[llvm] [LLVM] Add a C API for creating instructions with custom syncscopes. (PR #104775)

[Nikita Popov via llvm-commits]

================
@@ -4336,34 +4368,33 @@ int LLVMGetMaskValue(LLVMValueRef SVInst, unsigned Elt) {
 
 int LLVMGetUndefMaskElem(void) { return PoisonMaskElem; }
 
-LLVMBool LLVMIsAtomicSingleThread(LLVMValueRef AtomicInst) {
-  Value *P = unwrap(AtomicInst);
+LLVMBool LLVMIsAtomic(LLVMValueRef Inst) {
+  return unwrap<Instruction>(Inst)->isAtomic();
+}
 
-  if (AtomicRMWInst *I = dyn_cast<AtomicRMWInst>(P))
-    return I->getSyncScopeID() == SyncScope::SingleThread;
-  else if (FenceInst *FI = dyn_cast<FenceInst>(P))
-    return FI->getSyncScopeID() == SyncScope::SingleThread;
-  else if (StoreInst *SI = dyn_cast<StoreInst>(P))
-    return SI->getSyncScopeID() == SyncScope::SingleThread;
-  else if (LoadInst *LI = dyn_cast<LoadInst>(P))
-    return LI->getSyncScopeID() == SyncScope::SingleThread;
-  return cast<AtomicCmpXchgInst>(P)->getSyncScopeID() ==
-             SyncScope::SingleThread;
+LLVMBool LLVMIsAtomicSingleThread(LLVMValueRef AtomicInst) {
+  // Backwards compatibility: return false for non-atomic instructions
+  Instruction *I = unwrap<Instruction>(AtomicInst);
+  if (!I->isAtomic())
+    return 0;
+  return getAtomicSyncScopeID(I).value() == SyncScope::SingleThread;
----------------
nikic wrote:

```suggestion
  return *getAtomicSyncScopeID(I) == SyncScope::SingleThread;
```

https://github.com/llvm/llvm-project/pull/104775