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When deduplicating unreachable blocks, erase the source information. by khuey · Pull Request #128628 · rust-lang/rust

@khuey 

After deduplication the block conceptually belongs to multiple locations
in the source. Although these blocks are unreachable, in rust-lang#123341 we did
come across a real side effect, an unreachable block that survives into
the compiled code can cause a debugger to set a breakpoint on the wrong
instruction. Erasing the source information ensures that a debugger will
never be misled into thinking that the unreachable block is worth setting
a breakpoint on, especially after rust-lang#128627.

Technically we don't need to erase the source information if all the
deduplicated blocks have identical source information, but tracking
that seems like more effort than it's worth.

@rustbot 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.

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Aug 4, 2024

@khuey khuey mentioned this pull request

Aug 4, 2024

@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

Aug 18, 2024

bors added a commit to rust-lang-ci/rust that referenced this pull request

Aug 19, 2024 
Rollup of 7 pull requests

Successful merges:

 - rust-lang#127679 (Stabilize `raw_ref_op` (RFC 2582))
 - rust-lang#128084 (Suggest adding Result return type for associated method in E0277.)
 - rust-lang#128628 (When deduplicating unreachable blocks, erase the source information.)
 - rust-lang#128902 (doc: std::env::var: Returns None for names with '=' or NUL byte)
 - rust-lang#129048 (Update `crosstool-ng` for loongarch64)
 - rust-lang#129116 (Include a copy of `compiler-rt` source in the `download-ci-llvm` tarball)
 - rust-lang#129208 (Fix order of normalization and recursion in const folding.)

r? `@ghost`
`@rustbot` modify labels: rollup

rust-timer added a commit to rust-lang-ci/rust that referenced this pull request

Aug 19, 2024 
Rollup merge of rust-lang#128628 - khuey:simply-cfg-erase-source-info, r=nnethercote

When deduplicating unreachable blocks, erase the source information.

After deduplication the block conceptually belongs to multiple locations in the source. Although these blocks are unreachable, in rust-lang#123341 we did come across a real side effect, an unreachable block that survives into the compiled code can cause a debugger to set a breakpoint on the wrong instruction. Erasing the source information ensures that a debugger will never be misled into thinking that the unreachable block is worth setting a breakpoint on, especially after rust-lang#128627.

Technically we don't need to erase the source information if all the deduplicated blocks have identical source information, but tracking that seems like more effort than it's worth.

I'll let njn redirect this one too. r? `@nnethercote`