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<title>Assembler - GNU Compiler Collection (GCC) Internals</title>
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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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<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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