Stuff about VM and JIT internals
Hi hackers! Today the MoarVM JIT project is nearly 9 years old. I was inspired by Jonathan's presentation reflecting on the development of MoarVM, to do the same for the MoarVM JIT, for which I have been responsible. For those who are unfamiliar, what is commonly understood as 'JIT compilation' for virtual machines is performed by two components in MoarVM. A framework for runtime type…
Many years back, Larry Wall shared his thesis on the nature of scripting. Since recently even Java gained 'script' support I thought it would be fitting to revisit the topic, and hopefully relevant to the perl and raku language community. The weakness of Larry's treatment (which, to be fair to the author, I think is more intended to be enlightening than to be complete) is the contrast of scripting…
Hi hackers! Today First of all, I want to thank everybody who gave such useful feedback on my last post. For instance, I found out that the similarity between the expression JIT IR and the Testarossa Trees IR is quite remarkable, and that they have a fix for the problem that is quite different from what I had in mind. Today I want to write something about register allocation, however. Register…
Hi hackers! Today I want to write about optimizing IR in the MoarVM JIT, and also a little bit about IR design itself. One of the (major) design goals for the expression JIT was to have the ability to optimize code over the boundaries of individual MoarVM instructions. To enable this, the expression JIT first expands each VM instruction into a graph of lower-level operators. Optimization then…
Hi all. I usually write somewhat long-winded posts, but today I'm going to try and make an exception. Today I want to talk about the expression template language used to map the high-level MoarVM instructions to low-level constructs that the JIT compiler can easily work with: This 'language' was designed back in 2015 subject to three constraints: It should make it easy to develop 'templates' for…
Hi everybody! I recently read jnthn s Perl 6 new years resolutions post, and I realized that this was an excellent example to emulate. So here I will attempt to share what I've been doing in 2018 and what I'll be doing in 2019. In 2018, aside from the usual refactoring, bugfixing and the like: I added support for the fork() system call in the MoarVM backend. I removed the ' invokish ' control flow…
Hi hackers. Today I want to write about a new functionality that I've been developing for MoarVM that has very little to do with the JIT compiler. But it is still about VM internals so I guess it will fit. Many months ago, jnthn wrote a blog post on the relation between perl 5 and perl 6. And as a longtime and enthusiastic perl 5 user - most of the JIT's compile time support software is written in…
Hi everybody. After samcv++ released MoarVM again, it was finally time to introduce some updates to the expression template compiler. As you may or may not know, the expression JIT backend maps MoarVM opcodes to its internal representation via expression templates . At runtime (during the JIT compilation phase), these templates are combined to form an expression tree. The expression template…
Hi hackers! I recently saw a curious benchmark passed round on the #moarvm channel. (I understand that this originates from Ovid during his Future of Perl 5 and 6 presentation, but I haven't seen it myself, so if I'm wrong, don't hesitate to correct me). It's curious because it runs on perl5 and perl6, and because the difference is… significant: # reciprocal.pl my $x = 0; $x += 1/$_ for…
Dear readers, I recently came across the following comment on the internet (via Perl 6 weekly ): perl6 on MoarVM is starting to grow a JIT Which is very interesting because: Someone had at least heard of our efforts, so that's a win. But they had left with the impression that it was still in a beginning phase. Clearly, we have some PR work to do. Consider this my attempt. When people are talking…
Hi readers! Today I have a story about a recently-merged set of patches that allows MoarVM to use the on-stack return pointer to reduce the overhead of exception handling and other VM features for JIT compiled code. Maybe you'll find it interesting. As you might know, MoarVM Is a bytecode interpreter. In some situations, MoarVM internals need to know the current position in the execution of the…
Lately I've been fixing a few bugs here and there in the JIT compiler, as well as trying to advance the JIT expression optimizer. The story of those bugs is interesting but in this post I want to focus on something else, namely some support infrastructure that I think we should have that would make working on MoarVM and spesh/jit in particular much nicer. There are a bunch of things related to…
