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(as.info)MMIX-Expand

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Instruction expansion
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   When `as' encounters an instruction with an operand that is either
not known or does not fit the operand size of the instruction, `as'
(and `ld') 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:

`GETA'
     Expands to a sequence of four instructions: `SETL', `INCML',
     `INCMH' and `INCH'.  The operand must be a multiple of four.

Conditional branches
     A branch instruction is turned into a branch with the complemented
     condition and prediction bit over five instructions; four
     instructions setting `$255' to the operand value, which like with
     `GETA' must be a multiple of four, and a final `GO $255,$255,0'.

`PUSHJ'
     Similar to expansion for conditional branches; four instructions
     set `$255' to the operand value, followed by a `PUSHGO
     $255,$255,0'.

`JMP'
     Similar to conditional branches and `PUSHJ'.  The final instruction
     is `GO $255,$255,0'.

   The linker `ld' is expected to shrink these expansions for code
assembled with `--relax' (though not currently implemented).