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Re: use of LIKELY() and UNLIKELY() branch predictors

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January 29, 2013 00:50
Re: use of LIKELY() and UNLIKELY() branch predictors
Message ID: wrote:
>Do you know how this facility plays out in the presence of hardware branch

Depends rather on how that influences the translation to uops.  Very
dependent on the microarchitecture, and I'm a generation or two behind
in reading about them.  There's some excellent dynamic branch prediction
in current hardware, but unless it triggers retranslation the static
hints still have a role in putting the right defaults into the uop stream.

>but I really can't tell for sure from the online resources I've found.

Offline, there are some marvellous tomes about specific CPU architectures.
I rather enjoyed "The Complete Pentium 4", concerning the NetBurst
architecture, a work so massive that the last fifteen or so chapters
couldn't fit into a bindable printing and had to be relegated to the
bundled CD.  To get a good appreciation of current hardware one should
probably read up on Core (Intel), K10 (AMD), and anything newer on which
the books have been written yet.


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