| Age | Commit message (Collapse) | Author | Lines |
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Fix compiling other codegen backends when llvm is enabled
Extracted from #81746
Without this change rustbuild will not pass the required linker argument to find libllvm. While other backends likely don't use libllvm, it is necessary to be able to link against rustc_driver as the llvm backend is linked into it.
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Now that Cargo deduplicates diagnostics from different targets, this doesn't flood the console with
duplicate errors.
Note that this doesn't add `--all-targets` in `Builder::cargo` directly because `impl Step for Std`
actually wants to omit `--all-targets` the first time while it's still building libtest.
When passed `--all-targets`, this warns that the option isn't needed, but still continues to compile.
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Rollup of 7 pull requests
Successful merges:
- #85807 (bootstrap: Disable initial-exec TLS model on powerpc)
- #87761 (Fix overflow in rustc happening if the `err_count()` is reduced in a stage.)
- #87775 (Add hint for unresolved associated trait items if the trait has a single item)
- #87779 (Remove special case for statement `NodeId` assignment)
- #87787 (Use `C-unwind` ABI for `__rust_start_panic` in `panic_abort`)
- #87809 (Fix typo in the ptr documentation)
- #87816 (Sync rustc_codegen_cranelift)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
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r=Mark-Simulacrum
bootstrap: Disable initial-exec TLS model on powerpc
Fixes #81334.
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The options are `overflow-checks` and `overflow-checks-std`
defaulting to false.
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The recursion_limit attribute avoids the following error:
```
error[E0275]: overflow evaluating the requirement `std::ptr::Unique<rustc_ast::Pat>: std::marker::Send`
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= help: consider adding a `#![recursion_limit="256"]` attribute to your crate (`rustfmt_nightly`)
```
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* Make html-checker run by default on rust compiler docs as well
* Ensure html-checker is run on CI
* Lazify tidy binary presence check
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The `RustdocGUI::should_run` condition spawns `npm list` several times
which adds up to seconds of wall-time.
Evaluate the condition lazily to to keep `./x.py test tidy` and similar
short-running tasks fast.
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## User-facing changes
- Intra-doc links to primitives that currently go to rust-lang.org/nightly/std/primitive.x.html will start going to channel that rustdoc was built with. Nightly will continue going to /nightly; Beta will link to /beta; stable compilers will link to /1.52.1 (or whatever version they were built as).
- Cross-crate links from std to core currently go to /nightly unconditionally. They will start going to /1.52.0 on stable channels (but remain the same on nightly channels).
- Intra-crate links from std to std (or core to core) currently go to the same URL they are hosted at; they will continue to do so. Notably, this is different from everything else because it can preserve the distinction between /stable and /1.52.0 by using relative links.
Note that "links" includes both intra-doc links and rustdoc's own
automatically generated hyperlinks.
## Implementation changes
- Update the testsuite to allow linking to /beta and /1.52.1 in docs
- Use an html_root_url for the standard library that's dependent on the channel
This avoids linking to nightly docs on stable.
- Update rustdoc to use channel-dependent links for primitives from an
unknown crate
- Set DOC_RUST_LANG_ORG_CHANNEL from bootstrap to ensure it's in sync
- Include doc.rust-lang.org in the channel
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Fixes #81334.
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- Add rustfmt to `x.py check`
- Update Cargo.lock
- Remove rustfmt from the toolstate list
- Make rustfmt an in-tree tool
- Give an error on `x.py test rustfmt` if rustfmt fails to build or if tests fail
- Don't call `save_toolstate` when testing rustfmt
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Allow checking miri and RLS with `x.py check src/tools/{miri,rls}`
Helps with https://github.com/rust-lang/rust/issues/80639.
`@Xanewok` would you find this useful for RLS too?
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Now that stdarch has been updated, we can do this without breaking the
build.
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- Add clippy_dev to the rust workspace
Before, it would give an error that it wasn't either included or
excluded from the workspace:
```
error: current package believes it's in a workspace when it's not:
current: /home/joshua/rustc/src/tools/clippy/clippy_dev/Cargo.toml
workspace: /home/joshua/rustc/Cargo.toml
this may be fixable by adding `src/tools/clippy/clippy_dev` to the `workspace.members` array of the manifest located at: /home/joshua/rustc/Cargo.toml
Alternatively, to keep it out of the workspace, add the package to the `workspace.exclude` array, or add an empty `[workspace]` table to the package's manifest.
