(gccint.info.gz) GIMPLE Exception Handling

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 12.3 Exception Handling
 =======================
 
 Other exception handling constructs are represented using
 `GIMPLE_TRY_CATCH'.  `GIMPLE_TRY_CATCH' has two operands.  The first
 operand is a sequence of statements to execute.  If executing these
 statements does not throw an exception, then the second operand is
 ignored.  Otherwise, if an exception is thrown, then the second operand
 of the `GIMPLE_TRY_CATCH' is checked.  The second operand may have the
 following forms:
 
   1. A sequence of statements to execute.  When an exception occurs,
      these statements are executed, and then the exception is rethrown.
 
   2. A sequence of `GIMPLE_CATCH' statements.  Each `GIMPLE_CATCH' has
      a list of applicable exception types and handler code.  If the
      thrown exception matches one of the caught types, the associated
      handler code is executed.  If the handler code falls off the
      bottom, execution continues after the original `GIMPLE_TRY_CATCH'.
 
   3. An `GIMPLE_EH_FILTER' statement.  This has a list of permitted
      exception types, and code to handle a match failure.  If the
      thrown exception does not match one of the allowed types, the
      associated match failure code is executed.  If the thrown exception
      does match, it continues unwinding the stack looking for the next
      handler.
 
 
  Currently throwing an exception is not directly represented in GIMPLE,
 since it is implemented by calling a function.  At some point in the
 future we will want to add some way to express that the call will throw
 an exception of a known type.
 
  Just before running the optimizers, the compiler lowers the high-level
 EH constructs above into a set of `goto's, magic labels, and EH
 regions.  Continuing to unwind at the end of a cleanup is represented
 with a `GIMPLE_RESX'.
 

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