[docs][Bugpoint]Add notes about multiple crashes

Summary:
    When reducing case for a CodeGenCrash, bugpoint may generate a new
    reduced
    testcase that exposes/causes another crash or break something due to
    limitation.

    Bugpoint does not distiguish different crashes currently,
    so when this happens, bugpoint will go on reducing for the new crash,
    or just abort, we can't get the case reduced for the origial crash.

    An advice is added into usage doc to connect to recommend checking error
    message with scripts and `-compile-command`.

Reviewers: modocache, bogner, sebpop, reames, vsk, MatzeB

Reviewed By: vsk

Subscribers: mehdi_amini, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66832

llvm-svn: 372157

diff --git a/llvm/docs/Bugpoint.rst b/llvm/docs/Bugpoint.rst
index f3bb54c..7477817 100644 (file)
--- a/llvm/docs/Bugpoint.rst
+++ b/llvm/docs/Bugpoint.rst
@@ -121,6 +121,12 @@ non-obvious ways.  Here are some hints and tips:
   miscompilation.  Programs should be temporarily modified to disable outputs
   that are likely to vary from run to run.
 
+* In the `crash debugger`_, ``bugpoint`` does not distiguish different crashes
+  during reduction. Thus, if new crash or miscompilation happens, ``bugpoint``
+  will continue with the new crash instead. If you would like to stick to
+  particular crash, you should write check scripts to validate the error
+  message, see ``-compile-command`` in :doc:`/Bugpoint`_.
+
 * In the code generator and miscompilation debuggers, debugging will go faster
   if you manually modify the program or its inputs to reduce the runtime, but
   still exhibit the problem.