Clean up MIR drop generation #61872

matthewjasper · 2019-06-15T19:52:13Z

Don't assign twice to the destination of a while loop containing a break expression
Use as_temp to evaluate statement expression
Avoid consecutive StorageLives for the condition of a while loop
Unify return, break and continue handling, and move it to scopes.rs
Make some of the scopes.rs internals private
Don't use Places that are always Locals in MIR drop generation

Closes #42371
Closes #61579
Closes #61731
Closes #61834
Closes #61910
Closes #62115

rust-highfive · 2019-06-15T19:52:17Z

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Centril · 2019-06-15T21:10:15Z

src/librustc_mir/build/expr/into.rs

@@ -179,20 +179,19 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                        // conduct the test, if necessary
                        let body_block;
                        if let Some(cond_expr) = opt_cond_expr {


N.B. As part of implementing while a && let b = c { ... } I'll make a PR to remove hir::ExprKind::While and then hair::ExprKind::Loop will presumably need to drop it's condition field and so the else branch would be floated out and the if branch would be removed... I hope the changes here do not cause problems for this...?

That should be fine, this is only a problem because while loops are special cased. For any sensible HIR lowering this won't be a problem. The temporary will probably end up storage-live for the whole loop body, but that isn't observable. The following two functions generate almost identical optimized MIR after this PR, for example.

fn while_loop(c: bool) { while get_bool(c) { if get_bool(c) { break; } } } // What the above should probably expand to fn exp_while_loop(c: bool) { loop { match get_bool(c) { true => { {if get_bool(c) { break; }} continue; } _ => {} } break; } }

Cool.

For any sensible HIR lowering this won't be a problem.

Specifically, the HIR lowering should likely be:

'label: while $cond $block

==>

'label: loop { match DropTemps($cond) { true => $block, _ => break, } }

(is there a particular reason you are using continue; and an empty block?)

It's slightly closer to what the RFC specified. What you're suggesting is probably better.

This should be unnecessary now with #61988.

bors · 2019-06-16T12:30:33Z

☔ The latest upstream changes (presumably #60730) made this pull request unmergeable. Please resolve the merge conflicts.

bors · 2019-06-18T02:32:46Z

☔ The latest upstream changes (presumably #61915) made this pull request unmergeable. Please resolve the merge conflicts.

eddyb · 2019-06-18T16:20:38Z

r? @pnkfelix

Should be able to roll forward when rust-lang/rust#61872 is in a nightly.

nikomatsakis

This looks very good. I left a few questions.

src/librustc_mir/build/expr/stmt.rs

src/librustc_mir/build/matches/mod.rs

src/librustc_mir/build/expr/stmt.rs

src/test/mir-opt/while-storage.rs

src/librustc_mir/build/expr/as_rvalue.rs

nikomatsakis · 2019-06-25T17:52:56Z

@bors r+

bors · 2019-06-25T17:52:58Z

📌 Commit 07e5297faf2966a77c466b0b5ad936c0deb828ac has been approved by nikomatsakis

bors · 2019-06-25T21:38:02Z

☔ The latest upstream changes (presumably #62119) made this pull request unmergeable. Please resolve the merge conflicts.

cramertj · 2019-06-26T02:14:02Z

@bors r=nikomatsakis

bors · 2019-06-26T02:14:03Z

📌 Commit 3131427 has been approved by nikomatsakis

bors · 2019-06-26T04:42:40Z

⌛ Testing commit 3131427 with merge d3e2cec...

…sakis Clean up MIR drop generation * Don't assign twice to the destination of a `while` loop containing a `break` expression * Use `as_temp` to evaluate statement expression * Avoid consecutive `StorageLive`s for the condition of a `while` loop * Unify `return`, `break` and `continue` handling, and move it to `scopes.rs` * Make some of the `scopes.rs` internals private * Don't use `Place`s that are always `Local`s in MIR drop generation Closes #42371 Closes #61579 Closes #61731 Closes #61834 Closes #61910 Closes #62115

bors · 2019-06-26T07:24:15Z

☀️ Test successful - checks-travis, status-appveyor
Approved by: nikomatsakis
Pushing d3e2cec to master...

mati865 · 2019-07-03T12:54:13Z

Was this performance regression expected?
https://perf.rust-lang.org/compare.html?start=bdd4bda4d5fe7eb24a7209a6c0c968a54869d3b7&end=d3e2cec29225a46298ec4ebf082f34ebd7cfeecf

matthewjasper · 2019-07-07T11:52:39Z

The ctfe-stress benchmark is now generating more MIR, so I'm not surprised that it's slower. I can't really work out what's going on with unicode_normalization, since the generated MIR is unchanged for the large functions and constants.

