[gcc r13-4397] c++: ICE with <=> of incompatible pointers [PR107542]

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

https://gcc.gnu.org/g:000e9863120cbc75a0f8d497264519974c97669f

commit r13-4397-g000e9863120cbc75a0f8d497264519974c97669f
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Nov 29 19:25:37 2022 -0500

    c++: ICE with <=> of incompatible pointers [PR107542]
    
    In a SFINAE context composite_pointer_type returns error_mark_node if
    the given pointer types are incompatible.  But the SPACESHIP_EXPR case
    of cp_build_binary_op wasn't prepared for this error_mark_node result,
    which led to an ICE (from spaceship_comp_cat) for the below testcase.
    (In a non-SFINAE context composite_pointer_type issues a permerror and
    returns cv void* in this case, so this ICE seems specific to SFINAE.)
    
            PR c++/107542
    
    gcc/cp/ChangeLog:
    
            * typeck.cc (cp_build_binary_op): In the SPACESHIP_EXPR case,
            handle an error_mark_node result type.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp2a/spaceship-sfinae2.C: New test.

Diff:
---
 gcc/cp/typeck.cc                               |  5 +++--
 gcc/testsuite/g++.dg/cpp2a/spaceship-sfinae2.C | 29 ++++++++++++++++++++++++++
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index d5757b27f49..7dfe5acc67e 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -6215,8 +6215,9 @@ cp_build_binary_op (const op_location_t &location,
       tree_code orig_code0 = TREE_CODE (orig_type0);
       tree orig_type1 = TREE_TYPE (orig_op1);
       tree_code orig_code1 = TREE_CODE (orig_type1);
-      if (!result_type)
-	/* Nope.  */;
+      if (!result_type || result_type == error_mark_node)
+	/* Nope.  */
+	result_type = NULL_TREE;
       else if ((orig_code0 == BOOLEAN_TYPE) != (orig_code1 == BOOLEAN_TYPE))
 	/* "If one of the operands is of type bool and the other is not, the
 	   program is ill-formed."  */
diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-sfinae2.C b/gcc/testsuite/g++.dg/cpp2a/spaceship-sfinae2.C
new file mode 100644
index 00000000000..7105a2c7f2a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-sfinae2.C
@@ -0,0 +1,29 @@
+// PR c++/107542
+// { dg-do compile { target c++20 } }
+
+#include <compare>
+
+template<class T, class U>
+concept same_as = __is_same(T, U);
+
+template<class Lhs, class Rhs>
+concept Ord = requires(Lhs lhs, Rhs rhs) {
+  { lhs <=> rhs } -> same_as<std::strong_ordering>;
+};
+
+static_assert(Ord<int*, int*>);   // Works.
+static_assert(!Ord<int*, char*>); // ICE.
+
+template<class T>
+struct S {
+  T* p;
+};
+
+template<class T, class U>
+  requires(Ord<const T*, const U*>)
+constexpr inline auto operator<=>(const S<T>& l, const S<U>& r) noexcept {
+  return l.p <=> r.p;
+}
+
+static_assert(Ord<S<int>, S<int>>);   // Works.
+static_assert(!Ord<S<int>, S<char>>); // ICE.