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
	* cgraphbuild.cc: Include gimplify.h.
	(record_reference): Replace VAR_DECLs with DECL_HAS_VALUE_EXPR_P with
	their corresponding DECL_VALUE_EXPR expressions after unsharing.

	* cp-gimplify.cc (cp_fold_r): Revert 2023-01-19 changes.

	* g++.dg/cpp1z/decomp57.C: New test.
	* g++.dg/cpp1z/decomp58.C: New test.

4 files changed, 78 insertions, 10 deletions

diff --git a/gcc/cgraphbuild.cc b/gcc/cgraphbuild.cc
index f13abca..597831e 100644
--- a/gcc/cgraphbuild.cc
+++ b/gcc/cgraphbuild.cc
@@ -31,6 +31,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "gimple-walk.h"
 #include "ipa-utils.h"
 #include "except.h"
+#include "gimplify.h"
 
 /* Context of record_reference.  */
 struct record_reference_ctx
@@ -79,6 +80,17 @@ record_reference (tree *tp, int *walk_subtrees, void *data)
 
       if (VAR_P (decl))
 	{
+	  /* Replace vars with their DECL_VALUE_EXPR if any.
+	     This is normally done during gimplification, but
+	     static var initializers are never gimplified.  */
+	  if (DECL_HAS_VALUE_EXPR_P (decl))
+	    {
+	      tree *p;
+	      for (p = tp; *p != decl; p = &TREE_OPERAND (*p, 0))
+		;
+	      *p = unshare_expr (DECL_VALUE_EXPR (decl));
+	      return record_reference (tp, walk_subtrees, data);
+	    }
 	  varpool_node *vnode = varpool_node::get_create (decl);
 	  ctx->varpool_node->create_reference (vnode, IPA_REF_ADDR);
 	}
diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc
index 92cd309..a35cedd 100644
--- a/gcc/cp/cp-gimplify.cc
+++ b/gcc/cp/cp-gimplify.cc
@@ -1035,16 +1035,6 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_)
 	}
       break;
 
-    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)
-	{
-	  *stmt_p = stmt = unshare_expr (DECL_VALUE_EXPR (stmt));
-	  break;
-	}
-      break;
-
     default:
       break;
     }
diff --git a/gcc/testsuite/g++.dg/cpp1z/decomp57.C b/gcc/testsuite/g++.dg/cpp1z/decomp57.C
new file mode 100644
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
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 ()
+{
+}