```
- Change clippy's copy of compiletest not to special-case
rust-lang/rust. Using OUT_DIR confused `clippy_dev` and it couldn't find
the test outputs. This is one of the reasons why `cargo dev bless` used
to silently do nothing (the others were that `CARGO_TARGET_DIR` and
`PROFILE` weren't set appropriately).
- Run clippy_dev on test failure
I tested this by removing a couple lines from a stderr file, and they
were correctly replaced.
- Fix clippy_dev warnings
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Adds bootstrap rules to support installing rust-demangler.
When compiling with `-Z instrument-coverage`, the coverage reports are
generated by `llvm-cov`. `llvm-cov` includes a built-in demangler for
C++, and an option to supply an alternate demangler. For Rust, we have
`rust-demangler`, currently used in `rustc` coverage tests.
Fuchsia's toolchain for Rust is built via `./x.py install`. Fuchsia is
adding support for Rust coverage, and we need to include the
`rust-demangler` in the installed `bin` directory.
Configured rust-demangler as an in-tree extended tool.
Added tests to support `./x.py test rust-demangler`.
Install with extended tools by default only if `profiler = true`.
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- Rename `broken_intra_doc_links` to `rustdoc::broken_intra_doc_links`
- Ensure that the old lint names still work and give deprecation errors
- Register lints even when running doctests
Otherwise, all `rustdoc::` lints would be ignored.
- Register all existing lints as removed
This unfortunately doesn't work with `register_renamed` because tool
lints have not yet been registered when rustc is running. For similar
reasons, `check_backwards_compat` doesn't work either. Call
`register_removed` directly instead.
- Fix fallout
+ Rustdoc lints for compiler/
+ Rustdoc lints for library/
Note that this does *not* suggest `rustdoc::broken_intra_doc_links` for
`rustdoc::intra_doc_link_resolution_failure`, since there was no time
when the latter was valid.
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Remove `ENABLE_DOWNLOAD_RUSTC` constant
`ENABLE_DOWNLOAD_RUSTC` was introduced as part of the MVP for `download-rustc` as a way not to rebuild artifacts that have already been downloaded. Unfortunately, it doesn't work very well:
- Steps are ignored by default, which makes it easy to leave out a step
that should be built. For example, the MVP forgot to enable any tests,
so it was only possible to *build* locally.
- It didn't work correctly even when it was enabled: calling
`builder.ensure()` would completely ignore the constant and rebuild the
step anyway. This has no obvious fix since `ensure()` has to return a
`Step::Output`.
Instead, this handles `download-rustc` in `impl Step for Rustc` and
`impl Step for Std`, which to my knowledge are the only build steps that
don't first go through `impl Step for Sysroot` (`Rustc` is used for
the `rustc-dev` component).
See https://github.com/rust-lang/rust/pull/79540#discussion_r563350075 and https://github.com/rust-lang/rust/issues/81930 for further context.
Here are some example runs with these changes and `download-rustc`
enabled:
```
$ x.py build src/tools/clippy
Building stage1 tool clippy-driver (x86_64-unknown-linux-gnu)
Finished release [optimized] target(s) in 1m 09s
Building stage1 tool cargo-clippy (x86_64-unknown-linux-gnu)
Finished release [optimized] target(s) in 0.11s
$ x.py test src/tools/clippy
Finished dev [unoptimized + debuginfo] target(s) in 0.09s
Building stage1 tool clippy-driver (x86_64-unknown-linux-gnu)
Finished release [optimized] target(s) in 0.09s
Building rustdoc for stage1 (x86_64-unknown-linux-gnu)
Finished release [optimized] target(s) in 0.28s
Finished release [optimized] target(s) in 15.26s
Running build/x86_64-unknown-linux-gnu/stage1-tools/x86_64-unknown-linux-gnu/release/deps/clippy_driver-8b407b140e0aa91c
test result: ok. 592 passed; 0 failed; 3 ignored; 0 measured; 0 filtered out
$ x.py build src/tools/rustdoc
Building rustdoc for stage1 (x86_64-unknown-linux-gnu)
Finished release [optimized] target(s) in 41.28s
Build completed successfully in 0:00:41
$ x.py test src/test/rustdoc-ui
Building stage0 tool compiletest (x86_64-unknown-linux-gnu)
Finished release [optimized] target(s) in 0.12s
Building rustdoc for stage1 (x86_64-unknown-linux-gnu)
Finished release [optimized] target(s) in 0.10s
test result: ok. 105 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 8.15s
$ x.py build compiler/rustc
Finished dev [unoptimized + debuginfo] target(s) in 0.09s
Build completed successfully in 0:00:00
```
Note a few things:
- Clippy depends on stage1 rustc-dev artifacts, but rustc didn't have to
be recompiled. Instead, the artifacts were copied automatically.
