Summary - Build tools

Combine build.rs, LTO and flamegraph to write a build report.

Build tools summary

build.rs generates code before compilation and instructs the linker; outputs go to OUT_DIR. Cross compilation is done with a target triple, rustup target and a suitable linker. In the release profile, lto, codegen-units, panic and opt-level balance speed, size and build time. Optimization starts with a profile: perf/samply, flamegraph, criterion. Unsafe code is kept sound with // SAFETY: comments, contracts protected by assert!s, and Miri.

A small measurement helper

Measurement code usually calls a job n times and finds the average by dividing the time. A helper that counts calls also verifies that the setup works correctly:

fn olc<F: FnMut()>(n: u32, mut f: F) -> std::time::Duration {
    let bas = std::time::Instant::now();
    for _ in 0..n {
        f();
    }
    bas.elapsed() / n
}

The duration varies on every run; that's why benchmark tools use warm-up rounds and a statistical summary.

Exercise Measurement setup

Write fn olc<F: FnMut()>(n: u32, mut f: F) -> u32 that calls a closure n times and returns the call count. Call it 1000 times with a closure incrementing a counter and print it as 1000 çağrı, sayaç 1000.

Show example solution

fn olc<F: FnMut()>(n: u32, mut f: F) -> u32 {
    for _ in 0..n {
        f();
    }
    n
}

fn main() {
    let mut sayac = 0;
    let n = olc(1000, || sayac += 1);
    println!("{} çağrı, sayaç {}", n, sayac);
}

Test yourself

How do you stop the compiler from deleting the work in a simple measurement loop?
- It can't be prevented
- Use the result or pass it through black_box
- Build in debug
- Make the loop longer
Show answer

Use the result or pass it through black_box — A pure computation whose result is never used can be removed entirely by optimization.

Elapsed time

let bas = std::time::Instant::now();
is();
let sure = bas.____();

Show answer

let bas = std::time::Instant::now();
is();
let sure = bas.elapsed();

Group summary

build.rs

Before the build
--target

Cross compilation
lto

Link-time optimization
Miri

UB checking

Next lesson: Allocator

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