Stream: t-compiler

Topic: weekly meeting 2019-07-18 #54818


nagisa (Jul 18 2019 at 13:55, on Zulip):

Meeting in 5 minutes, @T-compiler/meeting

nagisa (Jul 18 2019 at 14:00, on Zulip):

Lets begin I guess. First, are there any announcements?

nagisa (Jul 18 2019 at 14:01, on Zulip):

I did some pre-triage, I expect the coming weeks to be quite quiet in terms of actionability on issues, but that is fine, I think.

eddyb (Jul 18 2019 at 14:03, on Zulip):

to add to the quiet vibe, I've been spending some time on #wg-grammar-related things this week (but feel free to ping me if you need me for something)

nagisa (Jul 18 2019 at 14:04, on Zulip):

Another thing, we will likely have no WG check-in this week at least, because I have no idea where the schedule currently is.

nagisa (Jul 18 2019 at 14:05, on Zulip):

Okay, so moving on, I’d like to get backport nominations handled first, there quite a few of them.

nagisa (Jul 18 2019 at 14:05, on Zulip):

Fix #62660 #62668

nagisa (Jul 18 2019 at 14:06, on Zulip):

This is a tiny PR, fixes an ICE, well tested.

nagisa (Jul 18 2019 at 14:06, on Zulip):

Note that this PR is also nominated for a stable backport, on which we will vote later.

nagisa (Jul 18 2019 at 14:07, on Zulip):

It appears that the consensus is to backport.

nagisa (Jul 18 2019 at 14:07, on Zulip):

The next one is Cancel unemitted diagnostics during error recovery #62666

nagisa (Jul 18 2019 at 14:09, on Zulip):

This is similarly small, but hasn’t tests, fixes an ICE.

nagisa (Jul 18 2019 at 14:09, on Zulip):

Perhaps a good idea to vote on Handle errors during error recovery gracefully #62604 at the same time, as these are strongly related

nagisa (Jul 18 2019 at 14:10, on Zulip):

That one adds tests.

nagisa (Jul 18 2019 at 14:12, on Zulip):

Next up is Correctly break out of recovery loop #62607

nagisa (Jul 18 2019 at 14:13, on Zulip):

(again the vote is for a beta-backport, we’ll vote for stable backports later)

nagisa (Jul 18 2019 at 14:14, on Zulip):

Much like the previous PRs, small, tested, fixes ICE.

nagisa (Jul 18 2019 at 14:16, on Zulip):

Okay, I see a majority.

nagisa (Jul 18 2019 at 14:16, on Zulip):

Moving on there is a pair of related PRs, first Emit warning when trying to use PGO in conjunction with unwinding on Windows #61853 and then Only error about MSVC + PGO + unwind if we're generating code #62615

nagisa (Jul 18 2019 at 14:17, on Zulip):

The 2nd PR is essentially a revert of the first

Wesley Wiser (Jul 18 2019 at 14:17, on Zulip):

The first PR seemed semi-controversial last week and I volunteered to find an alternative approach which is #62615.

Wesley Wiser (Jul 18 2019 at 14:18, on Zulip):

(Last week's discussion)

nagisa (Jul 18 2019 at 14:18, on Zulip):

I suggest that we vote for the end result, which would occur after both PRs are backported in correct order.

nagisa (Jul 18 2019 at 14:18, on Zulip):

In essence that would mean that the behaviour implemented by the 2nd PR gets backported.

nagisa (Jul 18 2019 at 14:19, on Zulip):

This fixes Firefox use-cases I believe.

nagisa (Jul 18 2019 at 14:19, on Zulip):

so it isn’t exactly something that we keep broken.

