Add dump_symbol_stats to dump symbol table stats at the end of a test run

vm/symbols.cc

Index: vm/symbols.cc
===================================================================
--- vm/symbols.cc	(revision 15988)
+++ vm/symbols.cc	(working copy)
@@ -33,7 +33,12 @@
 #undef DEFINE_SYMBOL_LITERAL
 };
 
+intptr_t Symbols::num_of_grows_;
+intptr_t Symbols::collision_count_[kMaxCollisionBuckets];
 
+DEFINE_FLAG(bool, dump_symbol_stats, false, "Dump symbol table statistics");
+
+
 const char* Symbols::Name(SymbolId symbol) {
   ASSERT((symbol > kIllegal) && (symbol < kMaxPredefinedId));
   return names[symbol];
@@ -44,6 +49,13 @@
   // Should only be run by the vm isolate.
   ASSERT(isolate == Dart::vm_isolate());
 
+  if (FLAG_dump_symbol_stats) {
+    num_of_grows_ = 0;
+    for (intptr_t i = 0; i < kMaxCollisionBuckets; i++) {
+      collision_count_[i] = 0;
+    }
+  }
+
   // Create and setup a symbol table in the vm isolate.
   SetupSymbolTable(isolate);
 
@@ -268,8 +280,41 @@
 }
 
 
+void Symbols::DumpStats() {
+  if (FLAG_dump_symbol_stats) {
+    intptr_t table_size = 0;
+    dart::Smi& used = Smi::Handle();
+    Array& symbol_table = Array::Handle(Array::null());
+
+    // First dump VM symbol table stats.
+    symbol_table = Dart::vm_isolate()->object_store()->symbol_table();
+    table_size = symbol_table.Length() - 1;
+    used ^= symbol_table.At(table_size);
+    OS::Print("VM Isolate: Number of symbols : %"Pd"\n", used.Value());
+    OS::Print("VM Isolate: Symbol table capacity : %"Pd"\n", table_size);
+
+    // Now dump regular isolate symbol table stats.
+    symbol_table = Isolate::Current()->object_store()->symbol_table();
+    table_size = symbol_table.Length() - 1;
+    used ^= symbol_table.At(table_size);
+    OS::Print("Isolate: Number of symbols : %"Pd"\n", used.Value());
+    OS::Print("Isolate: Symbol table capacity : %"Pd"\n", table_size);
+
+    // Dump overall collision and growth counts.
+    OS::Print("Number of symbol table grows = %"Pd"\n", num_of_grows_);
+    OS::Print("Collision counts on add and lookup :\n");
+    intptr_t i = 0;
+    for (i = 0; i < (kMaxCollisionBuckets - 1); i++) {
+      OS::Print("  %"Pd" collisions => %"Pd"\n", i, collision_count_[i]);
+    }
+    OS::Print("  > %"Pd" collisions => %"Pd"\n", i, collision_count_[i]);
+  }
+}
+
+
 void Symbols::GrowSymbolTable(const Array& symbol_table) {
   // TODO(iposva): Avoid exponential growth.
+  num_of_grows_ += 1;
   intptr_t table_size = symbol_table.Length() - 1;
   intptr_t new_table_size = table_size * 2;
   Array& new_symbol_table = Array::Handle(Array::New(new_table_size + 1));
@@ -325,13 +370,21 @@
   // Last element of the array is the number of used elements.
   intptr_t table_size = symbol_table.Length() - 1;
   intptr_t index = hash % table_size;
+  intptr_t num_collisions = 0;
 
   String& symbol = String::Handle();
   symbol ^= symbol_table.At(index);
   while (!symbol.IsNull() && !symbol.Equals(characters, len)) {
     index = (index + 1) % table_size;  // Move to next element.
     symbol ^= symbol_table.At(index);
+    num_collisions += 1;
   }
+  if (FLAG_dump_symbol_stats) {
+    if (num_collisions >= kMaxCollisionBuckets) {
+      num_collisions = (kMaxCollisionBuckets - 1);
+    }
+    collision_count_[num_collisions] += 1;
+  }
   return index;  // Index of symbol if found or slot into which to add symbol.
 }