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1 ==================================================
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2 Tips and Tricks on using and contributing to Polly
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3 ==================================================
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4
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5 Commiting to polly trunk
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6 ------------------------
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7 - `General reference to git-svn workflow <https://stackoverflow.com/questions/190431/is-git-svn-dcommit-after-merging-in-git-dangerous>`_
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8
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9
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10 Using bugpoint to track down errors in large files
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11 --------------------------------------------------
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12
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13 If you know the ``opt`` invocation and have a large ``.ll`` file that causes
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14 an error, ``bugpoint`` allows one to reduce the size of test cases.
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15
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16 The general calling pattern is:
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17
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18 - ``$ bugpoint <file.ll> <pass that causes the crash> -opt-args <opt option flags>``
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19
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20 An example invocation is:
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21
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22 - ``$ bugpoint crash.ll -polly-codegen -opt-args -polly-canonicalize -polly-process-unprofitable``
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23
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24 For more documentation on bugpoint, `Visit the LLVM manual <http://llvm.org/docs/Bugpoint.html>`_
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25
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26
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27 Understanding which pass makes a particular change
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28 --------------------------------------------------
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29
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30 If you know that something like `opt -O3 -polly` makes a change, but you wish to
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31 isolate which pass makes a change, the steps are as follows:
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32
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33 - ``$ bugpoint -O3 file.ll -opt-args -polly`` will allow bugpoint to track down the pass which causes the crash.
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34
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35 To do this manually:
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36
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37 - ``$ 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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38 - Bisect down to the pass that changes it.
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39
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40
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41 Debugging regressions introduced at some unknown earlier point
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42 --------------------------------------------------------------
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43
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44 In case of a regression in performance or correctness (e.g., an earlier version
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45 of Polly behaved as expected and a later version does not), bisecting over the
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46 version history is the standard approach to identify the commit that introduced
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47 the regression.
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48
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49 LLVM has a single repository that contains all projects. It can be cloned at:
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50 `<https://github.com/llvm/llvm-project>`_. How to bisect on a
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51 git repository is explained here
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52 `<https://www.metaltoad.com/blog/beginners-guide-git-bisect-process-elimination>`_.
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53 The bisect process can also be automated as explained here:
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54 `<https://www.metaltoad.com/blog/mechanizing-git-bisect-bug-hunting-lazy>`_.
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55 An LLVM specific run script is available here:
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56 `<https://gist.github.com/dcci/891cd98d80b1b95352a407d80914f7cf>`_.
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