Replace maybe_symbol with specific tighter scoped variables

This ensures that the variable is only in scope when it is non-null.

Author: thomasspriggs

src/goto-programs/mm_io.cpp

@@ -118,25 +118,23 @@ void mm_io(symbol_tablet &symbol_table, goto_functionst &goto_functions)
   const irep_idt id_r = CPROVER_PREFIX "mm_io_r";
   const irep_idt id_w = CPROVER_PREFIX "mm_io_w";
 
-  auto maybe_symbol=symbol_table.lookup(id_r);
-  if(maybe_symbol)
+  if(const auto mm_io_r_symbol = symbol_table.lookup(id_r))
   {
-    mm_io_r=maybe_symbol->symbol_expr();
+    mm_io_r = mm_io_r_symbol->symbol_expr();
 
     const auto &value_symbol = get_fresh_aux_symbol(
       to_code_type(mm_io_r.type()).return_type(),
       id2string(id_r) + "$value",
       id2string(id_r) + "$value",
-      maybe_symbol->location,
-      maybe_symbol->mode,
+      mm_io_r_symbol->location,
+      mm_io_r_symbol->mode,
       symbol_table);
 
     mm_io_r_value = value_symbol.symbol_expr();
   }
 
-  maybe_symbol=symbol_table.lookup(id_w);
-  if(maybe_symbol)
-    mm_io_w=maybe_symbol->symbol_expr();
+  if(const auto mm_io_w_symbol = symbol_table.lookup(id_w))
+    mm_io_w = mm_io_w_symbol->symbol_expr();
 
   for(auto & f : goto_functions.function_map)
     mm_io(mm_io_r, mm_io_r_value, mm_io_w, f.second, ns);