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Earlier quoted context omitted.
It was the instruction for interacting with XPoint DIMMs (I wouldn't call them SSDs but whatever), but now you just use CLWB instead.
Previously you would use CLWB, SFENCE, then PCOMMIT. Now you use CLWB, then SFENCE.
They've either just averted or triggered a temporal paradox, I'm not sure which
This is a nice improvement. Now instead of having sfence/pcommit/sfence to flush writes to nvram, you would use just an sfence to ensure ordering with subsequent stores (e.g. a store that publishes the written data.) Its analogous to fysnc() to ensure data reaches the disk in a way that survives power failure. This is like just treating all writes as fsynced and not needing to worry about fsync at all, like with O_DI…
Does GCC use PCOMMIT?
It looks like the encoding of PCOMMIT (+66 0F AE/7) is basically the same as CLFLUSH except with a +66 prefix, so if a CPU doesn't know about PCOMMIT it'll probably try to execute it as a CLFLUSH with an ignored prefix.
But hopefully this "deprecated" information stays around, if for nothing other than "archaeological" purposes:
Earlier quoted context omitted.
This isn't the kind of instruction a compiler would emit for regular code.
What would this be used for?
Obvious applications are filesystems and databases.