-fprofile-generate and -fprofile-use

[Zdenek Dvorak]

Hello,

> >A more likely source of performance degradation is that loop unrolling
> >is enabled when profiling, and loop unrolling is almost always a bad
> >pessimization on 32 bits x86 targets.
> 
> To clarify, I was compiling with -funroll-loops and -fpeel-loops
> enabled in both cases.
> 
> The FDO slowdown in my case was caused by the presence of some loop
> invariant code that was getting removed from the loop by the loop
> optimizer pass in the non-FDO case.

you may try adding -fmove-loop-invariants flag, which enables new
invariant motion pass.

Zdenek