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use the unstable carryless_mul in the pclmul implementation#4862

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folkertdev wants to merge 1 commit intorust-lang:masterfrom
folkertdev:use-carryless-mul
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use the unstable carryless_mul in the pclmul implementation#4862
folkertdev wants to merge 1 commit intorust-lang:masterfrom
folkertdev:use-carryless-mul

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Eventually we should be able to use the intrinsics in stdarch so that miri no longer needs a custom implementation. Unfortunately the required optimizations didn't make it into LLVM 22, so we'll have to wait ~6 months.

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rustbot commented Feb 17, 2026

Thank you for contributing to Miri! A reviewer will take a look at your PR, typically within a week or two.
Please remember to not force-push to the PR branch except when you need to rebase due to a conflict or when the reviewer asks you for it.

@rustbot rustbot added the S-waiting-on-review Status: Waiting for a review to complete label Feb 17, 2026
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CI uses 2026-01-21/rustc-nightly-x86_64-unknown-linux-gnu.tar.xz for that bootstrap job, How regularly does that update?

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RalfJung commented Feb 17, 2026

It always the current rust nightly bootstrap compiler (the file storing that is here). If the job here fails, that means merging this PR would cause the next sync into the Rust repo to fail.

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RalfJung commented Feb 17, 2026

The rust bootstrap compiler always gets updated around a release, so the next update will be around Feb 27th.

It is a fundamental part of the rustc development process that new standard library features can only be used inside rustc/miri after the next bootstrap bump (when nightly becomes beta and then that beta becomes the bootstrap compiler).

@RalfJung RalfJung added S-blocked Status: blocked on something happening somewhere else and removed S-waiting-on-review Status: Waiting for a review to complete labels Feb 17, 2026
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rustbot commented Mar 2, 2026

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.


let dest = ecx.project_index(&dest, i)?;
ecx.write_scalar(Scalar::from_u128(result), &dest)?;
ecx.write_scalar(Scalar::from_u128(left.widening_carryless_mul(right)), &dest)?;
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Please separately let-bind the result; currently it is easy to miss the main computation among all the other stuff.

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