Optimize conditional branches that have same true/false targets.

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
===================================================================
--- runtime/vm/intermediate_language.cc	(revision 27294)
+++ runtime/vm/intermediate_language.cc	(working copy)
@@ -961,6 +961,22 @@
 }
 
 
+void BlockEntryInstr::UnuseAllInstructions() {

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

The name is a bit off.  We don't use instructions (they use their inputs), so it
doesn't make sense to unuse them.  Maybe ClearAllInstructions?

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

Done.

+  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