Improve load IC so it can call a native accessor even if the holder is

src/arm/stub-cache-arm.cc

Index: src/arm/stub-cache-arm.cc
===================================================================
--- src/arm/stub-cache-arm.cc	(revision 12254)
+++ src/arm/stub-cache-arm.cc	(working copy)
@@ -1230,6 +1230,42 @@
 }
 
 
+void StubCompiler::GenerateDictionaryLoadCallback(Register receiver,
+                                                  Register name_reg,
+                                                  Register scratch1,
+                                                  Register scratch2,
+                                                  Register scratch3,
+                                                  Handle<AccessorInfo> callback,
+                                                  Handle<String> name,
+                                                  Label* miss) {
+  Register dictionary = scratch1;
+  __ ldr(dictionary, FieldMemOperand(receiver, JSObject::kPropertiesOffset));
+
+  // Probe the dictionary.
+  Label probe_done;
+  StringDictionaryLookupStub::GeneratePositiveLookup(masm(),
+                                                     miss,
+                                                     &probe_done,
+                                                     dictionary,
+                                                     name_reg,
+                                                     scratch2,
+                                                     scratch3);
+  __ bind(&probe_done);
+
+  // If probing finds an entry in the dictionary, scratch2 contains the
+  // index into the dictionary. Check that the value is the callback.
+  Register index = scratch2;

[Toon Verwaest, 2012/08/06 13:49:24]

If you do this assignment before passing scratch2 (index) into
GeneratePositiveLookup, half of the comment becomes unnecessary.

[Erik Corry, 2012/08/06 14:26:46]

Done.

+  const int kElementsStartOffset =
+      StringDictionary::kHeaderSize +
+      StringDictionary::kElementsStartIndex * kPointerSize;
+  const int kValueOffset = kElementsStartOffset + kPointerSize;
+  __ add(scratch1, dictionary, Operand(kValueOffset - kHeapObjectTag));
+  __ ldr(scratch3, MemOperand(scratch1, index, LSL, kPointerSizeLog2));
+  __ cmp(scratch3, Operand(callback));
+  __ b(ne, miss);
+}
+
+
 void StubCompiler::GenerateLoadCallback(Handle<JSObject> object,
                                         Handle<JSObject> holder,
                                         Register receiver,
@@ -1247,6 +1283,11 @@
   Register reg = CheckPrototypes(object, receiver, holder, scratch1,
                                  scratch2, scratch3, name, miss);
 
+  if (!holder->HasFastProperties() && !holder->IsJSGlobalObject()) {
+    GenerateDictionaryLoadCallback(
+        receiver, name_reg, scratch1, scratch2, scratch3, callback, name, miss);
+  }
+
   // Build AccessorInfo::args_ list on the stack and push property name below
   // the exit frame to make GC aware of them and store pointers to them.
   __ push(receiver);