RFR: 8370438: Offer link time optimization support on library level

[Matthias Baesken]

On Tue, 4 Nov 2025 13:37:11 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

>>>It would be a little awkward to refactor only the JVM LTO flags into configure flags while leaving the rest of the JVM feature flags set by the Makefile, just my 2 cents.
>> 
>> The part in the Makefile would probably stay, but could reuse common flags from configure, e.g. something like this
>> 
>> 
>>     JVM_LDFLAGS_FEATURES += $(CXX_O_FLAG_HIGHEST_JVM) -flto=auto \
>>         -fuse-linker-plugin -fno-strict-aliasing
>> =>
>>     JVM_LDFLAGS_FEATURES += $(CXX_O_FLAG_HIGHEST_JVM) $(LDFLAGS_LTO)
>
>> > It would be a little awkward to refactor only the JVM LTO flags into configure flags while leaving the rest of the JVM feature flags set by the Makefile, just my 2 cents.
>> 
>> The part in the Makefile would probably stay, but could reuse common flags from configure, e.g. something like this
>> 
>> ```
>>     JVM_LDFLAGS_FEATURES += $(CXX_O_FLAG_HIGHEST_JVM) -flto=auto \
>>         -fuse-linker-plugin -fno-strict-aliasing
>> =>
>>     JVM_LDFLAGS_FEATURES += $(CXX_O_FLAG_HIGHEST_JVM) $(LDFLAGS_LTO)
>> ```
> 
> Yes, please only define the values once and use the variables in the JVM makefile.

@erikj79 thanks for the review !
@mrserb are you fine with the change as it is now ?

@tstuefe maybe you can test it to see if there are issues with your specific toolchain versions at IBM and/or RedHat ?

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PR Comment: https://git.openjdk.org/jdk/pull/27976#issuecomment-3562836140