| <html lang="en"> |
| <head> |
| <title>MMIX-Expand - Using as</title> |
| <meta http-equiv="Content-Type" content="text/html"> |
| <meta name="description" content="Using as"> |
| <meta name="generator" content="makeinfo 4.13"> |
| <link title="Top" rel="start" href="index.html#Top"> |
| <link rel="up" href="MMIX_002dDependent.html#MMIX_002dDependent" title="MMIX-Dependent"> |
| <link rel="prev" href="MMIX_002dOpts.html#MMIX_002dOpts" title="MMIX-Opts"> |
| <link rel="next" href="MMIX_002dSyntax.html#MMIX_002dSyntax" title="MMIX-Syntax"> |
| <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> |
| <!-- |
| This file documents the GNU Assembler "as". |
| |
| Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, |
| 2000, 2001, 2002, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.3 |
| or any later version published by the Free Software Foundation; |
| with no Invariant Sections, with no Front-Cover Texts, and with no |
| Back-Cover Texts. A copy of the license is included in the |
| section entitled ``GNU Free Documentation License''. |
| |
| --> |
| <meta http-equiv="Content-Style-Type" content="text/css"> |
| <style type="text/css"><!-- |
| pre.display { font-family:inherit } |
| pre.format { font-family:inherit } |
| pre.smalldisplay { font-family:inherit; font-size:smaller } |
| pre.smallformat { font-family:inherit; font-size:smaller } |
| pre.smallexample { font-size:smaller } |
| pre.smalllisp { font-size:smaller } |
| span.sc { font-variant:small-caps } |
| span.roman { font-family:serif; font-weight:normal; } |
| span.sansserif { font-family:sans-serif; font-weight:normal; } |
| --></style> |
| <link rel="stylesheet" type="text/css" href="../cs.css"> |
| </head> |
| <body> |
| <div class="node"> |
| <a name="MMIX-Expand"></a> |
| <a name="MMIX_002dExpand"></a> |
| <p> |
| Next: <a rel="next" accesskey="n" href="MMIX_002dSyntax.html#MMIX_002dSyntax">MMIX-Syntax</a>, |
| Previous: <a rel="previous" accesskey="p" href="MMIX_002dOpts.html#MMIX_002dOpts">MMIX-Opts</a>, |
| Up: <a rel="up" accesskey="u" href="MMIX_002dDependent.html#MMIX_002dDependent">MMIX-Dependent</a> |
| <hr> |
| </div> |
| |
| <h4 class="subsection">9.25.2 Instruction expansion</h4> |
| |
| <p><a name="index-instruction-expansion_002c-MMIX-1325"></a>When <code>as</code> encounters an instruction with an operand that is |
| either not known or does not fit the operand size of the instruction, |
| <code>as</code> (and <code>ld</code>) will expand the instruction into |
| a sequence of instructions semantically equivalent to the operand fitting |
| the instruction. Expansion will take place for the following |
| instructions: |
| |
| <dl> |
| <dt>‘<samp><span class="samp">GETA</span></samp>’<dd>Expands to a sequence of four instructions: <code>SETL</code>, <code>INCML</code>, |
| <code>INCMH</code> and <code>INCH</code>. The operand must be a multiple of four. |
| <br><dt>Conditional branches<dd>A branch instruction is turned into a branch with the complemented |
| condition and prediction bit over five instructions; four instructions |
| setting <code>$255</code> to the operand value, which like with <code>GETA</code> must |
| be a multiple of four, and a final <code>GO $255,$255,0</code>. |
| <br><dt>‘<samp><span class="samp">PUSHJ</span></samp>’<dd>Similar to expansion for conditional branches; four instructions set |
| <code>$255</code> to the operand value, followed by a <code>PUSHGO $255,$255,0</code>. |
| <br><dt>‘<samp><span class="samp">JMP</span></samp>’<dd>Similar to conditional branches and <code>PUSHJ</code>. The final instruction |
| is <code>GO $255,$255,0</code>. |
| </dl> |
| |
| <p>The linker <code>ld</code> is expected to shrink these expansions for |
| code assembled with ‘<samp><span class="samp">--relax</span></samp>’ (though not currently implemented). |
| |
| </body></html> |
| |