RFR: 8345265: Minor improvements for LTO across all compilers [v2]

[Matthias Baesken]

On Tue, 17 Dec 2024 14:54:03 GMT, Julian Waters <jwaters at openjdk.org> wrote:

>> This is a general cleanup and improvement of LTO, as well as a quick fix to remove a workaround in the Makefiles that disabled LTO for g1ParScanThreadState.cpp due to the old poisoning mechanism causing trouble. The -Wno-attribute-warning change here can be removed once Kim's new poisoning solution is integrated.
>> 
>> - -fno-omit-frame-pointer is added to gcc to stop the linker from emitting code without the frame pointer
>> - -flto is set to $(JOBS) instead of auto to better match what the user requested
>> - -Gy is passed to the Microsoft compiler. This does not fully fix LTO under Microsoft, but prevents warnings about -LTCG:INCREMENTAL at least
>
> Julian Waters has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 12 additional commits since the last revision:
> 
>  - Merge branch 'openjdk:master' into patch-16
>  - -fno-omit-frame-pointer in JvmFeatures.gmk
>  - Revert compilerWarnings_gcc.hpp
>  - General LTO fixes JvmFeatures.gmk
>  - Revert DISABLE_POISONING_STOPGAP compilerWarnings_gcc.hpp
>  - Merge branch 'openjdk:master' into patch-16
>  - Revert os.cpp
>  - Fix memory leak in jvmciEnv.cpp
>  - Stopgap fix in os.cpp
>  - Declaration fix in compilerWarnings_gcc.hpp
>  - ... and 2 more: https://git.openjdk.org/jdk/compare/86057873...9d05cb8e

For Linux x86_64 / gcc 13 here are the sizes of the libs and debuginfos before (without) and WITH lto enabled on LIB level 

libfontmanager.debuginfo   54155720  =>  38059440
libfontmanager.so          1874776   =>  1194264
libfreetype.debuginfo      4143416   =>  3761080
libfreetype.so             742472    =>  778024


For the debug info one can see a good effect ;  but not always the lib size decreases, for libfreetype.so  it increases slightly.

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

PR Comment: https://git.openjdk.org/jdk/pull/22464#issuecomment-3443073093