c++: ICE with nested anonymous union [PR117153]

In a template, for

  union {
    union {
      T d;
    };
  };

build_anon_union_vars crates a malformed COMPONENT_REF: we have no
DECL_NAME for the nested anon union so we create something like "object.".
Most of the front end doesn't seem to care, but if such a tree gets to
potential_constant_expression, it can cause a crash.

We can use FIELD directly for the COMPONENT_REF's member.  tsubst_stmt
should build up a proper one in:

    if (VAR_P (decl) && !DECL_NAME (decl)
	&& ANON_AGGR_TYPE_P (TREE_TYPE (decl)))
      /* Anonymous aggregates are a special case.  */
      finish_anon_union (decl);

	PR c++/117153

gcc/cp/ChangeLog:

	* decl2.cc (build_anon_union_vars): Use FIELD for the second operand
	of a COMPONENT_REF.

gcc/testsuite/ChangeLog:

	* g++.dg/other/anon-union6.C: New test.
	* g++.dg/other/anon-union7.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>

diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
index ffe1aa3a3244449ccefde7a5a00c7d0e92ad1a45..9e61afd359fcfafeec239938a675acdeb32d2a2b 100644 (file)
--- a/gcc/cp/decl2.cc
+++ b/gcc/cp/decl2.cc
@@ -2032,7 +2032,7 @@ build_anon_union_vars (tree type, tree object)
 
       if (processing_template_decl)
        ref = build_min_nt_loc (UNKNOWN_LOCATION, COMPONENT_REF, object,
-                               DECL_NAME (field), NULL_TREE);
+                               field, NULL_TREE);
       else
        ref = build_class_member_access_expr (object, field, NULL_TREE,
                                              false, tf_warning_or_error);

diff --git a/gcc/testsuite/g++.dg/other/anon-union6.C b/gcc/testsuite/g++.dg/other/anon-union6.C
new file mode 100644 (file)
index 0000000..d1cde30
--- /dev/null
+++ b/gcc/testsuite/g++.dg/other/anon-union6.C
@@ -0,0 +1,13 @@
+// PR c++/117153
+// { dg-do compile }
+
+template<typename T>
+void f() {
+  union {
+    union {
+      T d;
+    };
+  };
+  (void) (d + 0);
+}
+template void f<double>();

diff --git a/gcc/testsuite/g++.dg/other/anon-union7.C b/gcc/testsuite/g++.dg/other/anon-union7.C
new file mode 100644 (file)
index 0000000..e89334a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/other/anon-union7.C
@@ -0,0 +1,16 @@
+// PR c++/117153
+// { dg-do compile { target c++11 } }
+
+using U = union { union { int a; }; };
+
+U
+foo ()
+{
+  return {};
+}
+
+void
+g ()
+{
+  [[maybe_unused]] auto u = foo ();
+}