Re: [PATCH] c++: Handle structured bindings like anon unions in initializers [PR108474]

[Jakub Jelinek <jakub@redhat.com>]

On Sun, Jan 22, 2023 at 03:40:26PM -0500, Jason Merrill wrote:
> > 2023-01-21  Jakub Jelinek  <jakub@redhat.com>
> > 
> > 	PR c++/108474
> > 	* cp-gimplify.cc (cp_fold_r): Handle structured bindings
> > 	vars like anon union artificial vars.
> > 
> > 	* g++.dg/cpp1z/decomp57.C: New test.
> > 	* g++.dg/cpp1z/decomp58.C: New test.
> > 
> > --- gcc/cp/cp-gimplify.cc.jj	2023-01-19 23:27:27.998400866 +0100
> > +++ gcc/cp/cp-gimplify.cc	2023-01-20 11:00:06.093446737 +0100
> > @@ -1012,8 +1012,12 @@ cp_fold_r (tree *stmt_p, int *walk_subtr
> >       case VAR_DECL:
> >         /* In initializers replace anon union artificial VAR_DECLs
> > -	 with their DECL_VALUE_EXPRs, as nothing will do it later.  */
> > -      if (DECL_ANON_UNION_VAR_P (stmt) && !data->genericize)
> > +	 with their DECL_VALUE_EXPRs, as nothing will do it later.
> > +	 Ditto for structured bindings.  */
> > +      if (!data->genericize
> > +	  && DECL_HAS_VALUE_EXPR_P (stmt)
> > +	  && (DECL_ANON_UNION_VAR_P (stmt)
> > +	      || (DECL_DECOMPOSITION_P (stmt) && DECL_DECOMP_BASE (stmt))))
> 
> Is there a reason not to do this for all cases of DECL_HAS_VALUE_EXPR_P,
> without the extra checks?

I was just trying to be careful, because unfortunately this spot
doesn't mean it really is only expanded in static var DECL_INITIAL,
it can make it into dynamic initializers, and most of DECL_VALUE_EXPRs
appear only in runtime code, otherwise we'd have much more of these issues.

But if you think it is ok, I'll test tonight a version just with
if (!data->genericize && DECL_HAS_VALUE_EXPR_P (stmt)

	Jakub