Optimize matches by matthewjasper · Pull Request #60730 · rust-lang/rust

matthewjasper · 2019-05-11T10:54:44Z

Attempt to fix or improve #60571

This is breaking some diagnostics because the MIR for match arms isn't in source order any more.

cc @Centril

rust-highfive · 2019-05-11T10:54:54Z

r? @pnkfelix

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matthewjasper · 2019-05-11T10:55:01Z

@bors try

bors · 2019-05-11T10:55:12Z

⌛ Trying commit d7f31a6 with merge df9b1d3...

@Centril

Optimize matches Attempt to fix or improve #60571 This is breaking some diagnostics because the MIR for match arms isn't in source order any more. cc @Centril

bors · 2019-05-11T13:06:19Z

☀️ Try build successful - checks-travis
Build commit: df9b1d3

matthewjasper · 2019-05-12T10:46:16Z

@rust-lang/infra Can I have a perf run?

emilyalbini · 2019-05-12T10:48:47Z

@rust-timer build df9b1d3

rust-timer · 2019-05-12T10:48:48Z

Success: Queued df9b1d3 with parent b8e0d0a, comparison URL.

rust-timer · 2019-05-12T14:45:44Z

Finished benchmarking try commit df9b1d3

pnkfelix · 2019-05-22T12:45:38Z

 /// The target normal control flow will take
 real_target: BasicBlock,
- /// The list of blocks control flow could conceptually take, but won't
+ /// A block control flow could conceptually take, but won't


Suggested change
/// A block control flow could conceptually take, but won't
/// A block control flow could conceptually jump to, but won't

pnkfelix · 2019-05-22T13:07:21Z

+ adt_def.variants.len() + 1
+ }
+ TestKind::SwitchInt { switch_ty, ref options, .. } => {
+ if switch_ty.is_bool() {


I'm trying to figure out the overall picture here.
My current best guess is that, for SwitchInt on a bool, the options ends up holding just some permutation of { 0, 1 } (and we know that to be exhaustive, since the type is bool), and thus options.len() + 1 would give the wrong number of target basic blocks.
Regardless of whether my hypothesis above is correct or incorrect, it might be nice to add some docs to SwitchInt explaining the role of the options field, and what invariants it upholds with respect to the other fields (switch_ty and indices).

pnkfelix · 2019-05-22T13:08:41Z

 // StorageLive(_4);
 // _4 = _2;
-// ((_0 as A).0: i32) = move _4;
-// discriminant(_0) = 0;


(I find this effect on the generated MIR interesting. I don't know whether its bad or good, in terms of code quality i.e. the ability of LLVM to optimize the result)

The diff is a little messed up, all that's happening here is the two blocks are being swapped

pnkfelix · 2019-05-22T13:13:06Z

 | ^^^^^ cannot assign twice to immutable variable
+LL | } else {
+LL | x = 2;
+ | ----- first assignment to `x`


(it always makes me a little sad to see leaking of the reality that our static analysis is happening on a control-flow graph that does not always bias itself to act like syntactic order should be favored when the control-flow is otherwise semi-arbitrary. But there are other instances where things like this leak through and its certainly not your job, or maybe anyone's job, to address it.)

pnkfelix · 2019-05-22T13:14:48Z

The perf results look entirely acceptable to me.

pnkfelix · 2019-05-22T13:15:28Z

@matthewjasper maybe I missed it, but did you add a test case for the actual problem described in #60571 somewhere in this PR?

pnkfelix · 2019-05-22T13:17:18Z

This all seems fine to me. I left some general feedback, but I don't see a problem with landing this PR as is.

Having said that, we can't merge draft pull requests.

So I'll just say: r=me, and switch this to S-waiting-on-author so that @matthewjasper can decide if its fully-baked, or if it needs more changes and then another round of review.

Centril · 2019-05-22T13:40:48Z

The perf results look entirely acceptable to me.

I am surprised that things don't look better tho... I would have expected to regain more of the loss. The mir-opt test for simplify_if looks almost as before (diff in https://github.com/rust-lang/rust/pull/59288/files?file-filters%5B%5D=.stderr#diff-2482362a90df359dd3fd19add1f77160) except for initial -> after-copy-prop. Maybe revert it back to initial to see how it looks then?

@matthewjasper maybe I missed it, but did you add a test case for the actual problem described in #60571 somewhere in this PR?

