Filter out short-lived LLVM diagnostics before they reach the rustc handler
During profiling I saw remark passes being unconditionally enabled: for example `Machine Optimization Remark Emitter`.
The diagnostic remarks enabled by default are [from missed optimizations and opt analyses](https://github.com/rust-lang/rust/pull/113339#discussion_r1259480303). They are created by LLVM, passed to the diagnostic handler on the C++ side, emitted to rust, where they are unpacked, C++ strings are converted to rust, etc.
Then they are discarded in the vast majority of the time (i.e. unless some kind of `-Cremark` has enabled some of these passes' output to be printed).
These unneeded allocations are very short-lived, basically only lasting between the LLVM pass emitting them and the rust handler where they are discarded. So it doesn't hugely impact max-rss, and is only a slight reduction in instruction count (cachegrind reports a reduction between 0.3% and 0.5%) _on linux_. It's possible that targets without `jemalloc` or with a worse allocator, may optimize these less.
It is however significant in the aggregate, looking at the total number of allocated bytes:
- it's the biggest source of allocations according to dhat, on the benchmarks I've tried e.g. `syn` or `cargo`
- allocations on `syn` are reduced by 440MB, 17% (from 2440722647 bytes total, to 2030461328 bytes)
- allocations on `cargo` are reduced by 6.6GB, 19% (from 35371886402 bytes total, to 28723987743 bytes)
Some of these diagnostics objects [are allocated in LLVM](https://github.com/rust-lang/rust/pull/113339#discussion_r1252387484) *before* they're emitted to our diagnostic handler, where they'll be filtered out. So we could remove those in the future, but that will require changing a few LLVM call-sites upstream, so I left a FIXME.
Move doc comment desugaring out of `TokenCursor`.
It's awkward that `TokenCursor` sometimes desugars doc comments on the fly, but usually doesn't.
r? `@petrochenkov`
now that remarks are filtered before cg_llvm's diagnostic handler callback
is called, we don't need to do the filtering post c++-to-rust conversion
of the diagnostic.
this will eliminate many short-lived allocations (e.g. 20% of the memory used
building cargo) when unpacking the diagnostic and converting its various
C++ strings into rust strings, just to be filtered out most of the time.
cleanup: remove pointee types
This can't be merged until the oldest LLVM version we support uses opaque pointers, which will be the case after #114148. (Also note `-Cllvm-args="-opaque-pointers=0"` can technically be used in LLVM 15, though I don't think we should support that configuration.)
I initially hoped this would provide some minor perf win, but in https://github.com/rust-lang/rust/pull/105412#issuecomment-1341224450 it had very little impact, so this is only valuable as a cleanup.
As a followup, this will enable #96242 to be resolved.
r? `@ghost`
`@rustbot` label S-blocked
[rustc_data_structures][perf] Simplify base_n::push_str.
This minor change removes the need to reverse resulting digits. Since reverse is O(|digit_num|) but bounded by 128, it's unlikely to be a noticeable in practice. At the same time, this code is also a 1 line shorter, so combined with tiny perf win, why not?
I ran https://gist.github.com/ttsugriy/ed14860ef597ab315d4129d5f8adb191 on M1 macbook air and got a small improvement
```
Running benches/base_n_benchmark.rs (target/release/deps/base_n_benchmark-825fe5895b5c2693)
push_str/old time: [14.180 µs 14.313 µs 14.462 µs]
Performance has improved.
Found 5 outliers among 100 measurements (5.00%)
4 (4.00%) high mild
1 (1.00%) high severe
push_str/new time: [13.741 µs 13.839 µs 13.973 µs]
Performance has improved.
Found 8 outliers among 100 measurements (8.00%)
3 (3.00%) high mild
5 (5.00%) high severe
```
Improve diagnostic for wrong borrow on binary operations
This PR improves the diagnostic for wrong borrow on binary operations by suggesting to reborrow on appropriate expressions.
```diff
+ = note: an implementation for `&Foo * &Foo` exist
+ help: consider reborrowing both sides
+ |
+ LL | let _ = &*ref_mut_foo * &*ref_mut_foo;
+ | ++ ++
```
Fixes https://github.com/rust-lang/rust/issues/109352
coverage: Replace `ExpressionOperandId` with enum `Operand`
*This is one step in my larger coverage refactoring ambitions described at <https://github.com/rust-lang/compiler-team/issues/645>.*
LLVM coverage has a concept of “mapping expressions” that allow a span's execution count to be computed as a simple arithmetic expression over other counters/expressions, instead of requiring a dedicated physical counter for every control-flow branch.
