That's because y is never used, so why should the pointer be dereferenced? If you call bar(y) instead of just bar(), "x86-64 clang 3.9.1" with -O3 does the load as well (but after the check)

    foo(int*):                               # @foo(int*)
        test    rdi, rdi
        je      .LBB0_1
        mov     edi, dword ptr [rdi]
        jmp     bar(int)                 # TAILCALL
    .LBB0_1:
        ret

Only GCC does the kind of aggressive optimization the article mentions (and might need to be tamed by -fno-delete-null-pointer-checks).