Make more float intrinsics generic by N1ark · Pull Request #162395 · rust-lang/rust

N1ark · 2026-09-07T00:48:19Z

Another (big) step of #153834 + #160989

Makemore remaining float intrinsics generic! Each commit is self-contained.

In order:

ceil, floor, trunc, round, round_ties_even, with const libm fallbacks (using #[rustc_do_not_const_check], see Intrinsics should allow a non-const fallback body if hooked for CTFE #150961, cc @RalfJung @tgross35)
sqrt, with libm fallbacks
powf, with libm fallbacks
fma and fmuladd, with libm fallbacks (+#[rustc_do_not_const_check]) and a shared fallback, respectively.
powi, with no fallback (it already didn't have any)

The first commit just removes the f16/f128 fallbacks for fabs, as mentioned here. I didn't try making the backends use more fallbacks, to make the PR less risky since it's quite large. Happy to do changes there though (cc @folkertdev)

copysign, minimum_number_nsz, maximum_number_nsz, minimum, maximum will be handled separately as they require rustc_allow_const_fn_unstable: #162414

rustbot · 2026-09-07T00:48:22Z

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

miri is developed in its own repository. If the Miri part of this change can be broken out, consider making this change to rust-lang/miri instead. However, if Miri needs adjusting for rustc changes, just ignore this message.

cc @rust-lang/miri

rustc_codegen_gcc is developed in its own repository. If possible, consider making this change to rust-lang/rustc_codegen_gcc instead.

cc @antoyo, @GuillaumeGomez

compiler-builtins is developed in its own repository. If possible, consider making this change to rust-lang/compiler-builtins instead.

cc @tgross35

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

stdarch is developed in its own repository. If possible, consider making this change to rust-lang/stdarch instead.

cc @Amanieu, @folkertdev, @sayantn

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

⚠️ #[miri::intrinsic_fallback_is_spec] must only be used if the function actively checks for all UB cases,
and explores the possible non-determinism of the intrinsic.

cc @rust-lang/miri

Any special-casing of Miri in the standard library requires review.

cc @rust-lang/miri

rustc_codegen_cranelift is developed in its own repository. If possible, consider making this change to rust-lang/rustc_codegen_cranelift instead.

cc @bjorn3

⚠️ #[rustc_intrinsic_const_stable_indirect] controls whether intrinsics can be exposed to stable const
code; adding it needs t-lang approval.

cc @rust-lang/wg-const-eval

rustbot · 2026-09-07T00:48:26Z

r? @JohnTitor

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RalfJung · 2026-09-07T06:47:20Z

+#[rustc_const_unstable(feature = "core_intrinsics", issue = "none")]
 #[rustc_intrinsic_const_stable_indirect]


Noted this required adding #[rustc_const_unstable] to the whole intrinsic,

Why was this needed? I guess it is because the body now needs unstable const features, namely const traits? We should ensure const traits are stable enough before we do that.
(I now notice that you already did the same for fabs. We should have already checked this there then but forgot.)

@BoxyUwU @lcnr @oli-obk are const traits in a state where we can use them internally in const functions that can be called by public monomorphic stable const functions? I think this still allows us to change the syntax and logic for const traits pretty much arbitrarily as long as we keep some way of invoking trait functions in a const fn.

View changes since the review

yep, because it needs const_trait_impl, const_ops, const_cmp

these were moved to #162414

cc @fee1-dead

This is not the only case of such usage. Equivalent behaviour is here to stay and syntactical changes don't cause bootstrap churn anymore, so to me personally it is fine to add more, especially for intrinsic bodies which can always be replaced by an actual impl again

rustbot · 2026-09-07T08:16:39Z

clippy is developed in its own repository. If possible, consider making this change to rust-lang/rust-clippy instead.

cc @rust-lang/clippy

RalfJung · 2026-09-07T09:58:03Z

Please also update the PR description to reflect which intrinsics are actually being changed here now.

RalfJung · 2026-09-07T10:00:43Z

    where
        F: rustc_apfloat::Float + rustc_apfloat::FloatConvert<F> + Into<Scalar<M::Provenance>>,
    {
-        let x: F = x.to_float()?;


By removing this here, now every caller needs to call to_float first... is that really better?

View changes since the review

i found it nicer, because it means outside of SIMD we only do the x: F = x.to_float()? thing in one place, avoiding additional wrappers or calls elsewhere. it does make the SIMD intrinsics slightly bigger but i think it's nicer for the more general case

folkertdev · 2026-10-22T20:54:33Z

@rustbot author

Co-authored-by: Folkert de Vries <folkert@folkertdev.nl>

N1ark · 2026-10-23T08:11:58Z

@rustbot ready oops sorry ! done

folkertdev · 2026-10-23T10:06:48Z

LGTM, thanks!

@bors r+

rust-bors · 2026-10-23T10:06:52Z

📌 Commit 49ec655 has been approved by folkertdev

It is now in the queue for this repository.

