[turbofan] Remove last_use_ field from Node.

test/cctest/compiler/test-node.cc

 // 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.
 
 #include <functional>
 
 #include "src/v8.h"
 
 #include "graph-tester.h"
 #include "src/compiler/node.h"
 #include "src/compiler/operator.h"
 
 using namespace v8::internal;
 using namespace v8::internal::compiler;
 
+#define NONE reinterpret_cast<Node*>(1)
+
 static Operator dummy_operator(IrOpcode::kParameter, Operator::kNoWrite,
                                "dummy", 0, 0, 0, 1, 0, 0);
 
+#define CHECK_USES(node, ...)                                    \
+  do {                                                           \
+    Node* __array[] = {__VA_ARGS__};                             \
+    size_t __size = __array[0] != NONE ? arraysize(__array) : 0; \
+    CheckUseChain(node, __array, __size);                        \
+  } while (false)
+
+
+typedef std::multiset<Node*, std::less<Node*>> NodeMSet;
+
+static void CheckUseChain(Node* node, Node** uses, size_t use_count) {
+  // Check ownership.
+  if (use_count == 1) CHECK(node->OwnedBy(uses[0]));
+  if (use_count > 1) {
+    for (size_t i = 0; i < use_count; i++) {
+      CHECK(!node->OwnedBy(uses[i]));
+    }
+  }
+
+  // Check the self-reported use count.
+  CHECK_EQ(use_count, node->UseCount());
+
+  // Build the expectation set.
+  NodeMSet expect_set;
+  for (size_t i = 0; i < use_count; i++) {
+    expect_set.insert(uses[i]);
+  }
+
+  {
+    // Check that iterating over the uses gives the right counts.
+    NodeMSet use_set;
+    for (auto use : node->uses()) {
+      use_set.insert(use);
+    }
+    CHECK(expect_set == use_set);
+  }
+
+  {
+    // Check that iterating over the use edges gives the right counts,
+    // input indices, from(), and to() pointers.
+    NodeMSet use_set;
+    for (auto edge : node->use_edges()) {
+      CHECK_EQ(node, edge.to());
+      CHECK_EQ(node, edge.from()->InputAt(edge.index()));
+      use_set.insert(edge.from());
+    }
+    CHECK(expect_set == use_set);
+  }
+
+  {
+    // Check the use nodes actually have the node as inputs.
+    for (Node* use : node->uses()) {
+      size_t count = 0;
+      for (Node* input : use->inputs()) {
+        if (input == node) count++;
+      }
+      CHECK_EQ(count, expect_set.count(use));
+    }
+  }
+}
+
+
+#define CHECK_INPUTS(node, ...)                                  \
+  do {                                                           \
+    Node* __array[] = {__VA_ARGS__};                             \
+    size_t __size = __array[0] != NONE ? arraysize(__array) : 0; \
+    CheckInputs(node, __array, __size);                          \
+  } while (false)
+
+
+static void CheckInputs(Node* node, Node** inputs, size_t input_count) {
+  CHECK_EQ(static_cast<int>(input_count), node->InputCount());
+  // Check InputAt().
+  for (size_t i = 0; i < input_count; i++) {
+    CHECK_EQ(inputs[i], node->InputAt(i));
+  }
+
+  // Check input iterator.
+  int index = 0;
+  for (Node* input : node->inputs()) {
+    CHECK_EQ(inputs[index], input);
+    index++;
+  }
+
+  // Check use lists of inputs.
+  for (int i = 0; i < static_cast<int>(input_count); i++) {
+    Node* input = inputs[i];
+    if (!input) continue;  // skip null inputs
+    bool found = false;
+    // Check regular use list.
+    for (Node* use : input->uses()) {
+      if (use == node) {
+        found = true;
+        break;
+      }
+    }
+    CHECK(found);
+    int count = 0;
+    // Check use edge list.
+    for (auto edge : input->use_edges()) {
+      if (edge.from() == node && edge.to() == input && edge.index() == i) {
+        count++;
+      }
+    }
+    CHECK_EQ(1, count);
+  }
+}
+
+
 TEST(NodeUseIteratorReplaceUses) {
   GraphTester graph;
   Node* n0 = graph.NewNode(&dummy_operator);
   Node* n1 = graph.NewNode(&dummy_operator, n0);
   Node* n2 = graph.NewNode(&dummy_operator, n0);
   Node* n3 = graph.NewNode(&dummy_operator);
-  auto i1(n0->uses().begin());
-  CHECK_EQ(n1, *i1);
-  ++i1;
-  CHECK_EQ(n2, *i1);
+
+  CHECK_USES(n0, n1, n2);
+
+  CHECK_INPUTS(n1, n0);
+  CHECK_INPUTS(n2, n0);
+
   n0->ReplaceUses(n3);
-  auto i2(n3->uses().begin());
-  CHECK_EQ(n1, *i2);
-  ++i2;
-  CHECK_EQ(n2, *i2);
-  auto i3(n1->inputs().begin());
-  CHECK_EQ(n3, *i3);
-  ++i3;
-  CHECK(n1->inputs().end() == i3);
-  auto i4(n2->inputs().begin());
-  CHECK_EQ(n3, *i4);
-  ++i4;
-  CHECK(n2->inputs().end() == i4);
+
+  CHECK_USES(n0, NONE);
+  CHECK_USES(n1, NONE);
+  CHECK_USES(n2, NONE);
+  CHECK_USES(n3, n1, n2);
+
+  CHECK_INPUTS(n1, n3);
+  CHECK_INPUTS(n2, n3);
 }
 
