c++: Reject ordered comparison of null pointers [PR99701]

When implementing DR 1512 in r11-467 I neglected to reject ordered
comparison of two null pointers, like nullptr < nullptr.  This patch
fixes that omission.

	DR 1512
	PR c++/99701

gcc/cp/ChangeLog:

	* cp-gimplify.c (cp_fold): Remove {LE,LT,GE,GT_EXPR} from
	a switch.
	* typeck.c (cp_build_binary_op): Reject ordered comparison
	of two null pointers.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/nullptr11.C: Remove invalid tests.
	* g++.dg/cpp0x/nullptr46.C: Add dg-error.
	* g++.dg/cpp2a/spaceship-err7.C: New test.
	* g++.dg/expr/ptr-comp4.C: New test.

libstdc++-v3/ChangeLog:

	* testsuite/20_util/tuple/comparison_operators/overloaded.cc:
	Move a line...
	* testsuite/20_util/tuple/comparison_operators/overloaded2.cc:
	...here.  New test.

6 files changed, 40 insertions, 33 deletions

diff --git a/gcc/cp/cp-gimplify.c b/gcc/cp/cp-gimplify.c
index ff0bff7..0520fa4 100644
--- a/gcc/cp/cp-gimplify.c
+++ b/gcc/cp/cp-gimplify.c
@@ -2433,13 +2433,9 @@ cp_fold (tree x)
 	  switch (code)
 	    {
 	    case EQ_EXPR:
-	    case LE_EXPR:
-	    case GE_EXPR:
 	      x = constant_boolean_node (true, TREE_TYPE (x));
 	      break;
 	    case NE_EXPR:
-	    case LT_EXPR:
-	    case GT_EXPR:
 	      x = constant_boolean_node (false, TREE_TYPE (x));
 	      break;
 	    default:
diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index a483e1f..738e69a 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -5483,7 +5483,9 @@ cp_build_binary_op (const op_location_t &location,
 	result_type = composite_pointer_type (location,
 					      type0, type1, op0, op1,
 					      CPO_COMPARISON, complain);
-      else if (code0 == POINTER_TYPE && null_ptr_cst_p (orig_op1))
+      else if ((code0 == POINTER_TYPE && null_ptr_cst_p (orig_op1))
+	       || (code1 == POINTER_TYPE && null_ptr_cst_p (orig_op0))
+	       || (null_ptr_cst_p (orig_op0) && null_ptr_cst_p (orig_op1)))
 	{
 	  /* Core Issue 1512 made this ill-formed.  */
 	  if (complain & tf_error)
@@ -5491,17 +5493,6 @@ cp_build_binary_op (const op_location_t &location,
 		      "integer zero (%qT and %qT)", type0, type1);
 	  return error_mark_node;
 	}
-      else if (code1 == POINTER_TYPE && null_ptr_cst_p (orig_op0))
-	{
-	  /* Core Issue 1512 made this ill-formed.  */
-	  if (complain & tf_error)
-	    error_at (location, "ordered comparison of pointer with "
-		      "integer zero (%qT and %qT)", type0, type1);
-	  return error_mark_node;
-	}
-      else if (null_ptr_cst_p (orig_op0) && null_ptr_cst_p (orig_op1))
-	/* One of the operands must be of nullptr_t type.  */
-        result_type = TREE_TYPE (nullptr_node);
       else if (code0 == POINTER_TYPE && code1 == INTEGER_TYPE)
 	{
 	  result_type = type0;
diff --git a/gcc/testsuite/g++.dg/cpp0x/nullptr11.C b/gcc/testsuite/g++.dg/cpp0x/nullptr11.C
index f81f0c3..b8bc682 100644
--- a/gcc/testsuite/g++.dg/cpp0x/nullptr11.C
+++ b/gcc/testsuite/g++.dg/cpp0x/nullptr11.C
@@ -9,31 +9,15 @@ void fun()
 {
   assert_true(nullptr == nullptr);
   assert_false(nullptr != nullptr);
-  assert_false(nullptr < nullptr);
-  assert_false(nullptr > nullptr);
-  assert_true(nullptr <= nullptr);
-  assert_true(nullptr >= nullptr);
 
