[turbofan] inline %StringIteratorPrototype%.next in JSBuiltinReducer.

src/compiler/simplified-lowering.cc

Index: src/compiler/simplified-lowering.cc
diff --git a/src/compiler/simplified-lowering.cc b/src/compiler/simplified-lowering.cc
index 447573f18546a2930f5513d3333b5d82761d254b..97aacd691c99dc562dfeaa9c03f10d4e33f2f636 100644
--- a/src/compiler/simplified-lowering.cc
+++ b/src/compiler/simplified-lowering.cc
@@ -2056,6 +2056,11 @@ class RepresentationSelector {
                   MachineRepresentation::kTagged);
         return;
       }
+      case IrOpcode::kStringFromCodePoint: {
+        VisitUnop(node, UseInfo::TruncatingWord32(),
+                  MachineRepresentation::kTagged);
+        return;
+      }
 
       case IrOpcode::kCheckBounds: {
         Type* index_type = TypeOf(node->InputAt(0));