Remove the fcontext field from all contexts.

src/arm/full-codegen-arm.cc

Index: src/arm/full-codegen-arm.cc
diff --git a/src/arm/full-codegen-arm.cc b/src/arm/full-codegen-arm.cc
index 89ca0bad3792226618ad944777743302cde65f3a..950ebc3de916c76970f318d4d72386b536ac53e5 100644
--- a/src/arm/full-codegen-arm.cc
+++ b/src/arm/full-codegen-arm.cc
@@ -713,10 +713,12 @@ void FullCodeGenerator::EmitDeclaration(Variable* variable,
         // context.
         ASSERT_EQ(0, scope()->ContextChainLength(variable->scope()));
         if (FLAG_debug_code) {
-          // Check that we're not inside a 'with'.
-          __ ldr(r1, ContextOperand(cp, Context::FCONTEXT_INDEX));
-          __ cmp(r1, cp);
-          __ Check(eq, "Unexpected declaration in current context.");
+          // Check that we're not inside a with or catch context.
+          __ ldr(r1, FieldMemOperand(cp, HeapObject::kMapOffset));
+          __ CompareRoot(r1, Heap::kWithContextMapRootIndex);
+          __ Check(ne, "Declaration in with context.");
+          __ CompareRoot(r1, Heap::kCatchContextMapRootIndex);
+          __ Check(ne, "Declaration in catch context.");
         }
         if (mode == Variable::CONST) {
           __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
@@ -1867,18 +1869,7 @@ void FullCodeGenerator::EmitVariableAssignment(Variable* var,
         __ b(ne, &skip);
         __ str(result_register(), MemOperand(fp, SlotOffset(slot)));
         break;
-      case Slot::CONTEXT: {
-        __ ldr(r1, ContextOperand(cp, Context::FCONTEXT_INDEX));
-        __ ldr(r2, ContextOperand(r1, slot->index()));
-        __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
-        __ cmp(r2, ip);
-        __ b(ne, &skip);
-        __ str(r0, ContextOperand(r1, slot->index()));
-        int offset = Context::SlotOffset(slot->index());
-        __ mov(r3, r0);  // Preserve the stored value in r0.
-        __ RecordWrite(r1, Operand(offset), r3, r2);
-        break;
-      }
+      case Slot::CONTEXT:

[Kevin Millikin (Chromium), 2011/06/28 14:37:48]

Const initialization can be nested inside a with or catch, but with our current
semantics they are hoisted.

We could implement the loop up the context chain in generated code (even unroll
the loop once the chain length is known statically), but I've opted to just call
the runtime.

[Mads Ager (chromium), 2011/06/29 05:56:27]

Let's file a bug report (internal cleanup?) about investigating the impact of
native code implementation of this to not forget. Context stores could be quite
frequent and this would slow it down quite a bit.

       case Slot::LOOKUP:
         __ push(r0);
         __ mov(r0, Operand(slot->var()->name()));