[Bug tree-optimization/71408] wrong code at -Os and above on x86_64-linux-gnu

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71408

--- Comment #1 from Marc Glisse <glisse at gcc dot gnu.org> ---
(Separately from the wrong code) some of the reads of c.f1 are represented as
BIT_FIELD_REF <c, 32, 0> & 262143, which prevents us from optimizing it to a
constant (others that are represented as c.f1 work just fine) :-(

  c.f1 = 7;
  c.f3 = 0;
  _1 = BIT_FIELD_REF <c, 32, 0>;
  _2 = _1 & 262143;
  if (_2 != 0)