[gcc r12-3995] c++: defaulted comparisons and vptr fields [PR95567]

[Patrick Palka <ppalka@gcc.gnu.org>]

https://gcc.gnu.org/g:b6bca2e631b54f992c058ca8e445b45e9816690b

commit r12-3995-gb6bca2e631b54f992c058ca8e445b45e9816690b
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Sep 30 17:29:05 2021 -0400

    c++: defaulted comparisons and vptr fields [PR95567]
    
    We need to explicitly skip over vptr fields when synthesizing a
    defaulted comparison operator, because next_initializable_field
    doesn't do so for us.
    
            PR c++/95567
    
    gcc/cp/ChangeLog:
    
            * method.c (build_comparison_op): Skip DECL_VIRTUAL_P fields.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp2a/spaceship-virtual1.C: New test.

Diff:
---
 gcc/cp/method.c                                 |  4 ++++
 gcc/testsuite/g++.dg/cpp2a/spaceship-virtual1.C | 20 ++++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/gcc/cp/method.c b/gcc/cp/method.c
index 32f7186a774..3c3495227ce 100644
--- a/gcc/cp/method.c
+++ b/gcc/cp/method.c
@@ -1426,6 +1426,10 @@ build_comparison_op (tree fndecl, tsubst_flags_t complain)
 	   field;
 	   field = next_initializable_field (DECL_CHAIN (field)))
 	{
+	  if (DECL_VIRTUAL_P (field))
+	    /* Don't compare vptr fields.  */
+	    continue;
+
 	  tree expr_type = TREE_TYPE (field);
 
 	  location_t field_loc = DECL_SOURCE_LOCATION (field);
diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-virtual1.C b/gcc/testsuite/g++.dg/cpp2a/spaceship-virtual1.C
new file mode 100644
index 00000000000..8067d3cd9d1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-virtual1.C
@@ -0,0 +1,20 @@
+// PR c++/95567
+// { dg-do run { target c++20 } }
+
+struct B {
+  B(int i) : i(i) {}
+  virtual ~B() = default;
+
+  bool operator==(B const&) const = default;
+  int i;
+};
+
+struct D : B {
+  D(int i, int j) : B(i), j(j) {}
+  int j;
+};
+
+int main() {
+  if (B(2) != D(2, 3))
+    __builtin_abort();
+}