[WIP] JSForInLowering and JSForInHasOwnProperty.

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 e4ab10f564989aac2eb12e41af7f30d49233ddce..a83a284aa53dc1a13fffd51dff567cc77bcbdbe6 100644
--- a/src/compiler/simplified-lowering.cc
+++ b/src/compiler/simplified-lowering.cc
@@ -2398,6 +2398,12 @@ class RepresentationSelector {
         SetOutput(node, MachineRepresentation::kTaggedPointer);
         return;
       }
+      case IrOpcode::kLoadFieldByIndex: {
+        if (truncation.IsUnused()) return VisitUnused(node);
+        VisitBinop(node, UseInfo::AnyTagged(), UseInfo::TruncatingWord32(),
+                   MachineRepresentation::kTagged);
+        return;
+      }
       case IrOpcode::kLoadField: {
         if (truncation.IsUnused()) return VisitUnused(node);
         FieldAccess access = FieldAccessOf(node->op());