Adjust pointer maps for branches when connecting live ranges.

src/lithium-allocator.cc

Index: src/lithium-allocator.cc
diff --git a/src/lithium-allocator.cc b/src/lithium-allocator.cc
index 9f5f1b97d8d60b0c5a084963224e4d98303f3401..d745b0c8d4f9a34fcfd878e6808b838494a16de2 100644
--- a/src/lithium-allocator.cc
+++ b/src/lithium-allocator.cc
@@ -1098,6 +1098,21 @@ void LAllocator::ResolveControlFlow(LiveRange* range,
       } else {
         ASSERT(pred->end()->SecondSuccessor() == NULL);
         gap = GetLastGap(pred);
+
+        // We are going to insert mov from one live-range to another before the
+        // branch instruction. Some branch instructions (e.g. loops' back edges)
+        // can potentially cause a GC so they have a pointer map.
+        // By insterting a move we essentially create a copy of a
+        // value which is invisible to PopulatePointerMaps(), because we store
+        // it into a location different from the operand of a live range
+        // covering a branch instruction.
+        // Thus we need to manually record a pointer.
+        if (HasTaggedValue(range->id())) {
+          LInstruction* branch = InstructionAt(pred->last_instruction_index());
+          if (branch->HasPointerMap()) {
+            branch->pointer_map()->RecordPointer(cur_op);
+          }
+        }
       }
       gap->GetOrCreateParallelMove(LGap::START)->AddMove(pred_op, cur_op);
     }