Null pointer can be constructed and dereferenced in safe code

[justinas]

Describe the bug

V allows constructing and dereferencing null pointers in safe code. This results in undefined behavior using the C backend.

Reproduction Steps

fn main() {
    bar := &int(0)
    println(*bar)
}

Expected Behavior

&T(nil) is already illegal, so I would expect V to give a compile time error when using &T(0) as well.

In fact, in safe code casting an arbitrary number to a pointer should probably never be allowed.

Current Behavior

$ v -cflags '-fsanitize=undefined' cast.v
$ ./cast
/run/user/1000/v_1000/cast.1175514313447606659.tmp.c:12702:2: runtime error: load of null pointer of type 'int'
signal 11: segmentation fault
                                                        |       0x4058b9 | ./cast()
                                                        | 0x7fc553a3ffce | /nix/store/qn3ggz5sf3hkjs2c797xf7nan3amdxmp-glibc-2.38-27/lib/libc.so.6(+0x27fce)
                                                        | 0x7fc553a40089 | /nix/store/qn3ggz5sf3hkjs2c797xf7nan3amdxmp-glibc-2.38-27/lib/libc.so.6(__libc_start_main+0x89)
                                                        |       0x4058f5 | ./cast()

Possible Solution

No response

Additional Information/Context

No response

V version

V 0.4.4 ac2dcc2

Environment details (OS name and version, etc.)

NixOS 23.11 (Tapir)
gcc (GCC) 12.3.0

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