Add another type JSPositiveInt to show a range analysis in the inferrer would be very beneficial :-…

sdk/lib/_internal/compiler/implementation/js_backend/backend.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of js_backend;
 
 const VERBOSE_OPTIMIZER_HINTS = false;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked = new Set<HInstruction>();
@@ skipping 176 matching lines @@
   ClassElement jsBoolClass;
   ClassElement jsPlainJavaScriptObjectClass;
   ClassElement jsUnknownJavaScriptObjectClass;
 
   ClassElement jsIndexableClass;
   ClassElement jsMutableIndexableClass;
 
   ClassElement jsMutableArrayClass;
   ClassElement jsFixedArrayClass;
   ClassElement jsExtendableArrayClass;
+  ClassElement jsPositiveIntClass;
   ClassElement jsUInt32Class;
   ClassElement jsUInt31Class;
 
   Element jsIndexableLength;
   Element jsArrayTypedConstructor;
   Element jsArrayRemoveLast;
   Element jsArrayAdd;
   Element jsStringSplit;
   Element jsStringToString;
   Element jsStringOperatorAdd;
@@ skipping 17 matching lines @@
    * interceptor.  See declaration of `mapTypeToInterceptor` in
    * `interceptors.dart`.
    */
   Element mapTypeToInterceptor;
 
   TypeMask get stringType => compiler.typesTask.stringType;
   TypeMask get doubleType => compiler.typesTask.doubleType;
   TypeMask get intType => compiler.typesTask.intType;
   TypeMask get uint32Type => compiler.typesTask.uint32Type;
   TypeMask get uint31Type => compiler.typesTask.uint31Type;
+  TypeMask get positiveIntType => compiler.typesTask.positiveIntType;
   TypeMask get numType => compiler.typesTask.numType;
   TypeMask get boolType => compiler.typesTask.boolType;
   TypeMask get dynamicType => compiler.typesTask.dynamicType;
   TypeMask get nullType => compiler.typesTask.nullType;
   TypeMask get emptyType => const TypeMask.nonNullEmpty();
   TypeMask indexablePrimitiveType;
   TypeMask readableArrayType;
   TypeMask mutableArrayType;
   TypeMask fixedArrayType;
   TypeMask extendableArrayType;
@@ skipping 329 matching lines @@
     inlineCache.markAsNonInlinable(getInterceptorMethod, insideLoop: true);
 
