RFR: JDK-8207169: X86: Modularize cmpxchg-oop assembler for C1 and C2

[Roland Westrelin]

Hi Erik,

> So if you have some kind of loop for your CAS, your
> ShenandoahBarrierSetC1 can generate the LIR for that, and allocate
> registers accordingly, letting the register allocator do its thing.

I doubt it's as simple as you make it sound. A loop or any control flow
construct would require us to hack the CFG. In c1, the CFG is
constructed at parse time from the bytecodes of the method being
compiled. There's no code that I know of that changes the CFG once
parsing is over. The c1 way of doing something like that is to implement
the loop (or any control flow) in assembly code in the backend.

Roland.