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How to express this complicated constraint in md file
- From: Dmitry Grinberg <dmitrygr at gmail dot com>
- To: gcc at gcc dot gnu dot org
- Date: Thu, 16 Jul 2015 13:32:15 -0700
- Subject: How to express this complicated constraint in md file
- Authentication-results: sourceware.org; auth=none
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?