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Optimizing WASM Size and Speed

This page contains some notes made while trying various options for optimizing WebAssembly files.

The tests were run on the slipwayhq.svg crate, compiled from Rust.

Initial size: 2,923,520 bytes.

Execution time: 160ms.

Remove image create​

This crate wasn't actually needed, I was just using it to create the final canvas out of habit.

Size: 2,922,496 bytes.

Strip symbols​

Add to Cargo.toml:

[profile.release]
strip = true

Size: 2,696,704 bytes

Optimize for Size​

See https://doc.rust-lang.org/cargo/reference/profiles.html#opt-level.

[profile.release]
opt-level = "z"

Size: 2,230,272 bytes

Execution time: 430ms. ❌

[profile.release]
opt-level = "s"

Size: 2,438,656 bytes.

Execution time: 230ms. ❌

I rolled back these optimizations to opt-level=3, as performance was more important than WASM size for my use case.

[profile.release]
lto = true

Size: 2,540,544 bytes.

Execution time: 160ms.

Reduce Parallel Code Generation Units​

[profile.release]
codegen-units = 1

Size: 2,489,344 bytes.

The wasm-opt tool

The wasm-opt tool doesn't currently support WASM Components, so I was unable to use this.

Using nanoserde crate instead of serde

Size: 2,468,352 bytes.

This didn't make much difference to the size or performance, and so didn't seem worth the tradeoff of switching to a less familiar serialization library.