An array's length is at most 2^32 - 1 (the runtime's SCR_ARR_MAX_LENGTH).
On 64-bit targets the length loads now carry that range (`!range`), so
LLVM folds a length converted to double and back to an integer, and
simplifies the comparisons that use it. A length stored into an int32
local or used as an index no longer goes through double: tsc-ts has 18%
fewer int/double conversion instructions.
Chris Tate
2bb7e7ec7a