[Bug libfortran/63689] New: -fcheck=array-temps should warn for temporaries during intrinsic assignment

["bardeau at iram dot fr" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63689

            Bug ID: 63689
           Summary: -fcheck=array-temps should warn for temporaries during
                    intrinsic assignment
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: libfortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bardeau at iram dot fr

Hi!

please consider this code:

program test
  real(kind=4), pointer :: a(:),b(:)
  allocate(a(2),b(2))
  b = a
end program test

In the assignment, because the LHS and RHS are pointers, they may alias
each-other, so the compiler generates a temporary/intermediate array for
evaluating the RHS. Fine.

This use-case is well detected by -Warray-temporaries:

$ gfortran test.f90 -Warray-temporaries -o test
test.f90:4.6:

  b = a
      1
Warning: Creating array temporary at (1)

On the other hand, -fcheck=array-temps gives no message at run-time:
$ gfortran test.f90 -fcheck=array-temps -o test && ./test
$

I know that the documentation for -fcheck=array-temps clearly states that it
warns for temporary arrays passed to a procedure. However, it would be useful
to extend the warnings to temporaries during intrinsic assignment because the
option name is opened to all temporaries, and because -Warray-temporaries warns
in both cases.

I am currently tracking temporaries, but I prefer runtime checks (temporaries
*are* actually created) instead of compilation checks (temporaries *may* be
created, too many false positives in my program).

I was not sure which version (all opened?) and which component could be
affected, I let you correct this. Thanks!