gcc/doc/gccint/gimple/exception-handling.rst

   1 ..
   2   Copyright 1988-2022 Free Software Foundation, Inc.
   3   This is part of the GCC manual.
   4   For copying conditions, see the copyright.rst file.
   5
   6 .. index:: GIMPLE Exception Handling
   7
   8 .. _gimple-exception-handling:
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  10 Exception Handling
  11 ******************
  12
  13 Other exception handling constructs are represented using
  14 ``GIMPLE_TRY_CATCH``.  ``GIMPLE_TRY_CATCH`` has two operands.  The
  15 first operand is a sequence of statements to execute.  If executing
  16 these statements does not throw an exception, then the second operand
  17 is ignored.  Otherwise, if an exception is thrown, then the second
  18 operand of the ``GIMPLE_TRY_CATCH`` is checked.  The second
  19 operand may have the following forms:
  20
  21 * A sequence of statements to execute.  When an exception occurs,
  22   these statements are executed, and then the exception is rethrown.
  23
  24 * A sequence of ``GIMPLE_CATCH`` statements.  Each
  25   ``GIMPLE_CATCH`` has a list of applicable exception types and
  26   handler code.  If the thrown exception matches one of the caught
  27   types, the associated handler code is executed.  If the handler
  28   code falls off the bottom, execution continues after the original
  29   ``GIMPLE_TRY_CATCH``.
  30
  31 * A ``GIMPLE_EH_FILTER`` statement.  This has a list of
  32   permitted exception types, and code to handle a match failure.  If the
  33   thrown exception does not match one of the allowed types, the
  34   associated match failure code is executed.  If the thrown exception
  35   does match, it continues unwinding the stack looking for the next
  36   handler.
  37
  38 Currently throwing an exception is not directly represented in
  39 GIMPLE, since it is implemented by calling a function.  At some
  40 point in the future we will want to add some way to express that
  41 the call will throw an exception of a known type.
  42
  43 Just before running the optimizers, the compiler lowers the
  44 high-level EH constructs above into a set of ``goto`` s, magic
  45 labels, and EH regions.  Continuing to unwind at the end of a
  46 cleanup is represented with a ``GIMPLE_RESX``.