Enable stepping into callback passed to builtins (e.g. Array.forEach).

src/array.js

 // Copyright 2012 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
@@ skipping 1009 matching lines @@
   }
   if (IS_NULL_OR_UNDEFINED(receiver)) {
     receiver = %GetDefaultReceiver(f) || receiver;
   } else if (!IS_SPEC_OBJECT(receiver)) {
     receiver = ToObject(receiver);
   }
 
   var result = new $Array();
   var accumulator = new InternalArray();
   var accumulator_length = 0;
-  for (var i = 0; i < length; i++) {
-    if (i in array) {
-      var element = array[i];
-      if (%_CallFunction(receiver, element, i, array, f)) {
-        accumulator[accumulator_length++] = element;
+  if (%DebugStepIntoBuiltinCallback(f)) {

[Søren Gjesse, 2012/04/20 08:33:25]

Maybe rename DebugStepIntoBuiltinCallback to something like
DebugDoesFunctionSupportStepping.

[Søren Gjesse, 2012/04/20 08:33:25]

The only thing I don't like here is the code duplication. I don't have an
immediate idea, but it would be great if we could get rid of it somehow. It will
be prone to errors when changing the code missing one of the places.

[Søren Gjesse, 2012/04/20 08:33:25]

An important thing performance wise is that it should be quite simple to write
%DebugStepIntoBuiltinCallback as a %_DebugStepIntoBuiltinCallback (inline
assembly) function if this runtime call gives performance problems.

[Yang, 2012/04/20 11:06:54]

This would be great, but I have no idea how to check whether the debugger is
active from generated code... I'll implement this as a follow-up CL if you can
give me some hints.

[Yang, 2012/04/20 11:06:54]

I don't see anything simple either. The one way I can think of is to trigger
recompile of builtins for debugging as well, and insert code for
%DebugPrepareStepInIfStepping only when compiling for debugging. But that is a
lot more work and we would need to distinguish between builtins that do callback
and therefore need recompiling, and those that do not.

The way it's currently implemented has little impact on performance. I'll mark
duplicate code pieces with comments.

+    for (var i = 0; i < length; i++) {
+      if (i in array) {
+        var element = array[i];
+        // Prepare break slots for debugger step in.
+        %PrepareBreakSlotsForCallback(f);

[Søren Gjesse, 2012/04/20 08:33:25]

I think the name here i somewhat misleading. Maybe
"%DebugPrepareStepInIfStepping".

[Yang, 2012/04/20 11:06:54]

Done.

+        if (%_CallFunction(receiver, element, i, array, f)) {
+          accumulator[accumulator_length++] = element;
+        }
+      }
+    }
+  } else {
+    for (var i = 0; i < length; i++) {
+      if (i in array) {
+        var element = array[i];
+        if (%_CallFunction(receiver, element, i, array, f)) {
+          accumulator[accumulator_length++] = element;
+        }
       }
     }
   }
   %MoveArrayContents(accumulator, result);
   return result;
 }
 
 
 function ArrayForEach(f, receiver) {
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["Array.prototype.forEach"]);
   }
 
   // Pull out the length so that modifications to the length in the
   // loop will not affect the looping and side effects are visible.
   var array = ToObject(this);
   var length = TO_UINT32(array.length);
 
   if (!IS_SPEC_FUNCTION(f)) {
     throw MakeTypeError('called_non_callable', [ f ]);
   }
   if (IS_NULL_OR_UNDEFINED(receiver)) {
     receiver = %GetDefaultReceiver(f) || receiver;
   } else if (!IS_SPEC_OBJECT(receiver)) {
     receiver = ToObject(receiver);
   }
-
-  for (var i = 0; i < length; i++) {
-    if (i in array) {
-      var element = array[i];
-      %_CallFunction(receiver, element, i, array, f);
+  if (%DebugStepIntoBuiltinCallback(f)) {
+    for (var i = 0; i < length; i++) {
+      if (i in array) {
+        var element = array[i];
+        // Prepare break slots for debugger step in.
+        %PrepareBreakSlotsForCallback(f);
+        %_CallFunction(receiver, element, i, array, f);
+      }
+    }
+  } else {
+    for (var i = 0; i < length; i++) {
+      if (i in array) {
+        var element = array[i];
+        %_CallFunction(receiver, element, i, array, f);
+      }
     }
   }
 }
 
 
 // Executes the function once for each element present in the
 // array until it finds one where callback returns true.
 function ArraySome(f, receiver) {
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["Array.prototype.some"]);
   }
 
   // Pull out the length so that modifications to the length in the
   // loop will not affect the looping and side effects are visible.
   var array = ToObject(this);
   var length = TO_UINT32(array.length);
 
   if (!IS_SPEC_FUNCTION(f)) {
     throw MakeTypeError('called_non_callable', [ f ]);
   }
   if (IS_NULL_OR_UNDEFINED(receiver)) {
     receiver = %GetDefaultReceiver(f) || receiver;
   } else if (!IS_SPEC_OBJECT(receiver)) {
     receiver = ToObject(receiver);
   }
 
-  for (var i = 0; i < length; i++) {
-    if (i in array) {
-      var element = array[i];
-      if (%_CallFunction(receiver, element, i, array, f)) return true;
+  if (%DebugStepIntoBuiltinCallback(f)) {
+    for (var i = 0; i < length; i++) {
+      if (i in array) {
+        var element = array[i];
+        // Prepare break slots for debugger step in.
+        %PrepareBreakSlotsForCallback(f);
+        if (%_CallFunction(receiver, element, i, array, f)) return true;
+      }
+    }
+  } else {
+    for (var i = 0; i < length; i++) {
+      if (i in array) {
+        var element = array[i];
+        if (%_CallFunction(receiver, element, i, array, f)) return true;
+      }
     }
   }
   return false;
 }
 
 
 function ArrayEvery(f, receiver) {
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["Array.prototype.every"]);
   }
 
