MIR inliner maintains unused var_debug_info #142890

kornelski · 2025-06-22T20:37:55Z

Only full debuginfo level promises variable-level debug information, but the MIR inline pass needlessly preserved the local variable debug info for the limited level too.

rustbot · 2025-06-22T20:37:59Z

r? @saethlin

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rustbot · 2025-06-22T20:38:01Z

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

mati865 · 2025-06-23T06:49:10Z

@bors2 try @rust-timer queue

rust-bors · 2025-06-23T06:49:15Z

⌛ Trying commit 8c3a8f8 with merge b8965fd…

To cancel the try build, run the command @bors2 try cancel.

MIR inliner maintains unused var_debug_info Only `full` debuginfo level promises variable-level debug information, but the MIR inline pass needlessly preserved the local variable debug info for the `limited` level too.

rust-bors · 2025-06-23T09:18:09Z

☀️ Try build successful (CI)
Build commit: b8965fd (b8965fdc8fbcbc0a9c8de4899202d47eb3ea7043, parent: 58d5e1169056f31553ecf680b009a5770eb0e859)

Kobzol · 2025-06-23T15:09:16Z

@rust-timer build b8965fd

rust-timer · 2025-06-23T20:41:47Z

Finished benchmarking commit (b8965fd): 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)	3.8%	[2.7%, 4.9%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.4%	[-1.4%, -1.4%]	1
Improvements ✅ (secondary)	-1.4%	[-1.4%, -1.4%]	1
All ❌✅ (primary)	2.1%	[-1.4%, 4.9%]	3

Max RSS (memory usage)

Results (primary 4.3%, secondary 2.5%)

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

	mean	range	count
Regressions ❌ (primary)	4.3%	[4.3%, 4.3%]	1
Regressions ❌ (secondary)	2.5%	[1.6%, 3.2%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	4.3%	[4.3%, 4.3%]	1

Cycles

Results (primary 3.8%)

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

	mean	range	count
Regressions ❌ (primary)	3.8%	[2.9%, 4.7%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.8%	[2.9%, 4.7%]	2

Binary size

Results (primary 1.3%)

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

	mean	range	count
Regressions ❌ (primary)	1.3%	[1.1%, 1.4%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.3%	[1.1%, 1.4%]	2

Bootstrap: 688.673s -> 690.365s (0.25%)
Artifact size: 371.94 MiB -> 371.93 MiB (-0.00%)

compiler/rustc_mir_transform/src/inline.rs

saethlin · 2025-07-03T22:29:40Z

tests/mir-opt/inline_var_debug_info_kept.rs

+//@ [NONE]compile-flags: -O -C debuginfo=0
+//@ [LIMITED]compile-flags: -O -C debuginfo=1
+
+#[inline(always)]


FYI, this doesn't mean anything beyond #[inline] to the MIR inliner.

saethlin · 2025-07-03T22:30:09Z

Looks good. Thanks for bearing with our slow review process.

@bors r+

bors · 2025-07-03T22:30:12Z

📌 Commit c9ef116 has been approved by saethlin

It is now in the queue for this repository.

bors · 2025-07-03T23:17:07Z

⌛ Testing commit c9ef116 with merge 837c5dd...

bors · 2025-07-04T02:19:38Z

☀️ Test successful - checks-actions
Approved by: saethlin
Pushing 837c5dd to master...

github-actions · 2025-07-04T02:22:51Z

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 da58c05 (parent) -> 837c5dd (this PR)

Test differences

Show 10 test diffs

Stage 1

[mir-opt] tests/mir-opt/inline_var_debug_info_kept.rs#FULL: [missing] -> pass (J0)
[mir-opt] tests/mir-opt/inline_var_debug_info_kept.rs#LIMITED: [missing] -> pass (J0)
[mir-opt] tests/mir-opt/inline_var_debug_info_kept.rs#NONE: [missing] -> pass (J0)
[mir-opt] tests/mir-opt/inline_var_debug_info_kept.rs#PRESERVE: [missing] -> pass (J0)

Stage 2

[mir-opt] tests/mir-opt/inline_var_debug_info_kept.rs#FULL: [missing] -> pass (J1)
[mir-opt] tests/mir-opt/inline_var_debug_info_kept.rs#LIMITED: [missing] -> pass (J1)
[mir-opt] tests/mir-opt/inline_var_debug_info_kept.rs#NONE: [missing] -> pass (J1)
[mir-opt] tests/mir-opt/inline_var_debug_info_kept.rs#PRESERVE: [missing] -> pass (J1)

