Summary:
I think there might be something to optimize in `atomic_store`.
Currently, if everything goes well (and we have a different new value), we
always iterate 3 times.
For example, `with a = 0`, `oldval = a`, `newval = 42`, we get:
```
oldval = 0, newval = 42, curval = 0
oldval = 0, newval = 42, curval = 42
oldval = 42, newval = 42, curval = 42
```
and then it breaks.
Unless I am not seeing something, I don't see a point to the third iteration.
If the current value is the one we want, we should just break.
This means that 2 iterations (with a different newval) should be sufficient to
achieve what we want.
Reviewers: dvyukov, alekseyshl
Reviewed By: dvyukov
Subscribers: kubamracek, delcypher, #sanitizers, llvm-commits
Differential Revision: https://reviews.llvm.org/D46597
llvm-svn: 331890
typename T::Type cur;
for (;;) {
cur = __sync_val_compare_and_swap(&a->val_dont_use, cmp, v);
- if (cmp == v)
+ if (cur == cmp || cur == v)
break;
cmp = cur;
}