Compiler and systems engineer specializing in dynamic language runtimes, WebAssembly, and untrusted code execution at scale. I architected Winch, Wasmtime’s baseline compiler tier, and built a narrow waist for WebAssembly at Shopify, helping untrusted code execution scale to 3M+ executions per minute through Wasmtime improvements, and bringing Wasm into Ruby applications through Javy and wasmtime-rb. I came to systems work from product engineering.
Rust · C · Zig · JavaScript · Ruby
saulecabrera@gmail.com · github.com/saulecabrera · saulecabrera.dev · +1 (438) 998-0834
Experience
Compiler Engineer — Igalia, Oct 2025 – August 2026 · remote
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A working profiler for JavaScript running on WebAssembly.
Took the WebAssembly Research Center’s research on instrumenting modules through bytecode rewriting, productionized it, and applied it inside Javy. How it works .
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Compilation for JavaScript running inside WebAssembly in Javy.
Leading the research with the WebAssembly Research Center to take it to production.
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Performance and spec correctness for WASI Preview 3.
Through the implementation of wasi-testsuite .
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General correctness and performance work in Wasmtime.
Senior Staff Software Engineer — Shopify, 2021 – 2025 · remote
Built the layer Shopify’s product teams ran untrusted third-party code on.
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A narrow waist for WebAssembly at Shopify.
One execution layer and the Wasm tooling around it, for product teams to build on. Enabled Shopify Functions to scale to 3M+ untrusted executions per minute at peak, through multiple improvements I made in Wasmtime. Shopify Flow reached it from Ruby, where Javy and wasmtime-rb let it embed Wasmtime and run untrusted JavaScript through Wasm.
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10–40× faster cold starts for Shopify Functions.
Identified cold start as the ceiling on Functions latency, then architected Winch, Wasmtime’s baseline compiler tier, involving work at multiple dimensions such as instruction selection, register allocation, calling conventions, ABI design and correctness verification through fuzzing.
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75% more Functions adoption, by bringing JavaScript to the platform.
Built Javy, a JavaScript-to-WebAssembly toolchain, so merchants’ developers could write Functions in the language they already had. Five years of it .
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30% faster and 40% smaller, across every Shopify Function.
Designed a new Wasm ABI and multiple SDKs on top of it (JavaScript, Rust, C, Zig) making Shopify Functions execution more efficient.
Senior Software Engineer — Shopify, 2020 – 2021 · remote
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Shopify Subscriptions, architected end to end, along with its public APIs.
The platform primitive third-party subscription apps are built on. Grew merchant GMV.
Software Engineer — Shopify, 2018 – 2020 · Montreal
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Checkout performance, on a path carrying millions of transactions.
Built and optimized Dynamic Checkout and the wider checkout experience.
Earlier
Full Stack Engineer, Breather — Montreal, 2017–2018 · Software Engineer, SAP Labs — Montreal, 2016–2017 · Lead Developer, Teem — remote, 2015–2016 · Software Engineer, SAP Labs Innovation Centre — Palo Alto, 2015.
Open source
- Winch — lead developer and maintainer, 2021 – present. Wasmtime’s baseline single-pass compiler tier, built for low-latency startup.
- Javy — lead developer and maintainer, 2021 – present. JavaScript-to-WebAssembly toolchain.
- wasmtime-rb — co-creator and maintainer, 2022 – present. Ruby bindings for Wasmtime.
- Wasmtime — core contributor, 2021 – present: performance, features, and testing infrastructure.
Research
Carnegie Mellon WebAssembly Research Center. Led research in partnership with the WRC, under Ben L. Titzer, on dynamic languages on WebAssembly and on WebAssembly observability and profiling.
Education
Universidad Tecnológica Centroamericana (UNITEC) — Tegucigalpa, Honduras. Computer Science, 2015.