cargo-llvm-lines

cargo-llvm-lines

Shows which functions generate the most LLVM IR lines, indicating compile time and binary size contributors.

Usage

cargo llvm-lines [OPTIONS]

Common Workflows

Analyze library crate

cargo llvm-lines --lib

Analyze specific binary

cargo llvm-lines --bin my_bin

Sort by copy count (monomorphization)

cargo llvm-lines --lib --sort copies

Filter to specific functions

cargo llvm-lines --lib | grep "my_module"

Key Options

• --lib - Analyze library target
• --bin <NAME> - Analyze specific binary
• --release - Use release profile
• --sort lines|copies - Sort by IR lines (default) or instantiation count

Reading Output

Output format: Lines | Copies | Function

  Lines  Copies  Function name
  -----  ------  -------------
  30000     100  core::fmt::write
   5000      50  alloc::vec::Vec<T>::push

• Lines - Total LLVM IR lines from all instantiations
• Copies - Number of monomorphized copies
• High copies with moderate lines = monomorphization bloat

Common Fixes

• Extract non-generic inner functions to reduce copies
• Use dyn Trait instead of generics for cold paths
• Consider #[inline(never)] on large generic functions