     List<ClassElement> classes = [
       jsInterceptorClass =
           compiler.findInterceptor('Interceptor'),
       jsStringClass = compiler.findInterceptor('JSString'),
       jsArrayClass = compiler.findInterceptor('JSArray'),
       // The int class must be before the double class, because the
       // emitter relies on this list for the order of type checks.
       jsIntClass = compiler.findInterceptor('JSInt'),
+      jsPositiveIntClass = compiler.findInterceptor('JSPositiveInt'),
       jsUInt32Class = compiler.findInterceptor('JSUInt32'),
       jsUInt31Class = compiler.findInterceptor('JSUInt31'),
       jsDoubleClass = compiler.findInterceptor('JSDouble'),
       jsNumberClass = compiler.findInterceptor('JSNumber'),
       jsNullClass = compiler.findInterceptor('JSNull'),
       jsBoolClass = compiler.findInterceptor('JSBool'),
       jsMutableArrayClass = compiler.findInterceptor('JSMutableArray'),
       jsFixedArrayClass = compiler.findInterceptor('JSFixedArray'),
       jsExtendableArrayClass = compiler.findInterceptor('JSExtendableArray'),
       jsPlainJavaScriptObjectClass =
@@ skipping 253 matching lines @@
     } else if (cls == compiler.listClass
                || cls == jsArrayClass
                || cls == jsFixedArrayClass
                || cls == jsExtendableArrayClass) {
       addInterceptors(jsArrayClass, enqueuer, elements);
       addInterceptors(jsMutableArrayClass, enqueuer, elements);
       addInterceptors(jsFixedArrayClass, enqueuer, elements);
       addInterceptors(jsExtendableArrayClass, enqueuer, elements);
     } else if (cls == compiler.intClass || cls == jsIntClass) {
       addInterceptors(jsIntClass, enqueuer, elements);
+      addInterceptors(jsPositiveIntClass, enqueuer, elements);
       addInterceptors(jsUInt32Class, enqueuer, elements);
       addInterceptors(jsUInt31Class, enqueuer, elements);
       addInterceptors(jsNumberClass, enqueuer, elements);
     } else if (cls == compiler.doubleClass || cls == jsDoubleClass) {
       addInterceptors(jsDoubleClass, enqueuer, elements);
       addInterceptors(jsNumberClass, enqueuer, elements);
     } else if (cls == compiler.boolClass || cls == jsBoolClass) {
       addInterceptors(jsBoolClass, enqueuer, elements);
     } else if (cls == compiler.nullClass || cls == jsNullClass) {
       addInterceptors(jsNullClass, enqueuer, elements);
     } else if (cls == compiler.numClass || cls == jsNumberClass) {
       addInterceptors(jsIntClass, enqueuer, elements);
+      addInterceptors(jsPositiveIntClass, enqueuer, elements);
       addInterceptors(jsUInt32Class, enqueuer, elements);
       addInterceptors(jsUInt31Class, enqueuer, elements);
       addInterceptors(jsDoubleClass, enqueuer, elements);
       addInterceptors(jsNumberClass, enqueuer, elements);
     } else if (cls == jsPlainJavaScriptObjectClass) {
       addInterceptors(jsPlainJavaScriptObjectClass, enqueuer, elements);
     } else if (cls == jsUnknownJavaScriptObjectClass) {
       addInterceptors(jsUnknownJavaScriptObjectClass, enqueuer, elements);
     } else if (Elements.isNativeOrExtendsNative(cls)) {
       addInterceptorsForNativeClassMembers(cls, enqueuer);
@@ skipping 541 matching lines @@
       if (nativeCheckOnly) return null;
       return typeCast
           ? 'numTypeCast'
           : 'numTypeCheck';
     } else if (element == jsBoolClass || element == compiler.boolClass) {
       if (nativeCheckOnly) return null;
       return typeCast
           ? 'boolTypeCast'
           : 'boolTypeCheck';
     } else if (element == jsIntClass || element == compiler.intClass
-               || element == jsUInt32Class || element == jsUInt31Class) {
+               || element == jsUInt32Class || element == jsUInt31Class
+               || element == jsPositiveIntClass) {
       if (nativeCheckOnly) return null;
       return typeCast
           ? 'intTypeCast'
           : 'intTypeCheck';
     } else if (Elements.isNumberOrStringSupertype(element, compiler)) {
       if (nativeCheck) {
         return typeCast
             ? 'numberOrStringSuperNativeTypeCast'
             : 'numberOrStringSuperNativeTypeCheck';
       } else {
@@ skipping 199 matching lines @@
     return compiler.findHelper("throwCyclicInit");
   }
 
   bool isNullImplementation(ClassElement cls) {
     return cls == jsNullClass;
   }
 
   ClassElement get intImplementation => jsIntClass;
   ClassElement get uint32Implementation => jsUInt32Class;
   ClassElement get uint31Implementation => jsUInt31Class;
+  ClassElement get positiveIntImplementation => jsPositiveIntClass;
   ClassElement get doubleImplementation => jsDoubleClass;
   ClassElement get numImplementation => jsNumberClass;
   ClassElement get stringImplementation => jsStringClass;
   ClassElement get listImplementation => jsArrayClass;
   ClassElement get constListImplementation => jsArrayClass;
   ClassElement get fixedListImplementation => jsFixedArrayClass;
   ClassElement get growableListImplementation => jsExtendableArrayClass;
   ClassElement get mapImplementation => mapLiteralClass;
   ClassElement get constMapImplementation => constMapLiteralClass;
   ClassElement get typeImplementation => typeLiteralClass;
@@ skipping 330 matching lines @@
     copy(constant.values);
     copy(constant.protoValue);
     copy(constant);
   }
 
   void visitConstructed(ConstructedConstant constant) {
     copy(constant.fields);
     copy(constant);
   }
 }