Irregexp: Backtrack past look-aheads works correctly.

Allows backtracking to clear registers instead of pushing and popping
them to restore state.
Redo of 1135 with bug fixed.


git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1156 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/ast.h

@@ -1521,9 +1521,15 @@ class RegExpCapture: public RegExpTree {
 
 class RegExpLookahead: public RegExpTree {
  public:
-  RegExpLookahead(RegExpTree* body, bool is_positive)
+  RegExpLookahead(RegExpTree* body,
+                  bool is_positive,
+                  int capture_count,
+                  int capture_from)
       : body_(body),
-        is_positive_(is_positive) { }
+        is_positive_(is_positive),
+        capture_count_(capture_count),
+        capture_from_(capture_from) { }
+
   virtual void* Accept(RegExpVisitor* visitor, void* data);
   virtual RegExpNode* ToNode(RegExpCompiler* compiler,
                              RegExpNode* on_success);
@@ -1535,9 +1541,13 @@ class RegExpLookahead: public RegExpTree {
   virtual int max_match() { return 0; }
   RegExpTree* body() { return body_; }
   bool is_positive() { return is_positive_; }
+  int capture_count() { return capture_count_; }
+  int capture_from() { return capture_from_; }
  private:
   RegExpTree* body_;
   bool is_positive_;
+  int capture_count_;
+  int capture_from_;
 };
 
 

src/jsregexp.h

@@ -719,13 +719,17 @@ class ActionNode: public SeqRegExpNode {
   };
   static ActionNode* SetRegister(int reg, int val, RegExpNode* on_success);
   static ActionNode* IncrementRegister(int reg, RegExpNode* on_success);
-  static ActionNode* StorePosition(int reg, RegExpNode* on_success);
+  static ActionNode* StorePosition(int reg,
+                                   bool is_capture,
+                                   RegExpNode* on_success);
   static ActionNode* ClearCaptures(Interval range, RegExpNode* on_success);
   static ActionNode* BeginSubmatch(int stack_pointer_reg,
                                    int position_reg,
                                    RegExpNode* on_success);
   static ActionNode* PositiveSubmatchSuccess(int stack_pointer_reg,
                                              int restore_reg,
+                                             int clear_capture_count,
+                                             int clear_capture_from,
                                              RegExpNode* on_success);
   static ActionNode* EmptyMatchCheck(int start_register,
                                      int repetition_register,
@@ -755,10 +759,13 @@ class ActionNode: public SeqRegExpNode {
     } u_increment_register;
     struct {
       int reg;
+      bool is_capture;
     } u_position_register;
     struct {
       int stack_pointer_register;
       int current_position_register;
+      int clear_register_count;
+      int clear_register_from;
     } u_submatch;
     struct {
       int start_register;
@@ -913,15 +920,22 @@ class EndNode: public RegExpNode {
 
 class NegativeSubmatchSuccess: public EndNode {
  public:
-  NegativeSubmatchSuccess(int stack_pointer_reg, int position_reg)
+  NegativeSubmatchSuccess(int stack_pointer_reg,
+                          int position_reg,
+                          int clear_capture_count,
+                          int clear_capture_start)
       : EndNode(NEGATIVE_SUBMATCH_SUCCESS),
         stack_pointer_register_(stack_pointer_reg),
-        current_position_register_(position_reg) { }
+        current_position_register_(position_reg),
+        clear_capture_count_(clear_capture_count),
+        clear_capture_start_(clear_capture_start) { }
   virtual bool Emit(RegExpCompiler* compiler, Trace* trace);
 
  private:
   int stack_pointer_register_;
   int current_position_register_;
+  int clear_capture_count_;
+  int clear_capture_start_;
 };
 
 
@@ -1087,18 +1101,20 @@ class Trace {
     friend class Trace;
   };
 
