Minor clarifications and simplifications as well as additional checks.

src/types.cc

Index: src/types.cc
diff --git a/src/types.cc b/src/types.cc
index db638ed141d604e95ffe7ab9f9099aac0ba34a2d..327eba0679bc9cb9efa5444a839ef02b8b8082e3 100644
--- a/src/types.cc
+++ b/src/types.cc
@@ -262,7 +262,7 @@ bool TypeImpl<Config>::SlowIs(TypeImpl* that) {
   if (this->IsBitset() && SEMANTIC(this->AsBitset()) == BitsetType::kNone) {
     // Bitsets only have non-bitset supertypes along the representation axis.
     int that_bitset = that->BitsetGlb();
-    return (this->AsBitset() | that_bitset) == that_bitset;
+    return (BitsetType::Is(this->AsBitset(), that_bitset));
   }
 
   if (that->IsClass()) {
@@ -313,16 +313,12 @@ bool TypeImpl<Config>::SlowIs(TypeImpl* that) {
 
   // T <= (T1 \/ ... \/ Tn)  <=>  (T <= T1) \/ ... \/ (T <= Tn)
   // (iff T is not a union)
-  ASSERT(!this->IsUnion());
-  if (that->IsUnion()) {
-    UnionHandle unioned = handle(that->AsUnion());
-    for (int i = 0; i < unioned->Length(); ++i) {
-      if (this->Is(unioned->Get(i))) return true;
-      if (this->IsBitset()) break;  // Fast fail, only first field is a bitset.
-    }
-    return false;
+  ASSERT(!this->IsUnion() && that->IsUnion());
+  UnionHandle unioned = handle(that->AsUnion());
+  for (int i = 0; i < unioned->Length(); ++i) {
+    if (this->Is(unioned->Get(i))) return true;
+    if (this->IsBitset()) break;  // Fast fail, only first field is a bitset.
   }
-
   return false;
 }
 
@@ -382,11 +378,8 @@ bool TypeImpl<Config>::Maybe(TypeImpl* that) {
   }
 
   ASSERT(!this->IsUnion() && !that->IsUnion());
-  if (this->IsBitset()) {
-    return BitsetType::IsInhabited(this->AsBitset() & that->BitsetLub());
-  }
-  if (that->IsBitset()) {
-    return BitsetType::IsInhabited(this->BitsetLub() & that->AsBitset());
+  if (this->IsBitset() || that->IsBitset()) {
+    return BitsetType::IsInhabited(this->BitsetLub() & that->BitsetLub());
   }
   if (this->IsClass()) {
     return that->IsClass()
@@ -441,7 +434,7 @@ bool TypeImpl<Config>::UnionType::Wellformed() {
 // Union and intersection
 
 template<class Config>
-typename TypeImpl<Config>::TypeHandle TypeImpl<Config>::Narrow(
+typename TypeImpl<Config>::TypeHandle TypeImpl<Config>::Rebound(
     int bitset, Region* region) {
   TypeHandle bound = BitsetType::New(bitset, region);
   if (this->IsClass()) {
@@ -555,7 +548,7 @@ int TypeImpl<Config>::ExtendUnion(
         new_bound |= type_i_bound;
         if (new_bound == type_i_bound) return size;
       }
-      if (new_bound != old_bound) type = type->Narrow(new_bound, region);
+      if (new_bound != old_bound) type = type->Rebound(new_bound, region);
       result->Set(i, type);
     }
   }
@@ -570,7 +563,7 @@ int TypeImpl<Config>::NormalizeUnion(UnionHandle result, int size, int bitset) {
   if (bitset != BitsetType::kNone && SEMANTIC(bitset) == BitsetType::kNone) {
     for (int i = 1; i < size; ++i) {
       int glb = result->Get(i)->BitsetGlb();
-      if ((bitset | glb) == glb) {
+      if (BitsetType::Is(bitset, glb)) {
         for (int j = 1; j < size; ++j) {
           result->Set(j - 1, result->Get(j));
         }