"David S. Miller" <[email protected]> writes:
> From: Alexey Dobriyan <[email protected]>
> Date: Sat, 27 Aug 2005 02:58:48 +0400
>
> > What's the point of having unlikely() attached to every possible if ()?
>
> If can result in smaller code, for one thing, even if it
> isn't a performance critical path.
Really? At least on x86 it tends to generate bigger code when
block reordering is enabled because a jump forward and a jump
backward and a possible label alignment are bigger than just
a single jump forward. But then it doesn't make that much difference
because the compiler does it on its own for every block.
On x86-64 I keep it disabled because:
- it generates bigger code
- it makes the assembly code unreadable
- it doesn't seem to help that much on modern CPUs with good
branch prediction and big icaches anyways.
-Andi (who originally introduced likely/unlikely, but regrets it these
days because it's far overused and makes code uglier everywhere)
-
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