“Going back to my first sentence about “at the margins”: optimize at the end. Apple famously added a “jvm” instruction — must have been the fruit of a lot of metering! Note that they didn’t have to do this for Objective-C: some extremely clever programming made dispatch cheap.”
I’m struggling to think of what you are referring to here. ARM added op codes for running JVM byte code on the processor itself, but I think those instructions were dropped a long time ago. ARM also added an instruction (floating point convert to fixed point rounding towards zero) as it became such a common operation in JS code. There have also been various GC related instructions and features added to POWER, but I think all that was well after Apple had abandoned the architecture.
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.
I’m struggling to think of what you are referring to here. ARM added op codes for running JVM byte code on the processor itself, but I think those instructions were dropped a long time ago. ARM also added an instruction (floating point convert to fixed point rounding towards zero) as it became such a common operation in JS code. There have also been various GC related instructions and features added to POWER, but I think all that was well after Apple had abandoned the architecture.
I may be forgetting sonething, could you clarify?