[llvm] [SDAG] More accurate approximation in DemandedBits (PR #171266)

[via llvm-commits]

natanelh-mobileye wrote:

seems like it is impossible to test.
it seems like this is not relevant for any backend in the open source, since the only one that specialized this overload is RISCV and only for vector types, which, coincidentally, are not supported by this function.

https://github.com/llvm/llvm-project/pull/171266