Index: lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -3534,7 +3534,12 @@
   unsigned SrcAS = SV->getType()->getPointerAddressSpace();
   unsigned DestAS = I.getType()->getPointerAddressSpace();
 
-  if (!TLI.isNoopAddrSpaceCast(SrcAS, DestAS))
+  // Do not insert address space conversion code when the target doesn't
+  // require it. Also skip cast expansion when casting an undefined
+  // value, as a casted undefined value is still an undefined value.
+  // to make it point
+  if (!TLI.isNoopAddrSpaceCast(SrcAS, DestAS) &&
+      !isa<UndefValue>(SV))
     N = DAG.getAddrSpaceCast(getCurSDLoc(), DestVT, N, SrcAS, DestAS);
 
   setValue(&I, N);
Index: test/CodeGen/AVR/undef-addrspacecast.ll
===================================================================
--- /dev/null
+++ test/CodeGen/AVR/undef-addrspacecast.ll
@@ -0,0 +1,10 @@
+; RUN: llc -mattr=avr6 < %s -march=avr | FileCheck %s
+
+; CHECK-LABEL: foo
+define void @foo() addrspace(1) {
+start:
+  %a = addrspacecast {} addrspace(1)* undef to {}*
+  store {}* %a, {}** undef, align 1
+  ret void
+}
+