[turbofan] Improve typing for CheckBounds.

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 d72fc827591350c7b4283b89ee861cb23bb340d8..6e560dbffcc68634665cc073444ff94a2ab3bd2c 100644
--- a/src/compiler/simplified-lowering.cc
+++ b/src/compiler/simplified-lowering.cc
@@ -2104,7 +2104,8 @@ class RepresentationSelector {
       }
 
       case IrOpcode::kCheckBounds: {
-        if (TypeOf(node->InputAt(0))->Is(Type::Unsigned32())) {
+        Type* index_type = TypeOf(node->InputAt(0));
+        if (index_type->Is(Type::Unsigned32())) {
           VisitBinop(node, UseInfo::TruncatingWord32(),
                      MachineRepresentation::kWord32);
         } else {
@@ -2112,6 +2113,13 @@ class RepresentationSelector {
                      UseInfo::TruncatingWord32(),
                      MachineRepresentation::kWord32);
         }
+        if (lower()) {
+          // The bounds check is redundant if we already know that
+          // the index is within the bounds of [0.0, length[.
+          if (index_type->Is(NodeProperties::GetType(node))) {
+            DeferReplacement(node, node->InputAt(0));
+          }
+        }
         return;
       }
       case IrOpcode::kCheckIf: {