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==================================================
Tips and Tricks on using and contributing to Polly
==================================================
Commiting to polly trunk
------------------------
- `General reference to git-svn workflow <https://stackoverflow.com/questions/190431/is-git-svn-dcommit-after-merging-in-git-dangerous>`_
Using bugpoint to track down errors in large files
--------------------------------------------------
If you know the ``opt`` invocation and have a large ``.ll`` file that causes
an error, ``bugpoint`` allows one to reduce the size of test cases.
The general calling pattern is:
- ``$ bugpoint <file.ll> <pass that causes the crash> -opt-args <opt option flags>``
An example invocation is:
- ``$ bugpoint crash.ll -polly-codegen -opt-args -polly-canonicalize -polly-process-unprofitable``
For more documentation on bugpoint, `Visit the LLVM manual <https://llvm.org/docs/Bugpoint.html>`_
Understanding which pass makes a particular change
--------------------------------------------------
If you know that something like `opt -O3 -polly` makes a change, but you wish to
isolate which pass makes a change, the steps are as follows:
- ``$ bugpoint -O3 file.ll -opt-args -polly`` will allow bugpoint to track down the pass which causes the crash.
To do this manually:
- ``$ opt -O3 -polly -debug-pass=Arguments`` to get all passes that are run by default. ``-debug-pass=Arguments`` will list all passes that have run.
- Bisect down to the pass that changes it.
Debugging regressions introduced at some unknown earlier point
--------------------------------------------------------------
In case of a regression in performance or correctness (e.g., an earlier version
of Polly behaved as expected and a later version does not), bisecting over the
version history is the standard approach to identify the commit that introduced
the regression.
LLVM has a single repository that contains all projects. It can be cloned at:
`<https://github.com/llvm/llvm-project>`_. How to bisect on a
git repository is explained here
`<https://www.metaltoad.com/blog/beginners-guide-git-bisect-process-elimination>`_.
The bisect process can also be automated as explained here:
`<https://www.metaltoad.com/blog/mechanizing-git-bisect-bug-hunting-lazy>`_.
An LLVM specific run script is available here:
`<https://gist.github.com/dcci/891cd98d80b1b95352a407d80914f7cf>`_.
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