[my123]

It’s pessimistic and converts over a lot of memory accesses to RCpc or atomics.

(on ARMv8.0 where you don’t have those, barriers are used more)

TSO pessimization is the only way to make the thing work at a translation time cost that isn’t too high.

[gpderetta]

Or you support TSO directly on your cpu like Apple does on M1.

[tsimionescu]

Sure, but Windows on ARM has to run on many ARM processors, not a specific one designed by MS. They could detect if the processor has non-standard TSO support and use that when running an x86 app, but they still have to do something to run the x86 app on a standard ARM processor.