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)

diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc
index 426b373689e4152256b655d17c7a0e4181cabc8b..c0a79e20749b3e2009ce904e840d179b9adf0bac 100644 (file)
--- a/gcc/cp/cp-gimplify.cc
+++ b/gcc/cp/cp-gimplify.cc
@@ -1006,8 +1006,12 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_)
 
     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;

diff --git a/gcc/testsuite/g++.dg/cpp1z/decomp57.C b/gcc/testsuite/g++.dg/cpp1z/decomp57.C
new file mode 100644 (file)
index 0000000..923862e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/decomp57.C
@@ -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 ()
+{
+}

diff --git a/gcc/testsuite/g++.dg/cpp1z/decomp58.C b/gcc/testsuite/g++.dg/cpp1z/decomp58.C
new file mode 100644 (file)
index 0000000..b260437
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/decomp58.C
@@ -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 ()
+{
+}