-  class DeferredCapture: public DeferredAction {
+  class DeferredCapture : public DeferredAction {
    public:
-    DeferredCapture(int reg, Trace* trace)
+    DeferredCapture(int reg, bool is_capture, Trace* trace)
         : DeferredAction(ActionNode::STORE_POSITION, reg),
           cp_offset_(trace->cp_offset()) { }
     int cp_offset() { return cp_offset_; }
+    bool is_capture() { return is_capture_; }
    private:
     int cp_offset_;
+    bool is_capture_;
     void set_cp_offset(int cp_offset) { cp_offset_ = cp_offset; }
   };
 
-  class DeferredSetRegister :public DeferredAction {
+  class DeferredSetRegister : public DeferredAction {
    public:
     DeferredSetRegister(int reg, int value)
         : DeferredAction(ActionNode::SET_REGISTER, reg),
@@ -1118,7 +1134,7 @@ class Trace {
     Interval range_;
   };
 
-  class DeferredIncrementRegister: public DeferredAction {
+  class DeferredIncrementRegister : public DeferredAction {
    public:
     explicit DeferredIncrementRegister(int reg)
         : DeferredAction(ActionNode::INCREMENT_REGISTER, reg) { }
@@ -1189,13 +1205,13 @@ class Trace {
   int FindAffectedRegisters(OutSet* affected_registers);
   void PerformDeferredActions(RegExpMacroAssembler* macro,
                                int max_register,
-                               OutSet& affected_registers);
+                               OutSet& affected_registers,
+                               OutSet* registers_to_pop,
+                               OutSet* registers_to_clear);
   void RestoreAffectedRegisters(RegExpMacroAssembler* macro,
                                 int max_register,
-                                OutSet& affected_registers);
-  void PushAffectedRegisters(RegExpMacroAssembler* macro,
-                             int max_register,
-                             OutSet& affected_registers);
+                                OutSet& registers_to_pop,
+                                OutSet& registers_to_clear);
   int cp_offset_;
   DeferredAction* actions_;
   Label* backtrack_;

src/parser.cc

@@ -4149,7 +4149,10 @@ RegExpTree* RegExpParser::ParseGroup() {
   } else {
     ASSERT(type == '=' || type == '!');
     bool is_positive = (type == '=');
-    return new RegExpLookahead(body, is_positive);
+    return new RegExpLookahead(body,
+                               is_positive,
+                               end_capture_index - capture_index,
+                               capture_index);
   }
 }
 

src/regexp-macro-assembler-ia32.cc

@@ -332,15 +332,29 @@ void RegExpMacroAssemblerIA32::CheckNotBackReferenceIgnoreCase(
     __ push(ebx);
     const int four_arguments = 4;
     FrameAlign(four_arguments, ecx);
-    // Put arguments into allocated stack area.
+    // Put arguments into allocated stack area, last argument highest on stack.
+    // Parameters are
+    //   UC16** buffer - really the String** of the input string
+    //   int byte_offset1 - byte offset from *buffer of start of capture
+    //   int byte_offset2 - byte offset from *buffer of current position
+    //   size_t byte_length - length of capture in bytes(!)
+
+    // Set byte_length.
     __ mov(Operand(esp, 3 * kPointerSize), ebx);
+    // Set byte_offset2.
+    // Found by adding negative string-end offset of current position (edi)
+    // to String** offset of end of string.
     __ mov(ecx, Operand(ebp, kInputEndOffset));
     __ add(edi, Operand(ecx));
     __ mov(Operand(esp, 2 * kPointerSize), edi);
+    // Set byte_offset1.
+    // Start of capture, where eax already holds string-end negative offset.
     __ add(eax, Operand(ecx));
     __ mov(Operand(esp, 1 * kPointerSize), eax);
+    // Set buffer. Original String** parameter to regexp code.
     __ mov(eax, Operand(ebp, kInputBuffer));
     __ mov(Operand(esp, 0 * kPointerSize), eax);
+
     Address function_address = FUNCTION_ADDR(&CaseInsensitiveCompareUC16);
     CallCFunction(function_address, four_arguments);
     // Pop original values before reacting on result value.
@@ -946,9 +960,12 @@ void RegExpMacroAssemblerIA32::WriteCurrentPositionToRegister(int reg,
 }
 
