RFR: 8304893: Link Time Optimization with gcc can be faster [v4]

[Julian Waters]

On Sun, 2 Apr 2023 06:59:02 GMT, Julian Waters <jwaters at openjdk.org> wrote:

>> A previous argument against link time optimization support that we have for gcc is that it was extremely slow. After some checks it turns out we are passing rather inefficient flags to gcc in optimized builds. Changing these flags to run the linker optimizations in parallel and passing additional flags to the compiler have the ability to speed this process up significantly. Also fixes some incorrect flags passed to ld for linking as well, since strict-aliasing is required for both linker and compiler, and the same optimization level should be specified instead of letting the default -O1 be passed to the linker
>
> Julian Waters has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Should auto detect cores as a safer fallback

Ah, sorry about that, I realized at the last moment that the auto option was available just before integration. Will keep that in mind next time

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PR Comment: https://git.openjdk.org/jdk/pull/13180#issuecomment-1494313299