 
 TEST(NodeUseIteratorReplaceUsesSelf) {
   GraphTester graph;
   Node* n0 = graph.NewNode(&dummy_operator);
   Node* n1 = graph.NewNode(&dummy_operator, n0);
-  Node* n3 = graph.NewNode(&dummy_operator);
+
+  CHECK_USES(n0, n1);
+  CHECK_USES(n1, NONE);
 
   n1->ReplaceInput(0, n1);  // Create self-reference.
 
-  auto i1(n1->uses().begin());
-  CHECK_EQ(n1, *i1);
+  CHECK_USES(n0, NONE);
+  CHECK_USES(n1, n1);
 
-  n1->ReplaceUses(n3);
+  Node* n2 = graph.NewNode(&dummy_operator);
 
-  CHECK(n1->uses().begin() == n1->uses().end());
+  n1->ReplaceUses(n2);
 
-  auto i2(n3->uses().begin());
-  CHECK_EQ(n1, *i2);
-  ++i2;
-  CHECK(n1->uses().end() == i2);
+  CHECK_USES(n0, NONE);
+  CHECK_USES(n1, NONE);
+  CHECK_USES(n2, n1);
 }
 
 
 TEST(ReplaceInput) {
   GraphTester graph;
   Node* n0 = graph.NewNode(&dummy_operator);
   Node* n1 = graph.NewNode(&dummy_operator);
   Node* n2 = graph.NewNode(&dummy_operator);
   Node* n3 = graph.NewNode(&dummy_operator, n0, n1, n2);
-  auto i1(n3->inputs().begin());
-  CHECK(n0 == *i1);
-  CHECK_EQ(n0, n3->InputAt(0));
-  ++i1;
-  CHECK_EQ(n1, *i1);
-  CHECK_EQ(n1, n3->InputAt(1));
-  ++i1;
-  CHECK_EQ(n2, *i1);
-  CHECK_EQ(n2, n3->InputAt(2));
-  ++i1;
-  CHECK(i1 == n3->inputs().end());
+  Node* n4 = graph.NewNode(&dummy_operator);
 
-  auto i2(n1->uses().begin());
-  CHECK_EQ(n3, *i2);
-  ++i2;
-  CHECK(i2 == n1->uses().end());
+  CHECK_USES(n0, n3);
+  CHECK_USES(n1, n3);
+  CHECK_USES(n2, n3);
+  CHECK_USES(n3, NONE);
+  CHECK_USES(n4, NONE);
 
-  Node* n4 = graph.NewNode(&dummy_operator);
-  auto i3(n4->uses().begin());
-  CHECK(i3 == n4->uses().end());
+  CHECK_INPUTS(n3, n0, n1, n2);
 
   n3->ReplaceInput(1, n4);
 
-  auto i4(n1->uses().begin());
-  CHECK(i4 == n1->uses().end());
+  CHECK_USES(n1, NONE);
+  CHECK_USES(n4, n3);
 
-  auto i5(n4->uses().begin());
-  CHECK_EQ(n3, *i5);
-  ++i5;
-  CHECK(i5 == n4->uses().end());
-
-  auto i6(n3->inputs().begin());
-  CHECK(n0 == *i6);
-  CHECK_EQ(n0, n3->InputAt(0));
-  ++i6;
-  CHECK_EQ(n4, *i6);
-  CHECK_EQ(n4, n3->InputAt(1));
-  ++i6;
-  CHECK_EQ(n2, *i6);
-  CHECK_EQ(n2, n3->InputAt(2));
-  ++i6;
-  CHECK(i6 == n3->inputs().end());
+  CHECK_INPUTS(n3, n0, n4, n2);
 }
 
