Optimize conditional branches that have same true/false targets.

runtime/vm/intermediate_language.cc

 // Copyright (c) 2013, 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/intermediate_language.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/bit_vector.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_allocator.h"
@@ skipping 943 matching lines @@
            use_idx += step) {
         phi->SetInputAt(use_idx, phi->InputAt(use_idx + step));
       }
       // Write the predecessor use.
       phi->SetInputAt(new_index, pred_use);
     }
   }
 }
 
 
+bool BlockEntryInstr::IsEmptyBlock() {
+  return !HasParallelMove() &&
+      next()->IsGoto() &&
+      !next()->AsGoto()->HasParallelMove() &&
+      (!IsJoinEntry() || (AsJoinEntry()->phis() == NULL));
+}
+
+
+void BlockEntryInstr::ClearAllInstructions() {
+  JoinEntryInstr* join = this->AsJoinEntry();
+  if (join != NULL) {
+    for (PhiIterator it(join); !it.Done(); it.Advance()) {
+      it.Current()->UnuseAllInputs();
+    }
+  }
+  UnuseAllInputs();
+  for (ForwardInstructionIterator it(this);
+       !it.Done();
+       it.Advance()) {
+    it.Current()->UnuseAllInputs();
+  }
+}
+
+
 void JoinEntryInstr::InsertPhi(intptr_t var_index, intptr_t var_count) {
   // Lazily initialize the array of phis.
   // Currently, phis are stored in a sparse array that holds the phi
   // for variable with index i at position i.
   // TODO(fschneider): Store phis in a more compact way.
   if (phis_ == NULL) {
     phis_ = new ZoneGrowableArray<PhiInstr*>(var_count);
     for (intptr_t i = 0; i < var_count; i++) {
       phis_->Add(NULL);
     }
@@ skipping 1694 matching lines @@
       return kCosRuntimeEntry;
     default:
       UNREACHABLE();
   }
   return kSinRuntimeEntry;
 }
 
 #undef __
 
 }  // namespace dart