[stubs] Optimize LoadGlobalViaContextStub and StoreGlobalViaContextStub.

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index acd47cb1f9cf02717795c135ce941ffaea8b5f92..7a15602ed500262592bc6b5b841ec5e4e937bcca 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -1370,15 +1370,18 @@ void FullCodeGenerator::EmitGlobalVariableLoad(VariableProxy* proxy,
     DCHECK(var->index() > 0);
     DCHECK(var->IsStaticGlobalObjectProperty());
     // Each var occupies two slots in the context: for reads and writes.
-    int slot_index = var->index();
-    int depth = scope()->ContextChainLength(var->scope());
-    __ Move(LoadGlobalViaContextDescriptor::DepthRegister(),
-            Smi::FromInt(depth));
-    __ Move(LoadGlobalViaContextDescriptor::SlotRegister(),
-            Smi::FromInt(slot_index));
-    __ Move(LoadGlobalViaContextDescriptor::NameRegister(), var->name());
-    LoadGlobalViaContextStub stub(isolate(), depth);
-    __ CallStub(&stub);
+    int const slot = var->index();
+    int const depth = scope()->ContextChainLength(var->scope());
+    if (depth <= LoadGlobalViaContextStub::kMaximumDepth) {
+      __ Set(LoadGlobalViaContextDescriptor::SlotRegister(), slot);
+      __ Move(LoadGlobalViaContextDescriptor::NameRegister(), var->name());
+      LoadGlobalViaContextStub stub(isolate(), depth);
+      __ CallStub(&stub);
+    } else {
+      __ Push(Smi::FromInt(slot));
+      __ Push(var->name());
+      __ CallRuntime(Runtime::kLoadGlobalViaContext, 2);
+    }
 
   } else {
     __ Move(LoadDescriptor::NameRegister(), var->name());
@@ -2615,16 +2618,23 @@ void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
     DCHECK(var->index() > 0);
     DCHECK(var->IsStaticGlobalObjectProperty());
     // Each var occupies two slots in the context: for reads and writes.
-    int slot_index = var->index() + 1;
-    int depth = scope()->ContextChainLength(var->scope());
-    __ Move(StoreGlobalViaContextDescriptor::DepthRegister(),
-            Smi::FromInt(depth));
-    __ Move(StoreGlobalViaContextDescriptor::SlotRegister(),
-            Smi::FromInt(slot_index));
-    __ Move(StoreGlobalViaContextDescriptor::NameRegister(), var->name());
-    DCHECK(StoreGlobalViaContextDescriptor::ValueRegister().is(rax));
-    StoreGlobalViaContextStub stub(isolate(), depth, language_mode());
-    __ CallStub(&stub);
+    int const slot = var->index() + 1;
+    int const depth = scope()->ContextChainLength(var->scope());
+    if (depth <= StoreGlobalViaContextStub::kMaximumDepth) {
+      __ Set(StoreGlobalViaContextDescriptor::SlotRegister(), slot);
+      __ Move(StoreGlobalViaContextDescriptor::NameRegister(), var->name());
+      DCHECK(StoreGlobalViaContextDescriptor::ValueRegister().is(rax));
+      StoreGlobalViaContextStub stub(isolate(), depth, language_mode());
+      __ CallStub(&stub);
+    } else {
+      __ Push(Smi::FromInt(slot));
+      __ Push(var->name());
+      __ Push(rax);
+      __ CallRuntime(is_strict(language_mode())
+                         ? Runtime::kStoreGlobalViaContext_Strict
+                         : Runtime::kStoreGlobalViaContext_Sloppy,
+                     3);
+    }
 
   } else if (var->mode() == LET && op != Token::INIT_LET) {
     // Non-initializing assignment to let variable needs a write barrier.