https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106603
Bug ID: 106603
Summary: Problem with character(:), allocatable, intent(out) ::
err for functions which return fixed arrays
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: wogan at uw dot edu
Target Milestone: ---
Consider the following code:
```fortran
program main
use iso_fortran_env, only: dp => real64
implicit none
call test_fun1()
contains
function fun1(a, err) result(b)
real(dp), intent(in) :: a
character(:), allocatable, intent(out) :: err
real(dp) :: b(2)
b = 1
if (a > 2) then
err = "a bigger than 2"
print*,'err in fun1: ',err
return
endif
err = "OK"
end function
subroutine test_fun1()
real(dp) :: a, b(2)
character(:), allocatable :: err
a = 3
b = fun1(a, err)
if (allocated(err)) then
print*,'err is allocated'
print*,'next line tries to print err'
print*,err
endif
end subroutine
end program
```
I compile the code with `gfortran main.f90`, then run with `./a.out`. The
result is
```
(base) nicholas@Nicholass-MacBook-Air test_gfortran_err % ./a.out
err in fun1: a bigger than 2
err is allocated
next line tries to print err
Program received signal SIGSEGV: Segmentation fault - invalid memory reference.
Backtrace for this error:
#0 0x100df21c7
#1 0x100df11a3
#2 0x194092c43
#3 0x100ee865b
zsh: segmentation fault ./a.out
```
When I compile with `-fno-strict-aliasing -fwrapv
-fno-aggressive-loop-optimizations` I get a slightly different result, which is
also not correct:
```
(base) nicholas@Nicholass-MacBook-Air test_gfortran_err % ./a.out
err in fun1: a bigger than 2
err is allocated
next line tries to print err
```
Instead of the results above, the program should print "a bigger than 2". Here
is a relevant form where I discussed the bug with others:
https://fortran-lang.discourse.group/t/what-is-wrong-with-this-code/4151 .
Exact version of GCC:
```
(base) nicholas@Nicholass-MacBook-Air test_gfortran_err % gfortran -v
Using built-in specs.
COLLECT_GCC=gfortran
COLLECT_LTO_WRAPPER=/opt/homebrew/Cellar/gcc/12.1.0/bin/../libexec/gcc/aarch64-apple-darwin20/12/lto-wrapper
Target: aarch64-apple-darwin20
Configured with: ../configure --prefix=/opt/homebrew/opt/gcc
--libdir=/opt/homebrew/opt/gcc/lib/gcc/current --disable-nls
--enable-checking=release --with-gcc-major-version-only
--enable-languages=c,c++,objc,obj-c++,fortran --program-suffix=-12
--with-gmp=/opt/homebrew/opt/gmp --with-mpfr=/opt/homebrew/opt/mpfr
--with-mpc=/opt/homebrew/opt/libmpc --with-isl=/opt/homebrew/opt/isl
--with-zstd=/opt/homebrew/opt/zstd --with-pkgversion='Homebrew GCC 12.1.0'
--with-bugurl=https://github.com/Homebrew/homebrew-core/issues
--with-system-zlib --build=aarch64-apple-darwin20
--with-sysroot=/Library/Developer/CommandLineTools/SDKs/MacOSX11.sdk
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.1.0 (Homebrew GCC 12.1.0)
```
