GNU Compiler Collection (GCC) Internals

9.2.4.8 Exception Handling

Other exception handling constructs are represented using TRY_CATCH_EXPR. The handler operand of a TRY_CATCH_EXPR can be a normal statement to be executed if the controlled block throws an exception, or it can have one of two special forms:

1. A CATCH_EXPR executes its handler if the thrown exception matches one of the allowed types. Multiple handlers can be expressed by a sequence of CATCH_EXPR statements.
2. An EH_FILTER_EXPR executes its handler if the thrown exception does not match one of the allowed types.

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 RESX_EXPR.