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90 lines
4.1 KiB
HTML
90 lines
4.1 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>Assembler - GNU Compiler Collection (GCC) Internals</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="GNU Compiler Collection (GCC) Internals">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="RTL.html#RTL" title="RTL">
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<link rel="prev" href="Incdec.html#Incdec" title="Incdec">
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<link rel="next" href="Debug-Information.html#Debug-Information" title="Debug Information">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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Copyright (C) 1988-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being ``Funding Free Software'', the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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``GNU Free Documentation License''.
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development.-->
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<style type="text/css"><!--
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--></style>
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</head>
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<body>
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<div class="node">
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<a name="Assembler"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Debug-Information.html#Debug-Information">Debug Information</a>,
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Previous: <a rel="previous" accesskey="p" href="Incdec.html#Incdec">Incdec</a>,
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Up: <a rel="up" accesskey="u" href="RTL.html#RTL">RTL</a>
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<hr>
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</div>
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<h3 class="section">13.17 Assembler Instructions as Expressions</h3>
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<p><a name="index-assembler-instructions-in-RTL-3062"></a>
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<a name="index-g_t_0040code_007basm_005foperands_007d_002c-usage-3063"></a>The RTX code <code>asm_operands</code> represents a value produced by a
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user-specified assembler instruction. It is used to represent
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an <code>asm</code> statement with arguments. An <code>asm</code> statement with
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a single output operand, like this:
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<pre class="smallexample"> asm ("foo %1,%2,%0" : "=a" (outputvar) : "g" (x + y), "di" (*z));
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</pre>
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<p class="noindent">is represented using a single <code>asm_operands</code> RTX which represents
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the value that is stored in <code>outputvar</code>:
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<pre class="smallexample"> (set <var>rtx-for-outputvar</var>
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(asm_operands "foo %1,%2,%0" "a" 0
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[<var>rtx-for-addition-result</var> <var>rtx-for-*z</var>]
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[(asm_input:<var>m1</var> "g")
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(asm_input:<var>m2</var> "di")]))
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</pre>
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<p class="noindent">Here the operands of the <code>asm_operands</code> RTX are the assembler
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template string, the output-operand's constraint, the index-number of the
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output operand among the output operands specified, a vector of input
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operand RTX's, and a vector of input-operand modes and constraints. The
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mode <var>m1</var> is the mode of the sum <code>x+y</code>; <var>m2</var> is that of
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<code>*z</code>.
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<p>When an <code>asm</code> statement has multiple output values, its insn has
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several such <code>set</code> RTX's inside of a <code>parallel</code>. Each <code>set</code>
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contains an <code>asm_operands</code>; all of these share the same assembler
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template and vectors, but each contains the constraint for the respective
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output operand. They are also distinguished by the output-operand index
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number, which is 0, 1, <small class="dots">...</small> for successive output operands.
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</body></html>
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