Update docs for -Clink-dead-code to discourage its use #135561
Merged
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters
| r? @Noratrieb rustbot has assigned @Noratrieb. Use |
rustbot added S-waiting-on-review 
saethlin reviewed Jan 16, 2025
Zalathar force-pushed the link-dead-code branch from 3fd2dde to 2238b00 Compare 
| I think the change here is pretty uncontroversial, the discouragement is not particularly strong and the other changes are just factually correct. The flag's description has been wrong for many years. r? saethlin |
bors added S-waiting-on-bors 
bors added a commit to rust-lang-ci/rust that referenced this pull request Jan 16, 2025
…iaskrgr Rollup of 7 pull requests Successful merges: - rust-lang#134754 (Implement `use` associated items of traits) - rust-lang#135481 (coverage: Completely overhaul counter assignment, using node-flow graphs) - rust-lang#135504 (Allow coercing safe-to-call target_feature functions to safe fn pointers) - rust-lang#135561 (Update docs for `-Clink-dead-code` to discourage its use) - rust-lang#135574 (ci: mirror ubuntu:22.04 to ghcr.io) - rust-lang#135585 (resolve symlinks of LLVM tool binaries before copying them) - rust-lang#135588 (Add license-metadata.json to rustc-src tarball.) r? `@ghost` `@rustbot` modify labels: rollup
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Jan 17, 2025
Rollup merge of rust-lang#135561 - Zalathar:link-dead-code, r=saethlin Update docs for `-Clink-dead-code` to discourage its use The `-Clink-dead-code` flag was originally added way back in rust-lang#31368, apparently to help improve the output of some older forms of code coverage measurement, and also to address some use-cases for wanting to suppress linker flags like `-dead_strip` and `--gc-section`. In the past it might have also been useful in conjunction with `-Cinstrument-coverage`, but subsequent improvements to coverage instrumentation have made it unnecessary there. [It is also currently used by cargo-fuzz by default](rust-fuzz/cargo-fuzz#391), for reasons that are possibly no longer relevant. --- The flag currently does more than its name suggests, affecting not just linker flags, but also monomorphization decisions. It has also contributed to ICEs (e.g. rust-lang#135515) that would not have occurred without link-dead-code. --- For now, this PR just updates the documentation to be more realistic about what the flag does, and when it should be used (approximately never). In the future, it might be worth looking into properly deprecating this flag, and perhaps making it a no-op if feasible.
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
5 participants
Add this suggestion to a batch that can be applied as a single commit. This suggestion is invalid because no changes were made to the code. Suggestions cannot be applied while the pull request is closed. Suggestions cannot be applied while viewing a subset of changes. Only one suggestion per line can be applied in a batch. Add this suggestion to a batch that can be applied as a single commit. Applying suggestions on deleted lines is not supported. You must change the existing code in this line in order to create a valid suggestion. Outdated suggestions cannot be applied. This suggestion has been applied or marked resolved. Suggestions cannot be applied from pending reviews. Suggestions cannot be applied on multi-line comments. Suggestions cannot be applied while the pull request is queued to merge. Suggestion cannot be applied right now. Please check back later.
The
-Clink-dead-codeflag was originally added way back in #31368, apparently to help improve the output of some older forms of code coverage measurement, and also to address some use-cases for wanting to suppress linker flags like-dead_stripand--gc-section.In the past it might have also been useful in conjunction with
-Cinstrument-coverage, but subsequent improvements to coverage instrumentation have made it unnecessary there.It is also currently used by cargo-fuzz by default, for reasons that are possibly no longer relevant.
The flag currently does more than its name suggests, affecting not just linker flags, but also monomorphization decisions. It has also contributed to ICEs (e.g. #135515) that would not have occurred without link-dead-code.
For now, this PR just updates the documentation to be more realistic about what the flag does, and when it should be used (approximately never). In the future, it might be worth looking into properly deprecating this flag, and perhaps making it a no-op if feasible.