Cast pointer instead of value when loading array/tuple lengths?

[ArchRobison]

Julia currently loads array lengths by loading a pointer and casting the loaded value to an int. E.g.:

  %3 = load %jl_value_t** %2, align 8, !dbg !160, !tbaa %jtbaa_arraylen
  %4 = ptrtoint %jl_value_t* %3 to i64, !dbg !160

In somewhat similar situations, Clang casts the pointer and then does the load. There's probably no net difference for now, but I see that LLVM trunk has range metadata that can be used to indicate the ranges of integers, such as an array length, which can enable it to eliminate unnecessary checks in some cases. (I'm investigating one for a common @simd use case.) Is there any reason for the Julia instruction sequence other than it was slightly simpler to implement?

[JeffBezanson]

I think this change would be good. Casting the pointer type first makes more sense to me. If somebody gets to it before I do, I'll merge it :)

[ArchRobison]

I'll take a stab at it since I need to do it anyway to play with the range metadata.