[16] RFR(S): 8248398: Add diagnostic RepeatCompilation utility

[Claes Redestad]

Hi Nils,

thanks for doing this!

This works perfectly - especially the compiler control directive that 
allowing us to isolate specific JIT compilations to profile and
benchmark them in a controlled manner.

I've run a number of startup tests to ensure there's no detectable
impact on normal runs.

/Claes

On 2020-06-26 16:48, Nils Eliasson wrote:
> Hi,
> 
> This is a diagnostic utility that was requested by Claes to enable 
> better profiling of the compilers.
> 
> This patch introduces the diagnostic flag RepeatCompilation.
> 
> RepeatCompilation hold he number of times the compilation gets repeated 
> without having the code installed. RepeatCompilation = 0 is the default 
> and means that only the regular compilation is done. RepeatCompilation = 
> 100 means that an extra 100 compilations are done but without installing 
> the code.
> 
> I have tried keeping the change small and non-intrusive, contained to 
> the CompilerBroker (except the boolean for disabling code install that 
> is passed to the compilers).
> 
> RepatCompilation works as a flag: "-XX:RepeatCompilation=100", a compile 
> command: "-XX:CompileCommand=option,*::toString,intx,RepeatCompilation,100"
> and a compiler directive: "RepeatCompilation : 100".
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8248398
> Webrev: http://cr.openjdk.java.net/~neliasso/8248398/webrev.04/
> 
> Please review!
> 
> Best regards,
> Nils Eliasson
>