c++: Fix [[no_unique_address]] and default mem-init [PR90432]

output_constructor doesn't like two consecutive entries with fields at the
same position; let's avoid adding the one for the empty field.

gcc/cp/ChangeLog
2020-03-04  Jason Merrill  <jason@redhat.com>

	PR c++/90432
	* init.c (perform_member_init): Don't do aggregate initialization of
	empty field.
	* constexpr.c (cx_check_missing_mem_inits): Don't enforce
	initialization of empty field.

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 34ff88e..254e5a3 100644 (file)
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,11 @@
+2020-03-04  Jason Merrill  <jason@redhat.com>
+
+       PR c++/90432
+       * init.c (perform_member_init): Don't do aggregate initialization of
+       empty field.
+       * constexpr.c (cx_check_missing_mem_inits): Don't enforce
+       initialization of empty field.
+
 2020-03-04  Martin Liska  <mliska@suse.cz>
 
        * method.c: Wrap array in ctor with braces in order

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index c2d4460..521c87f 100644 (file)
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -831,6 +831,9 @@ cx_check_missing_mem_inits (tree ctype, tree body, bool complain)
            /* A flexible array can't be intialized here, so don't complain
               that it isn't.  */
            continue;
+         if (DECL_SIZE (field) && integer_zerop (DECL_SIZE (field)))
+           /* An empty field doesn't need an initializer.  */
+           continue;
          ftype = strip_array_types (ftype);
          if (type_has_constexpr_default_constructor (ftype))
            {

diff --git a/gcc/cp/init.c b/gcc/cp/init.c
index 61ed3aa..27623cf 100644 (file)
--- a/gcc/cp/init.c
+++ b/gcc/cp/init.c
@@ -865,6 +865,11 @@ perform_member_init (tree member, tree init)
        }
       if (init == error_mark_node)
        return;
+      if (DECL_SIZE (member) && integer_zerop (DECL_SIZE (member))
+         && !TREE_SIDE_EFFECTS (init))
+       /* Don't add trivial initialization of an empty base/field, as they
+          might not be ordered the way the back-end expects.  */
+       return;
       /* A FIELD_DECL doesn't really have a suitable lifetime, but
         make_temporary_var_for_ref_to_temp will treat it as automatic and
         set_up_extended_ref_temp wants to use the decl in a warning.  */

diff --git a/gcc/testsuite/g++.dg/cpp2a/no_unique_address3.C b/gcc/testsuite/g++.dg/cpp2a/no_unique_address3.C
new file mode 100644 (file)
index 0000000..07108b8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/no_unique_address3.C
@@ -0,0 +1,16 @@
+// PR c++/90432
+// { dg-do compile { target c++11 } }
+
+struct empty {};
+
+struct has_empty {
+  [[no_unique_address]] empty brace_or_equal_initialized{};
+};
+
+struct has_value {
+  int non_zero = 1;
+};
+
+struct pair : has_empty, has_value {};
+
+pair a;