- All steps are always enabled. There is no danger of forgetting a step,
since only the entrypoints have to handle `download-rustc`.
- Building the compiler (`compiler/rustc`) automatically does no work.
Helps with https://github.com/rust-lang/rust/issues/81930.
r? `@Mark-Simulacrum`
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Add `build.print_step_rusage` to config.toml
Adds `build.print_step_rusage` to config.toml, which is meant to be an easy way to let compiler developers get feedback on the terminal during bootstrap about resource usage during each step.
The output is piggy-backed on `[PRINT-STEP-TIMINGS]`, mostly because the functionality seemed to naturally fit there in the overall control-flow and output structure (even if very little is shared between the implementations themselves).
Some sample output (from my Linux box, where I believe the `max rss` output to be somewhat trust-worthy...):
```
[...]
Compiling regex v1.4.3
[RUSTC-TIMING] tempfile test:false 0.323 user: 1.418662 sys: 0.81767 max rss (kb): 182084 page reclaims: 26615 page faults: 0 fs block inputs: 0 fs block outputs: 2160 voluntary ctxt switches: 798 involuntary ctxt switches: 131
Completed tempfile v3.1.0 in 0.3s
[RUSTC-TIMING] chalk_ir test:false 1.890 user: 1.893603 sys: 0.99663 max rss (kb): 239432 page reclaims: 32107 page faults: 0 fs block inputs: 0 fs block outputs: 25008 voluntary ctxt switches: 108 involuntary ctxt switches: 183
Completed chalk-ir v0.55.0 in 1.9s
Compiling rustc_data_structures v0.0.0 (/home/pnkfelix/Dev/Rust/rust.git/compiler/rustc_data_structures)
[RUSTC-TIMING] chrono test:false 1.244 user: 3.333198 sys: 0.134963 max rss (kb): 246612 page reclaims: 44857 page faults: 0 fs block inputs: 0 fs block outputs: 11704 voluntary ctxt switches: 1043 involuntary ctxt switches: 326
Completed chrono v0.4.15 in 1.3s
[RUSTC-TIMING] rustc_rayon test:false 1.332 user: 1.763912 sys: 0.75996 max rss (kb): 239076 page reclaims: 35285 page faults: 0 fs block inputs: 0 fs block outputs: 19576 voluntary ctxt switches: 359 involuntary ctxt switches: 168
Completed rustc-rayon v0.3.0 in 1.3s
Compiling matchers v0.0.1
[RUSTC-TIMING] matchers test:false 0.100 user: 0.94495 sys: 0.15119 max rss (kb): 140076 page reclaims: 8200 page faults: 0 fs block inputs: 0 fs block outputs: 392 voluntary ctxt switches: 43 involuntary ctxt switches: 12
Completed matchers v0.0.1 in 0.1s
[...]
```
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Propagate RUSTDOCFLAGS in the environment when documenting
Previously, RUSTDOCFLAGS would get overriden when bootstrap set
`RUSTDOCFLAGS` itself. Propagate the flag manually, using the same logic
as `RUSTFLAGS`.
Fixes https://github.com/rust-lang/rust/issues/75256.
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Intended to piggy-back on output from existing build.print_step_timings setting.
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This was introduced as part of the MVP for `download-rustc`.
Unfortunately, it doesn't work very well:
- Steps are ignored by default, which makes it easy to leave out a step
that should be built. For example, the MVP forgot to enable any tests,
so it was *only* possible to build locally.
- It didn't work correctly even when it was enabled: calling
`builder.ensure()` would completely ignore the constant and rebuild the
step anyway. This has no obvious fix since `ensure()` has to return a
`Step::Output`.
