[llvm] [RISCV] custom scmp(x, 0) and scmp(0, x) lowering for RVV (PR #151753)

[Craig Topper via llvm-commits]

================
@@ -8223,6 +8225,35 @@ SDValue RISCVTargetLowering::LowerOperation(SDValue Op,
   case ISD::SADDSAT:
   case ISD::SSUBSAT:
     return lowerToScalableOp(Op, DAG);
+  case ISD::SCMP: {
+    SDLoc DL(Op);
+    EVT VT = Op->getValueType(0);
+    SDValue LHS = DAG.getFreeze(Op->getOperand(0));
+    SDValue RHS = DAG.getFreeze(Op->getOperand(1));
+    unsigned SEW = VT.getScalarSizeInBits();
+
+    SDValue Shift = DAG.getConstant(SEW-1, DL, VT);
+    SDValue Zero = DAG.getConstant(0, DL, VT);
+    SDValue One = DAG.getConstant(1, DL, VT);
+    SDValue MinusOne = DAG.getAllOnesConstant(DL, VT);
+
+    if (ISD::isConstantSplatVectorAllZeros(RHS.getNode())) {
+      SDValue Sra = DAG.getNode(ISD::SRA, DL, VT, LHS, Shift);
+      if (SEW <= 32) {
+        // scmp(lhs, 0) -> vor.vv(vsra.vi(lhs,SEW-1), vmin.vx(lhs,1))
+        SDValue Min = DAG.getNode(ISD::SMIN, DL, VT, LHS, One);
+        return DAG.getNode(ISD::OR, DL, VT, Sra, Min);
+      }
+      // scmp(lhs, 0) -> vmerge.vi(vmsgt.vi(rhs,0), vsra.vx(lhs,SEW-1), 1)
+      return DAG.getSelectCC(DL, LHS, Zero, Sra, One, ISD::SETGT);
+    } else if (ISD::isConstantSplatVectorAllZeros(LHS.getNode())) {
----------------
topperc wrote:

No else after return.

https://github.com/llvm/llvm-project/pull/151753