Wrap write_bytes in a function. Move docs #57997

nitnelave · 2019-01-30T13:23:00Z

This will allow us to add debug assertions.
See issue #53871.

rust-highfive · 2019-01-30T13:23:04Z

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @KodrAus (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

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nitnelave · 2019-01-30T13:24:26Z

r? @RalfJung

RalfJung · 2019-01-30T13:28:10Z

src/libcore/intrinsics.rs

-    ///
-    /// // Now the box is fine
-    /// assert_eq!(*v, 42);
-    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]


This should then also be removed, I think.

EDIT: Uh, never mind. This is public.

Oh never mind. I did not know the functions in this module are pub. What the heck, why do we have public intrinsics?!?

That's what I was surprised about when writing the wrapper :D

RalfJung · 2019-01-30T13:39:36Z

Cc @rust-lang/libs Please advise: we'd like to replace ptr::write_bytes (currently a reexport) by a function so that we can add some debug assertions in there (see #53871). However, I just realized that the following compiles on stable:

fn main() {
    let mut x = 2;
    unsafe {
        core::intrinsics::write_bytes(&mut x, 0, 1);
    }
}

That's quite bad, obviously, because it allows direct access to the intrinsic. I am seriously surprised that anything in intrinsics got stabilized.

So we could either move this one intrinsic to a submodule, meaning core::intrinsics::write_bytes would not actually be an intrinsic, or we could replace the reexport by a wrapper function, meaning core::intrinsics::write_bytes and core::ptr::write_bytes would not be the same operation. Which do you prefer?

SimonSapin · 2019-01-30T13:51:42Z

That core::intrinsics::write_bytes works on Stable is a bug: #15702. I think we have precedent declaring this kind of bug not covered by the stability promise.

In fact I’d be in favor of actively unstabilizing everything in core::intrinsics, and replacing reexports by stable #[inline] wrapper functions.

nitnelave · 2019-01-30T14:01:01Z

I added the #[inline] annotation, but I'm leaving the destabilization of core::intrinsics for another issue.

alexcrichton · 2019-01-30T15:15:47Z

Wrapping raw intrinsics in new functions has historically caused a noticeable impact to compile times. I'd recommend holding off on landing a PR that wraps everything until we have a perf run at least to evaluate the impact.

nitnelave · 2019-01-30T15:23:58Z

@alexcrichton That's okay with me. How do I trigger a perf run? Or is it just going to come eventually from the CI?

alexcrichton · 2019-01-30T15:31:22Z

Oh triggering a perf run currently is still pretty manual. @nitnelave do you want to wrap a few more functions or just this one? Afterwards it's just @bors: try, wait for that, then @rustc-perf ...

RalfJung · 2019-01-30T15:34:51Z

I added the #[inline] annotation, but I'm leaving the destabilization of core::intrinsics for another issue.

What do we gain from separating this?

Anyway this PR currently removes the doc comment from a public stable function, I don't think that's a good idea (don't we have a lint against undocumented functions?).

That core::intrinsics::write_bytes works on Stable is a bug: #15702.

Hm, I don't see the connection to that issue. write_bytes is actively marked as stable in the intrinsics module, so it is not surprising that it is stable, is it?

EDIT: Oh, I @alexcrichton wrote "The intrinsics module is unstable but the function is stable because it's reexported in std::ptr". I thought we could attach a stability attribute to the reexport, but that doesn't seem to work then.

In fact I’d be in favor of actively unstabilizing everything in core::intrinsics, and replacing reexports by stable #[inline] wrapper functions.

Ah, that's great! I think it is impossible for transmute, but I suggest we do that here at least for the pointer methods.

nitnelave · 2019-01-30T15:36:00Z

I guess we'll eventually also wrap copy and copy_nonoverlapping, so I might as well do it all in one go.

RalfJung · 2019-01-30T15:37:46Z

Yes please do. That'll also make the perf impact bigger (if it exists) and hence easier to measure.

I'd even use #[inline(always)], and that has been necessary before, but it is worth trying without always first (I think @nnethercote prefers it that way).

src/libcore/intrinsics.rs

RalfJung · 2019-01-30T15:44:40Z

Thanks! Let's see what the timing says.

@bors try

bors · 2019-01-30T15:44:51Z

⌛ Trying commit 1c8b67b with merge 4f8466b...

Wrap write_bytes in a function. Move docs This will allow us to add debug assertions. See issue #53871.

SimonSapin · 2019-01-30T15:49:16Z

write_bytes is actively marked as stable in the intrinsics module, so it is not surprising that it is stable, is it?

Yes, but going "through" an unstable module in a path such as core::intrinsics::write_bytes should not be allowed on stable. In other words, the only difference on the stable channel between an unstable module and a non-existing module should be the contents of error messages.

nitnelave · 2019-02-04T11:21:33Z

@rustc-perf

nitnelave · 2019-02-04T13:00:13Z

I'm trying to run a benchmark, how do I trigger that? @RalfJung

tesuji · 2019-02-04T14:19:43Z

@nitnelave Try @rust-timer build 4f8466b.
Edit:

But why do you need to do a benchmark? I don't think this PR has much performance impact.
You must have enough permission to run rust-timer.

rust-timer · 2019-02-04T14:21:16Z

Insufficient permissions to issue commands to rust-timer.

rust-timer · 2019-02-04T14:22:05Z

Insufficient permissions to issue commands to rust-timer.

nitnelave · 2019-02-04T14:26:09Z

But why do you need to do a benchmark? I don't think this PR has much performance impact.

