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  1. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

  2. <html>

  3. <!-- This file documents the GNU Assembler "as".

  4. 

  5. Copyright (C) 1991-2020 Free Software Foundation, Inc.

  6. 

  7. Permission is granted to copy, distribute and/or modify this document

  8. under the terms of the GNU Free Documentation License, Version 1.3

  9. or any later version published by the Free Software Foundation;

  10. with no Invariant Sections, with no Front-Cover Texts, and with no

  11. Back-Cover Texts.  A copy of the license is included in the

  12. section entitled "GNU Free Documentation License".

  13.  -->

  14. <!-- Created by GNU Texinfo 6.5, http://www.gnu.org/software/texinfo/ -->

  15. <head>

  16. <meta http-equiv="Content-Type" content="text/html; charset=utf-8">

  17. <title>MMIX-Expand (Using as)</title>

  18. 

  19. <meta name="description" content="MMIX-Expand (Using as)">

  20. <meta name="keywords" content="MMIX-Expand (Using as)">

  21. <meta name="resource-type" content="document">

  22. <meta name="distribution" content="global">

  23. <meta name="Generator" content="makeinfo">

  24. <link href="index.html#Top" rel="start" title="Top">

  25. <link href="AS-Index.html#AS-Index" rel="index" title="AS Index">

  26. <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">

  27. <link href="MMIX_002dDependent.html#MMIX_002dDependent" rel="up" title="MMIX-Dependent">

  28. <link href="MMIX_002dSyntax.html#MMIX_002dSyntax" rel="next" title="MMIX-Syntax">

  29. <link href="MMIX_002dOpts.html#MMIX_002dOpts" rel="prev" title="MMIX-Opts">

  30. <style type="text/css">

  31. <!--

  32. a.summary-letter {text-decoration: none}

  33. blockquote.indentedblock {margin-right: 0em}

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  35. blockquote.smallquotation {font-size: smaller}

  36. div.display {margin-left: 3.2em}

  37. div.example {margin-left: 3.2em}

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  39. div.smalldisplay {margin-left: 3.2em}

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  43. pre.display {font-family: inherit}

  44. pre.format {font-family: inherit}

  45. pre.menu-comment {font-family: serif}

  46. pre.menu-preformatted {font-family: serif}

  47. pre.smalldisplay {font-family: inherit; font-size: smaller}

  48. pre.smallexample {font-size: smaller}

  49. pre.smallformat {font-family: inherit; font-size: smaller}

  50. pre.smalllisp {font-size: smaller}

  51. span.nolinebreak {white-space: nowrap}

  52. span.roman {font-family: initial; font-weight: normal}

  53. span.sansserif {font-family: sans-serif; font-weight: normal}

  54. ul.no-bullet {list-style: none}

  55. -->

  56. </style>

  57. 

  58. 

  59. </head>

  60. 

  61. <body lang="en">

  62. <a name="MMIX_002dExpand"></a>

  63. <div class="header">

  64. <p>

  65. Next: <a href="MMIX_002dSyntax.html#MMIX_002dSyntax" accesskey="n" rel="next">MMIX-Syntax</a>, Previous: <a href="MMIX_002dOpts.html#MMIX_002dOpts" accesskey="p" rel="prev">MMIX-Opts</a>, Up: <a href="MMIX_002dDependent.html#MMIX_002dDependent" accesskey="u" rel="up">MMIX-Dependent</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>

  66. </div>

  67. <hr>

  68. <a name="Instruction-expansion-1"></a>

  69. <h4 class="subsection">9.28.2 Instruction expansion</h4>

  70. 

  71. <a name="index-instruction-expansion_002c-MMIX"></a>

  72. <p>When <code>as</code> encounters an instruction with an operand that is

  73. either not known or does not fit the operand size of the instruction,

  74. <code>as</code> (and <code>ld</code>) will expand the instruction into

  75. a sequence of instructions semantically equivalent to the operand fitting

  76. the instruction.  Expansion will take place for the following

  77. instructions:

  78. </p>

  79. <dl compact="compact">

  80. <dt>&lsquo;<samp>GETA</samp>&rsquo;</dt>

  81. <dd><p>Expands to a sequence of four instructions: <code>SETL</code>, <code>INCML</code>,

  82. <code>INCMH</code> and <code>INCH</code>.  The operand must be a multiple of four.

  83. </p></dd>

  84. <dt>Conditional branches</dt>

  85. <dd><p>A branch instruction is turned into a branch with the complemented

  86. condition and prediction bit over five instructions; four instructions

  87. setting <code>$255</code> to the operand value, which like with <code>GETA</code> must

  88. be a multiple of four, and a final <code>GO $255,$255,0</code>.

  89. </p></dd>

  90. <dt>&lsquo;<samp>PUSHJ</samp>&rsquo;</dt>

  91. <dd><p>Similar to expansion for conditional branches; four instructions set

  92. <code>$255</code> to the operand value, followed by a <code>PUSHGO $255,$255,0</code>.

  93. </p></dd>

  94. <dt>&lsquo;<samp>JMP</samp>&rsquo;</dt>

  95. <dd><p>Similar to conditional branches and <code>PUSHJ</code>.  The final instruction

  96. is <code>GO $255,$255,0</code>.

  97. </p></dd>

  98. </dl>

  99. 

  100. <p>The linker <code>ld</code> is expected to shrink these expansions for

  101. code assembled with &lsquo;<samp>--relax</samp>&rsquo; (though not currently implemented).

  102. </p>

  103. 

  104. 

  105. 

  106. </body>

  107. </html>