[clang] [llvm] [AArch64][clang][llvm] Add ACLE `stshh` atomic store builtin (PR #181386)

[Kerry McLaughlin via llvm-commits]

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@@ -5278,6 +5278,46 @@ Value *CodeGenFunction::EmitAArch64BuiltinExpr(unsigned BuiltinID,
     return Builder.CreateCall(F, Args);
   }
 
+  if (BuiltinID == clang::AArch64::BI__builtin_arm_atomic_store_with_stshh) {
+    const Expr *Arg0 = E->getArg(0);
+    Value *StoreAddr = EmitScalarExpr(Arg0);
+    Value *StoreValue = EmitScalarExpr(E->getArg(1));
+    Value *Order = EmitScalarExpr(E->getArg(2));
+    Value *Policy = EmitScalarExpr(E->getArg(3));
+
+    auto *OrderC = dyn_cast<llvm::ConstantInt>(Order);
+    auto *PolicyC = dyn_cast<llvm::ConstantInt>(Policy);
+
+    assert(OrderC && PolicyC &&
+           "order/policy must be constant for __arm_atomic_store_with_stshh");
+
+    // Validate ordering argument; bail out if invalid
+    switch (OrderC->getZExtValue()) {
+    case 0: // __ATOMIC_RELAXED
+    case 3: // __ATOMIC_RELEASE
+    case 5: // __ATOMIC_SEQ_CST
+      break;
+    default:
+      llvm_unreachable(
+          "unexpected memory order for __arm_atomic_store_with_stshh");
+    }
+
+    llvm::Value *OrderArg =
+        llvm::ConstantInt::get(Int32Ty, OrderC->getZExtValue());
+    llvm::Value *PolicyArg =
+        llvm::ConstantInt::get(Int32Ty, PolicyC->getZExtValue());
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kmclaughlin-arm wrote:

Can `OrderC` and `PolicyC` be passed directly to `CreateCall` below?

https://github.com/llvm/llvm-project/pull/181386