[X86] Remove dead code.

[courbet]

Summary

Remove the (dead) option for X86 memset to copy ualigned bytes with a second REPMOVS. It's not efficient to copy <8 bytes with this instruction anyway.

[craig.topper]

LGTM

[andreadb]

LGTM. Thanks!

[courbet]

This was submitted as r300952. Thanks.

lib/Target/X86/X86SelectionDAGInfo.cpp

#endif
   }
 
   uint64_t SizeVal = ConstantSize->getZExtValue();
   SDValue InFlag;
   EVT AVT;
   SDValue Count;
   ConstantSDNode *ValC = dyn_cast<ConstantSDNode>(Src);
   unsigned BytesLeft = 0;
-  bool TwoRepStos = false;
   if (ValC) {
     unsigned ValReg;
     uint64_t Val = ValC->getZExtValue() & 255;
 
     // If the value is a constant, then we can potentially use larger sets.
     switch (Align & 3) {
     case 2:   // WORD aligned
       AVT = MVT::i16;
#endif
   Chain = DAG.getCopyToReg(Chain, dl, Subtarget.is64Bit() ? X86::RDI : X86::EDI,
                            Dst, InFlag);
   InFlag = Chain.getValue(1);
 
   SDVTList Tys = DAG.getVTList(MVT::Other, MVT::Glue);
   SDValue Ops[] = { Chain, DAG.getValueType(AVT), InFlag };
   Chain = DAG.getNode(X86ISD::REP_STOS, dl, Tys, Ops);
 
-  if (TwoRepStos) {
-    InFlag = Chain.getValue(1);
-    Count  = Size;
-    EVT CVT = Count.getValueType();
-    SDValue Left = DAG.getNode(ISD::AND, dl, CVT, Count,
-                               DAG.getConstant((AVT == MVT::i64) ? 7 : 3, dl,
-                                               CVT));
-    Chain = DAG.getCopyToReg(Chain, dl, (CVT == MVT::i64) ? X86::RCX : X86::ECX,
-                             Left, InFlag);
-    InFlag = Chain.getValue(1);
-    Tys = DAG.getVTList(MVT::Other, MVT::Glue);
-    SDValue Ops[] = { Chain, DAG.getValueType(MVT::i8), InFlag };
-    Chain = DAG.getNode(X86ISD::REP_STOS, dl, Tys, Ops);
-  } else if (BytesLeft) {
+  if (BytesLeft) {
     // Handle the last 1 - 7 bytes.
     unsigned Offset = SizeVal - BytesLeft;
     EVT AddrVT = Dst.getValueType();
     EVT SizeVT = Size.getValueType();
 
     Chain = DAG.getMemset(Chain, dl,
                           DAG.getNode(ISD::ADD, dl, AddrVT, Dst,
                                       DAG.getConstant(Offset, dl, AddrVT)),