[DAG] Extract helper for (neg x) [nfc]

This is a frequently reoccurring pattern, let's factor it out.

Differential Revision: https://reviews.llvm.org/D135301

llvm/include/llvm/CodeGen/SelectionDAG.h

@@ -926,6 +926,9 @@ public:
   /// BooleanContent for type OpVT or truncating it.
   SDValue getBoolExtOrTrunc(SDValue Op, const SDLoc &SL, EVT VT, EVT OpVT);
 
+  /// Create negative operation as (SUB 0, Val).
+  SDValue getNegative(SDValue Val, const SDLoc &DL, EVT VT);
+
   /// Create a bitwise NOT operation as (XOR Val, -1).
   SDValue getNOT(const SDLoc &DL, SDValue Val, EVT VT);
 

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -3981,8 +3981,7 @@ SDValue DAGCombiner::visitMUL(SDNode *N) {
 
   // fold (mul x, -1) -> 0-x
   if (N1IsConst && ConstValue1.isAllOnes())
-    return DAG.getNode(ISD::SUB, DL, VT,
+    return DAG.getNegative(N0, DL, VT);
-                       DAG.getConstant(0, DL, VT), N0);
 
   // fold (mul x, (1 << c)) -> x << c
   if (isConstantOrConstantVector(N1, /*NoOpaques*/ true) &&
@@ -4049,7 +4048,7 @@ SDValue DAGCombiner::visitMUL(SDNode *N) {
                                            DAG.getConstant(TZeros, DL, VT)))
                  : DAG.getNode(MathOp, DL, VT, Shl, N0);
       if (ConstValue1.isNegative())
-        R = DAG.getNode(ISD::SUB, DL, VT, DAG.getConstant(0, DL, VT), R);
+        R = DAG.getNegative(R, DL, VT);
       return R;
     }
   }
@@ -4303,7 +4302,7 @@ SDValue DAGCombiner::visitSDIV(SDNode *N) {
   // fold (sdiv X, -1) -> 0-X
   ConstantSDNode *N1C = isConstOrConstSplat(N1);
   if (N1C && N1C->isAllOnes())
-    return DAG.getNode(ISD::SUB, DL, VT, DAG.getConstant(0, DL, VT), N0);
+    return DAG.getNegative(N0, DL, VT);
 
   // fold (sdiv X, MIN_SIGNED) -> select(X == MIN_SIGNED, 1, 0)
   if (N1C && N1C->getAPIntValue().isMinSignedValue())
@@ -8682,8 +8681,7 @@ SDValue DAGCombiner::visitXOR(SDNode *N) {
   // fold (not (add X, -1)) -> (neg X)
   if (isAllOnesConstant(N1) && N0.getOpcode() == ISD::ADD &&
       isAllOnesOrAllOnesSplat(N0.getOperand(1))) {
-    return DAG.getNode(ISD::SUB, DL, VT, DAG.getConstant(0, DL, VT),
+    return DAG.getNegative(N0.getOperand(0), DL, VT);
-                       N0.getOperand(0));
   }
 
   // fold (xor (and x, y), y) -> (and (not x), y)
@@ -11305,8 +11303,7 @@ SDValue DAGCombiner::visitVSELECT(SDNode *N) {
               if (SatCC == ISD::SETUGT && Other.getOpcode() == ISD::ADD &&
                   ISD::matchBinaryPredicate(OpRHS, CondRHS, MatchUSUBSAT,
                                             /*AllowUndefs*/ true)) {
-                OpRHS = DAG.getNode(ISD::SUB, DL, VT,
+                OpRHS = DAG.getNegative(OpRHS, DL, VT);
-                                    DAG.getConstant(0, DL, VT), OpRHS);
                 return DAG.getNode(ISD::USUBSAT, DL, VT, OpLHS, OpRHS);
               }
 
