Make SIMD intrinsics available in `const`-contexts #147521

sayantn · 2025-10-09T11:46:47Z

successor to #146568, this PR actually makes the SIMD intrinsics const, and modifies the tests to test the const-eval implementations

r? @tgross35 ig (although feel free to reassign, this is not anything targeted really)

rustbot · 2025-10-09T11:46:50Z

Some changes occurred to the platform-builtins intrinsics. Make sure the
LLVM backend as well as portable-simd gets adapted for the changes.

cc @antoyo, @GuillaumeGomez, @bjorn3, @calebzulawski, @programmerjake

The Miri subtree was changed

cc @rust-lang/miri

Some changes occurred to the intrinsics. Make sure the CTFE / Miri interpreter
gets adapted for the changes, if necessary.

cc @rust-lang/miri, @RalfJung, @oli-obk, @lcnr

rustbot · 2025-10-09T11:46:53Z

tgross35 is currently at their maximum review capacity.
They may take a while to respond.

RalfJung · 2025-10-09T14:22:07Z

Cc @Amanieu

programmerjake · 2025-10-09T20:26:17Z

tests/ui/simd/intrinsic/generic-reduction-pass.rs

-        let r: f32 = simd_reduce_mul_unordered(x);
-        assert_eq!(r, -24_f32);
+        let x = f32x4::from_array([1., -2., 3., 4.]);
        let r: f32 = simd_reduce_add_ordered(x, 0.);


I know this wasn't there originally, but maybe we should add a test that requires being added in the proper order to return the right result? something like 1.0e20f32 + 1.0 - 1.0e20 - 1.0 == -1.0

that seems like a nice idea, but I really don't want to add new tests in this PR - this is pretty big by itself anyway

programmerjake

other than that idea for a new test, lgtm

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bors · 2025-11-05T11:46:41Z

☔ The latest upstream changes (presumably #148507) made this pull request unmergeable. Please resolve the merge conflicts.

tests/auxiliary/minisimd.rs

rustbot · 2025-11-10T21:58:10Z

This PR was rebased onto a different main 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.

sayantn · 2025-11-14T23:12:50Z

@rustbot reroll

Rerolling as @tgross35 is a bit busy

madsmtm

Haven't looked through all the tests, will wait until we figure out whether we can just overwrite assert_eq!, from a quick glance they look fine (they were also reviewed previously in #146568 by @tgross35).

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tests/auxiliary/minisimd.rs

madsmtm · 2025-11-15T16:19:18Z

library/core/src/intrinsics/simd.rs

 #[rustc_intrinsic]
 #[rustc_nounwind]
-pub unsafe fn simd_add<T>(x: T, y: T) -> T;
+pub const unsafe fn simd_add<T>(x: T, y: T) -> T;


I am unsure of the process here: does this need a compiler FCP to confirm that, yes, we do want t-libs to be able to start depending on these intrinsics being const?

#146568 was reviewed by Ralf, so I guess that's close to as good as it gets in terms of "wg-const-eval is fine with this".

I don't know, @Amanieu do we need to do some kind of libs fcp??

The team in charge of intrinsics is t-lang. They will have to be involved when stabilizing any of this, i.e., when adding rustc_intrinsic_const_stable_indirect to an intrinsic.

For the unstable part, notifying @rust-lang/wg-const-eval is enough. From my side this is fine: the only part that needs closer scrutiny is the fact that these are float operations, but we made them behave just like their scalar equivalents which seems right to me.

Ah so we can continue on this 🎉

tests/auxiliary/minisimd.rs

tests/ui/simd/intrinsic/float-math-pass.rs

library/core/src/intrinsics/simd.rs

tests/ui/simd/intrinsic/float-math-pass.rs

tests/ui/simd/intrinsic/generic-arithmetic-pass.rs

RalfJung · 2025-11-16T20:12:17Z

Haven't looked through all the tests, will wait until we figure out whether we can just overwrite assert_eq!, from a quick glance they look fine (they were also reviewed previously in #146568 by @tgross35).

Trevor left two comments but didn't indicate whether they even looked at the entire rest of the PR.

sayantn · 2025-11-16T20:54:01Z

thanks for your suggestion to shadow assert_eq! @madsmtm, it almost halved the diffcount

@rustbot ready

madsmtm

I've reviewed the tests now, generally happy with them.

Trevor left two comments but didn't indicate whether they even looked at the entire rest of the PR.

Yeah, I should've said "skimmed".

View changes since this review

tests/auxiliary/minisimd.rs

tests/ui/simd/intrinsic/generic-bitmask-pass.rs

tests/ui/simd/intrinsic/generic-cast-pointer-width.rs

tests/ui/simd/intrinsic/generic-gather-scatter-pass.rs

Co-authored-by: Mads Marquart <[email protected]>

madsmtm · 2025-11-17T00:55:49Z

Thanks for the answers, feel free to r=me when you've rebased, and when we've figured out if we've followed the right process.

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Oct 9, 2025

rustbot assigned tgross35 Oct 9, 2025

sayantn mentioned this pull request Oct 9, 2025

Port the remaining SIMD intrinsics to const-eval #147520

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sayantn force-pushed the simd-const-intrinsics branch from 8c71ce0 to 48324c2 Compare November 3, 2025 22:06

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Implement SIMD funnel shifts in const-eval/Miri #147534

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oli-obk reviewed Nov 5, 2025

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sayantn force-pushed the simd-const-intrinsics branch from 48324c2 to 76ddb6f Compare November 5, 2025 21:00

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sayantn force-pushed the simd-const-intrinsics branch from 76ddb6f to d1b2151 Compare November 10, 2025 11:14

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Make X86 intrinsics const rust-lang/stdarch#1925

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Make SIMD intrinsics available in const-contexts

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sayantn force-pushed the simd-const-intrinsics branch from d1b2151 to 8715316 Compare November 10, 2025 21:58

rustbot assigned madsmtm and unassigned tgross35 Nov 14, 2025

madsmtm added A-SIMD Area: SIMD (Single Instruction Multiple Data) A-const-eval Area: Constant evaluation, covers all const contexts (static, const fn, ...) labels Nov 15, 2025

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rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 15, 2025

Enable const-testing for the ported SIMD intrinsics

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sayantn force-pushed the simd-const-intrinsics branch from 8715316 to e48c21b Compare November 16, 2025 20:52

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Nov 16, 2025

madsmtm reviewed Nov 16, 2025

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add link to issue

24bfe49

Co-authored-by: Mads Marquart <[email protected]>

Make SIMD intrinsics available in const-contexts #147521

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Make SIMD intrinsics available in `const`-contexts #147521

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