Index: lib/Transforms/Utils/BuildLibCalls.cpp
===================================================================
--- lib/Transforms/Utils/BuildLibCalls.cpp
+++ lib/Transforms/Utils/BuildLibCalls.cpp
@@ -716,6 +716,11 @@
   return B.CreateBitCast(V, B.getInt8PtrTy(AS), "cstr");
 }
 
+static Value *castToIntPtr(Value *V, IRBuilder<> &B, const DataLayout &DL) {
+  assert(V->getType()->isIntegerTy() && "expected integer type");
+  return B.CreateIntCast(V, B.getIntPtrTy(DL), false, "len.cast");
+}
+
 Value *llvm::emitStrLen(Value *Ptr, IRBuilder<> &B, const DataLayout &DL,
                         const TargetLibraryInfo *TLI) {
   if (!TLI->has(LibFunc_strlen))
@@ -763,7 +768,9 @@
                                           DL.getIntPtrType(Context));
   inferLibFuncAttributes(*M->getFunction("strncmp"), *TLI);
   CallInst *CI = B.CreateCall(
-      StrNCmp, {castToCStr(Ptr1, B), castToCStr(Ptr2, B), Len}, "strncmp");
+      StrNCmp,
+      {castToCStr(Ptr1, B), castToCStr(Ptr2, B), castToIntPtr(Len, B, DL)},
+      "strncmp");
 
   if (const Function *F = dyn_cast<Function>(StrNCmp->stripPointerCasts()))
     CI->setCallingConv(F->getCallingConv());
@@ -793,12 +800,16 @@
     return nullptr;
 
   Module *M = B.GetInsertBlock()->getModule();
+  const DataLayout &DL = M->getDataLayout();
+  LLVMContext &Context = M->getContext();
   Type *I8Ptr = B.getInt8PtrTy();
   Value *StrNCpy = M->getOrInsertFunction(Name, I8Ptr, I8Ptr, I8Ptr,
-                                          Len->getType());
+                                          DL.getIntPtrType(Context));
   inferLibFuncAttributes(*M->getFunction(Name), *TLI);
   CallInst *CI = B.CreateCall(
-      StrNCpy, {castToCStr(Dst, B), castToCStr(Src, B), Len}, "strncpy");
+      StrNCpy,
+      {castToCStr(Dst, B), castToCStr(Src, B), castToIntPtr(Len, B, DL)},
+      "strncpy");
   if (const Function *F = dyn_cast<Function>(StrNCpy->stripPointerCasts()))
     CI->setCallingConv(F->getCallingConv());
   return CI;
@@ -821,7 +832,8 @@
       DL.getIntPtrType(Context));
   Dst = castToCStr(Dst, B);
   Src = castToCStr(Src, B);
-  CallInst *CI = B.CreateCall(MemCpy, {Dst, Src, Len, ObjSize});
+  CallInst *CI = B.CreateCall(MemCpy, {Dst, Src, castToIntPtr(Len, B, DL),
+                                       castToIntPtr(ObjSize, B, DL)});
   if (const Function *F = dyn_cast<Function>(MemCpy->stripPointerCasts()))
     CI->setCallingConv(F->getCallingConv());
   return CI;
@@ -838,7 +850,8 @@
                                          B.getInt8PtrTy(), B.getInt32Ty(),
                                          DL.getIntPtrType(Context));
   inferLibFuncAttributes(*M->getFunction("memchr"), *TLI);
-  CallInst *CI = B.CreateCall(MemChr, {castToCStr(Ptr, B), Val, Len}, "memchr");
+  CallInst *CI = B.CreateCall(
+      MemChr, {castToCStr(Ptr, B), Val, castToIntPtr(Len, B, DL)}, "memchr");
 
   if (const Function *F = dyn_cast<Function>(MemChr->stripPointerCasts()))
     CI->setCallingConv(F->getCallingConv());
@@ -857,8 +870,11 @@
                                          B.getInt8PtrTy(), B.getInt8PtrTy(),
                                          DL.getIntPtrType(Context));
   inferLibFuncAttributes(*M->getFunction("memcmp"), *TLI);
+
   CallInst *CI = B.CreateCall(
-      MemCmp, {castToCStr(Ptr1, B), castToCStr(Ptr2, B), Len}, "memcmp");
+      MemCmp,
+      {castToCStr(Ptr1, B), castToCStr(Ptr2, B), castToIntPtr(Len, B, DL)},
+      "memcmp");
 
   if (const Function *F = dyn_cast<Function>(MemCmp->stripPointerCasts()))
     CI->setCallingConv(F->getCallingConv());
Index: test/Transforms/InstCombine/strncmp-wrong-datalayout.ll
===================================================================
--- /dev/null
+++ test/Transforms/InstCombine/strncmp-wrong-datalayout.ll
@@ -0,0 +1,21 @@
+; Test that the strncpy simplification doesn't crash if datalayout specifies
+; 64 bit pointers while length is a 32 bit argument
+;
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+target datalayout = "e-p:64:64:64"
+
+declare i32 @strncmp(i8*, i8*, i32)
+
+define i32 @test6(i8* %str1, i8* %str2) {
+; CHECK-LABEL: @test6(
+; CHECK: [[LOAD1:%[a-z]+]] = load i8, i8* %str1, align 1
+; CHECK: [[ZEXT1:%[a-z]+]] = zext i8 [[LOAD1]] to i32
+; CHECK: [[LOAD2:%[a-z]+]] = load i8, i8* %str2, align 1
+; CHECK: [[ZEXT2:%[a-z]+]] = zext i8 [[LOAD2]] to i32
+; CHECK: [[RET:%[a-z]+]] = sub nsw i32 [[ZEXT1]], [[ZEXT2]]
+; CHECK: ret i32 [[RET]]
+
+  %temp1 = call i32 @strncmp(i8* %str1, i8* %str2, i32 1)
+  ret i32 %temp1
+}