Skip to content

Fix unsound optimization with explicit variant discriminants - #89489

Merged
bors merged 3 commits into
rust-lang:masterfrom
FabianWolff:issue-89485
Oct 4, 2021
Merged

Fix unsound optimization with explicit variant discriminants#89489
bors merged 3 commits into
rust-lang:masterfrom
FabianWolff:issue-89485

Conversation

@FabianWolff

@FabianWolffFabianWolff commented Oct 3, 2021•
edited
Loading

Copy link
Copy Markdown
Contributor

Fixes#89485.

@rust-highfive

rust-highfive commented Oct 3, 2021

Copy link
Copy Markdown
Contributor

r? @oli-obk

(rust-highfive has picked a reviewer for you, use r? to override)

@rust-highfiverust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Oct 3, 2021
@oli-obk

oli-obk commented Oct 3, 2021

Copy link
Copy Markdown
Contributor

lgtm, tho we should do some cleanups of the opt after this is merged

r? @tmiasko for another pair of eyes

@tmiasko

tmiasko commented Oct 3, 2021

Copy link
Copy Markdown
Contributor

The change seems reasonable.

At the same time I can't really follow the preexisting implementation. Why the left hand side of the assignment is ignored for the purposes of the comparison? How do we know that place that we read the discriminant from still holds the same value?

@camelidcamelid added the A-mir-opt Area: MIR optimizations label Oct 3, 2021
camelid
camelid reviewed Oct 3, 2021
View reviewed changes
Comment threadcompiler/rustc_mir_transform/src/simplify_try.rs Outdated
camelid
camelid reviewed Oct 3, 2021
View reviewed changes
Comment threadcompiler/rustc_mir_transform/src/simplify_try.rs
@oli-obk

oli-obk commented Oct 3, 2021•
edited
Loading

Copy link
Copy Markdown
Contributor

@tmiasko so I guess let's disable the opt in addition to this fix until we have a clearer picture of how it works?

@tmiasko

tmiasko commented Oct 3, 2021

Copy link
Copy Markdown
Contributor

let's disable the opt in addition to this fix until we have a clearer picture of how it works?

Sounds good to me.

@oli-obk

oli-obk commented Oct 3, 2021

Copy link
Copy Markdown
Contributor

@FabianWolff please also add an early abort in the mir opt with

if !tcx.sess.opts.debugging_opts.unsound_mir_opts {
return;
}

so that we don't run the opt at all in normal mode

@FabianWolff

FabianWolff commented Oct 3, 2021

Copy link
Copy Markdown
ContributorAuthor

@oli-obk Done.

@wesleywiser

wesleywiser commented Oct 3, 2021

Copy link
Copy Markdown
Member

@bors r=oli-obk p=1

Fixes P-critical issue.

@bors

bors commented Oct 3, 2021

Copy link
Copy Markdown
Collaborator

📌 Commit dd9b476 has been approved by oli-obk

@borsbors 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 3, 2021
@wesleywiser

wesleywiser commented Oct 3, 2021•
edited
Loading

Copy link
Copy Markdown
Member

Beta nominating so we can get this fix out sooner. The most important change is that we've disabled the pass by default which is safe and should be very easy to backport.

@wesleywiserwesleywiser added the beta-nominated Nominated for backporting to the compiler in the beta channel. label Oct 3, 2021
@camelidcamelid added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Oct 3, 2021
@bors

bors commented Oct 4, 2021

Copy link
Copy Markdown
Collaborator

⌛ Testing commit dd9b476 with merge a6bea3af357e9103d5a9470030a30980f63deed3...

@nbdd0121

nbdd0121 commented Oct 4, 2021

Copy link
Copy Markdown
Member

Should this be backported to stable?

Aaron1011
Aaron1011 reviewed Oct 4, 2021
View reviewed changes
Comment threadsrc/test/ui/mir/issue-89485.rs
@@ -0,0 +1,18 @@
// Regression test for issue #89485.

@Aaron1011Aaron1011Oct 4, 2021

Copy link
Copy Markdown
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I think it would be a good idea to add a copy of this test with -Zunsound-mir-opts enabled

@bors

bors commented Oct 4, 2021

Copy link
Copy Markdown
Collaborator

💥 Test timed out

@borsbors 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 Oct 4, 2021
@rust-log-analyzer

rust-log-analyzer commented Oct 4, 2021

Copy link
Copy Markdown
Collaborator

A job failed! Check out the build log: (web)(plain)

Click to see the possible cause of the failure (guessed by this bot)

@wesleywiser

wesleywiser commented Oct 4, 2021

Copy link
Copy Markdown
Member

@bors retry

@borsbors 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 4, 2021
@bors

bors commented Oct 4, 2021

Copy link
Copy Markdown
Collaborator

⌛ Testing commit dd9b476 with merge a479766...

