RFR (M): 8149159: Clean up Unsafe

[Mikael Vidstedt]

Please review the following change which does some relatively 
significant cleaning up of the Unsafe implementation.

Bug: https://bugs.openjdk.java.net/browse/JDK-8149159
Webrev (hotspot): 
http://cr.openjdk.java.net/~mikael/webrevs/8149159_unsafecleanup/hotspot/webrev.00/webrev/
Webrev (jdk): 
http://cr.openjdk.java.net/~mikael/webrevs/8149159_unsafecleanup/jdk/webrev.00/webrev/

Summary:

* To avoid code duplication sun.misc.Unsafe now delegates all work to 
jdk.internal.misc.Unsafe. This also means that the VM - and unsafe.cpp 
specifically - no longer needs to know or care about s.m.Unsafe.
* The s.m.Unsafe delegation methods have all been decorated with 
@ForceInline to minimize the risk of performance regressions, though it 
is highly likely that they will be inlined even without the annotations.
* The documentation has been updated to reflect that it is the 
responsibility of the user of Unsafe to make sure arguments are valid.
* The argument checking has, to the extent possible, been moved from 
unsafe.cpp up to Java to simplify the native code and allow the JIT to 
optimize it.
* Some of the argument checks have been relaxed. For example, the 
recently introduced U.copySwapMemory does not check for null pointers 
anymore. See docs for j.i.m.U.checkPointer for the complete reasoning 
behind this. Note that the Unsafe methods today, apart from 
U.copySwapMemory, do not perform the NULL related check(s).
* A test was added for j.i.m.U.copyMemory, based on U.copySwapMemory. 
Feel free to point out that I should merge them (because I should).

Also, unsafe.cpp was cleaned up rather dramatically. Some specific 
highlights:

* Unsafe_ functions are now declared static, as are the other unsafe.cpp 
local functions.
* Created unsafe.hpp and moved some functions used in other parts of the 
VM to that. Removed some "extern" function declarations (extern is bad, 
kittens die when extern is (over-)used).
* Remove scary looking comment about UNSAFE_LEAF not being possible to 
use - there's nothing special about it, it's just a JVM_LEAF.
* Used UNSAFE_LEAF for a few simple leaf methods
* Added helpful braces around UNSAFE_ENTRY/UNSAFE_END to help auto-indent
* Removed unused Unsafe_<...>##140 functions/macros
* Updated macro argument names to be consistent throughout unsafe.cpp 
macro definitions
* Replaced some checks with asserts - as per above the checks are now 
performed in j.i.m.Unsafe instead.
* Removed all the s.m.Unsafe related code


Testing:

* jtreg: hotspot_jprt group, jdk/internal
* JPRT: hotspot testset
* Perf: JMH unsafe-bench.jar (no significant changes)

I'm taking suggestions on additional things to test.

Cheers,
Mikael