Eliminate condition type check when possible.

runtime/vm/flow_graph_optimizer.cc

Index: runtime/vm/flow_graph_optimizer.cc
===================================================================
--- runtime/vm/flow_graph_optimizer.cc	(revision 10606)
+++ runtime/vm/flow_graph_optimizer.cc	(working copy)
@@ -9,6 +9,7 @@
 #include "vm/object_store.h"
 #include "vm/parser.h"
 #include "vm/scopes.h"
+#include "vm/symbols.h"
 
 namespace dart {
 
@@ -591,6 +592,26 @@
 }
 
 
+void FlowGraphTypePropagator::VisitAssertBoolean(AssertBooleanComp* comp,
+                                                 BindInstr* instr) {
+  if (FLAG_eliminate_type_checks &&
+      !comp->IsEliminated() &&
+      comp->value()->CompileTypeIsMoreSpecificThan(
+          Type::Handle(Type::BoolInterface()))) {
+    comp->Eliminate();
+    if (FLAG_trace_type_check_elimination) {
+      const String& name = String::Handle(Symbols::New("boolean expression"));
+      FlowGraphPrinter::PrintTypeCheck(parsed_function(),
+                                       comp->token_pos(),
+                                       comp->value(),
+                                       Type::Handle(Type::BoolInterface()),
+                                       name,
+                                       comp->IsEliminated());
+    }
+  }
+}
+
+
 void FlowGraphTypePropagator::VisitGraphEntry(GraphEntryInstr* graph_entry) {
   if (graph_entry->start_env() == NULL) {
     return;