Index: llvm/trunk/lib/Transforms/Scalar/Scalarizer.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Scalar/Scalarizer.cpp
+++ llvm/trunk/lib/Transforms/Scalar/Scalarizer.cpp
@@ -306,7 +306,11 @@
   ValueVector &SV = Scattered[Op];
   if (!SV.empty()) {
     for (unsigned I = 0, E = SV.size(); I != E; ++I) {
-      Instruction *Old = cast<Instruction>(SV[I]);
+      Value *V = SV[I];
+      if (V == nullptr)
+        continue;
+
+      Instruction *Old = cast<Instruction>(V);
       CV[I]->takeName(Old);
       Old->replaceAllUsesWith(CV[I]);
       Old->eraseFromParent();
Index: llvm/trunk/test/Transforms/Scalarizer/crash-bug.ll
===================================================================
--- llvm/trunk/test/Transforms/Scalarizer/crash-bug.ll
+++ llvm/trunk/test/Transforms/Scalarizer/crash-bug.ll
@@ -0,0 +1,24 @@
+; RUN: opt %s -scalarizer -S -o - | FileCheck %s
+
+; Don't crash
+
+define void @foo() {
+  br label %bb1
+
+bb2:                                        ; preds = %bb1
+  %bb2_vec = shufflevector <2 x i16> <i16 0, i16 10000>,
+                           <2 x i16> %bb1_vec,
+                           <2 x i32> <i32 0, i32 3>
+  br label %bb1
+
+bb1:                                        ; preds = %bb2, %0
+  %bb1_vec = phi <2 x i16> [ <i16 100, i16 200>, %0 ], [ %bb2_vec, %bb2 ]
+;CHECK: bb1:
+;CHECK: %bb1_vec.i0 = phi i16 [ 100, %0 ], [ 0, %bb2 ]
+;CHECK: %bb1_vec.i1 = phi i16 [ 200, %0 ], [ %bb1_vec.i1, %bb2 ]
+  br i1 undef, label %bb3, label %bb2
+
+bb3:
+  ret void
+}
+