[turbofan] Implicitly emit eager checkpoint at graph building.

src/compiler/checkpoint-elimination.cc

 // Copyright 2016 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/checkpoint-elimination.h"
 
 #include "src/compiler/node-properties.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 12 matching lines @@
   while (effect->op()->HasProperty(Operator::kNoWrite) &&
          effect->op()->EffectInputCount() == 1) {
     if (effect->opcode() == IrOpcode::kCheckpoint) return true;
     effect = NodeProperties::GetEffectInput(effect);
   }
   return false;
 }
 
 }  // namespace
 
-Reduction CheckpointElimination::Reduce(Node* node) {
-  if (node->opcode() != IrOpcode::kCheckpoint) return NoChange();
+Reduction CheckpointElimination::ReduceCheckpoint(Node* node) {
+  DCHECK_EQ(IrOpcode::kCheckpoint, node->opcode());
   if (IsRedundantCheckpoint(node)) {
     return Replace(NodeProperties::GetEffectInput(node));
   }
   return NoChange();
 }
 
+Reduction CheckpointElimination::ReduceReturn(Node* node) {
+  DCHECK_EQ(IrOpcode::kReturn, node->opcode());
+  Node* effect = NodeProperties::GetEffectInput(node);
+  if (effect->opcode() == IrOpcode::kCheckpoint && effect->OwnedBy(node)) {
+    // Any checkpoint that is wholly owned by a {Return} node can never be used
+    // for an actual bailout and can hence be cut out of the effect chain.
+    Node* replacement = NodeProperties::GetEffectInput(effect);
+    NodeProperties::ReplaceEffectInput(node, replacement);
+    return Changed(node);
+  }
+  return NoChange();
+}
+
+Reduction CheckpointElimination::Reduce(Node* node) {
+  switch (node->opcode()) {
+    case IrOpcode::kCheckpoint:
+      return ReduceCheckpoint(node);
+    case IrOpcode::kReturn:
+      return ReduceReturn(node);
+    default:
+      break;
+  }
+  return NoChange();
+}
+
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8