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

[Jakub Jelinek <jakub@redhat.com>]

Hi!

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.

Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok
for trunk?

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))))
 	{
 	  *stmt_p = stmt = unshare_expr (DECL_VALUE_EXPR (stmt));
 	  break;
--- gcc/testsuite/g++.dg/cpp1z/decomp57.C.jj	2023-01-20 11:02:08.547656638 +0100
+++ gcc/testsuite/g++.dg/cpp1z/decomp57.C	2023-01-20 10:53:01.781649565 +0100
@@ -0,0 +1,27 @@
+// PR c++/108474
+// { dg-do link { target c++17 } }
+
+struct T { int i, j; };
+T h;
+auto [i, j] = h;
+int &r = i;
+int s = i;
+int *t = &i;
+
+void
+foo (int **p, int *q)
+{
+  static int &u = i;
+  static int v = i;
+  static int *w = &i;
+  int &x = i;
+  int y = i;
+  int *z = &i;
+  *p = &i;
+  *q = i;
+}
+
+int
+main ()
+{
+}
--- gcc/testsuite/g++.dg/cpp1z/decomp58.C.jj	2023-01-20 11:02:12.314601575 +0100
+++ gcc/testsuite/g++.dg/cpp1z/decomp58.C	2023-01-20 10:54:02.117767542 +0100
@@ -0,0 +1,39 @@
+// PR c++/108474
+// { dg-do link { target c++17 } }
+
+namespace std {
+  template <typename T> struct tuple_size;
+  template <int, typename> struct tuple_element;
+}
+
+struct A {
+  int i;
+  template <int I> int& get() { return i; }
+};
+
+template <> struct std::tuple_size <A> { static const int value = 2; };
+template <int I> struct std::tuple_element <I, A> { using type = int; };
+
+struct A a;
+auto [i, j] = a;
+int &r = i;
+int s = i;
+int *t = &i;
+
+void
+foo (int **p, int *q)
+{
+  static int &u = i;
+  static int v = i;
+  static int *w = &i;
+  int &x = i;
+  int y = i;
+  int *z = &i;
+  *p = &i;
+  *q = i;
+}
+
+int
+main ()
+{
+}

	Jakub