c++: operator<=> and -Wzero-as-null-pointer-constant [PR95242]

In C++20, if there is no viable operator< available, lhs < rhs gets
rewritten to (lhs <=> rhs) < 0, where operator< for the comparison
categories is intended to accept literal 0 on the RHS but not other
integers.  We don't want this to produce a warning from
-Wzero-as-null-pointer-constant.

gcc/cp/ChangeLog:

	* call.c (build_new_op_1): Suppress
	warn_zero_as_null_pointer_constant across comparison of <=> result
	to 0.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/spaceship-synth2.C: Add
	-Wzero-as-null-pointer-constant.

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index d858288..a51ebb5 100644 (file)
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -6410,6 +6410,7 @@ build_new_op_1 (const op_location_t &loc, enum tree_code code, int flags,
                    tree rhs = integer_zero_node;
                    if (cand->reversed ())
                      std::swap (lhs, rhs);
+                   warning_sentinel ws (warn_zero_as_null_pointer_constant);
                    result = build_new_op (loc, code,
                                           LOOKUP_NORMAL|LOOKUP_REWRITTEN,
                                           lhs, rhs, NULL_TREE,

diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-synth2.C b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth2.C
index e6401d2..9b6cfa0 100644 (file)
--- a/gcc/testsuite/g++.dg/cpp2a/spaceship-synth2.C
+++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth2.C
@@ -1,6 +1,9 @@
 // Test with only spaceship defaulted.
 // { dg-do run { target c++20 } }
 
+// Add this warning to test PR c++/95242
+// { dg-additional-options -Wzero-as-null-pointer-constant }
+
 #include <compare>
 
 struct D