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Re: [PATCH] Take branch misprediction effects into account when RTL loop unrolling (issue6099055)
> Tree level unrollers (cunrolli and cunroll) do complete unroll. At O2,
> both of them are turned on, but gcc does not allow any code growth --
> which makes them pretty useless at O2 (very few loops qualify). The
> default max complete peel iteration is also too low compared with both
> icc and llvm. This needs to be tuned.
I found that at -O3 (where tree unroll is on by default) there is quite a
bit of useless unrolling. I got somewhat irritated that my printf debug loops
were commonly unrolled.