Fix LOperand aliasing bug in the register allocator, avoid splitting very short live ranges.

src/lithium-allocator.cc

 // Copyright 2012 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 833 matching lines @@
         cur_input->set_virtual_register(GetVirtualRegister());
         if (!AllocationOk()) return;
 
         if (RequiredRegisterKind(input_copy->virtual_register()) ==
             DOUBLE_REGISTERS) {
           double_artificial_registers_.Add(
               cur_input->virtual_register() - first_artificial_register_,
               zone_);
         }
 
-        AddConstraintsGapMove(gap_index, input_copy, cur_input);
+        LUnallocated* cur_input_copy = cur_input->CopyUnconstrained();
+        cur_input_copy->set_policy(cur_input->policy());
+
+        AddConstraintsGapMove(gap_index, input_copy, cur_input_copy);
       }
     }
   }
 
   // Handle "output same as input" for second instruction.
   if (second != NULL && second->Output() != NULL) {
     LUnallocated* second_output = LUnallocated::cast(second->Output());
     if (second_output->HasSameAsInputPolicy()) {
       LUnallocated* cur_input = LUnallocated::cast(second->FirstInput());
       int output_vreg = second_output->virtual_register();
@@ skipping 979 matching lines @@
 
 void LAllocator::AllocateBlockedReg(LiveRange* current) {
   UsePosition* register_use = current->NextRegisterPosition(current->Start());
   if (register_use == NULL) {
     // There is no use in the current live range that requires a register.
     // We can just spill it.
     Spill(current);
     return;
   }
 
-
   LifetimePosition use_pos[DoubleRegister::kNumAllocatableRegisters];
   LifetimePosition block_pos[DoubleRegister::kNumAllocatableRegisters];
 
   for (int i = 0; i < DoubleRegister::kNumAllocatableRegisters; i++) {
     use_pos[i] = block_pos[i] = LifetimePosition::MaxPosition();
   }
 
   for (int i = 0; i < active_live_ranges_.length(); ++i) {
     LiveRange* range = active_live_ranges_[i];
     int cur_reg = range->assigned_register();
@@ skipping 244 matching lines @@
     LiveRange* current = live_ranges()->at(i);
     if (current != NULL) current->Verify();
   }
 }
 
 
 #endif
 
 
 } }  // namespace v8::internal