Bug ID: JDK-8243205 Modularize JVM flags declaration

Versions (Unresolved/Resolved/Fixed)

The Version table provides details related to the release that this issue/RFE will be addressed.

Unresolved : Release in which this issue/RFE will be addressed.
Resolved: Release in which this issue/RFE has been resolved.
Fixed : Release in which this issue/RFE has been fixed. The release containing this fix may be available for download as an Early Access Release or a General Availability Release.

To download the current JDK release, click here.

JDK 17
17 b02Fixed

The purpose of this RFE is to improve modularization of the source code and speed up compilation of HotSpot C++ source code.

Today all global variables generated by the JVM XXX_FLAGS macros are declared at the end of globals.hpp.

http://hg.openjdk.java.net/jdk/jdk/file/4a5a7dc9d05c/src/hotspot/share/runtime/globals.hpp#l2498

As a result, any file that needs just one of such globals will need to include a large number of header files, with a total of over 1000 global declarations.

We should modularize this by doing the variable declaration in each individual header that has a XXX_FLAGS specification. E.g.,

c1_globals.hpp:

    #define C1_FLAGS(develop, develop_pd, product, .........) \
        develop(intx, C1FlagA, 123, "some flag A for C1) \
        product(intx, C1FlagB, 456, "some flag B for C1)
   DECLARE_FLAGS(C1_FLAGS)

The DECLARE_FLAGS macro will expand to this (in product build)
    extern intx C1FlagA;
    const intx C1FlagB = 456;

Most of the HotSpot files that reference C1FlagA/C1FlagB can simply include c1_globals.hpp, without including the other unrelated xxx_globals.hpp file.

DECLARE_FLAGS would be something like:

#define DECLARE_FLAGS(FLAG_SPECIFIER) \
    FLAG_SPECIFIER( 
          DECLARE_DEVELOPER_FLAG, \
          DECLARE_PD_DEVELOPER_FLAG, \
          DECLARE_PRODUCT_FLAG, \
          DECLARE_PD_PRODUCT_FLAG, \
          DECLARE_NOTPRODUCT_FLAG, \
          IGNORE_RANGE, \
          IGNORE_CONSTRAINT)

Changeset: 1d15ebe1 Author: Ioi Lam <iklam@openjdk.org> Date: 2020-12-11 04:18:54 +0000 URL: https://git.openjdk.java.net/jdk/commit/1d15ebe1

11-12-2020

Note, this approach is current not possible because the flag macros do not have the same number of parameters. E.g., http://hg.openjdk.java.net/jdk/jdk/file/4a5a7dc9d05c/src/hotspot/share/runtime/globals.hpp#l115 define RUNTIME_FLAGS(develop, \ develop_pd, \ product, \ product_pd, \ diagnostic, \ diagnostic_pd, \ experimental, \ notproduct, \ manageable, \ product_rw, \ lp64_product, \ range, \ constraint) \ http://hg.openjdk.java.net/jdk/jdk/file/4a5a7dc9d05c/src/hotspot/share/c1/c1_globals.hpp#l37 #define C1_FLAGS(develop, \ develop_pd, \ product, \ product_pd, \ diagnostic, \ diagnostic_pd, \ notproduct, \ range, \ constraint) \ So this RFE needs to be done after JDK-8243208, which will unify/simplify the parameters to the XXX_FLAGS macros so we always have 7 parameters.

23-08-2020

Blocks :	JDK-8243208 - Clean up JVMFlag implementation
Relates :	JDK-8258459 - Decouple gc_globals.hpp from globals.hpp
Relates :	JDK-8245226 - Clean-up FlagSetting and remove misuse.
Relates :	JDK-8258856 - VM build without C1/C2 fails after JDK-8243205
Relates :	JDK-8258074 - Move some flags related to compiler to compiler_globals.hpp
Relates :	JDK-8236988 - Modular Design for JVM Flags