Add a simple dominator based redundancy elimination.

runtime/vm/compiler.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/compiler.h"
 
 #include "vm/assembler.h"
 #include "vm/ast_printer.h"
 #include "vm/code_generator.h"
 #include "vm/code_patcher.h"
@@ skipping 16 matching lines @@
 #include "vm/scanner.h"
 #include "vm/symbols.h"
 #include "vm/timer.h"
 
 namespace dart {
 
 DEFINE_FLAG(bool, disassemble, false, "Disassemble dart code.");
 DEFINE_FLAG(bool, disassemble_optimized, false, "Disassemble optimized code.");
 DEFINE_FLAG(bool, trace_bailout, false, "Print bailout from ssa compiler.");
 DEFINE_FLAG(bool, trace_compiler, false, "Trace compiler operations.");
-DEFINE_FLAG(bool, local_cse, true, "Do local subexpression elimination.");
+DEFINE_FLAG(bool, cse, true, "Do common subexpression elimination.");
 DEFINE_FLAG(int, deoptimization_counter_threshold, 5,
     "How many times we allow deoptimization before we disallow"
     " certain optimizations");
 DECLARE_FLAG(bool, print_flow_graph);
 
 
 // Compile a function. Should call only if the function has not been compiled.
 //   Arg0: function object.
 DEFINE_RUNTIME_ENTRY(CompileFunction, 1) {
   ASSERT(arguments.Count() == kCompileFunctionRuntimeEntry.argument_count());
@@ skipping 134 matching lines @@
         FlowGraphOptimizer optimizer(*flow_graph);
         optimizer.ApplyICData();
 
         // Propagate types and eliminate more type tests.
         FlowGraphTypePropagator propagator(*flow_graph);
         propagator.PropagateTypes();
 
         // Do optimizations that depend on the propagated type information.
         optimizer.OptimizeComputations();
 
-        if (FLAG_local_cse) {
-          LocalCSE local_cse(*flow_graph);
-          local_cse.Optimize();
+        if (FLAG_cse) {
+          DominatorBasedCSE::Optimize(flow_graph->graph_entry());
         }
 
         // Perform register allocation on the SSA graph.
         FlowGraphAllocator allocator(*flow_graph);
         allocator.AllocateRegisters();
 
         if (FLAG_print_flow_graph) {
           OS::Print("After Optimizations:\n");
           FlowGraphPrinter printer(*flow_graph);
           printer.PrintBlocks();
@@ skipping 346 matching lines @@
     result = isolate->object_store()->sticky_error();
     isolate->object_store()->clear_sticky_error();
     isolate->set_long_jump_base(base);
     return result.raw();
   }
   UNREACHABLE();
   return Object::null();
 }
 
 }  // namespace dart