Use stability to only conditionally flush information from the CheckMaps table.

src/hydrogen-check-elimination.cc

Index: src/hydrogen-check-elimination.cc
diff --git a/src/hydrogen-check-elimination.cc b/src/hydrogen-check-elimination.cc
index dafb632dc7ea9b77dc0eacf4803e32b7bbf16603..f1274696db90085396925ffeb1233e3fa8992a24 100644
--- a/src/hydrogen-check-elimination.cc
+++ b/src/hydrogen-check-elimination.cc
@@ -50,6 +50,7 @@ struct HCheckTableEntry {
   HValue* object_;  // The object being approximated. NULL => invalid entry.
   HInstruction* check_;  // The last check instruction.
   MapSet maps_;          // The set of known maps for the object.
+  bool is_stable_;
 };
 
 
@@ -103,8 +104,9 @@ class HCheckTable : public ZoneObject {
       }
       default: {
         // If the instruction changes maps uncontrollably, drop everything.
-        if (instr->CheckChangesFlag(kMaps) ||
-            instr->CheckChangesFlag(kOsrEntries)) {
+        if (instr->CheckChangesFlag(kOsrEntries)) {
+          Reset();
+        } else if (instr->CheckChangesFlag(kMaps)) {
           Kill();
         }
       }
@@ -126,6 +128,7 @@ class HCheckTable : public ZoneObject {
       new_entry->object_ = old_entry->object_;
       new_entry->check_ = NULL;
       new_entry->maps_ = old_entry->maps_->Copy(phase_->zone());
+      new_entry->is_stable_ = old_entry->is_stable_;
     }
     copy->cursor_ = cursor_;
     copy->size_ = size_;
@@ -142,7 +145,8 @@ class HCheckTable : public ZoneObject {
         HCheckTableEntry* pred_entry = copy->Find(phi_operand);
         if (pred_entry != NULL) {
           // Create an entry for a phi in the table.
-          copy->Insert(phi, NULL, pred_entry->maps_->Copy(phase_->zone()));
+          copy->Insert(phi, NULL, pred_entry->maps_->Copy(phase_->zone()),
+                       pred_entry->is_stable_);
         }
       }
     }
@@ -158,7 +162,7 @@ class HCheckTable : public ZoneObject {
         HValue* object = cmp->value()->ActualValue();
         HCheckTableEntry* entry = copy->Find(object);
         if (entry == NULL) {
-          copy->Insert(object, cmp->map());
+          copy->Insert(object, cmp->map(), cmp->is_stable());
         } else {
           MapSet list = new(phase_->zone()) UniqueSet<Map>();
           list->Add(cmp->map(), phase_->zone());
@@ -175,10 +179,10 @@ class HCheckTable : public ZoneObject {
         HCheckTableEntry* re = copy->Find(right);
         if (le == NULL) {
           if (re != NULL) {
-            copy->Insert(left, NULL, re->maps_->Copy(zone));
+            copy->Insert(left, NULL, re->maps_->Copy(zone), re->is_stable_);
           }
         } else if (re == NULL) {
-          copy->Insert(right, NULL, le->maps_->Copy(zone));
+          copy->Insert(right, NULL, le->maps_->Copy(zone), le->is_stable_);
         } else {
           MapSet intersect = le->maps_->Intersect(re->maps_, zone);
           le->maps_ = intersect;
@@ -230,6 +234,8 @@ class HCheckTable : public ZoneObject {
           } else {
             this_entry->maps_ =
                 this_entry->maps_->Union(that_entry->maps_, phase_->zone());
+            this_entry->is_stable_ =
+                this_entry->is_stable_ && that_entry->is_stable_;
             if (this_entry->check_ != that_entry->check_) {
               this_entry->check_ = NULL;
             }
@@ -310,7 +316,8 @@ class HCheckTable : public ZoneObject {
       }
     } else {
       // No entry; insert a new one.
-      Insert(object, instr, instr->map_set().Copy(phase_->zone()));
+      Insert(object, instr, instr->map_set().Copy(phase_->zone()),
+             instr->is_stable());
     }
   }
 
@@ -362,7 +369,8 @@ class HCheckTable : public ZoneObject {
       }
     } else {
       // No prior information.
-      Insert(object, map);
+      // TODO(verwaest): Tag map constants with stability.
+      Insert(object, map, false);
     }
   }
 
