[llvm][NFC] Refactor AutoUpgrade case 'c'

[urnathan]

Summary

Here's a refactor of case 'c':, Both cttz and ctlz need the same upgrading, so they can be handled together. But we do split the mnemonic in the middle, rather than at a .. Even though we know the first letter is 'c', and so could have done Name[1] == 't', IMHO a consume_front("ct") conveys intent more clearly.

[nikic]

I'm not sure this is really an improvement. It seems better to repeat this small bit of code than do the awkward ct/lz, ct/tz split.

[urnathan]

Fair point. How about this way round -- check the number of args before looking at the name. IMHO That's likely to be more efficient. Of course common handling for a match is also good.

[arsenm]

Seems fine

llvm/lib/IR/AutoUpgrade.cpp

if (Name.consume_front("amdgcn.")) {
         // new declaration.
         NewFn = nullptr;
         return true;
       }
     }
 
     break;
   }
-  case 'c': {
-    if (Name.startswith("ctlz.") && F->arg_size() == 1) {
+  case 'c':
+    // cttz & ctlz intrinsics had another argument added.
+    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(), Intrinsic::ctlz,
+        NewFn = Intrinsic::getDeclaration(F->getParent(), ID,
                                           F->arg_begin()->getType());
         return true;
       }
-    if (Name.startswith("cttz.") && F->arg_size() == 1) {
-      rename(F);
-      NewFn = Intrinsic::getDeclaration(F->getParent(), Intrinsic::cttz,
-                                        F->arg_begin()->getType());
-      return true;
     }
     break;
-  }
   case 'd':
     if (Name.consume_front("dbg.")) {
       if (Name == "addr" || (Name == "value" && F->arg_size() == 4)) {
         rename(F);
         NewFn = Intrinsic::getDeclaration(F->getParent(), Intrinsic::dbg_value);
         return true;
       }
       break; // No other 'dbg.*'.