Reapply r18377 it was reverted due to the unrelated bug it surfaced.

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"
 #include "vm/dart_entry.h"
 #include "vm/debugger.h"
 #include "vm/deopt_instructions.h"
 #include "vm/disassembler.h"
 #include "vm/exceptions.h"
 #include "vm/flags.h"
 #include "vm/flow_graph.h"
 #include "vm/flow_graph_allocator.h"
 #include "vm/flow_graph_builder.h"
 #include "vm/flow_graph_compiler.h"
 #include "vm/flow_graph_inliner.h"
 #include "vm/flow_graph_optimizer.h"
+#include "vm/flow_graph_type_propagator.h"
 #include "vm/il_printer.h"
 #include "vm/longjump.h"
 #include "vm/object.h"
 #include "vm/object_store.h"
 #include "vm/os.h"
 #include "vm/parser.h"
 #include "vm/scanner.h"
 #include "vm/symbols.h"
 #include "vm/timer.h"
 
@@ skipping 12 matching lines @@
 DEFINE_FLAG(bool, propagate_types, true, "Do static type propagation.");
 DEFINE_FLAG(int, deoptimization_counter_threshold, 16,
     "How many times we allow deoptimization before we disallow optimization.");
 DEFINE_FLAG(bool, use_inlining, true, "Enable call-site inlining");
 DEFINE_FLAG(bool, range_analysis, true, "Enable range analysis");
 DEFINE_FLAG(bool, verify_compiler, false,
     "Enable compiler verification assertions");
 DECLARE_FLAG(bool, print_flow_graph);
 DECLARE_FLAG(bool, print_flow_graph_optimized);
 DECLARE_FLAG(bool, trace_failed_optimization_attempts);
-
+DECLARE_FLAG(bool, trace_type_propagation);
 
 // Compile a function. Should call only if the function has not been compiled.
 //   Arg0: function object.
 DEFINE_RUNTIME_ENTRY(CompileFunction, 1) {
   ASSERT(arguments.ArgCount() == kCompileFunctionRuntimeEntry.argument_count());
   const Function& function = Function::CheckedHandle(arguments.ArgAt(0));
   ASSERT(!function.HasCode());
   const Error& error = Error::Handle(Compiler::CompileFunction(function));
   if (!error.IsNull()) {
     Exceptions::PropagateError(error);
@@ skipping 116 matching lines @@
 
       // Inlining (mutates the flow graph)
       if (FLAG_use_inlining) {
         TimerScope timer(FLAG_compiler_stats,
                          &CompilerStats::graphinliner_timer);
         FlowGraphInliner inliner(flow_graph);
         inliner.Inline();
         // Use lists are maintained and validated by the inliner.
       }
 
+      if (FLAG_trace_type_propagation) {
+        OS::Print("Before type propagation:\n");
+        FlowGraphPrinter printer(*flow_graph);
+        printer.PrintBlocks();
+      }
+
       // Propagate types and eliminate more type tests.
       if (FLAG_propagate_types) {
         FlowGraphTypePropagator propagator(flow_graph);
-        propagator.PropagateTypes();
+        propagator.Propagate();
       }
 
-      // Propagate sminess from CheckSmi to phis.
+      if (FLAG_trace_type_propagation) {
+        OS::Print("After type propagation:\n");
+        FlowGraphPrinter printer(*flow_graph);
+        printer.PrintBlocks();
+      }
+
       flow_graph->ComputeUseLists();
-      optimizer.PropagateSminess();
 
       // Use propagated class-ids to optimize further.
       optimizer.ApplyClassIds();
 
       // Recompute use lists after applying class ids.
       flow_graph->ComputeUseLists();
 
       // Do optimizations that depend on the propagated type information.
       optimizer.Canonicalize();
 
@@ skipping 427 matching lines @@
       Object::Handle(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