Make some float methods unstable `const fn` #130568

eduardosm · 2024-09-19T16:50:08Z

Some float methods are now const fn under the const_float_methods feature gate (except f16 and f128 versions, which I placed under f16 and f128 feature gates respectively).

I also made some unstable methods const fn, keeping their constness under their respective feature gate.

In order to support min / max, the implementation of some intrinsics had to be moved from Miri to rustc_const_eval (cc @RalfJung).

Tracking issue: #130843

impl <float> {
    // #[feature(const_float_methods)]
    pub const fn recip(self) -> Self;
    pub const fn to_degrees(self) -> Self;
    pub const fn to_radians(self) -> Self;
    pub const fn max(self, other: Self) -> Self;
    pub const fn min(self, other: Self) -> Self;
    pub const fn clamp(self, min: Self, max: Self) -> Self;
    pub const fn abs(self) -> Self;
    pub const fn signum(self) -> Self;
    pub const fn copysign(self, sign: Self) -> Self;

    // #[feature(float_minimum_maximum)]
    pub const fn maximum(self, other: Self) -> Self;
    pub const fn minimum(self, other: Self) -> Self;

    // Only f16/f128 (f32/f64 already const)
    pub const fn is_sign_positive(self) -> bool;
    pub const fn is_sign_negative(self) -> bool;
    pub const fn next_up(self) -> Self;
    pub const fn next_down(self) -> Self;
}

r? libs-api

rustbot · 2024-09-19T16:50:18Z

The Miri subtree was changed

cc @rust-lang/miri

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

compiler/rustc_const_eval/src/interpret/intrinsics.rs

RalfJung · 2024-09-21T21:08:16Z

r=me on the interpreter and Miri parts.

eduardosm · 2024-09-24T19:45:22Z

I made clamp const too, using an approach similar to #130611 to handle the assert formatting.

tgross35 · 2024-09-24T23:28:06Z

If this is accepted, a tracking issue should be created (for now I set issue = "none").

You can go ahead and do this in advance, I don't think there is any reason these would be rejected

tgross35 · 2024-09-24T23:32:55Z

library/core/src/num/f128.rs

+    #[rustc_const_unstable(feature = "f128", issue = "116909")]
+    pub const fn is_sign_positive(self) -> bool {


Thanks for including f16 and f128 :) would you mind adding a commented out gate on methods from this feature? E.g.

// #[rustc_const_unstable(feature = "const_float_methods", issue = "...")] #[rustc_const_unstable(feature = "f128", issue = "116909")] pub const fn is_sign_positive(self) -> bool {

We just do that to keep things somewhat linked if API falls under >1 gate.

eduardosm · 2024-09-25T17:22:48Z

Created tracking issue: #130843

For f16/f32 methods, I placed commented gates under the same feature as f32/f64 (e.g., is_sign_positive under const_float_classify, next_up under float_next_up_down).

bors · 2024-10-04T21:32:39Z

☔ The latest upstream changes (presumably #130157) made this pull request unmergeable. Please resolve the merge conflicts.

eduardosm · 2024-10-04T22:05:39Z

I believe is_sign_positive / is_sign_negative do not need the second unstable gate since const_float_classify is now stable.

RalfJung · 2024-10-05T08:15:03Z

src/tools/miri/src/intrinsics/mod.rs

@@ -249,28 +249,18 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                this.write_scalar(res, dest)?;
            }

-            "minnumf32" | "maxnumf32" | "copysignf32" => {
+            "copysignf32" => {


Btw, is there a reason you are not including copy_sign in this?

I could move it to rustc_const_eval. But, do we want to make copysign and abs const? Ideally, we'd want to, but since they are implemented in libstd instead of libcore, I'm not sure what's the deal with those.

I don't see why we wouldn't make them const.

I also don't know why they are in std, maybe the intrinsic is sometimes compiled to a libcall or so... let's just leave them where they are. 🤷

I'll make them const. But I find it quite weird that we have operations like min/max or % in libcore, while we are afraid to have operations like abs or copysign that can be trivially implemented with bitwise operations.

I fully agree. Maybe file an issue for that?

EDIT: Ah, an issue already exists: #50145

I made abs, copysign and signum (which uses copysign) const.

RalfJung · 2024-10-05T13:29:41Z

compiler/rustc_const_eval/src/interpret/intrinsics.rs

+    }
+}
+
+enum FloatBinOp {


Suggested change

enum FloatBinOp {

enum FloatBinIntrinsic {

We use BinOp for the MIR binops, IMO we shouldn't mix up that terminology.

Also please move this above the functions that use it.

RalfJung · 2024-10-05T13:33:11Z

tests/ui/consts/const-eval/float_methods.rs

@@ -0,0 +1,46 @@
+//@ run-pass


Suggested change

//@ run-pass

//@ run-pass

//! Tests the float intrinsics: min, max, abs, copysign

RalfJung · 2024-10-05T13:53:20Z

LGTM from the interpreter side.

r? libs-api

eduardosm · 2024-10-05T14:07:56Z

Rebased to pick #131256 and remove #![feature(f16_const)] and #![feature(f128_const)].

bors · 2024-10-12T12:50:39Z

☔ The latest upstream changes (presumably #131581) made this pull request unmergeable. Please resolve the merge conflicts.

Some float methods are now `const fn` under the `const_float_methods` feature gate (except `f16` and `f128` versions, which I placed under `f16` and `f128` feature gates respectively). In order to support `min` / `max`, the implementation of some intrinsics had to be moved from Miri to rustc_const_eval.

tgross35 · 2024-10-12T16:40:50Z

If libs-api can just okay unstably adding const to the signatures, I'm happy to review the rest.

@rustbot label +I-libs-api-nominated

rustbot assigned joshtriplett Sep 19, 2024

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 Sep 19, 2024

jieyouxu added the T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. label Sep 19, 2024

RalfJung reviewed Sep 21, 2024

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eduardosm force-pushed the const-float-methods branch from 4c6f58d to e60ae9b Compare September 21, 2024 19:49

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Tracking Issue for #![feature(const_float_methods)] #130843

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eduardosm force-pushed the const-float-methods branch from c06c255 to a79103f Compare September 25, 2024 17:23

eduardosm mentioned this pull request Sep 25, 2024

Tracking Issue for float_minimum_maximum #91079

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eduardosm force-pushed the const-float-methods branch from a79103f to fa312ed Compare October 4, 2024 22:02

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eduardosm force-pushed the const-float-methods branch from 593f644 to ab0560c Compare October 5, 2024 14:07

eduardosm added 2 commits October 12, 2024 15:58

Make float abs, copysign and signum const too

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eduardosm force-pushed the const-float-methods branch from ab0560c to 3a32e66 Compare October 12, 2024 14:07

rustbot added the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Oct 12, 2024

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Make some float methods unstable `const fn` #130568

Make some float methods unstable `const fn` #130568

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		#[rustc_const_unstable(feature = "f128", issue = "116909")]
		pub const fn is_sign_positive(self) -> bool {

	//@ run-pass
	//@ run-pass
	//! Tests the float intrinsics: min, max, abs, copysign

Make some float methods unstable const fn #130568

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Make some float methods unstable `const fn` #130568

Make some float methods unstable `const fn` #130568

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