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

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

As reported by Andrew Pinski, structured bindings (with the exception
of the ones using std::tuple_{size,element} and get which are really
standalone variables in addition to the binding one) also use
DECL_VALUE_EXPR and needs the same treatment in static initializers.

On Sun, Jan 22, 2023 at 07:19:07PM -0500, Jason Merrill wrote:
> Though, actually, why not instead fix expand_expr_real_1 (and staticp) to
> look through DECL_VALUE_EXPR?

Doing it when emitting the initializers seems to be too late to me,
we in various spots try to put parts of the static var DECL_INITIAL expressions
into the IL, or e.g. for varpool purposes remember which vars are referenced
there.

This patch moves it to record_reference, which is called from varpool_node::analyze
and so about the same time as gimplification of the bodies which also
replaces DECL_VALUE_EXPRs.

2023-01-24  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.

(cherry picked from commit b84e21115700523b4d0ac44275443f7b9c670344)