The spec on return mentions that:
"At least one return statement, throw statement, or assert(0) expression is required if the function specifies a return type that is not void. "

However, in the inline asm docs the following example is there:

int foo(int x)
{
    asm
    {
	mov EAX,x[EBP]	;  // loads value of parameter x into EAX
	mov EAX,x	;  // does the same thing
    }
}


And DMD indeed allows inline asm to specify the return value, we've even had to take the time to emulate this undocumented behaviour in LDC. It should be in the spec, or there should be an assert(0) inserted after the inline asm!