[Bug fortran/120483] [15/16 Regression] character(len=:), allocatable, save variable returns incorrect substring since r15-2131

[tkoenig at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120483

--- Comment #4 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
Looking at

$ cat save.f90 
program memain
  implicit none
  character(len=:), allocatable, save :: s1
  s1 = 'ABC'
  if (s1(3:3) /= 'C') stop 1
end program memain
$ cat nosave.f90 
program memain
  implicit none
  character(len=:), allocatable :: s1
  s1 = 'ABC'
  if (s1(3:3) /= 'C') stop 1
end program memain

the diff of the .original dumps is

--- save.f90.006t.original      2025-05-31 18:03:56.345527407 +0200
+++ nosave.f90.006t.original    2025-05-31 18:04:01.699589312 +0200
@@ -1,9 +1,10 @@
 __attribute__((fn spec (". ")))
 void memain ()
 {
-  static integer(kind=8) _F.s1;
-  static character(kind=1) * s1 = 0B;
+  integer(kind=8) .s1;
+  character(kind=1)[1:.s1] * s1;

+  s1 = 0B;
   {
     integer(kind=8) D.4669;
     void * D.4670;
@@ -11,14 +12,14 @@
     integer(kind=8) D.4672;

     if (s1 != 0B) goto L.1;
-    s1 = (character(kind=1) *) __builtin_malloc (3);
+    s1 = (character(kind=1)[1:.s1] *) __builtin_malloc (3);
     goto L.2;
     L.1:;
-    if (_F.s1 == 3) goto L.2;
-    s1 = (character(kind=1) *) __builtin_realloc ((void *) s1, 3);
+    if (.s1 == 3) goto L.2;
+    s1 = (character(kind=1)[1:.s1] *) __builtin_realloc ((void *) s1, 3);
     L.2:;
-    _F.s1 = 3;
-    D.4669 = _F.s1;
+    .s1 = 3;
+    D.4669 = .s1;
     D.4670 = (void *) s1;
     D.4671 = (void *) &"ABC"[1]{lb: 1 sz: 1};
     D.4672 = NON_LVALUE_EXPR <D.4669> + -3;
@@ -35,7 +36,7 @@
           }
       }
   }
-  if (*s1 != 67)
+  if ((*s1)[3]{lb: 1 sz: 1} != 67)
     {
       _gfortran_stop_numeric (1, 0);
     }

it seems an uninitialized length is still used for the nosave variant
(which also looks suspicious) and the save case lacks the addition of
the offset of the string.