Use range analysis to improve constant 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"
@@ skipping 246 matching lines @@
       }
 
       if (FLAG_range_analysis) {
         // We have to perform range analysis after LICM because it
         // optimistically moves CheckSmi through phis into loop preheaders
         // making some phis smi.
         optimizer.InferSmiRanges();
         DEBUG_ASSERT(flow_graph->VerifyUseLists());
       }
 
+      if (FLAG_constant_propagation) {
+        // Constant propagation can use information from range analysis to
+        // find unreachable branch targets.
+        ConstantPropagator::OptimizeBranches(flow_graph);
+        DEBUG_ASSERT(flow_graph->VerifyUseLists());
+      }
+
       // The final canonicalization pass before the code generation.
       if (FLAG_propagate_types) {
         // Recompute types after code movement was done to ensure correct
         // reaching types for hoisted values.
         FlowGraphTypePropagator propagator(flow_graph);
         propagator.Propagate();
         DEBUG_ASSERT(flow_graph->VerifyUseLists());
       }
       optimizer.Canonicalize();
       DEBUG_ASSERT(flow_graph->VerifyUseLists());
@@ skipping 403 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