Optimize conditional branches that have same true/false targets.

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/block_scheduler.h"
@@ skipping 438 matching lines @@
           // 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);
+          // Eliminate branches that have the same true- and false-target.
+          ConstantPropagator::RemoveRedundantBranches(flow_graph);

[Kevin Millikin (Google), 2013/09/27 11:03:43]

Since Optimize and RemoveRedundant go together, I'd just move the redundant
branch elimination into OptimizeBranches.  (Plus, OptimizeBranches is too
generic if you have a separate, descriptively named RemoveRedundantBranches, and
it's confusing to have differently named public RemoveRedundant and private
EliminateRedundant that implements it.  You dodge all those issues by putting
EliminateRedundant inside Optimize).

[Florian Schneider, 2013/09/30 12:19:23]

Done.

           DEBUG_ASSERT(flow_graph->VerifyUseLists());
         }
 
         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());
         }
@@ skipping 455 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