The compiler can't see inside functions in the general case (because they're opaque binary blobs in a library that hasn't been linked yet), so no. It's limited to optimizing stuff it can "see", which broadly means the current function and anything inlinable into it.

But yes, if all your functions are marked inline and visible to the compiler, there's no theoretical limit to GCC's ability to hoist constants out of the innermost parts of the loop. In practice, there are surely some performance limits to how much inlining will be expanded.