By default, cargo build will build a debug binary at ./target/debug/filename, which is helpful for development/debug but without many binary optimizations, thus, runs slow.
When build with cargo build --release, it will build an optimized binary, which is ready for production:
--release Build artifacts in release mode, with optimizations
But it still not the fastest it can be.
Cargo profiles
Cargo has 4 builtin profiles: dev, release, test, and bench https://doc.rust-lang.org/cargo/reference/profiles.html which pre-defined build options.
User can customize them in Cargo.toml, e.g:
[profile.dev]
opt-level = 1
debug = true
LTO - Link time optimizations
https://doc.rust-lang.org/cargo/reference/profiles.html#lto
Default profile.release sets lto = false.
[profile.release]
opt-level = 3
debug = false
split-debuginfo = '...' # Platform-specific.
debug-assertions = false
overflow-checks = false
lto = false
panic = 'unwind'
incremental = false
codegen-units = 16
rpath = false
Set lto = true or lto = "fat" will
Performs "fat" LTO which attempts to perform optimizations across all crates within the dependency graph.
which makes build much slower, but the binary often faster 10-20% compare to lto = false. User may try lto = "thin" for faster build but the output still good comparable to lto = "fat"
"thin": Performs "thin" LTO. This is similar to "fat", but takes substantially less time to run while still achieving performance gains similar to "fat".
Reference
Happy building!