 
 TEST(OwnedBy) {
   GraphTester graph;
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n1 = graph.NewNode(&dummy_operator);
 
@@ skipping 37 matching lines @@
     CHECK(!n2->OwnedBy(n3));
   }
 }
 
 
 TEST(Uses) {
   GraphTester graph;
 
   Node* n0 = graph.NewNode(&dummy_operator);
   Node* n1 = graph.NewNode(&dummy_operator, n0);
-  CHECK_EQ(1, n0->UseCount());
-  printf("A: %d vs %d\n", n0->UseAt(0)->id(), n1->id());
-  CHECK(n0->UseAt(0) == n1);
+
+  CHECK_USES(n0, n1);
+  CHECK_USES(n1, NONE);
+
   Node* n2 = graph.NewNode(&dummy_operator, n0);
-  CHECK_EQ(2, n0->UseCount());
-  printf("B: %d vs %d\n", n0->UseAt(1)->id(), n2->id());
-  CHECK(n0->UseAt(1) == n2);
+
+  CHECK_USES(n0, n1, n2);
+  CHECK_USES(n2, NONE);
+
   Node* n3 = graph.NewNode(&dummy_operator, n0);
-  CHECK_EQ(3, n0->UseCount());
-  CHECK(n0->UseAt(2) == n3);
+
+  CHECK_USES(n0, n1, n2, n3);
+  CHECK_USES(n3, NONE);
 }
 
 
 TEST(Inputs) {
   GraphTester graph;
 
   Node* n0 = graph.NewNode(&dummy_operator);
   Node* n1 = graph.NewNode(&dummy_operator, n0);
   Node* n2 = graph.NewNode(&dummy_operator, n0);
   Node* n3 = graph.NewNode(&dummy_operator, n0, n1, n2);
-  CHECK_EQ(3, n3->InputCount());
-  CHECK(n3->InputAt(0) == n0);
-  CHECK(n3->InputAt(1) == n1);
-  CHECK(n3->InputAt(2) == n2);
+
+  CHECK_INPUTS(n3, n0, n1, n2);
+
   Node* n4 = graph.NewNode(&dummy_operator, n0, n1, n2);
   n3->AppendInput(graph.zone(), n4);
-  CHECK_EQ(4, n3->InputCount());
-  CHECK(n3->InputAt(0) == n0);
-  CHECK(n3->InputAt(1) == n1);
-  CHECK(n3->InputAt(2) == n2);
-  CHECK(n3->InputAt(3) == n4);
+
+  CHECK_INPUTS(n3, n0, n1, n2, n4);
+  CHECK_USES(n4, n3);
+
+  n3->AppendInput(graph.zone(), n4);
+
+  CHECK_INPUTS(n3, n0, n1, n2, n4, n4);
+  CHECK_USES(n4, n3, n3);
+
   Node* n5 = graph.NewNode(&dummy_operator, n4);
-  n3->AppendInput(graph.zone(), n4);
-  CHECK_EQ(5, n3->InputCount());
-  CHECK(n3->InputAt(0) == n0);
-  CHECK(n3->InputAt(1) == n1);
-  CHECK(n3->InputAt(2) == n2);
-  CHECK(n3->InputAt(3) == n4);
-  CHECK(n3->InputAt(4) == n4);
 
-  // Make sure uses have been hooked op correctly.
-  Node::Uses uses(n4->uses());
-  auto current = uses.begin();
-  CHECK(current != uses.end());
-  CHECK(*current == n3);
-  ++current;
-  CHECK(current != uses.end());
-  CHECK(*current == n5);
-  ++current;
-  CHECK(current != uses.end());
-  CHECK(*current == n3);
-  ++current;
-  CHECK(current == uses.end());
+  CHECK_USES(n4, n3, n3, n5);
 }
 
 
 TEST(RemoveInput) {
   GraphTester graph;
 
   Node* n0 = graph.NewNode(&dummy_operator);
   Node* n1 = graph.NewNode(&dummy_operator, n0);
   Node* n2 = graph.NewNode(&dummy_operator, n0, n1);
 
