1efaa73943
This PR updates the `UseList` type alias to a `SmallVec` with 4 `Use`s (which are 4 bytes each) rather than 2, because we get 16 bytes of space "for free" in a `SmallVec` on a 64-bit machine. This PR improves the compilation performance of Cranelift by 1% on SpiderMonkey.wasm (measured on a Linux desktop with pinned CPU frequency, and pinned to one core). It's worth noting also that before making these changes, I explored whether it would be possible to put the lists of uses and liveranges in single large backing `Vec`s; the basic reason why we can't do this is that during liverange construction, we append to many lists concurrently. One could use a linked-list arrangement, and in fact RA2 did this early in its development; the separate `SmallVec`s were better for performance overall because the cache locality wins when we traverse the lists many times. It may still be worth investigating use of an arena to allocate the vecs rather than the default heap allocator.
regalloc2: another register allocator
This is a register allocator that started life as, and is about 50% still, a port of IonMonkey's backtracking register allocator to Rust. In many regards, it has been generalized, optimized, and improved since the initial port, and now supports both SSA and non-SSA use-cases. (However, non-SSA should be considered deprecated; we want to move to SSA-only in the future, to enable some performance improvements. See #4.)
In addition, it contains substantial amounts of testing infrastructure (fuzzing harnesses and checkers) that does not exist in the original IonMonkey allocator.
See the design overview for (much!) more detail on how the allocator works.
License
This crate is licensed under the Apache 2.0 License with LLVM
Exception. This license text can be found in the file LICENSE.
Parts of the code are derived from regalloc.rs: in particular,
src/checker.rs and src/domtree.rs. This crate has the same license
as regalloc.rs, so the license on these files does not differ.