Is cargo/rustc that slow?

As a side-discussion from the ongoing mess I read this about Waiting 15 minutes for a small program, e.g. like Yazi to compile is wild.

I tried and on my laptop took about 2 minutes to build in release mode, not too bad.

❯ cargo build
...
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 27.51s
❯ cargo clean
❯ cargo build --release
...
    Finished `release` profile [optimized] target(s) in 2m 01s

yazi isn't exactly a small program:

❯ cargo tree | grep -v yazi | wc -l
     685
❯ tokei
===============================================================================
 Language            Files        Lines         Code     Comments       Blanks
===============================================================================
 JSON                    1            1            1            0            0
 Lua                    34         1973         1639           31          303
 Markdown                2          207            0          149           58
 Nix                     4          270          235            6           29
 Shell                   3           56           41            6            9
 TOML                   18         1819         1484          128          207
 YAML                    1           33           29            1            3
-------------------------------------------------------------------------------
 Rust                  463        27288        22926          280         4082
 |- Markdown             6           56            0           51            5
 (Total)                          27344        22926          331         4087
===============================================================================
 Total                 526        31647        26355          601         4691
===============================================================================

Then I looked a bit further and I saw:

[profile.release]
codegen-units = 1
lto           = true
panic         = "abort"
strip         = true

Definitely not friendly if you want a fast release build

codegen-units = 1 may generate a bit more optimal code but then you can use only 1 core and if you have many...
lto = true tends to take lots of time for some optimality, but lto = "thin" exists and the tradeoff tends to be very good, for rav1e on x86_64 for a long while managed to produce even a better binary.

So what happens if I do those changes?

❯ cargo build --release
...
    Finished `release` profile [optimized] target(s) in 47.05s

I guess sometimes it is better to not stop at the first program to evaluate if a toolchain is fast or slow :)

P.S.

If you are on Linux, at least right now the quickest combination seems to be clang as linker with mold doing the actual work.
gcc + mold seems sensibly slower and clang + ld.bfd is curiously a tad slower than gcc + ld.bfd.
Setting

[target.{yourarch}]
linker = "clang"
rustflags = ["-C", "link-arg=-fuse-ld=mold"]

in ~/.cargo/config.toml may be optimal at least right now.

Blog

Is cargo/rustc that slow?

Luca Barbato

P.S.

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