# cargo-llvm-lines [github](https://github.com/dtolnay/cargo-llvm-lines) [crates.io](https://crates.io/crates/cargo-llvm-lines) [build status](https://github.com/dtolnay/cargo-llvm-lines/actions?query=branch%3Amaster) This tool measures the number and size of instantiations of each generic function in a program, indicating which parts of your code offer the highest leverage in improving compilation metrics. Generic functions in Rust can be instantiated multiple times, so they can disproportionately affect compile time, compiler memory usage, and the size of compiled executables. ## Installation Install with `cargo install cargo-llvm-lines`. ## Output Example output from running `cargo llvm-lines` on its own codebase: ```console $ cargo llvm-lines | head -20 Lines Copies Function name ----- ------ ------------- 51637 1222 (TOTAL) 2240 (4.3%, 4.3%) 1 (0.1%, 0.1%) ::augment_args 1190 (2.3%, 6.6%) 1 (0.1%, 0.2%) ::from_arg_matches_mut 1005 (1.9%, 8.6%) 3 (0.2%, 0.4%) alloc::raw_vec::RawVec::grow_amortized 973 (1.9%, 10.5%) 7 (0.6%, 1.0%) clap_builder::parser::matches::arg_matches::ArgMatches::try_remove_arg_t 939 (1.8%, 12.3%) 7 (0.6%, 1.6%) alloc::sync::Arc::try_unwrap 935 (1.8%, 14.1%) 6 (0.5%, 2.0%) as alloc::vec::spec_from_iter_nested::SpecFromIterNested>::from_iter 861 (1.7%, 15.8%) 7 (0.6%, 2.6%) alloc::sync::Arc::downcast 761 (1.5%, 17.2%) 5 (0.4%, 3.0%) alloc::vec::Vec::extend_desugared 638 (1.2%, 18.5%) 1 (0.1%, 3.1%) cargo_llvm_lines::table::print 599 (1.2%, 19.6%) 16 (1.3%, 4.4%) core::option::Option::ok_or_else 592 (1.1%, 20.8%) 2 (0.2%, 4.6%) core::slice::sort::merge 574 (1.1%, 21.9%) 2 (0.2%, 4.7%) core::slice::sort::merge_sort 561 (1.1%, 23.0%) 7 (0.6%, 5.3%) clap_builder::parser::matches::any_value::AnyValue::downcast_into 556 (1.1%, 24.1%) 4 (0.3%, 5.6%) as core::iter::traits::iterator::Iterator>::next 541 (1.0%, 25.1%) 16 (1.3%, 7.0%) core::option::Option::map 536 (1.0%, 26.1%) 8 (0.7%, 7.6%) as core::ops::drop::Drop>::drop 533 (1.0%, 27.2%) 1 (0.1%, 7.7%) core::str::pattern::simd_contains ``` There is one line per function with three columns of output: 1. Total number of lines of LLVM IR generated across all instantiations of the function (plus the percentage of the total and the cumulative percentage of all functions so far). 2. Number of instantiations of the function (plus the percentage of the total and the cumulative percentage of all functions so far). For a generic function, the number of instantiations is roughly the number of distinct combinations of generic type parameters it is called with. 3. Name of the function. ## Multicrate Projects Interpreting the output in the presence of multiple crates and generics can be tricky. `cargo llvm-lines` only shows the contribution of the root crate; dependencies are not included. To assess the contribution of an intermediate crate, use the `-p` flag: ```console $ cargo llvm-lines -p some-dependency ``` Note however, that Rust generics are monomorphised — a generic function will be accounted for in the crates that use it, rather than in the defining crate. There is a trick to get a holistic view: enabling link time optimization causes all code generation to happen in the root crate. So you can use the following invocation to get a full picture: ```console $ CARGO_PROFILE_RELEASE_LTO=fat cargo llvm-lines --release ``` ## Acknowledgements Based on a suggestion from **@eddyb** on how to count monomorphized functions in order to debug compiler memory usage, executable size and compile time. > **\** unoptimized LLVM IR
> **\** first used grep '^define' to get only the lines defining function bodies
> **\** then regex replace in my editor to remove everything before @ and everything after (
> **\** then sort | uniq -c

#### License Licensed under either of Apache License, Version 2.0 or MIT license at your option.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.