![]() ![]() OPAL enables you to transform Java bytecode into a 3-address code (TAC) which is also sometimes called "Quadruples Code". Looking at just the control-flow to begin with, we see how this loop has a begin, and then it has both an end and an exit.3-Address Code / Quadruples Code / Static Single Assignment Form We draw it thickly because these edges are so important - loops are where key optimisations are to be found, and where many complex constraints come from. In a program with loops, we need to go backward to earlier parts of the program. So far all the arrows have pointed downward (except the dashed information edges.) This means the program has been going in only one direction. Private static int exampleArithOperator ( int x, int y ) The Graal compiler that we’re using uses a similar sea-of-nodes graphical IR to C2. That’s why we might want to draw them as graphs, which is what we’re going to do here. This highlights one drawback, which is that the loosely structured graph can be hard to comprehend - humans aren’t great at reasoning about graphs and it’s hard to express them as text. This compiler, designed by Cliff Click, uses a very free-form graph, called a sea-of-nodes, or sometimes a soup-of-nodes. This has been done for a long time, known as a Program Dependence Graph, or PDG, but it became particularly notable in the most common Java optimising JIT, called C2, which is what you normally use if you are using HotSpot or OpenJDK. We can also do away with the temporary names and instead make the values edges between instruction nodes in a graph. If we do away with the explicit ordering of instructions one after the other, we get a more free representation of the program. A model called Static Single Assignment, or SSA, constrains each temporary name to be only assigned in one source location. This is easy to reason about and easy to output as text. There is a graph of control flow between these blocks, but within each block the instructions are linear. Instructions pass information between each other using temporary names or entries on a stack. In this blog post I’m going to show a gallery of some Graal graphs for basic Java language constructs, and explain what each part of the graph means and what we can learn from this to understand how Java is compiled and optimized.Ī little bit of history is that compilers traditionally use a linear format for their IR, meaning there is a sequence of one instruction after another in chunks called basic blocks. ![]() I also find them really satisfying to look at and work with - I think they can be very artistic. Most representations of source code are some form of tree, without cycles, so for many people it’s a new way of looking at and thinking about their code. Graal’s IR is particularly interesting because it’s a cyclic graph - this means that if you follow the edges you can go in circles. We have to use special tools to do this - for example the Ideal Graph Visualizer, or IGV, from Oracle Labs, or Shopify’s internal Seafoam tool, which we’re using here. The compiler transforms and optimizes your code by manipulating this data structure, so you can get a lot of insight into what the compiler is doing by looking at it. Many people will also be familiar with a data structure called an abstract-syntax-tree, or AST, which is the way that the Java compiler represents your Java source code while compiling.įewer people will be aware that there’s another key data structure used at runtime to JIT compile Java programs to native code - the compiler intermediate representation, or the IR. Many people will know that when you use Java you compile your application using the javac compiler to a data structure called bytecode. At Shopify we’re using Graal to JIT compile Ruby to native code, using TruffleRuby, but this blog post is just about Java in order to keep things as simple as possible. Graal can also be used for other languages beyond Java, through the Truffle language implementation framework. It translates your Java program to machine code while it’s running. Graal is a new just-in-time, or JIT, compiler for the Java Virtual Machine, or JVM. Understanding Basic Graal Graphs Understanding Basic Graal Graphs Chris Seaton, 3 June 2020 ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |