c++: constexpr static data member instantiation [PR94523]

c++: constexpr static data member instantiation [PR94523]

Here due to my recent change to store_init_value we were expanding the
initializer of aw knowing that we were initializing aw.  When
cxx_eval_call_expression finished the constructor, it wanted to look up the
value of aw to set TREE_READONLY on it, but we haven't set DECL_INITIAL yet,
so decl_constant_value tried to instantiate the initializer again.  And
infinite recursion.  Stopped by optimizing the case of asking for the value
of ctx->object, which is ctx->value.  It also would have worked to look in
the values hash table, so let's move that up before decl_constant_value as
well.

gcc/cp/ChangeLog
2020-04-09  Jason Merrill  <jason@redhat.com>

	PR c++/94523
	* constexpr.c (cxx_eval_constant_expression) [VAR_DECL]: Look at
	ctx->object and ctx->global->values first.