CODEWITHSUNDEEP
fortrangfortran
narsonalin
narsonalin

Reputation: 79

Get rid of "pointer assignment might outlive the pointer target" in Fortran

I have a code similar to this:

module mod
    implicit none
    real, pointer :: p1=>null(), p2=>null()
end module mod

program target_lifetime
    use mod
    implicit none
    real, target  :: t(2)

    p1 => t(1)
    p2 => t(2)

    nullify( p1, p2 )

end program target_lifetime

When I compile this code with gfortran -Wall target_lifetime.f90 I obtain

target_lifetime.f90:14:4:

   14 |     p1 => t(1)
      |    1
Warning: Pointer at (1) in pointer assignment might outlive the pointer target [-Wtarget-lifetime]
target_lifetime.f90:15:4:

   15 |     p2 => t(2)
      |    1
Warning: Pointer at (1) in pointer assignment might outlive the pointer target [-Wtarget-lifetime]

What is the correct way to code this in order to get rid of the warning?

Upvotes: 0

Views: 192

Answers (2)

steve
steve

Reputation: 900

Vladimir is likely correct that this a side-effect of the implicit save of t1 and t2. Fortunately, the warning is generated from only one place within the gfortran source code. This means that you can easily suppress the warnings with this patch.

diff --git a/gcc/fortran/expr.cc b/gcc/fortran/expr.cc
index 290ddf360c8..543d4e24286 100644
--- a/gcc/fortran/expr.cc
+++ b/gcc/fortran/expr.cc
@@ -25,6 +25,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "gfortran.h"
 #include "arith.h"
 #include "match.h"
+#include "parse.h"
 #include "target-memory.h" /* for gfc_convert_boz */
 #include "constructor.h"
 #include "tree.h"
@@ -4523,7 +4524,10 @@ gfc_check_pointer_assign (gfc_expr *lvalue, gfc_expr *rvalue,
        break;
      }
 
-      if (warn)
+      if (warn
+     && (gfc_current_state () != COMP_PROGRAM)
+     && (!(gfc_current_state () == COMP_NONE
+           && !gfc_state_stack->previous)))
    gfc_warning (OPT_Wtarget_lifetime,
             "Pointer at %L in pointer assignment might outlive the "
             "pointer target", &lvalue->where);

Upvotes: 0

Vladimir F Героям слава
Vladimir F Героям слава

Reputation: 60018

The warning here is clearly bogus because of the lifetime of the main program variable is until the end of the program and the t array is implicitly save.

There is not much you can do. You can open a bug with GCC and ask whether it is possible to change the behaviour here.

I can see that it could be triggered by internally implementing the __MAIN (or some other name) procedure as a subroutine (actually a funciton in C or GIMPLE) and then treating the variables as local variables in some checks. But then the standard still says that the variables in the main program are save implicitly.

Upvotes: 2

Related Questions