Wesley Wiser (Jul 18 2019 at 14:19, on Zulip):

As I noted here, only commit 3622311d53 has to be backported if my patch is approved.

nagisa (Jul 18 2019 at 14:20, on Zulip):

@Wesley Wiser okay, in that case I’ll reject the backport for the Emit warning when trying to use PGO in conjunction with unwinding on Windows #61853 now.

nagisa (Jul 18 2019 at 14:22, on Zulip):

Please vote for/against backporting Only error about MSVC + PGO + unwind if we're generating code #62615 on the emojis above.

nagisa (Jul 18 2019 at 14:24, on Zulip):

I find the approach there okay, but I would also ask @Wesley Wiser how confident they are in implementation

nagisa (Jul 18 2019 at 14:24, on Zulip):

one question imediately arises is that the title says "when we are generating code"

nagisa (Jul 18 2019 at 14:24, on Zulip):

but what the implementation really checks for is sess.opts.prints.iter().all(|&p| p == PrintRequest::NativeStaticLibs)

Wesley Wiser (Jul 18 2019 at 14:25, on Zulip):

PrintRequest::NativeStaticLibs is special in that it's the only --print flag in which we actually generate code in addition to printing something out.

nagisa (Jul 18 2019 at 14:25, on Zulip):

but it is possible for code to be generated with PGO without anything being printed at all as well, isn’t it?

nagisa (Jul 18 2019 at 14:26, on Zulip):

i.e. assume rustc -Zwhatever-flag-that-enables-pgo --emit=link src/lib.rs

nagisa (Jul 18 2019 at 14:26, on Zulip):

Am I misunderstanding the initial issue?

nagisa (Jul 18 2019 at 14:27, on Zulip):

Oh, I see, all([]) is also true, never mind me

Wesley Wiser (Jul 18 2019 at 14:27, on Zulip):

Yes, but in that case sess.opts.prints.iter().all(|&p| p == PrintRequest::NativeStaticLibs) will return true which causes the error to be emitted.

Wesley Wiser (Jul 18 2019 at 14:27, on Zulip):

Iterator::all() on an empty iterable returns true

nagisa (Jul 18 2019 at 14:28, on Zulip):

Okay, I guess 3 for to 0 against is positive enough. Gimme a sec to mark as accepted for backport.

nagisa (Jul 18 2019 at 14:28, on Zulip):

Final beta backport is rustc_target: avoid negative register counts in the SysV x86_64 ABI. #62380

nagisa (Jul 18 2019 at 14:29, on Zulip):

Unlike the other backports, this is not as trivial, but we have tests!

nagisa (Jul 18 2019 at 14:29, on Zulip):

Fixes a soundness issue.

nagisa (Jul 18 2019 at 14:30, on Zulip):

A long standing one, though, so the only thing a backport achieves is fix arriving to users sooner.

nagisa (Jul 18 2019 at 14:31, on Zulip):

@oli want to elaborate?

oli (Jul 18 2019 at 14:32, on Zulip):

I'm fine with backporting, just don't think it's overly relevant to backport it

nagisa (Jul 18 2019 at 14:33, on Zulip):

Does it help if the backport is motivated by Firefox folks having to actively work-around this issue for extra 6 weeks if this does not get backported?

oli (Jul 18 2019 at 14:33, on Zulip):

definitely :D

nagisa (Jul 18 2019 at 14:33, on Zulip):

Got it, okay, accepting for backport.

eddyb (Jul 18 2019 at 14:33, on Zulip):

yeah I think the only user who cares right now is Firefox, given nobody seems to have hit it so far

eddyb (Jul 18 2019 at 14:34, on Zulip):

(you need a combination of floating-point, integer and struct arguments that is kind of rare in FFI outside of code like this that communicates internal browser stuff between C++ and Rust)

nagisa (Jul 18 2019 at 14:35, on Zulip):

Two of the PRs we discussed for backport are also nominated for a stable backport. While the release team has expressed no intention for a stable point release this cycle, we are supposed to handle these nominations disregarding this piece of information

nagisa (Jul 18 2019 at 14:35, on Zulip):

The PRs are:

nagisa (Jul 18 2019 at 14:35, on Zulip):

Fix #62660 #62668

nagisa (Jul 18 2019 at 14:35, on Zulip):

Correctly break out of recovery loop #62607

nagisa (Jul 18 2019 at 14:36, on Zulip):

Note that both ICEs fixed by these are already stable-to-stable regressions

nagisa (Jul 18 2019 at 14:38, on Zulip):

In that sense I personally feel these are not critical enough to backport to stable, even if we did end up making a point release.

nagisa (Jul 18 2019 at 14:38, on Zulip):

It is not like these fix a soundness issue or anything like that.

nagisa (Jul 18 2019 at 14:39, on Zulip):

