|author||Stephen Adams <firstname.lastname@example.org>||Mon Dec 20 22:48:03 2021 +0000|
|committer||Commit Bot <email@example.com>||Mon Dec 20 22:48:03 2021 +0000|
[vm, lib] Refine List copy loops `growableList.toList()` was 10-50% faster than `List.of(growableList)`. This change erases the performance difference. The loops were slightly different. The faster version created the _List backing store for the list rather than assigning to the _GrowableList. It is not clear if the speedup is from an easier type test (the _List is 'raw'), or from a less indirect assignment, or from a fixed length list having an an easier-to-optimize bounds check, or whether a non-zero loop trip count enables any hoisting. This change uses the faster pattern in the _GrowableList._ofXXXList methods. I tried to simplify `toList` to delegate to one of the methods with the faster loop, but it was 2-5% slower on ListCopy.toList.2, presumably the extra call is significant for a short list. If there was an annotation for aggressive inlining into `toList` perhaps that would close the gap. dart-aot-null armv8c, 0.5 noise and over ListCopy.List.num.from.2 24.17% (1.6 noise) ListCopy.List.of.2 28.08% (1.7 noise) ListCopy.spread.num.2 28.73% (2.1 noise) ListCopy.List.num.from.100 54.49% (1.9 noise) ListCopy.List.of.100 55.55% (1.9 noise) ListCopy.spread.num.100 55.77% (2.0 noise) Change-Id: I7b780835faf50b673fd4b1a08a8c4e2d350d7d5b Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/224780 Reviewed-by: Alexander Markov <firstname.lastname@example.org> Commit-Queue: Stephen Adams <email@example.com>
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