[PATCH] Add new built-in: __builtin_unreachable()

[Paolo Bonzini]

>> Could you explain why it is allowed to remove the trapping instruction?
>>
>> If this were java (which admittedly it is not), that would not be 
>> allowed.

Because of -fdelete-null-pointer-checks.  Without non-call exceptions, 
*f does not throw an exception but still the compiler is allowed to 
assume its address is not null in anything that postdominates it. 
Admittedly this case is a bit borderline.

Paolo