[clang] [CIR][X86] Implement lowering for `readwritebarrier` builtins (PR #171094)

[Sirui Mu via cfe-commits]

================
@@ -1523,13 +1523,37 @@ mlir::Value CIRGenFunction::emitX86BuiltinExpr(unsigned builtinID,
   case X86::BI__mulh:
   case X86::BI__umulh:
   case X86::BI_mul128:
-  case X86::BI_umul128:
-  case X86::BI__faststorefence:
+  case X86::BI_umul128: {
+    cgm.errorNYI(expr->getSourceRange(),
+                 std::string("unimplemented X86 builtin call: ") +
+                     getContext().BuiltinInfo.getName(builtinID));
+    return std::nullopt;
+  }
+  case X86::BI__faststorefence: {
+    cir::AtomicFenceOp::create(
+        builder, getLoc(expr->getExprLoc()),
+        cir::MemOrder::SequentiallyConsistent,
+        cir::SyncScopeKindAttr::get(&getMLIRContext(),
+                                    cir::SyncScopeKind::System));
+    return mlir::Value{};
+  }
   case X86::BI__shiftleft128:
-  case X86::BI__shiftright128:
+  case X86::BI__shiftright128: {
+    cgm.errorNYI(expr->getSourceRange(),
+                 std::string("unimplemented X86 builtin call: ") +
+                     getContext().BuiltinInfo.getName(builtinID));
+    return std::nullopt;
+  }
   case X86::BI_ReadWriteBarrier:
   case X86::BI_ReadBarrier:
-  case X86::BI_WriteBarrier:
+  case X86::BI_WriteBarrier: {
+    cir::AtomicFenceOp::create(
+        builder, getLoc(expr->getExprLoc()),
+        cir::MemOrder::SequentiallyConsistent,
+        cir::SyncScopeKindAttr::get(&getMLIRContext(),
+                                    cir::SyncScopeKind::SingleThread));
+    return mlir::Value{};
----------------
Lancern wrote:

```suggestion
    return {};
```

https://github.com/llvm/llvm-project/pull/171094