Allow optimistically hoisting elements transitions over accesses.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index dfffe41fca745672ace8ec5ec05774e91de132ed..e848b5e48ce2716d0f39205e1573e3fcd5026dc6 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -4661,19 +4661,9 @@ class HTransitionElementsKind: public HTemplateInstruction<1> {
         transitioned_map_(transitioned_map) {
     SetOperandAt(0, object);
     SetFlag(kUseGVN);
-    // Don't set GVN DependOn flags here. That would defeat GVN's detection of
-    // congruent HTransitionElementsKind instructions. Instruction hoisting
-    // handles HTransitionElementsKind instruction specially, explicitly adding
-    // DependsOn flags during its dependency calculations.
     SetGVNFlag(kChangesElementsKind);
-    if (original_map->has_fast_double_elements()) {
-      SetGVNFlag(kChangesElementsPointer);
-      SetGVNFlag(kChangesNewSpacePromotion);
-    }
-    if (transitioned_map->has_fast_double_elements()) {
-      SetGVNFlag(kChangesElementsPointer);
-      SetGVNFlag(kChangesNewSpacePromotion);
-    }
+    SetGVNFlag(kChangesElementsPointer);
+    SetGVNFlag(kChangesNewSpacePromotion);

[Michael Starzinger, 2012/10/01 13:13:48]

The kChangesNewSpacePromotion is mainly used for write-barrier removal. With
this change you defeat write-barrier removal for transitions that don't involve
doubles and hence won't allocate. Is this what you want?

[danno, 2012/10/01 14:08:47]

Please restore the original code with ifs, but still remove the comment, which
is no longer valid.

[Toon Verwaest, 2012/10/01 14:57:51]

Done.

     set_representation(Representation::Tagged());
   }