CODEWITHSUNDEEP
c++performanceoptimizationconditional-statementsx86-64
Palace Chan
Palace Chan

Reputation: 9183

Any way to handle "predictable branches" faster?

I have some code in which there are two or three branches which you don't know what way they will go, but after the first time they are hit, it is either 100% certain, or close to that, that the same path will happen again. I have noticed that use of the __builtin_likely doesn't do much in terms of avoiding branch misses. And even though branch prediction does a good job when my function is called repeatedly in a short time span..as soon as there is other stuff going on between calls to my function, performance degrades substantially. What are some ways around this or some techniques I can look into? Any way to somehow "tag" these branches for when they are reached again after some vagrancy?

Upvotes: 3

Views: 253

Answers (2)

Ben Voigt
Ben Voigt

Reputation: 283624

You could use templates to generate a different version of the function for each code path, then use a function pointer to select one at runtime when you find out which way the condition goes.

Upvotes: 3

Puppy
Puppy

Reputation: 146910

The branch predictor and compiler intrinsics are all you've got. At best, you can look at the assembly and try to hand-roll some optimization yourself, but you won't find much.

Upvotes: 1

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