tree 29997e0dd71383ae8e9ef744bb9b1ee4677d63d1
parent da4bf60a09563dcc545aad070b149a8a0b47cb84
author Vyacheslav Egorov <vegorov@google.com> 1715766980 +0000
committer Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> 1715766980 +0000

[vm/libs] Improve JsonUtf8Decoder performance.

This CL focuses on improving parsing of white space (between
JSON tokens) and simple strings which don't contain escape
sequences inside.

Improvements are achieved by changing the code to
table driven implementation instead of if-cascade: we
have a 256 element table which stores attributes for characters
(e.g. whether it is a white space or a terminal token for
a simple string) and use this table to make decisions
on whether to advance through characters or stop a loop and
do something else.

We also suppress bounds checks and interrupt checks in tight
loops - in tight loops like this a bound checks can cost
30% in overhead.

This CL brings 28% geomean improvement on benchmarks from the linked issue. (All measurements are done in X64 Product AOT)

Individual measurements are:

| Input JSON | ms/iter | vs HEAD | vs V8 |
| ---------- | ------- | ------- | ----- |
| apache_builds.json | 0.44 | 61.06% | 136.86% |
| canada.json | 31.04 | 96.54% | 187.15% |
| citm_catalog.json | 6.43 | 64.44% | 93.94% |
| github_events.json | 0.23 | 59.02% | 128.86% |
| google_maps_api_compact_response.json | 0.10 | 82.12% | 133.83% |
| google_maps_api_response.json | 0.12 | 68.79% | 140.07% |
| gsoc-2018.json | 9.25 | 44.89% | 147.43% |
| instruments.json | 1.08 | 70.18% | 167.38% |
| marine_ik.json | 21.07 | 88.25% | 142.58% |
| mesh.json | 4.51 | 94.56% | 136.57% |
| mesh.pretty.json | 9.97 | 83.76% | 193.79% |
| numbers.json | 0.57 | 91.88% | 83.37% |
| random.json | 3.79 | 78.32% | 107.18% |
| repeat.json | 0.06 | 71.51% | 118.47% |
| semanticscholar-corpus.json | 37.65 | 54.82% | 57.81% |
| tree-pretty.json | 0.17 | 68.68% | 162.33% |
| twitter_api_compact_response.json | 0.06 | 75.23% | 126.11% |
| twitter_api_response.json | 0.08 | 70.64% | 123.60% |
| twitterescaped.json | 3.88 | 84.66% | 177.94% |
| twitter.json | 3.54 | 73.01% | 105.33% |
| twitter_timeline.json | 0.37 | 81.52% | 271.37% |
| update-center.json | 2.85 | 66.75% | 89.01% |

vs HEAD (geomean): 72.94%
vs V8 (geomean): 130.99%
HEAD vs V8 (geomean): 179.59%

Issue https://github.com/dart-lang/sdk/issues/55522

TEST=covered by co19

Change-Id: Id673118c19250ab7781cc98c7656b972debc60ff
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/365803
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Commit-Queue: Slava Egorov <vegorov@google.com>