GVN: Evaluate constants lazily. #146869

cjgillot · 2025-09-22T01:18:29Z

GVN currently evaluates constants eagerly. This is not necessary. This PR makes constant evaluation on-demand to avoid unnecessary work.

r? @ghost for perf

cjgillot · 2025-09-22T01:20:52Z

@bors try @rust-timer queue

GVN: Evaluate constants lazily.

rust-bors · 2025-09-22T03:32:37Z

☀️ Try build successful (CI)
Build commit: ca09b36 (ca09b3628a00e674c41779a484ca277693d7c998, parent: 9f32ccf35fb877270bc44a86a126440f04d676d0)

rust-timer · 2025-09-22T04:43:04Z

Finished benchmarking commit (ca09b36): 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
Regressions ❌ (secondary)	0.1%	[0.1%, 0.1%]	1
Improvements ✅ (primary)	-0.1%	[-0.1%, -0.1%]	3
Improvements ✅ (secondary)	-0.2%	[-0.2%, -0.2%]	5
All ❌✅ (primary)	-0.1%	[-0.1%, -0.1%]	3

Max RSS (memory usage)

Results (primary 2.7%, secondary 3.7%)

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

	mean	range	count
Regressions ❌ (primary)	2.7%	[2.5%, 2.9%]	2
Regressions ❌ (secondary)	4.3%	[2.1%, 5.0%]	8
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.3%	[-1.3%, -1.3%]	1
All ❌✅ (primary)	2.7%	[2.5%, 2.9%]	2

Cycles

Results (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)	-	-	0
Regressions ❌ (secondary)	2.1%	[2.1%, 2.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.3%	[-4.1%, -2.1%]	6
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: 471.273s -> 473.396s (0.45%)
Artifact size: 387.92 MiB -> 389.96 MiB (0.53%)

bors · 2025-10-02T06:18:54Z

☔ The latest upstream changes (presumably #147055) made this pull request unmergeable. Please resolve the merge conflicts.

rustbot · 2025-10-06T23:19:21Z

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

cjgillot · 2025-10-06T23:28:57Z

r? @dianqk

dianqk · 2025-10-08T01:57:28Z

@bors r+

bors · 2025-10-08T01:57:31Z

📌 Commit de38c09 has been approved by dianqk

It is now in the queue for this repository.

GVN: Evaluate constants lazily. GVN currently evaluates constants eagerly. This is not necessary. This PR makes constant evaluation on-demand to avoid unnecessary work. r? `@ghost` for perf

bors · 2025-10-08T06:15:57Z

⌛ Testing commit de38c09 with merge e3b5da9...

bors · 2025-10-08T06:26:52Z

💔 Test failed - checks-actions

rustbot · 2025-10-08T12:26:36Z

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.

cjgillot · 2025-10-08T12:55:02Z

@bors r=dianqk

bors · 2025-10-08T12:55:04Z

📌 Commit 5da52f5 has been approved by dianqk

It is now in the queue for this repository.

bors · 2025-10-08T19:23:29Z

⌛ Testing commit 5da52f5 with merge b6f0945...

bors · 2025-10-08T22:32:50Z

☀️ Test successful - checks-actions
Approved by: dianqk
Pushing b6f0945 to master...

github-actions · 2025-10-08T22:36:01Z

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 7a52736 (parent) -> b6f0945 (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 b6f0945e4681bc4d2faa7c22c5f61dc36abf7dd2 --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-i686-linux: 6192.2s -> 7329.8s (18.4%)
x86_64-rust-for-linux: 2912.7s -> 2473.9s (-15.1%)
dist-x86_64-apple: 8488.6s -> 7355.3s (-13.4%)
i686-gnu-nopt-1: 8143.2s -> 7194.8s (-11.6%)
x86_64-gnu-stable: 7762.7s -> 7014.0s (-9.6%)
aarch64-gnu-llvm-20-2: 2344.2s -> 2121.9s (-9.5%)
aarch64-msvc-2: 4669.5s -> 5106.4s (9.4%)
armhf-gnu: 5311.2s -> 4846.2s (-8.8%)
dist-aarch64-apple: 7817.1s -> 7136.0s (-8.7%)
x86_64-gnu-llvm-20-3: 6700.7s -> 6129.9s (-8.5%)

