GVN: Evaluate constants lazily.

[cjgillot]

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]

@bors try @rust-timer queue

[rust-bors]

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

[rust-timer]

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]

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

[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[cjgillot]

r? @dianqk

[dianqk]

@bors r+

[bors]

📌 Commit de38c09 has been approved by dianqk

It is now in the queue for this repository.

[bors]

⌛ Testing commit de38c09 with merge e3b5da9...

[bors]

💔 Test failed - checks-actions

[rustbot]

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]

@bors r=dianqk

[bors]

📌 Commit 5da52f5 has been approved by dianqk

It is now in the queue for this repository.

[bors]

⌛ Testing commit 5da52f5 with merge b6f0945...

[bors]

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

1. dist-i686-linux: 6192.2s -> 7329.8s (18.4%)
2. x86_64-rust-for-linux: 2912.7s -> 2473.9s (-15.1%)
3. dist-x86_64-apple: 8488.6s -> 7355.3s (-13.4%)
4. i686-gnu-nopt-1: 8143.2s -> 7194.8s (-11.6%)
5. x86_64-gnu-stable: 7762.7s -> 7014.0s (-9.6%)
6. aarch64-gnu-llvm-20-2: 2344.2s -> 2121.9s (-9.5%)
7. aarch64-msvc-2: 4669.5s -> 5106.4s (9.4%)
8. armhf-gnu: 5311.2s -> 4846.2s (-8.8%)
9. dist-aarch64-apple: 7817.1s -> 7136.0s (-8.7%)
10. 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]

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%)