Apply RemoveNoopLandingPads post-monomorphization by Mark-Simulacrum · Pull Request #143208 · rust-lang/rust

Mark-Simulacrum · 2025-06-29T17:22:48Z

On Cargo this cuts ~5% of the LLVM IR lines we generate (measured with -Cno-prepopulate-passes).

Remove no-op cleanups as post-mono MIR opt On cargo this cuts ~5% of the LLVM IR lines we generate (measured with -Cno-prepopulate-passes). Opening to assess performance.

rust-timer · 2025-07-01T15:56:56Z

Finished benchmarking commit (e3a4b05): 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)	0.4%	[0.4%, 0.4%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.0%	[-4.6%, -0.2%]	22
Improvements ✅ (secondary)	-2.8%	[-18.0%, -0.8%]	17
All ❌✅ (primary)	-1.9%	[-4.6%, 0.4%]	23

Max RSS (memory usage)

Results (primary -2.6%, secondary -1.3%)

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)	-	-	0
Improvements ✅ (primary)	-2.6%	[-3.8%, -1.2%]	6
Improvements ✅ (secondary)	-1.3%	[-2.8%, -0.5%]	3
All ❌✅ (primary)	-2.6%	[-3.8%, -1.2%]	6

Cycles

Results (primary -2.4%, 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)	1.1%	[1.1%, 1.1%]	1
Regressions ❌ (secondary)	3.2%	[0.8%, 7.1%]	4
Improvements ✅ (primary)	-2.6%	[-4.3%, -1.2%]	22
Improvements ✅ (secondary)	-5.0%	[-20.0%, -0.5%]	11
All ❌✅ (primary)	-2.4%	[-4.3%, 1.1%]	23

Binary size

Results (primary -0.6%, secondary -0.8%)

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)	-	-	0
Improvements ✅ (primary)	-0.6%	[-1.4%, -0.0%]	66
Improvements ✅ (secondary)	-0.8%	[-3.6%, -0.0%]	30
All ❌✅ (primary)	-0.6%	[-1.4%, -0.0%]	66

Bootstrap: 461.485s -> 461.37s (-0.02%)
Artifact size: 372.20 MiB -> 371.78 MiB (-0.11%)

My suspicion is that it's getting inlined; the functions have `#[no_mangle]` but do not have `#[inline(never)]`. `#[no_mangle]` is already iffy on generics. I don't think it's worth trying to figure out why foo and bar are special on 32-bit msvc.

Mark-Simulacrum · 2026-07-21T12:17:19Z

@bors try jobs=msvc,mingw

Apply RemoveNoopLandingPads post-monomorphization try-job: *msvc* try-job: *mingw*

rust-bors · 2026-07-21T15:28:32Z

☀️ Try build successful (CI)
Build commit: 717e8b7 (717e8b7b44ba38ad879c523947f1818beb181da2)
Base parent: cde3f8a (cde3f8aee5a30928872e2438e3f18238a3fa306c)

Mark-Simulacrum · 2026-07-21T23:12:46Z

@rustbot ready

I removed the check on i686-msvc, I'm not seeing anything obvious for why we wouldn't expect inlining in the test case and it seems quite plausible this change makes inlining more likely.

oli-obk · 2026-07-22T10:04:27Z

@bors r+

rust-bors · 2026-07-22T10:04:31Z

📌 Commit dbbd8ee has been approved by oli-obk

It is now in the queue for this repository.

Apply RemoveNoopLandingPads post-monomorphization On Cargo this cuts ~5% of the LLVM IR lines we generate (measured with -Cno-prepopulate-passes). Closes #159399.

rust-log-analyzer · 2026-07-22T14:49:32Z

The job dist-loongarch64-linux failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

rust-bors · 2026-07-22T14:50:00Z

💔 Test for fa268ea failed: CI. Failed job:

auto - dist-loongarch64-linux (web logs, enhanced plaintext logs)

mati865 · 2026-07-22T16:05:41Z

The build just died without any info?

@bors retry

rust-bors · 2026-07-22T22:50:05Z

☀️ Test successful - CI
Approved by: oli-obk
Duration: 3h 16m 19s
Pushing 6f72b5d to main...

github-actions · 2026-07-22T22:53:22Z

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 ae3bbe7 (parent) -> 6f72b5d (this PR)

Test differences

Show 7 test diffs

Stage 1

[codegen] tests/codegen-llvm/unused-drop-pre-llvm.rs: [missing] -> pass (J1)
[codegen] tests/codegen-llvm/unused-drop-pre-llvm.rs: [missing] -> ignore (ignored on targets without unwinding support (- depends on landing pads being optimized away, so not useful to run without it)) (J2)

Stage 2

[codegen] tests/codegen-llvm/unused-drop-pre-llvm.rs: [missing] -> pass (J0)

Additionally, 4 doctest diffs were found. These are ignored, as they are noisy.

Job group index

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 6f72b5dd5f82226a2773d40efea7bab941892a73 --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

dist-x86_64-llvm-mingw: 1h 27m -> 2h 13m (+52.3%)
x86_64-gnu-miri: 1h 6m -> 1h 32m (+39.2%)
x86_64-gnu-nopt: 1h 51m -> 2h 30m (+35.3%)
x86_64-msvc-ext3: 1h 20m -> 1h 49m (+35.2%)
dist-arm-linux-musl: 1h 16m -> 1h 38m (+28.4%)
aarch64-apple-macos-26: 3h 21m -> 2h 24m (-28.3%)
x86_64-gnu-debug: 1h 29m -> 1h 53m (+27.4%)
dist-ohos-armv7: 1h 14m -> 56m 11s (-25.0%)
x86_64-gnu-llvm-22-3: 1h 22m -> 1h 40m (+22.4%)
dist-various-2: 45m 47s -> 35m 49s (-21.8%)

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 · 2026-07-23T00:00:22Z

Finished benchmarking commit (6f72b5d): 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)	0.1%	[0.1%, 0.1%]	1
Improvements ✅ (primary)	-2.2%	[-4.9%, -0.2%]	25
Improvements ✅ (secondary)	-3.4%	[-20.7%, -0.2%]	22
All ❌✅ (primary)	-2.2%	[-4.9%, -0.2%]	25

Max RSS (memory usage)

Results (primary -1.3%, 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)	-	-	0
Improvements ✅ (primary)	-1.3%	[-1.3%, -1.3%]	1
Improvements ✅ (secondary)	-4.8%	[-6.3%, -3.3%]	2
All ❌✅ (primary)	-1.3%	[-1.3%, -1.3%]	1

Cycles

Results (primary -3.1%, secondary -2.3%)

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)	21.9%	[20.3%, 23.5%]	2
Improvements ✅ (primary)	-3.1%	[-4.7%, -1.1%]	13
Improvements ✅ (secondary)	-6.7%	[-23.0%, -2.5%]	11
All ❌✅ (primary)	-3.1%	[-4.7%, -1.1%]	13

Binary size

Results (primary -0.7%, secondary -1.3%)

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)	-	-	0
Improvements ✅ (primary)	-0.7%	[-1.7%, -0.1%]	60
Improvements ✅ (secondary)	-1.3%	[-4.5%, -0.1%]	30
All ❌✅ (primary)	-0.7%	[-1.7%, -0.1%]	60

Bootstrap: 487.635s -> 486.811s (-0.17%)
Artifact size: 387.74 MiB -> 387.67 MiB (-0.02%)

rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Jun 29, 2025

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