   // Pull out the length so that modifications to the length in the
   // loop will not affect the looping and side effects are visible.
   var array = ToObject(this);
   var length = TO_UINT32(array.length);
 
   if (!IS_SPEC_FUNCTION(f)) {
     throw MakeTypeError('called_non_callable', [ f ]);
   }
   if (IS_NULL_OR_UNDEFINED(receiver)) {
     receiver = %GetDefaultReceiver(f) || receiver;
   } else if (!IS_SPEC_OBJECT(receiver)) {
     receiver = ToObject(receiver);
   }
 
-  for (var i = 0; i < length; i++) {
-    if (i in array) {
-      var element = array[i];
-      if (!%_CallFunction(receiver, element, i, array, f)) return false;
+  if (%DebugStepIntoBuiltinCallback(f)) {
+    for (var i = 0; i < length; i++) {
+      if (i in array) {
+        var element = array[i];
+        // Prepare break slots for debugger step in.
+        %PrepareBreakSlotsForCallback(f);
+        if (!%_CallFunction(receiver, element, i, array, f)) return false;
+      }
+    }
+  } else {
+    for (var i = 0; i < length; i++) {
+      if (i in array) {
+        var element = array[i];
+        if (!%_CallFunction(receiver, element, i, array, f)) return false;
+      }
     }
   }
   return true;
 }
 
 function ArrayMap(f, receiver) {
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["Array.prototype.map"]);
   }
 
   // Pull out the length so that modifications to the length in the
   // loop will not affect the looping and side effects are visible.
   var array = ToObject(this);
   var length = TO_UINT32(array.length);
 
   if (!IS_SPEC_FUNCTION(f)) {
     throw MakeTypeError('called_non_callable', [ f ]);
   }
   if (IS_NULL_OR_UNDEFINED(receiver)) {
     receiver = %GetDefaultReceiver(f) || receiver;
   } else if (!IS_SPEC_OBJECT(receiver)) {
     receiver = ToObject(receiver);
   }
 
   var result = new $Array();
   var accumulator = new InternalArray(length);
-  for (var i = 0; i < length; i++) {
-    if (i in array) {
-      var element = array[i];
-      accumulator[i] = %_CallFunction(receiver, element, i, array, f);
+  if (%DebugStepIntoBuiltinCallback(f)) {
+    for (var i = 0; i < length; i++) {
+      if (i in array) {
+        var element = array[i];
+        // Prepare break slots for debugger step in.
+        %PrepareBreakSlotsForCallback(f);
+        accumulator[i] = %_CallFunction(receiver, element, i, array, f);
+      }
+    }
+  } else {
+    for (var i = 0; i < length; i++) {
+      if (i in array) {
+        var element = array[i];
+        accumulator[i] = %_CallFunction(receiver, element, i, array, f);
+      }
     }
   }
   %MoveArrayContents(accumulator, result);
   return result;
 }
 
 
 function ArrayIndexOf(element, index) {
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
@@ skipping 135 matching lines @@
       current = array[i];
       if (!IS_UNDEFINED(current) || i in array) {
         i++;
         break find_initial;
       }
     }
     throw MakeTypeError('reduce_no_initial', []);
   }
 
   var receiver = %GetDefaultReceiver(callback);
-  for (; i < length; i++) {
-    if (i in array) {
-      var element = array[i];
-      current = %_CallFunction(receiver, current, element, i, array, callback);
+
+  if (%DebugStepIntoBuiltinCallback(callback)) {
+    for (; i < length; i++) {
+      if (i in array) {
+        var element = array[i];
+        // Prepare break slots for debugger step in.
+        %PrepareBreakSlotsForCallback(callback);
+        current =
+          %_CallFunction(receiver, current, element, i, array, callback);
+      }
+    }
+  } else {
+    for (; i < length; i++) {
+      if (i in array) {
+        var element = array[i];
+        current =
+          %_CallFunction(receiver, current, element, i, array, callback);
+      }
     }
   }
   return current;
 }
 
 function ArrayReduceRight(callback, current) {
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["Array.prototype.reduceRight"]);
   }
@@ skipping 13 matching lines @@
       current = array[i];
       if (!IS_UNDEFINED(current) || i in array) {
         i--;
         break find_initial;
       }
     }
     throw MakeTypeError('reduce_no_initial', []);
   }
 
   var receiver = %GetDefaultReceiver(callback);
-  for (; i >= 0; i--) {
-    if (i in array) {
-      var element = array[i];
-      current = %_CallFunction(receiver, current, element, i, array, callback);
+
+  if (%DebugStepIntoBuiltinCallback(callback)) {
+    for (; i >= 0; i--) {
+      if (i in array) {
+        var element = array[i];
+        // Prepare break slots for debugger step in.
+        %PrepareBreakSlotsForCallback(callback);
+        current =
+          %_CallFunction(receiver, current, element, i, array, callback);
+      }
+    }
+  } else {
+    for (; i >= 0; i--) {
+      if (i in array) {
+        var element = array[i];
+        current =
+          %_CallFunction(receiver, current, element, i, array, callback);
+      }
     }
   }
   return current;
 }
 
 // ES5, 15.4.3.2
 function ArrayIsArray(obj) {
   return IS_ARRAY(obj);
 }
 
@@ skipping 57 matching lines @@
   // exposed to user code.
   // Adding only the functions that are actually used.
   SetUpLockedPrototype(InternalArray, $Array(), $Array(
     "join", getFunction("join", ArrayJoin),
     "pop", getFunction("pop", ArrayPop),
     "push", getFunction("push", ArrayPush)
   ));
 }
 
 SetUpArray();