interpret: copy_provenance: avoid large intermediate buffer for large repeat counts #146331

RalfJung · 2025-09-08T14:02:16Z

Copying provenance worked in this odd way where the "preparation" phase (which is supposed to just extract the necessary information from the source range) already did all the work of repeating the result N times for the target range. This was needed to use the existing insert_presorted function on SortedMap.

This PR generalizes insert_presorted so that we can avoid this odd structure on copy-provenance, and maybe even improve performance.

rustbot · 2025-09-08T14:02:20Z

r? @petrochenkov

rustbot has assigned @petrochenkov.
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rustbot · 2025-09-08T14:02:22Z

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri, @RalfJung, @oli-obk, @lcnr

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

RalfJung · 2025-09-08T14:02:37Z

@bors try
@rust-timer queue

interpret: copy_provenance: avoid large intermediate buffer for large repeat counts

RalfJung · 2025-09-08T14:04:27Z

compiler/rustc_middle/src/mir/interpret/allocation/provenance_map.rs

+                self.ptrs.insert_presorted(
+                    copy.ptrs.iter().map(|&(offset, reloc)| (shift_offset(i, offset), reloc)),
+                );
+            }


This is the one change that may cost us performance... if there's a bunch of provenance after the range we are copying into, but none in the given range (i.e. we are hitting the fast-path in insert_presorted), it'll be moved around each time.

We'd need a single iterator yielding the entire repeated range to avoid this... which I guess is possible. Maybe I should try that.

it's pretty common for such operations to only be used when the rest is uninit. I guess that will still pessimize the other cases, but without more benchmarks I don't know if we should try anything.

FWIW the 2nd commit does implement the "single iterator" strategy to avoid copying N times for an array of size N.

insert_presorted could still have its slowpath improved by a lot, but that's orthogonal to this PR.

rust-bors · 2025-09-08T16:22:36Z

☀️ Try build successful (CI)
Build commit: 6215de8 (6215de8cada28c90f56dbebb1464cf1094884ed5, parent: beeb8e3af54295ba494c250e84ecda4c2c5d85ff)

rust-timer · 2025-09-08T17:32:29Z

Finished benchmarking commit (6215de8): 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)	-	-	0
Regressions ❌ (secondary)	0.2%	[0.2%, 0.2%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 4.1%, secondary 1.3%)

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

	mean	range	count
Regressions ❌ (primary)	4.1%	[3.7%, 4.5%]	2
Regressions ❌ (secondary)	1.3%	[1.3%, 1.3%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	4.1%	[3.7%, 4.5%]	2

Cycles

Results (primary 0.1%, secondary 2.9%)

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

	mean	range	count
Regressions ❌ (primary)	2.2%	[2.2%, 2.2%]	1
Regressions ❌ (secondary)	2.9%	[2.7%, 3.1%]	2
Improvements ✅ (primary)	-2.1%	[-2.1%, -2.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[-2.1%, 2.2%]	2

Binary size

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

Bootstrap: 466.876s -> 466.292s (-0.13%)
Artifact size: 387.41 MiB -> 387.38 MiB (-0.01%)

bors · 2025-09-09T16:44:57Z

☔ The latest upstream changes (presumably #146360) made this pull request unmergeable. Please resolve the merge conflicts.

rustbot · 2025-09-09T16:59:12Z

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.

RalfJung · 2025-09-09T16:59:44Z

@bors try
@rust-timer queue

interpret: copy_provenance: avoid large intermediate buffer for large repeat counts

rust-bors · 2025-09-09T19:05:16Z

☀️ Try build successful (CI)
Build commit: cd436dc (cd436dc33f3489ca3d38a80e30b843868de52c6e, parent: be8de5d6a0fc5cb2924e174a809a0aff303f281a)

rust-timer · 2025-09-09T20:34:05Z

Finished benchmarking commit (cd436dc): comparison URL.

Overall result: ❌✅ regressions and improvements - 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)	-	-	0
Regressions ❌ (secondary)	0.2%	[0.2%, 0.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.2%	[-0.2%, -0.2%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

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

Cycles

Results (primary -2.1%)

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)	-2.1%	[-2.1%, -2.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.1%	[-2.1%, -2.1%]	1

Binary size

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

Bootstrap: 467.841s -> 468.775s (0.20%)
Artifact size: 387.52 MiB -> 387.56 MiB (0.01%)

RalfJung · 2025-09-10T06:24:49Z

This looks slightly better than the first run (which only had the first commit), though that might be noise.

… repeat counts

petrochenkov · 2025-09-14T06:30:49Z

r? compiler
I'm on vacation and this is not my area.

