> even though the vast majority of programs are running on a processor that defines exactly what happens with integer overflow, and even sets a flag that can be tested for in a single jump
Widths matter. Platforms that do this don't overflow both 32 and 64 bit signed integers. So if you want to define signed integer overflow for all signed integer widths then for one (or both) of these widths you need to stick in runtime checks.
Widths matter. Platforms that do this don't overflow both 32 and 64 bit signed integers. So if you want to define signed integer overflow for all signed integer widths then for one (or both) of these widths you need to stick in runtime checks.