[gcc r12-6800] c++: [[no_unique_address]] and virtual base [PR104139]

[Jason Merrill <jason@gcc.gnu.org>]

https://gcc.gnu.org/g:23be9f83bbd2c6f03580757adbfe599de6bf702b

commit r12-6800-g23be9f83bbd2c6f03580757adbfe599de6bf702b
Author: Jason Merrill <jason@redhat.com>
Date:   Fri Jan 21 11:16:49 2022 -0500

    c++: [[no_unique_address]] and virtual base [PR104139]
    
    Fixing a thinko in my patch for 103681: when computing the size of a virtual
    base, it would help to use its binfo instead of the one for the derived
    class.
    
            PR c++/104139
            PR c++/103681
    
    gcc/cp/ChangeLog:
    
            * class.cc (end_of_class): Use base_binfo.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/abi/no_unique_address2.C: Adjust to detect this on x86-64.

Diff:
---
 gcc/cp/class.cc                               |  4 ++--
 gcc/testsuite/g++.dg/abi/no_unique_address2.C | 27 +++++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/class.cc b/gcc/cp/class.cc
index e5cc6f10e3b..5db3722ae46 100644
--- a/gcc/cp/class.cc
+++ b/gcc/cp/class.cc
@@ -6414,8 +6414,8 @@ end_of_class (tree t, eoc_mode mode)
       {
 	if (mode == eoc_nv_or_dsize)
 	  /* For dsize, don't count trailing empty bases.  */
-	  offset = size_binop (PLUS_EXPR, BINFO_OFFSET (binfo),
-			       CLASSTYPE_SIZE_UNIT (BINFO_TYPE (binfo)));
+	  offset = size_binop (PLUS_EXPR, BINFO_OFFSET (base_binfo),
+			       CLASSTYPE_SIZE_UNIT (BINFO_TYPE (base_binfo)));
 	else
 	  offset = end_of_base (base_binfo);
 	if (tree_int_cst_lt (result, offset))
diff --git a/gcc/testsuite/g++.dg/abi/no_unique_address2.C b/gcc/testsuite/g++.dg/abi/no_unique_address2.C
index bef6d5b43be..3bb3f76ac92 100644
--- a/gcc/testsuite/g++.dg/abi/no_unique_address2.C
+++ b/gcc/testsuite/g++.dg/abi/no_unique_address2.C
@@ -41,3 +41,30 @@ struct B4
 #define SA(X) static_assert ((X), #X)
 SA (sizeof (B2) == sizeof (B1));
 SA (sizeof (B3) == sizeof (B4));
+
+namespace N2
+{
+  // C as big as _vptr to test PR c++/104139
+  struct C
+  {
+    long c;
+  };
+
+  struct D: virtual C
+  {
+    virtual void f();
+  };
+
+  struct B3: D
+  {
+    char c2;
+  };
+
+  struct B4
+  {
+    D d [[no_unique_address]];
+    char c2;
+  };
+
+  SA (sizeof (B3) == sizeof (B4));
+}