A doccomment for CombineTo, and some NFC refactorings

[tyomitch]

Summary

Caching SDLoc(N), instead of recreating it in every single
function call, keeps the code denser, and allows to unwrap long lines.

[jmolloy]

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

159

Why doccomment this one but not any of the others?

[tyomitch]

Patch updated

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

void removeFromWorklist(SDNode *N) {
       // Null out the entry rather than erasing it to avoid a linear operation.
       Worklist[It->second] = nullptr;
       WorklistMap.erase(It);
     }
 
     void deleteAndRecombine(SDNode *N);
     bool recursivelyDeleteUnusedNodes(SDNode *N);
 
+    /// Replaces all uses of the results of one DAG node with new values.
     SDValue CombineTo(SDNode *N, const SDValue *To, unsigned NumTo,
                       bool AddTo = true);
 
     SDValue CombineTo(SDNode *N, SDValue Res, bool AddTo = true) {
       return CombineTo(N, &Res, 1, AddTo);
     }
 
     SDValue CombineTo(SDNode *N, SDValue Res0, SDValue Res1,
SDValue DAGCombiner::visitSUB(SDNode *N) {
 
   return SDValue();
 }
 
 SDValue DAGCombiner::visitSUBC(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
   EVT VT = N0.getValueType();
+  SDLoc DL(N);
 
   // If the flag result is dead, turn this into an SUB.
   if (!N->hasAnyUseOfValue(1))
-    return CombineTo(N, DAG.getNode(ISD::SUB, SDLoc(N), VT, N0, N1),
-                     DAG.getNode(ISD::CARRY_FALSE, SDLoc(N),
-                                 MVT::Glue));
+    return CombineTo(N, DAG.getNode(ISD::SUB, DL, VT, N0, N1),
+                     DAG.getNode(ISD::CARRY_FALSE, DL, MVT::Glue));
 
   // fold (subc x, x) -> 0 + no borrow
-  if (N0 == N1) {
-    SDLoc DL(N);
+  if (N0 == N1)
     return CombineTo(N, DAG.getConstant(0, DL, VT),
-                     DAG.getNode(ISD::CARRY_FALSE, DL,
-                                 MVT::Glue));
-  }
+                     DAG.getNode(ISD::CARRY_FALSE, DL, MVT::Glue));
 
   // fold (subc x, 0) -> x + no borrow
   if (isNullConstant(N1))
-    return CombineTo(N, N0, DAG.getNode(ISD::CARRY_FALSE, SDLoc(N),
-                                        MVT::Glue));
+    return CombineTo(N, N0, DAG.getNode(ISD::CARRY_FALSE, DL, MVT::Glue));
 
   // Canonicalize (sub -1, x) -> ~x, i.e. (xor x, -1) + no borrow
   if (isAllOnesConstant(N0))
-    return CombineTo(N, DAG.getNode(ISD::XOR, SDLoc(N), VT, N1, N0),
-                     DAG.getNode(ISD::CARRY_FALSE, SDLoc(N),
-                                 MVT::Glue));
+    return CombineTo(N, DAG.getNode(ISD::XOR, DL, VT, N1, N0),
+                     DAG.getNode(ISD::CARRY_FALSE, DL, MVT::Glue));
 
   return SDValue();
 }
 
 SDValue DAGCombiner::visitSUBE(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
   SDValue CarryIn = N->getOperand(2);
SDValue DAGCombiner::visitSDIV(SDNode *N) {
   SDValue N1 = N->getOperand(1);
   EVT VT = N->getValueType(0);
 
   // fold vector ops
   if (VT.isVector())
     if (SDValue FoldedVOp = SimplifyVBinOp(N))
       return FoldedVOp;
 
+  SDLoc DL(N);
+
   // fold (sdiv c1, c2) -> c1/c2
   ConstantSDNode *N0C = isConstOrConstSplat(N0);
   ConstantSDNode *N1C = isConstOrConstSplat(N1);
   if (N0C && N1C && !N0C->isOpaque() && !N1C->isOpaque())
-    return DAG.FoldConstantArithmetic(ISD::SDIV, SDLoc(N), VT, N0C, N1C);
+    return DAG.FoldConstantArithmetic(ISD::SDIV, DL, VT, N0C, N1C);
   // fold (sdiv X, 1) -> X
   if (N1C && N1C->isOne())
     return N0;
   // fold (sdiv X, -1) -> 0-X
-  if (N1C && N1C->isAllOnesValue()) {
-    SDLoc DL(N);
+  if (N1C && N1C->isAllOnesValue())
     return DAG.getNode(ISD::SUB, DL, VT,
                        DAG.getConstant(0, DL, VT), N0);
-  }
+
   // If we know the sign bits of both operands are zero, strength reduce to a
   // udiv instead.  Handles (X&15) /s 4 -> X&15 >> 2
   if (!VT.isVector()) {
     if (DAG.SignBitIsZero(N1) && DAG.SignBitIsZero(N0))
-      return DAG.getNode(ISD::UDIV, SDLoc(N), N1.getValueType(),
-                         N0, N1);
+      return DAG.getNode(ISD::UDIV, DL, N1.getValueType(), N0, N1);
   }
 
