cg_llvm: Move target machine command-line quoting from C++ to Rust

[Zalathar]

When this code was introduced in #130446 and #131805, it was complicated by the need to maintain compatibility with earlier versions of LLVM.

Now that LLVM 20 is the baseline (#145071), we can do all of the quoting in pure Rust code, and pass two flat strings to LLVM to be used as-is.

---

In this PR, my priority has been to preserve the existing behaviour as much as possible, without worrying too much about what the behaviour should be. (Though I did avoid a leading space before the first argument.)

[rustbot]

r? @lcnr

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[Zalathar]

cc @durin42 @nebulark @aeubanks (contributors to the C++ code being replaced)

[Zalathar]

@bors try jobs=x86_64-msvc-1,x86_64-msvc-2

[rust-bors]

💔 Test for bee730a failed: CI. Failed jobs:

• try - x86_64-msvc-1 (web logs, extended logs)

[Zalathar]

Oh I see, setting Quote = true causes each argument to always be quoted, regardless of whether it contains any parts that would need quoting.

@rustbot author

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[Zalathar]

I've heard second-hand that this function shows up on perf results. I don't know whether that's true, but it can't hurt to check.

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 44b341a (44b341a1c7f27c26b78205e3264d584b69a9c53f, parent: 93117677d857bb7c3f12c9dc500d77839f8fb13d)

[rust-timer]

Finished benchmarking commit (44b341a): comparison URL.

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

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.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@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)	0.2%	[0.2%, 0.2%]	2
Regressions ❌ (secondary)	0.2%	[0.1%, 0.3%]	16
Improvements ✅ (primary)	-0.4%	[-0.5%, -0.2%]	4
Improvements ✅ (secondary)	-3.1%	[-23.4%, -0.2%]	15
All ❌✅ (primary)	-0.2%	[-0.5%, 0.2%]	6

Max RSS (memory usage)

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

Cycles

Results (secondary -5.3%)

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)	2.1%	[2.1%, 2.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-9.0%	[-9.4%, -8.6%]	2
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 471.663s -> 472.562s (0.19%)
Artifact size: 387.94 MiB -> 387.87 MiB (-0.02%)

[Zalathar]

There's more followup that could be done here, like doing this quoting only once (instead of per-CGU), or skipping it for non-PDB targets. But I think that just moving the quoting step from C++ to Rust is worth landing on its own.

@rustbot ready

[lcnr]

r? @nikic (i can't read the replaced c++ code ✨ )

[nikic]

@bors r+

[bors]

📌 Commit 8b0a254 has been approved by nikic

It is now in the queue for this repository.

[bors]

⌛ Testing commit 8b0a254 with merge 0be8e16...

[bors]

☀️ Test successful - checks-actions
Approved by: nikic
Pushing 0be8e16 to master...

[github-actions]

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 5904356 (parent) -> 0be8e16 (this PR)

Test differences

Show 2 test diffs

2 doctest diffs were found. These are ignored, as they are noisy.

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 0be8e16088894483a7012c5026c3247c14a0c3c2 --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

1. aarch64-apple: 5671.4s -> 6397.4s (12.8%)
2. dist-aarch64-apple: 6108.6s -> 6660.7s (9.0%)
3. x86_64-mingw-2: 7795.4s -> 8429.4s (8.1%)
4. dist-x86_64-windows-gnullvm: 4769.5s -> 5093.2s (6.8%)
5. dist-x86_64-apple: 7808.8s -> 7298.5s (-6.5%)
6. x86_64-gnu: 6956.3s -> 6581.8s (-5.4%)
7. x86_64-msvc-2: 7157.6s -> 6782.6s (-5.2%)
8. x86_64-msvc-ext3: 6312.6s -> 6627.0s (5.0%)
9. dist-ohos-armv7: 4152.6s -> 3958.7s (-4.7%)
10. dist-x86_64-mingw: 9413.0s -> 9046.7s (-3.9%)

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]

Finished benchmarking commit (0be8e16): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -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)	-0.4%	[-0.6%, -0.2%]	4
Improvements ✅ (secondary)	-3.0%	[-23.4%, -0.2%]	16
All ❌✅ (primary)	-0.4%	[-0.6%, -0.2%]	4

Max RSS (memory usage)

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

Cycles

Results (secondary -4.8%)

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)	2.5%	[2.5%, 2.5%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-8.4%	[-9.5%, -7.3%]	2
All ❌✅ (primary)	-	-	0

Binary size

Results (secondary 0.0%)

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)	0.0%	[0.0%, 0.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Bootstrap: 471.972s -> 472.625s (0.14%)
Artifact size: 389.96 MiB -> 389.93 MiB (-0.01%)