Allow the target field of a CK_ToUnion to be more easily recovered.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@310963 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/AST/Expr.h

@@ -2772,6 +2772,16 @@ public:
   path_const_iterator path_begin() const { return path_buffer(); }
   path_const_iterator path_end() const { return path_buffer() + path_size(); }
 
+  const FieldDecl *getTargetUnionField() const {
+    assert(getCastKind() == CK_ToUnion);
+    return getTargetFieldForToUnionCast(getType(), getSubExpr()->getType());
+  }
+
+  static const FieldDecl *getTargetFieldForToUnionCast(QualType unionType,
+                                                       QualType opType);
+  static const FieldDecl *getTargetFieldForToUnionCast(const RecordDecl *RD,
+                                                       QualType opType);
+
   static bool classof(const Stmt *T) {
     return T->getStmtClass() >= firstCastExprConstant &&
            T->getStmtClass() <= lastCastExprConstant;

lib/AST/Expr.cpp

@@ -1695,6 +1695,26 @@ CXXBaseSpecifier **CastExpr::path_buffer() {
   }
 }
 
+const FieldDecl *CastExpr::getTargetFieldForToUnionCast(QualType unionType,
+                                                        QualType opType) {
+  auto RD = unionType->castAs<RecordType>()->getDecl();
+  return getTargetFieldForToUnionCast(RD, opType);
+}
+
+const FieldDecl *CastExpr::getTargetFieldForToUnionCast(const RecordDecl *RD,
+                                                        QualType OpType) {
+  auto &Ctx = RD->getASTContext();
+  RecordDecl::field_iterator Field, FieldEnd;
+  for (Field = RD->field_begin(), FieldEnd = RD->field_end();
+       Field != FieldEnd; ++Field) {
+    if (Ctx.hasSameUnqualifiedType(Field->getType(), OpType) &&
+        !Field->isUnnamedBitfield()) {
+      return *Field;
+    }
+  }
+  return nullptr;
+}
+
 ImplicitCastExpr *ImplicitCastExpr::Create(const ASTContext &C, QualType T,
                                            CastKind Kind, Expr *Operand,
                                            const CXXCastPath *BasePath,

lib/Sema/SemaCast.cpp

@@ -2458,24 +2458,17 @@ void CastOperation::CheckCStyleCast() {
     // GCC's cast to union extension.
     if (DestRecordTy && DestRecordTy->getDecl()->isUnion()) {
       RecordDecl *RD = DestRecordTy->getDecl();
-      RecordDecl::field_iterator Field, FieldEnd;
-      for (Field = RD->field_begin(), FieldEnd = RD->field_end();
-           Field != FieldEnd; ++Field) {
-        if (Self.Context.hasSameUnqualifiedType(Field->getType(), SrcType) &&
-            !Field->isUnnamedBitfield()) {
-          Self.Diag(OpRange.getBegin(), diag::ext_typecheck_cast_to_union)
-            << SrcExpr.get()->getSourceRange();
-          break;
-        }
-      }
-      if (Field == FieldEnd) {
+      if (CastExpr::getTargetFieldForToUnionCast(RD, SrcType)) {
+        Self.Diag(OpRange.getBegin(), diag::ext_typecheck_cast_to_union)
+          << SrcExpr.get()->getSourceRange();
+        Kind = CK_ToUnion;
+        return;
+      } else {
         Self.Diag(OpRange.getBegin(), diag::err_typecheck_cast_to_union_no_type)
           << SrcType << SrcExpr.get()->getSourceRange();
         SrcExpr = ExprError();
         return;
       }
-      Kind = CK_ToUnion;
-      return;
     }
 
     // OpenCL v2.0 s6.13.10 - Allow casts from '0' to event_t type.