+  CHECK_INPUTS(n0, NONE);
+  CHECK_INPUTS(n1, n0);
+  CHECK_INPUTS(n2, n0, n1);
+  CHECK_USES(n0, n1, n2);
+
   n1->RemoveInput(0);
-  CHECK_EQ(0, n1->InputCount());
-  CHECK_EQ(1, n0->UseCount());
+  CHECK_INPUTS(n1, NONE);
+  CHECK_USES(n0, n2);
 
   n2->RemoveInput(0);
-  CHECK_EQ(1, n2->InputCount());
-  CHECK_EQ(0, n0->UseCount());
-  CHECK_EQ(1, n1->UseCount());
+  CHECK_INPUTS(n2, n1);
+  CHECK_USES(n0, NONE);
+  CHECK_USES(n1, n2);
 
   n2->RemoveInput(0);
-  CHECK_EQ(0, n2->InputCount());
+  CHECK_INPUTS(n2, NONE);
+  CHECK_USES(n0, NONE);
+  CHECK_USES(n1, NONE);
+  CHECK_USES(n2, NONE);
 }
 
 
 TEST(AppendInputsAndIterator) {
   GraphTester graph;
 
   Node* n0 = graph.NewNode(&dummy_operator);
   Node* n1 = graph.NewNode(&dummy_operator, n0);
   Node* n2 = graph.NewNode(&dummy_operator, n0, n1);
 
-  Node::InputEdges inputs(n2->input_edges());
-  Node::InputEdges::iterator current = inputs.begin();
-  CHECK(current != inputs.end());
-  CHECK((*current).to() == n0);
-  ++current;
-  CHECK(current != inputs.end());
-  CHECK((*current).to() == n1);
-  ++current;
-  CHECK(current == inputs.end());
+  CHECK_INPUTS(n0, NONE);
+  CHECK_INPUTS(n1, n0);
+  CHECK_INPUTS(n2, n0, n1);
+  CHECK_USES(n0, n1, n2);
 
   Node* n3 = graph.NewNode(&dummy_operator);
+
   n2->AppendInput(graph.zone(), n3);
-  inputs = n2->input_edges();
-  current = inputs.begin();
-  CHECK(current != inputs.end());
-  CHECK((*current).to() == n0);
-  CHECK_EQ(0, (*current).index());
-  ++current;
-  CHECK(current != inputs.end());
-  CHECK((*current).to() == n1);
-  CHECK_EQ(1, (*current).index());
-  ++current;
-  CHECK(current != inputs.end());
-  CHECK((*current).to() == n3);
-  CHECK_EQ(2, (*current).index());
-  ++current;
-  CHECK(current == inputs.end());
+
+  CHECK_INPUTS(n2, n0, n1, n3);
+  CHECK_USES(n3, n2);
 }
 
 
 TEST(NullInputsSimple) {
   GraphTester graph;
 
   Node* n0 = graph.NewNode(&dummy_operator);
   Node* n1 = graph.NewNode(&dummy_operator, n0);
   Node* n2 = graph.NewNode(&dummy_operator, n0, n1);
-  CHECK_EQ(2, n2->InputCount());
 
-  CHECK(n0 == n2->InputAt(0));
-  CHECK(n1 == n2->InputAt(1));
-  CHECK_EQ(2, n0->UseCount());
-  n2->ReplaceInput(0, NULL);
-  CHECK(NULL == n2->InputAt(0));
-  CHECK(n1 == n2->InputAt(1));
-  CHECK_EQ(1, n0->UseCount());
+  CHECK_INPUTS(n0, NONE);
+  CHECK_INPUTS(n1, n0);
+  CHECK_INPUTS(n2, n0, n1);
+  CHECK_USES(n0, n1, n2);
+
+  n2->ReplaceInput(0, nullptr);
+
+  CHECK_INPUTS(n2, NULL, n1);
+
+  CHECK_USES(n0, n1);
+
+  n2->ReplaceInput(1, nullptr);
+
+  CHECK_INPUTS(n2, NULL, NULL);
+
+  CHECK_USES(n1, NONE);
 }
 
 
 TEST(NullInputsAppended) {
   GraphTester graph;
 
   Node* n0 = graph.NewNode(&dummy_operator);
   Node* n1 = graph.NewNode(&dummy_operator, n0);
   Node* n2 = graph.NewNode(&dummy_operator, n0);
   Node* n3 = graph.NewNode(&dummy_operator, n0);
   n3->AppendInput(graph.zone(), n1);
   n3->AppendInput(graph.zone(), n2);
-  CHECK_EQ(3, n3->InputCount());
 
-  CHECK(n0 == n3->InputAt(0));
-  CHECK(n1 == n3->InputAt(1));
-  CHECK(n2 == n3->InputAt(2));
-  CHECK_EQ(1, n1->UseCount());
+  CHECK_INPUTS(n3, n0, n1, n2);
+  CHECK_USES(n0, n1, n2, n3);
+  CHECK_USES(n1, n3);
+  CHECK_USES(n2, n3);
+
   n3->ReplaceInput(1, NULL);
-  CHECK(n0 == n3->InputAt(0));
-  CHECK(NULL == n3->InputAt(1));
-  CHECK(n2 == n3->InputAt(2));
-  CHECK_EQ(0, n1->UseCount());
+  CHECK_USES(n1, NONE);
+
+  CHECK_INPUTS(n3, n0, NULL, n2);
 }
 