   decltype(nullptr) mynull = 0;
 
   assert_true(mynull == nullptr);
   assert_false(mynull != nullptr);
-  assert_false(mynull < nullptr);
-  assert_false(mynull > nullptr);
-  assert_true(mynull <= nullptr);
-  assert_true(mynull >= nullptr);
 
   assert_true(nullptr == mynull);
   assert_false(nullptr != mynull);
-  assert_false(nullptr < mynull);
-  assert_false(nullptr > mynull);
-  assert_true(nullptr <= mynull);
-  assert_true(nullptr >= mynull);
 
   assert_true(mynull == mynull);
   assert_false(mynull != mynull);
-  assert_false(mynull < mynull);
-  assert_false(mynull > mynull);
-  assert_true(mynull <= mynull);
-  assert_true(mynull >= mynull);
 }
diff --git a/gcc/testsuite/g++.dg/cpp0x/nullptr46.C b/gcc/testsuite/g++.dg/cpp0x/nullptr46.C
index 1514cee..6c08eaa 100644
--- a/gcc/testsuite/g++.dg/cpp0x/nullptr46.C
+++ b/gcc/testsuite/g++.dg/cpp0x/nullptr46.C
@@ -7,5 +7,6 @@ decltype(nullptr) foo ();
 bool
 bar ()
 {
-  return foo () > nullptr || foo () < nullptr;
+  return foo () > nullptr // { dg-error "ordered comparison" }
+    || foo () < nullptr; // { dg-error "ordered comparison" }
 }
diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-err7.C b/gcc/testsuite/g++.dg/cpp2a/spaceship-err7.C
new file mode 100644
index 0000000..bc30923
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-err7.C
@@ -0,0 +1,14 @@
+// PR c++/99701
+// { dg-do compile { target c++20 } }
+
+#include <compare>
+
+decltype(nullptr) foo ();
+
+auto b0 = nullptr <=> nullptr; // { dg-error "ordered comparison" }
+auto b1 = 0 <=> nullptr; // { dg-error "ordered comparison" }
+auto b2 = nullptr <=> 0; // { dg-error "ordered comparison" }
+auto b3 = foo () <=> 0; // { dg-error "ordered comparison" }
+auto b4 = 0 <=> foo (); // { dg-error "ordered comparison" }
+auto b5 = foo () <=> nullptr; // { dg-error "ordered comparison" }
+auto b6 = nullptr <=> foo (); // { dg-error "ordered comparison" }
diff --git a/gcc/testsuite/g++.dg/expr/ptr-comp4.C b/gcc/testsuite/g++.dg/expr/ptr-comp4.C
new file mode 100644
index 0000000..da49518
--- /dev/null
+++ b/gcc/testsuite/g++.dg/expr/ptr-comp4.C
@@ -0,0 +1,21 @@
+// PR c++/99701
+// DR 1512
+// { dg-do compile { target c++11 } }
+
+/* Relational comparisons between null pointer constants and pointers are
+   ill-formed.  */
+
+decltype(nullptr) foo ();
+
+auto lt = nullptr < nullptr; // { dg-error "ordered comparison" }
+auto gt = nullptr > nullptr; // { dg-error "ordered comparison" }
+auto le = nullptr <= nullptr; // { dg-error "ordered comparison" }
+auto ge = nullptr >= nullptr; // { dg-error "ordered comparison" }
+auto eq = nullptr == nullptr;
+auto ne = nullptr != nullptr;
+auto a1 = nullptr > 0; // { dg-error "ordered comparison" }
+auto a2 = 0 < nullptr; // { dg-error "ordered comparison" }
+auto a3 = foo () > 0; // { dg-error "ordered comparison" }
+auto a4 = 0 < foo (); // { dg-error "ordered comparison" }
+auto a5 = 0 <= foo (); // { dg-error "ordered comparison" }
+auto a6 = foo () >= 0; // { dg-error "ordered comparison" }