 
-void RegExpMacroAssemblerIA32::ClearRegister(int reg) {
+void RegExpMacroAssemblerIA32::ClearRegisters(int reg_from, int reg_to) {
+  ASSERT(reg_from <= reg_to);
   __ mov(eax, Operand(ebp, kInputStartMinusOne));
-  __ mov(register_location(reg), eax);
+  for (int reg = reg_from; reg <= reg_to; reg++) {
+    __ mov(register_location(reg), eax);
+  }
 }
 
 
@@ -987,8 +1004,8 @@ RegExpMacroAssemblerIA32::Result RegExpMacroAssemblerIA32::Execute(
                             stack_top);
 
   if (result < 0 && !Top::has_pending_exception()) {
-    // We detected a stack overflow in RegExp code, but haven't created
-    // the exception yet.
+    // We detected a stack overflow (on the backtrack stack) in RegExp code,
+    // but haven't created the exception yet.
     Top::StackOverflow();
   }
   return (result < 0) ? EXCEPTION : (result ? SUCCESS : FAILURE);
@@ -1170,6 +1187,9 @@ void RegExpMacroAssemblerIA32::CheckStackLimit() {
 
 
 void RegExpMacroAssemblerIA32::FrameAlign(int num_arguments, Register scratch) {
+  // TODO(lrn): Since we no longer use the system stack arbitrarily, we
+  // know the current stack alignment - esp points to the last regexp register.
+  // We can do this simpler then.
   int frameAlignment = OS::ActivationFrameAlignment();
   if (frameAlignment != 0) {
     // Make stack end at alignment and make room for num_arguments words

src/regexp-macro-assembler-ia32.h

@@ -110,7 +110,7 @@ class RegExpMacroAssemblerIA32: public RegExpMacroAssembler {
   virtual void SetRegister(int register_index, int to);
   virtual void Succeed();
   virtual void WriteCurrentPositionToRegister(int reg, int cp_offset);
-  virtual void ClearRegister(int reg);
+  virtual void ClearRegisters(int reg_from, int reg_to);
   virtual void WriteStackPointerToRegister(int reg);
 
   static Result Execute(Code* code,

src/regexp-macro-assembler-irregexp.cc

@@ -104,8 +104,11 @@ void RegExpMacroAssemblerIrregexp::WriteCurrentPositionToRegister(
 }
 
 
-void RegExpMacroAssemblerIrregexp::ClearRegister(int reg) {
-  SetRegister(reg, -1);
+void RegExpMacroAssemblerIrregexp::ClearRegisters(int reg_from, int reg_to) {
+  ASSERT(reg_from <= reg_to);
+  for (int reg = reg_from; reg <= reg_to; reg++) {
+    SetRegister(reg, -1);
+  }
 }
 
 

src/regexp-macro-assembler-irregexp.h

@@ -66,7 +66,7 @@ class RegExpMacroAssemblerIrregexp: public RegExpMacroAssembler {
   virtual void AdvanceRegister(int reg, int by);  // r[reg] += by.
   virtual void SetRegister(int register_index, int to);
   virtual void WriteCurrentPositionToRegister(int reg, int cp_offset);
-  virtual void ClearRegister(int reg);
+  virtual void ClearRegisters(int reg_from, int reg_to);
   virtual void ReadCurrentPositionFromRegister(int reg);
   virtual void WriteStackPointerToRegister(int reg);
   virtual void ReadStackPointerFromRegister(int reg);

src/regexp-macro-assembler-tracer.cc

@@ -150,9 +150,9 @@ void RegExpMacroAssemblerTracer::WriteCurrentPositionToRegister(int reg,
 }
 
 
-void RegExpMacroAssemblerTracer::ClearRegister(int reg) {
-  PrintF(" ClearRegister(register=%d);\n", reg);
-  assembler_->ClearRegister(reg);
+void RegExpMacroAssemblerTracer::ClearRegisters(int reg_from, int reg_to) {
+  PrintF(" ClearRegister(from=%d, to=%d);\n", reg_from, reg_to);
+  assembler_->ClearRegisters(reg_from, reg_to);
 }
 
