427e041f1c
* Fix spillslot allocation to actually reuse spillslots. The old logic, which did some linked-list rearranging to try to probe more-likely-to-be-free slots first and which was inherited straight from the original IonMonkey allocator, was slightly broken (error in translation and not in IonMonkey, to be clear): it did not get the list-splicing right, so quite often dropped a slot on the floor and failed to consider it for further reuse. On some experimentation, it seems to work just as well to keep a SmallVec of spillslot indices per size class instead, and save the last probe-point in order to spread load throughout the allocated slots while limiting the number of probes (to bound quadratic behavior). This change moves the maximum slot count from 285 to 92 in `python.wasm` from bytecodealliance/wasmtime#4214, and the maximum frame size from 2384 bytes to 752 bytes.
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.
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.