[llvm][NFC] Refactor autoupdater's 'c' intrinsics (#73333)

With these three intrinsics it's probable faster to check the number of
arguments first and then check the names. We can also handle ctlz and
cttz in the same block.

Author: urnathan

llvm/lib/IR/AutoUpgrade.cpp

@@ -968,19 +968,20 @@ static bool UpgradeIntrinsicFunction1(Function *F, Function *&NewFn) {
     break;
   }
   case 'c': {
-    if (Name.starts_with("ctlz.") && F->arg_size() == 1) {
-      rename(F);
-      NewFn = Intrinsic::getDeclaration(F->getParent(), Intrinsic::ctlz,
-                                        F->arg_begin()->getType());
-      return true;
-    }
-    if (Name.starts_with("cttz.") && F->arg_size() == 1) {
-      rename(F);
-      NewFn = Intrinsic::getDeclaration(F->getParent(), Intrinsic::cttz,
-                                        F->arg_begin()->getType());
-      return true;
+    if (F->arg_size() == 1) {
+      Intrinsic::ID ID = StringSwitch<Intrinsic::ID>(Name)
+                             .StartsWith("ctlz.", Intrinsic::ctlz)
+                             .StartsWith("cttz.", Intrinsic::cttz)
+                             .Default(Intrinsic::not_intrinsic);
+      if (ID != Intrinsic::not_intrinsic) {
+        rename(F);
+        NewFn = Intrinsic::getDeclaration(F->getParent(), ID,
+                                          F->arg_begin()->getType());
+        return true;
+      }
     }
-    if (Name.equals("coro.end") && F->arg_size() == 2) {
+
+    if (F->arg_size() == 2 && Name.equals("coro.end")) {
       rename(F);
       NewFn = Intrinsic::getDeclaration(F->getParent(), Intrinsic::coro_end);
       return true;