c++: Fix ICE on defaulted spaceship with pointer return type [PR94162]

The spaceship-synth-neg6.C testcase ICEs because we call cat_tag_for
on the explicit return type, but pointer types don't have
TYPE_LINKAGE_IDENTIFIER.  The patch fixes that by checking for
CLASS_TYPE_P only and also adds verification that it is in std
namespace, so we don't return non-cc_last for my_namespace::partial_ordering.

The g++.dg/cpp2a/spaceship-synth11.C testcase is from a PR that has been
fixed with r12-619-gfc178519771db508c03611cff4a1466cf67fce1d (but
not backported to 11).

2021-08-12  Jakub Jelinek  <jakub@redhat.com>

gcc/cp/
	PR c++/94162
	* method.c (cat_tag_for): Return cc_last for !CLASS_TYPE_P
	or for classes not in std namespace.
gcc/testsuite/
	PR c++/99429
	* g++.dg/cpp2a/spaceship-synth11.C: New test.

	PR c++/94162
	* g++.dg/cpp2a/spaceship-synth-neg6.C: New test.

3 files changed, 42 insertions, 0 deletions

diff --git a/gcc/cp/method.c b/gcc/cp/method.c
index f268aab..353046d 100644
--- a/gcc/cp/method.c
+++ b/gcc/cp/method.c
@@ -1029,6 +1029,8 @@ is_cat (tree type, comp_cat_tag tag)
 static comp_cat_tag
 cat_tag_for (tree type)
 {
+  if (!CLASS_TYPE_P (type) || !decl_in_std_namespace_p (TYPE_MAIN_DECL (type)))
+    return cc_last;
   for (int i = 0; i < cc_last; ++i)
     {
       comp_cat_tag tag = (comp_cat_tag)i;
diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-synth-neg6.C b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth-neg6.C
new file mode 100644
index 0000000..d3f95e1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth-neg6.C
@@ -0,0 +1,11 @@
+// PR c++/94162
+// { dg-do compile { target c++20 } }
+
+#include <compare>
+
+struct S {
+  int a;			// { dg-error "three-way comparison of 'S::a' has type 'std::strong_ordering', which does not convert to 'int\\*'" }
+  int *operator<=>(const S&) const = default;
+};
+
+bool b = S{} < S{};		// { dg-error "use of deleted function 'constexpr int\\* S::operator<=>\\\(const S&\\\) const'" }
diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-synth11.C b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth11.C
new file mode 100644
index 0000000..37c8157
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth11.C
@@ -0,0 +1,29 @@
+// PR c++/99429
+// { dg-do compile { target c++20 } }
+
+namespace std {
+struct strong_ordering {
+  int _v;
+  constexpr strong_ordering (int v) :_v(v) {}
+  constexpr operator int (void) const { return _v; }
+  static const strong_ordering less;
+  static const strong_ordering equal;
+  static const strong_ordering greater;
+};
+constexpr strong_ordering strong_ordering::less = -1;
+constexpr strong_ordering strong_ordering::equal = 0;
+constexpr strong_ordering strong_ordering::greater = 1;
+}
+
+template <unsigned long N>
+struct duration {
+  static constexpr const long period = N;
+  constexpr duration (void) = default;
+  constexpr duration (const duration& d) = default;
+  constexpr bool operator== (const duration& d) const = default;
+  constexpr bool operator<=> (const duration& d) const = default;
+  long _d;
+};
+
+using nanoseconds = duration<1>;
+using microseconds = duration<nanoseconds::period * 1000>;