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Node:<a name="MMIX-Expand">MMIX-Expand</a>,

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<h4 class="section">Instruction expansion</h4>



   <p>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><code>GETA</code>

     <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><code>PUSHJ</code>

     <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><code>JMP</code>

     <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 <code>--relax</code> (though not currently implemented).



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