jit | 易学教程

How does the JVM decided to JIT-compile a method (categorize a method as “hot”)?

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I already worked with -XX:+PrintCompilation , and I know the basic techniques of the JIT-compiler and why JIT-compilation is used. Yet I still have not found out how the JVM decides to JIT-compile a method, i.e. "when the right time has come to JIT-compile a method". Am I right in the assumption that every method starts being interpreted, and as long as it is not categorized as "hot method" it will not be compiled? I have something in the back of my head that I read that a method is considered "hot" when it was executed at least 10.000 times (after interpreting the method 10.000 times, it will

When is a method eligible to be inlined by the CLR?

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问题 I\'ve observed a lot of \"stack-introspective\" code in applications, which often implicitly rely on their containing methods not being inlined for their correctness. Such methods commonly involve calls to: MethodBase.GetCurrentMethod Assembly.GetCallingAssembly Assembly.GetExecutingAssembly Now, I find the information surrounding these methods to be very confusing. I\'ve heard that the run-time will not inline a method that calls GetCurrentMethod, but I can\'t find any documentation to that

How to write self-modifying code in x86 assembly

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问题 I\'m looking at writing a JIT compiler for a hobby virtual machine I\'ve been working on recently. I know a bit of assembly, (I\'m mainly a C programmer. I can read most assembly with reference for opcodes I don\'t understand, and write some simple programs.) but I\'m having a hard time understanding the few examples of self-modifying code I\'ve found online. This is one such example: http://asm.sourceforge.net/articles/smc.html The example program provided does about four different

Preventing JIT inlining on a method

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问题 I\'ve got sort of a unique situation. I\'ve been working on an open source library for sending email. In this library, I need a reliable way to get the calling method. I\'ve done this with a StackTrace by analyzing the StackFrame objects inside it. This works without issue in a debug-mode project where optimizations are turned off. The problem occurs when I switch to release mode where optimizations are turned on. The stack trace looks like this: > FindActionName at offset 66 in file:line

JIT compiler vs offline compilers

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问题 Are there scenarios where JIT compiler is faster than other compilers like C++? Do you think in the future JIT compiler will just see minor optimizations, features but follow a similar performance, or will there be breakthroughs that will make it infinitely superior to other compilers? It looks like the multi core paradigm has some promise but it\'s not universal magic. Any insights? 回答1: Yes, there certainly are such scenarios. JIT compilation can use runtime profiling to optimize specific

Why doesn't the JVM cache JIT compiled code?

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问题 The canonical JVM implementation from Sun applies some pretty sophisticated optimization to bytecode to obtain near-native execution speeds after the code has been run a few times. The question is, why isn\'t this compiled code cached to disk for use during subsequent uses of the same function/class? As it stands, every time a program is executed, the JIT compiler kicks in afresh, rather than using a pre-compiled version of the code. Wouldn\'t adding this feature add a significant boost to

Differences between Just in Time compilation and On Stack Replacement

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问题 Both of them pretty much do the same thing. Identify that the method is hot and compile it instead of interpreting. With OSR, you just move to the compiled version right after it gets compiled, unlike with JIT, where the compiled code gets called when the method is called for the second time. Other than this, are there any other differences? 回答1: In general, Just-in-time compilation refers to compiling native code at runtime and executing it instead of (or in addition to) interpreting. Some

Call an absolute pointer in x86 machine code

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问题 What\'s the \"correct\" way to call an absolute pointer in x86 machine code? Is there a good way to do it in a single instruction? What I want to do: I\'m trying to build a kind of simplified mini-JIT (still) based on \"subroutine threading\". It\'s basically the shortest possible step up from a bytecode interpreter: each opcode is implemented as a separate function, so each basic block of bytecodes can be \"JITted\" into a fresh procedure of its own that looks something like this: {prologue}

C# JIT compiling and .NET

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问题 I\'ve become a bit confused about the details of how the JIT compiler works. I know that C# compiles down to IL. The first time it is run it is JIT\'d. Does this involve it getting translated into native code? Is the .NET runtime (as a Virtual Machine?) interact with the JIT\'d code? I know this is naive, but I\'ve really confused myself. My impression has always been that the assemblies are not interpreted by the .NET Runtime but I don\'t understand the details of the interaction. 回答1: Yes,

What does a just-in-time (JIT) compiler do?

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问题 What does a JIT compiler specifically do as opposed to a non-JIT compiler? Can someone give a succinct and easy to understand description? 回答1: A JIT compiler runs after the program has started and compiles the code (usually bytecode or some kind of VM instructions) on the fly (or just-in-time, as it's called) into a form that's usually faster, typically the host CPU's native instruction set. A JIT has access to dynamic runtime information whereas a standard compiler doesn't and can make