Use Is*() helpers to shorten code in the optimizing compiler.

Change-Id: I79f31833bc9a0aa2918381aa3fb0b05d45f75689
diff --git a/compiler/optimizing/live_ranges_test.cc b/compiler/optimizing/live_ranges_test.cc
index 8be4746..81e2887 100644
--- a/compiler/optimizing/live_ranges_test.cc
+++ b/compiler/optimizing/live_ranges_test.cc
@@ -72,7 +72,7 @@
   // Last use is the return instruction.
   ASSERT_EQ(9u, range->GetEnd());
   HBasicBlock* block = graph->GetBlocks().Get(1);
-  ASSERT_TRUE(block->GetLastInstruction()->AsReturn() != nullptr);
+  ASSERT_TRUE(block->GetLastInstruction()->IsReturn());
   ASSERT_EQ(8u, block->GetLastInstruction()->GetLifetimePosition());
   ASSERT_TRUE(range->GetNext() == nullptr);
 }
@@ -118,7 +118,7 @@
   // Last use is the return instruction.
   ASSERT_EQ(23u, range->GetEnd());
   HBasicBlock* block = graph->GetBlocks().Get(3);
-  ASSERT_TRUE(block->GetLastInstruction()->AsReturn() != nullptr);
+  ASSERT_TRUE(block->GetLastInstruction()->IsReturn());
   ASSERT_EQ(22u, block->GetLastInstruction()->GetLifetimePosition());
   ASSERT_TRUE(range->GetNext() == nullptr);
 }