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DateWed, 16 Jan 2002 17:00:14 +1100
FromAnton Blanchard <>
SubjectRe: likely/unlikely
Digg This

likely/unlikely set the branch prediction values to 99% or 1% respectively. If this causes the code generated to perform less optimally than without, I'm sure the gcc guys would be -very- interested to hear that...

On some ppc64 the branch prediction is quite good and static prediction will override the dynamic prediction. I think we avoid predicting a branch unless we are quite sure (95%/5%).

So if likely/unlikely is overused (on more marginal conditionals) then it could be a performance loss.

Anton
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