Index: lib/Target/ARM/ARMCodeGenPrepare.cpp
===================================================================
--- lib/Target/ARM/ARMCodeGenPrepare.cpp
+++ lib/Target/ARM/ARMCodeGenPrepare.cpp
@@ -114,8 +114,8 @@
   SmallPtrSet<Value*, 8> Promoted;
   Module *M = nullptr;
   LLVMContext &Ctx;
-  Type *ExtTy = nullptr;
-  Type *OrigTy = nullptr;
+  IntegerType *ExtTy = nullptr;
+  IntegerType *OrigTy = nullptr;
 
   void PrepareConstants(SmallPtrSetImpl<Value*> &Visited,
                          SmallPtrSetImpl<Instruction*> &SafeToPromote);
@@ -139,6 +139,8 @@
     }
     InstsToRemove.clear();
     NewInsts.clear();
+    TruncTysMap.clear();
+    Promoted.clear();
   }
 
   void Mutate(Type *OrigTy,
@@ -514,21 +516,24 @@
   IRBuilder<> Builder{Ctx};
 
   auto InsertZExt = [&](Value *V, Instruction *InsertPt) {
+    assert(V->getType() != ExtTy && "zext already extends to i32");
     LLVM_DEBUG(dbgs() << "ARM CGP: Inserting ZExt for " << *V << "\n");
     Builder.SetInsertPoint(InsertPt);
     if (auto *I = dyn_cast<Instruction>(V))
       Builder.SetCurrentDebugLocation(I->getDebugLoc());
-    auto *ZExt = cast<Instruction>(Builder.CreateZExt(V, ExtTy));
-    if (isa<Argument>(V))
-      ZExt->moveBefore(InsertPt);
-    else
-      ZExt->moveAfter(InsertPt);
+
+    Value *ZExt = Builder.CreateZExt(V, ExtTy);
+    if (auto *I = dyn_cast<Instruction>(ZExt)) {
+      if (isa<Argument>(V))
+        I->moveBefore(InsertPt);
+      else
+        I->moveAfter(InsertPt);
+      NewInsts.insert(I);
+    }
     ReplaceAllUsersOfWith(V, ZExt);
-    NewInsts.insert(ZExt);
     TruncTysMap[ZExt] = TruncTysMap[V];
   };
 
-
   // Now, insert extending instructions between the sources and their users.
   LLVM_DEBUG(dbgs() << "ARM CGP: Promoting sources:\n");
   for (auto V : Sources) {
@@ -673,7 +678,11 @@
                         SmallPtrSetImpl<Instruction*> &SafeToPromote) {
   LLVM_DEBUG(dbgs() << "ARM CGP: Promoting use-def chains to from "
              << ARMCodeGenPrepare::TypeSize << " to 32-bits\n");
-  this->OrigTy = OrigTy;
+
+  assert(isa<IntegerType>(OrigTy) && "expected integer type");
+  this->OrigTy = cast<IntegerType>(OrigTy);
+  assert(OrigTy->getPrimitiveSizeInBits() < ExtTy->getPrimitiveSizeInBits() &&
+         "original type not smaller than extended type");
 
   // Cache original types.
   for (auto *V : Visited)