GHC wiki contains an introductory article about STG written by Max Bolingbroke: The STG machine is an essential part of GHC, the world’s leading Haskell compiler. It defines how the Haskell evaluation model should be efficiently implemented on standard hardware. Despite this key role, it is generally poorly understood amongst GHC users. This document aims … Read more
Another use for the -O flag is that the value of the __debug__ builtin variable is set to False. So, basically, your code can have a lot of “debugging” paths like: if __debug__: # output all your favourite debugging information # and then more which, when running under -O, won’t even be included as bytecode … Read more
The problem is caused when the label (the classreader reads from a class file) is visited by a MethodVisitor pipeline. The label has a field int [] srcAndRefPositions. Two of its consecutive positions (cfr. the end of my original post) are updated once the label is accessed by a MethodVisitor. In my case, the label … Read more
There are only two possible explanations: the compiler contains a bug or it’s placing a kind of watermark for obscure reasons. That entry is certainly bogus because any exception thrown by a finally block itself must send execution flow to outer exception handler or finally block, but never “run again” the same finally block. Also, … Read more
Item 93 of Java Puzzlers (Joshua Bloch) says that you can work round this by preventing the final value from being considered a constant. For example: public class A { public static final int INT_VALUE = Integer.valueOf(1000).intValue(); public static final String STRING_VALUE = “foo”.toString(); } Of course none of this is relevant if you don’t … Read more
From this site The answer can be easily found if one reads the Java VM Spec carefully: The difference between the invokespecial and the invokevirtual instructions is that invokevirtual invokes a method based on the class of the object. The invokespecial instruction is used to invoke instance initialization methods as well as private methods and … Read more
Well I can’t tell you what the exact problem with Jacoco is, but I can show you how Try With Resources is compiled. Basically, there are a lot of compiler generated switches to handle exceptions thrown at various points. If we take the following code and compile it public static void main(String[] args){ String a … Read more
Java requires all classes that are loaded to be verified, in order to maintain the security of the sandbox and ensure that the code is safe to optimize. Note that this is done on the bytecode level, so the verification does not verify invariants of the Java language, it merely verifies that the bytecode makes … Read more
The Java frontend translates Java bytecode (.class files) into LLVM bytecode. Take a look at this link: https://llvm.org/svn/llvm-project/java/trunk/docs/java-frontend.txt
To expand on August’s answer, I figured I should explain exactly how this is compiled and what takes up space at the binary level. To simplify, I’ll use the following example with shorter strings. The important part is that there are some duplicate strings. public class StringArray { private static final String[] stringArray = { … Read more