…uwer Rollup of 5 pull requests Successful merges: - #162395 (Make more float intrinsics generic) - #164636 (Remove `record_*` macros from the metadata encoder) - #164624 (make `RustaceansAreAwesome` satisfy projection clauses) - #164695 ([tiny] Include trait definition line when pointing at assoc function in E0308) - #164744 (some `Attribute`/`AttributeExt` cleanups)

@RalfJung

Rollup merge of #162395 - N1ark:more-float-generics, r=folkertdev Make more float intrinsics generic Another (big) step of #153834 + #160989 Makemore remaining float intrinsics generic! Each commit is self-contained. In order: - `ceil`, `floor`, `trunc`, `round`, `round_ties_even`, with const libm fallbacks (using `#[rustc_do_not_const_check]`, see #150961, cc @RalfJung @tgross35) - `sqrt`, with libm fallbacks - `powf`, with libm fallbacks - `fma` and `fmuladd`, with libm fallbacks (+`#[rustc_do_not_const_check]`) and a shared fallback, respectively. - `powi`, with no fallback (it already didn't have any) The first commit just removes the f16/f128 fallbacks for `fabs`, as mentioned [here](#160989 (comment)). I didn't try making the backends use more fallbacks, to make the PR less risky since it's quite large. Happy to do changes there though (cc @folkertdev) `copysign`, `minimum_number_nsz`, `maximum_number_nsz`, `minimum`, `maximum` will be handled separately as they require `rustc_allow_const_fn_unstable`: #162414

…uwer Rollup of 5 pull requests Successful merges: - rust-lang/rust#162395 (Make more float intrinsics generic) - rust-lang/rust#164636 (Remove `record_*` macros from the metadata encoder) - rust-lang/rust#164624 (make `RustaceansAreAwesome` satisfy projection clauses) - rust-lang/rust#164695 ([tiny] Include trait definition line when pointing at assoc function in E0308) - rust-lang/rust#164744 (some `Attribute`/`AttributeExt` cleanups)

tgross35 · 2026-10-26T22:25:54Z

Note that this seems to have caused a regression in cranelift rust-lang/rustc_codegen_cranelift#1717. I think we should be prepared to revert unless there's an easy fix.

tgross35 · 2026-10-26T22:33:39Z

@@ -39,7 +67,7 @@ macro_rules! intrinsic_dispatch_on_type {
        }


This fn dispatch doesn't have #[inline] while the other instance does, perhaps that's related?

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Comment thread library/core/src/intrinsics/mod.rs

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N1ark force-pushed the more-float-generics branch from d78924b to 06625b8 Compare September 7, 2026 08:16

rustbot added the T-clippy Relevant to the Clippy team. label Sep 7, 2026

N1ark force-pushed the more-float-generics branch from 06625b8 to da4599d Compare September 7, 2026 08:18

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N1ark force-pushed the more-float-generics branch 2 times, most recently from ca3f9a9 to b4275be Compare September 7, 2026 09:12

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N1ark force-pushed the more-float-generics branch from b4275be to 49057d4 Compare September 7, 2026 09:53

N1ark changed the title ~~Make all float intrinsics generics~~ Make more float intrinsics generic Sep 7, 2026

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Comment thread compiler/rustc_const_eval/src/interpret/intrinsics.rs

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N1ark force-pushed the more-float-generics branch 2 times, most recently from 2bb83cf to 33503c2 Compare September 7, 2026 10:12

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 Oct 22, 2026

N1ark and others added 5 commits October 23, 2026 01:09

Make fma and fmuladd generic

ac667d2

Make powi generic

d428655

Add test for rustc_do_not_const_check intrinsics

eeaaf43

Add a fallback to powi

a350448

simplify macro

49ec655

Co-authored-by: Folkert de Vries <folkert@folkertdev.nl>

N1ark force-pushed the more-float-generics branch from 51f2c2e to 49ec655 Compare October 23, 2026 08:10

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 Oct 23, 2026

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 23, 2026

JonathanBrouwer mentioned this pull request Oct 23, 2026

Rollup of 5 pull requests #164788

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rust-bors Bot merged commit dd68b78 into rust-lang:main Oct 23, 2026
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rustbot added this to the 1.101.0 milestone Oct 23, 2026

TechnoPorg mentioned this pull request Oct 24, 2026

Make RISC-V bit manipulation intrinsics match C API rust-lang/stdarch#2247

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bjorn3 mentioned this pull request Oct 26, 2026

compiler_builtins cannot call functions through upstream monomorphizations rust-lang/rustc_codegen_cranelift#1717

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github-actions Bot mentioned this pull request Oct 26, 2026

Toolchain upgrade to nightly-2026-10-28 flux-rs/flux#1884

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tgross35 reviewed Oct 26, 2026

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		#[rustc_const_unstable(feature = "core_intrinsics", issue = "none")]
		#[rustc_intrinsic_const_stable_indirect]

		@@ -39,7 +67,7 @@ macro_rules! intrinsic_dispatch_on_type {
		}

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