[wasm] AOT huge build time

[sarosigy]

I ask here this first... and maybe at emscripten?

I creating a wasm head for an application, configure to AOT, the build time becomes huge, namely an hour.

I could pinpoint the main issue, that wasm-ld runs for forty-fifty minutes.
The issue is with wasm-ld that it is single threaded, at least with default parameters. While the (currently) eight CPUs are all sweating while compile and optimization / finalize phase, at linking phase only one processor is running at 100% meaning an overall 12% CPU usage.

Is there a way to run wasm-ld multithreaded?
Or should I ask at emscripten?

(( I applied some switches <WasmShellExtraEmccFlags Include="-Wl,-lto-O0" /> with I could reduce the build time to half an hour, but the linking is still single-threaded and could be helped ))

[jeromelaban]

Thanks for the report. You can find documentation about this here. Indeed, the wasm linker is particularly slow (there's no way to make it run multi-threaded that I know of), and you can adjust the optimizations, or use profiled AOT, which reduces the amount of AOTed code.

Make sure to have the IL Linker enabled as well, otherwise you'll have a lot of unused code being compiled.

[sarosigy]

OK, so all of the above and with the line <WasmShellEmccLinkOptimizationLevel>None</WasmShellEmccLinkOptimizationLevel> it is 16 minutes now. Not so fast, but for releasing it's fine enough.
If I'll have time I will play with profiling, and with the full optimized version, also.