[llvm] [IR] Add Instruction::maySynchronize() method (NFC) (PR #196052)

[Antonio Frighetto via llvm-commits]

================
@@ -1933,46 +1933,15 @@ static bool InstrBreaksNoFree(Instruction &I, const SCCNodeSet &SCCNodes) {
   return true;
 }
 
-// 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.
-static bool isOrderedAtomic(Instruction *I) {
-  if (!I->isAtomic())
-    return false;
-
-  if (auto *FI = dyn_cast<FenceInst>(I))
-    // All legal orderings for fence are stronger than monotonic.
-    return FI->getSyncScopeID() != SyncScope::SingleThread;
-  else if (isa<AtomicCmpXchgInst>(I) || isa<AtomicRMWInst>(I))
-    return true;
-  else if (auto *SI = dyn_cast<StoreInst>(I))
-    return !SI->isUnordered();
-  else if (auto *LI = dyn_cast<LoadInst>(I))
-    return !LI->isUnordered();
-  else {
-    llvm_unreachable("unknown atomic instruction?");
-  }
-}
-
 static bool InstrBreaksNoSync(Instruction &I, const SCCNodeSet &SCCNodes) {
-  // An ordered atomic may synchronize.  (See comment about on monotonic.)
-  if (isOrderedAtomic(&I))
-    return true;
-
-  auto *CB = dyn_cast<CallBase>(&I);
-  if (!CB)
-    // Non call site cases covered by the two checks above
+  if (!I.maySynchronize())
     return false;
 
-  if (CB->hasFnAttr(Attribute::NoSync))
-    return false;
-
-  // Speculatively assume in SCC.
-  if (Function *Callee = CB->getCalledFunction())
-    if (SCCNodes.contains(Callee))
-      return false;
+  // Speculatively assume nosync in SCC.
----------------
antoniofrighetto wrote:

While at it, could the previous comment use an update? (The intent would be to remind we're trying to find a reason to disqualify...)

```suggestion
  // Optimistically assume calls within the SCC are nosync: if nothing else
  // in the SCC synchronizes, the assumption holds.
```

https://github.com/llvm/llvm-project/pull/196052