while (condition) { … } Workflow: check condition; if false, jump to outside of loop; run one iteration; jump to top. if (condition) do { … } while (condition); Workflow: check condition; if false, jump to beyond the loop; run one iteration; check condition; if true, jump to step 3. Comparing these two you can … Read more
General usage As explained by other answers, you can run with the following JVM options: -XX:+UnlockDiagnosticVMOptions -XX:+PrintAssembly Filter on a specific method You can also filter on a specific method with the following syntax: -XX:+UnlockDiagnosticVMOptions -XX:CompileCommand=print,*MyClass.myMethod Notes: you might need to put the second argument within quotes depending on OS etc. if the method gets … Read more
Yes, JIT’ing IL code involves translating the IL into native machine instructions. Yes, the .NET runtime interacts with the JIT’ed native machine code, in the sense that the runtime owns the memory blocks occupied by the native machine code, the runtime calls into the native machine code, etc. You are correct that the .NET runtime … Read more
First off, Python 3(.x) is a language, for which there can be any number of implementations. Okay, to this day no implementation except CPython actually implements those versions of the language. But that will change (PyPy is catching up). To answer the question you meant to ask: CPython, 3.x or otherwise, does not, never did, … Read more
So, basically, you want your code to run faster. JNI is the answer. I know you said it didn’t work for you, but let me show you that you are wrong. Here’s Dot.java: import java.nio.FloatBuffer; import org.bytedeco.javacpp.*; import org.bytedeco.javacpp.annotation.*; @Platform(include = “Dot.h”, compiler = “fastfpu”) public class Dot { static { Loader.load(); } static float[] … Read more
Without resorting to cut’n’paste of the link that @MYYN posted, I suspect this is because the optimisations that the JVM performs are not static, but rather dynamic, based on the data patterns as well as code patterns. It’s likely that these data patterns will change during the application’s lifetime, rendering the cached optimisations less than … Read more
It is a JIT optimizer bug. It is unrolling the inner loop but not updating the oVec.y value properly: for (oVec.x = 0; oVec.x < 2; oVec.x++) { 0000000a xor esi,esi ; oVec.x = 0 for (oVec.y = 0; oVec.y < 2; oVec.y++) { 0000000c mov edi,2 ; oVec.y = 2, WRONG! oDoesSomething.Do(oVec); 00000011 push … Read more
Yes, HotSpot JVM is kind of “cheating”, because it has a special version of some BigInteger methods that you won’t find in Java code. These methods are called JVM intrinsics. In particular, BigInteger.multiplyToLen is an intrinsic method in HotSpot. There is a special hand-coded assembly implementation in JVM source base, but only for x86-64 architecture. … Read more
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 … Read more
NOTE: PyPy is more mature and better supported now than it was in 2013, when this question was asked. Avoid drawing conclusions from out-of-date information. PyPy, as others have been quick to mention, has tenuous support for C extensions. It has support, but typically at slower-than-Python speeds and it’s iffy at best. Hence a lot … Read more