 

src/regexp-macro-assembler-tracer.h

@@ -107,7 +107,7 @@ class RegExpMacroAssemblerTracer: public RegExpMacroAssembler {
   virtual void SetRegister(int register_index, int to);
   virtual void Succeed();
   virtual void WriteCurrentPositionToRegister(int reg, int cp_offset);
-  virtual void ClearRegister(int reg);
+  virtual void ClearRegisters(int reg_from, int reg_to);
   virtual void WriteStackPointerToRegister(int reg);
  private:
   RegExpMacroAssembler* assembler_;

src/regexp-macro-assembler.h

@@ -174,7 +174,7 @@ class RegExpMacroAssembler {
   virtual void SetRegister(int register_index, int to) = 0;
   virtual void Succeed() = 0;
   virtual void WriteCurrentPositionToRegister(int reg, int cp_offset) = 0;
-  virtual void ClearRegister(int reg) = 0;
+  virtual void ClearRegisters(int reg_from, int reg_to) = 0;
   virtual void WriteStackPointerToRegister(int reg) = 0;
 
  private:

test/mjsunit/regexp-capture.js

+// Copyright 2009 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.
+
+// Tests from http://blog.stevenlevithan.com/archives/npcg-javascript
+
+assertEquals(true, /(x)?\1y/.test("y"));
+assertEquals(["y", undefined], /(x)?\1y/.exec("y"));
+assertEquals(["y", undefined], /(x)?y/.exec("y"));
+assertEquals(["y", undefined], "y".match(/(x)?\1y/));
+assertEquals(["y", undefined], "y".match(/(x)?y/));
+assertEquals(["y"], "y".match(/(x)?\1y/g));
+assertEquals(["", undefined, ""], "y".split(/(x)?\1y/));
+assertEquals(["", undefined, ""], "y".split(/(x)?y/));
+assertEquals(0, "y".search(/(x)?\1y/));
+assertEquals("z", "y".replace(/(x)?\1y/, "z"));
+assertEquals("", "y".replace(/(x)?y/, "$1"));
+assertEquals("undefined", "y".replace(/(x)?\1y/,
+    function($0, $1){ 
+        return String($1); 
+    }));
+assertEquals("undefined", "y".replace(/(x)?y/, 
+    function($0, $1){ 
+        return String($1); 
+    }));
+assertEquals("undefined", "y".replace(/(x)?y/, 
+    function($0, $1){ 
+        return $1; 
+    }));

