[TargetLowering] Refactor BuildSDIV in preparation for D50765. NFCI.

Pull out magic factor calculators into a helper function, use 0/+1/-1 multiplication factor to (optionally) add/sub the numerator.

llvm-svn: 339898

1 files changed, 36 insertions, 24 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 13482e74c9e..dbc34442208 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -3522,6 +3522,23 @@ SDValue TargetLowering::BuildSDIV(SDNode *N, SelectionDAG &DAG,
   if (N->getFlags().hasExact())
     return BuildExactSDIV(*this, N, dl, DAG, Created);
 
+  auto BuildSDIVPattern = [&](const APInt &Divisor, SDValue &MagicFactor,
+                              SDValue &Factor, SDValue &Shift) {
+    APInt::ms magics = Divisor.magic();
+    int NumeratorFactor = 0;
+
+    // If d > 0 and m < 0, add the numerator.
+    if (Divisor.isStrictlyPositive() && magics.m.isNegative())
+      NumeratorFactor = 1;
+    // If d < 0 and m > 0, subtract the numerator.
+    else if (Divisor.isNegative() && magics.m.isStrictlyPositive())
+      NumeratorFactor = -1;
+
+    MagicFactor = DAG.getConstant(magics.m, dl, VT);
+    Factor = DAG.getConstant(NumeratorFactor, dl, VT);
+    Shift = DAG.getConstant(magics.s, dl, ShVT);
+  };
+
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
 
@@ -3529,41 +3546,36 @@ SDValue TargetLowering::BuildSDIV(SDNode *N, SelectionDAG &DAG,
   ConstantSDNode *C = isConstOrConstSplat(N1);
   if (!C || C->isNullValue())
     return SDValue();
-  const APInt &Divisor = C->getAPIntValue();
 
-  APInt::ms magics = Divisor.magic();
+  // Collect the shifts/magic values.
+  SDValue MagicFactor, Factor, Shift;
+  BuildSDIVPattern(C->getAPIntValue(), MagicFactor, Factor, Shift);
 
   // Multiply the numerator (operand 0) by the magic value
   // FIXME: We should support doing a MUL in a wider type
   SDValue Q;
   if (IsAfterLegalization ? isOperationLegal(ISD::MULHS, VT)
                           : isOperationLegalOrCustom(ISD::MULHS, VT))
-    Q = DAG.getNode(ISD::MULHS, dl, VT, N0, DAG.getConstant(magics.m, dl, VT));
+    Q = DAG.getNode(ISD::MULHS, dl, VT, N0, MagicFactor);
   else if (IsAfterLegalization ? isOperationLegal(ISD::SMUL_LOHI, VT)
-                               : isOperationLegalOrCustom(ISD::SMUL_LOHI, VT))
-    Q = SDValue(DAG.getNode(ISD::SMUL_LOHI, dl, DAG.getVTList(VT, VT), N0,
-                            DAG.getConstant(magics.m, dl, VT))
-                    .getNode(), 1);
-  else
-    return SDValue(); // No mulhs or equvialent
+                               : isOperationLegalOrCustom(ISD::SMUL_LOHI, VT)) {
+    SDValue LoHi =
+        DAG.getNode(ISD::SMUL_LOHI, dl, DAG.getVTList(VT, VT), N0, MagicFactor);
+    Q = SDValue(LoHi.getNode(), 1);
+  } else
+    return SDValue(); // No mulhs or equivalent
+  Created.push_back(Q.getNode());
 
+  // (Optionally) Add/subtract the numerator using Factor.
+  Factor = DAG.getNode(ISD::MUL, dl, VT, N0, Factor);
+  Created.push_back(Factor.getNode());
+  Q = DAG.getNode(ISD::ADD, dl, VT, Q, Factor);
+  Created.push_back(Q.getNode());
+
+  // Shift right algebraic by shift value.
+  Q = DAG.getNode(ISD::SRA, dl, VT, Q, Shift);
   Created.push_back(Q.getNode());
 
-  // If d > 0 and m < 0, add the numerator
-  if (Divisor.isStrictlyPositive() && magics.m.isNegative()) {
-    Q = DAG.getNode(ISD::ADD, dl, VT, Q, N0);
-    Created.push_back(Q.getNode());
-  }
-  // If d < 0 and m > 0, subtract the numerator.
-  if (Divisor.isNegative() && magics.m.isStrictlyPositive()) {
-    Q = DAG.getNode(ISD::SUB, dl, VT, Q, N0);
-    Created.push_back(Q.getNode());
-  }
-  // Shift right algebraic if shift value is nonzero
-  if (magics.s > 0) {
-    Q = DAG.getNode(ISD::SRA, dl, VT, Q, DAG.getConstant(magics.s, dl, ShVT));
-    Created.push_back(Q.getNode());
-  }
   // Extract the sign bit and add it to the quotient
   SDValue T =
       DAG.getNode(ISD::SRL, dl, VT, Q, DAG.getConstant(EltBits - 1, dl, ShVT));