[clang] [Clang] Add support for scoped atomic thread fence (PR #115545)

[Matt Arsenault via cfe-commits]

================
@@ -5133,6 +5133,132 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
     Builder.SetInsertPoint(ContBB);
     return RValue::get(nullptr);
   }
+  case Builtin::BI__scoped_atomic_thread_fence: {
+    auto ScopeModel = AtomicScopeModel::create(AtomicScopeModelKind::Generic);
+
+    Value *Order = EmitScalarExpr(E->getArg(0));
+    Value *Scope = EmitScalarExpr(E->getArg(1));
+    if (isa<llvm::ConstantInt>(Order) && isa<llvm::ConstantInt>(Scope)) {
+      int Ord = cast<llvm::ConstantInt>(Order)->getZExtValue();
+      int Scp = cast<llvm::ConstantInt>(Scope)->getZExtValue();
+      SyncScope SS = ScopeModel->isValid(Scp)
+                         ? ScopeModel->map(Scp)
+                         : ScopeModel->map(ScopeModel->getFallBackValue());
+      switch (Ord) {
+      case 0:  // memory_order_relaxed
+      default: // invalid order
+        break;
+      case 1: // memory_order_consume
+      case 2: // memory_order_acquire
+        Builder.CreateFence(
+            llvm::AtomicOrdering::Acquire,
+            getTargetHooks().getLLVMSyncScopeID(getLangOpts(), SS,
+                                                llvm::AtomicOrdering::Acquire,
+                                                getLLVMContext()));
+        break;
+      case 3: // memory_order_release
+        Builder.CreateFence(
+            llvm::AtomicOrdering::Release,
+            getTargetHooks().getLLVMSyncScopeID(getLangOpts(), SS,
+                                                llvm::AtomicOrdering::Release,
+                                                getLLVMContext()));
+        break;
+      case 4: // memory_order_acq_rel
+        Builder.CreateFence(llvm::AtomicOrdering::AcquireRelease,
+                            getTargetHooks().getLLVMSyncScopeID(
+                                getLangOpts(), SS,
+                                llvm::AtomicOrdering::AcquireRelease,
+                                getLLVMContext()));
+        break;
+      case 5: // memory_order_seq_cst
+        Builder.CreateFence(llvm::AtomicOrdering::SequentiallyConsistent,
+                            getTargetHooks().getLLVMSyncScopeID(
+                                getLangOpts(), SS,
+                                llvm::AtomicOrdering::SequentiallyConsistent,
+                                getLLVMContext()));
+        break;
+      }
+      return RValue::get(nullptr);
+    }
+
+    llvm::BasicBlock *ContBB = createBasicBlock("atomic.scope.continue", CurFn);
+
+    llvm::DenseMap<llvm::BasicBlock *, llvm::AtomicOrdering> OrderBBs;
----------------
arsenm wrote:

I don't see why this needs to be a map 

https://github.com/llvm/llvm-project/pull/115545