Allow arrays in build_gep

[Ianyourgod]

Recently I was writing a little compiler and was trying to add array support. While trying to implement subscripting & pointer arithmetic, though, I noticed that build_gep only took the pointer type, even though it's something you kinda need with arrays too.

Could build_gep either have another version for arrays or just allow the original function to take arrays?

[nickk-dv]

build_gep (specifically its modern untyped pointer version) uses "LLVMBuildGEP2" in which important parameters are pointee type, and pointer_value, its meant to only work with pointer values. Array values are semantically "temporary ssa" values, thus they cannot be used as a pointer value.

@Ianyourgod to implement indexing of arrays you pass the pointer value of stack allocated memory or global variable, then you use the array type of that variable as pointee type, and indices are [0, <index_value>].
Here are docs that explain the semantics and why indices are like that: llvm_gep_docs.

[Ianyourgod]

Ah, alright. Thank you!