Optimize `try_expand_impl_trait_type` #65293

tmandry · 2019-10-11T00:06:41Z

A lot of time was being spent expanding some large impl Future types in fuchsia. This PR takes the number of types being visited in one expansion from >3 billion to about a thousand, and eliminates the compile time regression in #65147 (in fact, compile times are better than they were before).

Thanks to @Mark-Simulacrum for helping identify the issue and to @matthewjasper for suggesting this change.

Fixes #65147.
r? @matthewjasper,@nikomatsakis

tmandry · 2019-10-11T00:41:31Z

@bors try

bors · 2019-10-11T00:41:48Z

⌛ Trying commit 6493e6b with merge 0d2ff89f766a2f16a09c41ee7c65453980e81908...

bors · 2019-10-11T03:34:40Z

☀️ Try build successful - checks-azure
Build commit: 0d2ff89f766a2f16a09c41ee7c65453980e81908 (0d2ff89f766a2f16a09c41ee7c65453980e81908)

tmandry · 2019-10-11T03:41:01Z

@rust-timer queue

rust-timer · 2019-10-11T03:41:02Z

Awaiting bors try build completion

tmandry · 2019-10-11T03:46:32Z

@rust-timer build 0d2ff89f766a2f16a09c41ee7c65453980e81908

rust-timer · 2019-10-11T03:46:33Z

Queued 0d2ff89f766a2f16a09c41ee7c65453980e81908 with parent 898f36c, future comparison URL.

Centril · 2019-10-11T06:49:13Z

src/librustc/ty/util.rs

@@ -697,6 +697,9 @@ impl<'tcx> TyCtxt<'tcx> {
 // that type, and when we finish expanding that type we remove the
 // its DefId.
 seen_opaque_tys: FxHashSet<DefId>,
+ // Cache of all expansions we've seen so far. This is a critical
+ // optimization for some large types produced by async fn trees.


Suggested change

// optimization for some large types produced by async fn trees.

// optimization for some large types produced by `async fn` trees.

Centril · 2019-10-11T06:50:07Z

src/librustc/ty/util.rs

- let concrete_ty = generic_ty.subst(self.tcx, substs);
- let expanded_ty = self.fold_ty(concrete_ty);
- self.seen_opaque_tys.remove(&def_id);
+ let expanded_ty = match self.expanded_cache.get(&def_id) {


Why not use the .entry API?

Yeah! Entry! Entry! I ❤️ Entry!

Oh, I think I see why not -- the self.fold_ty call would error out with entry, wouldn't it?

Yeah, the fact that the closure would need &mut self prevents me from using entry here :/

src/test/ui/impl-trait/recursive-impl-trait-type--through-non-recursize.stderr

nikomatsakis · 2019-10-11T17:03:19Z

@tmandry I'm not sure if we have a suitable test already, but if not, can you add something to perf that reflects this compile time gap?

nikomatsakis

Presuming this helps, and if we add a perf regression test, seems good to me! Nice detective work y'all.

rust-timer · 2019-10-11T20:16:32Z

Finished benchmarking try commit 0d2ff89f766a2f16a09c41ee7c65453980e81908, comparison URL.

tmandry · 2019-10-11T22:22:25Z

@tmandry I'm not sure if we have a suitable test already, but if not, can you add something to perf that reflects this compile time gap?

Will do. I was hoping something would turn up in the existing test suite, but it doesn't look that way :)

matthewjasper

I think the following test case shows the problem here:

#![type_length_limit="10000000"]
#![allow(unused)]

macro_rules! mk_async_fn {
    ($f:ident $g:ident) => {
        async fn $g() -> i32 {
            $f().await;
            $f().await;
            $f().await
        }
    }
}

async fn a() -> i32 { 1 }

mk_async_fn!(a b);
mk_async_fn!(b c);
mk_async_fn!(c d);
mk_async_fn!(d e);
mk_async_fn!(e f);
mk_async_fn!(f g);
mk_async_fn!(g h);
mk_async_fn!(h i);
mk_async_fn!(i j);

src/librustc/ty/util.rs

tmandry · 2019-10-14T22:50:45Z

@bors try

bors · 2019-10-14T22:50:55Z

⌛ Trying commit 6493e6b with merge 0c36cd3...

@matthewjasper

Optimize `try_expand_impl_trait_type` A lot of time was being spent expanding some large `impl Future` types in fuchsia. This PR takes the number of types being visited in one expansion from >3 billion to about a thousand, and eliminates the compile time regression in #65147 (in fact, compile times are better than they were before). Thanks to @matthewjasper for suggesting this change. Fixes #65147. r? @matthewjasper,@nikomatsakis

tmandry · 2019-10-15T01:18:17Z

@matthewjasper thanks for supplying the benchmark!

This should be ready, pending another timer run once rust-lang/rustc-perf#508 is merged.

bors · 2019-10-15T01:56:00Z

☀️ Try build successful - checks-azure
Build commit: 0c36cd3 (0c36cd32207594f45af4c9c92294f769113808b6)

tmandry · 2019-10-15T19:40:47Z

@bors r=matthewjasper

bors · 2019-10-15T19:40:48Z

📌 Commit 802554f has been approved by matthewjasper

@Mark-Simulacrum

…sper Optimize `try_expand_impl_trait_type` A lot of time was being spent expanding some large `impl Future` types in fuchsia. This PR takes the number of types being visited in one expansion from >3 billion to about a thousand, and eliminates the compile time regression in rust-lang#65147 (in fact, compile times are better than they were before). Thanks to @Mark-Simulacrum for helping identify the issue and to @matthewjasper for suggesting this change. Fixes rust-lang#65147. r? @matthewjasper,@nikomatsakis

@ghost

Rollup of 14 pull requests Successful merges: - #64603 (Reducing spurious unused lifetime warnings.) - #64623 (Remove last uses of gensyms) - #65235 (don't assume we can *always* find a return type hint in async fn) - #65242 (Fix suggestion to constrain trait for method to be found) - #65265 (Cleanup librustc mir err codes) - #65293 (Optimize `try_expand_impl_trait_type`) - #65307 (Try fix incorrect "explicit lifetime name needed") - #65308 (Add long error explanation for E0574) - #65353 (save-analysis: Don't ICE when resolving qualified type paths in struct members) - #65389 (Return `false` from `needs_drop` for all zero-sized arrays.) - #65402 (Add troubleshooting section to PGO chapter in rustc book.) - #65425 (Optimize `BitIter`) - #65438 (Organize `never_type` tests) - #65444 (Implement AsRef<[T]> for List<T>) Failed merges: - #65390 (Add long error explanation for E0576) r? @ghost

pnkfelix · 2019-10-17T14:24:45Z

discussed at T-compiler meeting. Accepted for beta-backport.

[beta] backport rollup This includes a bunch of PRs: * Fix redundant semicolon lint interaction with proc macro attributes #64387 * Upgrade async/await to "used" keywords. #64875 * syntax: fix dropping of attribute on first param of non-method assocated fn #64894 * async/await: improve not-send errors #64895 * Silence unreachable code lint from await desugaring #64930 * Always mark rust and rust-call abi's as unwind #65020 * Account for macro invocation in `let mut $pat` diagnostic. #65123 * Ensure that associated `async fn`s have unique fresh param names #65142 * Add troubleshooting section to PGO chapter in rustc book. #65402 * Upgrade GCC to 8.3.0, glibc to 1.17.0 and crosstool-ng to 1.24.0 for dist-armv7-linux #65302 * Optimize `try_expand_impl_trait_type` #65293 * use precalculated dominators in explain_borrow #65172 * Fix ICE #64964 #64989

[beta] backport rollup This includes a bunch of PRs: * Fix redundant semicolon lint interaction with proc macro attributes #64387 * Upgrade async/await to "used" keywords. #64875 * syntax: fix dropping of attribute on first param of non-method assocated fn #64894 * async/await: improve not-send errors #64895 * Silence unreachable code lint from await desugaring #64930 * Always mark rust and rust-call abi's as unwind #65020 * Account for macro invocation in `let mut $pat` diagnostic. #65123 * Ensure that associated `async fn`s have unique fresh param names #65142 * Add troubleshooting section to PGO chapter in rustc book. #65402 * Upgrade GCC to 8.3.0, glibc to 1.17.0 and crosstool-ng to 1.24.0 for dist-armv7-linux #65302 * Optimize `try_expand_impl_trait_type` #65293 * use precalculated dominators in explain_borrow #65172 * Fix ICE #64964 #64989 * [beta] Revert "Auto merge of #62948 - matklad:failable-file-loading, r=petro… #65273 * save-analysis: Don't ICE when resolving qualified type paths in struct members #65353 * save-analysis: Nest tables when processing impl block definitions #65511 * Avoid ICE when checking `Destination` of `break` inside a closure #65518 * Avoid ICE when adjusting bad self ty #65755 * workaround msys2 bug #65762

rust-highfive assigned matthewjasper Oct 11, 2019

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matthewjasper added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 12, 2019

tmandry mentioned this pull request Oct 14, 2019

Add await-call-tree benchmark rust-lang/rustc-perf#508

Merged

tmandry added 2 commits October 14, 2019 15:48

Add expanded type cache to OpaqueTypeExpander

fe09bb5

Only expand types that contain projections

802554f

tmandry added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Oct 14, 2019

tmandry force-pushed the turbo-expander branch from 6493e6b to 802554f Compare October 15, 2019 19:17

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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 15, 2019

tmandry added beta-nominated Nominated for backporting to the compiler in the beta channel. I-nominated T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Oct 15, 2019

tmandry mentioned this pull request Oct 15, 2019

Rollup of 14 pull requests #65454

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bors merged commit 802554f into rust-lang:master Oct 16, 2019

pnkfelix added the beta-accepted Accepted for backporting to the compiler in the beta channel. label Oct 17, 2019

Mark-Simulacrum removed beta-nominated Nominated for backporting to the compiler in the beta channel. I-nominated labels Oct 22, 2019

Mark-Simulacrum mentioned this pull request Oct 22, 2019

[beta] backport rollup #65708

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ibraheemdev mentioned this pull request Jul 25, 2021

Exponential compile time with recursive opaque type #87450

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Optimize `try_expand_impl_trait_type` #65293

Optimize `try_expand_impl_trait_type` #65293

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	// optimization for some large types produced by async fn trees.
	// optimization for some large types produced by `async fn` trees.

Optimize try_expand_impl_trait_type #65293

Optimize try_expand_impl_trait_type #65293

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Optimize `try_expand_impl_trait_type` #65293

Optimize `try_expand_impl_trait_type` #65293

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