[gcc r16-6938] c++: non-dep reversed <=> returning int [PR123601]

[Patrick Palka]

https://gcc.gnu.org/g:9fdccdaa54a176fc710972fa65caadee57b5f9c3

commit r16-6938-g9fdccdaa54a176fc710972fa65caadee57b5f9c3
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Jan 20 15:25:07 2026 -0500

    c++: non-dep reversed <=> returning int [PR123601]
    
    The code path for non-dependent operator expressions rewritten from a
    <=> returning a non-class type (added in r16-3727-gf2fddc4b84a843) is
    also reached for a reversed such <=> expression with the form
    0 @ (y <=> x) where the @ is <=>, so we need to relax the relevant
    assert accordingly.
    
            PR c++/123601
    
    gcc/cp/ChangeLog:
    
            * tree.cc (build_min_non_dep_op_overload): Relax
            COMPARISON_CLASS_P assert to accept SPACESHIP_EXPR too.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/lookup/operator-9.C: New test.

Diff:
---
 gcc/cp/tree.cc                           |  3 ++-
 gcc/testsuite/g++.dg/lookup/operator-9.C | 17 +++++++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index 030af4d219d1..ab9d0d532f54 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -3849,7 +3849,8 @@ build_min_non_dep_op_overload (enum tree_code op,
 
 	  if (TREE_CODE (non_dep) != CALL_EXPR)
 	    {
-	      gcc_checking_assert (COMPARISON_CLASS_P (non_dep));
+	      gcc_checking_assert (COMPARISON_CLASS_P (non_dep)
+				   || TREE_CODE (non_dep) == SPACESHIP_EXPR);
 	      if (reversed)
 		std::swap (op0, op1);
 	      return build_min_non_dep (TREE_CODE (non_dep), non_dep, op0, op1);
diff --git a/gcc/testsuite/g++.dg/lookup/operator-9.C b/gcc/testsuite/g++.dg/lookup/operator-9.C
new file mode 100644
index 000000000000..6c9326ec0503
--- /dev/null
+++ b/gcc/testsuite/g++.dg/lookup/operator-9.C
@@ -0,0 +1,17 @@
+// PR c++/123601
+// { dg-do compile { target c++20 } }
+
+#include <compare>
+
+struct A {
+  bool operator==(int);
+  int operator<=>(int);
+};
+
+template<class T>
+void f() {
+  A a;
+  (void)(0 <=> a);
+}
+
+template void f<int>();