Index: llvm/trunk/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
===================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -959,6 +959,16 @@
   return nullptr;
 }
 
+static bool canSimplifyNullStoreOrGEP(StoreInst &SI) {
+  if (SI.getPointerAddressSpace() != 0)
+    return false;
+
+  auto *Ptr = SI.getPointerOperand();
+  if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Ptr))
+    Ptr = GEPI->getOperand(0);
+  return isa<ConstantPointerNull>(Ptr);
+}
+
 static bool canSimplifyNullLoadOrGEP(LoadInst &LI, Value *Op) {
   if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Op)) {
     const Value *GEPI0 = GEPI->getOperand(0);
@@ -1447,7 +1457,8 @@
   }
 
   // store X, null    -> turns into 'unreachable' in SimplifyCFG
-  if (isa<ConstantPointerNull>(Ptr) && SI.getPointerAddressSpace() == 0) {
+  // store X, GEP(null, Y) -> turns into 'unreachable' in SimplifyCFG
+  if (canSimplifyNullStoreOrGEP(SI)) {
     if (!isa<UndefValue>(Val)) {
       SI.setOperand(0, UndefValue::get(Val->getType()));
       if (Instruction *U = dyn_cast<Instruction>(Val))
Index: llvm/trunk/test/Transforms/InstCombine/store.ll
===================================================================
--- llvm/trunk/test/Transforms/InstCombine/store.ll
+++ llvm/trunk/test/Transforms/InstCombine/store.ll
@@ -20,6 +20,14 @@
 ; CHECK-NEXT: ret void
 }
 
+define void @store_at_gep_off_null(i64 %offset) {
+; CHECK-LABEL: @store_at_gep_off_null
+; CHECK: store i32 undef, i32* %ptr
+   %ptr = getelementptr i32, i32 *null, i64 %offset
+   store i32 24, i32* %ptr
+   ret void
+}
+
 ;; Simple sinking tests
 
 ; "if then else"