 
 TEST(ReplaceUsesFromAppendedInputs) {
   GraphTester graph;
 
   Node* n0 = graph.NewNode(&dummy_operator);
   Node* n1 = graph.NewNode(&dummy_operator, n0);
   Node* n2 = graph.NewNode(&dummy_operator, n0);
   Node* n3 = graph.NewNode(&dummy_operator);
+
+  CHECK_INPUTS(n2, n0);
+
   n2->AppendInput(graph.zone(), n1);
+  CHECK_INPUTS(n2, n0, n1);
+  CHECK_USES(n1, n2);
+
   n2->AppendInput(graph.zone(), n0);
-  CHECK_EQ(0, n3->UseCount());
-  CHECK_EQ(3, n0->UseCount());
+  CHECK_INPUTS(n2, n0, n1, n0);
+  CHECK_USES(n1, n2);
+  CHECK_USES(n0, n2, n1, n2);
+
   n0->ReplaceUses(n3);
-  CHECK_EQ(0, n0->UseCount());
-  CHECK_EQ(3, n3->UseCount());
 
-  Node::Uses uses(n3->uses());
-  auto current = uses.begin();
-  CHECK(current != uses.end());
-  CHECK(*current == n1);
-  ++current;
-  CHECK(current != uses.end());
-  CHECK(*current == n2);
-  ++current;
-  CHECK(current != uses.end());
-  CHECK(*current == n2);
-  ++current;
-  CHECK(current == uses.end());
+  CHECK_USES(n0, NONE);
+  CHECK_INPUTS(n2, n3, n1, n3);
+  CHECK_USES(n3, n2, n1, n2);
 }
 
 
 TEST(ReplaceInputMultipleUses) {
   GraphTester graph;
 
   Node* n0 = graph.NewNode(&dummy_operator);
   Node* n1 = graph.NewNode(&dummy_operator);
   Node* n2 = graph.NewNode(&dummy_operator, n0);
   n2->ReplaceInput(0, n1);
   CHECK_EQ(0, n0->UseCount());
   CHECK_EQ(1, n1->UseCount());
 
   Node* n3 = graph.NewNode(&dummy_operator, n0);
   n3->ReplaceInput(0, n1);
   CHECK_EQ(0, n0->UseCount());
   CHECK_EQ(2, n1->UseCount());
 }
 
 
 TEST(TrimInputCountInline) {
   GraphTester graph;
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n1 = graph.NewNode(&dummy_operator, n0);
     n1->TrimInputCount(1);
-    CHECK_EQ(1, n1->InputCount());
-    CHECK_EQ(n0, n1->InputAt(0));
-    CHECK_EQ(1, n0->UseCount());
+    CHECK_INPUTS(n1, n0);
+    CHECK_USES(n0, n1);
   }
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n1 = graph.NewNode(&dummy_operator, n0);
     n1->TrimInputCount(0);
-    CHECK_EQ(0, n1->InputCount());
-    CHECK_EQ(0, n0->UseCount());
+    CHECK_INPUTS(n1, NONE);
+    CHECK_USES(n0, NONE);
   }
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n1 = graph.NewNode(&dummy_operator);
     Node* n2 = graph.NewNode(&dummy_operator, n0, n1);
     n2->TrimInputCount(2);
-    CHECK_EQ(2, n2->InputCount());
-    CHECK_EQ(1, n0->UseCount());
-    CHECK_EQ(1, n1->UseCount());
-    CHECK_EQ(0, n2->UseCount());
+    CHECK_INPUTS(n2, n0, n1);
+    CHECK_USES(n0, n2);
+    CHECK_USES(n1, n2);
   }
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n1 = graph.NewNode(&dummy_operator);
     Node* n2 = graph.NewNode(&dummy_operator, n0, n1);
     n2->TrimInputCount(1);
-    CHECK_EQ(1, n2->InputCount());
-    CHECK_EQ(1, n0->UseCount());
-    CHECK_EQ(0, n1->UseCount());
-    CHECK_EQ(0, n2->UseCount());
+    CHECK_INPUTS(n2, n0);
+    CHECK_USES(n0, n2);
+    CHECK_USES(n1, NONE);
   }
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n1 = graph.NewNode(&dummy_operator);
     Node* n2 = graph.NewNode(&dummy_operator, n0, n1);
     n2->TrimInputCount(0);
-    CHECK_EQ(0, n2->InputCount());
-    CHECK_EQ(0, n0->UseCount());
-    CHECK_EQ(0, n1->UseCount());
-    CHECK_EQ(0, n2->UseCount());
+    CHECK_INPUTS(n2, NONE);
+    CHECK_USES(n0, NONE);
+    CHECK_USES(n1, NONE);
   }
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n2 = graph.NewNode(&dummy_operator, n0, n0);
     n2->TrimInputCount(1);
-    CHECK_EQ(1, n2->InputCount());
-    CHECK_EQ(1, n0->UseCount());
-    CHECK_EQ(0, n2->UseCount());
+    CHECK_INPUTS(n2, n0);
+    CHECK_USES(n0, n2);
   }
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n2 = graph.NewNode(&dummy_operator, n0, n0);
     n2->TrimInputCount(0);
-    CHECK_EQ(0, n2->InputCount());
-    CHECK_EQ(0, n0->UseCount());
-    CHECK_EQ(0, n2->UseCount());
+    CHECK_INPUTS(n2, NONE);
+    CHECK_USES(n0, NONE);
   }
 }
 
