jiebi/CodeConvo huggingface dataset:
Code change:
#[link_name = "llvm.sqrt.f32"] fn sqrt(x: f32) -> f32; //~^ ERROR linking to LLVM intrinsics is experimental <del> //~| HELP add #![feature(link_llvm_intrinsics)] to the crate attributes </del> } fn main(){

Related discussion:
text: We'll see the effect of this patch in 1.0 and afterwards Beta, etc.
Whoops, I thought this made it in before beta. Thanks!
are there plans to release updates to the beta channel within a given 6 weeks cycle? Either this one or in the future.
I'm certain there will be updates; see discussion from last night here:
So how does one fix this error? I'm a new user of the rust library and I can't seem to use the collections library during the beta due to this problem. Given this git issue is a top google result, it would be nice if there were a solution here. Edit: Looks like the solution is to switch to the rust nightly. Is the entire collections library off-limits in the beta?
by design, you have access to the parts of that are re-exported from (and are stable).
Code change:
<ins> // Rustdoc shouldn't display `mut` in function arguments, which are // implementation details. Regression test for #81289. #![crate_name = "foo"] pub struct Foo; // @count foo/struct.Foo.html '//*[@class="impl-items"]//*[@class="method"]' 2 // @!has - '//*[@class="impl-items"]//*[@class="method"]' 'mut' impl Foo { pub fn foo(mut self) {} pub fn bar(mut bar: ()) {} } // @count foo/fn.baz.html '//*[@class="rust fn"]' 1 // @!has - '//*[@class="rust fn"]' 'mut' pub fn baz(mut foo: Foo) {} </ins>

Related discussion:
text: Rustdoc on [nightly documents][1] methods have signature of as while it only has to document it as . ! On [rustdoc stable][2], things are normal: ! : Version 1.49.0 ( 2020-12-29) [1]: [2]:
I'd like to investigate this :)
searched nightlies: from nightly-2020-12-29 to nightly-2021-01-22 regressed nightly: nightly-2021-01-09 searched commits: from to regressed commit: This regressed in , so this is probably caused by
This also affects Where will generate:
So a few observations: which displays mutability in patterns, causing to be displayed the mechanism for detecting and eliding works by , but as returns instead of , the comparison fails and displays the type.
I see two path to solving this bug: an option for to not display the mutability in patterns revert cc what do you think?
I would prefer to go for 1, there's no reason to have two completely different functions for pretty-printing.
Assigning and removing as in the prioritization working group.
(now a beta regression)
Code change:
// As a result 16 was chosen here! Mostly because it was a power of 2 // and most benchmarks agreed it was roughly a local optimum. Not very // scientific. <del> match self.opts.optimize { config::OptLevel::No => 16, _ => 1, // FIXME(#46346) this should be 16 } </del> <ins> 16 </ins> } /// Returns whether ThinLTO is enabled for this compilation

Related discussion:
text: I'm opening this up to serve as a tracking issue for enabling multiple codegen units in release mode by default. I've written up a before but the tl;dr; is that multiple codegen units enables us to run optimization/code generation in parallel, making use of all available computing resources often speeding up compilations by more than 2x. Historically this has not been done due to claims of a loss in performance, but the is intended to assuage such concerns. The most viable route forward seems to be to enable multiple CGUs and ThinLTO at the same time in release mode. Blocking issues: [x] Enable for libstd on all platforms - - - - Potential blockers/bugs: - -
cc
Presumably this will remain a stable compiler flag, but what else will change by default? Is the plan to make this only affect , or is the plan to also make this affect ? Do we want to make continue to use only a single CGU, to hedge against regressions for people who are already willing to trade off compiler time for runtime?
I would specifically propose that any opt level greater than 1 uses 16 codegen units and ThinLTO enabled by default for those 16 codegen units.
This is very interesting. One would think that ThinLTO-driven inlining should always have to do less work when our much more conservative pre-LLVM inlining. But that doesn't always seem to be the case, as in the . Most tests on the seem to profit though. Overall it's still not a clear picture to me.
was that comment meant for a different thread? I forget which one as well though, so I'll respond here! As a "quick benchmark" I compiled the regex test suite with 16 CGUs + ThinLTO and then toggled inlining in all CGUs on/off. Surprisingly inlining in all CGUs was 5s faster to compile, and additionally . In those timings is where inlining is only in one CGU, where is inlining in all CGUs. One benchmark, , got twice as slow!
Yeah, the comment was in response to (rust-doom) but since that was closed already, I put it here.
Code change:
// As a result 16 was chosen here! Mostly because it was a power of 2 // and most benchmarks agreed it was roughly a local optimum. Not very // scientific. <del> match self.opts.optimize { config::OptLevel::No => 16, _ => 1, // FIXME(#46346) this should be 16 } </del> <ins> 16 </ins> } /// Returns whether ThinLTO is enabled for this compilation

