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+<p>
+Next: <a href="LCSSA.html#LCSSA" accesskey="n" rel="next">LCSSA</a>, Previous: <a href="Loop-querying.html#Loop-querying" accesskey="p" rel="previous">Loop querying</a>, Up: <a href="Loop-Analysis-and-Representation.html#Loop-Analysis-and-Representation" accesskey="u" rel="up">Loop Analysis and Representation</a> &nbsp; [<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">16.3 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_body_to_header_edge</code>,
+<code>tree_duplicate_loop_body_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>: This function creates 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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