safe transmute: use `Assume` struct to provide analysis options #100726

jswrenn · 2022-08-18T19:54:15Z

This task was left as a TODO in #92268; resolving it brings BikeshedIntrinsicFrom more in line with the API defined in MCP411.

Before:

pub unsafe trait BikeshedIntrinsicFrom<
    Src,
    Context,
    const ASSUME_ALIGNMENT: bool,
    const ASSUME_LIFETIMES: bool,
    const ASSUME_VALIDITY: bool,
    const ASSUME_VISIBILITY: bool,
> where
    Src: ?Sized,
{}

After:

pub unsafe trait BikeshedIntrinsicFrom<Src, Context, const ASSUME: Assume = { Assume::NOTHING }>
where
    Src: ?Sized,
{}

Assume::visibility has also been renamed to Assume::safety, as library safety invariants are what's actually being assumed; visibility is just the mechanism by which it is currently checked (and that may change).

r? @oli-obk

rustbot · 2022-08-18T19:54:19Z

Hey! It looks like you've submitted a new PR for the library teams!

If this PR contains changes to any rust-lang/rust public library APIs then please comment with @rustbot label +T-libs-api -T-libs to tag it appropriately. If this PR contains changes to any unstable APIs please edit the PR description to add a link to the relevant API Change Proposal or create one if you haven't already. If you're unsure where your change falls no worries, just leave it as is and the reviewer will take a look and make a decision to forward on if necessary.

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Changing public documentation in ways that create new stability guarantees
Changing observable runtime behavior of library APIs

library/core/src/mem/transmutability.rs

jswrenn · 2022-08-18T20:29:26Z

I also attempted to implement Add and Sub for Assume (another part of MCP411):

#[unstable(feature = "transmutability", issue = "99571")]
#[rustc_const_unstable(feature = "transmutability", issue = "99571")]
impl const core::ops::Add for Assume {
    type Output = Assume;

    fn add(self, rhs: Assume) -> Assume {
        Assume {
            alignment: self.alignment || rhs.alignment,
            lifetimes: self.lifetimes || rhs.lifetimes,
            safety: self.safety || rhs.safety,
            validity: self.validity || rhs.validity,
        }
    }
}

#[unstable(feature = "transmutability", issue = "99571")]
#[rustc_const_unstable(feature = "transmutability", issue = "99571")]
impl const core::ops::Sub for Assume {
    type Output = Assume;

    fn sub(self, rhs: Assume) -> Assume {
        Assume {
            alignment: self.alignment && !rhs.alignment,
            lifetimes: self.lifetimes && !rhs.lifetimes,
            safety: self.safety && !rhs.safety,
            validity: self.validity && !rhs.validity,
        }
    }
}

...but attempting to use these impls in the UI tests results in errors; e.g.:

error[E0015]: cannot call non-const operator in constants
  --> /home/ubuntu/projects/rust/src/test/ui/transmutability/arrays/should_have_correct_length.rs:14:52
   |
LL |         Dst: BikeshedIntrinsicFrom<Src, Context, { Assume::SAFETY + Assume::VALIDITY }>
   |                                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: impl defined here, but it is not `const`
  --> /home/ubuntu/projects/rust/library/core/src/mem/transmutability.rs:65:1
   |
LL | impl const core::ops::Add for Assume {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: calls in constants are limited to constant functions, tuple structs and tuple variants

Anyone know what's going on here? The error message seems non-sensical.

library/core/src/mem/transmutability.rs

bors · 2022-08-22T01:27:23Z

☔ The latest upstream changes (presumably #100654) made this pull request unmergeable. Please resolve the merge conflicts.

This was left as a TODO in rust-lang#92268, and brings the trait more in line with what was defined in MCP411. `Assume::visibility` has been renamed to `Assume::safety`, as library safety is what's actually being assumed; visibility is just the mechanism by which it is currently checked (this may change). ref: rust-lang/compiler-team#411 ref: rust-lang#99571

resolves query instability issues, and probably better for performance

compiler/rustc_transmute/src/lib.rs

oli-obk

small suggestion for the future: your first commit did 3 different things at once, it can be easier to review if they are done in separate commits.

ref: rust-lang#100726 (comment)

oli-obk · 2022-09-01T06:37:05Z

@bors r+

bors · 2022-09-01T06:37:07Z

📌 Commit fbcc038 has been approved by oli-obk

It is now in the queue for this repository.

safe transmute: use `Assume` struct to provide analysis options This task was left as a TODO in rust-lang#92268; resolving it brings [`BikeshedIntrinsicFrom`](https://doc.rust-lang.org/nightly/core/mem/trait.BikeshedIntrinsicFrom.html) more in line with the API defined in [MCP411](rust-lang/compiler-team#411). **Before:** ```rust pub unsafe trait BikeshedIntrinsicFrom< Src, Context, const ASSUME_ALIGNMENT: bool, const ASSUME_LIFETIMES: bool, const ASSUME_VALIDITY: bool, const ASSUME_VISIBILITY: bool, > where Src: ?Sized, {} ``` **After:** ```rust pub unsafe trait BikeshedIntrinsicFrom<Src, Context, const ASSUME: Assume = { Assume::NOTHING }> where Src: ?Sized, {} ``` `Assume::visibility` has also been renamed to `Assume::safety`, as library safety invariants are what's actually being assumed; visibility is just the mechanism by which it is currently checked (and that may change). r? `@oli-obk` --- Related: - rust-lang/compiler-team#411 - rust-lang#99571

bors · 2022-09-04T07:55:47Z

⌛ Testing commit fbcc038 with merge 8521a8c...

bors · 2022-09-04T10:15:38Z

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing 8521a8c to master...

rust-timer · 2022-09-04T11:30:34Z

Finished benchmarking commit (8521a8c): comparison URL.

