[stubs] Optimize LoadGlobalViaContextStub and StoreGlobalViaContextStub.

src/ia32/full-codegen-ia32.cc

Index: src/ia32/full-codegen-ia32.cc
diff --git a/src/ia32/full-codegen-ia32.cc b/src/ia32/full-codegen-ia32.cc
index 6060b3616efe778e4742678675f3669894911d10..dd6db17956db9de6f563c4560f2377afd637bb2a 100644
--- a/src/ia32/full-codegen-ia32.cc
+++ b/src/ia32/full-codegen-ia32.cc
@@ -1408,15 +1408,18 @@ 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());
-    __ mov(LoadGlobalViaContextDescriptor::DepthRegister(),
-           Immediate(Smi::FromInt(depth)));
-    __ mov(LoadGlobalViaContextDescriptor::SlotRegister(),
-           Immediate(Smi::FromInt(slot_index)));
-    __ mov(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) {
+      __ Move(LoadGlobalViaContextDescriptor::SlotRegister(), Immediate(slot));

[jbramley, 2015/07/21 10:25:31]

Is it safe to pass raw (non-smi) integers to stubs? Can't CallStub trigger a GC?

+      __ mov(LoadGlobalViaContextDescriptor::NameRegister(), var->name());
+      LoadGlobalViaContextStub stub(isolate(), depth);
+      __ CallStub(&stub);
+    } else {
+      __ Push(Smi::FromInt(slot));
+      __ Push(var->name());
+      __ CallRuntime(Runtime::kLoadGlobalViaContext, 2);
+    }
 
   } else {
     __ mov(LoadDescriptor::ReceiverRegister(), GlobalObjectOperand());
@@ -2687,16 +2690,23 @@ 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());
-    __ mov(StoreGlobalViaContextDescriptor::DepthRegister(),
-           Immediate(Smi::FromInt(depth)));
-    __ mov(StoreGlobalViaContextDescriptor::SlotRegister(),
-           Immediate(Smi::FromInt(slot_index)));
-    __ mov(StoreGlobalViaContextDescriptor::NameRegister(), var->name());
-    DCHECK(StoreGlobalViaContextDescriptor::ValueRegister().is(eax));
-    StoreGlobalViaContextStub stub(isolate(), depth, language_mode());
-    __ CallStub(&stub);
+    int const slot = var->index() + 1;

[jbramley, 2015/07/21 10:25:31]

`slot` shadows a function argument.

+    int const depth = scope()->ContextChainLength(var->scope());

[jbramley, 2015/07/21 10:25:31]

Also, isn't the preferred style "const int" in Google V8?

+    if (depth <= StoreGlobalViaContextStub::kMaximumDepth) {
+      __ Move(StoreGlobalViaContextDescriptor::SlotRegister(), Immediate(slot));
+      __ mov(StoreGlobalViaContextDescriptor::NameRegister(), var->name());
+      DCHECK(StoreGlobalViaContextDescriptor::ValueRegister().is(eax));
+      StoreGlobalViaContextStub stub(isolate(), depth, language_mode());
+      __ CallStub(&stub);
+    } else {
+      __ Push(Smi::FromInt(slot));
+      __ Push(var->name());
+      __ Push(eax);
+      __ 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.