[stubs] Use a single slot for context globals.

src/full-codegen/arm/full-codegen-arm.cc

 // Copyright 2012 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/v8.h"
 
 #if V8_TARGET_ARCH_ARM
 
 #include "src/code-factory.h"
 #include "src/code-stubs.h"
@@ skipping 1396 matching lines @@
 
 
 void FullCodeGenerator::EmitGlobalVariableLoad(VariableProxy* proxy,
                                                TypeofMode typeof_mode) {
   Variable* var = proxy->var();
   DCHECK(var->IsUnallocatedOrGlobalSlot() ||
          (var->IsLookupSlot() && var->mode() == DYNAMIC_GLOBAL));
   if (var->IsGlobalSlot()) {
     DCHECK(var->index() > 0);
     DCHECK(var->IsStaticGlobalObjectProperty());
-    // Each var occupies two slots in the context: for reads and writes.
     const int slot = var->index();
     const int depth = scope()->ContextChainLength(var->scope());
     if (depth <= LoadGlobalViaContextStub::kMaximumDepth) {
       __ mov(LoadGlobalViaContextDescriptor::SlotRegister(), Operand(slot));
       LoadGlobalViaContextStub stub(isolate(), depth);
       __ CallStub(&stub);
     } else {
       __ Push(Smi::FromInt(slot));
       __ CallRuntime(Runtime::kLoadGlobalViaContext, 1);
     }
@@ skipping 1278 matching lines @@
     // Global var, const, or let.
     __ mov(StoreDescriptor::NameRegister(), Operand(var->name()));
     __ ldr(StoreDescriptor::ReceiverRegister(), GlobalObjectOperand());
     if (FLAG_vector_stores) EmitLoadStoreICSlot(slot);
     CallStoreIC();
 
   } else if (var->IsGlobalSlot()) {
     // Global var, const, or let.
     DCHECK(var->index() > 0);
     DCHECK(var->IsStaticGlobalObjectProperty());
-    // Each var occupies two slots in the context: for reads and writes.
-    const int slot = var->index() + 1;
+    const int slot = var->index();
     const int depth = scope()->ContextChainLength(var->scope());
     if (depth <= StoreGlobalViaContextStub::kMaximumDepth) {
       __ mov(StoreGlobalViaContextDescriptor::SlotRegister(), Operand(slot));
       DCHECK(StoreGlobalViaContextDescriptor::ValueRegister().is(r0));
       StoreGlobalViaContextStub stub(isolate(), depth, language_mode());
       __ CallStub(&stub);
     } else {
       __ Push(Smi::FromInt(slot));
       __ push(r0);
       __ CallRuntime(is_strict(language_mode())
@@ skipping 2743 matching lines @@
   DCHECK(interrupt_address ==
          isolate->builtins()->OsrAfterStackCheck()->entry());
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM