[turbofan] Move graph trimming functionality to dedicated GraphTrimmer.

test/unittests/compiler/graph-trimmer-unittest.cc

+// Copyright 2015 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/graph-trimmer.h"
+#include "test/unittests/compiler/graph-unittest.h"
+#include "testing/gmock-support.h"
+
+using testing::ElementsAre;
+using testing::UnorderedElementsAre;
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+class GraphTrimmerTest : public GraphTest {
+ public:
+  GraphTrimmerTest() : GraphTest(1) {}
+
+ protected:
+  void TrimGraph(Node* root) {
+    Node* const roots[1] = {root};
+    GraphTrimmer trimmer(zone(), graph());
+    trimmer.TrimGraph(&roots[0], &roots[arraysize(roots)]);
+  }
+  void TrimGraph() {
+    GraphTrimmer trimmer(zone(), graph());
+    trimmer.TrimGraph();
+  }
+};
+
+
+namespace {
+
+const Operator kDead0(IrOpcode::kDead, Operator::kNoProperties, "Dead0", 0, 0,
+                      1, 0, 0, 0);
+const Operator kLive0(IrOpcode::kDead, Operator::kNoProperties, "Live0", 0, 0,
+                      1, 0, 0, 1);
+
+}  // namespace
+
+
+TEST_F(GraphTrimmerTest, Empty) {
+  Node* const start = graph()->NewNode(common()->Start(0));
+  Node* const end = graph()->NewNode(common()->End(1), start);
+  graph()->SetStart(start);
+  graph()->SetEnd(end);
+  TrimGraph();
+  EXPECT_EQ(end, graph()->end());
+  EXPECT_EQ(start, graph()->start());
+  EXPECT_EQ(start, end->InputAt(0));
+}
+
+
+TEST_F(GraphTrimmerTest, DeadUseOfStart) {
+  Node* const dead0 = graph()->NewNode(&kDead0, graph()->start());
+  graph()->SetEnd(graph()->NewNode(common()->End(1), graph()->start()));
+  TrimGraph();
+  EXPECT_THAT(dead0->inputs(), ElementsAre(nullptr));
+  EXPECT_THAT(graph()->start()->uses(), ElementsAre(graph()->end()));
+}
+
+
+TEST_F(GraphTrimmerTest, DeadAndLiveUsesOfStart) {
+  Node* const dead0 = graph()->NewNode(&kDead0, graph()->start());
+  Node* const live0 = graph()->NewNode(&kLive0, graph()->start());
+  graph()->SetEnd(graph()->NewNode(common()->End(1), live0));
+  TrimGraph();
+  EXPECT_THAT(dead0->inputs(), ElementsAre(nullptr));
+  EXPECT_THAT(graph()->start()->uses(), ElementsAre(live0));
+  EXPECT_THAT(live0->uses(), ElementsAre(graph()->end()));
+}
+
+
+TEST_F(GraphTrimmerTest, Roots) {
+  Node* const live0 = graph()->NewNode(&kLive0, graph()->start());
+  Node* const live1 = graph()->NewNode(&kLive0, graph()->start());
+  graph()->SetEnd(graph()->NewNode(common()->End(1), live0));
+  TrimGraph(live1);
+  EXPECT_THAT(graph()->start()->uses(), UnorderedElementsAre(live0, live1));
+}
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8