Streamline MIR dataflow cursors #118230

nnethercote · 2023-11-24T05:48:53Z

rustc_mir_dataflow has two kinds of results (Results and ResultsCloned) and three kinds of results cursor (ResultsCursor, ResultsClonedCursor, ResultsRefCursor). I found this quite confusing.

This PR removes ResultsCloned, ResultsClonedCursor, and ResultsRefCursor, leaving just Results and ResultsCursor. This makes the relevant code shorter and easier to read, and there is no performance penalty.

r? @cjgillot

rustbot · 2023-11-24T05:48:58Z

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

nnethercote · 2023-11-24T05:49:11Z

@bors try @rust-timer queue

bors · 2023-11-24T05:50:21Z

⌛ Trying commit 0e0ffbd with merge d449aa5...

…ors, r=<try> Streamline MIR dataflow cursors r? `@ghost`

bors · 2023-11-24T07:14:37Z

☀️ Try build successful - checks-actions
Build commit: d449aa5 (d449aa59d57a9d5e76aa76b08a77ab46c8a0d77c)

rust-timer · 2023-11-24T12:22:46Z

Finished benchmarking commit (d449aa5): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to 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

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.6%	[-2.6%, -2.6%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.6%	[-2.6%, -2.6%]	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: 675.697s -> 677.516s (0.27%)
Artifact size: 313.74 MiB -> 313.73 MiB (-0.00%)

nnethercote · 2023-11-24T19:31:32Z

No change on perf, as expected. That's good news, it means the very small increase in cloning has no meaningful perf effect.

And insert some whitespace.

It's only implemented for analyses that implement `Copy`, which means it's basically a complicated synonym for `Copy`. So this commit removes it and uses `Copy` directly. (That direct use will be removed in a later commit.)

It's currently used because `requires_storage_results` is used in two locations: once with a cursor, and once later on without a cursor. The non-consuming `as_results_cursor` is used for the first location. But we can instead use the consuming `into_results_cursor` and then use `into_results` to extract the `Results` from the finished-with cursor for use at the second location.

The new code is a little clunky, but I couldn't see how to make it better.

It's no longer used.

By just cloning the entire `Results` in the one place where `ResultsClonedCursor` was used. This is extra allocations but the performance effect is negligible.

They're now unused.

They both now only ever contain a `Results<'tcx, A>`. This means `AnalysisResults` can be removed, as can many `borrow`/`borrow_mut` calls. Also `Results` no longer needs a `PhantomData` because `'tcx` is now named by `entry_sets`.

nnethercote · 2023-11-27T03:43:37Z

cc @Jarcho

Jarcho · 2023-11-27T20:42:25Z

Looked back at what this was before I changed it. The current mess of different cursor types was just a way to avoid cloning in all the cases it did before.

It might be possible to simplify things by only borrowing the entry sets and cloning the analysis.

nnethercote · 2023-11-27T21:07:01Z

It might be possible to simplify things by only borrowing the entry sets and cloning the analysis.

That's exactly what ResultsClonedCursor did, which required the assistance of CloneAnalysis and AnalysisResults. But the cost of cloning the entry sets is negligible, so it's not worth all the extra complexity to avoid cloning.

Jarcho · 2023-11-27T21:37:18Z

CloneAnalysis could just be Clone. There would have been (very small) perf hits on some of the stuff I was working on at time, but it's really not needed. If I were to do things now I wouldn't have added it at all.

AnalysisResults wouldn't be needed if the entry sets and analysis were stored directly as separate fields. I think that caused some other problems somewhere else, but I don't remember everything I tried at the time.

Since this doesn't have a big effect, I agree with the assessment that it doesn't really matter.

nnethercote · 2023-12-03T10:39:08Z

CloneAnalysis could just be Clone. There would have been (very small) perf hits on some of the stuff I was working on at time, but it's really not needed. If I were to do things now I wouldn't have added it at all.

The PR removes CloneAnalysis, exactly by just using Clone in a very small number of places.

AnalysisResults wouldn't be needed if the entry sets and analysis were stored directly as separate fields. I think that caused some other problems somewhere else, but I don't remember everything I tried at the time.

The PR removes AnalysisResults as well.

cjgillot · 2023-12-03T14:52:51Z

LGTM. Why is this still marked as draft?

nnethercote · 2023-12-03T22:29:58Z

Sorry, I forgot to remove the draft marker :)

nnethercote · 2023-12-04T21:10:19Z

@cjgillot: is your "LGTM" equivalent to an r+ ?

cjgillot · 2023-12-04T23:27:41Z

@bors r+

bors · 2023-12-04T23:27:44Z

📌 Commit e966c89 has been approved by cjgillot

It is now in the queue for this repository.

bors · 2023-12-05T02:36:54Z

⌛ Testing commit e966c89 with merge 317d14a...

bors · 2023-12-05T04:33:48Z

☀️ Test successful - checks-actions
Approved by: cjgillot
Pushing 317d14a to master...

bors · 2023-12-05T04:33:49Z

☀️ Test successful - checks-actions
Approved by: cjgillot
Pushing 317d14a to master...

rust-timer · 2023-12-05T06:07:37Z

Finished benchmarking commit (317d14a): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.2%	[-0.2%, -0.2%]	2
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

