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Yes, but in both cases this is because the JS runtimes (v8 in particular) makes it really difficult to feel okay with unconstrained control flow. The relooper may have been an influence but it was primarily pressure from the v8 people (I was in these meetings)

I'm less certain on my memory but I recall that Spidermonkey was more easily able to do fancier things with control flow.

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I worked at Mozilla Research in the early days of Asm.js and sat next to that team. I would frequently tell them that they should support arbitrary control flow, and that there were better ways to achieve it with Emscripten than the Relooper. There wasn't much interest in improvements at the time, although it appears that the LLVM WebAssembly backend now uses a better approach.

While SpiderMonkey itself might support fancier things with control-flow, they were writing a separate compiler for Asm.js that relied on structured control flow for SSA construction, but I have no experience with how things evolved after that. Reading the thread at https://github.com/WebAssembly/design/issues/796, it seems that V8 and SpiderMonkey have roughly equivalent design constraints.

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