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Comment by adamjs | Hacker News Reader

Two use-cases jump to mind:

* Allows incremental porting of large codebases to ARM. (It's not always feasible to port everything at once-- I have a few projects with lots of hand-optimized SSE code, for example.)

* Allows usage of third-party x64 DLLs in ARM apps without recompilation. (Source isn't always available or might be too much of a headache to port on your own.)

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3. Improve x64 emulation performance for everybody. Windows 11 on ARM ships system DLLs compiled as Arm64EC - makes the x64 binaries run native ARM code at least within system libraries.

It's not worth using ARM64EC for just for incremental porting -- it's an unusual mode with even less build/project support than Windows ARM64 and there are EC-specific issues like missing x64 intrinsic emulations and slower indirect calls. I wouldn't recommend it except for the second case with external x64 DLLs.

At that point why trust the emulator over the port? Either you have sufficient tests for your workload or you don’t, anything else is voodoo/tarot/tea leaves/SWAG.

We might be lucky and the emulator guys might have enough testing

"Why trust the emulator?" sounds a lot like asking "why trust the compiler?". It's going to be much more widely-used and broadly-tested than your own code, and probably more thoroughly optimized.

> Allows incremental porting of large codebases to ARM. (It's not always feasible to port everything at once-- I have a few projects with lots of hand-optimized SSE code, for example.)

Wouldn't it make more sense to have a translator that translates the assembly, instead of an emulator that runs the machine code?

Yeah but you need to port the SIMD before shipping anyways?

So if you're doing incremental stuff might as well stub out the calls with "not implemented", and start filling them in.

The SIMD part will be emulated as normal, as far as I understand. So you can ship a first version with all-emulated code, and then incrementally port hotspots to native code, while letting the emulator handle the non-critical parts.

At least in theory, we'll see how it actually pans out in practice.

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