Recover TableGen/LangRef, make it official

[oota-llvm.git] / docs / Passes.rst

diff --git a/docs/Passes.rst b/docs/Passes.rst
index d30c3ca4a00ffe8745ea897730f2eb7a75169d6a..a288933b7bc1fb2de207e8b8eca5beaf33fb2913 100644 (file)
--- a/docs/Passes.rst
+++ b/docs/Passes.rst
@@ -476,7 +476,7 @@ transformation obviously invalidates the CFG, but can update forward dominator
 -------------------------------------------------
 
 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
@@ -893,33 +893,14 @@ this would require knowledge of the entire call graph of the program including
 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
 -----------------------------------------------------