[ARC][ObjC++] Use ObjC semantic rules for comparisons between a point…

…er and

an ObjC object pointer

When ARC is enabled in Objective-C++, comparisons between a pointer and
Objective-C object pointer typically result in errors like this:
"invalid operands to a binary expression". This error message can be quite
confusing as it doesn't provide a solution to the problem, unlike the non-C++
diagnostic: "implicit conversion of Objective-C pointer type 'id' to C pointer
type 'void *' requires a bridged cast" (it also provides fix-its). This commit
forces comparisons between pointers and Objective-C object pointers in ARC to
use the Objective-C semantic rules to ensure that a better diagnostic is
reported.

rdar://31103857

Differential Revision: https://reviews.llvm.org/D31177

llvm-svn: 299080

clang/lib/Sema/SemaExpr.cpp

@@ -9423,7 +9423,10 @@ QualType Sema::CheckCompareOperands(ExprResult &LHS, ExprResult &RHS,
     //   If both operands are pointers, [...] bring them to their composite
     //   pointer type.
     if ((int)LHSType->isPointerType() + (int)RHSType->isPointerType() >=
-        (IsRelational ? 2 : 1)) {
+            (IsRelational ? 2 : 1) &&
+        (!LangOpts.ObjCAutoRefCount ||
+         !(LHSType->isObjCObjectPointerType() ||
+           RHSType->isObjCObjectPointerType()))) {
       if (convertPointersToCompositeType(*this, Loc, LHS, RHS))
         return QualType();
       else

clang/test/SemaObjCXX/arc-ptr-comparison.mm

@@ -0,0 +1,24 @@
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-apple-darwin11 -fsyntax-only -fobjc-arc -verify %s
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-apple-darwin11 -fsyntax-only -verify -DNOARC %s
+#ifdef NOARC
+// expected-no-diagnostics
+#endif
+
+int testObjCComparisonRules(void *v, id x, id y) {
+  return v == x;
+#ifndef NOARC
+// expected-error@-2 {{implicit conversion of Objective-C pointer type 'id' to C pointer type 'void *' requires a bridged cast}}
+// expected-note@-3 {{use __bridge to convert directly (no change in ownership)}}
+// expected-note@-4 {{use __bridge_retained to make an ARC object available as a +1 'void *'}}
+#endif
+  return v >= x;
+#ifndef NOARC
+// expected-error@-2 {{implicit conversion of Objective-C pointer type 'id' to C pointer type 'void *' requires a bridged cast}}
+// expected-note@-3 {{use __bridge to convert directly (no change in ownership)}}
+// expected-note@-4 {{use __bridge_retained to make an ARC object available as a +1 'void *'}}
+#endif
+  return v == (id)(void *)0; // OK
+  return v == nullptr; // OK
+  return v == (void *)0;
+  return x == y;
+}