diff --git a/llvm/lib/Analysis/TargetLibraryInfo.cpp b/llvm/lib/Analysis/TargetLibraryInfo.cpp
--- a/llvm/lib/Analysis/TargetLibraryInfo.cpp
+++ b/llvm/lib/Analysis/TargetLibraryInfo.cpp
@@ -53,9 +53,9 @@
   return true;
 }
 
-static bool hasBcmp(const Triple &TT) {
-  // Posix removed support from bcmp() in 2001, but the glibc and several
-  // implementations of the libc still have it.
+static bool hasPosix2001LibCFunctions(const Triple &TT) {
+  // Posix removed support from some libc functions in 2001 (bcmp, bzero), but
+  // the glibc and several implementations of the libc still have it.
   if (TT.isOSLinux())
     return TT.isGNUEnvironment() || TT.isMusl();
   // Both NetBSD and OpenBSD are planning to remove the function. Windows does
@@ -143,8 +143,10 @@
     TLI.setUnavailable(LibFunc_sincospif_stret);
   }
 
-  if (!hasBcmp(T))
+  if (!hasPosix2001LibCFunctions(T)) {
+    TLI.setUnavailable(LibFunc_bzero);
     TLI.setUnavailable(LibFunc_bcmp);
+  }
 
   if (T.isMacOSX() && T.getArch() == Triple::x86 &&
       !T.isMacOSXVersionLT(10, 7)) {
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -27,6 +27,7 @@
 #include "llvm/Analysis/BlockFrequencyInfo.h"
 #include "llvm/Analysis/MemoryLocation.h"
 #include "llvm/Analysis/ProfileSummaryInfo.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/CodeGen/ISDOpcodes.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
@@ -6613,8 +6614,8 @@
 }
 
 SDValue SelectionDAG::getMemset(SDValue Chain, const SDLoc &dl, SDValue Dst,
-                                SDValue Src, SDValue Size, Align Alignment,
-                                bool isVol, bool isTailCall,
+                                SDValue ByteValue, SDValue Size,
+                                Align Alignment, bool isVol, bool isTailCall,
                                 MachinePointerInfo DstPtrInfo) {
   // Check to see if we should lower the memset to stores first.
   // For cases within the target-specified limits, this is the best choice.
@@ -6624,7 +6625,7 @@
     if (ConstantSize->isNullValue())
       return Chain;
 
-    SDValue Result = getMemsetStores(*this, dl, Chain, Dst, Src,
+    SDValue Result = getMemsetStores(*this, dl, Chain, Dst, ByteValue,
                                      ConstantSize->getZExtValue(), Alignment,
                                      isVol, DstPtrInfo);
 
@@ -6636,39 +6637,55 @@
   // code. If the target chooses to do this, this is the next best.
   if (TSI) {
     SDValue Result = TSI->EmitTargetCodeForMemset(
-        *this, dl, Chain, Dst, Src, Size, Alignment, isVol, DstPtrInfo);
+        *this, dl, Chain, Dst, ByteValue, Size, Alignment, isVol, DstPtrInfo);
     if (Result.getNode())
       return Result;
   }
 
   checkAddrSpaceIsValidForLibcall(TLI, DstPtrInfo.getAddrSpace());
 
+  const auto MakeArg = [](Type *Ty, SDValue Node) {
+    TargetLowering::ArgListEntry Entry;
+    Entry.Node = Node;
+    Entry.Ty = Ty;
+    return Entry;
+  };
+
   // Emit a library call.
-  TargetLowering::ArgListTy Args;
-  TargetLowering::ArgListEntry Entry;
-  Entry.Node = Dst; Entry.Ty = Type::getInt8PtrTy(*getContext());
-  Args.push_back(Entry);
-  Entry.Node = Src;
-  Entry.Ty = Src.getValueType().getTypeForEVT(*getContext());
-  Args.push_back(Entry);
-  Entry.Node = Size;
-  Entry.Ty = getDataLayout().getIntPtrType(*getContext());
-  Args.push_back(Entry);
+  llvm::LLVMContext &Ctx = *getContext();
+  const llvm::DataLayout &DL = getDataLayout();
+  ConstantSDNode *ConstantByteValue = dyn_cast<ConstantSDNode>(ByteValue);
+  if (ConstantByteValue && ConstantByteValue->isNullValue() &&
+      LibInfo->has(LibFunc_bzero)) {
+    TargetLowering::CallLoweringInfo CLI(*this);
+    CLI.setDebugLoc(dl)
+        .setChain(Chain)
+        .setLibCallee(CallingConv::C, Dst.getValueType().getTypeForEVT(Ctx),
+                      getExternalSymbol(LibInfo->getName(LibFunc_bzero).data(),
+                                        TLI->getPointerTy(DL)),
+                      {MakeArg(Type::getInt8PtrTy(Ctx), Dst),
+                       MakeArg(DL.getIntPtrType(Ctx), Size)})
+        .setDiscardResult();
+
+    return TLI->LowerCallTo(CLI).second;
+  }
 
   // FIXME: pass in SDLoc
   TargetLowering::CallLoweringInfo CLI(*this);
   CLI.setDebugLoc(dl)
       .setChain(Chain)
-      .setLibCallee(TLI->getLibcallCallingConv(RTLIB::MEMSET),
-                    Dst.getValueType().getTypeForEVT(*getContext()),
-                    getExternalSymbol(TLI->getLibcallName(RTLIB::MEMSET),
-                                      TLI->getPointerTy(getDataLayout())),
-                    std::move(Args))
+      .setLibCallee(
+          TLI->getLibcallCallingConv(RTLIB::MEMSET),
+          Dst.getValueType().getTypeForEVT(Ctx),
+          getExternalSymbol(TLI->getLibcallName(RTLIB::MEMSET),
+                            TLI->getPointerTy(DL)),
+          {MakeArg(Type::getInt8PtrTy(Ctx), Dst),
+           MakeArg(ByteValue.getValueType().getTypeForEVT(Ctx), ByteValue),
+           MakeArg(DL.getIntPtrType(Ctx), Size)})
       .setDiscardResult()
       .setTailCall(isTailCall);
 
-  std::pair<SDValue,SDValue> CallResult = TLI->LowerCallTo(CLI);
-  return CallResult.second;
+  return TLI->LowerCallTo(CLI).second;
 }
 
 SDValue SelectionDAG::getAtomicMemset(SDValue Chain, const SDLoc &dl,