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