cargo-llvm-lines

Count the number of lines of LLVM IR across all instantiations of a generic function. 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

Installation

Install with cargo install cargo-llvm-lines.

Output

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.

``` $ cargo llvm-lines | head -20

Lines Copies Function name ----- ------ ------------- 52262 1872 (TOTAL) 1815 (3.5%, 3.5%) 1 (0.1%, 0.1%) ::augmentsubcommands 1806 (3.5%, 6.9%) 1 (0.1%, 0.1%) ::fromargmatchesmut 1546 (3.0%, 9.9%) 34 (1.8%, 1.9%) core::option::Option::map 1045 (2.0%, 11.9%) 5 (0.3%, 2.2%) clap::parser::matches::argmatches::ArgMatches::tryremoveargt 738 (1.4%, 13.3%) 2 (0.1%, 2.3%) alloc::slice::mergesort 648 (1.2%, 14.5%) 4 (0.2%, 2.5%) alloc::rawvec::RawVec::growamortized 645 (1.2%, 15.8%) 6 (0.3%, 2.8%) as alloc::vec::specfromiternested::SpecFromIterNested>::fromiter 636 (1.2%, 17.0%) 43 (2.3%, 5.1%) ::fromargmatchesmut::{{closure}} 587 (1.1%, 18.1%) 15 (0.8%, 5.9%) as core::ops::trytrait::Try>::branch 565 (1.1%, 19.2%) 6 (0.3%, 6.2%) core::iter::traits::iterator::Iterator::tryfold 533 (1.0%, 20.2%) 1 (0.1%, 6.3%) cargollvmlines::printtable 520 (1.0%, 21.2%) 6 (0.3%, 6.6%) alloc::vec::Vec::extenddesugared 509 (1.0%, 22.2%) 5 (0.3%, 6.9%) clap::parser::matches::anyvalue::AnyValue::downcastinto 504 (1.0%, 23.1%) 5 (0.3%, 7.2%) alloc::sync::Arc::tryunwrap 470 (0.9%, 24.0%) 11 (0.6%, 7.7%) core::option::Option::okorelse 438 (0.8%, 24.9%) 2 (0.1%, 7.9%) alloc::slice::merge 414 (0.8%, 25.7%) 9 (0.5%, 8.3%) core::result::Result::andthen

```

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-depenency

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

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.}