flang + wasm = <3 (?)

Serge « sans paille » Guelton

Compiler Engineer / Story Teller / Wood Chopper

FOSDEM — 1st February 2025

flang

fortran

elder

science

matrices

LAPACK

scipy

Python

Education

Jupyter Notebooks

WebAssembly

Summary

• People want to run scipy in the browser
• They want it fast: they use WebAssembly
• Scipy depends on Fortran: use flang to generate WASM code

Problem

Flang is not a cross compiler!

but

We can bypass the configuration step:

1. Configure a different host and target
2. Modify the few places where flang assumes host == target

Not Sustainable?

• Most hacks needed to by-pass host == target upstreamed
• sizeof(integral_type) hard-coded and patched downstream

</(o_0)\ >

This is how people currently run R and Python in the browser

</(o_0)\ />

Credits

Dr George W Stagg for the original blog post: https://gws.phd/posts/fortran_wasm/#compiling-blas-and-lapack-for-webassembly

Wizards of the Coast for the illustration of Game of Chaos and Elder Land Wurm

xkcd, «a treasured and carefully guarded point in the space of four-character strings»