Emit retags in codegen to support BorrowSanitizer (part 2) by icmccorm · Pull Request #156210 · rust-lang/rust

icmccorm · 2026-05-05T21:32:04Z

This is one of several PRs that will add experimental support for emitting retags as function calls in codegen. Each PR will be a minimal, improved slice of the changes in #155965.

This PR adds a new unstable flag -Zcodegen-emit-retag, which will enable experimental retag calls in generated code. This flag is a nop for now, but the relevant methods have been added to codegen_ssa, and they are called wherever retags are necessary. Subsequent PRs will complete this implementation.

This does not depend on #156208.

r? @RalfJung

rustbot · 2026-05-05T21:32:09Z

RalfJung is not on the review rotation at the moment.
They may take a while to respond.

saethlin · 2026-05-05T21:46:05Z

r? saethlin

icmccorm · 2026-05-07T17:03:41Z

Now that #154327 has been merged, we no longer need special handling for drop glue.

saethlin · 2026-05-18T14:06:03Z

+                LocalRef::PendingOperand => LocalRef::PendingOperand,
+            })
+            .collect::<Vec<_>>();
+        // If we branched during retagging, then we need to update the


How would retagging introduce a branch?

View changes since the review

We selectively retag variants of enums that contain references or Box. For example,

fn foo(opt: Option<Box<i32>>) { .. }

This will branch on the discriminant of opt to retag the Box, if it's there.

rustbot · 2026-05-20T18:54:49Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

saethlin · 2026-06-04T01:23:25Z

@bors r+ rollup=iffy

rust-bors · 2026-06-04T01:23:27Z

📌 Commit 23602aa has been approved by saethlin

It is now in the queue for this repository.

Rollup of 3 pull requests Successful merges: - #156210 (Emit retags in codegen to support BorrowSanitizer (part 2)) - #157317 (Fix ICE when wrong intra-doc link on type alias) - #157391 (Reorganize `tests/ui/issues` [4/N])

rust-bors · 2026-06-04T03:54:02Z

⌛ Testing commit 23602aa with merge 509a1fb...

Workflow: https://github.com/rust-lang/rust/actions/runs/26929479425

@RalfJung

Emit retags in codegen to support BorrowSanitizer (part 2) Tracking issue: #154760 [Zulip Thread](https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/Staging.20for.20emitting.20retags.20in.20codegen/with/593004012) This is one of several PRs that will add experimental support for emitting retags as function calls in codegen. Each PR will be a minimal, improved slice of the changes in #155965. This PR adds a new unstable flag `-Zcodegen-emit-retag`, which will enable experimental retag calls in generated code. This flag is a nop for now, but the relevant methods have been added to codegen_ssa, and they are called wherever retags are necessary. Subsequent PRs will complete this implementation. This does not depend on #156208. r? @RalfJung

jhpratt · 2026-06-04T03:55:57Z

@bors yield

rust-bors · 2026-06-04T03:56:01Z

Auto build was cancelled. Cancelled workflows:

https://github.com/rust-lang/rust/actions/runs/26929479425

The next pull request likely to be tested is #157404.

Rollup of 3 pull requests Successful merges: - #156210 (Emit retags in codegen to support BorrowSanitizer (part 2)) - #157317 (Fix ICE when wrong intra-doc link on type alias) - #157391 (Reorganize `tests/ui/issues` [4/N])

@RalfJung

Rollup merge of #156210 - BorrowSanitizer:codegen-emit-retag-2, r=saethlin Emit retags in codegen to support BorrowSanitizer (part 2) Tracking issue: #154760 [Zulip Thread](https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/Staging.20for.20emitting.20retags.20in.20codegen/with/593004012) This is one of several PRs that will add experimental support for emitting retags as function calls in codegen. Each PR will be a minimal, improved slice of the changes in #155965. This PR adds a new unstable flag `-Zcodegen-emit-retag`, which will enable experimental retag calls in generated code. This flag is a nop for now, but the relevant methods have been added to codegen_ssa, and they are called wherever retags are necessary. Subsequent PRs will complete this implementation. This does not depend on #156208. r? @RalfJung

