Re: C++ PATCH for c++/87372, __func__ constexpr evaluation

[Marek Polacek <polacek at redhat dot com>]

On Fri, Sep 21, 2018 at 09:37:53AM +0200, Jakub Jelinek wrote:
> On Thu, Sep 20, 2018 at 11:56:37PM -0400, Marek Polacek wrote:
> > The patch for P0595R1 - is_constant_evaluated had this hunk:
> > 
> > @@ -5279,7 +5315,9 @@ maybe_constant_init_1 (tree t, tree decl, bool allow_non_constant)
> >    else if (CONSTANT_CLASS_P (t) && allow_non_constant)
> >      /* No evaluation needed.  */;
> >    else
> > -    t = cxx_eval_outermost_constant_expr (t, allow_non_constant, false, decl);
> > +    t = cxx_eval_outermost_constant_expr (t, allow_non_constant,
> > +                     !allow_non_constant,
> > +                     pretend_const_required, decl);
> >    if (TREE_CODE (t) == TARGET_EXPR)
> >      {
> >        tree init = TARGET_EXPR_INITIAL (t);
> > 
> > the false -> !allow_non_constant change means that when calling
> > cxx_constant_init strict will be true because cxx_constant_init does not allow
> > non constants.  That means that for VAR_DECLs such as __func__ we'll call
> > decl_really_constant_value instead of decl_constant_value.  But only the latter
> > can evaluate __func__ to "foo()".
> > 
> > Jakub, was there a specific reason for this change?  Changing it back still
> > regtests cleanly and the attached test compiles again.
> 
> It just didn't feel right that cxx_constant_init which looks like a function
> that requires strict conformance still passes false as strict.
> If there is a reason to pass false, I think we need a comment that explains
> it.

I think we use strict = true for *_constant_value, but *_constant_init should
get strict = false.

Marek