jit | 易学教程

Java: JIT method inlining

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问题 When does Java JIT inline a method call? Is it based on #times the caller method is called (if yes, what would that number be?), or some other criteria (and what would that be?) I've read that JIT can inline 'final' methods, but it also inlines nonfinal methods based on runtime statistics, so want to know what is that triggering criteria. I guess the answers would differ based on JVM implementation, but maybe there's something common across all of them? 回答1: The short answer is whenever it

At what level C# compiler or JIT optimize the application code?

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问题 I want to know this info to reduce my code size so I will not waste my time optimize things that will be done by compiler or JIT. for example: if we assume the compiler inline the call to the get function of a property so I do not have to save the return value in a local variable to avoid function call. I want to recommend a good reference that describes what is going on? 回答1: You may want to take a look at these articles: JIT Optimizations - (Sasha Goldshtein - CodeProject) Jit Optimizations

Any tutorial for embedding Clang as script interpreter into C++ Code?

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问题 I have no experience with llvm or clang, yet. From what I read clang is said to be easily embeddable Wikipedia-Clang, however, I did not find any tutorials about how to achieve this. So is it possible to provide the user of a c++ application with scripting-powers by JIT compiling and executing user-defined code at runtime? Would it be possible to call the applications own classes and methods and share objects? edit: I'd prefer a C-like syntax for the script-languge (or even C++ itself) 回答1: I

CLR vs JIT

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问题 What is the difference between the JIT compiler and CLR? If you compile your code to il and CLR runs that code then what is the JIT doing? How has JIT compilation changed with the addition of generics to the CLR? 回答1: The JIT is one aspect of the CLR. Specifically it is the part responsible for changing CIL/MSIL (hereafter called IL) produced by the original language's compiler (csc.exe for Microsoft c# for example) into machine code native to the current processor (and architecture that it

Java: how much time does an empty loop use?

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I am trying to test the speed of autoboxing and unboxing in Java, but when I try to compare it against an empty loop on a primitive, I noticed one curious thing. This snippet: for (int j = 0; j < 10; j++) { long t = System.currentTimeMillis(); for (int i = 0; i < 10000000; i++) ; t = System.currentTimeMillis() - t; System.out.print(t + " "); } Every time I run this, it returns the same result: 6 7 0 0 0 0 0 0 0 0 Why does the first two loops always take some time, then the rest just seem to be skipped by the system? In this answer to this post, it is said that Just-In-Time compilation will be

Does it help to use NGEN?

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Is it better to use NGEN an ASP.NET application when we know it is not going to change much? Or is the JIT good enough? The only reason I asked was because this article by Jeffrey Richter in 2002 says : And, of course, Microsoft is working quite hard at improving the CLR and its JIT compiler so that it runs faster, produces more optimized code, and uses memory more efficiently. These improvements will take time. For developers that can't wait, the .NET Framework redistributable includes a utility called NGen.exe. NGen will only help startup time - it doesn't make the code execute any faster

Java loop gets slower after some runs / JIT's fault?

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问题 So I wanted to benchmark some basic java functionality to add some imformation to this question: What is the gain from declaring a method as static. I know writing benchmarks is sometimes not easy but what happens here I cannot explain. Please note that I'm not interessted in how to fix this but on why this happens* The Test class: public class TestPerformanceOfStaticVsDynamicCalls { private static final long RUNS = 1_000_000_000L; public static void main( String [] args ){ new

Where is the .NET JIT-compiled code cached?

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问题 A .NET program is first compiled into MSIL code. When it is executed, the JIT compiler will compile it into native machine code. I am wondering: Where is these JIT-compiled machine code stored? Is it only stored in address space of the process? But since the second startup of the program is much faster than the first time, I think this native code must have been stored on disk somewhere even after the execution has finished. But where? 回答1: Memory. It can be cached, that's the job of ngen.exe

Is there any instruction reordering done by the Hotspot JIT compiler that can be reproduced?

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问题 As we know, some JIT allows reordering for object initialization, for example, someRef = new SomeObject(); can be decomposed into below steps: objRef = allocate space for SomeObject; //step1 call constructor of SomeObject; //step2 someRef = objRef; //step3 JIT compiler may reorder it as below: objRef = allocate space for SomeObject; //step1 someRef = objRef; //step3 call constructor of SomeObject; //step2 namely, step2 and step3 can be reordered by JIT compiler. Even though this is

Is there a runtime benefit to using const local variables?

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问题 Outside of the ensuring that they cannot be changed (to the tune of a compiler error), does the JIT make any optimisations for const locals? Eg. public static int Main(string[] args) { const int timesToLoop = 50; for (int i=0; i<timesToLoop; i++) { // ... } } 回答1: The generated IL is different (using Release mode): using constant local using normal local --------------------------------------------------------------------- .entrypoint .entrypoint .maxstack 2 .maxstack 2 .locals init ( .locals