…_mention, r=compiler-errors Fixup method doc that mentions removed param The param was removed in rust-lang#61872 (101a2f5)

rust-highfive assigned eddyb Jun 15, 2019

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jun 15, 2019

matthewjasper changed the title ~~Refactor MIR drop generation~~ Clean up MIR drop generation Jun 15, 2019

Centril reviewed Jun 15, 2019

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matthewjasper force-pushed the refactor-mir-drop-gen branch from 5ae55a3 to 2c93002 Compare June 16, 2019 19:36

cramertj mentioned this pull request Jun 17, 2019

error: internal compiler error: broken MIR in DefId ... #61910

Closed

matthewjasper force-pushed the refactor-mir-drop-gen branch from 2c93002 to 13218c2 Compare June 17, 2019 18:58

rust-highfive assigned pnkfelix and unassigned eddyb Jun 18, 2019

cramertj mentioned this pull request Jun 18, 2019

Fix HIR visit order #61572

Merged

anp added a commit to anp/moxie that referenced this pull request Jun 20, 2019

Roll toolchain back to avoid a known ICE.

3cd1acc

Should be able to roll forward when rust-lang/rust#61872 is in a nightly.

anp mentioned this pull request Jun 21, 2019

Enable clippy in CI anp/moxie#7

Closed

matthewjasper mentioned this pull request Jun 22, 2019

Make into schedule drop for the destination #61430

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matthewjasper force-pushed the refactor-mir-drop-gen branch from 13218c2 to 07e5297 Compare June 22, 2019 17:04

r3v2d0g added a commit to aktoro-rs/aktoro that referenced this pull request Jun 22, 2019

Removed the examples until rust-lang/rust#61872 is fixed.

a503a0d

This was referenced Jun 23, 2019

ICE compiling with futures compat #61986

Closed

Broken MIR: generator contains type impl std::future::Future in MIR, but typeck only knows about {impl std::future::Future, ()} #61834

Closed

l-7-l mentioned this pull request Jun 24, 2019

Tide-cookies fails to compile with Rust Nightly newer than 2019-06-01 http-rs/tide#278

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r3v2d0g mentioned this pull request Jun 24, 2019

TCP/UDP streams/sockets aktoro-rs/aktoro#12

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4 tasks

nikomatsakis approved these changes Jun 24, 2019

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pnkfelix mentioned this pull request Jun 25, 2019

Cannot assign twice to immutable variable with 'l: while break 'l {} as initializer #62115

Closed

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 25, 2019

matthewjasper added 6 commits June 25, 2019 22:41

Fix incorrect double assignment in MIR for while loops

62bec71

Use as_temp to evaluate statement expressions

101a2f5

Avoid checking if references implement drop

82a1a89

Unify return, break and continue handling

be23bd4

Add StorageDead statements for while conditions

b86e675

Use Locals instead of Places in MIR drop generation

3131427

matthewjasper force-pushed the refactor-mir-drop-gen branch from 07e5297 to 3131427 Compare June 25, 2019 21:41

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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jun 26, 2019

bors added the merged-by-bors This PR was explicitly merged by bors. label Jun 26, 2019

bors merged commit 3131427 into rust-lang:master Jun 26, 2019

This was referenced Jun 26, 2019

Place 2.0 change from enum to struct #60913

Merged

[let_chains, 3/6] And then there was only Loop #61988

Merged

mati865 mentioned this pull request Jun 26, 2019

Broken MIR: generator contains type std::vec::Vec<()> #62025

Closed

taiki-e mentioned this pull request Jun 26, 2019

Revert "Ignore doc tests which "Broken MIR" ICE occurred" rust-lang/futures-rs#1685

Merged

This was referenced Jun 26, 2019

Add regression test for MIR drop generation in async loops #62155

Merged

src/librustc_mir/transform/generator.rs:715: Broken MIR #62126

Closed

theduke mentioned this pull request Jun 26, 2019

[Stabilization] async/await MVP #62149

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4 tasks

goffrie mentioned this pull request Jun 27, 2019

incorrect "cannot assign twice to immutable variable _" with try_blocks + never_type + nll #62165

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matthewjasper deleted the refactor-mir-drop-gen branch July 7, 2019 09:48

WaffleLapkin mentioned this pull request Dec 12, 2022

Fixup method doc that mentions removed param #105615

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Clean up MIR drop generation #61872

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