+        // the identifier with its constant value.
Not keen to the use of SM.getAddImmPrefix() as a mean of distinguish whether we are parsing a bracketed expression. I know it is currently turned on when parsing it, but it isn't asserted/guaranteed.
Regardless - I'm pretty sure we can manage without this rewrite, or at the very least - should, now that TYPE/LENGTH/SIZE are part of the State Machine.
-      // Just add a prefix if this wasn't a complex immediate expression.
-      // Otherwise, rewrite the complex expression as a single immediate.
+      // Rewrite the complex expression as a single immediate.