Introduce Diamond, a helper for building diamond-shaped control patterns.

test/cctest/compiler/test-control-reducer.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 #include "test/cctest/cctest.h"
 
 #include "src/base/bits.h"
 #include "src/compiler/common-operator.h"
 #include "src/compiler/control-reducer.h"
@@ skipping 955 matching lines @@
 
   Branch(ControlReducerTester& R, Node* cond, Node* control = NULL) {
     if (control == NULL) control = R.start;
     branch = R.graph.NewNode(R.common.Branch(), cond, control);
     if_true = R.graph.NewNode(R.common.IfTrue(), branch);
     if_false = R.graph.NewNode(R.common.IfFalse(), branch);
   }
 };
 
 
+// TODO(titzer): use the diamonds from src/compiler/diamond.h here.
 struct Diamond {
   Node* branch;
   Node* if_true;
   Node* if_false;
   Node* merge;
   Node* phi;
 
   Diamond(ControlReducerTester& R, Node* cond) {
     branch = R.graph.NewNode(R.common.Branch(), cond, R.start);
     if_true = R.graph.NewNode(R.common.IfTrue(), branch);
@@ skipping 685 matching lines @@
 
   Node* ret = R.Return(d1.phi, R.start, d1.merge);
 
   R.ReduceGraph();  // d1 gets folded true.
 
   CheckInputs(ret, y2, R.start, R.start);
   CheckDeadDiamond(d1);
   CheckDeadDiamond(d2);
   CheckDeadDiamond(d3);
 }