Refactor dependent code.

This simplifies the layout of dependent code array and optimizes it for sparse dependency groups.

BUG=chromium:554488
LOG=NO

Review URL: https://codereview.chromium.org/1435313002

Cr-Commit-Position: refs/heads/master@{#32170}

src/crankshaft/lithium.cc

@@ -441,8 +441,7 @@ void LChunk::RegisterWeakObjectsInOptimizedCode(Handle<Code> code) const {
     }
   }
   for (int i = 0; i < maps.length(); i++) {
-    if (maps.at(i)->dependent_code()->number_of_entries(
-            DependentCode::kWeakCodeGroup) == 0) {
+    if (maps.at(i)->dependent_code()->IsEmpty(DependentCode::kWeakCodeGroup)) {
       isolate()->heap()->AddRetainedMap(maps.at(i));
     }
     Map::AddDependentCode(maps.at(i), DependentCode::kWeakCodeGroup, code);

src/objects-debug.cc

@@ -351,8 +351,7 @@ void Map::VerifyOmittedMapChecks() {
   if (!is_stable() ||
       is_deprecated() ||
       is_dictionary_map()) {
-    CHECK_EQ(0, dependent_code()->number_of_entries(
-        DependentCode::kPrototypeCheckGroup));
+    CHECK(dependent_code()->IsEmpty(DependentCode::kPrototypeCheckGroup));
   }
 }
 

src/objects-inl.h

@@ -4873,14 +4873,38 @@ bool Map::CanOmitMapChecks() {
 }
 
 
-int DependentCode::number_of_entries(DependencyGroup group) {
-  if (length() == 0) return 0;
-  return Smi::cast(get(group))->value();
+DependentCode* DependentCode::next_link() {
+  return DependentCode::cast(get(kNextLinkIndex));
 }
 
 
-void DependentCode::set_number_of_entries(DependencyGroup group, int value) {
-  set(group, Smi::FromInt(value));
+void DependentCode::set_next_link(DependentCode* next) {
+  set(kNextLinkIndex, next);
+}
+
+
+int DependentCode::flags() { return Smi::cast(get(kFlagsIndex))->value(); }
+
+
+void DependentCode::set_flags(int flags) {
+  set(kFlagsIndex, Smi::FromInt(flags));
+}
+
+
+int DependentCode::count() { return CountField::decode(flags()); }
+
+void DependentCode::set_count(int value) {
+  set_flags(CountField::update(flags(), value));
+}
+
+
+DependentCode::DependencyGroup DependentCode::group() {
+  return static_cast<DependencyGroup>(GroupField::decode(flags()));
+}
+
+
+void DependentCode::set_group(DependentCode::DependencyGroup group) {
+  set_flags(GroupField::update(flags(), static_cast<int>(group)));
 }
 
 
@@ -4904,16 +4928,6 @@ void DependentCode::copy(int from, int to) {
 }
 
 
-void DependentCode::ExtendGroup(DependencyGroup group) {
-  GroupStartIndexes starts(this);
-  for (int g = kGroupCount - 1; g > group; g--) {
-    if (starts.at(g) < starts.at(g + 1)) {
-      copy(starts.at(g), starts.at(g + 1));
-    }
-  }
-}
-
-
 void Code::set_flags(Code::Flags flags) {
   STATIC_ASSERT(Code::NUMBER_OF_KINDS <= KindField::kMax + 1);
   WRITE_INT_FIELD(this, kFlagsOffset, flags);

src/objects.h

@@ -5343,24 +5343,24 @@ class Code: public HeapObject {
 };
 
 
-// This class describes the layout of dependent codes array of a map. The
-// array is partitioned into several groups of dependent codes. Each group
-// contains codes with the same dependency on the map. The array has the
-// following layout for n dependency groups:
+// Dependent code is a singly linked list of fixed arrays. Each array contains
+// code objects in weak cells for one dependent group. The suffix of the array
+// can be filled with the undefined value if the number of codes is less than
+// the length of the array.
 //
-// +----+----+-----+----+---------+----------+-----+---------+-----------+
-// | C1 | C2 | ... | Cn | group 1 |  group 2 | ... | group n | undefined |
-// +----+----+-----+----+---------+----------+-----+---------+-----------+
+// +------+-----------------+--------+--------+-----+--------+-----------+-----+
+// | next | count & group 1 | code 1 | code 2 | ... | code n | undefined | ... |
+// +------+-----------------+--------+--------+-----+--------+-----------+-----+
+//    |
+//    V
+// +------+-----------------+--------+--------+-----+--------+-----------+-----+
+// | next | count & group 2 | code 1 | code 2 | ... | code m | undefined | ... |
+// +------+-----------------+--------+--------+-----+--------+-----------+-----+
+//    |
+//    V
+// empty_fixed_array()
 //
-// The first n elements are Smis, each of them specifies the number of codes
-// in the corresponding group. The subsequent elements contain grouped code
-// objects in weak cells. The suffix of the array can be filled with the
-// undefined value if the number of codes is less than the length of the
-// array. The order of the code objects within a group is not preserved.
-//
-// All code indexes used in the class are counted starting from the first
-// code object of the first group. In other words, code index 0 corresponds
-// to array index n = kCodesStartIndex.
+// The list of fixed arrays is ordered by dependency groups.
 
