Add flag to measure impact of type check elimination.

runtime/vm/flow_graph_builder.cc

 // Copyright (c) 2012, 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 "vm/flow_graph_builder.h"
 
 #include "vm/ast_printer.h"
 #include "vm/bit_vector.h"
 #include "vm/code_descriptors.h"
 #include "vm/dart_entry.h"
 #include "vm/flags.h"
 #include "vm/il_printer.h"
 #include "vm/intermediate_language.h"
 #include "vm/longjump.h"
 #include "vm/object_store.h"
 #include "vm/os.h"
 #include "vm/parser.h"
 #include "vm/resolver.h"
 #include "vm/stub_code.h"
 
 namespace dart {
 
+DEFINE_FLAG(bool, eliminate_type_checks, true,
+            "Eliminate type checks when allowed by static type analysis");
+DEFINE_FLAG(bool, print_ast, false, "Print abstract syntax tree.");
 DEFINE_FLAG(bool, print_flow_graph, false, "Print the IR flow graph.");
 DECLARE_FLAG(bool, enable_type_checks);
-DEFINE_FLAG(bool, print_ast, false, "Print abstract syntax tree.");
 
 
 FlowGraphBuilder::FlowGraphBuilder(const ParsedFunction& parsed_function)
   : parsed_function_(parsed_function),
     preorder_block_entries_(),
     postorder_block_entries_(),
     context_level_(0),
     last_used_try_index_(CatchClauseNode::kInvalidTryIndex),
     try_index_(CatchClauseNode::kInvalidTryIndex),
     graph_entry_(NULL) { }
@@ skipping 268 matching lines @@
 void EffectGraphVisitor::VisitTypeNode(TypeNode* node) { UNREACHABLE(); }
 
 
 // Returns true if the type check can be skipped, for example, if the
 // destination type is Dynamic or if the static type of the value is a subtype
 // of the destination type.
 static bool CanSkipTypeCheck(Value* value, const AbstractType& dst_type) {
   ASSERT(FLAG_enable_type_checks);
   ASSERT(!dst_type.IsNull());
   ASSERT(dst_type.IsFinalized());
+  if (!FLAG_eliminate_type_checks) {
+    return false;
+  }
 
   // Any expression is assignable to the Dynamic type and to the Object type.
   // Skip the test.
   if (!dst_type.IsMalformed() &&
       (dst_type.IsDynamicType() || dst_type.IsObjectType())) {
     return true;
   }
 
   // It is a compile-time error to explicitly return a value (including null)
   // from a void function. However, functions that do not explicitly return a
@@ skipping 2070 matching lines @@
   char* chars = reinterpret_cast<char*>(
       Isolate::Current()->current_zone()->Allocate(len));
   OS::SNPrint(chars, len, kFormat, function_name, reason);
   const Error& error = Error::Handle(
       LanguageError::New(String::Handle(String::New(chars))));
   Isolate::Current()->long_jump_base()->Jump(1, error);
 }
 
 
 }  // namespace dart