These expressions have an operator (`+` or `-`) and two operands. Operands are currently represented as `ExpressionOperandId`, which wraps a `u32` with the following semantics:
- 0 represents a special counter that always has a value of zero
- Values ascending from 1 represent counter IDs
- Values descending from `u32::MAX` represent the IDs of other expressions
---
This change replaces that whole `ExpressionOperandId` scheme with a simple enum that explicitly distinguishes between the three cases.
This lets us remove a lot of fiddly code for dealing with the different operand kinds:
- Previously it was only possible to distinguish between counter-ID operands and expression-ID operands by comparing the operand ID with the total number of counters in a function. This is unnecessary now that the enum distinguishes them explicitly.
- There's no need for expression IDs to descend from `u32::MAX` and then get translated into zero-based indices in certain places. Now that they ascend from zero, they can be used as indices directly.
- There's no need to reserve ID number 0 for the special zero operand, since it can just have its own variant in the enum, so counter IDs can count up from 0.
(Making counter IDs ascend from 0 also lets us fix an off-by-one error in the query for counting the total number of counters, which would cause LLVM to emit an extra unused counter for every instrumented function.)
---
This PR may be easiest to review as individual patches, since that breaks it up into clearly distinct parts:
- Replace a `u32` wrapper with an explicit enum, without changing the semantics of the underlying IDs being stored.
- Change the numbering scheme used by `Operand::Expression` to make expression IDs ascend from 0 (instead of descending from `u32::MAX`).
- Change the numbering scheme used by `Operand::Counter` to make counter IDs ascend from 0 (instead of ascending from 1).
Change default panic handler message format.
This changes the default panic hook's message format from:
```
thread '{thread}' panicked at '{message}', {location}
```
to
```
thread '{thread}' panicked at {location}:
{message}
```
This puts the message on its own line without surrounding quotes, making it easiser to read. For example:
Before:
```
thread 'main' panicked at 'env variable `IMPORTANT_PATH` should be set by `wrapper_script.sh`', src/main.rs:4:6
```
After:
```
thread 'main' panicked at src/main.rs:4:6:
env variable `IMPORTANT_PATH` should be set by `wrapper_script.sh`
```
---
See this PR by `@nyurik,` which does that for only multi-line messages (specifically because of `assert_eq`): https://github.com/rust-lang/rust/pull/111071
This is the change that does that for *all* panic messages.
[rustc_data_structures] Simplify SortedMap::insert.
It looks like current usage of `swap` is aimed at achieving what `std::mem::replace` does but more concisely and idiomatically.
Improve the rust style guide doc
- Make the levels of headings consistent in this whole document.
Before this change, the highest level of headings in some file is level 1, but in most of the files the that is level 2. Not consistent.
- Fix some headings
- Follow the markdown linter advices
- Remove redundant empty lines
- Surround each heading with empty lines
- Use the same symbol for different levels of unordered list entries
Directly link more target docs
Some platforms were not linked from platform-support.md
This fixes that, but errs towards extremely conservative, only directly linking platform docs if the docs actively mention the target, as otherwise I do not necessarily know if there was a reason for the omission.
bootstrap: use git merge-base for LLVM CI download logic
Fixes https://github.com/rust-lang/rust/issues/101907
I tested this with a local branch that has extra merge commits due to Miri, and it worked fine there. But I am sure there are tons of other situations I did not think of...
r? `@jyn514`
style-guide: Document style editions, start 2024 style edition
Link to a snapshot for the 2015/2018/2021 style edition.
This is a draft, because I'd like to wait for a few style guide fixes to merge
before snapshotting the 2015/2018/2021 style edition:
- https://github.com/rust-lang/rust/pull/113145
- https://github.com/rust-lang/rust/pull/113380
- https://github.com/rust-lang/rust/pull/113384
- https://github.com/rust-lang/rust/pull/113385
- https://github.com/rust-lang/rust/pull/113386
- https://github.com/rust-lang/rust/pull/113392
I'd like to wait for these for two reasons: to make it easier to see the
differences between the 2015/2018/2021 style edition and the 2024 style
edition (without the noise of guide-wide changes), and to minimize confusion so
that bugfixes to the style guide that we include in the previous edition don't
look like they're only part of the 2024 style edition.
I've used "Miscellaneous `rustfmt` bugfixes" as a starting point for the list
of 2024 changes, for now. We can update that when we add more 2024 changes.
The section added in this PR can then serve as a baseline for our drafts of
2024 style edition changes.
In the meantime, I'd like to get someone from `@rust-lang/style` to review and
approve the text here; I'll update it with a commit hash when the above PRs
have merged.
