[Bug fortran/57360] Implement a warning for implied save

[w6ws at earthlink dot net via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57360

--- Comment #8 from Walter Spector <w6ws at earthlink dot net> ---
Hi,

It is a good point.  The message is helpful when issued within a procedure.

At module scope, it doesn't mean much since everything at that level is SAVE
anyway.  This is similar to what happens in C:

int x = 3;  // statically allocated
void fn () {
  int i=3;  // stack allocated
}

Walter

-----Original Message-----
From: kargl at gcc dot gnu.org <gcc-bugzi...@gcc.gnu.org>
Sent: Jan 21, 2024 9:43 AM
To: <w...@earthlink.net>
Subject: [Bug fortran/57360] Implement a warning for implied save

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57360

--- Comment #7 from kargl at gcc dot gnu.org ---
Upon some additional thinking, I wonder how useful this will be compared
to the possible volume of warning messages from modern Fortran. Consider
this code:

module foo
integer :: j = 2
type a
integer :: k = 3
end type
type(a) :: b = a(4)
integer, target :: n
integer, pointer :: m => n
end module foo

subroutine t()
integer :: i=1
write(6,*) i
i=i+1
end subroutine t

call t()
call t()
end

with the patch at the end of this email, I see

% gfcx -c -Wsurprising -Wall a.f90
a.f90:2:14:

2 | integer :: j = 2
| 1
Warning: Entity at (1) has an implicit SAVE attribute [-Wsurprising]
a.f90:6:14:

6 | type(a) :: b = a(4)
| 1
Warning: Entity at (1) has an implicit SAVE attribute [-Wsurprising]
a.f90:7:22:

7 | integer, target :: n
| 1
Warning: Entity at (1) has an implicit SAVE attribute [-Wsurprising]
a.f90:8:23:

8 | integer, pointer :: m => n
| 1
Warning: Entity at (1) has an implicit SAVE attribute [-Wsurprising]
a.f90:12:13:

12 | integer :: i=1
| 1
Warning: &lsquo;i&rsquo; at (1) has an implicit SAVE attribute [-Wsurprising]


diff --git a/gcc/fortran/decl.cc b/gcc/fortran/decl.cc
index 503ecb8d9b5..d6ef37e51f2 100644
--- a/gcc/fortran/decl.cc
+++ b/gcc/fortran/decl.cc
@@ -2278,7 +2278,12 @@ add_init_expr_to_sym (const char *name, gfc_expr
**initp, locus *var_locus)

sym->value = init;
if (sym->attr.save == SAVE_NONE)
- sym->attr.save = SAVE_IMPLICIT;
+ {
+ sym->attr.save = SAVE_IMPLICIT;
+ if (warn_surprising)
+ gfc_warning (OPT_Wsurprising, "%qs at %L has an implicit SAVE "
+ "attribute", sym->name, &amp;sym->declared_at);
+ }
*initp = NULL;
}

@@ -5868,7 +5873,12 @@ match_attr_spec (void)
|| gfc_current_state () == COMP_SUBMODULE)
&amp;&amp; !current_attr.save
&amp;&amp; (gfc_option.allow_std &amp; GFC_STD_F2008) != 0)
- current_attr.save = SAVE_IMPLICIT;
+ {
+ current_attr.save = SAVE_IMPLICIT;
+ if (warn_surprising)
+ gfc_warning (OPT_Wsurprising, "Entity at %C has an implicit SAVE "
+ "attribute");
+ }

colon_seen = 1;
return MATCH_YES;

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