VM: [Kernel] Add kernel::ConstantEvaluator support for string.length

runtime/vm/kernel_to_il.cc

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include <map>
 #include <set>
 #include <string>
 
 #include "vm/kernel_to_il.h"
 
@@ skipping 1752 matching lines @@
 
 
 void ConstantEvaluator::VisitNot(Not* node) {
   EvaluateExpression(node->expression());
   ASSERT(result_.IsBool());
   result_ =
       Bool::Cast(result_).value() ? Bool::False().raw() : Bool::True().raw();
 }
 
 
+void ConstantEvaluator::VisitPropertyGet(PropertyGet* node) {
+  const size_t kLengthLen = strlen("length");
+
+  String* string = node->name()->string();
+  if (string->size() == kLengthLen &&
+      memcmp(string->buffer(), "length", kLengthLen) == 0) {
+    node->receiver()->AcceptExpressionVisitor(this);
+    if (result_.IsString()) {
+      const dart::String& str =
+          dart::String::Handle(Z, dart::String::RawCast(result_.raw()));
+      result_ = Integer::New(str.Length());
+    } else {
+      H.ReportError(
+          "Constant expressions can only call "
+          "'length' on string constants.");
+    }
+  } else {
+    VisitDefaultExpression(node);
+  }
+}
+
+
 const TypeArguments* ConstantEvaluator::TranslateTypeArguments(
     const Function& target,
     dart::Class* target_klass,
     Arguments* kernel_arguments) {
   List<DartType>& kernel_type_arguments = kernel_arguments->types();
 
   const TypeArguments* type_arguments = NULL;
   if (kernel_type_arguments.length() > 0) {
     type_arguments = &T.TranslateInstantiatedTypeArguments(
         *target_klass, kernel_type_arguments.raw_array(),
@@ skipping 4063 matching lines @@
   instructions += LoadLocal(parsed_function_->current_context_var());
   instructions += StoreInstanceField(Closure::context_offset());
 
   return instructions;
 }
 
 
 }  // namespace kernel
 }  // namespace dart
 #endif  // !defined(DART_PRECOMPILED_RUNTIME)