@@ -379,12 +387,13 @@ class HCheckTable : public ZoneObject {
     if (instr->has_transition()) {
       // This store transitions the object to a new map.
       Kill(object);
-      Insert(object, MapConstant(instr->transition()));
+      Insert(object, MapConstant(instr->transition()), instr->is_stable());
     } else if (IsMapAccess(instr->access())) {
       // This is a store directly to the map field of the object.
       Kill(object);
       if (!instr->value()->IsConstant()) return;
-      Insert(object, MapConstant(instr->value()));
+      // TODO(verwaest): Tag with stability.
+      Insert(object, MapConstant(instr->value()), false);
     } else {
       // If the instruction changes maps, it should be handled above.
       CHECK(!instr->CheckChangesFlag(kMaps));
@@ -424,12 +433,26 @@ class HCheckTable : public ZoneObject {
     }
   }
 
-  // Kill everything in the table.
-  void Kill() {
+  // Reset the table.
+  void Reset() {
     size_ = 0;
     cursor_ = 0;
   }
 
+  // Kill everything in the table.
+  void Kill() {

[Igor Sheludko, 2014/02/12 12:58:20]

KillNonStableEntries(); ?

[Toon Verwaest, 2014/02/12 14:53:34]

Done.

+    bool compact = false;
+    for (int i = 0; i < size_; i++) {
+      HCheckTableEntry* entry = &entries_[i];
+      ASSERT(entry->object_ != NULL);
+      if (!entry->is_stable_) {
+        entry->object_ = NULL;
+        compact = true;
+      }
+    }
+    if (compact) Compact();
+  }
+
   // Kill everything in the table that may alias {object}.
   void Kill(HValue* object) {
     bool compact = false;
@@ -513,17 +536,18 @@ class HCheckTable : public ZoneObject {
     return entry == NULL ? NULL : entry->maps_;
   }
 
-  void Insert(HValue* object, Unique<Map> map) {
+  void Insert(HValue* object, Unique<Map> map, bool is_stable) {
     MapSet list = new(phase_->zone()) UniqueSet<Map>();
     list->Add(map, phase_->zone());
-    Insert(object, NULL, list);
+    Insert(object, NULL, list, is_stable);
   }
 
-  void Insert(HValue* object, HCheckMaps* check, MapSet maps) {
+  void Insert(HValue* object, HCheckMaps* check, MapSet maps, bool is_stable) {
     HCheckTableEntry* entry = &entries_[cursor_++];
     entry->object_ = object;
     entry->check_ = check;
     entry->maps_ = maps;
+    entry->is_stable_ = is_stable;
     // If the table becomes full, wrap around and overwrite older entries.
     if (cursor_ == kMaxTrackedObjects) cursor_ = 0;
     if (size_ < kMaxTrackedObjects) size_++;
@@ -553,6 +577,7 @@ class HCheckMapsEffects : public ZoneObject {
  public:
   explicit HCheckMapsEffects(Zone* zone)
     : maps_stored_(false),
+      requires_reset_(false),
       stores_(5, zone) { }
 
   inline bool Disabled() {
@@ -568,7 +593,8 @@ class HCheckMapsEffects : public ZoneObject {
       }
       case HValue::kOsrEntry: {
         // Kill everything. Loads must not be hoisted past the OSR entry.
-        maps_stored_ = true;
+        requires_reset_ = true;
+        break;
       }
       default: {
         maps_stored_ |= (instr->CheckChangesFlag(kMaps) |
@@ -579,6 +605,10 @@ class HCheckMapsEffects : public ZoneObject {
 
   // Apply these effects to the given check elimination table.
   void Apply(HCheckTable* table) {
+    if (requires_reset_) {
+      table->Reset();
+      return;
+    }
     if (maps_stored_) {
       // Uncontrollable map modifications; kill everything.
       table->Kill();
@@ -596,6 +626,7 @@ class HCheckMapsEffects : public ZoneObject {
 
   // Union these effects with the other effects.
   void Union(HCheckMapsEffects* that, Zone* zone) {
+    requires_reset_ |= that->requires_reset_;
     maps_stored_ |= that->maps_stored_;
     for (int i = 0; i < that->stores_.length(); i++) {
       stores_.Add(that->stores_[i], zone);
@@ -604,6 +635,7 @@ class HCheckMapsEffects : public ZoneObject {
 
  private:
   bool maps_stored_ : 1;
+  bool requires_reset_ : 1;

[Igor Sheludko, 2014/02/12 12:58:20]

Consider replacing these flags with GVNFlagSet as was recently done in load
elimination (r19322).

[Toon Verwaest, 2014/02/12 14:53:34]

Done.

   ZoneList<HStoreNamedField*> stores_;
 };
 
@@ -620,7 +652,7 @@ void HCheckEliminationPhase::Run() {
   } else {
     // Perform only local analysis.
     for (int i = 0; i < graph()->blocks()->length(); i++) {
-      table->Kill();
+      table->Reset();
       engine.AnalyzeOneBlock(graph()->blocks()->at(i), table);
     }
   }