   // fold (sdiv X, pow2) -> simple ops after legalize
   // FIXME: We check for the exact bit here because the generic lowering gives
   // better results in that case. The target-specific lowering should learn how
   // to handle exact sdivs efficiently.
   if (N1C && !N1C->isNullValue() && !N1C->isOpaque() &&
       !cast<BinaryWithFlagsSDNode>(N)->Flags.hasExact() &&
       (N1C->getAPIntValue().isPowerOf2() ||
        (-N1C->getAPIntValue()).isPowerOf2())) {
     // Target-specific implementation of sdiv x, pow2.
     if (SDValue Res = BuildSDIVPow2(N))
       return Res;
 
     unsigned lg2 = N1C->getAPIntValue().countTrailingZeros();
-    SDLoc DL(N);
 
     // Splat the sign bit into the register
     SDValue SGN =
         DAG.getNode(ISD::SRA, DL, VT, N0,
                     DAG.getConstant(VT.getScalarSizeInBits() - 1, DL,
                                     getShiftAmountTy(N0.getValueType())));
     AddToWorklist(SGN.getNode());
 
SDValue DAGCombiner::visitSDIV(SDNode *N) {
   // trade-offs.
   AttributeSet Attr = DAG.getMachineFunction().getFunction()->getAttributes();
   if (N1C && !TLI.isIntDivCheap(N->getValueType(0), Attr))
     if (SDValue Op = BuildSDIV(N))
       return Op;
 
   // undef / X -> 0
   if (N0.getOpcode() == ISD::UNDEF)
-    return DAG.getConstant(0, SDLoc(N), VT);
+    return DAG.getConstant(0, DL, VT);
   // X / undef -> undef
   if (N1.getOpcode() == ISD::UNDEF)
     return N1;
 
   return SDValue();
 }
 
 SDValue DAGCombiner::visitUDIV(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
   EVT VT = N->getValueType(0);
 
   // fold vector ops
   if (VT.isVector())
     if (SDValue FoldedVOp = SimplifyVBinOp(N))
       return FoldedVOp;
 
+  SDLoc DL(N);
+
   // fold (udiv c1, c2) -> c1/c2
   ConstantSDNode *N0C = isConstOrConstSplat(N0);
   ConstantSDNode *N1C = isConstOrConstSplat(N1);
   if (N0C && N1C)
-    if (SDValue Folded = DAG.FoldConstantArithmetic(ISD::UDIV, SDLoc(N), VT,
+    if (SDValue Folded = DAG.FoldConstantArithmetic(ISD::UDIV, DL, VT,
                                                     N0C, N1C))
       return Folded;
   // fold (udiv x, (1 << c)) -> x >>u c
-  if (N1C && !N1C->isOpaque() && N1C->getAPIntValue().isPowerOf2()) {
-    SDLoc DL(N);
+  if (N1C && !N1C->isOpaque() && N1C->getAPIntValue().isPowerOf2())
     return DAG.getNode(ISD::SRL, DL, VT, N0,
                        DAG.getConstant(N1C->getAPIntValue().logBase2(), DL,
                                        getShiftAmountTy(N0.getValueType())));
-  }
+
   // fold (udiv x, (shl c, y)) -> x >>u (log2(c)+y) iff c is power of 2
   if (N1.getOpcode() == ISD::SHL) {
     if (ConstantSDNode *SHC = getAsNonOpaqueConstant(N1.getOperand(0))) {
       if (SHC->getAPIntValue().isPowerOf2()) {
         EVT ADDVT = N1.getOperand(1).getValueType();
-        SDLoc DL(N);
         SDValue Add = DAG.getNode(ISD::ADD, DL, ADDVT,
                                   N1.getOperand(1),
                                   DAG.getConstant(SHC->getAPIntValue()
                                                                   .logBase2(),
                                                   DL, ADDVT));
         AddToWorklist(Add.getNode());
         return DAG.getNode(ISD::SRL, DL, VT, N0, Add);
       }
     }
   }
 
   // fold (udiv x, c) -> alternate
   AttributeSet Attr = DAG.getMachineFunction().getFunction()->getAttributes();
   if (N1C && !TLI.isIntDivCheap(N->getValueType(0), Attr))
     if (SDValue Op = BuildUDIV(N))
       return Op;
 
