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| <a name="Assembler-Instructions-as-Expressions"></a> |
| <h3 class="section">13.17 Assembler Instructions as Expressions</h3> |
| <a name="index-assembler-instructions-in-RTL"></a> |
| |
| <a name="index-asm_005foperands_002c-usage"></a> |
| <p>The RTX code <code>asm_operands</code> represents a value produced by a |
| user-specified assembler instruction. It is used to represent |
| an <code>asm</code> statement with arguments. An <code>asm</code> statement with |
| a single output operand, like this: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">asm ("foo %1,%2,%0" : "=a" (outputvar) : "g" (x + y), "di" (*z)); |
| </pre></div> |
| |
| <p>is represented using a single <code>asm_operands</code> RTX which represents |
| the value that is stored in <code>outputvar</code>: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(set <var>rtx-for-outputvar</var> |
| (asm_operands "foo %1,%2,%0" "a" 0 |
| [<var>rtx-for-addition-result</var> <var>rtx-for-*z</var>] |
| [(asm_input:<var>m1</var> "g") |
| (asm_input:<var>m2</var> "di")])) |
| </pre></div> |
| |
| <p>Here the operands of the <code>asm_operands</code> RTX are the assembler |
| template string, the output-operand’s constraint, the index-number of the |
| output operand among the output operands specified, a vector of input |
| operand RTX’s, and a vector of input-operand modes and constraints. The |
| mode <var>m1</var> is the mode of the sum <code>x+y</code>; <var>m2</var> is that of |
| <code>*z</code>. |
| </p> |
| <p>When an <code>asm</code> statement has multiple output values, its insn has |
| several such <code>set</code> RTX’s inside of a <code>parallel</code>. Each <code>set</code> |
| contains an <code>asm_operands</code>; all of these share the same assembler |
| template and vectors, but each contains the constraint for the respective |
| output operand. They are also distinguished by the output-operand index |
| number, which is 0, 1, … for successive output operands. |
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