Related discussion:
text: Regarding the compilation time difference between pre- and post-trans inlining, my hypothesis would be that sometimes pre-trans inlining will lead to more code being eliminated early on (as in the case of regex apparently) and sometimes it will have the opposite effect. I suspect that there's room for improvement by tuning which LLVM passes we run specifically for ThinLTO. Or do we do that already?
Heh it's true yeah, I'd imagine that there's always room for improvement in pass tuning in Rust :). Right now we perform (afaik) 0 customization of any pass manager in LLVM. All of the normal optimization passes, LTO optimization passes, and ThinLTO optimization passes are all the same as what's in LLVM itself.
I wanted to also take the time and tabulate all the results from the to make sure it's all visibile in one place. Note that all the timings below are comparing a release build to a release build with 16 CGUs and ThinLTO enabled Improvements All of the following compile times improved, sorted by most improved to least improved Regressions The following crates regressed in compile times, sorted from smallest regression to largest alexcrichton's attempt to reproduce the regressions Here I attempt to reproduce the regressions on my own machine with Unfortunately the only regression I was able to reproduce was the rust-belt regression. I'll be looking more into that.
Looking into , one interesting thing I've found is that the crate takes longer to compile with ThinLTO than it would otherwise. Looking at it appears that one codegen unit in this crate takes 99% of the time in LLVM. This codegen unit appears to be basically entirely dominated by . Almost all of the benefit of multiple codegen units is spreading out the work across all CPUs. Enabling ThinLTO to avoid losing any perf is fundamentally doing more work than what's already happening at , but we get speedups across the board in most cases. If we have one huge CGU, split it in two, and work on those in parallel then we've got 50% of the original time to run ThinLTO (in a perfect world). If ThinLTO takes more than 50% of the time then we'd have a build time regression, but that's almost never happening.
Code change:
// As a result 16 was chosen here! Mostly because it was a power of 2 // and most benchmarks agreed it was roughly a local optimum. Not very // scientific. <del> match self.opts.optimize { config::OptLevel::No => 16, _ => 1, // FIXME(#46346) this should be 16 } </del> <ins> 16 </ins> } /// Returns whether ThinLTO is enabled for this compilation

Related discussion:
text: What's happening here is that we have one huge CGU, but when we split it up we still have one huge CGU. This means that the CGU which may take ~1% less time in LLVM only gives us a tiny sliver of a window to run ThinLTO passes. In the case of the crate this means that adding ThinLTO passes is an overall build time regression. So generalizing even further, I think that enabling ThinLTO and multiple CGUs by default is going to regress compile time performance in any crate where our paritioning implementation doesn't actually partition very well. In the case of we've got one huge function which hogs almost all the optimization time (I think) and the entire crate is basically dominated by that one function. I would be willing to conclude, however, that such a situation is likely quite rare. Almost all other crates in the ecosystem will benefit from the partitioning which should basically evenly split up a crate. maybe you have thoughts on this though?
Thank you so much for collecting and analyzing such a large amount of data, Your conclusions make sense to me. Unevenly distributed CGU sizes are also a problem for incremental compilation; e.g. the test sees 90% CGU re-use, yet compile time is almost the same as from-scratch. In the non-incremental case it might be an option to detect the problematic case right after partitioning and then switch to non-LTO mode? I'm not sure it's worth the extra complexity though. For cases where there is one big CGU but that CGU contains multiple functions, we should be able to rather easily redistribute functions to other CGUs. We'd only need a metric for the size of a . The number of MIR instructions might be a sufficient heuristic here. That would not help for but it might help for other crates. In conclusion, judging from the table above, I think we should make the default sooner rather than later. Open questions I see: What to do about ? I would have thought that it would always be a clear win to disable this when ThinLTO is enabled but that doesn't seem to be the case. Are there hardware configurations where this never is a win? E.g. should we default to traditional compilation if ?
Code change:
// As a result 16 was chosen here! Mostly because it was a power of 2 // and most benchmarks agreed it was roughly a local optimum. Not very // scientific. <del> match self.opts.optimize { config::OptLevel::No => 16, _ => 1, // FIXME(#46346) this should be 16 } </del> <ins> 16 </ins> } /// Returns whether ThinLTO is enabled for this compilation

