jit | 易学教程

What is the size of methods that JIT automatically inlines?

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I've heard that JIT automatically inlines small methods, like getters (they have about 5 bytes). What is the boundary? Is there any JVM flag? HotSpot JIT inlining policy is rather complicated. It involves many heuristics like caller method size, callee method size, IR node count, inlining depth, invocation count, call site count, throw count, method signatures etc. Some limits are skipped for accessor methods (getters/setters) and for trivial methods (bytecode count less than 6). The related source code is mostly in bytecodeInfo.cpp . See InlineTree::try_to_inline , should_inline , should_not

Do redundant casts get optimized?

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问题 I am updating some old code, and have found several instances where the same object is being cast repeatedly each time one of its properties or methods needs to be called. Example: if (recDate != null && recDate > ((System.Windows.Forms.DateTimePicker)ctrl).MinDate) { ((System.Windows.Forms.DateTimePicker)ctrl).CustomFormat = "MM/dd/yyyy"; ((System.Windows.Forms.DateTimePicker)ctrl).Value = recDate; } else { (System.Windows.Forms.DateTimePicker)ctrl).CustomFormat = " "; } ((System.Windows

Defining Local Variable const vs Class const

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问题 If I am using a constant that is needed only in a method , is it best to declare the const within the method scope, or in the class scope? Is there better performance declaring it in the method? If that is true, I think it's more standard to define them at class scope (top of file) to change the value and recompile easier. public class Bob { private const int SomeConst = 100; // declare it here? public void MyMethod() { const int SomeConst = 100; // or declare it here? // Do soemthing with

Does the Python 3 interpreter have a JIT feature?

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问题 I found that when I ask something more to Python, python doesn't use my machine resource at 100% and it's not really fast, it's fast if compared to many other interpreted languages, but when compared to compiled languages i think that the difference is really remarkable. Is it possible to speedup things with a Just In Time (JIT) compiler in Python 3? Usually a JIT compiler is the only thing that can improve performances in interpreted languages, so i'm referring to this one, if other

Is there a way to get the .Net JIT or C# compiler to optimize away empty for-loops?

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A followup to Does .NET JIT optimize empty loops away? : The following program just runs an empty loop a billion times and prints out the time to run. It takes 700 ms on my machine, and I'm curious if there's a way to get the jitter to optimize away the empty loop. using System; namespace ConsoleApplication1 { class Program { static void Main() { var start = DateTime.Now; for (var i = 0; i < 1000000000; i++) {} Console.WriteLine((DateTime.Now - start).TotalMilliseconds); } } } As far as I can tell the answer is no, but I don't know if there are hidden compiler options I might not have tried. I

Java JIT Compiler causing OutOfMemoryError

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问题 An application that we have recently started sporadically crashing with a message about "java.lang.OutOfMemoryError: requested 8589934608 bytes for Chunk::new. Out of swap space?". I've looked around on the net, and everywhere suggestions are limited to revert to a previous version of Java fiddle with the memory settings use client instead of server mode Reverting to a previous version implies that the new Java has a bug, but I haven't seen any indication of that. The memory isn't an issue at

Java/JVM (HotSpot): Is there a way to save JIT performance gains at compile time?

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问题 When I measure the throughput of my Java application, I see a 50% performance increase over time: For the first 100K messages, I get ~3,000 messages per second For the second 100K messages, I get ~4,500 messages per second. I believe the performance improves as JIT optimizes the execution path. The reason given for not saving the JIT compilation is that "the optimizations that the JVM performs are not static, but rather dynamic, based on the data patterns as well as code patterns. It's likely

(How) does the Java JIT compiler optimize my code?

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问题 I'm writing fairly low level code that must be highly optimized for speed. Every CPU cycle counts. Since the code is in Java I can't write as low level as in C for example, but I want to get everything out of the VM that I can. I'm processing an array of bytes. There are two parts of my code that I'm primarily interested in at the moment. The first one is: int key = (data[i] & 0xff) | ((data[i + 1] & 0xff) << 8) | ((data[i + 2] & 0xff) << 16) | ((data[i + 3] & 0xff) << 24); and the second one

Java: what is JITC's reflection inflation?

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问题 I recently came across this interesting term and searched on Net to know more about it. However the info I found is sketchy. Could someone pl. give me a somewhat detailed explanation of what this is and why is this useful? From the info I found, it looks like this mechanism makes reflective method execution faster, at the expense of creating a lot of dynamic classes and hogging perm gen memory area, but I'm not sure about it. 回答1: Did some source code digging and coding myself to figure this

Disassemble Java JIT compiled native bytecode

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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? Jesper 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 useful as you think. The JVM does some very sophisticated optimizations, and it can even de-optimize