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

[Kim Barrett]

On 10/8/25 8:06 AM, Julian Waters wrote:
>> Paging with the mailing list bridge to restart discussion, which I need in order to be able to continue working on this

As I've said before, we (Oracle) think LTO support is a substantial project,
we haven't made it a priority, and nobody here has offered up time to work on
it. Someone else might have time for this; we don't seem to. That might change
in the future, but for now...

Some of the issues that make it a substantial project include:

The LTO vs flattening problem.

There are functions that assume (or even rely upon) implicit noinline via
being in a different translation unit from callers. I think that's probably a
much harder problem to resolve, since it's generally not obvious. Functions
that do things like getting the current stack pointer or frame pointer may be
relevant? Not sure what else.

Build time issues, and their impact on development time and testing resources.

Is LTO an alternative mode, different from how things are "normally" done?
That increases testing resource requirements, else it will bit rot.

There might be others that I'm not remembering or I'm completely unaware of.