Rust Compiler Internals

Guide to rustc flags and codegen knobs based on The rustc Book. For measurement-first performance work, prefer the rust-performance skill; use this skill when you need accurate rustc/Cargo flag semantics.

When to Use This Skill

• Interpreting or setting rustc codegen flags (-C …)
• Tuning Cargo [profile.*] keys that map to those flags
• Setting up profile-guided optimization (PGO)
• Understanding LTO / codegen-units / panic strategy trade-offs
• Contributing to or reading about rustc (see rustc-dev-guide)

Triage: when to touch these knobs