@RalfJung

…-3, r=saethlin Emit retags in codegen to support BorrowSanitizer (part 3) Tracking issue: rust-lang#154760 [Zulip Thread](https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/Staging.20for.20emitting.20retags.20in.20codegen/with/593004012) This is one of several PRs that will add experimental support for emitting retags as function calls in codegen. This PR adds `RetagPlan`, which describes where the pointers that need to be retagged live within the layout of a type. We create a `RetagPlan` ahead of time because only a subset of the variants of a type might contain retagable values. We only want to branch to these variants, and ignore all of the others. If a type can generate a `RetagPlan`, then we will use it as a guide for inserting calls to our retag intrinsics. If a type does not generate a `RetagPlan`, then it does not need to be retagged, and we can skip it. This does not emit a `RetagPlan::EmitRetag` yet. That will come in a subsequent PR. Previous parts: rust-lang#156208, rust-lang#156210 cc: @RalfJung r? @saethlin

@RalfJung

Rollup merge of #157825 - BorrowSanitizer:codegen-emit-retag-3, r=saethlin Emit retags in codegen to support BorrowSanitizer (part 3) Tracking issue: #154760 [Zulip Thread](https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/Staging.20for.20emitting.20retags.20in.20codegen/with/593004012) This is one of several PRs that will add experimental support for emitting retags as function calls in codegen. This PR adds `RetagPlan`, which describes where the pointers that need to be retagged live within the layout of a type. We create a `RetagPlan` ahead of time because only a subset of the variants of a type might contain retagable values. We only want to branch to these variants, and ignore all of the others. If a type can generate a `RetagPlan`, then we will use it as a guide for inserting calls to our retag intrinsics. If a type does not generate a `RetagPlan`, then it does not need to be retagged, and we can skip it. This does not emit a `RetagPlan::EmitRetag` yet. That will come in a subsequent PR. Previous parts: #156208, #156210 cc: @RalfJung r? @saethlin

@RalfJung

…-4, r=saethlin Emit retags in codegen to support BorrowSanitizer (part 4) Tracking issue: rust-lang#154760 [Zulip Thread](https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/Staging.20for.20emitting.20retags.20in.20codegen/with/593004012) This is one of several PRs that add experimental support for emitting retags as function calls in codegen. This PR emits our retag intrinsics based on the structure of a `RetagPlan`. The feature works end-to-end now! But, it has two limitations: * We do not track interior mutable or pinned ranges precisely. This will come in the next PR, which should be the last one that we need to complete this feature (excluding documentation and compile tests). * We recurse into `repr(simd)` types when building a `RetagPlan`, but we do not emit retags for their fields. We would need `BuilderMethods::insert_element`, which isn't available. I'm not sure what the best workaround would be for this. Related: rust-lang#157825, rust-lang#156210, rust-lang#156208 Cc: @RalfJung r? @saethlin

rustbot assigned RalfJung May 5, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels May 5, 2026

rustbot assigned saethlin and unassigned RalfJung May 5, 2026

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icmccorm force-pushed the codegen-emit-retag-2 branch from 951a9ed to 4e3df71 Compare May 7, 2026 17:02

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icmccorm force-pushed the codegen-emit-retag-2 branch from 4e3df71 to 5135340 Compare May 15, 2026 16:53

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saethlin reviewed May 18, 2026

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Comment thread compiler/rustc_codegen_ssa/src/mir/block.rs Outdated

saethlin reviewed May 18, 2026

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Comment thread compiler/rustc_codegen_ssa/src/mir/retag.rs Outdated

icmccorm mentioned this pull request May 18, 2026

Interop Safety: Improving cross-language analysis by augmenting LLVM IR with Rust type information rust-lang/all-hands-2026#26

Open

icmccorm added 5 commits May 19, 2026 22:14

Add -Zcodegen-emit-retag with nop retags.

a22eaef

Add missing import.

c8d945e

Remove special handling for drop glue.

ae7078a

Do not skip retagging indirect places.

0a470b6

Ensure that providing no option still enables the flag.

23602aa

icmccorm force-pushed the codegen-emit-retag-2 branch from 5135340 to 23602aa Compare May 20, 2026 18:54

icmccorm mentioned this pull request May 30, 2026

BorrowSanitizer rust-lang/rust-project-goals#624

Open

rust-bors Bot 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 Jun 4, 2026

jhpratt mentioned this pull request Jun 4, 2026

Rollup of 3 pull requests #157404

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rust-bors Bot merged commit fa82c8d into rust-lang:main Jun 4, 2026
11 of 12 checks passed

rustbot added this to the 1.98.0 milestone Jun 4, 2026

icmccorm deleted the codegen-emit-retag-2 branch June 7, 2026 21:12

icmccorm mentioned this pull request Jun 12, 2026

Emit retags in codegen to support BorrowSanitizer (part 3) #157825

Merged

icmccorm mentioned this pull request Jun 18, 2026

Emit retags in codegen to support BorrowSanitizer (part 4) #158100

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