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

src/array.js

Index: src/array.js
diff --git a/src/array.js b/src/array.js
index d61183779c7a283e73218dd3032bf08421aac04c..26dbcd8fbea491d279ea97ace2287040f89d5bb5 100644
--- a/src/array.js
+++ b/src/array.js
@@ -1027,11 +1027,24 @@ function ArrayFilter(f, 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;
+        }
       }
     }
   }
@@ -1059,11 +1072,21 @@ function ArrayForEach(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);
+      }
     }
   }
 }
@@ -1091,10 +1114,21 @@ function ArraySome(f, 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;
@@ -1121,10 +1155,21 @@ function ArrayEvery(f, 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;
@@ -1152,10 +1197,21 @@ function ArrayMap(f, 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);
@@ -1311,10 +1367,24 @@ function ArrayReduce(callback, current) {
   }
 
   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;
@@ -1348,10 +1418,24 @@ function ArrayReduceRight(callback, current) {
   }
 
   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;