   // undef / X -> 0
   if (N0.getOpcode() == ISD::UNDEF)
-    return DAG.getConstant(0, SDLoc(N), VT);
+    return DAG.getConstant(0, DL, VT);
   // X / undef -> undef
   if (N1.getOpcode() == ISD::UNDEF)
     return N1;
 
   return SDValue();
 }
 
 // handles ISD::SREM and ISD::UREM
 SDValue DAGCombiner::visitREM(SDNode *N) {
   unsigned Opcode = N->getOpcode();
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
   EVT VT = N->getValueType(0);
+  bool isSigned = (Opcode == ISD::SREM);
+  SDLoc DL(N);
 
   // fold (rem c1, c2) -> c1%c2
   ConstantSDNode *N0C = isConstOrConstSplat(N0);
   ConstantSDNode *N1C = isConstOrConstSplat(N1);
   if (N0C && N1C)
-    if (SDValue Folded = DAG.FoldConstantArithmetic(Opcode, SDLoc(N), VT,
-                                                    N0C, N1C))
+    if (SDValue Folded = DAG.FoldConstantArithmetic(Opcode, DL, VT, N0C, N1C))
       return Folded;
 
-  if (Opcode == ISD::SREM) {
+  if (isSigned) {
     // If we know the sign bits of both operands are zero, strength reduce to a
     // urem instead.  Handles (X & 0x0FFFFFFF) %s 16 -> X&15
     if (!VT.isVector()) {
       if (DAG.SignBitIsZero(N1) && DAG.SignBitIsZero(N0))
-        return DAG.getNode(ISD::UREM, SDLoc(N), VT, N0, N1);
+        return DAG.getNode(ISD::UREM, DL, VT, N0, N1);
     }
   } else {
     // fold (urem x, pow2) -> (and x, pow2-1)
     if (N1C && !N1C->isNullValue() && !N1C->isOpaque() &&
         N1C->getAPIntValue().isPowerOf2()) {
-      SDLoc DL(N);
       return DAG.getNode(ISD::AND, DL, VT, N0,
                          DAG.getConstant(N1C->getAPIntValue() - 1, DL, VT));
     }
     // fold (urem x, (shl pow2, y)) -> (and x, (add (shl pow2, y), -1))
     if (N1.getOpcode() == ISD::SHL) {
       if (ConstantSDNode *SHC = getAsNonOpaqueConstant(N1.getOperand(0))) {
         if (SHC->getAPIntValue().isPowerOf2()) {
-          SDLoc DL(N);
           SDValue Add =
             DAG.getNode(ISD::ADD, DL, VT, N1,
                    DAG.getConstant(APInt::getAllOnesValue(VT.getSizeInBits()),
                                    DL, VT));
           AddToWorklist(Add.getNode());
           return DAG.getNode(ISD::AND, DL, VT, N0, Add);
         }
       }
     }
   }
 
   // If X/C can be simplified by the division-by-constant logic, lower
   // X%C to the equivalent of X-X/C*C.
   if (N1C && !N1C->isNullValue()) {
-    unsigned DivOpcode = (Opcode == ISD::SREM ? ISD::SDIV : ISD::UDIV);
-    SDValue Div = DAG.getNode(DivOpcode, SDLoc(N), VT, N0, N1);
+    unsigned DivOpcode = isSigned ? ISD::SDIV : ISD::UDIV;
+    SDValue Div = DAG.getNode(DivOpcode, DL, VT, N0, N1);
     AddToWorklist(Div.getNode());
     SDValue OptimizedDiv = combine(Div.getNode());
     if (OptimizedDiv.getNode() && OptimizedDiv.getNode() != Div.getNode()) {
-      SDValue Mul = DAG.getNode(ISD::MUL, SDLoc(N), VT,
-                                OptimizedDiv, N1);
-      SDValue Sub = DAG.getNode(ISD::SUB, SDLoc(N), VT, N0, Mul);
+      SDValue Mul = DAG.getNode(ISD::MUL, DL, VT, OptimizedDiv, N1);
+      SDValue Sub = DAG.getNode(ISD::SUB, DL, VT, N0, Mul);
       AddToWorklist(Mul.getNode());
       return Sub;
     }
   }
 
   // undef % X -> 0
   if (N0.getOpcode() == ISD::UNDEF)
-    return DAG.getConstant(0, SDLoc(N), VT);
+    return DAG.getConstant(0, DL, VT);
   // X % undef -> undef
   if (N1.getOpcode() == ISD::UNDEF)
     return N1;
 
   return SDValue();
 }
 
 SDValue DAGCombiner::visitMULHS(SDNode *N) {