Related discussion:
text: FWIW, as the author of , which is a made-for-fun Piston game, I am more than happy to take a small compile regression when it seems like vast majority of crates get huge real-time improvements!
This seems like a good thing to have in our back pocket, but I'm also wary of trying to do this by default. For example the case is one where we may wish to disable ThinLTO but the one massive function could also critically rely on a function in a different CGU being inlined? That sort of case would be difficult for us to determine... In any case though I agree that we probably don't need the complexity just yet so I think we can defer this for later. Agreed! So far all the crate's I've seen the O(instructions) has been quite a good metric for "how long this takes in all LLVM-related passes", so counting MIR sounds reasonable to me as well. Again though I also feel like this is ok to have in our back pocket. I'd want dig more into the minor change example, I'm curious how awry the CGU distribution is there and whether a heuristic like this would help. Quite surprisingly I've yet to see any data that it's beneficial to compile time in release mode or doesn't hurt runtime. (all data is that it hurts both compile time and runtime performance!) That being said we're seeing such big wins from ThinLTO on big projects today that we can probably just save this as a possible optimization for the future. On the topic of inline functions I recently dug up again (later closed in favor of , but the latter may no longer be true today). I suspect that may "fix" quite a bit of the compile time issue here without coming at a loss of performance? In any case possibly lots of interesting things we could do there. Also a good question! I find this to be a difficult one, however, because the CGU number will affect the output artifact, which means that if we do this sort of probing it'll be beneficial for performance but come at the cost of more difficult deterministic builds. You'd have to specify the CGUs manually or build on the same-ish hardware to get a deterministic build I think? I think though that if you have 1 CPU then this is universaly a huge regression.
Code change:
// As a result 16 was chosen here! Mostly because it was a power of 2 // and most benchmarks agreed it was roughly a local optimum. Not very // scientific. <del> match self.opts.optimize { config::OptLevel::No => 16, _ => 1, // FIXME(#46346) this should be 16 } </del> <ins> 16 </ins> } /// Returns whether ThinLTO is enabled for this compilation

Related discussion:
text: With one CPU we'd split the preexisting one huge CGU into N different ones, probably take roughly the same amount of time to opimize those, and then tack on ThinLTO and more optimization passes. My guess is that with one CPU we'd easily see 50% regressions. With 2+ CPUs however I'd probably expect to see benefits to compile time. Anything giving us twice the resources to churn the cgus more quickly should quickly start seeing wins in theory I think. For now though the deterministic builds wins me over in terms of leaving this as-is for all hardware configurations. That and I doubt anyone's compiling Rust on single-core machines nowadays!
One thing I think that's also worth pointing out is that up to this point we've mostly been measuring the runtime of an entire . That's actually, I believe, the absolute worst case scenario for where ThinLTO will provide benefit. Despite this, it's showing huge improvements for lots of projects! The benefit of ThinLTO and multiple CGUs is leveraging otherwise idle parallelism on the build machine. It's overall increasing the amount of work the compiler does. For a from scratch, though, you typically already have tons of crates compiling for the first half of the build in parallel. In that sense there's not actually any idle parallelism. Put another way, ThinLTO and multiple CGUs should only be beneficial for builds which dont have many crates compiling in parallel for long parts of the build. If a build is 100% parallel for the entire time then ThinLTO will likely regress compile time performance. Now you might realize, however, that one very common case where you're only building one crate is in an incremental build! Typically if you do an incremental build you're only building a handful of crates, often serially. In that sense I think that there's some massive wins of ThinLTO + multiple CGUs in incremental builds rather than entire crate builds. Although improving both is of course great as well :)
For deterministic builds you have to do some extra configuration anyway (e.g. path remapping) so I would not consider that a blocker. And I guess there are single core VMs around somewhere.
Code change:
// As a result 16 was chosen here! Mostly because it was a power of 2 // and most benchmarks agreed it was roughly a local optimum. Not very // scientific. <del> match self.opts.optimize { config::OptLevel::No => 16, _ => 1, // FIXME(#46346) this should be 16 } </del> <ins> 16 </ins> } /// Returns whether ThinLTO is enabled for this compilation

