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

[Magnus Ihse Bursie]

On Fri, 10 Jan 2025 10:42:50 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Or maybe LTO is breaking us in some other way (such as taking advantage of no-UB constraints that aren't found
by normal compilation).

That seems definitely likely. With LTO the linker has a whole lot of room to try many exciting optimizations. I think it is more than likely that this can trigger some UB holes.

The question is: should we decouple "fixing LTO build" from "fixing a working LTO JVM"? I tend to think so; that the problem for the build system is to be able to build the product, and if it then crashes during use, it's the problem of the component owners instead. OTOH, this fix is relatively trivial, and if the JVM is DOA so we can't even finish the build, then maybe it makes no point to integrate it until that is fixed.

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PR Comment: https://git.openjdk.org/jdk/pull/22464#issuecomment-2582678823