Why doesn't GCC optimize structs?

Question

Systems demand that certain primitives be aligned to certain points within the memory (ints to bytes that are multiples of 4, shorts to bytes that are multiples of 2, etc.).

Answer 1

You might want to try the latest gcc trunk or, struct-reorg-branch which is under active development.

https://gcc.gnu.org/wiki/cauldron2015?action=AttachFile&do=view&target=Olga+Golovanevsky_+Memory+Layout+Optimizations+of+Structures+and+Objects.pdf