It shouldn't, but we're trying to assess that, see #57997 (comment)

You must have enough permission to run rust-timer.

Who does? Who can I ask?

tesuji · 2019-02-04T14:38:43Z

It shouldn't, but we're trying to assess that, see #57997 (comment)

Ah, yeah!

Who does? Who can I ask?

If you're not in the whitelist and try to run the timer, the timer will complain.

I will try to cc @RalfJung .

RalfJung · 2019-02-04T22:19:26Z

@rust-timer build 4f8466b

rust-timer · 2019-02-04T22:19:28Z

Success: Queued 4f8466b with parent 43b4c4a, comparison URL.

bors · 2019-02-15T19:36:07Z

💔 Test failed - checks-travis

rust-highfive · 2019-02-15T19:36:08Z

Your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

pietroalbini · 2019-02-15T20:21:47Z

@bors retry -- apparently we can't clone the repo anymore on macOS

Wrap write_bytes in a function. Move docs This will allow us to add debug assertions. See issue rust-lang#53871.

bors · 2019-02-22T13:52:49Z

⌛ Testing commit 26bd433 with merge e1c6d00...

Wrap write_bytes in a function. Move docs This will allow us to add debug assertions. See issue #53871.

bors · 2019-02-22T16:32:26Z

☀️ Test successful - checks-travis, status-appveyor
Approved by: RalfJung
Pushing e1c6d00 to master...

bors · 2019-02-22T16:32:36Z

☀️ Test successful - checks-travis, status-appveyor
Approved by: RalfJung
Pushing e1c6d00 to master...

nitnelave · 2019-02-22T16:36:16Z

Yay! \o\ \o\ /o/ /o/

The interface, though marked stable, is actually not. See rust-lang/rust#57997.

directly expose copy and copy_nonoverlapping intrinsics This effectively un-does rust-lang#57997. That should help with `ptr::read` codegen in debug builds (and any other of these low-level functions that bottoms out at `copy`/`copy_nonoverlapping`), where the wrapper function will not get inlined. See the discussion in rust-lang#80290 and rust-lang#81163. Cc `@bjorn3` `@therealprof`

directly expose copy and copy_nonoverlapping intrinsics This effectively un-does rust-lang/rust#57997. That should help with `ptr::read` codegen in debug builds (and any other of these low-level functions that bottoms out at `copy`/`copy_nonoverlapping`), where the wrapper function will not get inlined. See the discussion in rust-lang/rust#80290 and rust-lang/rust#81163. Cc `@bjorn3` `@therealprof`

rust-highfive assigned KodrAus Jan 30, 2019

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jan 30, 2019

rust-highfive assigned RalfJung and unassigned KodrAus Jan 30, 2019

RalfJung reviewed Jan 30, 2019

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bors added a commit that referenced this pull request Jan 30, 2019

Auto merge of #57997 - nitnelave:master, r=<try>

4f8466b

Wrap write_bytes in a function. Move docs This will allow us to add debug assertions. See issue #53871.

bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Feb 15, 2019

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 Feb 15, 2019

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GuillaumeGomez added a commit to GuillaumeGomez/rust that referenced this pull request Feb 17, 2019

Rollup merge of rust-lang#57997 - nitnelave:master, r=RalfJung

5843709

Wrap write_bytes in a function. Move docs This will allow us to add debug assertions. See issue rust-lang#53871.

GuillaumeGomez mentioned this pull request Feb 17, 2019

Rollup of 7 pull requests #58550

Closed

Centril added a commit to Centril/rust that referenced this pull request Feb 20, 2019

Rollup merge of rust-lang#57997 - nitnelave:master, r=RalfJung

9f7f3af

Wrap write_bytes in a function. Move docs This will allow us to add debug assertions. See issue rust-lang#53871.

Centril mentioned this pull request Feb 20, 2019

Rollup of 12 pull requests #58594

Closed

bors added a commit that referenced this pull request Feb 22, 2019

Auto merge of #57997 - nitnelave:master, r=RalfJung

e1c6d00

Wrap write_bytes in a function. Move docs This will allow us to add debug assertions. See issue #53871.

bors added the merged-by-bors This PR was explicitly merged by bors. label Feb 22, 2019

bors merged commit 26bd433 into rust-lang:master Feb 22, 2019

nitnelave mentioned this pull request Feb 27, 2019

Add debug assertions to write_bytes and copy* #58783

Closed

RalfJung mentioned this pull request Jun 3, 2019

All intrinsics are callable in const fn #61495

Closed

suemto pushed a commit to mwcproject/rust-secp256k1-zkp that referenced this pull request Oct 28, 2020

stop depending on intrinsics (mimblewimble#43)

5118054

The interface, though marked stable, is actually not. See rust-lang/rust#57997.

RalfJung mentioned this pull request Jan 21, 2021

directly expose copy and copy_nonoverlapping intrinsics #81238

Merged

RalfJung mentioned this pull request May 1, 2021

ICE when reifying function pointers to copy / copy_nonoverlapping using an if #84297

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Wrap write_bytes in a function. Move docs #57997

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Wrap write_bytes in a function. Move docs #57997

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