Instead, this handles `download-rustc` in `impl Step for Rustc` and
`impl Step for Std`, which to my knowledge are the only build steps that
don't first go through `impl Step for Sysroot` (`Rustc` is used for
the `rustc-dev` component).
See https://github.com/rust-lang/rust/pull/79540#discussion_r563350075
and https://github.com/rust-lang/rust/issues/81930 for further context.
Here are some example runs with these changes and `download-rustc`
enabled:
```
$ x.py build src/tools/clippy
Building stage1 tool clippy-driver (x86_64-unknown-linux-gnu)
Finished release [optimized] target(s) in 1m 09s
Building stage1 tool cargo-clippy (x86_64-unknown-linux-gnu)
Finished release [optimized] target(s) in 0.11s
$ x.py test src/tools/clippy
Updating only changed submodules
Submodules updated in 0.01 seconds
Finished dev [unoptimized + debuginfo] target(s) in 0.09s
Building stage1 tool clippy-driver (x86_64-unknown-linux-gnu)
Finished release [optimized] target(s) in 0.09s
Building rustdoc for stage1 (x86_64-unknown-linux-gnu)
Finished release [optimized] target(s) in 0.28s
Finished release [optimized] target(s) in 15.26s
Running build/x86_64-unknown-linux-gnu/stage1-tools/x86_64-unknown-linux-gnu/release/deps/clippy_driver-8b407b140e0aa91c
test result: ok. 592 passed; 0 failed; 3 ignored; 0 measured; 0 filtered out
$ x.py build src/tools/rustdoc
Building rustdoc for stage1 (x86_64-unknown-linux-gnu)
Finished release [optimized] target(s) in 41.28s
Build completed successfully in 0:00:41
$ x.py test src/test/rustdoc-ui
Building stage0 tool compiletest (x86_64-unknown-linux-gnu)
Finished release [optimized] target(s) in 0.12s
Building rustdoc for stage1 (x86_64-unknown-linux-gnu)
Finished release [optimized] target(s) in 0.10s
test result: ok. 105 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 8.15s
$ x.py build compiler/rustc
Finished dev [unoptimized + debuginfo] target(s) in 0.09s
Build completed successfully in 0:00:00
```
Note a few things:
- Clippy depends on stage1 rustc-dev artifacts, but rustc didn't have to
be recompiled. Instead, the artifacts were copied automatically.
- All steps are always enabled. There is no danger of forgetting a step,
since only the entrypoints have to handle `download-rustc`.
- Building the compiler (`compiler/rustc`) automatically does no work.
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Update the bootstrap compiler
This updates the bootstrap compiler, notably leaving out a change to enable semicolon in macro expressions lint, because stdarch still depends on the old behavior.
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Previously, RUSTDOCFLAGS would get overriden when bootstrap set
`RUSTDOCFLAGS` itself. Propagate the flag manually, using the same logic
as `RUSTFLAGS`.
This also extracts the logic into a helper function to make sure it's
the same.
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std_detect is still using this and as it's in a submodule updating it will be a
pain. We can catch this either after a stdarch submodule bump or just on the
next cycle.
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Note this does not change `core::derive` since it was merged after the
beta bump.
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Remove unnecessary `Option` in `default_doc`
Previously, there were two different ways to encode the same info: `None` or
`Some(&[])`. Now there is only one way, `&[]`.
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Previously, there two different ways to encode the same info: `None` or
`Some(&[])`. Now there is only one way, `&[]`.
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Use format string in bootstrap panic instead of a string directly
This fixes the following warning when compiling with nightly:
```
warning: panic message is not a string literal
--> src/bootstrap/builder.rs:1515:24
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1515 | panic!(out);
| ^^^
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= note: `#[warn(non_fmt_panic)]` on by default
= note: this is no longer accepted in Rust 2021
help: add a "{}" format string to Display the message
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1515 | panic!("{}", out);
| ^^^^^
help: or use std::panic::panic_any instead
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1515 | std::panic::panic_any(out);
| ^^^^^^^^^^^^^^^^^^^^^^
```
Found while working on https://github.com/rust-lang/rust/pull/79540. cc https://github.com/rust-lang/rust/pull/81645, which landed in 1.51.
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- Use the same compiler for stage0 and stage1. This should be fixed at
some point (so bootstrap isn't constantly rebuilt).
