If I create an LLVM array as
%a = alloca [3 x i32]
and want to assign a value to the first element in the array, how do I do that? Do I have to recreate the array with that value in place somehow? I want to use pure LLVM code and not the LLVM API.
First you need to get the pointer to the first element using the getelementptr instruction, which you then use to store your value:
%p = getelementptr [3 x i32], [3 x i32]* %a, i32 0, i32 0
store i32 4, i32* %p
This stores the value 4 in the first element. To store in a different index, you change the last integer to the index you need:
%p = getelementptr [3 x i32], [3 x i32]* %a, i32 0, i32 2
store i32 4, i32* %p
This one stores 4 in index 2.