JumpThreading: compute place and value indices on-demand #142881

cjgillot · 2025-06-22T16:10:49Z

Profiling JumpThreading reveals that a large part of the runtime happens constructing the place and value Map. This is unfortunate, as jump-threading may end up not even doing anything.

The cause for this large up-front cost is following: Map attempts to create a PlaceIndex for each place that may hold a relevant value. This means all places that appear in MIR, but also all places whose value is accessed by a projection of a copy of a larger place.

This PR refactors the creation of Map to happen on-demand: place and value indices are created when threading computation happens.

The up-front mode is still relevant for DataflowConstProp, so is not touched.

cjgillot · 2025-06-22T16:11:20Z

@bors try @rust-timer queue

JumpThreading: compute place and value indices on-demand Perf experiment r? `@ghost`

bors · 2025-06-22T16:12:30Z

⌛ Trying commit ba3a8c5 with merge 1587bef...

bors · 2025-06-22T18:42:05Z

☀️ Try build successful - checks-actions
Build commit: 1587bef (1587bef3b2c2aea88de9b552efbf7febe7cd5fc4)

rust-timer · 2025-06-23T08:01:06Z

Finished benchmarking commit (1587bef): 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)	1.0%	[0.7%, 1.3%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.3%	[-1.4%, -0.1%]	142
Improvements ✅ (secondary)	-0.4%	[-1.7%, -0.1%]	93
All ❌✅ (primary)	-0.3%	[-1.4%, 1.3%]	144

Max RSS (memory usage)

Results (primary 3.6%, secondary 2.0%)

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

	mean	range	count
Regressions ❌ (primary)	3.6%	[3.4%, 3.8%]	2
Regressions ❌ (secondary)	2.0%	[2.0%, 2.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.6%	[3.4%, 3.8%]	2

Cycles

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

Binary size

Results (primary -0.1%, secondary 0.1%)

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

	mean	range	count
Regressions ❌ (primary)	0.2%	[0.0%, 0.4%]	12
Regressions ❌ (secondary)	0.2%	[0.0%, 0.4%]	42
Improvements ✅ (primary)	-0.3%	[-1.4%, -0.0%]	20
Improvements ✅ (secondary)	-0.3%	[-0.9%, -0.0%]	5
All ❌✅ (primary)	-0.1%	[-1.4%, 0.4%]	32

Bootstrap: 689.082s -> 684.233s (-0.70%)
Artifact size: 371.89 MiB -> 372.00 MiB (0.03%)

rustbot · 2025-06-23T09:47:19Z

r? @eholk

rustbot has assigned @eholk.
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

rustbot · 2025-06-23T09:47:20Z

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

rustbot · 2025-06-23T18:56:14Z

Some changes occurred in coverage tests.

cc @Zalathar

cjgillot · 2025-07-20T13:41:08Z

r? compiler

bors · 2025-07-28T09:46:42Z

☔ The latest upstream changes (presumably #144469) made this pull request unmergeable. Please resolve the merge conflicts.

bors · 2025-12-02T03:31:20Z

☔ The latest upstream changes (presumably #142821) made this pull request unmergeable. Please resolve the merge conflicts.

rustbot · 2025-12-14T16:42:26Z

This PR was rebased onto a different main 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 · 2025-12-14T21:02:15Z

@bors try @rust-timer queue

JumpThreading: compute place and value indices on-demand

rust-bors · 2025-12-14T23:20:11Z

☀️ Try build successful (CI)
Build commit: 27d3ab5 (27d3ab51bc0ae9029d0c94e6a28b4dd891d93f7c, parent: 0208ee09be465f69005a7a12c28d5eccac7d5f34)

rust-timer · 2025-12-15T00:01:19Z

Finished benchmarking commit (27d3ab5): 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)	0.6%	[0.2%, 1.5%]	5
Regressions ❌ (secondary)	0.1%	[0.1%, 0.1%]	1
Improvements ✅ (primary)	-0.4%	[-1.3%, -0.1%]	109
Improvements ✅ (secondary)	-0.5%	[-1.9%, -0.1%]	84
All ❌✅ (primary)	-0.4%	[-1.3%, 1.5%]	114

Max RSS (memory usage)

Results (primary 0.5%, 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)	4.0%	[2.0%, 7.0%]	3
Regressions ❌ (secondary)	0.8%	[0.8%, 0.8%]	1
Improvements ✅ (primary)	-2.9%	[-3.3%, -2.6%]	3
Improvements ✅ (secondary)	-3.7%	[-4.2%, -3.3%]	2
All ❌✅ (primary)	0.5%	[-3.3%, 7.0%]	6

Cycles

Results (primary -1.9%, secondary -4.6%)

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)	-1.9%	[-1.9%, -1.9%]	1
Improvements ✅ (secondary)	-4.6%	[-4.6%, -4.6%]	1
All ❌✅ (primary)	-1.9%	[-1.9%, -1.9%]	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%, 0.3%]	6
Regressions ❌ (secondary)	0.2%	[0.1%, 0.3%]	7
Improvements ✅ (primary)	-0.4%	[-1.4%, -0.0%]	16
Improvements ✅ (secondary)	-0.3%	[-0.6%, -0.1%]	4
All ❌✅ (primary)	-0.2%	[-1.4%, 0.3%]	22

Bootstrap: 479.155s -> 476.389s (-0.58%)
Artifact size: 390.26 MiB -> 390.47 MiB (0.05%)

saethlin · 2025-12-27T01:33:24Z

The perf results are quite compelling. Well done!