(I myself vote :stop:, need more votes for consensus :slight_smile:)

nagisa (Jul 18 2019 at 14:42, on Zulip):

Okay, lets proceed, feel free to vote while meeting is still in progress and I’ll check if we reach a consensus there by the time meeting is over.

nagisa (Jul 18 2019 at 14:43, on Zulip):

Lets proceed with a mix of nominated and P-high issues.

nagisa (Jul 18 2019 at 14:43, on Zulip):

The first one I think we should check is STATUS_ACCESS_VIOLATION on 'index out of bounds' Windows 7 with lto and avx #62762

nagisa (Jul 18 2019 at 14:44, on Zulip):

it appears like a fairly serious codegen issue to me, the question is whether anybody wants to be assigned on this?

nagisa (Jul 18 2019 at 14:44, on Zulip):

@Nikita Popov perhaps?

nagisa (Jul 18 2019 at 14:46, on Zulip):

I guess I can assign to myself and Nikic seeing as they are already somewhat actively interacting with the reporter.

nagisa (Jul 18 2019 at 14:48, on Zulip):

Spurious unused variable lint warning on enum with no variants #62083 is nominated for a T-compiler decision on what the compiler should be allowed to do

nagisa (Jul 18 2019 at 14:49, on Zulip):

I essentially share pnkfelix’s opinion on this issue

nagisa (Jul 18 2019 at 14:50, on Zulip):

Are there any objections to closing this as WORKS-AS-INTENDED?

oli (Jul 18 2019 at 14:51, on Zulip):

Nope, this is all perfectly fine imo (other than it could have more lints complaining about dead code)

nagisa (Jul 18 2019 at 14:52, on Zulip):

There is then ICE: Rust spins when referencing associated types in where clause #62430

nagisa (Jul 18 2019 at 14:53, on Zulip):

Ah, never mind I assigned myself on this.

nagisa (Jul 18 2019 at 14:53, on Zulip):

Moving on…

nagisa (Jul 18 2019 at 14:54, on Zulip):

There is ICE: Generic type alias to invalid type crashes during type check on latest stable #62742

nagisa (Jul 18 2019 at 14:54, on Zulip):

There are plenty of similar issues but those reproductions all involve const generics.

nagisa (Jul 18 2019 at 14:55, on Zulip):

Would be great to have somebody investigate this, but I’m not sure who the best person would be. Also a P-tag. Looks P-high to me.

nagisa (Jul 18 2019 at 14:56, on Zulip):

Any objections to P-high?

nagisa (Jul 18 2019 at 14:57, on Zulip):

Okay marked P-high.

nagisa (Jul 18 2019 at 14:57, on Zulip):

With 3 minutes remaining for the meeting, I think it is fine to check back on the stable backport votes and adjourn.

nagisa (Jul 18 2019 at 14:58, on Zulip):

#62668 seems like pretty :stop:

nagisa (Jul 18 2019 at 14:59, on Zulip):

and #62607 is somewhat in the middle with 1 vote difference in favour of :stop:.

nagisa (Jul 18 2019 at 14:59, on Zulip):

Thus rejecting both for a stable backport I guess.

nagisa (Jul 18 2019 at 14:59, on Zulip):

With that the meeting is over, thanks all for exercising your right to vote :slight_smile:

Wesley Wiser (Jul 18 2019 at 15:00, on Zulip):

If any one is interested in reviewing #62615, I'd appreciate it! :slight_smile:

Vadim Petrochenkov (Jul 18 2019 at 15:00, on Zulip):

By the way, is Niko already on vacation?

Wesley Wiser (Jul 18 2019 at 15:00, on Zulip):

Yeah, I believe so

Vadim Petrochenkov (Jul 18 2019 at 15:00, on Zulip):

(I need to decide whether to reassign some PRs or not.)

nagisa (Jul 18 2019 at 15:00, on Zulip):

Yes, both @nikomatsakis and @pnkfelix are on vacation

Vadim Petrochenkov (Jul 18 2019 at 15:01, on Zulip):

Ok.

oli (Jul 18 2019 at 15:02, on Zulip):

I'm kinda back, still digging myself out of the 1k notification hole that my vacation dug for me :D

Last update: Nov 22 2019 at 05:10UTC