Comment by leiroigh

The main problem with that is that it doesn't play nice with most languages. Consider

  int foo(int* ptr) {
    int x = ptr[1<<16];
    *ptr += 1;
    return x + ptr[1<<16];
  }

Compilers/languages/specs tend to decide that `ptr` and `ptr + (1<<16)` cannot alias, and this can be compiled into e.g.

  foo(int*):
        mov     eax, dword ptr [rdi + 262144]
        inc     dword ptr [rdi]
        add     eax, eax
        ret

which gives undesired results if `ptr` and `ptr + (1<<16)` happen to be mapped to the same physical address. This is also pretty shit to debug/test -- some day, somebody will enable LTO for an easy performance win on release builds, and bad code with a security vuln gets shipped.