[turbofan] Add support for String.prototype.charCodeAt/charAt.

src/compiler/js-typed-lowering.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/code-factory.h"
 #include "src/compilation-dependencies.h"
 #include "src/compiler/access-builder.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/js-typed-lowering.h"
 #include "src/compiler/linkage.h"
@@ skipping 637 matching lines @@
     }
     r.ChangeToPureOperator(stringOp);
     return Changed(node);
   }
 
   CompareOperationHints::Hint hint = r.GetNumberCompareOperationFeedback();
   if (hint != CompareOperationHints::kAny ||
       r.OneInputCannotBe(Type::StringOrReceiver())) {
     const Operator* less_than;
     const Operator* less_than_or_equal;
-    if (hint != CompareOperationHints::kAny) {
+    if (r.BothInputsAre(Type::Signed32()) ||
+        r.BothInputsAre(Type::Unsigned32())) {
+      less_than = simplified()->NumberLessThan();
+      less_than_or_equal = simplified()->NumberLessThanOrEqual();
+    } else if (hint != CompareOperationHints::kAny) {
       less_than = simplified()->SpeculativeNumberLessThan(hint);
       less_than_or_equal = simplified()->SpeculativeNumberLessThanOrEqual(hint);
     } else if (r.BothInputsAre(Type::PlainPrimitive()) ||
                !(flags() & kDeoptimizationEnabled)) {
       r.ConvertInputsToNumber();
       less_than = simplified()->NumberLessThan();
       less_than_or_equal = simplified()->NumberLessThanOrEqual();
     } else {
       return NoChange();
     }
@@ skipping 1393 matching lines @@
 }
 
 
 CompilationDependencies* JSTypedLowering::dependencies() const {
   return dependencies_;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8