Remove non-trivial subtyping between bitset and non-bitset types.

R=rossberg@chromium.org
BUG=

Review URL: https://codereview.chromium.org/444503005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22903 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/types.cc

@@ -21,26 +21,9 @@ int TypeImpl<Config>::BitsetType::Glb(TypeImpl* type) {
     return type->AsBitset();
   } else if (type->IsUnion()) {
     UnionHandle unioned = handle(type->AsUnion());
-    int bitset = kNone;
-    for (int i = 0; i < unioned->Length(); ++i) {
-      bitset |= unioned->Get(i)->BitsetGlb();
-    }
-    return bitset;
-  } else if (type->IsClass()) {
-    // Little hack to avoid the need for a region for handlification here...
-    return REPRESENTATION(Config::is_class(type)
-        ? Lub(*Config::as_class(type))
-        : type->AsClass()->Bound(NULL)->AsBitset());
-  } else if (type->IsConstant()) {
-    return REPRESENTATION(type->AsConstant()->Bound()->AsBitset());
-  } else if (type->IsContext()) {
-    return REPRESENTATION(type->AsContext()->Bound()->AsBitset());
-  } else if (type->IsArray()) {
-    return REPRESENTATION(type->AsArray()->Bound()->AsBitset());
-  } else if (type->IsFunction()) {
-    return REPRESENTATION(type->AsFunction()->Bound()->AsBitset());
+    DCHECK(unioned->Wellformed());
+    return unioned->Get(0)->BitsetGlb();  // Other BitsetGlb's are kNone anyway.
   } else {
-    UNREACHABLE();
     return kNone;
   }
 }
@@ -260,10 +243,6 @@ bool TypeImpl<Config>::SlowIs(TypeImpl* that) {
   if (that->IsBitset()) {
     return BitsetType::Is(BitsetType::Lub(this), that->AsBitset());
   }
-  if (this->IsBitset() && SEMANTIC(this->AsBitset()) == BitsetType::kNone) {
-    // Bitsets only have non-bitset supertypes along the representation axis.
-    return BitsetType::Is(this->AsBitset(), that->BitsetGlb());
-  }
 
   if (that->IsClass()) {
     return this->IsClass()
@@ -555,26 +534,6 @@ int TypeImpl<Config>::ExtendUnion(
 }
 
 
-// If bitset is subsumed by another entry in the result, remove it.
-// (Only bitsets with empty semantic axis can be subtypes of non-bitsets.)
-template<class Config>
-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 (BitsetType::Is(bitset, glb)) {
-        for (int j = 1; j < size; ++j) {
-          result->Set(j - 1, result->Get(j));
-        }
-        --size;
-        break;
-      }
-    }
-  }
-  return size;
-}
-
-
 // Union is O(1) on simple bitsets, but O(n*m) on structured unions.
 template<class Config>
 typename TypeImpl<Config>::TypeHandle TypeImpl<Config>::Union(
@@ -613,7 +572,6 @@ typename TypeImpl<Config>::TypeHandle TypeImpl<Config>::Union(
   }
   size = ExtendUnion(unioned, size, type1, type2, false, region);
   size = ExtendUnion(unioned, size, type2, type1, false, region);
-  size = NormalizeUnion(unioned, size, bitset);
 
   if (size == 1) {
     return unioned->Get(0);
@@ -663,7 +621,6 @@ typename TypeImpl<Config>::TypeHandle TypeImpl<Config>::Intersect(
   }
   size = ExtendUnion(unioned, size, type1, type2, true, region);
   size = ExtendUnion(unioned, size, type2, type1, true, region);
-  size = NormalizeUnion(unioned, size, bitset);
 
   if (size == 0) {
     return None(region);