 
 TEST(TrimInputCountOutOfLine1) {
   GraphTester graph;
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n1 = graph.NewNode(&dummy_operator);
     n1->AppendInput(graph.zone(), n0);
+    CHECK_INPUTS(n1, n0);
+    CHECK_USES(n0, n1);
+
     n1->TrimInputCount(1);
-    CHECK_EQ(1, n1->InputCount());
-    CHECK_EQ(n0, n1->InputAt(0));
-    CHECK_EQ(1, n0->UseCount());
+    CHECK_INPUTS(n1, n0);
+    CHECK_USES(n0, n1);
   }
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n1 = graph.NewNode(&dummy_operator);
     n1->AppendInput(graph.zone(), n0);
     CHECK_EQ(1, n1->InputCount());
     n1->TrimInputCount(0);
     CHECK_EQ(0, n1->InputCount());
     CHECK_EQ(0, n0->UseCount());
   }
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n1 = graph.NewNode(&dummy_operator);
     Node* n2 = graph.NewNode(&dummy_operator);
     n2->AppendInput(graph.zone(), n0);
     n2->AppendInput(graph.zone(), n1);
-    CHECK_EQ(2, n2->InputCount());
+    CHECK_INPUTS(n2, n0, n1);
     n2->TrimInputCount(2);
-    CHECK_EQ(2, n2->InputCount());
-    CHECK_EQ(n0, n2->InputAt(0));
-    CHECK_EQ(n1, n2->InputAt(1));
-    CHECK_EQ(1, n0->UseCount());
-    CHECK_EQ(1, n1->UseCount());
-    CHECK_EQ(0, n2->UseCount());
+    CHECK_INPUTS(n2, n0, n1);
+    CHECK_USES(n0, n2);
+    CHECK_USES(n1, n2);
+    CHECK_USES(n2, NONE);
   }
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n1 = graph.NewNode(&dummy_operator);
     Node* n2 = graph.NewNode(&dummy_operator);
     n2->AppendInput(graph.zone(), n0);
     n2->AppendInput(graph.zone(), n1);
-    CHECK_EQ(2, n2->InputCount());
+    CHECK_INPUTS(n2, n0, n1);
     n2->TrimInputCount(1);
-    CHECK_EQ(1, n2->InputCount());
-    CHECK_EQ(n0, n2->InputAt(0));
-    CHECK_EQ(1, n0->UseCount());
-    CHECK_EQ(0, n1->UseCount());
-    CHECK_EQ(0, n2->UseCount());
+    CHECK_INPUTS(n2, n0);
+    CHECK_USES(n0, n2);
+    CHECK_USES(n1, NONE);
+    CHECK_USES(n2, NONE);
   }
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n1 = graph.NewNode(&dummy_operator);
     Node* n2 = graph.NewNode(&dummy_operator);
     n2->AppendInput(graph.zone(), n0);
     n2->AppendInput(graph.zone(), n1);
-    CHECK_EQ(2, n2->InputCount());
+    CHECK_INPUTS(n2, n0, n1);
     n2->TrimInputCount(0);
-    CHECK_EQ(0, n2->InputCount());
-    CHECK_EQ(0, n0->UseCount());
-    CHECK_EQ(0, n1->UseCount());
-    CHECK_EQ(0, n2->UseCount());
+    CHECK_INPUTS(n2, NONE);
+    CHECK_USES(n0, NONE);
+    CHECK_USES(n1, NONE);
+    CHECK_USES(n2, NONE);
   }
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n2 = graph.NewNode(&dummy_operator);
     n2->AppendInput(graph.zone(), n0);
     n2->AppendInput(graph.zone(), n0);
-    CHECK_EQ(2, n2->InputCount());
-    CHECK_EQ(2, n0->UseCount());
+    CHECK_INPUTS(n2, n0, n0);
+    CHECK_USES(n0, n2, n2);
     n2->TrimInputCount(1);
-    CHECK_EQ(1, n2->InputCount());
-    CHECK_EQ(1, n0->UseCount());
-    CHECK_EQ(0, n2->UseCount());
+    CHECK_INPUTS(n2, n0);
+    CHECK_USES(n0, n2);
   }
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n2 = graph.NewNode(&dummy_operator);
     n2->AppendInput(graph.zone(), n0);
     n2->AppendInput(graph.zone(), n0);
-    CHECK_EQ(2, n2->InputCount());
-    CHECK_EQ(2, n0->UseCount());
+    CHECK_INPUTS(n2, n0, n0);
+    CHECK_USES(n0, n2, n2);
     n2->TrimInputCount(0);
-    CHECK_EQ(0, n2->InputCount());
-    CHECK_EQ(0, n0->UseCount());
-    CHECK_EQ(0, n2->UseCount());
+    CHECK_INPUTS(n2, NONE);
+    CHECK_USES(n0, NONE);
   }
 }
 
