Implement control reducer, which reduces branches and phis together in a single fixpoint.

src/compiler/scheduler.cc

Index: src/compiler/scheduler.cc
diff --git a/src/compiler/scheduler.cc b/src/compiler/scheduler.cc
index 82cc95972a151006ff362a262b1304d6be0140af..fe2aba43b81a9332042255326bd765ad4d078ed2 100644
--- a/src/compiler/scheduler.cc
+++ b/src/compiler/scheduler.cc
@@ -381,7 +381,8 @@ class CFGBuilder {
   }
 
   bool IsFinalMerge(Node* node) {
-    return (node == scheduler_->graph_->end()->InputAt(0));
+    return (node->opcode() == IrOpcode::kMerge &&
+            node == scheduler_->graph_->end()->InputAt(0));
   }
 };