Overall result: ❌✅ regressions and improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean¹	range	count²
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	1.6%	[1.0%, 2.1%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.4%	[-1.4%, -1.4%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean¹	range	count²
Regressions ❌ (primary)	2.0%	[2.0%, 2.0%]	1
Regressions ❌ (secondary)	4.0%	[1.3%, 6.8%]	5
Improvements ✅ (primary)	-3.1%	[-3.1%, -3.1%]	1
Improvements ✅ (secondary)	-3.4%	[-9.8%, -1.4%]	7
All ❌✅ (primary)	-0.5%	[-3.1%, 2.0%]	2

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean¹	range	count²
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.5%	[-2.5%, -2.5%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.5%	[-2.5%, -2.5%]	1

the arithmetic mean of the percent change ↩ ↩² ↩³
number of relevant changes ↩ ↩² ↩³

RalfJung · 2024-04-05T14:09:43Z

library/core/src/lib.rs

@@ -93,6 +93,7 @@
 #![warn(missing_debug_implementations)]
 #![warn(missing_docs)]
 #![allow(explicit_outlives_requirements)]
+#![allow(incomplete_features)]


I am quite concerned about this allow. That makes it way too easy to use features such as generic_const_exprs that are just not ready yet for use in the standard library.

This PR should at least have consulted t-types to ensure that adt_const_params is sufficiently stable that it can be used internally in the standard library. Cc @lcnr

But even then I think we actually want forbid(incomplete_features) here to avoid people just adding feature gates when it seems convenient. Or even better, set some flag in bootstrap which ensures that the entire sysroot is built without incomplete features.

rust-highfive assigned oli-obk Aug 18, 2022

rustbot added 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 Aug 18, 2022

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 18, 2022

fbstj reviewed Aug 18, 2022

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jswrenn mentioned this pull request Aug 19, 2022

Tracking Issue for Transmutability Trait: #[transmutability] #99571

Open

7 tasks

jswrenn force-pushed the transmute branch from bf446b2 to 3004029 Compare August 19, 2022 20:35

jswrenn force-pushed the transmute branch from 3004029 to f46fffc Compare August 22, 2022 18:38

safe transmute: use FxIndex{Map,Set} instead of FxHash{Map,Set}

1d844fe

resolves query instability issues, and probably better for performance

oli-obk reviewed Aug 25, 2022

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compiler/rustc_transmute/src/lib.rs Outdated Show resolved Hide resolved

oli-obk reviewed Aug 25, 2022

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safe transmute: use to_valtree to destructure const Assume

fbcc038

ref: rust-lang#100726 (comment)

bors 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 Sep 1, 2022

matthiaskrgr mentioned this pull request Sep 3, 2022

Rollup of 7 pull requests #101355

Closed

bors added the merged-by-bors This PR was explicitly merged by bors. label Sep 4, 2022

bors merged commit 8521a8c into rust-lang:master Sep 4, 2022

rustbot added this to the 1.65.0 milestone Sep 4, 2022

matthiaskrgr mentioned this pull request Sep 3, 2023

ICE: has escaping bound vars, so it cannot be wrapped in a dummy binder. #115517

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safe transmute: use `Assume` struct to provide analysis options #100726

safe transmute: use `Assume` struct to provide analysis options #100726

jswrenn commented Aug 18, 2022

rustbot commented Aug 18, 2022

jswrenn commented Aug 18, 2022

bors commented Aug 22, 2022

oli-obk left a comment

oli-obk commented Sep 1, 2022

bors commented Sep 1, 2022

bors commented Sep 4, 2022

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rust-timer commented Sep 4, 2022

RalfJung Apr 5, 2024 •

edited

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safe transmute: use Assume struct to provide analysis options #100726

safe transmute: use Assume struct to provide analysis options #100726

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jswrenn commented Aug 18, 2022

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oli-obk commented Sep 1, 2022

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bors commented Sep 4, 2022

bors commented Sep 4, 2022

rust-timer commented Sep 4, 2022

Overall result: ❌✅ regressions and improvements - no action needed

Instruction count

Max RSS (memory usage)

Cycles

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RalfJung Apr 5, 2024 • edited Loading

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safe transmute: use `Assume` struct to provide analysis options #100726

safe transmute: use `Assume` struct to provide analysis options #100726

RalfJung Apr 5, 2024 •

edited

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