Micro-optimization attempt in coroutine layout computation #147858

yotamofek · 2025-10-18T19:58:38Z

In compute_layout, there were a bunch of collections (IndexVecs) that were being created by pushing in a loop, instead of a, hopefully, more performant usage of iterator combinators. Second commit is just a small cleanup.

I'd love a perf run to see if this shows up in benchmarks.

rustbot · 2025-10-18T19:58:41Z

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

rustbot · 2025-10-18T19:58:43Z

r? @jdonszelmann

rustbot has assigned @jdonszelmann.
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

Kobzol · 2025-10-18T20:59:39Z

@bors try @rust-timer queue

Micro-optimization attempt in coroutine layout computation

cjgillot · 2025-10-18T20:59:53Z

@bors try @rust-timer queue

Micro-optimization attempt in coroutine layout computation

cjgillot · 2025-10-18T21:00:54Z

compiler/rustc_mir_transform/src/coroutine.rs


    // Gather live local types and their indices.
-    let mut locals = IndexVec::<CoroutineSavedLocal, _>::new();
-    let mut tys = IndexVec::<CoroutineSavedLocal, _>::new();


Can we do simpler? The original code but using IndexVec::with_capacity?

cjgillot · 2025-10-18T21:03:23Z

compiler/rustc_mir_transform/src/coroutine.rs

    // Build the coroutine variant field list.
    // Create a map from local indices to coroutine struct indices.
-    let mut variant_fields: IndexVec<VariantIdx, IndexVec<FieldIdx, CoroutineSavedLocal>> =
-        iter::repeat(IndexVec::new()).take(CoroutineArgs::RESERVED_VARIANTS).collect();


Instead of pushing, could we use IndexVec::from_elem_n(IndexVec::new(), CoroutineArgs::RESERVED_VARIANTS + live_locals_at_suspension_points.len())? And then assign to each element?

yotamofek · 2025-10-18T21:20:31Z

@cjgillot both suggestions sound good, but I'd like to try them after this perf run to see if they have any effect on it

rust-bors · 2025-10-18T23:16:16Z

☀️ Try build successful (CI)
Build commit: 32cc823 (32cc823f9cad9f0599aac2707d559bed821f7548, parent: 6380899f32599ea25615d4ccd708d0e8da652b0c)

rust-timer · 2025-10-19T00:27:55Z

Finished benchmarking commit (32cc823): 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)

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

Cycles

Results (primary 2.4%, 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)	2.4%	[2.4%, 2.4%]	1
Regressions ❌ (secondary)	3.8%	[3.8%, 3.8%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.4%	[2.4%, 2.4%]	1

Binary size

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

Bootstrap: 471.955s -> 474.126s (0.46%)
Artifact size: 390.54 MiB -> 390.51 MiB (-0.01%)

rustbot · 2025-10-19T19:47:18Z

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.

yotamofek · 2025-10-19T19:48:29Z

@cjgillot might have gone a bit overboard here with the izip, but it does make that loop body more succinct. WDYT?

I don't mind just closing this PR since it doesn't affect perf, maybe it's not worth touching this at all.

jdonszelmann · 2025-10-20T13:11:54Z

r? compiler

davidtwco · 2025-10-25T11:11:45Z

@bors try @rust-timer queue

Micro-optimization attempt in coroutine layout computation

rust-bors · 2025-10-25T13:28:09Z

☀️ Try build successful (CI)
Build commit: f6307c2 (f6307c2d83816dc4bc953e2b19d09b0ecd4cc041, parent: 04ff05c9c0cfbca33115c5f1b8bb20a66a54b799)

rust-timer · 2025-10-25T14:37:28Z

Finished benchmarking commit (f6307c2): 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 0.5%)

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

	mean	range	count
Regressions ❌ (primary)	0.5%	[0.5%, 0.5%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.5%	[0.5%, 0.5%]	1

Cycles

Results (secondary -4.3%)

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)	-4.3%	[-4.3%, -4.3%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 473.373s -> 475.989s (0.55%)
Artifact size: 390.48 MiB -> 390.45 MiB (-0.01%)

cjgillot · 2025-10-30T00:51:15Z

@bors r+ rollup

bors · 2025-10-30T00:51:17Z

📌 Commit a67c615 has been approved by cjgillot

It is now in the queue for this repository.

…opt, r=cjgillot Micro-optimization attempt in coroutine layout computation In `compute_layout`, there were a bunch of collections (`IndexVec`s) that were being created by `push`ing in a loop, instead of a, hopefully, more performant usage of iterator combinators. [Second commit](rust-lang@6f682c2) is just a small cleanup. I'd love a perf run to see if this shows up in benchmarks.

