Code generation for load/store packed data

Hello,

I am very interested in to know how compilers generate optimized code
for loading or storing data at unaligned memory locations and that
located inside bitfields (i. e., like that generated by using GNU C
"packed attribute" or packed ANSI C bitfield type definitions).

I suppose that is a well-known subject that was solved by somebody a
long time ago. Do you know some well-known technique or literature
about that subject? I would appreciate some pointers.

Thanks in advance!