jit

问题 I hear a lot about what JVM JITs can do, but don't see a lot of information on how to profile what the JIT is actually doing in a given run of your program. There are lots of tips about using -XX:+PrintCompilation and -XX:+PrintOptoAssembly but it results in really low-level information that is hard to interpret. In general, during optimization, I like to have a benchmark suite of common operations with dedicated JIT warmup time and so on, but I'd like to be able to see which optimizations

问题 I'm learning LLVM and trying to compile a simple function: int sum(int a, int b) { return a+b; }; on the fly. So here's the code I have so far: #include <string> #include <vector> #include "llvm/IR/LLVMContext.h" #include "llvm/IR/Module.h" #include "llvm/IR/IRBuilder.h" #include "llvm/IR/Verifier.h" using namespace llvm; static LLVMContext &Context = getGlobalContext(); static std::unique_ptr<Module> MyModule = make_unique<Module>("my compiler", Context); Function *createFunc(IRBuilder<>

问题 I've been testing a cacheing system of my making. Its purpose is to speed up a Django web application. It stores everything in-memory. According to cProfile most of the time in my tests is spent inside QuerySet._clone() which turns out to be terribly inefficient (it's actually not that strange given the implementation). I was having high hopes for using PyPy to speed things up. I've got a 64-bit machine. However after installing all the required libraries it turns out that PyPy compiled code

问题 I am not expecting a definite yes or no. Any knowledge you might have I will consider as an answer. private String CalculateCharge(Nullable<Decimal> bill, Nullable<Decimal> rate) { return ((bill ?? 0.0m) * (rate ?? 0.0m)).ToString("C"); } 回答1: Inlining is an implementation detail of the JIT, not of the C# compiler. From Eric Gunnerson's blog: The JIT uses a number of heuristics to decide whether a method should be in-lined. The following is a list of the more significant of those (note that

问题 java has an argument -XX:MaxInlineLevel (with a default value of 9) which controls the maximum number of nested calls to inline. Why is there any such limit? Why aren't the usual heuristics based on frequency and code size sufficient for the JVM to decide for itself how deeply to inline? (this is prompted by JitWatch showing me that a deeply nested Guava checkArgument call was not being inlined due to depth) 回答1: Some significant searching uncovers this interesting little fragment (I actually

问题 I wrote a server application in Java 8, and running it with java 1.8.0u25. It works fine for the first several hours, but after it gets about 5k~10k requests, a thread of the VM process uses 100% of one of the CPUs. So I tried jstack for the VM process to check what the problematic thread was, and it showed that the thread(thread id was 14303=0x37df) was "C2 CompilerThread0": "C2 CompilerThread0" #6 daemon prio=9 os_prio=0 tid=0x00002aaabc12a000 nid=0x37df runnable [0x0000000000000000] java

问题 By now, most mainstream browsers have started integrating optimizing JIT compilers to their JavaScript interpreters/virtual machines. That's good for everyone. Now, I'd be hard-pressed to know exactly which optimizations they do perform and how to best take advantage of them. What are references on optimizations in each of the major JavaScript engines? Background: I'm working on a compiler that generates JavaScript from a higher-level & safer language (shameless plug: it's called OPA and it's

问题 I have a performance-critical method called often when my app starts up. Eventually, it gets JIT-compiled, but not after some noticeable time being run in the interpreter. Is there any way I can tell the JVM that I want this method compiled right from the start (without tweaking other internals with stuff like -XX:CompileThreshold )? 回答1: The only way I know of is the -Xcomp flag, but that is not generally advisable to use. It forces immediate JIT compilation of ALL classes and methods first

问题 I couldn't find the difference between JIT and Interpreters. Jit is intermediary to Interpreters and Compilers. During runtime, it converts byte code to machine code ( JVM or Actual Machine ?) For the next time, it takes from the cache and runs Am I right? Interpreters will directly execute bytecode without transforming it into machine code. Is that right? How the real processor in our pc will understand the instruction.? Please clear my doubts. 回答1: First thing first: With JVM, both

问题 I am wondering if there is any performance differences between String s = someObject.toString(); System.out.println(s); and System.out.println(someObject.toString()); Looking at the generated bytecode, it seems to have differences. Is the JVM able to optimize this bytecode at runtime to have both solutions providing same performances ? In this simple case, of course solution 2 seems more appropriate but sometimes I would prefer solution 1 for readability purposes and I just want to be sure to