[Bug c++/58950] [4.9 Regression] Missing "statement has no effect"

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58950

--- Comment #6 from Marc Glisse <glisse at gcc dot gnu.org> ---
For:

void f(){
  int i = 2;
  (i+i);
}

we always set TREE_NOWARNING in finish_parenthesized_expr. The comment next to
it says this is to avoid warning in c_common_truthvalue_conversion. If that's
the only reason, the hammer seems a bit heavy, in C we only set the bit for
MODIFY_EXPR.