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Gentoo users in shambles
this post was submitted on 30 Oct 2024
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Jokes on you, my system is (mostly) -O3
Bah, they'll never have my precious -march=native!
Not like Ubuntu works very well on old hardware but hopefully O2 support will still be there. Many people need it.
-O2 vs -O3 adds
-fgcse-after-reload -fipa-cp-clone -floop-interchange -floop-unroll-and-jam -fpeel-loops -fpredictive-commoning -fsplit-loops -fsplit-paths -ftree-loop-distribution -ftree-partial-pre -funswitch-loops -fvect-cost-model=dynamic -fversion-loops-for-strides
I don't think any of these optimizations require more modern hardware?
Right. GCC -f optimizations are basically like "how hard are we going to try to be clever" and are, I believe, orthogonal to the actual instructions used. Machine dependent args start with -m, like -march or -mavx etc.
I was reasonably certain, but left it open in case OP knew of some edge case where flags that are intended to be machine independent caused bugs on different architectures
How do they avoid the subsequent bugs O3 tends to produce?
They don't.