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Remove both StorageLive and StorageDead in CopyProp.#107524

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cjgillot:both-storage
Feb 2, 2023
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Remove both StorageLive and StorageDead in CopyProp.#107524
bors merged 3 commits intorust-lang:masterfrom
cjgillot:both-storage

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@cjgillot cjgillot commented Jan 31, 2023 •
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Fixes #107511

#106908 removed StorageDead without the accompanying StorageLive. In loops, execution would see repeated StorageLive, without any StorageDead, which is UB.

So when removing storage statements, we have to remove both StorageLive and StorageDead.

I also added a MIR validation pass for StorageLive. It may be a bit overzealous.

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r? @davidtwco

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rustbot commented Jan 31, 2023

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

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cjgillot commented Jan 31, 2023

cc @RalfJung

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RalfJung commented Jan 31, 2023

Thanks for the quick fix!

#106908 removed StorageDead without the accompanying StorageLive. In loops, execution would see repeated StorageLive, without any StorageDead, which is UB.

Ah, I see. Makes sense.
(FWIW whether we really want redundant StorageLive to be UB is kind of an open question, but for now it's an invariant we want to enforce -- see #99160. If having to remove StorageLive here is for some reason a burden or disadvantage, please leave a note in that issue. It would be nice to enforce the same for StorageDead but due to #98896 that is not currently possible.)

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RalfJung commented Jan 31, 2023

I also added a MIR validation pass for StorageLive. It may be a bit overzealous.

I'm afraid I can't review that part, I don't know the APIs it uses so I don't even know what it actually checks.

So either r=me with that part moved to a separate PR, or we wait for another reviewer.

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RalfJung reviewed Jan 31, 2023
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tests/mir-opt/copy-prop/issue_107511.rs Outdated
sum += a[i];
}

let _ = sum;
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let _val = sum might be better, _ patterns can be quite surprising...

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cjgillot commented Jan 31, 2023

I don't really have an opinion on whether this should be UB. This is not a (currently) difficult invariant to preserve, so optimizations should probably preserve it.

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RalfJung commented Jan 31, 2023

@bors r+

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bors commented Jan 31, 2023

📌 Commit e8ac040 has been approved by RalfJung

It is now in the queue for this repository.

@bors 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 Jan 31, 2023
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bors commented Feb 1, 2023

⌛ Testing commit e8ac040 with merge 9fcf4e35c49a654a7cbdfaf59a2e5d8882938b9b...

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bors commented Feb 1, 2023

💔 Test failed - checks-actions

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compiler-errors commented Feb 1, 2023

@bors retry CI was broken

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rust-log-analyzer commented Feb 2, 2023

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

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cjgillot commented Feb 2, 2023

@bors retry

matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Feb 2, 2023
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Rollup merge of rust-lang#107524 - cjgillot:both-storage, r=RalfJung
4cf01cf 
Remove both StorageLive and StorageDead in CopyProp.

Fixes rust-lang#107511

rust-lang#106908 removed StorageDead without the accompanying StorageLive. In loops, execution would see repeated StorageLive, without any StorageDead, which is UB.

So when removing storage statements, we have to remove both StorageLive and StorageDead.

~I also added a MIR validation pass for StorageLive. It may be a bit overzealous.~
This was referenced Feb 2, 2023
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bors added a commit to rust-lang-ci/rust that referenced this pull request Feb 2, 2023
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Auto merge of rust-lang#107601 - matthiaskrgr:rollup-07zaafe, r=matth…
f312650 
…iaskrgr

Rollup of 7 pull requests

Successful merges:

 - rust-lang#106919 (Recover `_` as `..` in field pattern)
 - rust-lang#107493 (Improve diagnostic for missing space in range pattern)
 - rust-lang#107515 (Improve pretty-printing of `HirIdValidator` errors)
 - rust-lang#107524 (Remove both StorageLive and StorageDead in CopyProp.)
 - rust-lang#107532 (Erase regions before doing uninhabited check in borrowck)
 - rust-lang#107559 (Rename `rust_2015` → `is_rust_2015`)
 - rust-lang#107577 (Reinstate the `hir-stats.rs` tests on stage 1.)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 6917040 into rust-lang:master Feb 2, 2023
@rustbot rustbot added this to the 1.69.0 milestone Feb 2, 2023
@cjgillot cjgillot deleted the both-storage branch February 2, 2023 23:21
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Bad MIR: StorageLive on a local that was already live with opt-level=4

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