[stubs] Use a single slot for context globals.

src/full-codegen/mips/full-codegen-mips.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_MIPS
 
 // Note on Mips implementation:
 //
@@ skipping 1388 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.
     int const slot = var->index();
     int const depth = scope()->ContextChainLength(var->scope());
     if (depth <= LoadGlobalViaContextStub::kMaximumDepth) {
       __ li(LoadGlobalViaContextDescriptor::SlotRegister(), Operand(slot));
       LoadGlobalViaContextStub stub(isolate(), depth);
       __ CallStub(&stub);
     } else {
       __ Push(Smi::FromInt(slot));
       __ CallRuntime(Runtime::kLoadGlobalViaContext, 1);
     }
@@ skipping 1276 matching lines @@
     __ lw(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());
     DCHECK(StoreGlobalViaContextDescriptor::ValueRegister().is(a0));
     __ mov(StoreGlobalViaContextDescriptor::ValueRegister(), result_register());
-    // Each var occupies two slots in the context: for reads and writes.
-    int const slot = var->index() + 1;
+    int const slot = var->index();
     int const depth = scope()->ContextChainLength(var->scope());
     if (depth <= StoreGlobalViaContextStub::kMaximumDepth) {
       __ li(StoreGlobalViaContextDescriptor::SlotRegister(), Operand(slot));
       StoreGlobalViaContextStub stub(isolate(), depth, language_mode());
       __ CallStub(&stub);
     } else {
       __ Push(Smi::FromInt(slot));
       __ Push(a0);
       __ CallRuntime(is_strict(language_mode())
                          ? Runtime::kStoreGlobalViaContext_Strict
@@ skipping 2714 matching lines @@
          reinterpret_cast<uint32_t>(
              isolate->builtins()->OsrAfterStackCheck()->entry()));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_MIPS