9mo ago

Ubuntu 25.04 "Plucky Puffin" Development Opens - Defaulting To -O3 Optimizations

Just a moment...

14 comments

Gentoo users in shambles
- Bah, they'll never have my precious -march=native!
  
  I doubt they want my fun and safe math optimizations either tbh
- too fancy for -O2? lol
How do they avoid the subsequent bugs O3 tends to produce?
- They don't.
- First time I'm hearing of this. Do you have some more details?
  
  It's complicated.
op-ti-mize [verb (trans.)]* … (gcc) to modify executable code so that it fails more quickly.
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.
  
  Yeah, adding a separate microarchitecture like amd64v3 would be a separate item. They might be able to do that with amd64v3 overlay repos that only contain packages that most benefit from the newer microarchitecture.

14 comments