https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114612
Bug ID: 114612
Summary: Deep copy missing for allocatable derived type
components
Product: gcc
Version: 13.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: vterzi1996 at gmail dot com
Target Milestone: ---
Consider the following minimal example:
```
program prog
type node
integer::val
type(node),allocatable::next
end type
type(node)::a,b
allocate(a%next)
a%val=1
a%next%val=2
print*,a%val,a%next%val
b=a
b%val=3
b%next%val=4
print*,a%val,a%next%val
deallocate(b%next)
print*,a%val,a%next%val
end
```
The output of the code compiled with the GNU (gfortran-13.1.0) compiler is as
follows:
```
1 2
1 4
1 0
```
While the output of the code compiled with the Intel (ifx-2024.1.0) or NAG
(nagfor-7.1) compiler is different:
```
1 2
1 2
1 2
```
It seems like gfortran treats allocatable derived type components somewhat as
pointers: after assignment `b=a`, the memory addresses of `a%next` and `b%next`
are the same, and you can change `a%next%val` by changing `b%next%val`.
However, deallocation of `b%next` will not deallocate `a%next` and will only
change its content.
In contrast to this behavior, the Intel and NAG compilers perform a deep copy
in the assignment `b=a` allocating new memory for elements of b.
The question to this example was asked here:
https://stackoverflow.com/questions/78282004/are-allocatable-derived-type-components-just-pointers-for-gnu-compiler?noredirect=1#comment138008854_78282004
and received an answer that this result is a bug of `gfortran`.
