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