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

[Julian Waters]

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/3f725101...9d05cb8e

> Member

Fixing the JVM under LTO is likely to be a heavy undertaking, much more so than just unbreaking compilation and linking of the JVM (Ignoring that the JVM later crashes when the newly compiled JDK is used to build parts of itself), I'm not sure it would be feasible under the current Pull Request

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PR Comment: https://git.openjdk.org/jdk/pull/22464#issuecomment-2597685300