[gcc/devel/omp/gcc-10] c++: operator<=> and -Wzero-as-null-pointer-constant [PR95242]

[Tobias Burnus]

https://gcc.gnu.org/g:fac77bd88dc450f6bcc8f5945186990c094b5cfc

commit fac77bd88dc450f6bcc8f5945186990c094b5cfc
Author: Jason Merrill <jason@redhat.com>
Date:   Tue May 26 17:27:55 2020 -0400

    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.
    
    (cherry picked from commit 6c66c692043d680a5efcd9616b94f9629c417038)

Diff:
---
 gcc/cp/call.c                                 | 1 +
 gcc/testsuite/g++.dg/cpp2a/spaceship-synth2.C | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index 8345997ccf9..4a2754bcd1f 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -6391,6 +6391,7 @@ 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 cf23c9771e0..a064df72a49 100644
--- 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++2a } }
 
+// Add this warning to test PR c++/95242
+// { dg-additional-options -Wzero-as-null-pointer-constant }
+
 #include <compare>
 
 struct D