How Does Java Both Optimize Hot Loops and Allow Debugging

I wrote about a similar topic, but in the context of Ruby rather than Java if people find understanding that easier http://chrisseaton.com/rubytruffle/deoptimizing/

So to take the example from the article, if your optimising compiler unrolls the loop so there are four loop iterations per jump, and i is incrementing 0, 4, 8, 12... if you set a conditional breakpoint on i=10, how does it work out that it needs to break at the earlier safepoint (when i=8) and switch to the non-optimised code?

There is a problem with the html escape codes in the sample programs. It shows:

    for( int i=0; i<N; i++ )
      sum += A[i]  // set a breakpoint here, for "i>1e6" or maybe "i>1e7"