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

[via cfe-commits]

================
@@ -5290,6 +5290,56 @@ 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);
+    const Expr *Arg1 = E->getArg(1);
+    const Expr *Arg2 = E->getArg(2);
+    const Expr *Arg3 = E->getArg(3);
+
+    Value *StoreAddr = EmitScalarExpr(Arg0);
+    Value *StoreValue = EmitScalarExpr(Arg1);
+
+    llvm::APSInt OrderVal = Arg2->EvaluateKnownConstInt(getContext());
+    llvm::APSInt RetentionPolicy = Arg3->EvaluateKnownConstInt(getContext());
----------------
CarolineConcatto wrote:

Not sure what  is better, but what I see usually in the code is:
```
Value *Order = EmitScalarExpr(E->getArg(2));
auto Ord = dyn_cast<llvm::ConstantInt>(Order);
switch (Ord->getZExtValue()) {
```
I dont see EvaluateKnownConstInt being used much here.

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