Maintain proper pointer map for branches when resolving phis.

The same was done for gap moves connecting live ranges in r6858.

Review URL: http://codereview.chromium.org/6873053

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7650 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/lithium-allocator.cc

@@ -1029,6 +1029,22 @@ void LAllocator::ResolvePhis(HBasicBlock* block) {
       chunk_->AddGapMove(cur_block->last_instruction_index() - 1,
                          operand,
                          phi_operand);
+
+      // We are going to insert a move before the branch instruction.
+      // Some branch instructions (e.g. loops' back edges)
+      // can potentially cause a GC so they have a pointer map.
+      // By inserting 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 (phi->representation().IsTagged()) {
+        LInstruction* branch =
+            InstructionAt(cur_block->last_instruction_index());
+        if (branch->HasPointerMap()) {
+          branch->pointer_map()->RecordPointer(phi_operand);
+        }
+      }
     }
 
     LiveRange* live_range = LiveRangeFor(phi->id());
@@ -1116,7 +1132,7 @@ void LAllocator::ResolveControlFlow(LiveRange* range,
         // We are going to insert a move 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
+        // By inserting 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.