[webkit-dev] Time to remove LIKELY and UNLIKELY macros?

Adam Barth abarth at webkit.org
Mon Oct 1 22:55:21 PDT 2012

According to <http://stackoverflow.com/questions/1851299/is-it-possible-to-tell-the-branch-predictor-how-likely-it-is-to-follow-the-branc>,
__builtin_expect (what our LIKELY and UNLIKELY macros expand to [1])
doesn't do anything on modern CPUs.  Apparently, these used to be
important for PowerPC, but I don't think many folks use WebKit on
PowerPC anymore.

Should we remove these macros?  I wasted some time today experimenting
with them without realizing that they compile to no-ops in clang.


[1] http://trac.webkit.org/browser/trunk/Source/WTF/wtf/Compiler.h#L188

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