Fix bugs in IfBuilder and improve functionality

src/arm/lithium-arm.cc

Index: src/arm/lithium-arm.cc
diff --git a/src/arm/lithium-arm.cc b/src/arm/lithium-arm.cc
index f6029b51435fcadc41f5b86487855c3692e18463..64083e8597381c7549a356bb79e253cc6a8f13c5 100644
--- a/src/arm/lithium-arm.cc
+++ b/src/arm/lithium-arm.cc
@@ -823,11 +823,15 @@ void LChunkBuilder::DoBasicBlock(HBasicBlock* block, HBasicBlock* next_block) {
     HEnvironment* last_environment = pred->last_environment();
     for (int i = 0; i < block->phis()->length(); ++i) {
       HPhi* phi = block->phis()->at(i);
-      last_environment->SetValueAt(phi->merged_index(), phi);
+      if (phi->merged_index() < last_environment->length()) {
+        last_environment->SetValueAt(phi->merged_index(), phi);
+      }
     }
     for (int i = 0; i < block->deleted_phis()->length(); ++i) {
-      last_environment->SetValueAt(block->deleted_phis()->at(i),
-                                   graph_->GetConstantUndefined());
+      if (block->deleted_phis()->at(i) < last_environment->length()) {
+        last_environment->SetValueAt(block->deleted_phis()->at(i),
+                                     graph_->GetConstantUndefined());
+      }
     }
     block->UpdateEnvironment(last_environment);
     // Pick up the outgoing argument count of one of the predecessors.