RFR: 8258459: Decouple gc_globals.hpp from globals.hpp

[Lois Foltan]

On Wed, 16 Dec 2020 06:24:59 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> Currently, [globals.hpp](https://github.com/openjdk/jdk/blob/17ace8339dd8235f3811e3975d9ccc77910b0c77/src/hotspot/share/runtime/globals.hpp#L29) is including gc_globals.hpp. This exposes all the GC command-line flags to almost all cpp files. However, only about 1/3 of the cpp files would require gc_globals.hpp.
> 
> This RFE improves modularity and HotSpot build time.
> 
> **Review notes:**
> - Please start with globals.hpp, gc_globals.hpp.
> - Flags related to TLAB are frequently used by other header files. I moved these flags to a new header tlab_globals.hpp.
> - Some tweaking of oop.hpp to avoid including gc_globals.hpp in this popular header file. (Otherwise gc_globals.hpp would be included by everyone).
> - The other changes are just files that use GC flags. They should have included gc_globals.hpp but didn't.
> 
> **Testing:**
> Tested with mach5: tier1, builds-tier2, builds-tier3, builds-tier4 and builds-tier5. Also locally: aarch64, arm, ppc64, s390, x86, and zero.

LGTM.
Lois

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

Marked as reviewed by lfoltan (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1797