Friday, August 29, 2008

Cecil Reloaded

For our hack week here at Novell I continued hacking on making vbnc work with Cecil, and yesterday I reached the point where vbnc is able to compile itself using only Cecil (in my previous post I also said vbnc was able to bootstrap, but back then vbnc was still using SRE to do all the hard work, and Cecil just to write the final assembly to disk).

The initial performance problems are mostly gone, it's still not quite as fast as before, but there are also quite a few low-hanging fruit yet in that area. The first successful bootstrap yesterday took 40 seconds (compared to 12 seconds for the normal vbnc), and after a few optimizations I'm now down at 24 seconds. Almost all of that time was gained by allocating less strings, the first non-optimized version allocated ~1.4 GB of strings, and it's now down to 119 MB.

I'm also using a delay-loading mechanism to load data from referenced assemblies on-demand, this is not that visible when you compile a lot of code in one go, but it sure make a difference when compiling thousands of 15-20 line tests one by one.

I'm pretty confident I can get compilation time down to the 12 seconds I had before, especially given that Cecil hasn't been much optimized [1] (not actually used by compilers) before, while Mono's SRE implementation is known to be quite fast.

As a sidenote the actual amount of code in the compiler has decreased, from ~75k lines with the normal vbnc to ~68k for the cecil version.

[1] S├ębastien Pouliot corrected me, cecil is used by some know compilers, and probably some unknown too. Some parts of Cecil has also been optimized already.

Monday, January 7, 2008


When I started writing vbnc, there weren't many options when it came to deciding which library to use to write the assemblies, only System.Reflection.Emit (SRE) was a real option.

SRE is very powerful, but unfortunately it has a few known and unknown limitations, mostly because it was never designed to be used by a full-fledged compiler.

Since I heard about Cecil, I've wanted to switch, and for the last months I've slowly added support for emitting assemblies with Cecil. Yesterday I reached a very important milestone: vbnc is able to bootstrap itself when using Cecil!

And I have to say that Cecil is A LOT easier to use than SRE, especially with generics.

There are still some problems for switching right away to only using Cecil, one of the biggest being that it's quite slow if you have many referenced assemblies (since Cecil loads everything from an assembly when loading it), though there is work in progress here.

Hopefully these issues will be solved shortly, and I can finally remove everything SRE-related, which has caused me quite a few head-aches!