Remove current code for embedding command-line args in PDB #147022

Zalathar · 2025-09-25T11:21:51Z

The compiler currently has code that will obtain a list of quoted command-line arguments, and pass it through to TargetMachine creation, so that the command-line args can be embedded in PDB output.

This PR removes that code, due to subtle concerns that might not have been apparent when it was originally added.

Those concerns include:

The entire command-line quoting process is repeated every time a target-machine-factory is created. In incremental builds this typically occurs 500+ times, instead of happening only once. The repeated quoting constitutes a large chunk of instructions executed in the large-workspace benchmark.
- See (EXPERIMENT) Perf experiments for target-machine command-line quoting #146804 (comment) for an example of the perf consequences of skipping all that work.
- This overhead occurs even when building for targets or configurations that don't emit PDB output.
Command-line arguments are obtained in a way that completely bypasses the query system, which is a problem for the integrity of incremental compilation.
- Fixing this alone is likely to inhibit incremental rebuilds for most or all CGUs, even in builds that don't emit PDB output.
Command-line arguments and the executable path are obtained in a way that completely bypasses the compiler's path-remapping system, which is a reproducibility hazard.
- LF_BUILDINFO introduces non-determinism to Windows rlib builds #128842

Relevant PRs:

Zulip thread:

https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/Some.20PDB.20info.20bypasses.20the.20query.20system.20and.20path.20remapping/with/541432211

According to #96475, one of the big motivations for embedding the command-line arguments was to enable tools like Live++. It appears that Live++ doesn't actually support Rust yet, so it's possible that there aren't any existing workflows for this removal to break.

In the future, there could be a case for reintroducing some or all of this functionality, guarded behind an opt-in flag so that it doesn't cause problems for other users. But as it stands, the current implementation puts a disproportionate burden on other users and on compiler maintainers.

rustbot · 2025-09-25T11:21:54Z

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

rustbot · 2025-09-25T11:21:56Z

r? @petrochenkov

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Zalathar · 2025-09-25T13:50:24Z

@bors try @rust-timer queue

Remove current code for embedding command-line args in PDB

Zalathar · 2025-09-25T14:16:49Z

Looks flaky. Let’s try again.

@bors try @rust-timer queue

Remove current code for embedding command-line args in PDB

rust-bors · 2025-09-25T16:27:39Z

☀️ Try build successful (CI)
Build commit: e4d7ba7 (e4d7ba78e779e732d68b8f16c4348091513822d2, parent: 7cfd7d328b14b936c7ffede92cacebe8557c6388)

rust-timer · 2025-09-25T17:38:13Z

Finished benchmarking commit (e4d7ba7): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.3%	[-0.5%, -0.2%]	8
Improvements ✅ (secondary)	-3.7%	[-20.6%, -0.7%]	17
All ❌✅ (primary)	-0.3%	[-0.5%, -0.2%]	8

Max RSS (memory usage)

Results (primary 4.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	4.1%	[4.1%, 4.1%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	4.1%	[4.1%, 4.1%]	1

Cycles

Results (secondary -2.8%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.4%	[2.0%, 2.7%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.2%	[-7.2%, -2.1%]	11
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 469.935s -> 470.607s (0.14%)
Artifact size: 388.04 MiB -> 388.06 MiB (0.01%)

rust-rfcbot · 2025-10-17T21:23:06Z

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

rustbot · 2025-10-17T23:30:33Z

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

Zalathar · 2025-10-17T23:30:52Z

(Rebased; no changes.)

Also, one of the ui-fulldeps tests needed a trivial fix.

wesleywiser · 2025-10-21T19:41:25Z

@bors r+

bors · 2025-10-21T19:41:28Z

📌 Commit 98c95c9 has been approved by wesleywiser

It is now in the queue for this repository.

bors · 2025-10-22T00:21:12Z

⌛ Testing commit 98c95c9 with merge 96fe3c3...

bors · 2025-10-22T03:31:37Z

☀️ Test successful - checks-actions
Approved by: wesleywiser
Pushing 96fe3c3 to master...

github-actions · 2025-10-22T03:34:55Z

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 37ec98f (parent) -> 96fe3c3 (this PR)

Test differences

Show 3 test diffs

Stage 1

[run-make] tests/run-make/pdb-buildinfo-cl-cmd: ignore (only executed when the operating system and target environment are windows-msvc) -> [missing] (J2)

Stage 2

[run-make] tests/run-make/pdb-buildinfo-cl-cmd: ignore (only executed when the operating system and target environment are windows-msvc) -> [missing] (J0)
[run-make] tests/run-make/pdb-buildinfo-cl-cmd: pass -> [missing] (J1)

