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| <a name="IV-analysis-on-RTL"></a> |
| <h3 class="section">15.6 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> |
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