Rollup of 9 pull requests Successful merges: - #138217 (Turn `Cow::is_borrowed,is_owned` into associated functions.) - #147858 (Micro-optimization attempt in coroutine layout computation) - #147923 (Simplify rustc_public context handling) - #147935 (Add LLVM realtime sanitizer) - #148115 (rustdoc: Rename unstable option `--nocapture` to `--no-capture` in accordance with `libtest`) - #148137 (Couple of changes for Redox OS) - #148176 ([rustdoc] Include attribute and derive macros when filtering on "macros") - #148193 (Remove `QPath::LangItem`) - #148253 (Handle default features and -Ctarget-features in the dummy backend) r? `@ghost` `@rustbot` modify labels: rollup

Rollup of 8 pull requests Successful merges: - #138217 (Turn `Cow::is_borrowed,is_owned` into associated functions.) - #147858 (Micro-optimization attempt in coroutine layout computation) - #147923 (Simplify rustc_public context handling) - #148115 (rustdoc: Rename unstable option `--nocapture` to `--no-capture` in accordance with `libtest`) - #148137 (Couple of changes for Redox OS) - #148176 ([rustdoc] Include attribute and derive macros when filtering on "macros") - #148253 (Handle default features and -Ctarget-features in the dummy backend) - #148272 (Align VEX V5 boot routine to 4 bytes) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #147858 - yotamofek:pr/mir/coroutine-layout-opt, r=cjgillot Micro-optimization attempt in coroutine layout computation In `compute_layout`, there were a bunch of collections (`IndexVec`s) that were being created by `push`ing in a loop, instead of a, hopefully, more performant usage of iterator combinators. [Second commit](6f682c2) is just a small cleanup. I'd love a perf run to see if this shows up in benchmarks.

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 Oct 18, 2025

rustbot assigned jdonszelmann Oct 18, 2025

This comment has been minimized.

Sign in to view

rust-bors bot added a commit that referenced this pull request Oct 18, 2025

Auto merge of #147858 - yotamofek:pr/mir/coroutine-layout-opt, r=<try>

db63cf8

Micro-optimization attempt in coroutine layout computation

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 18, 2025

This comment has been minimized.

Sign in to view

rust-bors bot added a commit that referenced this pull request Oct 18, 2025

Auto merge of #147858 - yotamofek:pr/mir/coroutine-layout-opt, r=<try>

32cc823

Micro-optimization attempt in coroutine layout computation

This comment has been minimized.

Sign in to view

cjgillot reviewed Oct 18, 2025

View reviewed changes

This comment has been minimized.

Sign in to view

rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 19, 2025

yotamofek added 2 commits October 19, 2025 22:46

Allocate vec capacity upfront in coroutine layout computation

f0c98c2

Reduce rightward drift in locals_live_across_suspend_points

a67c615

yotamofek force-pushed the pr/mir/coroutine-layout-opt branch from 6f682c2 to a67c615 Compare October 19, 2025 19:47

rustbot assigned davidtwco and unassigned jdonszelmann Oct 20, 2025

This comment has been minimized.

Sign in to view

rust-bors bot added a commit that referenced this pull request Oct 25, 2025

Auto merge of #147858 - yotamofek:pr/mir/coroutine-layout-opt, r=<try>

f6307c2

Micro-optimization attempt in coroutine layout computation

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 25, 2025

This comment has been minimized.

Sign in to view

rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 25, 2025

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 30, 2025

Zalathar mentioned this pull request Oct 30, 2025

Rollup of 9 pull requests #148276

Closed

jhpratt mentioned this pull request Oct 30, 2025

Rollup of 8 pull requests #148280

Merged

bors merged commit 1ae00ba into rust-lang:master Oct 30, 2025
12 checks passed

rustbot added this to the 1.93.0 milestone Oct 30, 2025

yotamofek deleted the pr/mir/coroutine-layout-opt branch October 30, 2025 18:17

Micro-optimization attempt in coroutine layout computation #147858

Micro-optimization attempt in coroutine layout computation #147858

Uh oh!

Conversation

yotamofek commented Oct 18, 2025

Uh oh!

rustbot commented Oct 18, 2025

Uh oh!

rustbot commented Oct 18, 2025

Uh oh!

Kobzol commented Oct 18, 2025

Uh oh!

This comment has been minimized.

This comment has been minimized.

cjgillot commented Oct 18, 2025

Uh oh!

This comment has been minimized.

This comment has been minimized.

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

yotamofek commented Oct 18, 2025

Uh oh!

rust-bors bot commented Oct 18, 2025

Uh oh!

This comment has been minimized.

rust-timer commented Oct 19, 2025

Overall result: no relevant changes - no action needed

Uh oh!

rustbot commented Oct 19, 2025

Uh oh!

yotamofek commented Oct 19, 2025

Uh oh!

jdonszelmann commented Oct 20, 2025

Uh oh!

davidtwco commented Oct 25, 2025

Uh oh!

This comment has been minimized.

This comment has been minimized.

rust-bors bot commented Oct 25, 2025

Uh oh!

This comment has been minimized.

rust-timer commented Oct 25, 2025

Overall result: no relevant changes - no action needed

Uh oh!

cjgillot commented Oct 30, 2025

Uh oh!

bors commented Oct 30, 2025

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

8 participants