RFR: 8183574: Unify the is_power_of_2 functions

[Kim Barrett]

> On Feb 13, 2020, at 9:47 AM, Stefan Karlsson <stefan.karlsson at oracle.com> wrote:
> 
> Hi all,
> 
> Please review this patch to consolidate all is_power_of_2 functions into one template function and place it in the existing powerOfTwo.hpp file.
> 
> To resolve a circular dependency between globalDefinitions.hpp and powerOfTwo.hpp, I also moved exact_log2 and exact_log2_long. These functions take a power-of-two value and returns the log2 value, so I think it makes sense to move them to powerOfTwo.hpp.
> 
> https://cr.openjdk.java.net/~stefank/8183574/webrev.01
> https://bugs.openjdk.java.net/browse/JDK-8183574
> 
> Tested with tier1,2,3
> Also built locally with {fastdebug,release}x{minimal,zero,aarch64,ppc,s390,arm32,shenandoah}
> 
> Thanks,
> StefanK

That was a lot(!) of files to click through.

Looks good.

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src/hotspot/share/code/vtableStubs.cpp
 132     assert(is_power_of_2(int(N)), "N must be a power of 2");

Conversion of N to int is because it's defined via enum (because
that's what we used to do).  Better would be to no longer define N
that way.  (Also the related mask.)

This could be a followup cleanup if that's more convenient.  And I
don't need a new webrev if you change this now.

------------------------------------------------------------------------------

I also noticed some probably unnecessary casts here and there.  I
think those are better dealt with separately (perhaps as the code is
touched for other reasons), rather than adding clutter to this change.