RFR(S): 8207011: Remove uses of the register storage class specifier

[Mikael Vidstedt]

Please review the below change which removes *most* uses of the register keyword/storage class specifier.

Bug: https://bugs.openjdk.java.net/browse/JDK-8207011 <https://bugs.openjdk.java.net/browse/JDK-8207011>
Webrev: http://cr.openjdk.java.net/~mikael/webrevs/8207011/webrev.01/open/webrev/ <http://cr.openjdk.java.net/~mikael/webrevs/8207011/webrev.01/open/webrev/>

* Background (from the bug)

The C/C++ register keyword/storage class specifier may have made a difference many moons ago, but the C++11 standard deprecated it, and starting with C++17 it is a reserved keyword. Some compilers emit deprecation warnings even when targeting earlier C++ standards such as C++14.


* Commentary

The one case where the register keyword remains is when compiling (effectively) inline assembly with gcc, patterns like:

address os::current_stack_pointer() {
…
#else // gcc
  register void *esp __asm__ (SPELL_REG_SP);
  return (address) esp;
#endif
}

Removing the register keyword here breaks the code, and gcc does *not* complain about using it for these patterns, so I chose to leave it there. An alternative to that would be to always use the “clang” style mov instruction. I know there is another thread[1] discussing how to move forward with the current_stack_pointer on clang 4.0. I’ll keep my eyes on that to make sure we don’t collide (and cc:ing Martin for good luck).

Would appreciate some help from the respective porting folks to verify the aix/ppc/s390 changes.

Cheers,
Mikael

[1] http://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2018-July/029099.html <http://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2018-July/029099.html>