Ensure lower <= upper bound

src/types.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 208 matching lines @@
   // - no field is a union
   typedef FixedArray Unioned;
 
   enum {
     #define DECLARE_TYPE(type, value) k##type = (value),
     TYPE_LIST(DECLARE_TYPE)
     #undef DECLARE_TYPE
     kUnusedEOL = 0
   };
 
+  bool is_none() { return this == None(); }
   bool is_bitset() { return this->IsSmi(); }
   bool is_class() { return this->IsMap(); }
   bool is_constant() { return this->IsBox(); }
   bool is_union() { return this->IsFixedArray(); }
 
   bool SlowIs(Type* that);
 
   int as_bitset() { return Smi::cast(this)->value(); }
   Handle<Map> as_class() { return Handle<Map>::cast(handle()); }
   Handle<v8::internal::Object> as_constant() {
@@ skipping 53 matching lines @@
   }
 };
 
 
 // A simple struct to represent a pair of lower/upper type bounds.
 struct Bounds {
   Handle<Type> lower;
   Handle<Type> upper;
 
   Bounds() {}
-  Bounds(Handle<Type> l, Handle<Type> u) : lower(l), upper(u) {}
-  Bounds(Type* l, Type* u, Isolate* isl) : lower(l, isl), upper(u, isl) {}
-  explicit Bounds(Handle<Type> t) : lower(t), upper(t) {}
-  Bounds(Type* t, Isolate* isl) : lower(t, isl), upper(t, isl) {}
+  Bounds(Handle<Type> l, Handle<Type> u) : lower(l), upper(u) {
+    ASSERT(lower->Is(upper));
+  }
+  Bounds(Type* l, Type* u, Isolate* isl) : lower(l, isl), upper(u, isl) {
+    ASSERT(lower->Is(upper));
+  }
+  explicit Bounds(Handle<Type> t) : lower(t), upper(t) {
+    ASSERT(lower->Is(upper));
+  }
+  Bounds(Type* t, Isolate* isl) : lower(t, isl), upper(t, isl) {
+    ASSERT(lower->Is(upper));
+  }
 
   // Unrestricted bounds.
   static Bounds Unbounded(Isolate* isl) {
     return Bounds(Type::None(), Type::Any(), isl);
   }
 
   // Meet: both b1 and b2 are known to hold.
   static Bounds Both(Bounds b1, Bounds b2, Isolate* isl) {
-    return Bounds(
-        handle(Type::Union(b1.lower, b2.lower), isl),
-        handle(Type::Intersect(b1.upper, b2.upper), isl));
+    Handle<Type> lower(Type::Union(b1.lower, b2.lower), isl);
+    Handle<Type> upper(Type::Intersect(b1.upper, b2.upper), isl);
+    // Lower bounds are considered approximate, correct as necessary.
+    lower = handle(Type::Intersect(lower, upper), isl);
+    return Bounds(lower, upper);
   }
 
   // Join: either b1 or b2 is known to hold.
   static Bounds Either(Bounds b1, Bounds b2, Isolate* isl) {
     return Bounds(
         handle(Type::Intersect(b1.lower, b2.lower), isl),
         handle(Type::Union(b1.upper, b2.upper), isl));
   }
 
   static Bounds NarrowLower(Bounds b, Handle<Type> t, Isolate* isl) {
+    // Lower bounds are considered approximate, correct as necessary.
+    t = handle(Type::Intersect(t, b.upper), isl);
     return Bounds(handle(Type::Union(b.lower, t), isl), b.upper);
   }
   static Bounds NarrowUpper(Bounds b, Handle<Type> t, Isolate* isl) {
-    return Bounds(b.lower, handle(Type::Intersect(b.upper, t), isl));
+    return Bounds(
+        handle(Type::Intersect(b.lower, t), isl),
+        handle(Type::Intersect(b.upper, t), isl));
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_TYPES_H_