The language allows the implementation to choose whether the int type and uint types are 32 or 64 bits. Previous Go implementations made int and uint 32 bits on all systems. Both the gc and gccgo implementations (TODO: check that gccgo does) now make int and uint 64 bits on 64-bit platforms such as AMD64/x86-64.
Among other things, this enables the allocation of slices with
more than 2 billion elements on 64-bit platforms.
Updating:
Most programs will be unaffected by this change.
Because Go does not allow implicit conversions between distinct
numeric types,
no programs will stop compiling due to this change.
However, programs that contain implicit assumptions
that int is only 32 bits may change behavior.
For example, this code prints a positive number on 64-bit systems and
a negative one on 32-bit systems:
x := ^uint32(0) // x is 0xffffffff i := int(x) // i is -1 on 32-bit systems, 0xffffffff on 64-bit fmt.Println(i)
Portable code intending 32-bit sign extension (yielding -1 on all systems) would instead say:
i := int(int32(x))
Due to the int and TODO: OTHER changes, the placement of function arguments on the stack has changed. Functions written in assembly will need to be revised at least to adjust frame pointer offsets.