 
 TEST(TrimInputCountOutOfLine2) {
   GraphTester graph;
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n1 = graph.NewNode(&dummy_operator);
     Node* n2 = graph.NewNode(&dummy_operator, n0);
     n2->AppendInput(graph.zone(), n1);
-    CHECK_EQ(2, n2->InputCount());
+    CHECK_INPUTS(n2, n0, n1);
     n2->TrimInputCount(2);
-    CHECK_EQ(2, n2->InputCount());
-    CHECK_EQ(n0, n2->InputAt(0));
-    CHECK_EQ(n1, n2->InputAt(1));
-    CHECK_EQ(1, n0->UseCount());
-    CHECK_EQ(1, n1->UseCount());
-    CHECK_EQ(0, n2->UseCount());
+    CHECK_INPUTS(n2, n0, n1);
+    CHECK_USES(n0, n2);
+    CHECK_USES(n1, n2);
+    CHECK_USES(n2, NONE);
   }
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n1 = graph.NewNode(&dummy_operator);
     Node* n2 = graph.NewNode(&dummy_operator, n0);
     n2->AppendInput(graph.zone(), n1);
-    CHECK_EQ(2, n2->InputCount());
+    CHECK_INPUTS(n2, n0, n1);
     n2->TrimInputCount(1);
-    CHECK_EQ(1, n2->InputCount());
-    CHECK_EQ(n0, n2->InputAt(0));
-    CHECK_EQ(1, n0->UseCount());
-    CHECK_EQ(0, n1->UseCount());
-    CHECK_EQ(0, n2->UseCount());
+    CHECK_INPUTS(n2, n0);
+    CHECK_USES(n0, n2);
+    CHECK_USES(n1, NONE);
+    CHECK_USES(n2, NONE);
   }
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n1 = graph.NewNode(&dummy_operator);
     Node* n2 = graph.NewNode(&dummy_operator, n0);
     n2->AppendInput(graph.zone(), n1);
-    CHECK_EQ(2, n2->InputCount());
+    CHECK_INPUTS(n2, n0, n1);
     n2->TrimInputCount(0);
-    CHECK_EQ(0, n2->InputCount());
-    CHECK_EQ(0, n0->UseCount());
-    CHECK_EQ(0, n1->UseCount());
-    CHECK_EQ(0, n2->UseCount());
+    CHECK_INPUTS(n2, NONE);
+    CHECK_USES(n0, NONE);
+    CHECK_USES(n1, NONE);
+    CHECK_USES(n2, NONE);
   }
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n2 = graph.NewNode(&dummy_operator, n0);
     n2->AppendInput(graph.zone(), n0);
-    CHECK_EQ(2, n2->InputCount());
-    CHECK_EQ(2, n0->UseCount());
+    CHECK_INPUTS(n2, n0, n0);
+    CHECK_USES(n0, n2, n2);
     n2->TrimInputCount(1);
-    CHECK_EQ(1, n2->InputCount());
-    CHECK_EQ(1, n0->UseCount());
-    CHECK_EQ(0, n2->UseCount());
+    CHECK_INPUTS(n2, n0);
+    CHECK_USES(n0, n2);
+    CHECK_USES(n2, NONE);
   }
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n2 = graph.NewNode(&dummy_operator, n0);
     n2->AppendInput(graph.zone(), n0);
     CHECK_EQ(2, n2->InputCount());
     CHECK_EQ(2, n0->UseCount());
     n2->TrimInputCount(0);
     CHECK_EQ(0, n2->InputCount());
     CHECK_EQ(0, n0->UseCount());
     CHECK_EQ(0, n2->UseCount());
   }
 }
 