Related discussion:
text: But all of this is such a niche case that I don't really care MIR-only RLIBs should put us into a pretty good spot regarding this, so I'm quite confident that we're on the right path overall.
That's really interesting. For incremental compilation enabled the situation might be different (because pre-trans inlining hurts re-use) but for the non-incremental case it sounds like it's pretty clear what to do.
Yeah, maybe we should revisit this at some point. Although I have to say the current solution of only and symbols and nothing in between is really nice and simple.
Hm yeah that's a good point about needing configuration anyway for deterministic builds. It now seems like a more plausible route to take! Also that's a very interesting apoint about incremental and inlining on our own end... Maybe we should dig more into those ThinLTO runtime regressions at some point! Also yeah I don't really want to change how we trans inline functions just yet, I do like the simplicity too :)
out of curiosity how did you figure out this and which function it was. I've wanted to look into why the webrender build is so slow and would welcome tips.
oh sure I'd love to explain! So I originally found as a problematic crate when compiling rust-belt as it just took awhile and I decided to dig deeper. I checked out the crate and ran: That drops in the current directory, and opening that up I see: ! The graph here isn't always the easiest to read, but we've clearly got two huge bars, both of which correspond to taking a huge amount of time for that one CGU (first is optimization, second is ThinLTO + codegen). Next I ran: and that command dumps a bunch of IR files into . Our interesting CGU is so I opened up (we sure do love our long filenames). Inside that file it was 70k lines and some poking around showed that one function was 66k lines of IR. I sort of forget now how at this point I went from that IR to determining there was a huge function in there though...
I don't know if this is the right place, but I think it should be considered whether the symbol issues reported in the Nightly section here: should be considered a blocker or not.
Code change:
// As a result 16 was chosen here! Mostly because it was a power of 2 // and most benchmarks agreed it was roughly a local optimum. Not very // scientific. <del> match self.opts.optimize { config::OptLevel::No => 16, _ => 1, // FIXME(#46346) this should be 16 } </del> <ins> 16 </ins> } /// Returns whether ThinLTO is enabled for this compilation

Related discussion:
text: The tl;dr is that certain versions of llvm, (i've seen this on 3.8, and whatever llvm rustc nightly uses) appends seemingly random garbage to the end of some names, e.g. we get: instead of: This knocks the debuginfo out of sync (it doesn't have the garbage appended). I've been able to repro this with clang3.8 for c++ files as well (haven't tested on other llvm), and switching to 5.0 seems to have fixed the issue. I don't know if its within reach, but perhaps we should attempt upgrading to llvm 5.0 before releasing this on stable? Note I understand this is for release mode, but i see this in debug mode on rustc nightly right now as well...
Code change:
<ins> #![feature(extern_types)] pub mod aaaaaaa { extern { pub type MyForeignType; } impl MyForeignType { pub fn my_method() {} } } </ins>