test/mjsunit/regexp-lookahead.js

+// Copyright 2009 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.
+
+// Tests captures in positive and negative look-ahead in regular expressions.
+
+function stringEscape(string) {
+  // Converts string to source literal.
+  return '"' + string.replace(/["\\]/g, "\\$1") + '"';
+}
+
+function testRE(re, input, expected_result) {
+  var testName = re + ".test(" + stringEscape(input) +")";
+  if (expected_result) {
+    assertTrue(re.test(input), testName);
+  } else {
+    assertFalse(re.test(input), testName);
+  }
+}
+
+function execRE(re, input, expected_result) {
+  var testName = re + ".exec('" + stringEscape(input) +"')";
+  assertEquals(expected_result, re.exec(input), testName);
+}
+
+// Test of simple positive lookahead.
+
+var re = /^(?=a)/;
+testRE(re, "a", true);
+testRE(re, "b", false);
+execRE(re, "a", [""]);
+
+re = /^(?=\woo)f\w/;
+testRE(re, "foo", true);
+testRE(re, "boo", false);
+testRE(re, "fao", false);
+testRE(re, "foa", false);
+execRE(re, "foo", ["fo"]);
+
+re = /(?=\w).(?=\W)/;
+testRE(re, ".a! ", true);
+testRE(re, ".! ", false);
+testRE(re, ".ab! ", true);
+execRE(re, ".ab! ", ["b"]);
+
+re = /(?=f(?=[^f]o))../;
+testRE(re, ", foo!", true);
+testRE(re, ", fo!", false);
+testRE(re, ", ffo", false);
+execRE(re, ", foo!", ["fo"]);
+
+// Positive lookahead with captures.
+re = /^[^\'\"]*(?=([\'\"])).*\1(\w+)\1/;
+testRE(re, "  'foo' ", true);
+testRE(re, '  "foo" ', true);
+testRE(re, " \" 'foo' ", false);
+testRE(re, " ' \"foo\" ", false);
+testRE(re, "  'foo\" ", false);
+testRE(re, "  \"foo' ", false);
+execRE(re, "  'foo' ", ["  'foo'", "'", "foo"]);
+execRE(re, '  "foo" ', ['  "foo"', '"', 'foo']);
+
+// Captures are cleared on backtrack past the look-ahead.
+re = /^(?:(?=(.))a|b)\1$/;
+testRE(re, "aa", true);
+testRE(re, "b", true);
+testRE(re, "bb", false);
+testRE(re, "a", false);
+execRE(re, "aa", ["aa", "a"]);
+execRE(re, "b", ["b", undefined]);
+
+re = /^(?=(.)(?=(.)\1\2)\2\1)\1\2/;
+testRE(re, "abab", true);
+testRE(re, "ababxxxxxxxx", true);
+testRE(re, "aba", false);
+execRE(re, "abab", ["ab", "a", "b"]);
+
+re = /^(?:(?=(.))a|b|c)$/;
+testRE(re, "a", true);
+testRE(re, "b", true);
+testRE(re, "c", true);
+testRE(re, "d", false);
+execRE(re, "a", ["a", "a"]);
+execRE(re, "b", ["b", undefined]);
+execRE(re, "c", ["c", undefined]);
+
+execRE(/^(?=(b))b/, "b", ["b", "b"]);
+execRE(/^(?:(?=(b))|a)b/, "ab", ["ab", undefined]);
+execRE(/^(?:(?=(b)(?:(?=(c))|d))|)bd/, "bd", ["bd", "b", undefined]);
+
+
+
+// Test of Negative Look-Ahead.
+
+re = /(?!x)./;
+testRE(re, "y", true);
+testRE(re, "x", false);
+execRE(re, "y", ["y"]);
+
+re = /(?!(\d))|\d/;
+testRE(re, "4", true);
+execRE(re, "4", ["4", undefined]);
+execRE(re, "x", ["", undefined]);
+
+
+// Test mixed nested look-ahead with captures.
+
+re = /^(?=(x)(?=(y)))/;
+testRE(re, "xy", true);
+testRE(re, "xz", false);
+execRE(re, "xy", ["", "x", "y"]);
+
+re = /^(?!(x)(?!(y)))/;
+testRE(re, "xy", true);
+testRE(re, "xz", false);
+execRE(re, "xy", ["", undefined, undefined]);
+
+re = /^(?=(x)(?!(y)))/;
+testRE(re, "xz", true);
+testRE(re, "xy", false)
+execRE(re, "xz", ["", "x", undefined]);
+
+re = /^(?!(x)(?=(y)))/;
+testRE(re, "xz", true);
+testRE(re, "xy", false);
+execRE(re, "xz", ["", undefined, undefined]);
+
+re = /^(?=(x)(?!(y)(?=(z))))/;
+testRE(re, "xaz", true);
+testRE(re, "xya", true);
+testRE(re, "xyz", false);
+testRE(re, "a", false);
+execRE(re, "xaz", ["", "x", undefined, undefined]);
+execRE(re, "xya", ["", "x", undefined, undefined]);
+
+re = /^(?!(x)(?=(y)(?!(z))))/;
+testRE(re, "a", true);
+testRE(re, "xa", true);
+testRE(re, "xyz", true);
+testRE(re, "xya", false);
+execRE(re, "a", ["", undefined, undefined, undefined]);
+execRE(re, "xa", ["", undefined, undefined, undefined]);
+execRE(re, "xyz", ["", undefined, undefined, undefined]);

test/mjsunit/regress/regress-187.js

+// Copyright 2008 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.
+
+// See http://code.google.com/p/v8/issues/detail?id=187
+
+assertEquals("f,", "foo".match(/(?:(?=(f)o)fx|)./));