To nitpick, compilers nor linkers typically are not able to do "binary optimization", if by that you mean analyzing the asm and optimizing that. What happens wh

To nitpick, compilers nor linkers typically are not able to do "binary optimization", if by that you mean analyzing the asm and optimizing that. What happens when you compile with -flto or equivalent is that the compiler hides some internal representation in a special section in the object files, then at the link stage (if you also use -flto when linking) is that the linker invokes the compiler again which deserializes those trees from the object files, and does the inter-procedural optimizations on those.