[turbofan] Fix impossible type handling for TypeGuard and BooleanNot.

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 f0fdb931a849cd6812dbeeb0958bbd4613224b9d..a71054977ce5e61c3446072b1e45f97934a5cff6 100644
--- a/src/compiler/simplified-lowering.cc
+++ b/src/compiler/simplified-lowering.cc
@@ -1531,11 +1531,14 @@ class RepresentationSelector {
             // BooleanNot(x: kRepBit) => Word32Equal(x, #0)
             node->AppendInput(jsgraph_->zone(), jsgraph_->Int32Constant(0));
             NodeProperties::ChangeOp(node, lowering->machine()->Word32Equal());
-          } else {
-            DCHECK(CanBeTaggedPointer(input_info->representation()));
+          } else if (CanBeTaggedPointer(input_info->representation())) {
             // BooleanNot(x: kRepTagged) => WordEqual(x, #false)
             node->AppendInput(jsgraph_->zone(), jsgraph_->FalseConstant());
             NodeProperties::ChangeOp(node, lowering->machine()->WordEqual());
+          } else {
+            DCHECK_EQ(MachineRepresentation::kNone,
+                      input_info->representation());
+            DeferReplacement(node, lowering->jsgraph()->Int32Constant(0));
           }
         } else {
           // No input representation requirement; adapt during lowering.
@@ -2779,9 +2782,15 @@ class RepresentationSelector {
         // We just get rid of the sigma here. In principle, it should be
         // possible to refine the truncation and representation based on
         // the sigma's type.
-        MachineRepresentation output =
+        MachineRepresentation representation =
             GetOutputInfoForPhi(node, TypeOf(node->InputAt(0)), truncation);
-        VisitUnop(node, UseInfo(output, truncation), output);
+
+        // For now, we just handle specially the impossible case.
+        MachineRepresentation output = TypeOf(node)->IsInhabited()
+                                           ? representation
+                                           : MachineRepresentation::kNone;
+
+        VisitUnop(node, UseInfo(representation, truncation), output);
         if (lower()) DeferReplacement(node, node->InputAt(0));
         return;
       }