[llvm] Extend MemoryEffects to Support Target-Specific Memory Locations (PR #148650)

[Paul Walker via llvm-commits]

paulwalker-arm wrote:

I've take a look over the PR and think it's worth breaking in two.  It looks like we've settled on a design whereby there are a set of InaccessibleMem locations that are reserved for use by target specific operations only. Then on top of this we have an optional target specific veneer to enable pretty parsing and printing of these to better fit their use within the target's domain.  It would be better to have separate PRs to show this (i.e. one to add the generic TargetMem# locations, and another to add the AArch64 veneer to parse/print "aarch64_fpmr/za".

To shorten the naming I'm wondering if we can settle on TargetMem/target_mem and then implicitly assume (well document in the langref) these to be variants of inaccessible memory, albeit ones that are specifically independent to InaccessibleMem, which is the location to use for non-target-specific or non-named-target-specific variants of inaccessible memory.

https://github.com/llvm/llvm-project/pull/148650