DR583, DR1512: Implement a rewrite to C++'s 'composite pointer type' rules.

This has two significant effects:

1) Direct relational comparisons between null pointer constants (0 and nullopt)
   and pointers are now ill-formed. This was always the case for C, and it
   appears that C++ only ever permitted by accident. For instance, cases like
     nullptr < &a
   are now rejected.

2) Comparisons and conditional operators between differently-cv-qualified
   pointer types now work, and produce a composite type that both source
   pointer types can convert to (when possible). For instance, comparison
   between 'int **' and 'const int **' is now valid, and uses an intermediate
   type of 'const int *const *'.

Clang previously supported #2 as an extension.

We do not accept the cases in #1 as an extension. I've tested a fair amount of
code to check that this doesn't break it, but if it turns out that someone is
relying on this, we can easily add it back as an extension.

This is a re-commit of r284800.

llvm-svn: 284890

1 files changed, 15 insertions, 17 deletions

diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index 8cc592e21e5..8d6c562dd0c 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -7624,12 +7624,12 @@ public:
   }
 
   // C++ [over.match.oper]p16:
-  //   For every pointer to member type T, there exist candidate operator
-  //   functions of the form
+  //   For every pointer to member type T or type std::nullptr_t, there
+  //   exist candidate operator functions of the form
   //
   //        bool operator==(T,T);
   //        bool operator!=(T,T);
-  void addEqualEqualOrNotEqualMemberPointerOverloads() {
+  void addEqualEqualOrNotEqualMemberPointerOrNullptrOverloads() {
     /// Set of (canonical) types that we've already handled.
     llvm::SmallPtrSet<QualType, 8> AddedTypes;
 
@@ -7646,13 +7646,22 @@ public:
         QualType ParamTypes[2] = { *MemPtr, *MemPtr };
         S.AddBuiltinCandidate(S.Context.BoolTy, ParamTypes, Args, CandidateSet);
       }
+
+      if (CandidateTypes[ArgIdx].hasNullPtrType()) {
+        CanQualType NullPtrTy = S.Context.getCanonicalType(S.Context.NullPtrTy);
+        if (AddedTypes.insert(NullPtrTy).second) {
+          QualType ParamTypes[2] = { NullPtrTy, NullPtrTy };
+          S.AddBuiltinCandidate(S.Context.BoolTy, ParamTypes, Args,
+                                CandidateSet);
+        }
+      }
     }
   }
 
   // C++ [over.built]p15:
   //
-  //   For every T, where T is an enumeration type, a pointer type, or 
-  //   std::nullptr_t, there exist candidate operator functions of the form
+  //   For every T, where T is an enumeration type or a pointer type,
+  //   there exist candidate operator functions of the form
   //
   //        bool       operator<(T, T);
   //        bool       operator>(T, T);
@@ -7737,17 +7746,6 @@ public:
         QualType ParamTypes[2] = { *Enum, *Enum };
         S.AddBuiltinCandidate(S.Context.BoolTy, ParamTypes, Args, CandidateSet);
       }
-      
-      if (CandidateTypes[ArgIdx].hasNullPtrType()) {
-        CanQualType NullPtrTy = S.Context.getCanonicalType(S.Context.NullPtrTy);
-        if (AddedTypes.insert(NullPtrTy).second &&
-            !UserDefinedBinaryOperators.count(std::make_pair(NullPtrTy,
-                                                             NullPtrTy))) {
-          QualType ParamTypes[2] = { NullPtrTy, NullPtrTy };
-          S.AddBuiltinCandidate(S.Context.BoolTy, ParamTypes, Args,
-                                CandidateSet);
-        }
-      }
     }
   }
 
@@ -8443,7 +8441,7 @@ void Sema::AddBuiltinOperatorCandidates(OverloadedOperatorKind Op,
 
   case OO_EqualEqual:
   case OO_ExclaimEqual:
-    OpBuilder.addEqualEqualOrNotEqualMemberPointerOverloads();
+    OpBuilder.addEqualEqualOrNotEqualMemberPointerOrNullptrOverloads();
     // Fall through.
 
   case OO_Less: