Don't run various MIR optimizations at mir-opt-level=0 #70073

wesleywiser · 2020-03-17T12:21:01Z

Add missing checks for mir-opt-level to non-essential MIR passes.

I verified that this can still bootstrap even with these passes disabled.

r? @oli-obk cc @RalfJung

oli-obk · 2020-03-17T13:46:51Z

@bors r+

bors · 2020-03-17T13:46:52Z

📌 Commit d158587eb76428d060bb08170813e8b9ada881aa has been approved by oli-obk

src/librustc_mir/transform/deaggregator.rs

wesleywiser · 2020-03-17T15:26:57Z

@bors r-

src/librustc_mir/transform/mod.rs

src/librustc_mir/transform/copy_prop.rs

RalfJung · 2020-03-18T11:50:36Z

src/librustc_mir/transform/mod.rs

+            // Deaggregation isn't technically an optimization but it unlocks opportunities
+            // for later optimization passes.
            &deaggregator::Deaggregator,


But then why is it not run earlier?

I don't know but I think the only passes that would be affected by this are CopyPropagation and SimplifyLocals which both run after this one.

@eddyb said "people just probably didn't care much about it and added passes before and after".

So I'd vote for moving it up to the other lowering passes.

I recall someone mentioning that drop elaboration relies on aggregates still being intact, and the generator transform performs drop elaboration. Not very sure though.

Dylan-DPC-zz · 2020-03-30T15:52:00Z

@wesleywiser you have conflicts to resolve

wesleywiser · 2020-03-30T15:52:57Z

I can resolve them but we're really waiting on some feedback from @oli-obk 🙂

src/librustc_mir/transform/mod.rs

wesleywiser · 2020-04-26T01:12:12Z

@bors retry

bors · 2020-04-26T11:26:58Z

⌛ Testing commit f4dfb99 with merge fadd2a48ae5148f9181745a3956dee1523d291c5...

bors · 2020-04-26T11:30:34Z

💔 Test failed - checks-azure

RalfJung · 2020-04-26T11:49:49Z

Setting up python3-setuptools (20.7.0-1) ...
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed

  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0curl: (7) Couldn't connect to server
tar: This does not look like a tar archive
tar: Exiting with failure status due to previous errors

##[error]Bash exited with code '2'.

Network failure.

@bors retry

bors · 2020-04-27T07:04:52Z

⌛ Testing commit f4dfb99 with merge d81f559...

bors · 2020-04-27T09:59:58Z

☀️ Test successful - checks-azure
Approved by: oli-obk
Pushing d81f559 to master...

…chievink smoke-test for async fn with mir-opt-level=0 MIR opt levels heavily influence which MIR transformations run, and we barely test non-default opt levels. I am particularly worried about `async fn` lowering and how it might (not) work when the set of preceding MIR passes changes -- see rust-lang#70073. This adds some basic smoke testing, where at least a few `async fn` `run-pass` test are ensured to also work with mir-opt-level=0.

@wesleywiser

…leywiser move Deaggregate pass to post_borrowck_cleanup Reopen of rust-lang#71946 Only the second commit is from this PR, the other commit is a bugfix that's in the process of getting merged. I'll rebase once that's done In rust-lang#70073 MIR pass handling got reorganized, but with the goal of not changing behavior (except for disabling some optimizations on opt-level = 0). But there we realized that the Deaggregator pass, while conceptually more of a "cleanup" pass (and one that should be run before optimizations), was run in the middle of the optimization chain. Likely this is an accident of history, so I suggest we try and clean that up by making it a proper cleanup pass. This does change mir-opt output, because deaggregation now runs before const-prop instead of after. r? @wesleywiser @rust-lang/wg-mir-opt cc @RalfJung

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bors mentioned this pull request Apr 27, 2020

Modify SimplifyArmIdentity so it can trigger on mir-opt-level=1 #69756

Merged

This was referenced May 6, 2020

Broken MIR: generator contains type &str in MIR, but typeck only knows about {std::future::ResumeTy, impl std::future::Future, ()} #71793

Closed

move Deaggregate pass to post_borrowck_cleanup #71946

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ecstatic-morse mentioned this pull request May 13, 2020

Check for live drops in constants after drop elaboration #71824

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oli-obk mentioned this pull request Jun 23, 2020

move Deaggregate pass to post_borrowck_cleanup #73656

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wesleywiser mentioned this pull request Jun 23, 2020

-Zmir-opt-level Reform rust-lang/compiler-team#319

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Don't run various MIR optimizations at mir-opt-level=0 #70073

Don't run various MIR optimizations at mir-opt-level=0 #70073

wesleywiser commented Mar 17, 2020

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Don't run various MIR optimizations at mir-opt-level=0 #70073

Don't run various MIR optimizations at mir-opt-level=0 #70073

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