Job group index

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 96fe3c31c2ec385f3d3263346bcdde3d118cdaf6 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

x86_64-gnu-llvm-20: 2328.3s -> 2794.9s (20.0%)
dist-aarch64-apple: 7586.1s -> 6360.8s (-16.2%)
x86_64-gnu-llvm-20-1: 3198.1s -> 3611.7s (12.9%)
aarch64-apple: 8042.2s -> 9058.7s (12.6%)
aarch64-gnu-llvm-20-2: 2269.8s -> 2531.4s (11.5%)
x86_64-rust-for-linux: 2744.5s -> 3049.8s (11.1%)
tidy: 187.7s -> 205.5s (9.5%)
dist-apple-various: 3722.5s -> 4071.3s (9.4%)
pr-check-1: 1832.4s -> 1996.8s (9.0%)
x86_64-gnu-llvm-20-3: 6271.2s -> 6694.2s (6.7%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

rust-timer · 2025-10-22T04:43:14Z

Finished benchmarking commit (96fe3c3): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Our benchmarks found a performance regression caused by this PR.
This might be an actual regression, but it can also be just noise.

Next Steps:

If the regression was expected or you think it can be justified,
please write a comment with sufficient written justification, and add
@rustbot label: +perf-regression-triaged to it, to mark the regression as triaged.
If you think that you know of a way to resolve the regression, try to create
a new PR with a fix for the regression.
If you do not understand the regression or you think that it is just noise,
you can ask the @rust-lang/wg-compiler-performance working group for help (members of this group
were already notified of this PR).

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	1.2%	[1.2%, 1.2%]	1
Regressions ❌ (secondary)	1.2%	[1.2%, 1.2%]	1
Improvements ✅ (primary)	-0.3%	[-0.4%, -0.2%]	6
Improvements ✅ (secondary)	-4.2%	[-20.9%, -0.3%]	14
All ❌✅ (primary)	-0.1%	[-0.4%, 1.2%]	7

Max RSS (memory usage)

This benchmark run did not return any relevant results for this metric.

Cycles

Results (secondary -5.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-5.0%	[-6.6%, -2.9%]	5
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 472.516s -> 472.935s (0.09%)
Artifact size: 388.62 MiB -> 388.69 MiB (0.02%)

Zalathar · 2025-10-22T05:44:18Z

The syn regressions are pretty clearly noise.

panstromek · 2025-10-27T14:47:58Z

perf triage:

syn regression is noise as noted in the above comment.

