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From: "msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/90404] No warning on attempts to modify a const object
Date: Mon, 16 Mar 2020 16:54:34 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D90404

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=3D/dev/stdout x.C
const char a[] =3D "012.45";

int f (void)
{
  char *p =3D __builtin_strchr (a, '.');
  *p =3D 0;

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

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

;; Function f (_Z1fv, funcdef_no=3D0, decl_uid=3D2328, cgraph_uid=3D1,
symbol_order=3D1)

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

}=