- Cache on backtracking stack in the irregexp interpreter for future use.

src/interpreter-irregexp.cc

Index: src/interpreter-irregexp.cc
===================================================================
--- src/interpreter-irregexp.cc	(revision 2340)
+++ src/interpreter-irregexp.cc	(working copy)
@@ -142,6 +142,49 @@
 }
 
 
+// A simple abstraction over the backtracking stack used by the interpreter.
+// This backtracking stack does not grow automatically, but it ensures that the
+// the memory held by the stack is released or remembered in a cache if the
+// matching terminates.
+class BacktrackStack {
+ public:
+  explicit BacktrackStack() {
+    if (cache_ != NULL) {
+      // If the cache is not empty reuse the previously allocated stack.
+      data_ = cache_;
+      cache_ = NULL;
+    } else {
+      // Cache was empty. Allocate a new backtrack stack.
+      data_ = NewArray<int>(kBacktrackStackSize);
+    }
+  }
+
+  ~BacktrackStack() {
+    if (cache_ == NULL) {
+      // The cache is empty. Keep this backtrack stack around.
+      cache_ = data_;
+    } else {
+      // A backtrack stack was already cached, just release this one.
+      DeleteArray(data_);
+    }
+  }
+
+  int* data() const { return data_; }
+
+  int max_size() const { return kBacktrackStackSize; }
+
+ private:
+  static const int kBacktrackStackSize = 10000;
+
+  int* data_;
+  static int* cache_;
+
+  DISALLOW_COPY_AND_ASSIGN(BacktrackStack);
+};
+
+int* BacktrackStack::cache_ = NULL;
+
+
 template <typename Char>
 static bool RawMatch(const byte* code_base,
                      Vector<const Char> subject,
@@ -149,13 +192,13 @@
                      int current,
                      uint32_t current_char) {
   const byte* pc = code_base;
-  static const int kBacktrackStackSize = 10000;
-  // Use a SmartPointer here to ensure that the memory gets freed when the
-  // matching finishes.
-  SmartPointer<int> backtrack_stack(NewArray<int>(kBacktrackStackSize));
-  int* backtrack_stack_base = *backtrack_stack;
+  // BacktrackStack ensures that the memory allocated for the backtracking stack
+  // is returned to the system or cached if there is no stack being cached at
+  // the moment.
+  BacktrackStack backtrack_stack;
+  int* backtrack_stack_base = backtrack_stack.data();
   int* backtrack_sp = backtrack_stack_base;
-  int backtrack_stack_space = kBacktrackStackSize;
+  int backtrack_stack_space = backtrack_stack.max_size();
 #ifdef DEBUG
   if (FLAG_trace_regexp_bytecodes) {
     PrintF("\n\nStart bytecode interpreter\n\n");
@@ -210,7 +253,7 @@
         break;
       BYTECODE(SET_SP_TO_REGISTER)
         backtrack_sp = backtrack_stack_base + registers[insn >> BYTECODE_SHIFT];
-        backtrack_stack_space = kBacktrackStackSize -
+        backtrack_stack_space = backtrack_stack.max_size() -
                                 (backtrack_sp - backtrack_stack_base);
         pc += BC_SET_SP_TO_REGISTER_LENGTH;
         break;