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

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	1.8%	[1.8%, 1.8%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 673.516s -> 673.262s (-0.04%)
Artifact size: 314.15 MiB -> 314.18 MiB (0.01%)

`ResultsCursor` currently owns its `Results`. But sometimes the `Results` is needed again afterwards. So there is `ResultsCursor::into_results` for extracting the `Results`, which leads to some awkwardness. This commit adds `ResultsHandle`, a `Cow`-like type that can either borrow or own a a `Results`. `ResultsCursor` now uses it. This is good because some `ResultsCursor`s really want to own their `Results`, while others just want to borrow it. We end with with a few more lines of code, but get some nice cleanups. - `ResultsCursor::into_results` is removed. - `Formatter::into_results` is removed. - `write_graphviz_results` now just borrows a `Results`, instead of the awkward "take ownership of a `Results` and then return it unchanged" pattern. - `MaybeRequiresStorage` can borrow the `MaybeBorrowedLocals` results, avoiding two `clone` calls: one in `check_for_move` and one in `locals_live_across_suspend_points`. - `Results` no longer needs to derive `Clone`. This reinstates the cursor flexibility that was lost in rust-lang#118230 -- which removed the old `ResultsRefCursor` and `ResultsCloneCursor` types -- but in a *much* simpler way. Hooray!

…aflow-cleanups, r=<try> Still more `rustc_mir_dataflow` cleanups A sequel to rust-lang#118203, rust-lang#118230, rust-lang#118638, and rust-lang#131481. I'm pleased with this PR. It cleans up a few things that have been bugging me for a while. It took quite some effort to find these improvements. r? `@cjgillot`

`ResultsCursor` currently owns its `Results`. But sometimes the `Results` is needed again afterwards. So there is `ResultsCursor::into_results` for extracting the `Results`, which leads to some awkwardness. This commit adds `ResultsHandle`, a `Cow`-like type that can either borrow or own a a `Results`. `ResultsCursor` now uses it. This is good because some `ResultsCursor`s really want to own their `Results`, while others just want to borrow it. We end with with a few more lines of code, but get some nice cleanups. - `ResultsCursor::into_results` is removed. - `Formatter::into_results` is removed. - `write_graphviz_results` now just borrows a `Results`, instead of the awkward "take ownership of a `Results` and then return it unchanged" pattern. - `MaybeRequiresStorage` can borrow the `MaybeBorrowedLocals` results, avoiding two `clone` calls: one in `check_for_move` and one in `locals_live_across_suspend_points`. - `Results` no longer needs to derive `Clone`. This reinstates the cursor flexibility that was lost in rust-lang#118230 -- which removed the old `ResultsRefCursor` and `ResultsCloneCursor` types -- but in a *much* simpler way. Hooray!

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 Nov 24, 2023

nnethercote marked this pull request as draft November 24, 2023 05:49

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Nov 24, 2023

bors added a commit to rust-lang-ci/rust that referenced this pull request Nov 24, 2023

Auto merge of rust-lang#118230 - nnethercote:streamline-dataflow-curs…

d449aa5

…ors, r=<try> Streamline MIR dataflow cursors r? `@ghost`

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Nov 24, 2023

nnethercote added 9 commits November 27, 2023 10:35

Use typedefs to clarify some impls.

b85cba8

And insert some whitespace.

Remove some unused code relating to ResultsCloned.

389e2cc

Remove CloneAnalysis.

d957c47

It's only implemented for analyses that implement `Copy`, which means it's basically a complicated synonym for `Copy`. So this commit removes it and uses `Copy` directly. (That direct use will be removed in a later commit.)

Remove another use of as_results_cursor.

cf82b41

The new code is a little clunky, but I couldn't see how to make it better.

Remove ResultsRefCursor.

5f5263b

It's no longer used.

Remove uses of ResultsClonedCursor.

500e55b

By just cloning the entire `Results` in the one place where `ResultsClonedCursor` was used. This is extra allocations but the performance effect is negligible.

Remove ResultsCloned and ResultsClonedCursor.

34aa36b

They're now unused.

Deparameterize Results and ResultsCursor.

e966c89

They both now only ever contain a `Results<'tcx, A>`. This means `AnalysisResults` can be removed, as can many `borrow`/`borrow_mut` calls. Also `Results` no longer needs a `PhantomData` because `'tcx` is now named by `entry_sets`.

nnethercote force-pushed the streamline-dataflow-cursors branch from 0e0ffbd to e966c89 Compare November 27, 2023 03:40

rustbot assigned cjgillot Nov 27, 2023

nnethercote marked this pull request as ready for review December 3, 2023 22:29

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 4, 2023

bors added merged-by-bors This PR was explicitly merged by bors. labels Dec 5, 2023

bors merged commit 317d14a into rust-lang:master Dec 5, 2023
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rustbot added this to the 1.76.0 milestone Dec 5, 2023

nnethercote deleted the streamline-dataflow-cursors branch December 5, 2023 04:55

nnethercote mentioned this pull request Oct 23, 2024

Still more rustc_mir_dataflow cleanups #132062

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Streamline MIR dataflow cursors #118230

Streamline MIR dataflow cursors #118230

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Streamline MIR dataflow cursors #118230

Streamline MIR dataflow cursors #118230

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Overall result: no relevant changes - no action needed

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Overall result: ✅ improvements - no action needed

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