Because the code should be somewhat portable, and not all processors act the same. This is why left and right shift are weird with overflow. Not consistent betw

Because the code should be somewhat portable, and not all processors act the same. This is why left and right shift are weird with overflow. Not consistent between x86 and some other instruction set. Similar for accessing the null address. Besides that, how would you specify the behavior of reading from an address the user randomly generated himself? What is stored at an address not generated by the compiler is out of scope for the compiler. If you try to define something like 'always trap' or 'always return 0', you incur massive overhead. Besides that. The fact that signed integer over/underflow is undefined behavior actually unlocks a lot of reasonable optimizations that treat integers like actual integers. Things like (a+1 > a) always being true.