620e4b4e82
It does this by providing an implementation of the CLIF instructions `AtomicRmw`, `AtomicCas`, `AtomicLoad`, `AtomicStore` and `Fence`. The translation is straightforward. `AtomicCas` is translated into x64 `cmpxchg`, `AtomicLoad` becomes a normal load because x64-TSO provides adequate sequencing, `AtomicStore` becomes a normal store followed by `mfence`, and `Fence` becomes `mfence`. `AtomicRmw` is the only complex case: it becomes a normal load, followed by a loop which computes an updated value, tries to `cmpxchg` it back to memory, and repeats if necessary. This is a minimum-effort initial implementation. `AtomicRmw` could be implemented more efficiently using LOCK-prefixed integer read-modify-write instructions in the case where the old value in memory is not required. Subsequent work could add that, if required. The x64 emitter has been updated to emit the new instructions, obviously. The `LegacyPrefix` mechanism has been revised to handle multiple prefix bytes, not just one, since it is now sometimes necessary to emit both 0x66 (Operand Size Override) and F0 (Lock). In the aarch64 implementation of atomics, there has been some minor renaming for the sake of clarity, and for consistency with this x64 implementation.
This crate contains the core Cranelift code generator. It translates code from an intermediate representation into executable machine code.