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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}
}

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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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