jit

问题 Watching Towards a Universal VM presentation, I studied this slide, which lists all the optimisations that HotSpot JIT does: In the language-specific techniques section there is a de-reflection. I tried to find some information about it accross the Internet, but failed. I understood that this optimization eliminates reflection costs in some way, but I'm interested in details. Can someone clarify this, or give some useful links? 回答1: Yes, there is an optimization to reduce Reflection costs,

问题 Is there any way to do an assembly dump of the native code generated by the Java just-in-time compiler? And a related question: Is there any way to use the JIT compiler without running the JVM to compile my code into native machine code? 回答1: Yes, there is a way to print the generated native code (requires OpenJDK 7). No, there is no way to compile your Java bytecode to native code using the JDK's JIT and save it as a native executable. Even if this were possible, it would probably not as

问题 HotSpot's tiered compilation uses the interpreter until a threshold of invocations (for methods) or iterations (for loops) triggers a client compilation with self-profiling. The client compilation is used until another threshold of invocations or iterations triggers a server compilation. Printing HotSpot's flags shows the following flag values with -XX:+TieredCompilation. intx CompileThreshold = 10000 {pd product} intx Tier2CompileThreshold = 0 {product} intx Tier3CompileThreshold = 2000

问题 This question already has answers here : Closed 8 years ago . Possible Duplicate: JIT compiler vs offline compilers I have heard that under certain circumstances, Java programs or rather parts of java programs are able to be executed faster than the "same" code in C++ (or other precompiled code) due to JIT optimizations. This is due to the compiler being able to determine the scope of some variables, avoid some conditionals and pull similar tricks at runtime. Could you give an (or better -

问题 We are making some kNN and SVD implementations in Python. Others picked Java. Our execution times are very different. I used cProfile to see where I make mistakes but everything is quite fine actually. Yes, I use numpy also. But I would like to ask simple question. total = 0.0 for i in range(9999): # xrange is slower according for j in range(1, 9999): #to my test but more memory-friendly. total += (i / j) print total This snippet takes 31.40s on my computer. Java version of this code takes 1

问题 I have generated a bc file with the online compiler on llvm.org, and I would like to know if it is possible to load this bc file from a c or c++ program, execute the IR in the bc file with the llvm jit (programmatically in the c program), and get the results. How can I accomplish this? 回答1: Here's some working code based on Nathan Howell's: #include <string> #include <memory> #include <iostream> #include <llvm/LLVMContext.h> #include <llvm/Target/TargetSelect.h> #include <llvm/Bitcode

问题 Why does commenting out the first two lines of this for loop and uncommenting the third result in a 42% speedup? int count = 0; for (uint i = 0; i < 1000000000; ++i) { var isMultipleOf16 = i % 16 == 0; count += isMultipleOf16 ? 1 : 0; //count += i % 16 == 0 ? 1 : 0; } Behind the timing is vastly different assembly code: 13 vs. 7 instructions in the loop. The platform is Windows 7 running .NET 4.0 x64. Code optimization is enabled, and the test app was run outside VS2010. [ Update: Repro

问题 What are the differences between a Just-in-Time-Compiler and an Interpreter, and are there differences between the .NET and the Java JIT compiler? 回答1: Just-in-time compilation is the conversion of non-native code, for example bytecode, into native code just before it is executed. From Wikipedia: JIT builds upon two earlier ideas in run-time environments: bytecode compilation and dynamic compilation. It converts code at runtime prior to executing it natively, for example bytecode into native

问题 I'm having an issue in my Java application where the JIT breaks the code. If I disable the JIT, everything works fine, but runs 10-20x slower. Is there any way to disable the JIT for a specific method or class? Edit: I'm using Ubuntu 10.10, getting the same results both with: OpenJDK Runtime Environment (IcedTea6 1.9) (6b20-1.9-0ubuntu1) OpenJDK 64-Bit Server VM (build 17.0-b16, mixed mode) and: Java(TM) SE Runtime Environment (build 1.6.0_16-b01) Java HotSpot(TM) 64-Bit Server VM (build 14.2

问题 We are taking a hit the first time some heavy UI screens are loaded. Our project is divided into one main executable and several DLL files. The DLL files can also contain UI screens which are slow the first time they are loaded. Is there a way (in code) we can preload all the referenced assemblies so as to avoid the JIT compilation hit? I know there is a tool called NGen. Is it possible to operate NGen in a development environment so we can see its effects instantly? Ideally though, we would