[mir-opt] Introduce a new flag to enable experimental/unsound mir opts #76899

wesleywiser · 2020-09-19T02:09:32Z

This implements part of rust-lang/compiler-team#319. The exact name of this flag was not decided as part of that MCP and some people expressed that it should include "unsound" in some way.

I've chosen to use enable-experimental-unsound-mir-opts as the name. While long, I don't think that matters too much as really it will only be used by some mir-opt tests. If you object or have a better name, please leave a comment!

r? @oli-obk
cc @rust-lang/wg-mir-opt @RalfJung

Aaron1011 · 2020-09-19T02:17:49Z

I would personally prefer unsound-mir-opts:

It's easier to type.
We could theoretically move a non-experimental optimization pass behind this flag if we discovered it was unsound.
I think 'enable' is implied by the presence of the flag itself.

src/test/mir-opt/inline/inline-any-operand.rs

src/test/mir-opt/inline/inline-closure-borrows-arg.rs

src/test/mir-opt/inline/inline-trait-method_2.rs

src/test/mir-opt/nrvo-simple.rs

wesleywiser · 2020-09-19T11:29:39Z

@oli-obk I tried to keep our MIR opt tests' output as close to the current ones as possible. Some of these passes run after copy-prop so the effects of it being disabled by default (even under mir-opt-level=2) show up as changes in the tests.

If you think we should not add this flag to those tests and accept the changes instead, I'd be happy to do so.

oli-obk · 2020-09-19T11:44:02Z

If you think we should not add this flag to those tests and accept the changes instead, I'd be happy to do so.

Maybe remove the flag again in a separate commit so we keep the changes separate?

oli-obk · 2020-09-19T11:44:48Z

With that and the flag renamed to unsound-mir-opts as suggested: r=me

RalfJung · 2020-09-19T12:12:12Z

// FIXME(76740): This opt is buggy and can cause unsoundness.

Is "opt" short for option or optimization? It is used for option in the next line, so probably better to spell it out here.

wesleywiser · 2020-09-19T13:08:32Z

@RalfJung I remember you felt quite strongly the option name should include "unsound". Does unsound-mir-opts work for you?

tmiasko · 2020-09-19T14:18:17Z

Is this option intended only for unsound passes or also that are buggy in other ways e.g., ICE? If the latter I would also include inlining pass. Recently when I evaluated mir-opt-level=2 on a different crates, rustc generally ICEd due to normalization issues in inliner or other issues exposed indirectly by inlining. The attempt to enable inlining in #75495 didn't fare any better.

wesleywiser · 2020-09-19T18:11:54Z

Originally, I was thinking this flag could handle both but now I'm thinking we should probably have two. The optimizations that have bugs which result in unsoundness are far worse than the ones that "just" ICE the compiler.

bors · 2020-09-20T04:50:16Z

☔ The latest upstream changes (presumably #72632) made this pull request unmergeable. Please resolve the merge conflicts.

Note that reviewers usually do not review pull requests until merge conflicts are resolved! Once you resolve the conflicts, you should change the labels applied by bors to indicate that your PR is ready for review. Post this as a comment to change the labels:

@rustbot modify labels: +S-waiting-on-review -S-waiting-on-author

RalfJung · 2020-09-20T10:54:11Z

@RalfJung I remember you felt quite strongly the option name should include "unsound". Does unsound-mir-opts work for you?

Yes I like that name. :)

wesleywiser · 2020-09-21T10:55:18Z

@bors r=oli-obk

bors · 2020-09-21T10:55:19Z

📌 Commit 3498511 has been approved by oli-obk

@oli-obk

…r_opts_flag, r=oli-obk [mir-opt] Introduce a new flag to enable experimental/unsound mir opts This implements part of rust-lang/compiler-team#319. The exact name of this flag was not decided as part of that MCP and some people expressed that it should include "unsound" in some way. I've chosen to use `enable-experimental-unsound-mir-opts` as the name. While long, I don't think that matters too much as really it will only be used by some mir-opt tests. If you object or have a better name, please leave a comment! r? @oli-obk cc @rust-lang/wg-mir-opt @RalfJung

Dylan-DPC-zz · 2020-09-23T00:23:31Z

failed in rollup CI

@bors r-

wesleywiser · 2020-09-25T01:19:07Z

Rebased and resolved the failing test from the rollup.

@bors r=oli-obk

bors · 2020-09-25T01:19:09Z

📌 Commit 2c5f061d187b346c7f9e229a53be41723164ec30 has been approved by oli-obk

bors · 2020-09-25T06:49:55Z

☔ The latest upstream changes (presumably #76844) made this pull request unmergeable. Please resolve the merge conflicts.

Note that reviewers usually do not review pull requests until merge conflicts are resolved! Once you resolve the conflicts, you should change the labels applied by bors to indicate that your PR is ready for review. Post this as a comment to change the labels:

@rustbot modify labels: +S-waiting-on-review -S-waiting-on-author

wesleywiser · 2020-09-28T15:10:34Z

Rebased

@bors r=oli-obk

bors · 2020-09-28T15:10:35Z

📌 Commit c653af8 has been approved by oli-obk

bors · 2020-09-28T15:32:33Z

⌛ Testing commit c653af8 with merge d62d3f7...

bors · 2020-09-28T18:02:37Z

☀️ Test successful - checks-actions, checks-azure
Approved by: oli-obk
Pushing d62d3f7 to master...

rust-highfive assigned oli-obk Sep 19, 2020

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wesleywiser force-pushed the experimental_unsound_mir_opts_flag branch 2 times, most recently from 4f4cc60 to 3498511 Compare September 21, 2020 02:11

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 Sep 21, 2020

Dylan-DPC-zz mentioned this pull request Sep 22, 2020

Rollup of 9 pull requests #77061

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pnkfelix mentioned this pull request Sep 24, 2020

[mir-opt] Disable the ConsideredEqual logic in SimplifyBranchSame opt #76837

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wesleywiser force-pushed the experimental_unsound_mir_opts_flag branch from 3498511 to 2c5f061 Compare September 25, 2020 00:50

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 Sep 25, 2020

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wesleywiser added 2 commits September 27, 2020 19:21

[mir-opt] Introduce a new flag to enable experimental/unsound mir opts

b9d0ea9

Remove unnecessary -Zunsound-mir-opts uses in tests

c653af8

wesleywiser force-pushed the experimental_unsound_mir_opts_flag branch from 2c5f061 to c653af8 Compare September 27, 2020 23:29

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wesleywiser mentioned this pull request Sep 29, 2020

Add unstable book docs for -Zunsound-mir-opts #77322

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[mir-opt] Introduce a new flag to enable experimental/unsound mir opts #76899

[mir-opt] Introduce a new flag to enable experimental/unsound mir opts #76899

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[mir-opt] Introduce a new flag to enable experimental/unsound mir opts #76899

[mir-opt] Introduce a new flag to enable experimental/unsound mir opts #76899

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