[turbofan] Redundant load elimination.

src/compiler/load-elimination.cc

Index: src/compiler/load-elimination.cc
diff --git a/src/compiler/load-elimination.cc b/src/compiler/load-elimination.cc
new file mode 100644
index 0000000000000000000000000000000000000000..fe0714ebc1aee4567b80f1a4a0ad3f93031ef8ea
--- /dev/null
+++ b/src/compiler/load-elimination.cc
@@ -0,0 +1,76 @@
+// 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/load-elimination.h"
+
+#include "src/compiler/node-properties-inl.h"
+#include "src/compiler/simplified-operator.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+LoadElimination::~LoadElimination() {}
+
+
+Reduction LoadElimination::Reduce(Node* node) {
+  switch (node->opcode()) {
+    case IrOpcode::kLoadField:
+      return ReduceLoadField(node);
+    default:
+      break;
+  }
+  return NoChange();
+}
+
+
+Reduction LoadElimination::ReduceLoadField(Node* node) {
+  DCHECK_EQ(IrOpcode::kLoadField, node->opcode());
+  FieldAccess const access = FieldAccessOf(node->op());
+  Node* const object = NodeProperties::GetValueInput(node, 0);
+  for (Node* effect = NodeProperties::GetEffectInput(node);;
+       effect = NodeProperties::GetEffectInput(effect)) {
+    switch (effect->opcode()) {
+      case IrOpcode::kLoadField: {
+        if (object == NodeProperties::GetValueInput(effect, 0) &&
+            access == FieldAccessOf(effect->op())) {
+          Node* const value = effect;
+          NodeProperties::ReplaceWithValue(node, value);
+          return Replace(value);
+        }
+        break;
+      }
+      case IrOpcode::kStoreField: {
+        if (access == FieldAccessOf(effect->op())) {
+          if (object == NodeProperties::GetValueInput(effect, 0)) {
+            Node* const value = NodeProperties::GetValueInput(effect, 1);
+            NodeProperties::ReplaceWithValue(node, value);
+            return Replace(value);
+          }
+          // TODO(turbofan): Alias analysis to the rescue?
+          return NoChange();
+        }
+        break;
+      }
+      case IrOpcode::kStoreBuffer:
+      case IrOpcode::kStoreElement: {
+        // These can never interfere with field loads.
+        break;
+      }
+      default: {
+        if (!effect->op()->HasProperty(Operator::kNoWrite) ||
+            effect->op()->EffectInputCount() != 1) {
+          return NoChange();
+        }
+        break;
+      }
+    }
+  }
+  UNREACHABLE();
+  return NoChange();
+}
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8