Cleanup handling of NullType in type propagation.

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 153 matching lines @@
       // generated code.
       intptr_t length = graph_builder.postorder_block_entries().length();
       for (intptr_t i = length - 1; i >= 0; --i) {
         block_order.Add(graph_builder.postorder_block_entries()[i]);
       }
       if (optimized) {
         FlowGraphOptimizer optimizer(block_order);
         optimizer.ApplyICData();
 
         // Propagate types and eliminate more type tests.
-        FlowGraphTypePropagator propagator(parsed_function, block_order);
+        FlowGraphTypePropagator propagator(parsed_function,
+                                           block_order,
+                                           optimized && use_ssa);
         propagator.PropagateTypes();
 
         // Do optimizations that depend on the propagated type information.
         optimizer.OptimizeComputations();
 
         if (use_ssa) {
           // Perform register allocation on the SSA graph.
           FlowGraphAllocator allocator(block_order, &graph_builder);
           allocator.AllocateRegisters();
         }
@@ 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