-fms-compatibility: Use C++98 null pointer constant rules

Patch by Will Wilson!

llvm-svn: 194441

clang/lib/AST/Expr.cpp

@@ -3051,7 +3051,8 @@ bool Expr::hasNonTrivialCall(ASTContext &Ctx) {
 Expr::NullPointerConstantKind
 Expr::isNullPointerConstant(ASTContext &Ctx,
                             NullPointerConstantValueDependence NPC) const {
-  if (isValueDependent() && !Ctx.getLangOpts().CPlusPlus11) {
+  if (isValueDependent() &&
+      (!Ctx.getLangOpts().CPlusPlus11 || Ctx.getLangOpts().MicrosoftMode)) {
     switch (NPC) {
     case NPC_NeverValueDependent:
       llvm_unreachable("Unexpected value dependent expression!");
@@ -3133,8 +3134,13 @@ Expr::isNullPointerConstant(ASTContext &Ctx,
   if (Ctx.getLangOpts().CPlusPlus11) {
     // C++11 [conv.ptr]p1: A null pointer constant is an integer literal with
     // value zero or a prvalue of type std::nullptr_t.
+    // Microsoft mode permits C++98 rules reflecting MSVC behavior.
     const IntegerLiteral *Lit = dyn_cast<IntegerLiteral>(this);
-    return (Lit && !Lit->getValue()) ? NPCK_ZeroLiteral : NPCK_NotNull;
+    if (Lit && !Lit->getValue())
+      return NPCK_ZeroLiteral;
+    else if (!Ctx.getLangOpts().MicrosoftMode ||
+             !isCXX98IntegralConstantExpr(Ctx))
+      return NPCK_NotNull;
   } else {
     // If we have an integer constant expression, we need to *evaluate* it and
     // test for the value 0.

clang/test/SemaCXX/MicrosoftCompatibility.cpp

@@ -178,3 +178,19 @@ namespace PR11791 {
     del((void*)a);  // expected-note {{in instantiation of function template specialization}}
   }
 }
+
+namespace IntToNullPtrConv {
+  struct Foo {
+    static const int ZERO = 0;
+    typedef void (Foo::*MemberFcnPtr)();
+  };
+
+  struct Bar {
+    const Foo::MemberFcnPtr pB;
+  };
+
+  Bar g_bar = { (Foo::MemberFcnPtr)Foo::ZERO };
+
+  template<int N> int *get_n() { return N; }   // expected-warning {{expression which evaluates to zero treated as a null pointer constant}}
+  int *g_nullptr = get_n<0>();  // expected-note {{in instantiation of function template specialization}}
+}