[llvm] [verify][swift] Allow passing swifterror to phi instructions (PR #138598)

[Matthias Braun via llvm-commits]

================
@@ -3653,20 +3653,22 @@ void Verifier::visitCallBase(CallBase &Call) {
   // well.
   for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i) {
     if (Call.paramHasAttr(i, Attribute::SwiftError)) {
-      SetVector<const Value *> Args;
-      Args.insert(Call.getArgOperand(i));
-      bool DidChange;
-      do {
-        DidChange = false;
-        // Inherit the incoming values of phi instructions to capture all
-        // values.
-        for (const Value *Arg : Args)
-          if (auto *PhiI = dyn_cast<PHINode>(Arg))
-            for (const auto &Op : PhiI->incoming_values())
-              DidChange |= Args.insert(Op.get());
-      } while (DidChange);
-
-      for (const Value *SwiftErrorArg : Args) {
+      const Value *Arg = Call.getArgOperand(i);
+      SetVector<const Value *> Values;
+      Values.insert(Arg);
+      SmallVector<const PHINode *> PHIWorkList;
+      if (auto *PhiI = dyn_cast<PHINode>(Arg))
+        PHIWorkList.push_back(PhiI);
+
+      while (!PHIWorkList.empty()) {
+        const auto *PhiI = PHIWorkList.pop_back_val();
+        for (const auto &Op : PhiI->incoming_values()) {
+          const auto *NextPhiI = dyn_cast<PHINode>(Op.get());
+          if (Values.insert(Op.get()) && NextPhiI)
+            PHIWorkList.push_back(NextPhiI);
+        }
----------------
MatzeB wrote:

Does this work using implicit conversion from `Use` to `Value`?
```suggestion
        const auto *PhiI = PHIWorkList.pop_back_val();
        for (Value *Op : PhiI->incoming_values()) {
          const auto *NextPhiI = dyn_cast<PHINode>(Op);
          if (Values.insert(Op) && NextPhiI)
            PHIWorkList.push_back(NextPhiI);
        }
```

https://github.com/llvm/llvm-project/pull/138598