GP probably meant a “JS” instruction rather than a “JVM” one: FJCVTZS, “Floating-point Javascript Convert to Signed fixed-point rounding towards Zero”[1,2], introduced in ARMv8.3 at Apple’s behest (or so it is said). Apparently the point is that ARM float-to-integer conversions normally saturate on overflow while x86 reduces the integer mod 2^width, and JavaScript baked the x86 behaviour into the language.

[1] https://developer.arm.com/documentation/ddi0602/2022-12/SIMD...

[2] https://news.ycombinator.com/item?id=24808207