[LLVMdev] Replacing Platform Specific IR Codes with Generic Implementation and Introducing Macro Facilities

[Tim Northover]

>> In my experience, CodeGen has improved with the change. ISelDAG gets
>> to make use of more information when choosing how to do the operation:
>> values already known to be sign/zero extended, immediates, etc.
>
> Yes, it's definitely an improvement in the short term, but I'm not convinced
> by the approach in the long term.  It's a useful hack that works around a
> shortcoming in the IR, not a solution.

Hmm, so it sounds like you're not actually after an IR-level LL/SC,
but a higher-level  "cmpxchg weak". Fair enough, I suppose I'd
envisaged putting that burden on Clang.

Tim.