Enable constant evaluation of implicit calls to constexpr conversion operators.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@148333 91177308-0d34-0410-b5e6-96231b3b80d8

lib/AST/ExprConstant.cpp

@@ -2280,6 +2280,7 @@ public:
     case CK_AtomicToNonAtomic:
     case CK_NonAtomicToAtomic:
     case CK_NoOp:
+    case CK_UserDefinedConversion:
       return StmtVisitorTy::Visit(E->getSubExpr());
 
     case CK_LValueToRValue: {
@@ -4525,13 +4526,13 @@ bool IntExprEvaluator::VisitCastExpr(const CastExpr *E) {
   case CK_BitCast:
   case CK_Dependent:
   case CK_LValueBitCast:
-  case CK_UserDefinedConversion:
   case CK_ARCProduceObject:
   case CK_ARCConsumeObject:
   case CK_ARCReclaimReturnedObject:
   case CK_ARCExtendBlockObject:
     return Error(E);
 
+  case CK_UserDefinedConversion:
   case CK_LValueToRValue:
   case CK_AtomicToNonAtomic:
   case CK_NonAtomicToAtomic:

test/SemaCXX/constant-expression-cxx11.cpp

@@ -687,6 +687,28 @@ static_assert((Bottom*)nullB == 0, "");
 static_assert((Derived*)nullB == 0, "");
 static_assert((void*)(Bottom*)nullB == (void*)(Derived*)nullB, "");
 
+namespace ConversionOperators {
+
+struct T {
+  constexpr T(int n) : k(5*n - 3) {}
+  constexpr operator int() { return k; }
+  int k;
+};
+
+struct S {
+  constexpr S(int n) : k(2*n + 1) {}
+  constexpr operator int() { return k; }
+  constexpr operator T() { return T(k); }
+  int k;
+};
+
+constexpr bool check(T a, T b) { return a == b.k; }
+
+static_assert(S(5) == 11, "");
+static_assert(check(S(5), 11), "");
+
+}
+
 }
 
 namespace Temporaries {