botirkhaltaevbotirkhaltaev/botir-skills/skills/rust-compiler-internals/SKILL.md

rust-compiler-internals

Skill4 starsChanged 3 months agoApache-2.0View on GitHub

Understand Rust compiler internals and rustc usage. Use when optimizing build times, understanding compiler errors, using codegen options, setting up PGO, or contributing to Rust.

We split this skill into the rules it gives an agent

2 rules. About 0 are common, 0 are distinctive, and 2 are very specific to this project.

≈0
Common · estimate
Many files like this have a rule of this kind.
≈0
Distinctive · estimate
This author's own choices. Worth a look.
2
Very specific
Tied to their project's names, files or tools. Probably skip.

Common
Distinctive
Very specific

Very specific:
Default release profile is already fairly strong (opt-level = 3).
line 29
Very specific:
Use instrumented release builds, merge with llvm-profdata, then -C profile-use=….
line 54

≈ “Common” is an estimate: at least 1 in 5 of the 308,232 skill files we read have a rule of the same kind, not the same words. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.

Files

SKILL.md

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

Situation	Prefer
“Is my program slow?” / allocations / algorithms	rust-performance (measure first)
Release binary still hot after profiling points at codegen	`[profile.release]` `lto`, `codegen-units`, then re-bench
Binary size	`opt-level = "s"`/`"z"`, `panic = "abort"`, `strip`, LTO
Compile time too high	Raise `codegen-units`, disable fat LTO, reduce debuginfo; see rust-performance compile-times
PGO	Only after a stable release benchmark loop exists; see `references/pgo.md`
Target CPU features	`-C target-cpu=…` when deployment CPU is known

Default release profile is already fairly strong (opt-level = 3). Change one knob at a time and benchmark.

Cargo profile keys (preferred interface)

[profile.release]
opt-level = 3
lto = "thin"          # false | "thin" | true | "fat" | "off"
codegen-units = 1
panic = "unwind"      # or "abort"
debug = false
strip = "none"        # "debuginfo" | "symbols"

Details: references/codegen.md, references/lto.md.

rustc `-C` equivalents

RUSTFLAGS="-C opt-level=3 -C lto=thin -C codegen-units=1" cargo build --release
RUSTFLAGS="-C target-cpu=native" cargo build --release

Profile-Guided Optimization (PGO)

Use instrumented release builds, merge with llvm-profdata, then -C profile-use=…. Do not invent rustup “profile” subcommands.

rustup component add llvm-tools-preview
# see references/pgo.md for the full Cargo workflow

Reference Map

references/codegen.md — opt-level, codegen-units, debuginfo, panic
references/lto.md — LTO modes and Cargo keys
references/pgo.md — Profile-guided optimization
references/targets.md — Target / CPU options

Key References

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