...
Counterexample. The following code is meant to atomically remove the head item from a linked list and return the pointer the item. The output argument "tmp" is not marked early-clobber with "&" so the compiler is in principle free to reuse the register used for the input "&_head". In one case the compiler used r0 for both ("%2" and "%1"). Note also that in this case "%2" may be used more than once if we have to loop, making it especially important to never to change it.
| Code Block |
|---|
Flink<T>* head;
Flink<T>* tmp;
asm volatile ("1:;"
"lwarx %0,0,%2;"
"lwzx %1,0,(%0);"
"stwcx. %1,0,%2;"
"bne- 1b;"
: "=&r" (head), "=r" (tmp) : "r" (&_head) : "cc", "memory");
return static_cast<T*>(head);
|
...