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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/94130] [8/9/10 Regression] Unintended result
 with optimization option when assigning two structures, memset and 0
Date: Wed, 11 Mar 2020 12:15:32 +0000
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X-Bugzilla-Component: tree-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94130

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Slightly reduced testcase:
struct A { char a[6]; void *b; };
struct B { unsigned int c, d; };

static void __attribute__((noipa))
foo (struct A *x)
{
  struct B *b =3D (struct B *) x->b;
  if (b->c !=3D 1234 || b->d)
    __builtin_abort ();
}

int
main ()
{
  struct A a;
  struct B b;
  __builtin_memset (&a, 0, sizeof (a));
  __builtin_strncpy (a.a, "Hello", sizeof (a.a));
  a.b =3D __builtin_memset (&b, 0, sizeof (b));
  b.c =3D 1234;
  b.d =3D 0;
  foo (&a);
  return 0;
}=