Fix lower bound violation

src/types.h

 // 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.
 
 #ifndef V8_TYPES_H_
 #define V8_TYPES_H_
 
 #include "src/conversions.h"
 #include "src/factory.h"
 #include "src/handles.h"
@@ skipping 1017 matching lines @@
   // Unrestricted bounds.
   static BoundsImpl Unbounded(Region* region) {
     return BoundsImpl(Type::None(region), Type::Any(region));
   }
 
   // Meet: both b1 and b2 are known to hold.
   static BoundsImpl Both(BoundsImpl b1, BoundsImpl b2, Region* region) {
     TypeHandle lower = Type::Union(b1.lower, b2.lower, region);
     TypeHandle upper = Type::Intersect(b1.upper, b2.upper, region);
     // Lower bounds are considered approximate, correct as necessary.
-    lower = Type::Intersect(lower, upper, region);
+    if (!lower->Is(upper)) lower = upper;
     return BoundsImpl(lower, upper);
   }
 
   // Join: either b1 or b2 is known to hold.
   static BoundsImpl Either(BoundsImpl b1, BoundsImpl b2, Region* region) {
     TypeHandle lower = Type::Intersect(b1.lower, b2.lower, region);
     TypeHandle upper = Type::Union(b1.upper, b2.upper, region);
     return BoundsImpl(lower, upper);
   }
 
   static BoundsImpl NarrowLower(BoundsImpl b, TypeHandle t, Region* region) {
+    TypeHandle lower = Type::Union(b.lower, t, region);
     // Lower bounds are considered approximate, correct as necessary.
-    t = Type::Intersect(t, b.upper, region);
-    TypeHandle lower = Type::Union(b.lower, t, region);
+    if (!lower->Is(b.upper)) lower = b.upper;
     return BoundsImpl(lower, b.upper);
   }
   static BoundsImpl NarrowUpper(BoundsImpl b, TypeHandle t, Region* region) {
-    TypeHandle lower = Type::Intersect(b.lower, t, region);
+    TypeHandle lower = b.lower;
     TypeHandle upper = Type::Intersect(b.upper, t, region);
+    // Lower bounds are considered approximate, correct as necessary.
+    if (!lower->Is(upper)) lower = upper;
     return BoundsImpl(lower, upper);
   }
 
   bool Narrows(BoundsImpl that) {
     return that.lower->Is(this->lower) && this->upper->Is(that.upper);
   }
 };
 
 typedef BoundsImpl<ZoneTypeConfig> Bounds;
 
 } }  // namespace v8::internal
 
 #endif  // V8_TYPES_H_