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How to express this complicated constraint in md file


Hi,

I have not been able to find an answer in the ".md" files i've read
through, or the docs, so I wanted to try here.

If we have an instruction on a machine that does "ADD x, y", where
register x is both input and output, in the ".md" file one can express
this easily (referencing it as "0" instead of "r"). But what if sizes
differ? Consider a hypothetical instruction on a 32-bit machine:

WUMUL x, y     which will multiply 32-bit register x by 32-bit
register y, and produce a 64-bit result, storing the high bits into
register x and low bits into register y

Despite all the searching, I still do not quite know how to express
this in the ".md" file
Are there more docs I need to read? Is there an obvious solution I am missing?


Thanks,
Dmitry


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