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 · 2025-10-09T00:33:56Z

Finished benchmarking commit (b6f0945): 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)	-0.1%	[-0.1%, -0.1%]	2
Improvements ✅ (secondary)	-1.1%	[-1.1%, -1.1%]	1
All ❌✅ (primary)	-0.1%	[-0.1%, -0.1%]	2

Max RSS (memory usage)

Results (primary 7.4%, secondary 3.5%)

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

	mean	range	count
Regressions ❌ (primary)	7.4%	[7.4%, 7.4%]	1
Regressions ❌ (secondary)	3.5%	[3.5%, 3.5%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	7.4%	[7.4%, 7.4%]	1

Cycles

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

Binary size

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

Bootstrap: 472.232s -> 479.914s (1.63%)
Artifact size: 388.41 MiB -> 388.45 MiB (0.01%)

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Sep 22, 2025

This comment has been minimized.

Sign in to view

rust-bors bot added a commit that referenced this pull request Sep 22, 2025

Auto merge of #146869 - cjgillot:gvn-lazy-const, r=<try>

ca09b36

GVN: Evaluate constants lazily.

This comment has been minimized.

Sign in to view

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Sep 22, 2025

This comment has been minimized.

Sign in to view

rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Sep 22, 2025

cjgillot force-pushed the gvn-lazy-const branch from 95f7c2e to 9a3310d Compare September 26, 2025 23:51

cjgillot force-pushed the gvn-lazy-const branch 2 times, most recently from bc72f9c to de38c09 Compare October 6, 2025 19:33

cjgillot marked this pull request as ready for review October 6, 2025 23:19

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Oct 6, 2025

rustbot assigned dianqk Oct 6, 2025

dianqk approved these changes Oct 8, 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 Oct 8, 2025

This comment has been minimized.

Sign in to view

bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Oct 8, 2025

Evaluate constants lazily in GVN.

5da52f5

cjgillot force-pushed the gvn-lazy-const branch from de38c09 to 5da52f5 Compare October 8, 2025 12:26

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 Oct 8, 2025

bors added the merged-by-bors This PR was explicitly merged by bors. label Oct 8, 2025

bors merged commit b6f0945 into rust-lang:master Oct 8, 2025
11 checks passed

rustbot added this to the 1.92.0 milestone Oct 8, 2025

cjgillot deleted the gvn-lazy-const branch October 8, 2025 22:37

This was referenced Oct 8, 2025

Extend GVN to perform local value numbering. #143333

Draft

Replace SingleUseConsts by GVN. #147079

Draft

rustbot removed the perf-regression Performance regression. label Oct 9, 2025

GVN: Evaluate constants lazily. #146869

GVN: Evaluate constants lazily. #146869

Conversation

cjgillot commented Sep 22, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

cjgillot commented Sep 22, 2025

Uh oh!

This comment has been minimized.

This comment has been minimized.

rust-bors bot commented Sep 22, 2025

Uh oh!

This comment has been minimized.

rust-timer commented Sep 22, 2025

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

Uh oh!

bors commented Oct 2, 2025

Uh oh!

rustbot commented Oct 6, 2025

Uh oh!

cjgillot commented Oct 6, 2025

Uh oh!

dianqk commented Oct 8, 2025

Uh oh!

bors commented Oct 8, 2025

Uh oh!

bors commented Oct 8, 2025

Uh oh!

This comment has been minimized.

bors commented Oct 8, 2025

Uh oh!

rustbot commented Oct 8, 2025

Uh oh!

cjgillot commented Oct 8, 2025

Uh oh!

bors commented Oct 8, 2025

Uh oh!

bors commented Oct 8, 2025

Uh oh!

bors commented Oct 8, 2025

Uh oh!

Uh oh!

github-actions bot commented Oct 8, 2025

Test differences

Job duration changes

Uh oh!

rust-timer commented Oct 9, 2025

Overall result: ✅ improvements - no action needed

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

6 participants

cjgillot commented Sep 22, 2025 •

edited

Loading