pizlonator

This document explains how I would implement an SSA-based compiler if I was writing one today.

This document is intentionally opinionated. It just tells you how I would do it. This document is intended for anyone who has read about SSA and understands the concept, but is confused about how exactly to put it into practice. If you're that person, then I'm here to show you a way to do it that works well for me. If you're looking for a review of other ways to do it, I recommend this post.

My approach works well when implementing the compiler in any language that easily permits cyclic mutable data structures. I know from experience that it'll work great in C++, C#, or Java. The memory management of this approach is simple (and I'll explain it), so you won't have to stress about use after frees.

I like my approach because it leads to an ergonomic API by minimizing the amount of special cases you have to worry about. Most of the compiler is analyses and transformations ov

pizlonator

Here's a much more complete description of how I do SSA, beyond just how I do Phis.

This describes how I do SSA form, which avoids the need to have any coupling between CFG data structures and SSA data structures.

Let's first define a syntax for SSA and some terminology. Here's an example SSA node:

A = Add(B, C)

In reality, this will be a single object in your in-memory representation, and the names are really addresses of those objects. So, this node has an "implicit variable" called A; it's the variable that is implicitly assigned to when you execute the node. If you then do:

borkdude

;; deps.edn:

;; {
;;  :deps {
;;         clj-kondo/clj-kondo {:mvn/version "2021.10.19"}
;;         org.clojars.quoll/asami {:mvn/version "2.2.3"}
;;         }
;;  }

kendfrey

import tactic

def transform : ℚ × ℚ × ℚ × ℚ × ℚ × ℚ × ℚ × ℚ × ℚ → ℚ × ℚ → ℚ × ℚ
| (a, b, c, d, e, f, g, h, i) (x, y) := ((a * x + b * y + c) / (g * x + h * y + i), (d * x + e * y + f) / (g * x + h * y + i))

def xy : ℚ × ℚ := (1, 1)
def xy' : ℚ × ℚ := (1, -1)
def x'y' : ℚ × ℚ := (-1, -1)
def x'y : ℚ × ℚ := (-1, 1)

pesterhazy

This gist lists challenges you run into when building offline-first applications based on IndexedDB, including open-source libraries like Firebase, pouchdb and AWS amplify (more).

Note that some of the following issues affect only Safari. Out of the major browsers, Chrome's IndexedDB implementation is the best.

Backing file on disk (WAL file) keeps growing (Safari)

When this bug occurs, every time you use the indexeddb, the WAL file grows. Garbage collection doesn't seem to be working, so after a while, you end up with gigabytes of data.

Random exceptions when working with a large number of indexeddb databases (Safari)

seancorfield

NOTE: Clojure 1.11 Alpha 2 added update-keys and update-vals which provide similar functionality directly in clojure.core, but with the hash map first and the function second.

Running this code:

clj -Sdeps '{:deps 
             {seancorfield/map-utils 
              {:git/url "https://gist.github.com/seancorfield/6e8dd10799e9cc7527da5510c739e52f"
               :sha "cfde3c2c83379e93ab1a49752611ae663008129f"}}}'

That starts a REPL:

jboner

Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
L2 cache reference                           7   ns                      14x L1 cache
Mutex lock/unlock                           25   ns
Main memory reference                      100   ns                      20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy             3,000   ns        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD

athos

(import '[clojure.asm Opcodes Type ClassWriter]
        '[clojure.asm.commons Method GeneratorAdapter])

(defn make-class [name]
  (let [cw (ClassWriter. ClassWriter/COMPUTE_FRAMES)
        init (Method/getMethod "void <init>()")
        meth (Method/getMethod "int fact(int)")]
    (.visit cw Opcodes/V1_6 Opcodes/ACC_PUBLIC (.replace name \. \/) nil "java/lang/Object" nil)
    (doto (GeneratorAdapter. Opcodes/ACC_PUBLIC init nil nil cw)
      (.visitCode)