[stubs] Use a single slot for context globals.

src/full-codegen/ppc/full-codegen-ppc.cc

Index: src/full-codegen/ppc/full-codegen-ppc.cc
diff --git a/src/full-codegen/ppc/full-codegen-ppc.cc b/src/full-codegen/ppc/full-codegen-ppc.cc
index 0654a9a64abd4d92ea47bee487ab154613be656d..68a0dc0bdee861b76a0e9e910a0d7c6dfdceae5f 100644
--- a/src/full-codegen/ppc/full-codegen-ppc.cc
+++ b/src/full-codegen/ppc/full-codegen-ppc.cc
@@ -1377,7 +1377,6 @@ void FullCodeGenerator::EmitGlobalVariableLoad(VariableProxy* proxy,
   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) {
@@ -2715,8 +2714,7 @@ void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
     // 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));