I don't see a mir-opt test for match cond { true => expr, _ => expr } -- maybe add one?

matthewjasper · 2019-05-25T14:16:10Z

Just to give an update here: it's taken me awhile to get back to this. I've had a look at the encoding perf regression and I think I've identified the problem there. There are some other things that I want to check as well. I'll push an updated PR and mark this ready for review once I'm happy.

bors · 2019-05-25T19:03:05Z

☔ The latest upstream changes (presumably #59276) made this pull request unmergeable. Please resolve the merge conflicts.

rust-highfive · 2019-05-25T20:03:13Z

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matthewjasper · 2019-05-26T09:10:52Z

@bors try

bors · 2019-06-16T04:02:19Z

⌛ Testing commit 89ea69a with merge 8e774d33f9956f3e6a69fb85878dc754cb879f63...

bors · 2019-06-16T04:46:10Z

💔 Test failed - checks-travis

rust-highfive · 2019-06-16T04:46:11Z

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Centril · 2019-06-16T04:55:52Z

@bors retry spurious 30 min

bors · 2019-06-16T09:30:41Z

⌛ Testing commit 89ea69a with merge 6865502...

@Centril

Optimize matches Attempt to fix or improve #60571 This is breaking some diagnostics because the MIR for match arms isn't in source order any more. cc @Centril

bors · 2019-06-16T12:14:55Z

☀️ Test successful - checks-travis, status-appveyor
Approved by: pnkfelix
Pushing 6865502 to master...

rust-highfive · 2019-06-16T12:17:59Z

📣 Toolstate changed by #60730!

Tested on commit 6865502.
Direct link to PR: #60730

💔 rls on windows: test-pass → test-fail (cc @Xanewok, @rust-lang/infra).

@Xanewok

Tested on commit rust-lang/rust@6865502. Direct link to PR: <rust-lang/rust#60730> 💔 rls on windows: test-pass → test-fail (cc @Xanewok, @rust-lang/infra).

Nadrieril · 2023-12-18T21:04:24Z

@matthewjasper what benchmark did you use to measure the impact of a1d0266 (#60730)? You mention "encoding" but that's a compile-time benchmark today. Context is that I just tried reverting that commit to see if it was still useful and nothing on perf.rlo picked up a difference (see here).

matthewjasper · 2023-12-19T09:25:37Z

I can't really remember using anything other than the perf.rlo benchmarks. Maybe I had a test that consisted only of a very large match against a lot of string literals.

Nadrieril · 2023-12-19T10:25:51Z

Oh wait, your commit says "spend less time optimizing", so it was a compile time problem! The encoding benchmark makes sense then. I remember encoding existed already at the time, must be that. That's awesome it means we can remove the hack!

… r=<try> match lowering: Remove the `make_target_blocks` hack This hack was introduced 4 years ago in [`a1d0266` (rust-lang#60730)](rust-lang@a1d0266) to improve LLVM optimization time, specifically noticed in the `encoding` benchmark. Measurements today indicate it is no longer needed. r? `@matthewjasper`

… r=matthewjasper match lowering: Remove the `make_target_blocks` hack This hack was introduced 4 years ago in [`a1d0266` (rust-lang#60730)](rust-lang@a1d0266) to improve LLVM optimization time, specifically noticed in the `encoding` benchmark. Measurements today indicate it is no longer needed. r? `@matthewjasper`

rust-highfive assigned pnkfelix May 11, 2019

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label May 11, 2019

pnkfelix reviewed May 22, 2019
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matthewjasper force-pushed the optimize-false-edges branch from d7f31a6 to cafb9d7Compare May 25, 2019 18:43

matthewjasper marked this pull request as ready for review May 25, 2019 18:44

matthewjasper force-pushed the optimize-false-edges branch 2 times, most recently from 9425a84 to 967d806Compare May 25, 2019 19:45

matthewjasper force-pushed the optimize-false-edges branch from 967d806 to 2f57a82Compare May 26, 2019 07:19

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 Jun 15, 2019

bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Jun 16, 2019

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 Jun 16, 2019

bors added the merged-by-bors This PR was explicitly merged by bors. label Jun 16, 2019

bors merged commit 89ea69a into rust-lang:masterJun 16, 2019

This was referenced Jun 16, 2019
Allow cross-compiling doctests #60387
Merged
Remove rustc_mir dependency from rustc_borrowck #61590
Merged
Clean up MIR drop generation #61872
Merged

pnkfelix mentioned this pull request Jun 25, 2019
&mut &T coerced to &T suggests &mut mut x#57431
Open

RalfJung mentioned this pull request Jun 29, 2019
Spurious RLS test failures #62225
Closed

matthewjasper deleted the optimize-false-edges branch July 29, 2019 19:53

matthiaskrgr mentioned this pull request Sep 20, 2023
ICE due to bad sized to unsized pointer cast in const item #115998
Closed

	/// A block control flow could conceptually take, but won't
	/// A block control flow could conceptually jump to, but won't

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