rust-lang
[PERF] Don't spawn so many compilers (3/2) (19m -> 250k)
Optimize needless_doctest_main, make it short-circuit, make sure that we don't spin up a new compiler on EVERY code block.
The old implementation was creating a new compiler, new parser, new thread, new SessionGlobals, new everything for each code block. No matter if they actually didn't even contain fn main() or anything relevant.
On callgrind, seems that we're reducing about a 6.7242% de cycle count (which turns out to be a 38 million instruction difference, great!). Benchmarked in bumpalo-3.16.0. Also on bumpalo we spawn 78 less threads. This moves SessionGlobals::new from the top time-consuming function by itself in some benchmarks, into one not even in the top 500.
Also, populate the test files.
changelog:[needless_doctest_main]: Avoid spawning so many threads in unnecessary circumstances
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Weird CI error 🤔 html5ever fails to build?
This is https://github.com/rust-lang/rust/pull/142785
