Build options (security, performance...) are defined at the distribution level (and changes happen on each new version)

I don't think changing this will have a huge performance improvment (> ~1%) without also rebuilding all libraries, and most of the system (kernel, glibc...)
I remember a project doing this >15 years ago...for 32-bit... and they gave up (too much work for too low benefit)

PGO is interesting but requires profiling (and huge build time), so it will result in a build optimized for some app, not for everything

> If not, do you offer any way to download SRPMS for a PHP version so that we can implement those changes in our own builds?

Everything is OpenSource and available on the web site (see repository main page)

> Possible that I'm just looking in the wrong place but if you happen to know where I'd find those and can direct me

As I said, see the repository main page, and the last link at the bottom.

Many thanks for the clarifying this issue Remi.

I've considered this exact issue many times over the years and have often been amazed that people with so much more experience than me have come to the conclusion that recompiling for a specific architecture nets so little benefit. Especially when considering there has been over 25 years of CPU instruction extensions to consider. (I'm old enough to remember mucking about with AMD's 3Dnow! extensions in assembler)

Do you have any idea which libraries would net the most benefit for machine specific optimization, and if so how much benefit is had?

Many thanks for an amazing repo.