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On Wed, 2013-07-17 at 20:49 +0100, Richard Sandiford wrote: > Steve, this is going to seem like a bit of a pointless distraction, sorry, > but do you have any internal info about how the "udi..." instructions are > being used in practice? Since the whole point is that the instructions are > _user_-defined, I realise the answer's probably "no" by design. > > The instructions were added in: > > http://article.gmane.org/gmane.comp.gnu.binutils/27744/match=udi0 > > I was just wondering about the way that they all have WR_d|RD_s|RD_t > (write to the rd register, read from the rs and rt registers). > The use of these flags is pretty limited, so it probably isn't going to > matter in practice. But the ISA manual doesn't AIUI force a particular > format for the middle part of user SPECIAL2 opcodes, and things like > Octeon's CINS write to rt instead of rd, so I was wondering whether > it would be safer to assume that "udi..." modifies all GPRs (except $0, > of course). Anyone agree or disagree? > > The only reason I'm asking is that I'm trying to make the opcode descriptions > list the read and write operands by operand number rather than field type, > and this is one of the few cases where that isn't possible. We could have > a special flag for the equivalent of "modifies rd, rs and rt" instead, > if assuming all GPRs seems too heavyweight. > > Thanks, > Richard I am afraid I don't have any real information for you. I didn't even know these instructions existed until this email. I talked to a few people here and while they think a couple of customers used them they don't have any details. I did see a couple of documents over at developer.mips.com about using CorExtend (the MIPS name for UDI's) but I don't know if they bear any relationship to what people have actually implemented on any chips. Steve Ellcey sellcey@mips.com
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