit none
integer, allocatable :: x(:)
! allocate(x(0))
! deallocate(x)
x = foo()
write(*,*) x
contains
function foo() result(a)
integer, allocatable :: a(:)
allocate(a(5))
a = 0
end function
end program
$ gfortran -fdump-tree-original -Wall -O3 -fno-inline -o realloc_uninitialized
realloc_uninitialized.f90
realloc_uninitialized.f90:8:0:
x = foo()
Warning: ‘x.offset’ is used uninitialized in this function [-Wuninitialized]
realloc_uninitialized.f90:8:0: Warning: ‘x.dim[0].lbound’ is used uninitialized
in this function [-Wuninitialized]
realloc_uninitialized.f90:8:0: Warning: ‘x.dim[0].ubound’ is used uninitialized
in this function [-Wuninitialized]
Uncommenting the allocate/deallocate makes the warning go away.
I'm using gcc version 8.1.1 20180502 (Red Hat 8.1.1-1) (GCC) (stock Fedora 28
compiler), but I have also seen this previously on GCC 7. My self-compiled gcc
version 6.4.1 20180314 (GCC) doesn't trigger the warning.
I guess this is because of the following references to "x" at the very start of
"realloc_uninitialized ()" in "realloc_uninitialized.f90.003t.original":
D.3797 = (integer(kind=4)[0:] * restrict) x.data;
D.3798 = x.offset;
D.3799 = x.dim[0].lbound;
D.3800 = x.dim[0].ubound;
None of these D.*s is subsequently used.
