[turbofan] Fix silly bug in loop variable analysis.

src/compiler/loop-variable-optimizer.cc

 // Copyright 2016 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/compiler/loop-variable-optimizer.h"
 
 #include "src/compiler/common-operator.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/node-marker.h"
 #include "src/compiler/node-properties.h"
@@ skipping 203 matching lines @@
       return VisitLoopExit(node);
     default:
       return VisitOtherControl(node);
   }
 }
 
 void LoopVariableOptimizer::VisitMerge(Node* node) {
   // Merge the limits of all incoming edges.
   VariableLimits* merged = limits_[node->InputAt(0)->id()]->Copy(zone());
   for (int i = 1; i < node->InputCount(); i++) {
-    merged->Merge(limits_[node->InputAt(0)->id()]);
+    merged->Merge(limits_[node->InputAt(i)->id()]);
   }
   limits_[node->id()] = merged;
 }
 
 void LoopVariableOptimizer::VisitLoop(Node* node) {
   DetectInductionVariables(node);
   // Conservatively take the limits from the loop entry here.
   return TakeConditionsFromFirstControl(node);
 }
 
@@ skipping 160 matching lines @@
                                         backedge_value, backedge_control);
         induction_var->phi()->ReplaceInput(1, rename);
       }
     }
   }
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8