799e8919fe
DHAT reports that when compiling the Spidermonkey Sightglass benchmark, there are over 100k of these Vec allocations, averaging less than 4 bytes, and with an average lifetime of only about 500 instructions. This function is only called from one place, which immediately converts it into an iterator. So this commit just returns the iterator that was previously being collected into a Vec. The iterator has to borrow from the DataFlowGraph, so this would change borrow-check results, but in the one caller that turns out to be okay. (That sole caller is in cranelift/codegen/src/machinst/lower.rs, in Lower::lower().) According to Sightglass, this is a compile-time improvement of between 2% and 12% on the Spidermonkey benchmark: instantiation :: nanoseconds :: benchmarks/spidermonkey/benchmark.wasm Δ = 14628.76 ± 10318.59 (confidence = 99%) main-0e6ffd024.so is 0.87x to 0.98x faster than no-small-vecs.so! no-small-vecs.so is 1.02x to 1.14x faster than main-0e6ffd024.so! [142023 187464.24 301522] main-0e6ffd024.so [103742 172835.48 263917] no-small-vecs.so compilation :: nanoseconds :: benchmarks/spidermonkey/benchmark.wasm Δ = 362392705.93 ± 267070467.06 (confidence = 99%) main-0e6ffd024.so is 0.89x to 0.98x faster than no-small-vecs.so! no-small-vecs.so is 1.02x to 1.12x faster than main-0e6ffd024.so! [3655734131 5522594697.83 6471126699] main-0e6ffd024.so [3278129811 5160201991.90 5810600015] no-small-vecs.so
This crate contains the core Cranelift code generator. It translates code from an intermediate representation into executable machine code.