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+<p>
+Next: <a href="Number-of-iterations.html#Number-of-iterations" accesskey="n" rel="next">Number of iterations</a>, Previous: <a href="Scalar-evolutions.html#Scalar-evolutions" accesskey="p" rel="previous">Scalar evolutions</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>
+</div>
+<hr>
+<a name="IV-analysis-on-RTL"></a>
+<h3 class="section">16.6 IV analysis on RTL</h3>
+<a name="index-IV-analysis-on-RTL"></a>
+
+<p>The induction variable on RTL is simple and only allows analysis of
+affine induction variables, and only in one loop at once.  The interface
+is declared in <samp>cfgloop.h</samp>.  Before analyzing induction variables
+in a loop L, <code>iv_analysis_loop_init</code> function must be called on L.
+After the analysis (possibly calling <code>iv_analysis_loop_init</code> for
+several loops) is finished, <code>iv_analysis_done</code> should be called.
+The following functions can be used to access the results of the
+analysis:
+</p>
+<ul>
+<li> <code>iv_analyze</code>: Analyzes a single register used in the given
+insn.  If no use of the register in this insn is found, the following
+insns are scanned, so that this function can be called on the insn
+returned by get_condition.
+</li><li> <code>iv_analyze_result</code>: Analyzes result of the assignment in the
+given insn.
+</li><li> <code>iv_analyze_expr</code>: Analyzes a more complicated expression.
+All its operands are analyzed by <code>iv_analyze</code>, and hence they must
+be used in the specified insn or one of the following insns.
+</li></ul>
+
+<p>The description of the induction variable is provided in <code>struct
+rtx_iv</code>.  In order to handle subregs, the representation is a bit
+complicated; if the value of the <code>extend</code> field is not
+<code>UNKNOWN</code>, the value of the induction variable in the i-th
+iteration is
+</p>
+<div class="smallexample">
+<pre class="smallexample">delta + mult * extend_{extend_mode} (subreg_{mode} (base + i * step)),
+</pre></div>
+
+<p>with the following exception:  if <code>first_special</code> is true, then the
+value in the first iteration (when <code>i</code> is zero) is <code>delta +
+mult * base</code>.  However, if <code>extend</code> is equal to <code>UNKNOWN</code>,
+then <code>first_special</code> must be false, <code>delta</code> 0, <code>mult</code> 1
+and the value in the i-th iteration is
+</p>
+<div class="smallexample">
+<pre class="smallexample">subreg_{mode} (base + i * step)
+</pre></div>
+
+<p>The function <code>get_iv_value</code> can be used to perform these
+calculations.
+</p>
+<hr>
+<div class="header">
+<p>
+Next: <a href="Number-of-iterations.html#Number-of-iterations" accesskey="n" rel="next">Number of iterations</a>, Previous: <a href="Scalar-evolutions.html#Scalar-evolutions" accesskey="p" rel="previous">Scalar evolutions</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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