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2021-04-21.md

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2021-04-21 Triage Log

Another quiet week with very small changes to compiler performance.

Triage done by @rylev. Revision range: 5258a74c887f8ae14717e1f98b652b470877ce4e..6df26f897cffb2d86880544bb451c6b5f8509b2d

1 Regressions, 0 Improvements, 1 Mixed 0 of them in rollups

Regressions

Fix lookahead with None-delimited group #84130

  • Moderate regression in instruction counts (up to 1.4% on incr-unchanged builds of deep-vector-check)
  • While this change fixes a bug, it does introduce moderate regressions in runtime performance on some benchmarks and a fairly large regression on the compilation of the rustc_parse crate itself.
  • We will follow up on this particularly in the matter of rustc_parse's compilation times regressing.

Improvements

Mixed

Add some #[inline(always)] to arithmetic methods of integers #84061

  • Moderate regression in instruction counts (up to 1.7% on full builds of regex-debug)
  • Moderate improvement in instruction counts (up to -1.3% on incr-unchanged builds of cargo-check)
  • This change inlines a bunch of code that might not have been previously. It's not really a surprise that codegen now is taking longer to churn through all those inline calls.
  • While this tradeoff on compile times for runtime performance is likely worth it, we are checking in with the PR author and reviewer to make sure this is discussed.

Nags requiring follow up