@@ -12394,7 +12391,7 @@ SDValue DAGCombiner::visitSIGN_EXTEND(SDNode *N) {
       N0.getOperand(1).getOpcode() == ISD::ZERO_EXTEND &&
       TLI.isOperationLegalOrCustom(ISD::SUB, VT)) {
     SDValue Zext = DAG.getZExtOrTrunc(N0.getOperand(1).getOperand(0), DL, VT);
-    return DAG.getNode(ISD::SUB, DL, VT, DAG.getConstant(0, DL, VT), Zext);
+    return DAG.getNegative(Zext, DL, VT);
   }
   // Eliminate this sign extend by doing a decrement in the destination type:
   // sext i32 ((zext i8 X to i32) + (-1)) to i64 --> (zext i8 X to i64) + (-1)

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -1461,6 +1461,10 @@ SDValue SelectionDAG::getPtrExtendInReg(SDValue Op, const SDLoc &DL, EVT VT) {
   return getZeroExtendInReg(Op, DL, VT);
 }
 
+SDValue SelectionDAG::getNegative(SDValue Val, const SDLoc &DL, EVT VT) {
+  return getNode(ISD::SUB, DL, VT, getConstant(0, DL, VT), Val);
+}
+
 /// getNOT - Create a bitwise NOT operation as (XOR Val, -1).
 SDValue SelectionDAG::getNOT(const SDLoc &DL, SDValue Val, EVT VT) {
   return getNode(ISD::XOR, DL, VT, Val, getAllOnesConstant(DL, VT));

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -3421,8 +3421,7 @@ void SelectionDAGBuilder::visitSelect(const User &I) {
       Values[i] =
           DAG.getNode(OpCode, dl, VT, LHSVal.getValue(LHSVal.getResNo() + i));
       if (Negate)
-        Values[i] = DAG.getNode(ISD::SUB, dl, VT, DAG.getConstant(0, dl, VT),
+        Values[i] = DAG.getNegative(Values[i], dl, VT);
-                                Values[i]);
     }
   } else {
     for (unsigned i = 0; i != NumValues; ++i) {

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -3254,8 +3254,7 @@ static SDValue lowerCTLZ_CTTZ_ZERO_UNDEF(SDValue Op, SelectionDAG &DAG) {
   // For CTTZ_ZERO_UNDEF, we need to extract the lowest set bit using X & -X.
   // The trailing zero count is equal to log2 of this single bit value.
   if (Op.getOpcode() == ISD::CTTZ_ZERO_UNDEF) {
-    SDValue Neg =
+    SDValue Neg = DAG.getNegative(Src, DL, VT);
-        DAG.getNode(ISD::SUB, DL, VT, DAG.getConstant(0, DL, VT), Src);
     Src = DAG.getNode(ISD::AND, DL, VT, Src, Neg);
   }
 
@@ -8207,8 +8206,7 @@ performSIGN_EXTEND_INREGCombine(SDNode *N, SelectionDAG &DAG,
       DAG.ComputeNumSignBits(Src.getOperand(0)) > 32) {
     SDLoc DL(N);
     SDValue Freeze = DAG.getFreeze(Src.getOperand(0));
-    SDValue Neg =
+    SDValue Neg = DAG.getNegative(Freeze, DL, VT);
-        DAG.getNode(ISD::SUB, DL, VT, DAG.getConstant(0, DL, MVT::i64), Freeze);
     Neg = DAG.getNode(ISD::SIGN_EXTEND_INREG, DL, MVT::i64, Neg,
                       DAG.getValueType(MVT::i32));
     return DAG.getNode(ISD::SMAX, DL, MVT::i64, Freeze, Neg);
@@ -9458,8 +9456,7 @@ SDValue RISCVTargetLowering::PerformDAGCombine(SDNode *N,
                             DAG.getConstant(1, DL, VT));
         else
           Neg = LHS;
-        SDValue Mask = DAG.getNode(ISD::SUB, DL, VT, DAG.getConstant(0, DL, VT),
+        SDValue Mask = DAG.getNegative(Neg, DL, VT);               // -x
-                                   Neg); // -(and (x, 0x1))
         SDValue And = DAG.getNode(ISD::AND, DL, VT, Mask, Src1); // Mask & z
         return DAG.getNode(Opcode, DL, VT, And, Src2);           // And Op y
       }