New unified type representation

src/types.cc

+// 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
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "types.h"
+
+namespace v8 {
+namespace internal {
+
+// Get the smallest bitset subsuming this type.
+int Type::LubBitset() {
+  if (this->is_bitset()) {
+    return this->as_bitset();
+  } else if (this->is_union()) {
+    Handle<Unioned> unioned = this->as_union();
+    int bitset = kNone;
+    for (int i = 0; i < unioned->length(); ++i)
+      bitset |= union_get(unioned, i)->LubBitset();
+    return bitset;
+  } else {
+    Map* map = this->is_class()? *this->as_class() : this->as_constant()->map();
+    switch (map->instance_type()) {
+      case STRING_TYPE:
+      case ASCII_STRING_TYPE:
+      case CONS_STRING_TYPE:
+      case CONS_ASCII_STRING_TYPE:
+      case SLICED_STRING_TYPE:
+      case EXTERNAL_STRING_TYPE:
+      case EXTERNAL_ASCII_STRING_TYPE:
+      case EXTERNAL_STRING_WITH_ONE_BYTE_DATA_TYPE:
+      case SHORT_EXTERNAL_STRING_TYPE:
+      case SHORT_EXTERNAL_ASCII_STRING_TYPE:
+      case SHORT_EXTERNAL_STRING_WITH_ONE_BYTE_DATA_TYPE:
+      case INTERNALIZED_STRING_TYPE:
+      case ASCII_INTERNALIZED_STRING_TYPE:
+      case CONS_INTERNALIZED_STRING_TYPE:
+      case CONS_ASCII_INTERNALIZED_STRING_TYPE:
+      case EXTERNAL_INTERNALIZED_STRING_TYPE:
+      case EXTERNAL_ASCII_INTERNALIZED_STRING_TYPE:
+      case EXTERNAL_INTERNALIZED_STRING_WITH_ONE_BYTE_DATA_TYPE:
+      case SHORT_EXTERNAL_INTERNALIZED_STRING_TYPE:
+      case SHORT_EXTERNAL_ASCII_INTERNALIZED_STRING_TYPE:
+      case SHORT_EXTERNAL_INTERNALIZED_STRING_WITH_ONE_BYTE_DATA_TYPE:
+        return kString;
+      case SYMBOL_TYPE:
+        return kSymbol;
+      case ODDBALL_TYPE:
+        return kOddball;
+      case HEAP_NUMBER_TYPE:
+        return kDouble;
+      case JS_VALUE_TYPE:
+      case JS_DATE_TYPE:
+      case JS_OBJECT_TYPE:
+      case JS_CONTEXT_EXTENSION_OBJECT_TYPE:
+      case JS_GENERATOR_OBJECT_TYPE:
+      case JS_MODULE_TYPE:
+      case JS_GLOBAL_OBJECT_TYPE:
+      case JS_BUILTINS_OBJECT_TYPE:
+      case JS_GLOBAL_PROXY_TYPE:
+      case JS_ARRAY_BUFFER_TYPE:
+      case JS_TYPED_ARRAY_TYPE:
+      case JS_WEAK_MAP_TYPE:
+      case JS_REGEXP_TYPE:
+        return kOtherObject;
+      case JS_ARRAY_TYPE:
+        return kArray;
+      case JS_FUNCTION_TYPE:
+        return kFunction;
+      case JS_PROXY_TYPE:
+      case JS_FUNCTION_PROXY_TYPE:
+        return kProxy;
+      default:

[Sven Panne, 2013/06/05 08:02:41]

Are there really unhandled cases? If yes, how many? Default cases are a road to
maintenance hell...

[rossberg, 2013/06/05 09:44:24]

I know, unfortunately, there are several dozens of them -- as many as we have
'internal' heap objects...

If you forget to add a new instance type you'll get an assertion failure right
away, so it's not too bad.

