Hello,

IMHO I think the desire to include these features is leading to a slightly cavalier attitude towards reordering concerns.  Even assuming that the Cmm code generator doesn't reorder reads/writes around `CallishMachOp`, I don't see why this behavior should always be true, leading to possible future pain.  Also, it's possible that LLVM may decide to reorder memory accesses AIUI because the underlying LLVM variables won't be synchronized.

In a nutshell, even though everything may work now I suspect it'll become an ill-specified mess in a few years time.  I don't have a ton of experience implementing these sorts of features in compilers though, so probably only worth a half cent.

John L.