swift234

Instead of enumerating all the LSValues before RLE is ran on the function. we
enumerate them lazily.

This leads to compilation time improvement, as some of the LSValues previously
enumerated do not be created in this approach.

i.e. we enumerate LSValues created by loads previously, but the LoadInsts could be
target for RLE. In such case, the enumerated LSValues are not used.

Compilation time improvement: 1775ms to 1721ms (2.7% to 2.6% of the entire
compilation time for stdlib -O).

Existing tests ensure correctness.

Note: we still enumerate locations, as we need to know how many locations there are
in the function to resize the bitvector appropriately before the data flow runs.