Re: [Jikesrvm-researchers] Coaxing JikesRVM to recompile at O2 and O3

[David P G. <gr...@us...>]

Hi,

      The adaptive system makes recompilation decisions using a
cost/benefit model that takes as some of its  inputs  (1) data in the file
VM_CompilerDNA and (2) measured compilation times from the current run.
The default DNA for Linux/IA32 in version 2.2.0 reflects the fact that on
average O2 is currently not profitable on that platform. Therefore the
adaptive system will not use O2 on Linux/IA32 unless you change the DNA.
Also note that in a BaseAdaptive image the opt compiler is itself
baseline-compled.  Therefore the measured opt compilation times (input 2)
are going to be very large, which will cause the system to pretty much
decide to never  recompile the same method a second time.  Also, the system
will expend a fair amount of effort optimizing the opt compiler itself.  If
you are seriously using the adaptive system (not just debugging a
modification), you should use either FullAdaptive or FastAdaptive images.
      Also there isn't a real  O3.  You can set the optimization level to 3
(or 4, or 100) but you get the same optimizations as O2.

--dave