Does Java JIT cheat when running JDK code?

by

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.

You may disable this intrinsic with -XX:-UseMultiplyToLenIntrinsic option to force JVM to use pure Java implementation. In this case the performance will be similar to the performance of your copied code.

P.S. Here is a list of other HotSpot intrinsic methods.

More Related Contents:

  1. How does the JVM decided to JIT-compile a method (categorize a method as “hot”)?
  2. What is the size of methods that JIT automatically inlines?
  3. How do I write a correct micro-benchmark in Java?
  4. Real differences between “java -server” and “java -client”?
  5. How to see JIT-compiled code in JVM?
  6. Running jmap getting Unable to open socket file
  7. Why I can’t create an array with large size?
  8. Class JavaLaunchHelper is implemented in both … libinstrument.dylib. One of the two will be used. Which one is undefined
  9. Analyzing gc logs
  10. Java Exceptions counter on JVM HotSpot
  11. Read Java JVM startup parameters (eg -Xmx)
  12. Encourage the JVM to GC rather than grow the heap?
  13. What are ReservedCodeCacheSize and InitialCodeCacheSize?
  14. Differences between Just in Time compilation and On Stack Replacement
  15. Why doesn’t the JVM cache JIT compiled code?
  16. -XX:MaxPermSize with or without -XX:PermSize
  17. When can Hotspot allocate objects on the stack? [duplicate]
  18. Why does the JVM still not support tail-call optimization?
  19. Differences between “java -cp” and “java -jar”?
  20. Print All JVM Flags
  21. Size of Huge Objects directly allocated to Old Generation
  22. Java: Which of multiple resources on classpath JVM takes?
  23. Limit jvm process memory on ubuntu
  24. Why does the JVM require warmup?
  25. Support for Compressed Strings being Dropped in HotSpot JVM?
  26. Will the jit optimize new objects
  27. What is a stack map frame
  28. How to emit and execute Java bytecode at runtime?
  29. How can I add a Javaagent to a JVM without stopping the JVM?
  30. Java Memory explained (SUN JVM)

Leave a Comment