[turbofan] Optimized lowering of DYNAMIC_GLOBAL lookup slot loads.

src/compiler/js-typed-lowering.cc

Index: src/compiler/js-typed-lowering.cc
diff --git a/src/compiler/js-typed-lowering.cc b/src/compiler/js-typed-lowering.cc
index 4a4bcbfd6516c8d4c992afc4b84544d530e83f87..987f73fd83c6ae4ce616cb1e184db429e651f7fa 100644
--- a/src/compiler/js-typed-lowering.cc
+++ b/src/compiler/js-typed-lowering.cc
@@ -924,6 +924,64 @@ Reduction JSTypedLowering::ReduceJSStoreContext(Node* node) {
 }
 
 
+Reduction JSTypedLowering::ReduceJSLoadDynamicGlobal(Node* node) {
+  DCHECK_EQ(IrOpcode::kJSLoadDynamicGlobal, node->opcode());
+  DynamicGlobalAccess const& access = DynamicGlobalAccessOf(node->op());
+  Node* const context = NodeProperties::GetContextInput(node);
+  Node* const state1 = NodeProperties::GetFrameStateInput(node, 0);
+  Node* const state2 = NodeProperties::GetFrameStateInput(node, 1);
+  Node* const effect = NodeProperties::GetEffectInput(node);
+  Node* const control = NodeProperties::GetControlInput(node);
+  if (access.RequiresFullCheck()) return NoChange();
+
+  // Perform checks whether the fast mode applies, by looking for any extension
+  // object which might shadow the optimistic declaration.
+  uint32_t bitset = access.check_bitset();
+  Node* check_true = control;
+  Node* check_false = graph()->NewNode(common()->Merge(0));
+  for (int depth = 0; bitset != 0; bitset >>= 1, depth++) {
+    if ((bitset & 1) == 0) continue;
+    Node* load = graph()->NewNode(
+        javascript()->LoadContext(depth, Context::EXTENSION_INDEX, false),
+        context, context, effect);
+    Node* check = graph()->NewNode(simplified()->ObjectIsSmi(), load);
+    Node* branch = graph()->NewNode(common()->Branch(BranchHint::kTrue), check,
+                                    check_true);
+    Node* if_true = graph()->NewNode(common()->IfTrue(), branch);
+    Node* if_false = graph()->NewNode(common()->IfFalse(), branch);
+    check_false->set_op(common()->Merge(check_false->InputCount() + 1));
+    check_false->AppendInput(graph()->zone(), if_false);
+    check_true = if_true;
+  }
+
+  // Fast case, because variable is not shadowed. Perform global object load.
+  Unique<Name> name = Unique<Name>::CreateUninitialized(access.name());
+  Node* global = graph()->NewNode(
+      javascript()->LoadContext(0, Context::GLOBAL_OBJECT_INDEX, true), context,
+      context, effect);
+  Node* fast = graph()->NewNode(
+      javascript()->LoadNamed(name, access.feedback(), access.mode()), global,
+      context, state1, state2, global, check_true);
+
+  // Slow case, because variable potentially shadowed. Perform dynamic lookup.
+  uint32_t check_bitset = DynamicGlobalAccess::kFullCheckRequired;
+  Node* slow = graph()->NewNode(
+      javascript()->LoadDynamicGlobal(access.name(), check_bitset,
+                                      access.feedback(), access.mode()),
+      context, context, state1, state2, effect, check_false);
+
+  // Replace value, effect and control uses accordingly.
+  Node* new_control =
+      graph()->NewNode(common()->Merge(2), check_true, check_false);
+  Node* new_effect =
+      graph()->NewNode(common()->EffectPhi(2), fast, slow, new_control);
+  Node* new_value = graph()->NewNode(common()->Phi(kMachAnyTagged, 2), fast,
+                                     slow, new_control);
+  ReplaceWithValue(node, new_value, new_effect, new_control);
+  return Changed(new_value);
+}
+
+
 Reduction JSTypedLowering::ReduceJSCreateClosure(Node* node) {
   DCHECK_EQ(IrOpcode::kJSCreateClosure, node->opcode());
   CreateClosureParameters const& p = CreateClosureParametersOf(node->op());
@@ -1429,6 +1487,8 @@ Reduction JSTypedLowering::Reduce(Node* node) {
       return ReduceJSLoadContext(node);
     case IrOpcode::kJSStoreContext:
       return ReduceJSStoreContext(node);
+    case IrOpcode::kJSLoadDynamicGlobal:
+      return ReduceJSLoadDynamicGlobal(node);
     case IrOpcode::kJSCreateClosure:
       return ReduceJSCreateClosure(node);
     case IrOpcode::kJSCreateLiteralArray: