[ADT] Add llvm::countr_zero_constexpr (#164188)

This patch implements llvm::countr_zero_constexpr, a constexpr version
of llvm::countr_zero, in terms of llvm::popcount while making
llvm::popcount a constexpr function at the same time.

The new function is intended to serve as a marker.  When we switch to
C++20, we will most likely go through functions in llvm/ADT/bit.h and
replace them with their counterparts from <bit>.  With
llvm::countr_zero_constexpr, we can easily replace its use with
std::countr_zero.

This patch reimplements ConstantLog2 in terms of the new function.

0 files changed, 0 insertions, 0 deletions