Codegen: Support memory accesses with different types

Every once in a while we see code that accesses memory with different types,
e.g. to perform operations on a piece of memory using type 'float', but to copy
data to this memory using type 'int'. Modeled in C, such codes look like:

    void foo(float A[], float B[]) {
      for (long i = 0; i < 100; i++)
        *(int *)(&A[i]) = *(int *)(&B[i]);
      for (long i = 0; i < 100; i++)
        A[i] += 10;
    }

We already used the correct types during normal operations, but fall back to our
detected type as soon as we import changed memory access functions. For these
memory accesses we may generate invalid IR due to a mismatch between the element
type of the array we detect and the actual type used in the memory access.  To
address this issue, we always cast the newly created address of a memory access
back to the type of the memory access where the address will be used.

llvm-svn: 248781