Hi there, it's been about a month since last I wrote on the progress of the even-moar-jit branch, so it is probably time for another update. Already two months ago I wrote about adding support for function calls in the expression JIT compiler. This was a major milestone as calling C functions is essential for almost everything that is not pure numerical computing. Now we can also use the return…
Hi everybody, today I'd like to promote a minor, but important improvement in the ' expression template compiler ' for the new JIT backend. This is a tool designed to make it easy to develop expression templates, which are themselves a way to make it easy to generate the ' expression tree ' intermediate representation used by the new JIT backend. This is important because MoarVM instructions…
Hi everybody. It's high time for another update, and this time I have good news. The 'expression' JIT compiler can now compile native ('C') function calls (although it's not able to use the results). This is a major milestone because function calls are hard! (At least from the perspective of a compiler, and especially from the perspective of the register allocator). Also because native function…
Hi everybody, I thought some yof you might be interested in an update regarding the JIT register allocator, which is after all the last missing piece for the new 'expression' JIT backend. Well, the last complicated piece, at least. Because register allocation is such a broad topic, I don't expect to cover all topics relevant to design decisions here, and reserve a future post for that purpose. I…
This is the first post in what I intend to be a series on the register allocator for the MoarVM JIT compiler. It may be a bit less polished than usual, because I also intend to write more of these posts than I have in the past few months. The main reason to write a register allocator is that it is needed by the compiler. The original 'lego' MoarVM JIT didn't need one, because it used what is…
Hi everybody, welcome back. I'd like to share with you the things that have been happening in the MoarVM JIT since I've last posted, which was in fact March. To be brief, the JIT has been adapted to deal with moving frames, and I've started to rewrite the register allocator towards a much better design, if I do say so myself. First, moving frames. jnthn has already written quite a bit about them.…
Hi all, I realise I haven't written one of these posts for a long time. Since November, in fact. So you could be forgiven for believing I had stopped working on the MoarVM JIT. Fortunately, that is not entirely true. I have, in fact, been very busy with a project that has nothing to do with perl6, namely SciGRID , for which I've developed GridKit . GridKit is a toolkit for extracting a power…
Hello there, I thought it high time to write to you again and update you on the world of JITs. Since last I wrote, PyPy 4.0 was released. Also in python-land, Pyston 0.4 was released, and finally Guile 2.1.1 was released and Andy Wingo wrote a nice piece about that, as is his custom. I present these links not only to give these projects the attention they deserve, but also because I think they are…
Earlier this week my attention was brought to an article claiming that the dusk was setting for JIT compilation . Naturally, I disagree. I usually try to steer clear of internet arguments, but this time I think I may have something to contribute. Nota bene, this is not a perl- or perl6 related argument, so if that is strictly your interest this is probably not an interesting post for you. The main…
This week I think I fixed irregular behavior in the x64 instruction encoding register selction of DynASM. I think it'll be a fun story to share, so I thought it'd be time to blog. The astonishingly irregular thing about x64 instruction encoding is that it is mostly very regular. Ignoring for the moment instruction prefixes and constants, an x86 instruction consists of two bytes, one for the…
Hi everybody, it's been a while since I've blogged, and I think you deserve an update. Last week, of course, was YAPC::EU, which was awesome. Granada is a very nice place, and the weather was excellent. Tapas lunch was very nice, as was the gala diner (also with tapas). There were many interesting people and presentations (many more than I could actually see). It was also very interesting to…
In my last blog I talked a bit about a problem I had with generating all possible sets of rules from the tile 'grammar'. I've since solved that problem, and thought it'd be nice to share my results. (NB: I use the word 'grammar' loosely today and on other days. In compiler jargon a grammar is usually a thing that matches a linear stream of lexical tokens to a tree structure. In this case, it's…
Hi everybody, I realise I haven't blogged in a while now, and it'd be a good time to write you an update. I've hit a few problems, but am still making progress. I've written the tiler algorithm for the JIT compiler. This caused a difficulty because the input graph is not a tree but a DAG, meaning that a node may have more than one 'parent' or 'consumer' nodes. Since consumers decide the tiling of…