[PATCH] c++: defaulted comparisons and vptr fields [PR95567]

[Patrick Palka via Gcc-patches]

We need to skip over vptr fields when synthesizing a defaulted
comparison operator.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk/11?

        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.
---
 gcc/cp/method.c                               |  4 ++++
 .../g++.dg/cpp2a/spaceship-virtual1.C         | 20 +++++++++++++++++++
 2 files changed, 24 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/spaceship-virtual1.C

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();
+}
-- 
2.33.0.610.gcefe983a32