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Optimizing the Ion compiler back end

(spidermonkey.dev)
164 points undercut | 1 comments | 16 Oct 24 17:15 UTC | HN request time: 0.205s | source
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tlb ◴[17 Oct 24 09:29 UTC] No.41867866[source]▶
> control flow graph contained 132856 basic blocks

That is a stunningly large function. I've looked around the onnxruntime sources and can't find anything like it. The largest C file is under 6000 lines. Does anyone know what function it's referring to?

replies(1): >>41868882 #
1. flohofwoe ◴[17 Oct 24 12:10 UTC] No.41868882[source]▶
IME Clang/LLVM can be extremely agressive about inlining. Some of my home computer emulators are (almost) collapsed into a single massive function (the compiler can see all function bodies in my build setup even without LTO).

Also the CPU emulator tick function which is a single huge switch statement with several thousand case branches was actually running into a slow path in Clang a couple of years ago (it took like 30 seconds to build that one source file). This was fixed at some point though.

I also seem to remember that Emscripten had a build setting to break up large WASM functions into smaller snippets to work around such quadratic outliers in browser WASM engines.