Have gen* methods use the optimized BitOperations where possible #81697
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The only real change here is that:
BitOperations::BitScanReverse
doesn't require an "out" parameter, it just directly asserts "not zero"BitOperations::BitScanForward
is the same, which means it can use__builtin_ctz
on Unix, leading to better codegengenCountBits
uses__builtin_popcount
on Clang/GCC and the well-known bit twiddling hacks on MSVC (which is what Clang/GCC use for their builtin).The other functions are just being made consistent and forwarding to a centralized impl. In a couple places comments were added to clarify edge case behavior that a given
gen*
method was assuming (e.g.genLog2
is not a reallog2
, but rather assumes the input has exactly one bit set).