Related discussion:
text: There are bad (404) links in search results with nightly rustdoc. E.g. go to and then click the result. This leads to which does not exist. Cc
Actually, this issue seems to exist even on stable -- somehow it went unnoticed for quite a while, it seems.
I think it's because we are badly handling a reexport/type alias.
I think this is a duplicate of
Code change:
<ins> error: mismatched closing delimiter: `}` --> $DIR/mismatched-delimiter-corner-case-issue-127868.rs:4:42 | LL | fn main() { |           - closing delimiter possibly meant for this LL |     let a = [[[[[[[[[[[[[[[[[[[[1, {, (, [,; |                                          ^ unclosed delimiter LL | } | ^ mismatched closing delimiter error: this file contains an unclosed delimiter --> $DIR/mismatched-delimiter-corner-case-issue-127868.rs:6:52 | LL | fn main() { |           - unclosed delimiter LL |     let a = [[[[[[[[[[[[[[[[[[[[1, {, (, [,; |             -----                  - this delimiter might not be properly closed... |             ||||| |             ||||another 16 unclosed delimiters begin from here |             |||unclosed delimiter |             ||unclosed delimiter |             |unclosed delimiter |             unclosed delimiter LL | } | - ...as it matches this but it has different indentation LL | |                                                   ^ error: aborting due to 2 previous errors </ins>

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text: In my Fedora installation ended up being a corrupted file. It took me hours to realize, given that the output does not bring any clarity to it. rustc should really have ratelimit detection or something to detect corrupted file instead and inform about this to the user. !
This indeed seems quite confusing; and counter-productive to try to show this blob of errors. Would you be able to provide us with a reproducible example of the issue? Or if you still have it the corrupted file. labels +T-compiler +A-diagnostics +D-verbose +D-confusing +S-needs-repro -needs-triage
So this a problem because I unfortunately deleted the trashed file before someone told me that I should report this as a bug. I regret that I did not store it :-/ BUT I recalled that it was probably for reason a long string of ANSI escape codes. So I did a test string: This creates somewhat similar output as I got, except probably the string was a bit longer in my case.
OK doubling that starts to be almost perfect match:
! ... I'm considering T-shirt design ;-) Made by me and rustc. EDIT: and rendered by excellent terminal emulator foot
Somehow rustc should be able to detect corrupted file in cargo's source repository (or whatever it is called). It was pretty bizarre sight when I encountered this by accident.
Thanks for the repro. label -S-needs-repro
Yeah I mean it is really a huge corner case but it can happen in the case of data corruption (e.g. power outage in middle of write operation). I'd detect frequency of errors and maybe a threshold parameter when it is interpreted as corruption with a sane default value.
yeah, I believe this error comes out from the phase of lexing, which rustc are trying to find all the mismatched delimiters, maybe a threshold is ok for resolve it.
Code change:
<ins> error[E0573]: expected type, found variant `Ok` --> $DIR/issue-106062.rs:15:64 | LL |     async fn connection_handler(handler: impl Sized) -> Result<Ok, std::io::Error> { |                                                                ^^ not a type | help: try using the variant's enum | LL |     async fn connection_handler(handler: impl Sized) -> Result<core::result::Result, std::io::Error> { |                                                                ~~~~~~~~~~~~~~~~~~~~ LL |     async fn connection_handler(handler: impl Sized) -> Result<std::result::Result, std::io::Error> { |                                                                ~~~~~~~~~~~~~~~~~~~ error: aborting due to previous error For more information about this error, try `rustc --explain E0573`. </ins>

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text: The full repo is here: : </p</details<!-- TRIAGEBOTSTART --<!-- TRIAGEBOTASSIGNSTART --<!-- TRIAGEBOTASSIGNDATASTARTTRIAGEBOTASSIGNDATAEND --<!-- TRIAGEBOTASSIGNEND --<!-- TRIAGEBOT_END --
For what it's worth, I can reproduce this issue with version 1.63.0, but it doesn't happen with 1.64.0 nor with the latest stable version 1.66.0.
The ICE disappeared in nightly-2022-07-01, which contains the following merges: [x] : ICEs [x] : ICEs [x] : ICEs [x] : ICEs [ ] [x] : ICEs
Here is it minified, and standalone-ed:
Triage: This has been fixed on the latest nightly, as reported, and needs a test to close.
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