- Make sure `x.py build` and `x.py check` work.
- Use `git merge-base` to determine the most recent commit to download.
- Copy stage0 to the various sysroots in `Sysroot`, and delegate to
Sysroot in Assemble. Leave all other code unchanged.
- Rename date -> key
This can also be a commit hash, so 'date' is no longer a good name.
- Add the commented-out option to config.toml.example
- Disable all steps by default when `download-rustc` is enabled
Most steps don't make sense when downloading a compiler, because they'll
be pre-built in the sysroot. Only enable the ones that might be useful,
in particular Rustdoc and all `check` steps.
At some point, this should probably enable other tools, but rustdoc is
enough to test out `download-rustc`.
- Don't print 'Skipping' twice in a row
Bootstrap forcibly enables a dry run if it isn't already set, so
previously it would print the message twice:
```
Skipping bootstrap::compile::Std because it is not enabled for `download-rustc`
Skipping bootstrap::compile::Std because it is not enabled for `download-rustc`
```
Now it correctly only prints once.
## Future work
- Add FIXME about supporting beta commits
- Debug logging will never work. This should be fixed.
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This fixes the following warning when compiling with nightly:
```
warning: panic message is not a string literal
--> src/bootstrap/builder.rs:1515:24
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1515 | panic!(out);
| ^^^
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= note: `#[warn(non_fmt_panic)]` on by default
= note: this is no longer accepted in Rust 2021
help: add a "{}" format string to Display the message
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1515 | panic!("{}", out);
| ^^^^^
help: or use std::panic::panic_any instead
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1515 | std::panic::panic_any(out);
| ^^^^^^^^^^^^^^^^^^^^^^
```
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r=petrochenkov
Add `SEMICOLON_IN_EXPRESSIONS_FROM_MACROS` lint
cc #79813
This PR adds an allow-by-default future-compatibility lint
`SEMICOLON_IN_EXPRESSIONS_FROM_MACROS`. It fires when a trailing semicolon in a
macro body is ignored due to the macro being used in expression
position:
```rust
macro_rules! foo {
() => {
true; // WARN
}
}
fn main() {
let val = match true {
true => false,
_ => foo!()
};
}
```
The lint takes its level from the macro call site, and
can be allowed for a particular macro by adding
`#[allow(macro_trailing_semicolon)]`.
The lint is set to warn for all internal rustc crates (when being built
by a stage1 compiler). After the next beta bump, we can enable
the lint for the bootstrap compiler as well.
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This commit adds a new stable codegen option to rustc,
`-Csplit-debuginfo`. The old `-Zrun-dsymutil` flag is deleted and now
subsumed by this stable flag. Additionally `-Zsplit-dwarf` is also
subsumed by this flag but still requires `-Zunstable-options` to
actually activate. The `-Csplit-debuginfo` flag takes one of
three values:
* `off` - This indicates that split-debuginfo from the final artifact is
not desired. This is not supported on Windows and is the default on
Unix platforms except macOS. On macOS this means that `dsymutil` is
not executed.
* `packed` - This means that debuginfo is desired in one location
separate from the main executable. This is the default on Windows
(`*.pdb`) and macOS (`*.dSYM`). On other Unix platforms this subsumes
`-Zsplit-dwarf=single` and produces a `*.dwp` file.
* `unpacked` - This means that debuginfo will be roughly equivalent to
object files, meaning that it's throughout the build directory
rather than in one location (often the fastest for local development).
This is not the default on any platform and is not supported on Windows.
Each target can indicate its own default preference for how debuginfo is
handled. Almost all platforms default to `off` except for Windows and
macOS which default to `packed` for historical reasons.
Some equivalencies for previous unstable flags with the new flags are:
* `-Zrun-dsymutil=yes` -> `-Csplit-debuginfo=packed`
* `-Zrun-dsymutil=no` -> `-Csplit-debuginfo=unpacked`
* `-Zsplit-dwarf=single` -> `-Csplit-debuginfo=packed`
* `-Zsplit-dwarf=split` -> `-Csplit-debuginfo=unpacked`
Note that `-Csplit-debuginfo` still requires `-Zunstable-options` for
non-macOS platforms since split-dwarf support was *just* implemented in
rustc.
