Index: lib/CodeGen/GlobalISel/IRTranslator.cpp
===================================================================
--- lib/CodeGen/GlobalISel/IRTranslator.cpp
+++ lib/CodeGen/GlobalISel/IRTranslator.cpp
@@ -1129,6 +1129,17 @@
   ValToVReg.clear();
   FrameIndices.clear();
   MachinePreds.clear();
+  // MachineIRBuilder holds a DebugLoc which can hold on to a TrackingMDRef
+  // that can outlive the context.
+  // When the LLVMContext is destroyed, it first releases all MDNode references
+  // and then destroys the passes. If we don't clear the Builders(which may
+  // hold some ref), the DebugLoc will again get destroyed leading to
+  // undefined behavior.
+  // We do it here - but we could probably also do it in
+  // releaseMemory.
+  // This also clears various pointers that the Builders hold on to.
+  EntryBuilder = MachineIRBuilder();
+  CurBuilder = MachineIRBuilder();
 }
 
 bool IRTranslator::runOnMachineFunction(MachineFunction &CurMF) {