Maintain proper pointer map for branches when resolving phis.

src/lithium-allocator.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1011 matching lines @@
         LUnallocated* unalloc = new LUnallocated(LUnallocated::NONE);
         unalloc->set_virtual_register(op->id());
         operand = unalloc;
       }
       HBasicBlock* cur_block = block->predecessors()->at(j);
       // The gap move must be added without any special processing as in
       // the AddConstraintsGapMove.
       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 insterting a move we essentially create a copy of a

[fschneider, 2011/04/18 20:20:05]

->inserting

+      // 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());
     LLabel* label = chunk_->GetLabel(phi->block()->block_id());
     label->GetOrCreateParallelMove(LGap::START)->
         AddMove(phi_operand, live_range->GetSpillOperand());
     live_range->SetSpillStartIndex(phi->block()->first_instruction_index());
   }
 }
 
@@ skipping 1054 matching lines @@
     LiveRange* current = live_ranges()->at(i);
     if (current != NULL) current->Verify();
   }
 }
 
 
 #endif
 
 
 } }  // namespace v8::internal