@bors r+

bors · 2025-12-27T01:33:27Z

📌 Commit 9415102 has been approved by saethlin

It is now in the queue for this repository.

bors · 2025-12-27T03:12:21Z

⌛ Testing commit 9415102 with merge c7aa99f...

bors · 2025-12-27T06:25:48Z

☀️ Test successful - checks-actions
Approved by: saethlin
Pushing c7aa99f to main...

github-actions · 2025-12-27T06:29:05Z

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 38ed770 (parent) -> c7aa99f (this PR)

Test differences

Show 3 test diffs

3 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 c7aa99f36ccad2c127edec5be493cab0b152f436 --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-aarch64-msvc: 6942.8s -> 5824.8s (-16.1%)
aarch64-gnu-debug: 4560.5s -> 3869.7s (-15.1%)
pr-check-1: 1934.8s -> 1667.7s (-13.8%)
tidy: 173.8s -> 150.9s (-13.2%)
aarch64-msvc-1: 7397.6s -> 6532.5s (-11.7%)
x86_64-gnu-tools: 3718.4s -> 3315.7s (-10.8%)
i686-gnu-2: 6032.1s -> 5441.3s (-9.8%)
x86_64-rust-for-linux: 3217.4s -> 2913.3s (-9.5%)
aarch64-gnu-llvm-20-2: 3267.6s -> 2960.9s (-9.4%)
dist-apple-various: 4350.7s -> 3957.2s (-9.0%)

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 · 2025-12-27T07:07:02Z

Finished benchmarking commit (c7aa99f): 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)	1.4%	[1.4%, 1.4%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.4%	[-1.4%, -0.2%]	117
Improvements ✅ (secondary)	-0.5%	[-1.9%, -0.1%]	93
All ❌✅ (primary)	-0.4%	[-1.4%, 1.4%]	118

Max RSS (memory usage)

Results (primary -1.0%, secondary -3.8%)

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

	mean	range	count
Regressions ❌ (primary)	1.8%	[1.2%, 2.7%]	3
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.9%	[-7.8%, -1.4%]	3
Improvements ✅ (secondary)	-3.8%	[-3.8%, -3.8%]	1
All ❌✅ (primary)	-1.0%	[-7.8%, 2.7%]	6

Cycles

Results (secondary 4.7%)

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)	4.7%	[4.7%, 4.7%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

Results (primary -0.3%, 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)	1.1%	[1.1%, 1.1%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.4%	[-1.3%, -0.0%]	12
Improvements ✅ (secondary)	-0.2%	[-0.3%, -0.1%]	4
All ❌✅ (primary)	-0.3%	[-1.3%, 1.1%]	13

Bootstrap: 486.937s -> 480.868s (-1.25%)
Artifact size: 392.46 MiB -> 390.80 MiB (-0.42%)

lqd · 2025-12-27T09:54:15Z

Improvements in icounts heavily outweigh the one regression (which is also a proc-macro in an opt scenario: not a default cargo config)

@rustbot label: +perf-regression-triaged

rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Jun 22, 2025

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bors added a commit that referenced this pull request Jun 22, 2025

Auto merge of #142881 - cjgillot:minimap, r=<try>

1587bef

JumpThreading: compute place and value indices on-demand Perf experiment r? `@ghost`

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cjgillot marked this pull request as ready for review June 23, 2025 09:47

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cjgillot added 3 commits December 14, 2025 16:33

Split Map::register.

3d83b95

Pre-allocate places vectors.

051dd12

Create place and value indices on-demand.

9415102

cjgillot force-pushed the minimap branch from 9272fe6 to 9415102 Compare December 14, 2025 16:42

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Auto merge of #142881 - cjgillot:minimap, r=<try>

27d3ab5

JumpThreading: compute place and value indices on-demand

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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 Dec 27, 2025

bors added the merged-by-bors This PR was explicitly merged by bors. label Dec 27, 2025

bors merged commit c7aa99f into rust-lang:main Dec 27, 2025
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rustbot added this to the 1.94.0 milestone Dec 27, 2025

rustbot added the perf-regression-triaged The performance regression has been triaged. label Dec 27, 2025

cjgillot deleted the minimap branch December 27, 2025 10:52

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JumpThreading: compute place and value indices on-demand #142881

JumpThreading: compute place and value indices on-demand #142881

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

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

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Test differences

Job duration changes

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

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