@rustbot label: +perf-regression-triaged

This MR contains the following updates: | Package | Update | Change | |---|---|---| | [rust](https://github.com/rust-lang/rust) | minor | `1.91.1` -> `1.92.0` | MR created with the help of [el-capitano/tools/renovate-bot](https://gitlab.com/el-capitano/tools/renovate-bot). **Proposed changes to behavior should be submitted there as MRs.** --- ### Release Notes <details> <summary>rust-lang/rust (rust)</summary> ### [`v1.92.0`](https://github.com/rust-lang/rust/blob/HEAD/RELEASES.md#Version-1920-2025-12-11) [Compare Source](rust-lang/rust@1.91.1...1.92.0) \========================== <a id="1.92.0-Language"></a> ## Language - [Document `MaybeUninit` representation and validity](rust-lang/rust#140463) - [Allow `&raw [mut | const]` for union field in safe code](rust-lang/rust#141469) - [Prefer item bounds of associated types over where-bounds for auto-traits and `Sized`](rust-lang/rust#144064) - [Do not materialize `X` in `[X; 0]` when `X` is unsizing a const](rust-lang/rust#145277) - [Support combining `#[track_caller]` and `#[no_mangle]` (requires every declaration specifying `#[track_caller]` as well)](rust-lang/rust#145724) - [Make never type lints `never_type_fallback_flowing_into_unsafe` and `dependency_on_unit_never_type_fallback` deny-by-default](rust-lang/rust#146167) - [Allow specifying multiple bounds for same associated item, except in trait objects](rust-lang/rust#146593) - [Slightly strengthen higher-ranked region handling in coherence](rust-lang/rust#146725) - [The `unused_must_use` lint no longer warns on `Result<(), Uninhabited>` (for instance, `Result<(), !>`), or `ControlFlow<Uninhabited, ()>`](rust-lang/rust#147382). This avoids having to check for an error that can never happen. <a id="1.92.0-Compiler"></a> ## Compiler - [Make `mips64el-unknown-linux-muslabi64` link dynamically](rust-lang/rust#146858) - [Remove current code for embedding command-line args in PDB](rust-lang/rust#147022) Command-line information is typically not needed by debugging tools, and the removed code was causing problems for incremental builds even on targets that don't use PDB debuginfo. <a id="1.92.0-Libraries"></a> ## Libraries - [Specialize `Iterator::eq{_by}` for `TrustedLen` iterators](rust-lang/rust#137122) - [Simplify `Extend` for tuples](rust-lang/rust#138799) - [Added details to `Debug` for `EncodeWide`](rust-lang/rust#140153). - [`iter::Repeat::last`](rust-lang/rust#147258) and [`count`](rust-lang/rust#146410) will now panic, rather than looping infinitely. <a id="1.92.0-Stabilized-APIs"></a> ## Stabilized APIs - [`NonZero<u{N}>::div_ceil`](https://doc.rust-lang.org/stable/std/num/struct.NonZero.html#method.div_ceil) - [`Location::file_as_c_str`](https://doc.rust-lang.org/stable/std/panic/struct.Location.html#method.file_as_c_str) - [`RwLockWriteGuard::downgrade`](https://doc.rust-lang.org/stable/std/sync/struct.RwLockWriteGuard.html#method.downgrade) - [`Box::new_zeroed`](https://doc.rust-lang.org/stable/std/boxed/struct.Box.html#method.new_zeroed) - [`Box::new_zeroed_slice`](https://doc.rust-lang.org/stable/std/boxed/struct.Box.html#method.new_zeroed_slice) - [`Rc::new_zeroed`](https://doc.rust-lang.org/stable/std/rc/struct.Rc.html#method.new_zeroed) - [`Rc::new_zeroed_slice`](https://doc.rust-lang.org/stable/std/rc/struct.Rc.html#method.new_zeroed_slice) - [`Arc::new_zeroed`](https://doc.rust-lang.org/stable/std/sync/struct.Arc.html#method.new_zeroed) - [`Arc::new_zeroed_slice`](https://doc.rust-lang.org/stable/std/sync/struct.Arc.html#method.new_zeroed_slice) - [`btree_map::Entry::insert_entry`](https://doc.rust-lang.org/stable/std/collections/btree_map/enum.Entry.html#method.insert_entry) - [`btree_map::VacantEntry::insert_entry`](https://doc.rust-lang.org/stable/std/collections/btree_map/struct.VacantEntry.html#method.insert_entry) - [`impl Extend<proc_macro::Group> for proc_macro::TokenStream`](https://doc.rust-lang.org/stable/proc_macro/struct.TokenStream.html#impl-Extend%3CGroup%3E-for-TokenStream) - [`impl Extend<proc_macro::Literal> for proc_macro::TokenStream`](https://doc.rust-lang.org/stable/proc_macro/struct.TokenStream.html#impl-Extend%3CLiteral%3E-for-TokenStream) - [`impl Extend<proc_macro::Punct> for proc_macro::TokenStream`](https://doc.rust-lang.org/stable/proc_macro/struct.TokenStream.html#impl-Extend%3CPunct%3E-for-TokenStream) - [`impl Extend<proc_macro::Ident> for proc_macro::TokenStream`](https://doc.rust-lang.org/stable/proc_macro/struct.TokenStream.html#impl-Extend%3CIdent%3E-for-TokenStream) These previously stable APIs are now stable in const contexts: - [`<[_]>::rotate_left`](https://doc.rust-lang.org/stable/std/primitive.slice.html#method.rotate_left) - [`<[_]>::rotate_right`](https://doc.rust-lang.org/stable/std/primitive.slice.html#method.rotate_right) <a id="1.92.0-Cargo"></a> ## Cargo - [Added a new chapter](rust-lang/cargo#16119) to the Cargo book, ["Optimizing Build Performance"](https://doc.rust-lang.org/stable/cargo/guide/build-performance.html). <a id="1.92.0-Rustdoc"></a> ## Rustdoc - [If a trait item appears in rustdoc search, hide the corresponding impl items](rust-lang/rust#145898). 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Build with `-C force-unwind-tables=no` to keep omitting unwind tables. * As part of the larger effort refactoring compiler built-in attributes and their diagnostics, [the future-compatibility lint `invalid_macro_export_arguments` is upgraded to deny-by-default and will be reported in dependencies too.](rust-lang/rust#143857) * [Update the minimum external LLVM to 20](rust-lang/rust#145071) * [Prevent downstream `impl DerefMut for Pin<LocalType>`](rust-lang/rust#145608) * [Don't apply temporary lifetime extension rules to the arguments of non-extended `pin!` and formatting macros](rust-lang/rust#145838) </details> --- ### Configuration 📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined). 🚦 **Automerge**: Disabled by config. 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rustbot assigned petrochenkov Sep 25, 2025

This was referenced Sep 25, 2025

cg_llvm: Perform target-machine command-line quoting as bytes, not characters #146957

Closed

Compute quoted args for debuginfo at most once per session #146973

Closed