Introduce Type::Intersect function

src/types.cc

Index: src/types.cc
diff --git a/src/types.cc b/src/types.cc
index 20e8a4c994541fc18f10e3cdbece64843645acd8..22a108b7206b0bd657ae57e90af4c20a11770190 100644
--- a/src/types.cc
+++ b/src/types.cc
@@ -243,6 +243,7 @@ bool Type::Is(Type* that) {
 
   // T <= (T1 \/ ... \/ Tn)  <=>  (T <= T1) \/ ... \/ (T <= Tn)
   // (iff T is not a union)
+  ASSERT(!this->is_union());
   if (that->is_union()) {
     Handle<Unioned> unioned = that->as_union();
     for (int i = 0; i < unioned->length(); ++i) {
@@ -267,13 +268,6 @@ bool Type::Maybe(Type* that) {
     return (this->LubBitset() & that->as_bitset()) != 0;
   }
 
-  if (this->is_class()) {
-    return that->is_class() && *this->as_class() == *that->as_class();
-  }
-  if (this->is_constant()) {
-    return that->is_constant() && *this->as_constant() == *that->as_constant();
-  }
-
   // (T1 \/ ... \/ Tn) overlaps T <=> (T1 overlaps T) \/ ... \/ (Tn overlaps T)
   if (this->is_union()) {
     Handle<Unioned> unioned = this->as_union();
@@ -294,6 +288,14 @@ bool Type::Maybe(Type* that) {
     return false;
   }
 
+  ASSERT(!that->is_union());
+  if (this->is_class()) {
+    return that->is_class() && *this->as_class() == *that->as_class();
+  }
+  if (this->is_constant()) {
+    return that->is_constant() && *this->as_constant() == *that->as_constant();
+  }
+
   return false;
 }
 
@@ -302,12 +304,12 @@ bool Type::InUnion(Handle<Unioned> unioned, int current_size) {
   ASSERT(!this->is_union());
   for (int i = 0; i < current_size; ++i) {
     Handle<Type> type = union_get(unioned, i);
-    if (type->is_bitset() ? this->Is(type) : this == *type) return true;
+    if (this->Is(type)) return true;
   }
   return false;
 }
 
-// Get non-bitsets from this which are not subsumed by that, store at unioned,
+// Get non-bitsets from this which are not subsumed by union, store at unioned,
 // starting at index. Returns updated index.
 int Type::ExtendUnion(Handle<Unioned> result, int current_size) {
   int old_size = current_size;
@@ -374,6 +376,79 @@ Type* Type::Union(Handle<Type> type1, Handle<Type> type2) {
 }
 
 
+// Get non-bitsets from this which are also in that, store at unioned,
+// starting at index. Returns updated index.
+int Type::ExtendIntersection(
+    Handle<Unioned> result, Handle<Type> that, int current_size) {
+  int old_size = current_size;
+  if (this->is_class() || this->is_constant()) {
+    if (this->Is(that) && !this->InUnion(result, old_size))
+      result->set(current_size++, this);
+  } else if (this->is_union()) {
+    Handle<Unioned> unioned = this->as_union();
+    for (int i = 0; i < unioned->length(); ++i) {
+      Handle<Type> type = union_get(unioned, i);
+      ASSERT(i == 0 || !(type->is_bitset() || type->Is(union_get(unioned, 0))));
+      if (type->is_bitset()) continue;
+      if (type->Is(that) && !type->InUnion(result, old_size))
+        result->set(current_size++, *type);
+    }
+  }
+  return current_size;
+}
+
+
+// Intersection is O(1) on simple bit unions, but O(n*m) on structured unions.
+// TODO(rossberg): Should we use object sets somehow? Is it worth it?
+Type* Type::Intersect(Handle<Type> type1, Handle<Type> type2) {
+  // Fast case: bit sets.
+  if (type1->is_bitset() && type2->is_bitset()) {
+    return from_bitset(type1->as_bitset() & type2->as_bitset());
+  }
+
+  // Semi-fast case: Unioned objects are neither involved nor produced.
+  if (!(type1->is_union() || type2->is_union())) {
+    if (type1->Is(type2)) return *type1;
+    if (type2->Is(type1)) return *type2;
+  }
+
+  // Slow case: may need to produce a Unioned object.
+  Isolate* isolate = NULL;
+  int size = 0;
+  if (!type1->is_bitset()) {
+    isolate = HeapObject::cast(*type1)->GetIsolate();
+    size = (type1->is_union() ? type1->as_union()->length() : 2);
+  }
+  if (!type2->is_bitset()) {
+    isolate = HeapObject::cast(*type2)->GetIsolate();
+    int size2 = (type2->is_union() ? type2->as_union()->length() : 2);
+    size = (size == 0 ? size2 : Min(size, size2));
+  }
+  ASSERT(isolate != NULL);
+  ASSERT(size >= 2);
+  Handle<Unioned> unioned = isolate->factory()->NewFixedArray(size);
+  size = 0;
+
+  int bitset = type1->GlbBitset() & type2->GlbBitset();
+  if (bitset != kNone) unioned->set(size++, from_bitset(bitset));
+  size = type1->ExtendIntersection(unioned, type2, size);
+  size = type2->ExtendIntersection(unioned, type1, size);
+
+  if (size == 0) {
+    return None();
+  } else if (size == 1) {
+    return *union_get(unioned, 0);
+  } else if (size == unioned->length()) {
+    return from_handle(unioned);
+  }
+
+  // There were dropped cases. Copy to smaller union.
+  Handle<Unioned> result = isolate->factory()->NewFixedArray(size);
+  for (int i = 0; i < size; ++i) result->set(i, unioned->get(i));
+  return from_handle(result);
+}
+
+
 Type* Type::Optional(Handle<Type> type) {
   return type->is_bitset()
       ? from_bitset(type->as_bitset() | kUndefined)