top-type-sizes

Nightly rustc provides the print-type-sizes option for printing sizes of all types. It's especially useful for analyzing why futures are soo big, that can hurt performance a lot if such futures are moved.

However, print-type-sizes produces unordered and cluttered output. This crate parses that output, refine it and show top types by size in compact form.

Features:

Sorts types by size.
Deduplicates same types.
Merges variants with similar layout.
Shows layouts in compact form.
Sorts fields by size (-s).
Hides small fields (-h).
Hides wrappers like MaybeUninit and custom ones (-w).
Limits output (-l).

Usage

Firstly, install by using cargo install top-type-sizes or clone the repository and run cargo build --release.

Secondly, compile your project:

$ RUSTFLAGS=-Zprint-type-sizes cargo +nightly build -j 1 > type-sizes.txt

-Zprint-type-sizes requires the nightly compiler.
-j 1 is required to avoid incorrect shuffled output.

Finally, use this crate:

$ top-type-sizes < type-sizes.txt | less

Help

$ top-type-sizes --help

top-type-sizes 0.1.1

USAGE:
    top-type-sizes [FLAGS] [OPTIONS]

FLAGS:
        --help               Prints help information
    -w, --remove-wrappers    Removes wrappers like `MaybeUninit`
    -r, --reverse            Prints top `limit` types in ascending order
    -s, --sort-fields        Sorts fields by size and removes paddings
    -V, --version            Prints version information

OPTIONS:
    -h, --hide-less <hide-less>    Hides fields with size less than this value [default: 0]
    -l, --limit <limit>            Shows only this number of top types [default: 100]

Example

3456 [async block@/home/.cargo/registry/src/github.com-1ecc6299db9ec823/trust-dns-resolver-0.22.0/src/name_server/name_server_pool.rs:256:23: 296:10] align=8
      1 <discriminant>
   3455 variant Suspend1
        128 opts align=8 offset=0
         16 datagram_conns
         16 stream_conns
        216 request
        216 tcp_message
          1 generator_field3
          1 generator_field4
          1 generator_field5
          1 generator_field6
          1 generator_field7
          1 generator_field8
          1 generator_field9
          1 <padding>
        200 udp_res align=8
       2656 __awaitee
   3255 variant Suspend0
        128 opts align=8 offset=0
         16 datagram_conns
         16 stream_conns
        216 request
        216 tcp_message
          3 <padding>
          1 generator_field6 align=1
          1 generator_field7
          1 generator_field8
          1 generator_field9
          1 <padding>
       2656 __awaitee align=8
    592 variant Unresumed, Returned, Panicked
        128 opts align=8 offset=0
         16 datagram_conns
         16 stream_conns
        216 request
        216 tcp_message