RFR: 8370438: Offer link time optimization support on library level [v5]

[Matthias Baesken]

On Thu, 6 Nov 2025 13:53:07 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

>>> I don't think adding the LTO flags to the OPT flags is the right move
>> 
>> So where should I move it? After all it is link time *optimization* so it is an optimization related tool feature. 
>> But should I remove it completely from SetupCompileFileFlags because having it in  SetupCompilerFlags is sufficient for out task ?
>
> Again, the optimization flags aren't handled as a separate set of variables because they are of the category "optimization". It's because optimization flags are handled on a higher level with an abstraction of "low", "medium", "high" etc, and that abstraction allows for specific file overrides. That's what the `*_OPT_C*FLAGS` are there to handle. Since the LTO flags are not related to this abstraction, they should not be mixed into these variables, that is just confusing and adding unnecessary complexity.
> 
> The LTO flags should just be stacked on to the `$1_EXTRA_*` flags like any other.

I adjusted my changes to Flags.gmk .

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PR Review Comment: https://git.openjdk.org/jdk/pull/27976#discussion_r2504024684