@bors

bors commented Oct 4, 2021

Copy link
Copy Markdown
Collaborator

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing a479766 to master...

@borsbors added the merged-by-bors This PR was explicitly merged by bors. label Oct 4, 2021
@bors
bors merged commit a479766 into rust-lang:masterOct 4, 2021
@rustbotrustbot added this to the 1.57.0 milestone Oct 4, 2021
@wesleywiser

wesleywiser commented Oct 4, 2021

Copy link
Copy Markdown
Member

Should this be backported to stable?

It's a good question @nbdd0121 . IMO, since we're about 1.5 weeks from the next release, beta backport seems sufficient to me.

@rust-timer

rust-timer commented Oct 4, 2021

Copy link
Copy Markdown
Collaborator

Finished benchmarking commit (a479766): comparison url.

Summary: This change led to small relevant regressions 😿 in compiler performance.

  • Small regression in instruction counts (up to 2.3% on full builds of style-servo)

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

Next Steps: If you can justify the regressions found in this perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please open an issue or create a new PR that fixes the regressions, add a comment linking to the newly created issue or PR, and then add the perf-regression-triaged label to this PR.

@rustbot label: +perf-regression

@rustbotrustbot added the perf-regression Performance regression. label Oct 4, 2021
@oli-obk

oli-obk commented Oct 4, 2021

Copy link
Copy Markdown
Contributor

@rustbot label: +perf-regression-triaged

we disabled an unsound MIR opt. LLVM can't figure this out on its own sadly.

@rustbotrustbot added the perf-regression-triaged The performance regression has been triaged. label Oct 4, 2021
@apiraino

apiraino commented Oct 7, 2021

Copy link
Copy Markdown
Contributor

Beta backport accepted as per compiler team on Zulip

Note from the meeting: "if there’s any issue at all, its also fine to just backport solely the bit that disables the pass"

@rustbot label +beta-accepted

@rustbotrustbot added the beta-accepted Accepted for backporting to the compiler in the beta channel. label Oct 7, 2021
@cuvipercuviper mentioned this pull request Oct 13, 2021
Merged
@cuvipercuviper removed the beta-nominated Nominated for backporting to the compiler in the beta channel. label Oct 13, 2021
@cuvipercuviper modified the milestones: 1.57.0, 1.56.0Oct 13, 2021
bors added a commit to rust-lang-ci/rust that referenced this pull request Oct 14, 2021
@bors
Auto merge ofrust-lang#89854- cuviper:beta-next, r=Mark-Simulacrum
58268ff
[beta] backports
- 2229: Consume IfLet expr rust-lang#89282
- Wrapper for -Z gcc-ld=lld to invoke rust-lld with the correct flavor rust-lang#89288
- Fix unsound optimization with explicit variant discriminants rust-lang#89489
- Fix stabilization version for bindings_after_at rust-lang#89605
- Turn vtable_allocation() into a query rust-lang#89619
- Revert "Stabilize Iterator::intersperse()" rust-lang#89638
- Ignore type of projections for upvar capturing rust-lang#89648
- ~~Add Poll::ready and~~ revert stabilization of task::ready! rust-lang#89651
- CI: Use mirror for libisl downloads for more docker dist builds rust-lang#89661
- Use correct edition for panic in [debug_]assert!(). rust-lang#89622
- Switch to our own mirror of libisl plus ct-ng oldconfig fixesrust-lang#89599
- Emit item no type error even if type inference fails rust-lang#89585
- Revert enum discriminants rust-lang#89884
Sign up for freeto join this conversation on GitHub. Already have an account? Sign in to comment

Reviewers

@camelidcamelidcamelid left review comments
+1 more reviewer
@Aaron1011Aaron1011Aaron1011 left review comments
Reviewers whose approvals may not affect merge requirements

Assignees

@oli-obkoli-obk

Labels

A-mir-optArea: MIR optimizationsbeta-acceptedAccepted for backporting to the compiler in the beta channel.merged-by-borsThis PR was explicitly merged by bors.perf-regressionPerformance regression.perf-regression-triagedThe performance regression has been triaged.S-waiting-on-borsStatus: Waiting on bors to run and complete tests. Bors will change the label on completion.T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.

Projects

None yet

Milestone

1.56.0

Development

Successfully merging this pull request may close these issues.

SimplifyBranchSame assumes discriminant is the same as variant index.

14 participants

@FabianWolff@rust-highfive@oli-obk@tmiasko@wesleywiser@bors@nbdd0121@rust-log-analyzer@rust-timer@apiraino@Aaron1011@camelid@cuviper@rustbot