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DOI: 10.4230/LIPIcs.ECOOP.2026.16

Characterizing Type Feedback in Just-In-Time Compilation

Authors: Sebastián Krynski, Filip Říha, Filip Křikava, and Jan Vitek

Published in: LIPIcs, Volume 372, 40th European Conference on Object-Oriented Programming (ECOOP 2026)

Abstract

Just-in-time (JIT) compilers leverage type feedback to optimize dynamic languages by recording runtime observations during interpretation and using them to generate specialized code. However, this recording process introduces significant execution time overhead to program warmup. This paper presents a characterization study of how feedback information is utilized by JIT compilers, providing motivation for future work on reducing recording overhead. We instrument the Ř compiler for the R language to track feedback slot usage throughout compilation, analyzing well-known benchmarks and real-world programs. Our measurements reveal that recording adds overhead to the interpreter up to 1.6× (mean 1.2×), yet at least 59% of non-empty slots are not used by the compiler. A large fraction of these unused slots can be attributed to dead code that the compiler eliminated. Most of the remaining slots are type-stable - meaning the inferred type matches the observed type - making speculation futile. To quantify the potential for improvement, we evaluate two oracle-based configurations that establish upper bounds on achievable reduction: a conservative set approach that preserves optimization quality while improving warmup, and an optimistic set approach that sacrifices some compiled code performance for faster interpretation.

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Sebastián Krynski, Filip Říha, Filip Křikava, and Jan Vitek. Characterizing Type Feedback in Just-In-Time Compilation. In 40th European Conference on Object-Oriented Programming (ECOOP 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 372, pp. 16:1-16:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{krynski_et_al:LIPIcs.ECOOP.2026.16,
  author =	{Krynski, Sebasti\'{a}n and \v{R}{\'\i}ha, Filip and K\v{r}ikava, Filip and Vitek, Jan},
  title =	{{Characterizing Type Feedback in Just-In-Time Compilation}},
  booktitle =	{40th European Conference on Object-Oriented Programming (ECOOP 2026)},
  pages =	{16:1--16:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-423-9},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{372},
  editor =	{Krebbers, Robbert and Silva, Alexandra},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2026.16},
  URN =		{urn:nbn:de:0030-drops-261124},
  doi =		{10.4230/LIPIcs.ECOOP.2026.16},
  annote =	{Keywords: Feedback vector, JIT compilation, type speculation, deoptimization}
}

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Artifact

DOI: 10.4230/DARTS.12.1.4

Characterizing Type Feedback in Just-in-Time Compilation (Artifact)

Authors: Sebastián Krynski, Filip Říha, Filip Křikava, and Jan Vitek

Published in: DARTS, Volume 12, Issue 1, Special Issue of the 40th European Conference on Object-Oriented Programming (ECOOP 2026)

Abstract

This artifact provides the means to validate and reproduce the results of the associated paper "Characterizing Type Feedback in Just-in-Time Compilation". It enables to reproduce experimental claims made in the paper, including the claimed numbers and contained figures.

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Sebastián Krynski, Filip Říha, Filip Křikava, and Jan Vitek. Characterizing Type Feedback in Just-in-Time Compilation (Artifact). In Special Issue of the 40th European Conference on Object-Oriented Programming (ECOOP 2026). Dagstuhl Artifacts Series (DARTS), Volume 12, Issue 1, pp. 4:1-4:2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@Article{krynski_et_al:DARTS.12.1.4,
  author =	{Krynski, Sebasti\'{a}n and \v{R}{\'\i}ha, Filip and K\v{r}ikava, Filip and Vitek, Jan},
  title =	{{Characterizing Type Feedback in Just-in-Time Compilation (Artifact)}},
  pages =	{4:1--4:2},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2026},
  volume =	{12},
  number =	{1},
  editor =	{Krynski, Sebasti\'{a}n and \v{R}{\'\i}ha, Filip and K\v{r}ikava, Filip and Vitek, Jan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DARTS.12.1.4},
  URN =		{urn:nbn:de:0030-drops-261415},
  doi =		{10.4230/DARTS.12.1.4},
  annote =	{Keywords: Feedback vector, JIT compilation, type speculation, deoptimization}
}

Document

Extended Abstract

DOI: 10.4230/OASIcs.Programming.2025.24

Toward a Typed Intermediate Language for R (Extended Abstract)

Authors: Mickaël Laurent, Jakob Hain, Filip Krikava, Sebastián Krynski, and Jan Vitek

Published in: OASIcs, Volume 134, Companion Proceedings of the 9th International Conference on the Art, Science, and Engineering of Programming (Programming 2025)

Abstract

Compilers for dynamic languages often rely on intermediate representations with explicit type annotations to facilitate writing program transformations. This paper documents the design of a new typed intermediate representation for a just-in-time compiler for the R programming language called FIŘ. Type annotations, in FIŘ, capture properties such as sharing, the potential for effects, and compiler speculations. In this extended abstract, we focus on the sharing properties that may be used to optimize away some copies of values.

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Mickaël Laurent, Jakob Hain, Filip Krikava, Sebastián Krynski, and Jan Vitek. Toward a Typed Intermediate Language for R (Extended Abstract). In Companion Proceedings of the 9th International Conference on the Art, Science, and Engineering of Programming (Programming 2025). Open Access Series in Informatics (OASIcs), Volume 134, pp. 24:1-24:4, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{laurent_et_al:OASIcs.Programming.2025.24,
  author =	{Laurent, Micka\"{e}l and Hain, Jakob and Krikava, Filip and Krynski, Sebasti\'{a}n and Vitek, Jan},
  title =	{{Toward a Typed Intermediate Language for R}},
  booktitle =	{Companion Proceedings of the 9th International Conference on the Art, Science, and Engineering of Programming (Programming 2025)},
  pages =	{24:1--24:4},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-382-9},
  ISSN =	{2190-6807},
  year =	{2025},
  volume =	{134},
  editor =	{Edwards, Jonathan and Perera, Roly and Petricek, Tomas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.Programming.2025.24},
  URN =		{urn:nbn:de:0030-drops-243086},
  doi =		{10.4230/OASIcs.Programming.2025.24},
  annote =	{Keywords: JIT, compilation, static typing, ownership, copy-on-write, dynamic language}
}

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Documents authored by Krynski, Sebastián

Characterizing Type Feedback in Just-In-Time Compilation

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Characterizing Type Feedback in Just-in-Time Compilation (Artifact)

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Toward a Typed Intermediate Language for R (Extended Abstract)

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