I have a heavily optimized worker thread for a Win64 program and while preserving the registers is not much overhead at all I was wondering if it is really necessary.

You preserve registers inside of calls that your program makes or inside of procedures of a DLL but do you need to inside of a thread procedure.

The thread has it's own context so destroying every register (r0-r15 and xmm0-xmm15) shouldn't affect anything else ... am I right in assuming this?

Thread procedures don't need to save the registers, but if you're worried about that overhead you might want to consider the time it takes to create and destroy a thread, which is likely far more.

Thanks thats what I figured.

This was more of a programming standard and convention question than an optimization question.


Although avoiding

Could be considered a significant 'size' optimization.

Looks like the 680x0, with the difference that it did it in hardware

Dunno if you need register preservation in the thread. If you "ret" you might - no way to tell whether your code would break on a future service pack. If you "call ExitThread" you probably don't, but perhaps that's more overhead than preservation + ret.