RalfJung · 2025-09-14T09:16:04Z

r? @oli-obk

rustbot · 2025-09-14T09:16:08Z

oli-obk is not on the review rotation at the moment.
They may take a while to respond.

oli-obk

the things we do for perf 😆

View changes since this review

oli-obk · 2025-09-16T15:54:02Z

compiler/rustc_data_structures/src/sorted_map.rs

+    pub fn insert_presorted(
+        &mut self,
+        // We require `TrustedLen` to ensure that the `splice` below is actually efficient.
+        mut elements: impl Iterator<Item = (K, V)> + DoubleEndedIterator + TrustedLen,


could use IntoIterator<Item = (K, V), Iter: DoubleEndedIterator + TrustedLen> to avoid needing to change callers, but since it's mostly tests, doesn't really matter

oli-obk · 2025-09-16T15:57:53Z

@bors r+

bors · 2025-09-16T15:57:56Z

📌 Commit 7abbc9c has been approved by oli-obk

It is now in the queue for this repository.

bors · 2025-09-17T13:56:58Z

⌛ Testing commit 7abbc9c with merge 5d1b897...

bors · 2025-09-17T17:12:09Z

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing 5d1b897 to master...

github-actions · 2025-09-17T17:15:35Z

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 ce6daf3 (parent) -> 5d1b897 (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 5d1b897a07dc30d810dd541795125c1c216266c7 --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-apple-various: 3369.0s -> 4051.3s (20.3%)
i686-gnu-2: 5400.6s -> 6448.9s (19.4%)
dist-x86_64-apple: 7189.6s -> 8481.1s (18.0%)
x86_64-gnu-llvm-20-1: 3228.5s -> 3779.3s (17.1%)
pr-check-1: 1358.2s -> 1558.7s (14.8%)
aarch64-apple: 6624.5s -> 5656.9s (-14.6%)
x86_64-gnu-llvm-20: 2476.2s -> 2830.4s (14.3%)
i686-gnu-1: 7465.5s -> 8518.7s (14.1%)
pr-check-2: 2199.3s -> 2500.5s (13.7%)
x86_64-rust-for-linux: 2645.6s -> 2992.0s (13.1%)

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 · 2025-09-17T18:22:21Z

Finished benchmarking commit (5d1b897): comparison URL.

Overall result: ❌✅ regressions and 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)	0.2%	[0.2%, 0.4%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.3%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -9.2%)

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)	-9.2%	[-9.2%, -9.2%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-9.2%	[-9.2%, -9.2%]	1

Cycles

Results (secondary -3.2%)

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)	-	-	0
Improvements ✅ (secondary)	-3.2%	[-3.2%, -3.2%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 472.939s -> 471.616s (-0.28%)
Artifact size: 387.93 MiB -> 387.94 MiB (0.00%)

rustbot assigned petrochenkov Sep 8, 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 Sep 8, 2025

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rust-bors bot added a commit that referenced this pull request Sep 8, 2025

Auto merge of #146331 - RalfJung:copy-prov-repeat, r=<try>

6215de8

interpret: copy_provenance: avoid large intermediate buffer for large repeat counts

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Sep 8, 2025

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Sep 8, 2025

RalfJung force-pushed the copy-prov-repeat branch from 317df91 to d098505 Compare September 9, 2025 16:59

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rust-bors bot added a commit that referenced this pull request Sep 9, 2025

Auto merge of #146331 - RalfJung:copy-prov-repeat, r=<try>

cd436dc

interpret: copy_provenance: avoid large intermediate buffer for large repeat counts

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Sep 9, 2025

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Sep 9, 2025

RalfJung added 2 commits September 10, 2025 08:40

interpret: copy_provenance: avoid large intermediate buffer for large…

64ea775

… repeat counts

avoid calling insert_presorted more than once

7abbc9c

RalfJung force-pushed the copy-prov-repeat branch from d098505 to 7abbc9c Compare September 10, 2025 06:40

rustbot assigned davidtwco and unassigned petrochenkov Sep 14, 2025

rustbot assigned oli-obk and unassigned davidtwco Sep 14, 2025

oli-obk approved these changes Sep 16, 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 Sep 16, 2025

bors added the merged-by-bors This PR was explicitly merged by bors. label Sep 17, 2025

bors merged commit 5d1b897 into rust-lang:master Sep 17, 2025
11 checks passed

rustbot added this to the 1.92.0 milestone Sep 17, 2025

github-actions bot mentioned this pull request Sep 18, 2025

Toolchain upgrade to nightly-2025-09-18 flux-rs/flux#1271

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interpret: copy_provenance: avoid large intermediate buffer for large repeat counts #146331

interpret: copy_provenance: avoid large intermediate buffer for large repeat counts #146331

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Overall result: ❌ regressions - no action needed

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Overall result: ❌✅ regressions and improvements - no action needed

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Test differences

Job duration changes

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Overall result: ❌✅ regressions and improvements - no action needed

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