FeedCity: Max Bernstein's Blog

Travel notes: PLDI Boulder

I had another excellent PLDI this past June. It was my fourth1. I continued to meet new people and learn new things! Overall: I got to meet a lot of new people, which was exciting. I had some good chats about research. I asked a question at a talk! I got to show Aaron and J...

Max Bernstein's Blog
03 Jun 00:00

A survey of inlining heuristics

Compilers, especially method just-in-time compilers, operate on one function at a time. It is a natural code unit size, especially for a dynamic language JIT: at a given point in time, what more information can you gather about other parts of a running, changing system? I d...

Max Bernstein's Blog
01 Jun 00:00

Checking assembly with Z3

Short post today. New ZJIT contributor dak2 submitted a PR to fix an overflow bug in fixnum division in ZJIT. We did the division fine, but lied about the type of the result in the case of dividing FIXNUM_MIN by -1. You can see how this is special-cased in CRuby: static inl...

Max Bernstein's Blog
18 May 00:00

Travel notes: RubyKaigi Hakodate

I just got back from a three and a half week trip to Japan. It was the longest trip I have ever been on (aside from studying abroad in Germany, which felt different). I made the following wild circuit with only a backpack and a duffel: Tokyo Toyama Kanazawa Nara is...

Max Bernstein's Blog
12 May 00:00

Partial static single information form

In compilers, static single information form (SSI) is a common extension to static single assignment form (SSA). It was introduced by C. Scott Ananian in 1999 in his MS thesis (PDF) 1. SSI extends your existing SSA intermediate representation by discovering facts from your ...

Max Bernstein's Blog
04 Apr 00:00

Value numbering

Welcome back to compiler land. Today we’re going to talk about value numbering, which is like SSA, but more. Static single assignment (SSA) gives names to values: every expression has a name, and each name corresponds to exactly one expression. It transforms programs like t...

Max Bernstein's Blog
27 Mar 00:00

Using Perfetto in ZJIT

Originally published on Rails At Scale. Look! A trace of slow events in a benchmark! Hover over the image to see it get bigger. A sneak preview of what the trace looks like. Now read on to see what the slow events are and how we got this pretty picture. The ...

Max Bernstein's Blog
25 Feb 00:00

A fuzzer for the Toy Optimizer

Another entry in the Toy Optimizer series. It’s hard to get compiler optimizers right. Even if you build up a painstaking test suite by hand, you will likely miss corner cases, especially corner cases at the interactions of multiple components or multiple optimization passe...

Max Bernstein's Blog
16 Feb 00:00

Type-based alias analysis in the Toy Optimizer

Another entry in the Toy Optimizer series. Last time, we did load-store forwarding in the context of our Toy Optimizer. We managed to cache the results of both reads from and writes to the heap—at compile-time! We were careful to mind object aliasing: we separated our heap...

Max Bernstein's Blog
22 Jan 00:00

A multi-entry CFG design conundrum

Background and bytecode design The ZJIT compiler compiles Ruby bytecode (YARV) to machine code. It starts by transforming the stack machine bytecode into a high-level graph-based intermediate representation called HIR. We use a more or less typical1 control-flow graph (CFG...

Max Bernstein's Blog
31 Jan 2024

Sorry for marking all the posts as unread

I noticed that the URLs were all a little off (had two slashes instead of one) and went in and fixed it. I did not think everyone's RSS software was going to freak out the way it did. PS: this is a special RSS-only post that is not visible on the site. Enjoy.