tree a14d3bdc1416dc3db74983d34a408a8b48cbce9c
parent 6aadaef35ea52506db61e463910c2520b702ca5e
author Aart Bik <ajcbik@google.com> 1452897312 -0800
committer Aart Bik <ajcbik@google.com> 1453349640 -0800

Implemented BitCount as an intrinsic. With unit test.

Rationale:
Recognizing this important operation as an intrinsic has
various advantages:
(1) having the no-side-effects/no-throw allows for
    much more GVN/LICM/BCE.
(2) Some architectures, like x86_64, provide direct
    support for this operation.

Performance improvements on X86_64:
CheckersEvalBench (32-bit bitboard): 27,210KNS -> 36,798KNS  =  + 35%
ReversiEvalBench  (64-bit bitboard): 52,562KNS -> 89,086KNS  =  + 69%

Change-Id: I65d549b0469b7909b12c6611cdc34a8640a5751f