RFR: 8373696: AArch64: Refine post-call NOPs

[Andrew Haley]

On 18/12/2025 13:55, Andrew Haley wrote:
>> However, I had considered using |CBNZ XZR, <#imm>|. So far, I avoided
>> implementing it because it is unclear what performance effects this
>> might have.
 >> I've tried it, and it's definitely a lot slower than a NOP or a MOVZ.

Something else to bear in mind is that we don't always have to succeed 
placing a post-call NOP. They are not used as frequently as they were in 
the past, in particular because we found a way to save and restore 
virtual thread stacks without usually having to trace them. In practice 
this means that we only have to copy the stack memory, so we don't need 
the post-call NOPs so often.