2020-11-03.md

2020-11-03 Triage Log

A number of improvements on various benchmarks. The most notable news this week in compiler performance is the progress on instruction metric collection on a per-query level; see measureme#143 for the latest.

Otherwise, this week was an excellent one for performance (though mostly on stress tests rather than commonly seen code).

Triage done by @simulacrum. Revision range: 824f900a96d752da2d882863c65f9736e5f2b347..5cdf5b882da9e8b7c73b5cadeb7745cb68f6ff63

0 Regressions, 5 Improvements, 0 Mixed

Improvements

#78323

• Slight improvement in instruction counts (up to -1.3% on incr-unchanged builds of packed-simd-check)
• Possibly within noise; unclear.

#78508

• Moderate improvement in instruction counts (up to -2.0% on incr-unchanged builds of packed-simd-check)

#78432

• Large improvement in instruction counts (up to -5.7% on full builds of match-stress-enum-check)
• An unexpected improvement for a seemingly bugfix PR; would be good to verify this is not an unintentional behavior change (nag left).

#78553

• Very large improvement in instruction counts (up to -10.1% on full builds of match-stress-enum-check)

#78448

• Very large improvement in instruction counts (up to -95.4% on full builds of externs-debug)
• Notable case of adding a new benchmark to perf; this is much appreciated and illustrates that perf does not yet have full coverage of Rust code (though this is not really expected either, though is always a goal).

#78430

• Very large improvement in instruction counts (up to -23.6% on incr-patched: println builds of unicode_normalization-check)
• Fairly large refactor to the match checking infrastructure, with a correspondigly large performance improvement. There does appear to be a slight regression on #58319, but this is in the "Improvements" category since it seem categorically a win.

Nags requiring follow up

Compiler team attention requested:

• rust-lang/rust#78432 (comment)