Dear GCC development team, We've been trying to build reproducibly the minimal NixOS image, and gcc was one of the last issues we had. We found that disabling profiled bootstrap compilation of GCC allowed us to get a reproducible build of gcc. Our efforts can be followed here: https://github.com/NixOS/nixpkgs/pull/112928
But I measured disabling this optimization to cost around 7-12% depending on the build. Because of this performance regression, we're trying to find a middle ground. Ideally we'd like to keep the performance of gcc as untouched as possible (even if that costs us on compilation time of gcc itself). Compiling gcc twice on the same machine gets us the same output, but compiling on a different architecture gets us a different result. Reading the documentation, it would seem that autoprofiledback bootstrap would use machine metrics and injects them in the build (and we don't use autoprofiledback), But I would not expect the stagetrain of profiledbootstrap to do that. I tried disabling concurrency of the stagetrain without luck. It feels like I'm missing something. Would anyone have any idea what could inject the host's behavior here? Thank you for your help! Best, -- Arthur
