[turbofan] Assign better types to various String builtins.

src/compiler/typer.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/compiler/typer.h"
 
 #include "src/base/flags.h"
 #include "src/bootstrapper.h"
 #include "src/compilation-dependencies.h"
 #include "src/compiler/common-operator.h"
@@ skipping 1511 matching lines @@
         case kMathAtan2:
         case kMathPow:
         case kMathMax:
         case kMathMin:
           return Type::Number();
         case kMathImul:
           return Type::Signed32();
         case kMathClz32:
           return t->cache_.kZeroToThirtyTwo;
         // String functions.
+        case kStringCharCodeAt:
+          return Type::Union(Type::Range(0, kMaxUInt16, t->zone()), Type::NaN(),
+                             t->zone());
         case kStringCharAt:
+        case kStringConcat:
         case kStringFromCharCode:
+        case kStringToLowerCase:
+        case kStringToUpperCase:
           return Type::String();
         // Array functions.
         case kArrayIndexOf:
         case kArrayLastIndexOf:
           return Type::Number();
         default:
           break;
       }
     }
   }
@@ skipping 29 matching lines @@
     case Runtime::kInlineMathAsin:
     case Runtime::kInlineMathAtan:
     case Runtime::kInlineMathAtan2:
       return Type::Number();
     case Runtime::kInlineMathClz32:
       return Type::Range(0, 32, zone());
     case Runtime::kInlineCreateIterResultObject:
     case Runtime::kInlineRegExpConstructResult:
       return Type::OtherObject();
     case Runtime::kInlineSubString:
+    case Runtime::kInlineStringCharFromCode:
       return Type::String();
     case Runtime::kInlineToInteger:
       return TypeUnaryOp(node, ToInteger);
     case Runtime::kInlineToLength:
       return TypeUnaryOp(node, ToLength);
     case Runtime::kInlineToName:
       return TypeUnaryOp(node, ToName);
     case Runtime::kInlineToNumber:
       return TypeUnaryOp(node, ToNumber);
     case Runtime::kInlineToObject:
@@ skipping 830 matching lines @@
   }
   if (Type::IsInteger(*value)) {
     return Type::Range(value->Number(), value->Number(), zone());
   }
   return Type::Constant(value, zone());
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8