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

src/compiler/diamond.h

Index: src/compiler/diamond.h
diff --git a/src/compiler/diamond.h b/src/compiler/diamond.h
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+// Copyright 2013 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.
+
+#ifndef V8_COMPILER_DIAMOND_H_
+#define V8_COMPILER_DIAMOND_H_
+
+#include "src/v8.h"
+
+#include "src/compiler/common-operator.h"
+#include "src/compiler/graph-inl.h"
+#include "src/compiler/node.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+// A helper to make it easier to build diamond-shaped control patterns.
+struct Diamond {
+  Graph* graph;
+  CommonOperatorBuilder* common;
+  Node* branch;
+  Node* if_true;
+  Node* if_false;
+  Node* merge;
+
+  Diamond(Graph* g, CommonOperatorBuilder* b, Node* cond,
+          BranchHint hint = BranchHint::kNone) {
+    graph = g;
+    common = b;
+    branch = graph->NewNode(common->Branch(hint), cond, graph->start());
+    if_true = graph->NewNode(common->IfTrue(), branch);
+    if_false = graph->NewNode(common->IfFalse(), branch);
+    merge = graph->NewNode(common->Merge(2), if_true, if_false);
+  }
+
+  // Place {this} after {that} in control flow order.
+  void Chain(Diamond& that) { branch->ReplaceInput(1, that.merge); }
+
+  // Place {this} after {that} in control flow order.
+  void Chain(Node* that) { branch->ReplaceInput(1, that); }
+
+  // Nest {this} into either the if_true or if_false branch of {that}.
+  void Nest(Diamond& that, bool if_true) {
+    if (if_true) {
+      branch->ReplaceInput(1, that.if_true);
+      that.merge->ReplaceInput(0, merge);
+    } else {
+      branch->ReplaceInput(1, that.if_false);
+      that.merge->ReplaceInput(1, merge);
+    }
+  }
+
+  Node* Phi(MachineType machine_type, Node* tv, Node* fv) {
+    return graph->NewNode(common->Phi(machine_type, 2), tv, fv, merge);
+  }
+
+  Node* EffectPhi(Node* tv, Node* fv) {
+    return graph->NewNode(common->EffectPhi(2), tv, fv, merge);
+  }
+
+  void OverwriteWithPhi(Node* node, MachineType machine_type, Node* tv,
+                        Node* fv) {
+    DCHECK(node->InputCount() >= 3);
+    node->set_op(common->Phi(machine_type, 2));
+    node->ReplaceInput(0, tv);
+    node->ReplaceInput(1, fv);
+    node->ReplaceInput(2, merge);
+    node->TrimInputCount(3);
+  }
+
+  void OverwriteWithEffectPhi(Node* node, Node* te, Node* fe) {
+    DCHECK(node->InputCount() >= 3);
+    node->set_op(common->EffectPhi(2));
+    node->ReplaceInput(0, te);
+    node->ReplaceInput(1, fe);
+    node->ReplaceInput(2, merge);
+    node->TrimInputCount(3);
+  }
+};
+}
+}
+}  // namespace v8::internal::compiler
+
+#endif  // V8_COMPILER_DIAMOND_H_