[turbofan] Fix silly bug in loop variable analysis.

src/compiler/loop-variable-optimizer.cc

Index: src/compiler/loop-variable-optimizer.cc
diff --git a/src/compiler/loop-variable-optimizer.cc b/src/compiler/loop-variable-optimizer.cc
index 39268f4303069a15a0bf586b7a395f7c1ee1ec6f..818cca8cfd67b46b5a96877c7b0a1ff58cfaf77d 100644
--- a/src/compiler/loop-variable-optimizer.cc
+++ b/src/compiler/loop-variable-optimizer.cc
@@ -221,7 +221,7 @@ 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;
 }