[llvm] [ValueTracking] Conservative nosync check prevents vectorization (PR #181345)

[Florian Hahn via llvm-commits]

================
@@ -821,6 +821,13 @@ inline bool isGuaranteedNotToBePoison(const Value *V, AssumptionCache *AC,
   return isGuaranteedNotToBePoison(V, AC, &*CtxI, DT, Depth);
 }
 
+// Return true if this is an atomic which has an ordering stronger than
+// unordered.  Note that this is different than the predicate we use in
+// Attributor.  Here we chose to be conservative and consider monotonic
+// operations potentially synchronizing.  We generally don't do much with
+// monotonic operations, so this is simply risk reduction.
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fhahn wrote:

```suggestion
/// Returns true if this is an atomic which has an ordering stronger than
/// unordered.
```

Not sure if we need to reference attributor here?

https://github.com/llvm/llvm-project/pull/181345