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| Next: <a href="Examples.html#Examples" accesskey="n" rel="next">Examples</a>, Previous: <a href="Defining-Mode-Iterators.html#Defining-Mode-Iterators" accesskey="p" rel="prev">Defining Mode Iterators</a>, Up: <a href="Mode-Iterators.html#Mode-Iterators" accesskey="u" rel="up">Mode Iterators</a> [<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="Substitution-in-Mode-Iterators"></a> |
| <h4 class="subsubsection">16.23.1.2 Substitution in Mode Iterators</h4> |
| <a name="index-define_005fmode_005fattr"></a> |
| |
| <p>If an <samp>.md</samp> file construct uses mode iterators, each version of the |
| construct will often need slightly different strings or modes. For |
| example: |
| </p> |
| <ul> |
| <li> When a <code>define_expand</code> defines several <code>add<var>m</var>3</code> patterns |
| (see <a href="Standard-Names.html#Standard-Names">Standard Names</a>), each expander will need to use the |
| appropriate mode name for <var>m</var>. |
| |
| </li><li> When a <code>define_insn</code> defines several instruction patterns, |
| each instruction will often use a different assembler mnemonic. |
| |
| </li><li> When a <code>define_insn</code> requires operands with different modes, |
| using an iterator for one of the operand modes usually requires a specific |
| mode for the other operand(s). |
| </li></ul> |
| |
| <p>GCC supports such variations through a system of “mode attributes”. |
| There are two standard attributes: <code>mode</code>, which is the name of |
| the mode in lower case, and <code>MODE</code>, which is the same thing in |
| upper case. You can define other attributes using: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(define_mode_attr <var>name</var> [(<var>mode1</var> "<var>value1</var>") … (<var>moden</var> "<var>valuen</var>")]) |
| </pre></div> |
| |
| <p>where <var>name</var> is the name of the attribute and <var>valuei</var> |
| is the value associated with <var>modei</var>. |
| </p> |
| <p>When GCC replaces some <var>:iterator</var> with <var>:mode</var>, it will scan |
| each string and mode in the pattern for sequences of the form |
| <code><<var>iterator</var>:<var>attr</var>></code>, where <var>attr</var> is the name of a |
| mode attribute. If the attribute is defined for <var>mode</var>, the whole |
| <code><…></code> sequence will be replaced by the appropriate attribute |
| value. |
| </p> |
| <p>For example, suppose an <samp>.md</samp> file has: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(define_mode_iterator P [(SI "Pmode == SImode") (DI "Pmode == DImode")]) |
| (define_mode_attr load [(SI "lw") (DI "ld")]) |
| </pre></div> |
| |
| <p>If one of the patterns that uses <code>:P</code> contains the string |
| <code>"<P:load>\t%0,%1"</code>, the <code>SI</code> version of that pattern |
| will use <code>"lw\t%0,%1"</code> and the <code>DI</code> version will use |
| <code>"ld\t%0,%1"</code>. |
| </p> |
| <p>Here is an example of using an attribute for a mode: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(define_mode_iterator LONG [SI DI]) |
| (define_mode_attr SHORT [(SI "HI") (DI "SI")]) |
| (define_insn … |
| (sign_extend:LONG (match_operand:<LONG:SHORT> …)) …) |
| </pre></div> |
| |
| <p>The <code><var>iterator</var>:</code> prefix may be omitted, in which case the |
| substitution will be attempted for every iterator expansion. |
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