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

src/compiler/select-lowering.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/compiler/select-lowering.h"
 
 #include "src/compiler/common-operator.h"
+#include "src/compiler/diamond.h"
 #include "src/compiler/generic-node-inl.h"
 #include "src/compiler/graph.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 SelectLowering::SelectLowering(Graph* graph, CommonOperatorBuilder* common)
     : common_(common),
       graph_(graph),
       merges_(Merges::key_compare(), Merges::allocator_type(graph->zone())) {}
 
 
 SelectLowering::~SelectLowering() {}
 
 
 Reduction SelectLowering::Reduce(Node* node) {
   if (node->opcode() != IrOpcode::kSelect) return NoChange();
   SelectParameters const p = SelectParametersOf(node->op());
 
   Node* const cond = node->InputAt(0);
-  Node* const control = graph()->start();
 
   // Check if we already have a diamond for this condition.
   auto i = merges_.find(cond);
   if (i == merges_.end()) {
     // Create a new diamond for this condition and remember its merge node.
-    Node* branch = graph()->NewNode(common()->Branch(p.hint()), cond, control);
-    Node* if_true = graph()->NewNode(common()->IfTrue(), branch);
-    Node* if_false = graph()->NewNode(common()->IfFalse(), branch);
-    Node* merge = graph()->NewNode(common()->Merge(2), if_true, if_false);
-    i = merges_.insert(std::make_pair(cond, merge)).first;
+    Diamond d(graph(), common(), cond);
+    i = merges_.insert(std::make_pair(cond, d.merge)).first;
   }
 
   DCHECK_EQ(cond, i->first);
 
   // Create a Phi hanging off the previously determined merge.
   node->set_op(common()->Phi(p.type(), 2));
   node->ReplaceInput(0, node->InputAt(1));
   node->ReplaceInput(1, node->InputAt(2));
   node->ReplaceInput(2, i->second);
   return Changed(node);
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8