There's some more rationale listed on #79361, but the main gist of the
motivation for this commit is that `dsymutil` can take quite a long time
to execute in debug builds and provides little benefit. This means that
incremental compile times appear that much worse on macOS because the
compiler is constantly running `dsymutil` over every single binary it
produces during `cargo build` (even build scripts!). Ideally rustc would
switch to not running `dsymutil` by default, but that's a problem left
to get tackled another day.
Closes #79361
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cc #79813
This PR adds an allow-by-default future-compatibility lint
`SEMICOLON_IN_EXPRESSIONS_FROM_MACROS`. It fires when a trailing semicolon in a
macro body is ignored due to the macro being used in expression
position:
```rust
macro_rules! foo {
() => {
true; // WARN
}
}
fn main() {
let val = match true {
true => false,
_ => foo!()
};
}
```
The lint takes its level from the macro call site, and
can be allowed for a particular macro by adding
`#[allow(semicolon_in_expressions_from_macros)]`.
The lint is set to warn for all internal rustc crates (when being built
by a stage1 compiler). After the next beta bump, we can enable
the lint for the bootstrap compiler as well.
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addresses:
clippy::or_fun_call
clippy::single_char_add_str
clippy::comparison_to_empty
clippy::or_fun_call
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Utilize PGO for rustc linux dist builds
This implements support for applying PGO to the rustc compilation step (not
standard library or any tooling, including rustdoc). Expanding PGO to more tools
is not terribly difficult but will involve more work and greater CI time
commitment.
For the same reason of avoiding greater implementation time commitment,
implementing for platforms outside of x86_64-unknown-linux-gnu is skipped.
In practice it should be quite simple to extend over time to more platforms. The
initial implementation is intentionally minimal here to avoid too much work
investment before we start seeing wins for a subset of Rust users.
The choice of workloads to profile here is somewhat arbitrary, but the general
rationale was to aim for a small set that largely avoided time regressions on
perf.rust-lang.org's full suite of crates. The set chosen is libcore, cargo (and
its dependencies), and a few ad-hoc stress tests from perf.rlo. The stress tests
are arguably the most controversial, but they benefit those cases (avoiding
regressions) and do not really remove wins from other benchmarks.
The primary next step after this PR lands is to implement support for PGO in
LLVM. It is unclear whether we can afford a full LLVM rebuild in CI, though, so
the approach taken there may need to be more staggered. rustc-only PGO seems
well affordable on linux at least, giving us up to 20% wall time wins on some
crates for 15 minutes of extra CI time (1 hour with this PR, up from 45 minutes).
The PGO data is uploaded to allow others to reuse it if attempting to reproduce
the CI build or potentially, in the future, on other platforms where an
off-by-one strategy is used for dist builds at minimal performance cost.
r? `@michaelwoerister` (but tell me if you don't want to / don't feel comfortable approving and we can find others)
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This implements support for applying PGO to the rustc compilation step (not
standard library or any tooling, including rustdoc). Expanding PGO to more tools
is not terribly difficult but will involve more work and greater CI time
commitment.
For the same reason of avoiding greater time commitment, this currently avoids
implementing for platforms outside of x86_64-unknown-linux-gnu, though in
practice it should be quite simple to extend over time to more platforms. The
initial implementation is intentionally minimal here to avoid too much work
investment before we start seeing wins for a subset of Rust users.
The choice of workloads to profile here is somewhat arbitrary, but the general
rationale was to aim for a small set that largely avoided time regressions on
perf.rust-lang.org's full suite of crates. The set chosen is libcore, cargo (and
its dependencies), and a few ad-hoc stress tests from perf.rlo. The stress tests
are arguably the most controversial, but they benefit those cases (avoiding
regressions) and do not really remove wins from other benchmarks.
The primary next step after this PR lands is to implement support for PGO in
LLVM. It is unclear whether we can afford a full LLVM rebuild in CI, though, so
the approach taken there may need to be more staggered. rustc-only PGO seems
well affordable on linux at least, giving us up to 20% wall time wins on some
crates for 15 minutes of extra CI time (1 hour up from 45 minutes).
The PGO data is uploaded to allow others to reuse it if attempting to reproduce
the CI build or potentially, in the future, on other platforms where an
off-by-one strategy is used for dist builds at minimal performance cost.
|