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117 lines
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117 lines
5.4 KiB
HTML
4 years ago
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<title>Loop querying - GNU Compiler Collection (GCC) Internals</title>
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<link rel="up" href="Loop-Analysis-and-Representation.html#Loop-Analysis-and-Representation" title="Loop Analysis and Representation">
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<link rel="prev" href="Loop-representation.html#Loop-representation" title="Loop representation">
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<link rel="next" href="Loop-manipulation.html#Loop-manipulation" title="Loop manipulation">
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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</head>
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<body>
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<div class="node">
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<a name="Loop-querying"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Loop-manipulation.html#Loop-manipulation">Loop manipulation</a>,
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Previous: <a rel="previous" accesskey="p" href="Loop-representation.html#Loop-representation">Loop representation</a>,
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Up: <a rel="up" accesskey="u" href="Loop-Analysis-and-Representation.html#Loop-Analysis-and-Representation">Loop Analysis and Representation</a>
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<hr>
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</div>
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<h3 class="section">15.2 Loop querying</h3>
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<p><a name="index-Loop-querying-3231"></a>
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The functions to query the information about loops are declared in
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<samp><span class="file">cfgloop.h</span></samp>. Some of the information can be taken directly from
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the structures. <code>loop_father</code> field of each basic block contains
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the innermost loop to that the block belongs. The most useful fields of
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loop structure (that are kept up-to-date at all times) are:
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<ul>
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<li><code>header</code>, <code>latch</code>: Header and latch basic blocks of the
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loop.
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<li><code>num_nodes</code>: Number of basic blocks in the loop (including
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the basic blocks of the sub-loops).
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<li><code>depth</code>: The depth of the loop in the loops tree, i.e., the
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number of super-loops of the loop.
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<li><code>outer</code>, <code>inner</code>, <code>next</code>: The super-loop, the first
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sub-loop, and the sibling of the loop in the loops tree.
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</ul>
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<p>There are other fields in the loop structures, many of them used only by
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some of the passes, or not updated during CFG changes; in general, they
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should not be accessed directly.
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<p>The most important functions to query loop structures are:
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<ul>
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<li><code>flow_loops_dump</code>: Dumps the information about loops to a
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file.
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<li><code>verify_loop_structure</code>: Checks consistency of the loop
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structures.
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<li><code>loop_latch_edge</code>: Returns the latch edge of a loop.
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<li><code>loop_preheader_edge</code>: If loops have preheaders, returns
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the preheader edge of a loop.
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<li><code>flow_loop_nested_p</code>: Tests whether loop is a sub-loop of
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another loop.
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<li><code>flow_bb_inside_loop_p</code>: Tests whether a basic block belongs
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to a loop (including its sub-loops).
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<li><code>find_common_loop</code>: Finds the common super-loop of two loops.
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<li><code>superloop_at_depth</code>: Returns the super-loop of a loop with
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the given depth.
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<li><code>tree_num_loop_insns</code>, <code>num_loop_insns</code>: Estimates the
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number of insns in the loop, on GIMPLE and on RTL.
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<li><code>loop_exit_edge_p</code>: Tests whether edge is an exit from a
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loop.
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<li><code>mark_loop_exit_edges</code>: Marks all exit edges of all loops
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with <code>EDGE_LOOP_EXIT</code> flag.
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<li><code>get_loop_body</code>, <code>get_loop_body_in_dom_order</code>,
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<code>get_loop_body_in_bfs_order</code>: Enumerates the basic blocks in the
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loop in depth-first search order in reversed CFG, ordered by dominance
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relation, and breath-first search order, respectively.
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<li><code>single_exit</code>: Returns the single exit edge of the loop, or
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<code>NULL</code> if the loop has more than one exit. You can only use this
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function if LOOPS_HAVE_MARKED_SINGLE_EXITS property is used.
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<li><code>get_loop_exit_edges</code>: Enumerates the exit edges of a loop.
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<li><code>just_once_each_iteration_p</code>: Returns true if the basic block
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is executed exactly once during each iteration of a loop (that is, it
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does not belong to a sub-loop, and it dominates the latch of the loop).
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</ul>
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</body></html>
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