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 448 matching lines @@
 
           // 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.
+          // find unreachable branch targets and eliminate branches that have
+          // the same true- and false-target.
           ConstantPropagator::OptimizeBranches(flow_graph);
           DEBUG_ASSERT(flow_graph->VerifyUseLists());
         }
 
         // Recompute types after code movement was done to ensure correct
         // reaching types for hoisted values.
         FlowGraphTypePropagator::Propagate(flow_graph);
         DEBUG_ASSERT(flow_graph->VerifyUseLists());
 
         // Optimize try-blocks.
@@ skipping 482 matching lines @@
     const Object& result =
       Object::Handle(isolate->object_store()->sticky_error());
     isolate->object_store()->clear_sticky_error();
     return result.raw();
   }
   UNREACHABLE();
   return Object::null();
 }
 
 }  // namespace dart