-------------------------------------------------
This pass munges the code in the input function to better prepare it for
-SelectionDAG-based code generation. This works around limitations in it's
+SelectionDAG-based code generation. This works around limitations in its
basic-block-at-a-time approach. It should eventually be removed.
``-constmerge``: Merge Duplicate Global Constants
``-constprop``: Simple constant propagation
-------------------------------------------
-This file implements constant propagation and merging. It looks for
+This pass implements constant propagation and merging. It looks for
instructions involving only constant operands and replaces them with a constant
value instead of an instruction. For example:
i32 3
NOTE: this pass has a habit of making definitions be dead. It is a good idea
-to to run a :ref:`Dead Instruction Elimination <passes-die>` pass sometime
-after running this pass.
+to run a :ref:`Dead Instruction Elimination <passes-die>` pass sometime after
+running this pass.
.. _passes-dce:
any libraries which may not be available in bitcode form); it simply lowers
every atomic intrinsic.
-``-lowerinvoke``: Lower invoke and unwind, for unwindless code generators
--------------------------------------------------------------------------
+``-lowerinvoke``: Lower invokes to calls, for unwindless code generators
+------------------------------------------------------------------------
This transformation is designed for use by code generators which do not yet
-support stack unwinding. This pass supports two models of exception handling
-lowering, the "cheap" support and the "expensive" support.
-
-"Cheap" exception handling support gives the program the ability to execute any
-program which does not "throw an exception", by turning "``invoke``"
-instructions into calls and by turning "``unwind``" instructions into calls to
-``abort()``. If the program does dynamically use the "``unwind``" instruction,
-the program will print a message then abort.
-
-"Expensive" exception handling support gives the full exception handling
-support to the program at the cost of making the "``invoke``" instruction
-really expensive. It basically inserts ``setjmp``/``longjmp`` calls to emulate
-the exception handling as necessary.
-
-Because the "expensive" support slows down programs a lot, and EH is only used
-for a subset of the programs, it must be specifically enabled by the
-``-enable-correct-eh-support`` option.
-
-Note that after this pass runs the CFG is not entirely accurate (exceptional
-control flow edges are not correct anymore) so only very simple things should
-be done after the ``lowerinvoke`` pass has run (like generation of native
-code). This should not be used as a general purpose "my LLVM-to-LLVM pass
-doesn't support the ``invoke`` instruction yet" lowering pass.
+support stack unwinding. This pass converts ``invoke`` instructions to
+``call`` instructions, so that any exception-handling ``landingpad`` blocks
+become dead code (which can be removed by running the ``-simplifycfg`` pass
+afterwards).
``-lowerswitch``: Lower ``SwitchInst``\ s to branches
-----------------------------------------------------
* Proves conditional branches to be unconditional
Note that this pass has a habit of making definitions be dead. It is a good
-idea to to run a :ref:`DCE <passes-dce>` pass sometime after running this pass.
+idea to run a :ref:`DCE <passes-dce>` pass sometime after running this pass.
``-simplify-libcalls``: Simplify well-known library calls
---------------------------------------------------------