Additionally, 2 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 837c5dd7de03aa97190593aef4e70d53e1bb574b --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-apple-1: 10898.6s -> 6968.0s (-36.1%)
dist-apple-various: 7932.5s -> 6392.3s (-19.4%)
x86_64-apple-2: 5528.6s -> 4853.5s (-12.2%)
dist-arm-linux-gnueabi: 4668.4s -> 5066.4s (8.5%)
x86_64-gnu-llvm-19-3: 6388.5s -> 6920.0s (8.3%)
x86_64-mingw-2: 7160.7s -> 7632.9s (6.6%)
tidy: 74.4s -> 70.0s (-5.9%)
x86_64-msvc-ext2: 5804.4s -> 5493.8s (-5.4%)
dist-aarch64-apple: 5705.2s -> 5405.2s (-5.3%)
x86_64-gnu-llvm-19-1: 3426.5s -> 3268.4s (-4.6%)

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 · 2025-07-04T10:32:16Z

Finished benchmarking commit (837c5dd): 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)	1.8%	[1.8%, 1.8%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.9%	[-2.9%, -2.9%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.6%	[-2.9%, 1.8%]	2

Max RSS (memory usage)

Results (secondary 0.4%)

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)	0.4%	[0.4%, 0.5%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

Results (primary -0.4%, secondary -2.6%)

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

	mean	range	count
Regressions ❌ (primary)	2.1%	[2.1%, 2.1%]	1
Regressions ❌ (secondary)	0.6%	[0.4%, 0.7%]	2
Improvements ✅ (primary)	-2.9%	[-2.9%, -2.9%]	1
Improvements ✅ (secondary)	-4.2%	[-6.8%, -1.5%]	4
All ❌✅ (primary)	-0.4%	[-2.9%, 2.1%]	2

Binary size

Results (primary -1.1%)

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)	-1.1%	[-1.1%, -1.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.1%	[-1.1%, -1.1%]	1

Bootstrap: 462.222s -> 462.019s (-0.04%)
Artifact size: 372.18 MiB -> 372.15 MiB (-0.01%)

panstromek · 2025-07-07T14:16:59Z

perf triage:

clap_derive improvement is bimodal noise. ripgrep regression doesn't make sense to me. We either do less work or the same amount of work here (not sure which debuginfo option we use for this benchmark). Wall time has no relevant changes, though, so I assume it's spurious.

@rustbot label: +perf-regression-triaged

rustbot assigned saethlin Jun 22, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jun 22, 2025

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rustbot added the perf-regression Performance regression. label Jun 23, 2025

Kobzol mentioned this pull request Jun 24, 2025

At debuginfo=0, don't inline debuginfo when inlining #123949

Merged

tmiasko reviewed Jun 25, 2025

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compiler/rustc_mir_transform/src/inline.rs Outdated Show resolved Hide resolved

kornelski force-pushed the unused-var-debug branch from 8c3a8f8 to b7eaae1 Compare June 27, 2025 21:47

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kornelski added 2 commits June 28, 2025 12:20

Test MIR inlined var debug info

db9daab

Keep inlined var_debug_info only when full debug info is used

c9ef116

kornelski force-pushed the unused-var-debug branch from b7eaae1 to c9ef116 Compare June 28, 2025 11:22

saethlin reviewed Jul 3, 2025

View reviewed changes

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 3, 2025

bors added the merged-by-bors This PR was explicitly merged by bors. label Jul 4, 2025

bors merged commit 837c5dd into rust-lang:master Jul 4, 2025
11 checks passed

rustbot added this to the 1.90.0 milestone Jul 4, 2025

kornelski deleted the unused-var-debug branch July 4, 2025 15:46

rustbot added the perf-regression-triaged The performance regression has been triaged. label Jul 7, 2025

MIR inliner maintains unused var_debug_info #142890

MIR inliner maintains unused var_debug_info #142890

Conversation

kornelski commented Jun 22, 2025

Uh oh!

rustbot commented Jun 22, 2025

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rustbot commented Jun 22, 2025

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mati865 commented Jun 23, 2025

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rust-bors bot commented Jun 23, 2025

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rust-bors bot commented Jun 23, 2025

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Kobzol commented Jun 23, 2025

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rust-timer commented Jun 23, 2025

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

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saethlin commented Jul 3, 2025

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bors commented Jul 3, 2025

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bors commented Jul 3, 2025

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bors commented Jul 4, 2025

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github-actions bot commented Jul 4, 2025

Test differences

Stage 1

Stage 2

Job duration changes

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rust-timer commented Jul 4, 2025

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

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panstromek commented Jul 7, 2025

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