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Ubuntu Provides More Insight Into Their Decision Not To "-O3" Optimize All Packages
Since last year Canonical had been investigating using -O3 compiler optimizations for their Ubuntu package builds in the name of delivering better performance for Ubuntu Linux
Long story short, with distribution-wide -O3 compiler optimizations they didn't have enough compelling performance benefits to justify the effort. They also found some performance regressions and the -O3 optimizations adversely impacting some load times as well as larger binary sizes in some cases. In addition, in some situations -O3 and Link Time Optimization together can result in excessive function inlining which then in turn regresses performance (presumably through register pressure or instruction cache thrashing).
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