[Bug middle-end/90404] No warning on attempts to modify a const object

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90404

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |11.0
          Component|c                           |middle-end

--- Comment #4 from Martin Sebor <msebor at gcc dot gnu.org> ---
No progress for GCC 10.  I plan to work on it for GCC 11.

Here's a test case where the fact that the modification is invalid is less
obvious and doesn't trigger a warning.  The dump shows how the code emitted by
GCC makes assumptions that make the undefined behavior manifest without ever
causing the program to crash at runtime.

$ cat x.C && gcc -O2 -S -Wall -Wextra -Wcast-qual -Wpedantic
-fdump-tree-optimized=/dev/stdout x.C
const char a[] = "012.45";

int f (void)
{
  char *p = __builtin_strchr (a, '.');
  *p = 0;

  if (__builtin_strlen (p) != 3)   // folded to false
    __builtin_abort ();

  return a[3] == 0;                // also folded to false
}

;; Function f (_Z1fv, funcdef_no=0, decl_uid=2328, cgraph_uid=1,
symbol_order=1)

f ()
{
  <bb 2> [local count: 1073741824]:
  return 0;

}