 
 TEST(RemoveAllInputs) {
   GraphTester graph;
 
   for (int i = 0; i < 2; i++) {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n1 = graph.NewNode(&dummy_operator, n0);
     Node* n2;
     if (i == 0) {
       n2 = graph.NewNode(&dummy_operator, n0, n1);
+      CHECK_INPUTS(n2, n0, n1);
     } else {
       n2 = graph.NewNode(&dummy_operator, n0);
+      CHECK_INPUTS(n2, n0);
       n2->AppendInput(graph.zone(), n1);  // with out-of-line input.
+      CHECK_INPUTS(n2, n0, n1);
     }
 
     n0->RemoveAllInputs();
-    CHECK_EQ(0, n0->InputCount());
+    CHECK_INPUTS(n0, NONE);
 
-    CHECK_EQ(2, n0->UseCount());
+    CHECK_USES(n0, n1, n2);
     n1->RemoveAllInputs();
-    CHECK_EQ(1, n1->InputCount());
-    CHECK_EQ(1, n0->UseCount());
-    CHECK(!n1->InputAt(0));
+    CHECK_INPUTS(n1, NULL);
+    CHECK_INPUTS(n2, n0, n1);
+    CHECK_USES(n0, n2);
 
-    CHECK_EQ(1, n1->UseCount());
     n2->RemoveAllInputs();
-    CHECK_EQ(2, n2->InputCount());
-    CHECK_EQ(0, n0->UseCount());
-    CHECK_EQ(0, n1->UseCount());
-    CHECK(!n2->InputAt(0));
-    CHECK(!n2->InputAt(1));
+    CHECK_INPUTS(n1, NULL);
+    CHECK_INPUTS(n2, NULL, NULL);
+    CHECK_USES(n0, NONE);
   }
 
   {
     Node* n0 = graph.NewNode(&dummy_operator);
     Node* n1 = graph.NewNode(&dummy_operator, n0);
     n1->ReplaceInput(0, n1);  // self-reference.
 
-    CHECK_EQ(0, n0->UseCount());
-    CHECK_EQ(1, n1->UseCount());
+    CHECK_INPUTS(n0, NONE);
+    CHECK_INPUTS(n1, n1);
+    CHECK_USES(n0, NONE);
+    CHECK_USES(n1, n1);
     n1->RemoveAllInputs();
-    CHECK_EQ(1, n1->InputCount());
-    CHECK_EQ(0, n1->UseCount());
-    CHECK(!n1->InputAt(0));
+
+    CHECK_INPUTS(n0, NONE);
+    CHECK_INPUTS(n1, NULL);
+    CHECK_USES(n0, NONE);
+    CHECK_USES(n1, NONE);
   }
 }
+
+
+TEST(AppendAndTrim) {
+  GraphTester graph;
+
+  Node* nodes[] = {
+      graph.NewNode(&dummy_operator), graph.NewNode(&dummy_operator),
+      graph.NewNode(&dummy_operator), graph.NewNode(&dummy_operator),
+      graph.NewNode(&dummy_operator)};
+
+  Node* last = graph.NewNode(&dummy_operator);
+
+  for (size_t i = 0; i < arraysize(nodes); i++) {
+    last->AppendInput(graph.zone(), nodes[i]);
+    CheckInputs(last, nodes, static_cast<int>(i + 1));
+
+    for (size_t j = 0; j < arraysize(nodes); j++) {
+      if (j <= i) CHECK_USES(nodes[j], last);
+      if (j > i) CHECK_USES(nodes[j], NONE);
+    }
+
+    CHECK_USES(last, NONE);
+  }
+
+  for (int i = static_cast<int>(arraysize(nodes)); i >= 0; i--) {
+    last->TrimInputCount(i);
+    CheckInputs(last, nodes, static_cast<int>(i));
+
+    for (size_t j = 0; j < i; j++) {
+      if (j < i) CHECK_USES(nodes[j], last);
+      if (j >= i) CHECK_USES(nodes[j], NONE);
+    }
+
+    CHECK_USES(last, NONE);
+  }
+}