[turbofan] Introduces another DCHECK in the register allocator.

src/compiler/register-allocator.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/base/adapters.h"
 #include "src/compiler/linkage.h"
 #include "src/compiler/register-allocator.h"
 #include "src/string-stream.h"
 
 namespace v8 {
@@ skipping 1096 matching lines @@
     first_interval_ = interval;
     last_interval_ = interval;
   } else {
     if (end == first_interval_->start()) {
       first_interval_->set_start(start);
     } else if (end < first_interval_->start()) {
       UseInterval* interval = new (zone) UseInterval(start, end);
       interval->set_next(first_interval_);
       first_interval_ = interval;
     } else {
+      // Order of instruction's processing (see ProcessInstructions) guarantees
+      // that each new use interval either precedes, intersects with or touches
+      // the last added interval.
+      DCHECK(start <= first_interval_->end());
       first_interval_->set_start(Min(start, first_interval_->start()));
       first_interval_->set_end(Max(end, first_interval_->end()));
     }
   }
 }
 
 
 void TopLevelLiveRange::AddUsePosition(UsePosition* use_pos) {
   LifetimePosition pos = use_pos->pos();
   TRACE("Add to live range %d use position %d\n", vreg(), pos.value());
@@ skipping 2492 matching lines @@
         }
       }
     }
   }
 }
 
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8