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[v26.x] build: enable V8 undefined double support - #66733

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@inoway46 inoway46 commented Oct 14, 2026 •

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Enable V8_ENABLE_UNDEFINED_DOUBLE in the V8 GYP configuration, matching the setting added on main by 8394db37d800.

With this change, a local d8 build no longer exhibits the repeated wrong-map deoptimizations from #66717. This was verified with five seeds, both with and without Maglev.

Refs: #66717

Enable V8_ENABLE_UNDEFINED_DOUBLE in the V8 GYP configuration,
matching the setting added on main by 8394db3.

This is a candidate for the repeated wrong-map deoptimizations in
big.js reported in nodejs#66717. Preserve the existing v26 GYP settings
and apply only the undefined double feature configuration.

Refs: nodejs@8394db3
Refs: nodejs#66717
Signed-off-by: inoway46 <inoueyuya416@gmail.com>
Assisted-by: Codex
@nodejs-github-bot

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Review requested:

  • @nodejs/gyp
  • @nodejs/v8-update

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@nodejs-github-bot nodejs-github-bot added needs-ci PRs that need a full CI run. tools Issues and PRs related to the tools directory. v26.x Issues that can be reproduced on v26.x or PRs targeting the v26.x-staging branch. v8 engine Issues and PRs related to the V8 dependency. labels Oct 14, 2026
@inoway46

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A before/after comparison is running on macOS arm64:
https://github.com/inoway46/node/actions/runs/38592855428

It builds the parent commit and this PR’s commit, then runs the reproduction with five seeds, both with and without Maglev. I’ll share the results once it completes.

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