Remove the redundant load on every context lookup.

src/ia32/macro-assembler-ia32.cc

Index: src/ia32/macro-assembler-ia32.cc
diff --git a/src/ia32/macro-assembler-ia32.cc b/src/ia32/macro-assembler-ia32.cc
index a4c9b11879725be6330c1cca5b5301ed24abe4a8..ee4e3d9cd64aa0b10492709f9c2f7e09334bd108 100644
--- a/src/ia32/macro-assembler-ia32.cc
+++ b/src/ia32/macro-assembler-ia32.cc
@@ -1523,11 +1523,21 @@ void MacroAssembler::LoadContext(Register dst, int context_chain_length) {
       mov(dst, Operand(dst, Context::SlotOffset(Context::CLOSURE_INDEX)));
       mov(dst, FieldOperand(dst, JSFunction::kContextOffset));
     }
-    // The context may be an intermediate context, not a function context.
-    mov(dst, Operand(dst, Context::SlotOffset(Context::FCONTEXT_INDEX)));
-  } else {  // Slot is in the current function context.
-    // The context may be an intermediate context, not a function context.
-    mov(dst, Operand(esi, Context::SlotOffset(Context::FCONTEXT_INDEX)));
+  } else {
+    // Slot is in the current function context.  Move it into the
+    // destination register in case we store into it (the write barrier
+    // cannot be allowed to destroy the context in esi).
+    mov(dst, esi);
+  }
+
+  // We should not have found a 'with' context by walking the context chain
+  // (i.e., the static scope chain and runtime context chain do not agree).
+  // A variable occurring in such a scope should have slot type LOOKUP and
+  // not CONTEXT.
+  if (FLAG_debug_code) {
+    cmp(dst, Operand(dst, Context::SlotOffset(Context::FCONTEXT_INDEX)));
+    Check(equal, "Yo dawg, I heard you liked function contexts "
+                 "so I put function contexts in all your contexts");
   }
 }