Tracking issue for MCP 976: Add -Z dead-fn-elimination to skip codegen of BFS-unreachable functions

This is a tracking issue for MCP "Add -Z dead-fn-elimination to skip codegen of BFS-unreachable functions" (rust-lang/compiler-team#976).

[!NOTE]
Tracking issues are used to record the overall progress of implementation.
They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions.

A tracking issue is however not meant for large scale discussion, questions, or bug reports.
Instead, open a dedicated issue for the specific matter, link to this tracking issue and ping the MCP author.
Alternatively, post in the Zulip stream linked from the MCP.

Discussion comments will get marked as off-topic or deleted.
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Steps

• Implement the MCP
• Adjust the documentation
  • In the Rust Compiler Development Guide if applicable (e.g., for refactorings)
  • In the Rust Forge if applicable (e.g., for policy changes)
  • In the rustc book if applicable (e.g., for target tier or CLI changes)
  • In the Unstable Book if applicable (e.g., for unstable CLI changes)

Unresolved questions

None so far.

Implementation history

Empty so far.

@yijunyu, consider @rustbot claim'ing the work.

Start with the MCP in rust-lang/compiler-team#976, then review this tracking issue's implementation and documentation checklist. The work is complete when the MCP is implemented and applicable guidance is updated in the Rust Compiler Development Guide, Rust Forge, rustc book, or Unstable Book.