modernize-use-std-bit

Finds common idioms which can be replaced by standard functions from the <bit> C++20 header.

Covered scenarios:

Expression	Replacement
x && !(x & (x - 1))	std::has_one_bit(x)
(x != 0) && !(x & (x - 1))	std::has_one_bit(x)
(x > 0) && !(x & (x - 1))	std::has_one_bit(x)
std::bitset<N>(x).count()	std::popcount(x)
x << 3 | x >> 61	std::rotl(x, 3)
x << 61 | x >> 3	std::rotr(x, 3)

Options

HonorIntPromotion

When set to true (default is false), insert explicit cast to make sure the type of the substituted expression is unchanged. Example:

// Return type is deduced as 'int' (not 'unsigned char') due to implicit conversions.
auto foo(unsigned char x) {
  return x << 3 | x >> 5;
}

Becomes:

#include <bit>

auto foo(unsigned char x) {
  return static_cast<int>(std::rotl(x, 3));
}