Error: shifting a negative signed value is undefined

[ClearScript Developers]

Hello V8 folks!

We're seeing this error in 11.8 Linux builds:

../../../src/maglev/maglev-ir.cc:2033:43: error: shifting a negative signed value is undefined [-Werror,-Wshift-negative-value]
 2033 |                       ((kIsDoubleBit - 2) << (kTaggedSizeLog2 - 1)));
      |                        ~~~~~~~~~~~~~~~~~~ ^
../../../src/maglev/maglev-ir.cc:2100:35: error: shifting a negative signed value is undefined [-Werror,-Wshift-negative-value]
 2100 |               ((kIsDoubleBit - 2) << (kTaggedSizeLog2 - 1)));
      |                ~~~~~~~~~~~~~~~~~~ ^

It's easy enough to suppress via "-Wno-shift-negative-value", but is that safe?

Thanks!

[Jakob Linke]

+Leszek Swirski 

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[Marja Hölttä]

Seems to be fixed by https://chromium-review.googlesource.com/c/v8/v8/+/4846416 .

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[v8-dev]

Thanks, Marja. Do you know if this fix will eventually appear on the 11.8 branch?

[Marja Hölttä]

It's in 11.9 and I'm guessing it won't be merged back to 11.8. We generally backmerge fixes which are important for the main embedder, Chromium, and this one isn't. We also don't maintain separate version-X branches for Chromium and other embedders.

Happy to be wrong though.

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[ClearScript Developers]

Thanks again, Marja. We'll cherry pick it :)