Jittery

Jittery is the first (research) work on understanding and detecting performance bugs in just-in-time (JIT) compilers.

Our work was published at OOPSLA'26. This repository contains: (a) crawler that we used to obtain the raw data for the study (here), (b) data we collected after manual inspection and used in our empirical study (here), and (c) list of bugs discovered by our tool (Jittery) in Oracle JIT compilers (here). (Note that the tool itself, which relies on LeJit is currently not avaialble.)

Performance Bug Crawler

The crawler fetches raw bug reports from public trackers and writes it to a local JSONL file for later analysis.

The crawler is available in empirical/script/crawler.py.

Requirements

• Python 3.9+ (3.10/3.11 recommended)

Install Python dependencies:

python -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt

Supported engines

Engine	Tracker	API
HotSpot	bugs.openjdk.org	JIRA REST API
Graal	github.com/oracle/graal	GitHub Search API
SpiderMonkey	bugzilla.mozilla.org	Bugzilla REST API

Usage

Run from repo root:

python empirical/script/crawler.py --engine <engine> --query <query> [--offset N] [--max_limit N]

Arguments:

Argument	Description	Default
--engine	hotspot, graal, spidermonkey	—
--query	Query preset (jit-perf) or custom:...	—
--offset	Pagination offset	0
--max_limit	Maximum number of results to fetch	500

Query presets

Each engine has a jit-perf preset that reproduces the queries documented in empirical/data/queries.md (V8 issue tracker does not support public API access, please refer the documentation for the query we use and view it on the website).

Examples

# Preset JIT performance bugs
python empirical/script/crawler.py --engine [hotspot|graal|spidermonkey] --query jit-perf

# HotSpot with custom JQL
python empirical/script/crawler.py --engine hotspot --query "custom:<JQL>"

# Graal with custom GitHub search
python empirical/script/crawler.py --engine graal --query "custom:repo:oracle/graal is:issue label:performance"

# SpiderMonkey with custom Bugzilla params (JSON)
python empirical/script/crawler.py --engine spidermonkey --query 'custom:{"product":"Core","component":"JavaScript Engine: JIT","resolution":"FIXED"}'

Outputs (what you should see)

On success, the crawler writes:

• Raw JSONL: empirical/script/raw_data/<engine>_<query>_<offset>_<end>_bugs.jsonl
  • Each line is one JSON object of a bug report.
• Logs: empirical/script/.log/<timestamp>.log

Performance Bug Data

empirical/data/ holds CSV datasets used in the empirical study:

Engine	CSV dataset
HotSpot	empirical/data/HotSpot.csv
Graal	empirical/data/Graal.csv
V8	empirical/data/V8.csv
SpiderMonkey	empirical/data/SpiderMonkey.csv

empirical/data/ALL.yml holds the unified dataset for the empirical study.

Bugs Found by Jittery

In bugs/ we provide minimal Java programs that can be used to reproduce bugs that we detected with Jittery.

Bug ID	Java reproducer	Bug report
JDK-8345766	bugs/JDK-8345766.java	JDK-8345766
JDK-8346989	bugs/JDK-8346989.java	JDK-8346989
JDK-8349364	bugs/JDK-8349364.java	JDK-8349364
JDK-8349401	bugs/JDK-8349401.java	JDK-8349401
JDK-8349452	bugs/JDK-8349452.java	JDK-8349452
JDK-8350494	bugs/JDK-8350494.java	JDK-8350494
JDK-8350720	bugs/JDK-8350720.java	JDK-8350720
JDK-8353638	bugs/JDK-8353638.java	JDK-8353638
Graal-10565	bugs/Graal-10565.java	Graal-10565
Graal-10609	bugs/Graal-10609.java	Graal-10609
Graal-10776	bugs/Graal-10776.java	Graal-10776

Citation

If you use this artifact in your work or you end up exploring topics related to performance of JIT compilers, please cite:

@inproceedings{yi26understanding,
  author = {Yi, Zijian and Ding, Cheng and Shi, August and Gligoric, Milos},
  title = {Understanding and Finding {JIT} Compiler Performance Bugs},
  booktitle = {International Conference on Object-Oriented Programming Systems, Languages, and Applications},
  note = {To appear},
  year = {2026},
}