Index: lib/CodeGen/GlobalISel/InstructionSelect.cpp
===================================================================
--- lib/CodeGen/GlobalISel/InstructionSelect.cpp
+++ lib/CodeGen/GlobalISel/InstructionSelect.cpp
@@ -100,8 +100,9 @@
     for (auto MII = std::prev(MBB->end()), Begin = MBB->begin();
          !ReachedBegin;) {
       // Keep track of the insertion range for debug printing.
-      const auto AfterIt = std::next(MII);
-
+      DEBUG({
+        const auto AfterIt = std::next(MII);
+      });
       // Select this instruction.
       MachineInstr &MI = *MII;
 
@@ -134,6 +135,7 @@
     }
   }
 
+#ifndef NDEBUG
   // Now that selection is complete, there are no more generic vregs.  Verify
   // that the size of the now-constrained vreg is unchanged and that it has a
   // register class.
@@ -161,6 +163,7 @@
   }
 
   MRI.getVRegToType().clear();
+#endif
 
   if (!TPC.isGlobalISelAbortEnabled() && (Failed || MF.size() == NumBlocks)) {
     MF.getProperties().set(MachineFunctionProperties::Property::FailedISel);