Primitive replaceFrom:to:with:startingAt: in the JIT
For a long time I was willing to add primitive #replaceFrom:to:with:startingAt: in the JIT but did not take time to do it. These days I am showing the JIT to one of my students and as an example of how one would write code in the JIT we implemented this primitive together, Spur-only. This is part of commit 2273.
I implemented quick paths for byte objects and array-like objects only. The rationale behind this is that the most common cases I see in Pharo user benchmarks in the profiler is copy of arrays and byteStrings. Typically some application benchmarks would show 3-5% of time spent in copying small things, and switching from the JIT runtime to C runtime is an important part of the cost.
First evaluation shows the following speed-ups, but I've just done that quickly in my machine:
Copy of size 0
Copy of size 1
Copy of size 3
Copy of size 8
Copy of size 64
Copy of size 1000
Failure paths are quicker too.
So I would expect some macro benchmarks to get 1 to 3% percent speed-up. Not as much as I expected but it's there.
Can someone who is good at benchmarks such as Levente have a look and provide us with a better evaluation of the performance difference ?
PS: Sry for double post Levente. First one got rejected by vm-dev, wrong sender mail address.