[NFC] Fix auto usage to avoid copies

[akshaykhadse]

Summary

Fixes some usages of the "auto" keyword to avoid creation of copies.

[LuoYuanke]

llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp

857 ↗

(On Diff #507621)

I notice in https://llvm.org/docs/CodingStandards.html#use-auto-type-deduction-to-make-code-more-readable, the example code show "auto &Val". Should we follow the same style "auto &Pair". Ditto for others?

[craig.topper]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

20966

Doesn't the deference operator for enumerate return by value?

[craig.topper]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

20966

So I'm not sure this is really preventing a copy.

[akshaykhadse]

Addressed comments

[LuoYuanke]

llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp

857 ↗

(On Diff #507631)

@craig.topper, how about this one? Does the iteration return reference? For basic practice "auto &" is better than "auto"?

[akshaykhadse]

Avoid using references for enumerate

[akshaykhadse]

Address Craig's comments

[LuoYuanke]

LGTM

[LuoYuanke]

@akshaykhadse, do you want me to help merge the patch?

[akshaykhadse]

In D146694#4218796, @LuoYuanke wrote:

@akshaykhadse, do you want me to help merge the patch?

Yes. That would be great!

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

for (SDValue CurVec = InVec; CurVec;) {
       // update the shuffle mask (and second operand if we started with unary
       // shuffle) and create a new legal shuffle.
       if (CurVec.getOpcode() == ISD::VECTOR_SHUFFLE && CurVec.hasOneUse()) {
         auto *SVN = cast<ShuffleVectorSDNode>(CurVec);
         SDValue LHS = SVN->getOperand(0);
         SDValue RHS = SVN->getOperand(1);
         SmallVector<int, 16> Mask(SVN->getMask());
         bool Merged = true;
-        for (auto const &I : enumerate(Ops)) {
+        for (auto I : enumerate(Ops)) {
           SDValue &Op = I.value();
           if (Op) {
             SmallVector<int, 16> NewMask;
             if (!mergeEltWithShuffle(LHS, RHS, Mask, NewMask, Op, I.index())) {
               Merged = false;
               break;
             }
             Mask = std::move(NewMask);
if (!Factor)
     return SDValue();
 
   SDLoc DL(N);
   SDValue ZeroOp = DAG.getConstant(0, DL, NewScalarIntVT);
 
   // Recreate the BUILD_VECTOR, with elements now being Factor times smaller.
   SmallVector<SDValue, 16> NewOps;
   NewOps.reserve(NewIntVT.getVectorNumElements());
-  for (auto const &I : enumerate(N->ops())) {
+  for (auto I : enumerate(N->ops())) {
     SDValue Op = I.value();
     assert(!Op.isUndef() && "FIXME: after allowing UNDEF's, handle them here.");
     unsigned SrcOpIdx = I.index();
     if (KnownZeroOps[SrcOpIdx]) {
       NewOps.append(*Factor, ZeroOp);
       continue;
     }
     Op = DAG.getBitcast(OpIntVT, Op);

llvm/utils/TableGen/InstrInfoEmitter.cpp

private:
   std::vector<std::string> GetOperandInfo(const CodeGenInstruction &Inst);
 };
 
 } // end anonymous namespace
 
 static void PrintDefList(const std::vector<Record *> &Uses, unsigned Num,
                          raw_ostream &OS) {
   OS << "static const MCPhysReg ImplicitList" << Num << "[] = { ";
-  for (auto const & [Idx, U] : enumerate(Uses))
+  for (auto [Idx, U] : enumerate(Uses))
     OS << (Idx ? ", " : "") << getQualifiedName(U);
   OS << " };\n";
 }
 
 //===----------------------------------------------------------------------===//
 // Operand Info Emission.
 //===----------------------------------------------------------------------===//