Re: [C/C++ PATCH] PR c++/66572. Fix Wlogical-op false positive

[Marek Polacek <polacek at redhat dot com>]

On Sat, Jun 20, 2015 at 03:02:06AM +0300, Mikhail Maltsev wrote:
> -  /* We do not warn for constants because they are typical of macro
> -     expansions that test for features.  */
> -  if (CONSTANT_CLASS_P (op_left) || CONSTANT_CLASS_P (op_right))
> +  /* We do not warn for literal constants because they are typical of macro
> +     expansions that test for features.  Likewise, we do not warn for
> +     const-qualified and constexpr variables which are initialized by constant
> +     expressions, because they can come from e.g. <type_traits> or similar user
> +     code.  */
> +  if (TREE_CONSTANT (op_left) || TREE_CONSTANT (op_right))
>      return;

That looks wrong, because with TREE_CONSTANT we'd warn in C but not in C++
for the following:

const int a = 4;
void
f (void)
{
  const int b = 4;
  static const int c = 5;
  if (a && a) {}
  if (b && b) {}
  if (c && c) {}
}

Note that const-qualified types are checked using TYPE_READONLY.

But I'm not even sure that the warning in the original testcase in the PR
is bogus; you won't get any warning when using e.g.
  foo<unsigned, signed>();
in main().

	Marek