[TargetLowering] Add SimplifyDemandedBits funnel shift support

llvm-svn: 353539

1 files changed, 39 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 550fab1bda6..c8b66d05a01 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -1025,6 +1025,45 @@ bool TargetLowering::SimplifyDemandedBits(
     }
     break;
   }
+  case ISD::FSHL:
+  case ISD::FSHR: {
+    SDValue Op0 = Op.getOperand(0);
+    SDValue Op1 = Op.getOperand(1);
+    SDValue Op2 = Op.getOperand(2);
+    bool IsFSHL = (Op.getOpcode() == ISD::FSHL);
+
+    if (ConstantSDNode *SA = isConstOrConstSplat(Op2)) {
+      unsigned Amt = SA->getAPIntValue().urem(BitWidth);
+
+      // For fshl, 0-shift returns the 1st arg.
+      // For fshr, 0-shift returns the 2nd arg.
+      if (Amt == 0) {
+        if (SimplifyDemandedBits(IsFSHL ? Op0 : Op1, DemandedBits, DemandedElts,
+                                 Known, TLO, Depth + 1))
+          return true;
+        break;
+      }
+
+      // fshl: (Op0 << Amt) | (Op1 >> (BW - Amt))
+      // fshr: (Op0 << (BW - Amt)) | (Op1 >> Amt)
+      APInt Demanded0 = DemandedBits.lshr(IsFSHL ? Amt : (BitWidth - Amt));
+      APInt Demanded1 = DemandedBits << (IsFSHL ? (BitWidth - Amt) : Amt);
+      if (SimplifyDemandedBits(Op0, Demanded0, DemandedElts, Known2, TLO,
+                               Depth + 1))
+        return true;
+      if (SimplifyDemandedBits(Op1, Demanded1, DemandedElts, Known, TLO,
+                               Depth + 1))
+        return true;
+
+      Known2.One <<= (IsFSHL ? Amt : (BitWidth - Amt));
+      Known2.Zero <<= (IsFSHL ? Amt : (BitWidth - Amt));
+      Known.One.lshrInPlace(IsFSHL ? (BitWidth - Amt) : Amt);
+      Known.Zero.lshrInPlace(IsFSHL ? (BitWidth - Amt) : Amt);
+      Known.One |= Known2.One;
+      Known.Zero |= Known2.Zero;
+    }
+    break;
+  }
   case ISD::SIGN_EXTEND_INREG: {
     SDValue Op0 = Op.getOperand(0);
     EVT ExVT = cast<VTSDNode>(Op.getOperand(1))->getVT();