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+<title>GNU Compiler Collection (GCC) Internals: Loop querying</title>
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+<a name="Loop-querying"></a>
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+<p>
+Next: <a href="Loop-manipulation.html#Loop-manipulation" accesskey="n" rel="next">Loop manipulation</a>, Previous: <a href="Loop-representation.html#Loop-representation" accesskey="p" rel="previous">Loop representation</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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+<hr>
+<a name="Loop-querying-1"></a>
+<h3 class="section">16.2 Loop querying</h3>
+<a name="index-Loop-querying"></a>
+
+<p>The functions to query the information about loops are declared in
+<samp>cfgloop.h</samp>.  Some of the information can be taken directly from
+the structures.  <code>loop_father</code> field of each basic block contains
+the innermost loop to that the block belongs.  The most useful fields of
+loop structure (that are kept up-to-date at all times) are:
+</p>
+<ul>
+<li> <code>header</code>, <code>latch</code>: Header and latch basic blocks of the
+loop.
+</li><li> <code>num_nodes</code>: Number of basic blocks in the loop (including
+the basic blocks of the sub-loops).
+</li><li> <code>outer</code>, <code>inner</code>, <code>next</code>: The super-loop, the first
+sub-loop, and the sibling of the loop in the loops tree.
+</li></ul>
+
+<p>There are other fields in the loop structures, many of them used only by
+some of the passes, or not updated during CFG changes; in general, they
+should not be accessed directly.
+</p>
+<p>The most important functions to query loop structures are:
+</p>
+<ul>
+<li> <code>loop_depth</code>: The depth of the loop in the loops tree, i.e., the
+number of super-loops of the loop.
+</li><li> <code>flow_loops_dump</code>: Dumps the information about loops to a
+file.
+</li><li> <code>verify_loop_structure</code>: Checks consistency of the loop
+structures.
+</li><li> <code>loop_latch_edge</code>: Returns the latch edge of a loop.
+</li><li> <code>loop_preheader_edge</code>: If loops have preheaders, returns
+the preheader edge of a loop.
+</li><li> <code>flow_loop_nested_p</code>: Tests whether loop is a sub-loop of
+another loop.
+</li><li> <code>flow_bb_inside_loop_p</code>: Tests whether a basic block belongs
+to a loop (including its sub-loops).
+</li><li> <code>find_common_loop</code>: Finds the common super-loop of two loops.
+</li><li> <code>superloop_at_depth</code>: Returns the super-loop of a loop with
+the given depth.
+</li><li> <code>tree_num_loop_insns</code>, <code>num_loop_insns</code>: Estimates the
+number of insns in the loop, on GIMPLE and on RTL.
+</li><li> <code>loop_exit_edge_p</code>: Tests whether edge is an exit from a
+loop.
+</li><li> <code>mark_loop_exit_edges</code>: Marks all exit edges of all loops
+with <code>EDGE_LOOP_EXIT</code> flag.
+</li><li> <code>get_loop_body</code>, <code>get_loop_body_in_dom_order</code>,
+<code>get_loop_body_in_bfs_order</code>: Enumerates the basic blocks in the
+loop in depth-first search order in reversed CFG, ordered by dominance
+relation, and breath-first search order, respectively.
+</li><li> <code>single_exit</code>: Returns the single exit edge of the loop, or
+<code>NULL</code> if the loop has more than one exit.  You can only use this
+function if <code>LOOPS_HAVE_RECORDED_EXITS</code> is used.
+</li><li> <code>get_loop_exit_edges</code>: Enumerates the exit edges of a loop.
+</li><li> <code>just_once_each_iteration_p</code>: Returns true if the basic block
+is executed exactly once during each iteration of a loop (that is, it
+does not belong to a sub-loop, and it dominates the latch of the loop).
+</li></ul>
+
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