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<a name="Pass-manager"></a>
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Next: <a href="Tree-SSA-passes.html#Tree-SSA-passes" accesskey="n" rel="next">Tree SSA passes</a>, Previous: <a href="Gimplification-pass.html#Gimplification-pass" accesskey="p" rel="prev">Gimplification pass</a>, Up: <a href="Passes.html#Passes" accesskey="u" rel="up">Passes</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Pass-manager-1"></a>
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<h3 class="section">9.4 Pass manager</h3>
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<p>The pass manager is located in <samp>passes.c</samp>, <samp>tree-optimize.c</samp>
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and <samp>tree-pass.h</samp>.
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It processes passes as described in <samp>passes.def</samp>.
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Its job is to run all of the individual passes in the correct order,
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and take care of standard bookkeeping that applies to every pass.
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</p>
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<p>The theory of operation is that each pass defines a structure that
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represents everything we need to know about that pass—when it
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should be run, how it should be run, what intermediate language
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form or on-the-side data structures it needs. We register the pass
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to be run in some particular order, and the pass manager arranges
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for everything to happen in the correct order.
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</p>
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<p>The actuality doesn’t completely live up to the theory at present.
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Command-line switches and <code>timevar_id_t</code> enumerations must still
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be defined elsewhere. The pass manager validates constraints but does
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not attempt to (re-)generate data structures or lower intermediate
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language form based on the requirements of the next pass. Nevertheless,
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what is present is useful, and a far sight better than nothing at all.
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</p>
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<p>Each pass should have a unique name.
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Each pass may have its own dump file (for GCC debugging purposes).
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Passes with a name starting with a star do not dump anything.
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Sometimes passes are supposed to share a dump file / option name.
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To still give these unique names, you can use a prefix that is delimited
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by a space from the part that is used for the dump file / option name.
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E.g. When the pass name is "ud dce", the name used for dump file/options
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is "dce".
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</p>
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<p>TODO: describe the global variables set up by the pass manager,
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and a brief description of how a new pass should use it.
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I need to look at what info RTL passes use first<small class="enddots">...</small>
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Next: <a href="Tree-SSA-passes.html#Tree-SSA-passes" accesskey="n" rel="next">Tree SSA passes</a>, Previous: <a href="Gimplification-pass.html#Gimplification-pass" accesskey="p" rel="prev">Gimplification pass</a>, Up: <a href="Passes.html#Passes" accesskey="u" rel="up">Passes</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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