 class DependentCode: public FixedArray {
  public:
@@ -5395,19 +5395,8 @@ class DependentCode: public FixedArray {
 
   static const int kGroupCount = kAllocationSiteTransitionChangedGroup + 1;
 
-  // Array for holding the index of the first code object of each group.
-  // The last element stores the total number of code objects.
-  class GroupStartIndexes {
-   public:
-    explicit GroupStartIndexes(DependentCode* entries);
-    void Recompute(DependentCode* entries);
-    int at(int i) { return start_indexes_[i]; }
-    int number_of_entries() { return start_indexes_[kGroupCount]; }
-   private:
-    int start_indexes_[kGroupCount + 1];
-  };
-
   bool Contains(DependencyGroup group, WeakCell* code_cell);
+  bool IsEmpty(DependencyGroup group);
 
   static Handle<DependentCode> InsertCompilationDependencies(
       Handle<DependentCode> entries, DependencyGroup group,
@@ -5431,8 +5420,12 @@ class DependentCode: public FixedArray {
 
   // The following low-level accessors should only be used by this class
   // and the mark compact collector.
-  inline int number_of_entries(DependencyGroup group);
-  inline void set_number_of_entries(DependencyGroup group, int value);
+  inline DependentCode* next_link();
+  inline void set_next_link(DependentCode* next);
+  inline int count();
+  inline void set_count(int value);
+  inline DependencyGroup group();
+  inline void set_group(DependencyGroup group);
   inline Object* object_at(int i);
   inline void set_object_at(int i, Object* object);
   inline void clear_at(int i);
@@ -5446,10 +5439,9 @@ class DependentCode: public FixedArray {
   static Handle<DependentCode> Insert(Handle<DependentCode> entries,
                                       DependencyGroup group,
                                       Handle<Object> object);
+  static Handle<DependentCode> New(DependencyGroup group, Handle<Object> object,
+                                   Handle<DependentCode> next);
   static Handle<DependentCode> EnsureSpace(Handle<DependentCode> entries);
-  // Make a room at the end of the given group by moving out the first
-  // code objects of the subsequent groups.
-  inline void ExtendGroup(DependencyGroup group);
   // Compact by removing cleared weak cells and return true if there was
   // any cleared weak cell.
   bool Compact();
@@ -5457,7 +5449,14 @@ class DependentCode: public FixedArray {
     if (number_of_entries < 5) return number_of_entries + 1;
     return number_of_entries * 5 / 4;
   }
-  static const int kCodesStartIndex = kGroupCount;
+  inline int flags();
+  inline void set_flags(int flags);
+  class GroupField : public BitField<int, 0, 3> {};
+  class CountField : public BitField<int, 3, 27> {};
+  STATIC_ASSERT(kGroupCount <= GroupField::kMax + 1);
+  static const int kNextLinkIndex = 0;
+  static const int kFlagsIndex = 1;
+  static const int kCodesStartIndex = 2;
 };
 
 

test/cctest/test-heap.cc

@@ -4723,12 +4723,12 @@ TEST(EnsureAllocationSiteDependentCodesProcessed) {
 
     CompileRun("%OptimizeFunctionOnNextCall(bar); bar();");
 
-    DependentCode::GroupStartIndexes starts(site->dependent_code());
-    CHECK_GE(starts.number_of_entries(), 1);
-    int index = starts.at(DependentCode::kAllocationSiteTransitionChangedGroup);
-    CHECK(site->dependent_code()->object_at(index)->IsWeakCell());
+    CHECK_EQ(DependentCode::kAllocationSiteTransitionChangedGroup,
+             site->dependent_code()->group());
+    CHECK_EQ(1, site->dependent_code()->count());
+    CHECK(site->dependent_code()->object_at(0)->IsWeakCell());
     Code* function_bar = Code::cast(
-        WeakCell::cast(site->dependent_code()->object_at(index))->value());
+        WeakCell::cast(site->dependent_code()->object_at(0))->value());
     Handle<JSFunction> bar_handle = Handle<JSFunction>::cast(
         v8::Utils::OpenHandle(*v8::Local<v8::Function>::Cast(
             CcTest::global()
@@ -4745,10 +4745,8 @@ TEST(EnsureAllocationSiteDependentCodesProcessed) {
 
   // The site still exists because of our global handle, but the code is no
   // longer referred to by dependent_code().
-  DependentCode::GroupStartIndexes starts(site->dependent_code());
-  int index = starts.at(DependentCode::kAllocationSiteTransitionChangedGroup);
-  CHECK(site->dependent_code()->object_at(index)->IsWeakCell() &&
-        WeakCell::cast(site->dependent_code()->object_at(index))->cleared());
+  CHECK(site->dependent_code()->object_at(0)->IsWeakCell() &&
+        WeakCell::cast(site->dependent_code()->object_at(0))->cleared());
 }