+        UNREACHABLE();
+        return kNone;
+    }
+  }
+}
+
+
+// Get the largest bitset subsumed by this type.
+int Type::GlbBitset() {
+  if (this->is_bitset()) {
+    return this->as_bitset();
+  } else if (this->is_union()) {
+    // All but the first are non-bitsets and thus would yield kNone anyway.
+    return union_get(this->as_union(), 0)->GlbBitset();
+  } else {
+    return kNone;
+  }
+}
+
+
+// Check this <= that.
+bool Type::Is(Handle<Type> that) {
+  // Fast path for bitsets.
+  if (that->is_bitset()) {
+    return (this->LubBitset() | that->as_bitset()) == that->as_bitset();
+  }
+
+  if (that->is_class()) {
+    return this->is_class() && *this->as_class() == *that->as_class();
+  }
+  if (that->is_constant()) {
+    return this->is_constant() && *this->as_constant() == *that->as_constant();
+  }
+
+  // T <= (T1 \/ ... \/ Tn)  <=>  (T <= T1) \/ ... \/ (T <= Tn)
+  if (that->is_union()) {
+    Handle<Unioned> unioned = that->as_union();
+    for (int i = 0; i < unioned->length(); ++i) {
+      Handle<Type> that_i = union_get(unioned, i);
+      if (this->Is(that_i)) return true;
+      if (this->is_bitset()) break;  // Fast fail, no other field is a bitset.
+    }
+    return false;
+  }
+
+  // (T1 \/ ... \/ Tn) <= T  <=>  (T1 <= T) /\ ... /\ (Tn <= T)
+  if (this->is_union()) {
+    Handle<Unioned> unioned = this->as_union();
+    for (int i = 0; i < unioned->length(); ++i) {
+      Handle<Type> this_i = union_get(unioned, i);
+      if (!this_i->Is(that)) return false;
+    }
+    return true;
+  }
+
+  return false;
+}
+
+
+// Check this overlaps that.
+bool Type::Maybe(Handle<Type> that) {
+  // Fast path for bitsets.
+  if (this->is_bitset()) {
+    return (this->as_bitset() & that->LubBitset()) != 0;
+  }
+  if (that->is_bitset()) {
+    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();
+    for (int i = 0; i < unioned->length(); ++i) {
+      Handle<Type> this_i = union_get(unioned, i);
+      if (this_i->Maybe(that)) return true;
+    }
+    return false;
+  }
+
+  // T overlaps (T1 \/ ... \/ Tn) <=> (T overlaps T1) \/ ... \/ (T overlaps Tn)
+  if (that->is_union()) {
+    Handle<Unioned> unioned = that->as_union();
+    for (int i = 0; i < unioned->length(); ++i) {
+      Handle<Type> that_i = union_get(unioned, i);
+      if (this->Maybe(that_i)) return true;
+    }
+    return false;
+  }
+
+  return false;
+}
+
+
+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;
+  }
+  return false;
+}
+
+// Get non-bitsets from this which are not subsumed by that, store at unioned,
+// starting at index. Returns updated index.
+int Type::ExtendUnion(Handle<Unioned> result, int current_size) {
+  int old_size = current_size;
+  if (this->is_class() || this->is_constant()) {
+    if (!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->InUnion(result, old_size)) result->set(current_size++, *type);
+    }
+  }
+  return current_size;
+}
+
+
+// Union 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::Union(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 *type2;
+    if (type2->Is(type1)) return *type1;
+  }
+
+  // Slow case: may need to produce a Unioned object.
+  Isolate* isolate = NULL;
+  int size = type1->is_bitset() || type2->is_bitset() ? 1 : 0;
+  if (!type1->is_bitset()) {
+    isolate = HeapObject::cast(*type1)->GetIsolate();
+    size += (type1->is_union() ? type1->as_union()->length() : 1);
+  }
+  if (!type2->is_bitset()) {
+    if (isolate == NULL) isolate = HeapObject::cast(*type2)->GetIsolate();

[Sven Panne, 2013/06/05 08:02:41]

The test is a nano-optimization, leaving it out makes things more symmetrical.

[rossberg, 2013/06/05 09:44:24]

Done.

+    size += (type2->is_union() ? type2->as_union()->length() : 1);
+  }
+  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->ExtendUnion(unioned, size);
+  size = type2->ExtendUnion(unioned, size);
+
+  if (size == 1)
+    return *union_get(unioned, 0);
+  else if (size == unioned->length())
+    return from_handle(unioned);
+
+  // There was an overlap. 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) {
+  if (type->is_bitset())

[Sven Panne, 2013/06/05 08:02:41]

I would have expected a ternary ?: from you... ;-)

[rossberg, 2013/06/05 09:44:24]

Right you are! :)

+    return from_bitset(type->as_bitset() | kUndefined);
+  else
+    return Union(type, Undefined()->handle_via(*type));
+}
+
+} }  // namespace v8::internal