[clang] [llvm] [AArch64] Implement the atomic store with hint intrinsic (PR #198316)

[Kerry McLaughlin via cfe-commits]

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@@ -2065,6 +2066,60 @@ static Value *EmitRangePrefetchBuiltin(CodeGenFunction &CGF, unsigned BuiltinID,
                             Ops);
 }
 
+static Value *EmitAtomicStoreWithHintBuiltin(CodeGenFunction &CGF,
+                                             unsigned BuiltinID,
+                                             const CallExpr *E) {
+  CodeGen::CGBuilderTy &Builder = CGF.Builder;
+  CodeGen::CodeGenModule &CGM = CGF.CGM;
+  Expr::EvalResult Result;
+  if (!E->getArg(2)->EvaluateAsInt(Result, CGM.getContext()))
+    llvm_unreachable(
+        "Expected integer policy argument to atomic store with hint.");
+
+  StoreInst *Store =
+      Builder.CreateStore(CGF.EmitScalarExpr(E->getArg(1)),            // Value
+                          CGF.EmitPointerWithAlignment(E->getArg(0))); // Ptr;
+
+  AtomicOrdering Ordering;
+  unsigned OrderingArg = Result.Val.getInt().getExtValue();
+  assert(isValidAtomicOrderingCABI(OrderingArg) && "Invalid atomic ordering");
+
+  switch (static_cast<AtomicOrderingCABI>(OrderingArg)) {
+  default:
+    llvm_unreachable("Unsupported atomic ordering found.");
+  case AtomicOrderingCABI::relaxed:
+    Ordering = AtomicOrdering::Monotonic;
+    break;
+  case AtomicOrderingCABI::release:
+    Ordering = AtomicOrdering::Release;
+    break;
+  case AtomicOrderingCABI::seq_cst:
+    Ordering = AtomicOrdering::SequentiallyConsistent;
+    break;
+  }
+  Store->setAtomic(Ordering);
+
+  if (!E->getArg(3)->EvaluateAsInt(Result, CGM.getContext()))
+    llvm_unreachable(
+        "Expected integer hint argument to atomic store with hint.");
+  unsigned HintArg = Result.Val.getInt().getExtValue();
+
+  // Attach the hint if valid
+  if (getAtomicStoreHintFromMD(HintArg) != AArch64AtomicStoreHint::HINT_NONE) {
+    LLVMContext &Ctx = CGM.getLLVMContext();
+    MDNode *AtomicHint = MDNode::get(
+        Ctx, {MDString::get(Ctx, "aarch64.atomic_hint"),
----------------
kmclaughlin-arm wrote:

I've renamed this to the more generic `aarch64.mem_hint`, and renamed `AArch64AtomicHints` to `AArch64MemoryHints`. I also don't think there is a reason to add different groups, although in future we may want to make sure that a hint is dropped if it does not apply to the type of instruction it was added to. 

https://github.com/llvm/llvm-project/pull/198316