CSC448: Code Generation Revisited: Implementation Strategies I [128/133]

Exception handling complicates the runtime system.

We must ensure that we can find the right exception handler block in the current function/method if there is one.

If not, we must remove one activation record and look for exception handler blocks in the preceding activation record.

Moreover, we must ensure execution of each dynamically enclosing finally block, and call destructors/finalizers in languages such as C++.

A simple strategy is to maintain a stack of exception handlers. Whenever we enter a new exception handler block, we push a new handler onto the stack. As with case statements, there are several implementation strategies: the handler might be a pointer to code, or it might be a pointer to a jump table with an entry for each exception handled.

In addition, handlers must be inserted to remove activation records when a function/method ends because of an exception.

This strategy has significant runtime costs, because we must maintain the stack of exception handlers as the normal flow of execution passes through them. Thus, we are constantly paying for the rare case when an exception is thrown.