GVN: stop hashing opaque values

[cjgillot]

GVN generates values that are not meant to be unified with any other. For instance Opaque (aka we don't know anything), non-deterministic constants and borrows.

The current algorithm generates a unique index, so the generated Value will be different from all the existing. This is wasteful, as we should not hash that Value at all.

This PR proposes to do this. This involves partially reimplementing a FxIndexSet, but yields a small but consistent perf improvement (#145737 (comment)).

[cjgillot]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: b1206a5 (b1206a5638d835852d82f15f0f0f66e4f33420a5, parent: 6ba0ce40941eee1ca02e9ba49c791ada5158747a)

[rust-timer]

Finished benchmarking commit (b1206a5): comparison URL.

Overall result: no relevant changes - 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

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

Max RSS (memory usage)

Results (primary -0.9%, secondary -0.9%)

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

	mean	range	count
Regressions ❌ (primary)	4.2%	[4.2%, 4.2%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-6.1%	[-6.1%, -6.1%]	1
Improvements ✅ (secondary)	-0.9%	[-0.9%, -0.9%]	1
All ❌✅ (primary)	-0.9%	[-6.1%, 4.2%]	2

Cycles

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

Binary size

Results (primary -0.0%, secondary 0.2%)

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

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.0%, 0.1%]	2
Regressions ❌ (secondary)	1.0%	[1.0%, 1.0%]	1
Improvements ✅ (primary)	-0.1%	[-0.2%, -0.1%]	3
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	3
All ❌✅ (primary)	-0.0%	[-0.2%, 0.1%]	5

Bootstrap: 471.281s -> 472.689s (0.30%)
Artifact size: 378.27 MiB -> 378.24 MiB (-0.01%)

[cjgillot]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 08b7b9c (08b7b9c5ab0fbe6eb9e66c5f59e9c8d90709f453, parent: c5a6a7bdd89f099544fa0d3fad4d833d238377ad)

[rust-timer]

Finished benchmarking commit (08b7b9c): comparison URL.

Overall result: ❌ regressions - 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)	1.1%	[1.1%, 1.1%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.1%	[1.1%, 1.1%]	1

Max RSS (memory usage)

Results (primary -1.4%, secondary -1.5%)

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

	mean	range	count
Regressions ❌ (primary)	2.5%	[2.5%, 2.5%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.7%	[-3.8%, -1.9%]	3
Improvements ✅ (secondary)	-1.5%	[-1.9%, -1.1%]	2
All ❌✅ (primary)	-1.4%	[-3.8%, 2.5%]	4

Cycles

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

Binary size

Results (primary 0.0%, secondary 0.5%)

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

	mean	range	count
Regressions ❌ (primary)	0.3%	[0.1%, 0.4%]	4
Regressions ❌ (secondary)	1.0%	[1.0%, 1.0%]	1
Improvements ✅ (primary)	-0.3%	[-0.7%, -0.1%]	3
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	1
All ❌✅ (primary)	0.0%	[-0.7%, 0.4%]	7

Bootstrap: 467.196s -> 468.333s (0.24%)
Artifact size: 378.17 MiB -> 378.18 MiB (0.00%)

[bors]

☔ The latest upstream changes (presumably #145923) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #146292) made this pull request unmergeable. Please resolve the merge conflicts.

[cjgillot]

@bors try @rust-timer queue

[rustbot]

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[rustbot]

r? @saethlin

rustbot has assigned @saethlin.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[saethlin]

Did you check if these debug assertions were actually too expensive to be enabled in all builds? Users make the compiler do really weird stuff, so I'm always wary of having assertions that are off in distributed builds.

That being said, if you do want to do that perf experiment, it'll be easier to do after this is merged.

@bors r+

[bors]

📌 Commit df04be8 has been approved by saethlin

It is now in the queue for this repository.

[bors]

⌛ Testing commit df04be8 with merge e10aa88...

[bors]

☀️ Test successful - checks-actions
Approved by: saethlin
Pushing e10aa88 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 2f4dfc7 (parent) -> e10aa88 (this PR)

Test differences

Show 4 test diffs

4 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 e10aa8891182378de002bd71bf4d04181fb8231d --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. x86_64-gnu-llvm-20: 2347.2s -> 2855.0s (21.6%)
2. pr-check-1: 1408.6s -> 1678.9s (19.2%)
3. aarch64-gnu-llvm-20-2: 2205.9s -> 2572.2s (16.6%)
4. dist-aarch64-apple: 9204.9s -> 7720.1s (-16.1%)
5. aarch64-apple: 5583.1s -> 6477.4s (16.0%)
6. dist-x86_64-apple: 6881.1s -> 5881.2s (-14.5%)
7. aarch64-gnu: 6260.8s -> 7163.4s (14.4%)
8. x86_64-rust-for-linux: 2557.2s -> 2891.0s (13.0%)
9. aarch64-msvc-2: 4733.1s -> 5350.0s (13.0%)
10. i686-gnu-nopt-1: 7134.1s -> 8048.3s (12.8%)

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]

Finished benchmarking commit (e10aa88): 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)	-1.7%	[-1.9%, -1.5%]	2
Improvements ✅ (secondary)	-1.4%	[-1.4%, -1.4%]	1
All ❌✅ (primary)	-1.7%	[-1.9%, -1.5%]	2

Max RSS (memory usage)

Results (primary -2.9%)

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

	mean	range	count
Regressions ❌ (primary)	2.7%	[2.7%, 2.7%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-4.7%	[-9.8%, -1.9%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.9%	[-9.8%, 2.7%]	4

Cycles

Results (primary 6.0%, secondary 2.2%)

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

	mean	range	count
Regressions ❌ (primary)	6.0%	[6.0%, 6.0%]	1
Regressions ❌ (secondary)	2.2%	[2.2%, 2.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	6.0%	[6.0%, 6.0%]	1

Binary size

Results (primary -0.2%, 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)	0.2%	[0.1%, 0.2%]	3
Regressions ❌ (secondary)	0.1%	[0.0%, 0.1%]	3
Improvements ✅ (primary)	-0.4%	[-0.9%, -0.1%]	5
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	1
All ❌✅ (primary)	-0.2%	[-0.9%, 0.2%]	8

Bootstrap: 470.95s -> 471.12s (0.04%)
Artifact size: 389.99 MiB -> 389.97 MiB (-0.01%)