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| <h4 class="subsection">9.28.2 Instruction expansion</h4> |
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| <p><a name="index-instruction-expansion_002c-MMIX-1680"></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). |
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