This patch implements recently ratified extension Zmmul, a subextension of M (Integer Multiplication and Division) consisting only multiplication part of it.
Yes, that, but also RISCVAsmParser::parseDirectiveAttribute and ELFObjectFileBase::getRISCVFeatures, though it seems that last one has been a bit neglected.
These are supposed to be (approximately) sorted in terms of their canonical ordering. I don't know where Zmmul is proposed to go relative to the other Zfoo's, but it belongs down somewhere in there, I guess alphabetical if we don't know any better, not up here with the single-letter extensions.
I have took a look into ELFObjectFile.cpp but I am not sure what work I need to do there since it seems other Z* extensions are not being handled there.
The pattern here seems to be that Z* extensions is following its parent their parent extensions, should we follow it? (See B and V)