[gcc(refs/users/marxin/heads/opt-parse-enum-sanity)] c++: Fix [[no_unique_address]] and default mem-init [PR90432]

[Martin Liska]

https://gcc.gnu.org/g:6876b269bc7fe6465fedfed87c31e6175992129f

commit 6876b269bc7fe6465fedfed87c31e6175992129f
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Mar 4 12:08:42 2020 -0500

    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:
---
 gcc/cp/ChangeLog                                |  8 ++++++++
 gcc/cp/constexpr.c                              |  3 +++
 gcc/cp/init.c                                   |  5 +++++
 gcc/testsuite/g++.dg/cpp2a/no_unique_address3.C | 16 ++++++++++++++++
 4 files changed, 32 insertions(+)

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 34ff88ee033..254e5a31096 100644
--- 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 c2d44605764..521c87f6210 100644
--- 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 61ed3aa7e93..27623cf4db1 100644
--- 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
index 00000000000..07108b8b715
--- /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;