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| <a name="Loop-manipulation"></a> |
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| Next: <a href="LCSSA.html#LCSSA" accesskey="n" rel="next">LCSSA</a>, Previous: <a href="Loop-querying.html#Loop-querying" accesskey="p" rel="prev">Loop querying</a>, Up: <a href="Loop-Analysis-and-Representation.html#Loop-Analysis-and-Representation" accesskey="u" rel="up">Loop Analysis and Representation</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="Loop-manipulation-1"></a> |
| <h3 class="section">15.3 Loop manipulation</h3> |
| <a name="index-Loop-manipulation"></a> |
| |
| <p>The loops tree can be manipulated using the following functions: |
| </p> |
| <ul> |
| <li> <code>flow_loop_tree_node_add</code>: Adds a node to the tree. |
| </li><li> <code>flow_loop_tree_node_remove</code>: Removes a node from the tree. |
| </li><li> <code>add_bb_to_loop</code>: Adds a basic block to a loop. |
| </li><li> <code>remove_bb_from_loops</code>: Removes a basic block from loops. |
| </li></ul> |
| |
| <p>Most low-level CFG functions update loops automatically. The following |
| functions handle some more complicated cases of CFG manipulations: |
| </p> |
| <ul> |
| <li> <code>remove_path</code>: Removes an edge and all blocks it dominates. |
| </li><li> <code>split_loop_exit_edge</code>: Splits exit edge of the loop, |
| ensuring that PHI node arguments remain in the loop (this ensures that |
| loop-closed SSA form is preserved). Only useful on GIMPLE. |
| </li></ul> |
| |
| <p>Finally, there are some higher-level loop transformations implemented. |
| While some of them are written so that they should work on non-innermost |
| loops, they are mostly untested in that case, and at the moment, they |
| are only reliable for the innermost loops: |
| </p> |
| <ul> |
| <li> <code>create_iv</code>: Creates a new induction variable. Only works on |
| GIMPLE. <code>standard_iv_increment_position</code> can be used to find a |
| suitable place for the iv increment. |
| </li><li> <code>duplicate_loop_to_header_edge</code>, |
| <code>tree_duplicate_loop_to_header_edge</code>: These functions (on RTL and |
| on GIMPLE) duplicate the body of the loop prescribed number of times on |
| one of the edges entering loop header, thus performing either loop |
| unrolling or loop peeling. <code>can_duplicate_loop_p</code> |
| (<code>can_unroll_loop_p</code> on GIMPLE) must be true for the duplicated |
| loop. |
| </li><li> <code>loop_version</code>, <code>tree_ssa_loop_version</code>: These function |
| create a copy of a loop, and a branch before them that selects one of |
| them depending on the prescribed condition. This is useful for |
| optimizations that need to verify some assumptions in runtime (one of |
| the copies of the loop is usually left unchanged, while the other one is |
| transformed in some way). |
| </li><li> <code>tree_unroll_loop</code>: Unrolls the loop, including peeling the |
| extra iterations to make the number of iterations divisible by unroll |
| factor, updating the exit condition, and removing the exits that now |
| cannot be taken. Works only on GIMPLE. |
| </li></ul> |
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