[RISCV] Support saturated truncate

Add support for `ISD::TRUNCATE_[US]SAT`.

Author: ParkHanbum

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -853,7 +853,9 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
 
       // Integer VTs are lowered as a series of "RISCVISD::TRUNCATE_VECTOR_VL"
       // nodes which truncate by one power of two at a time.
-      setOperationAction(ISD::TRUNCATE, VT, Custom);
+      setOperationAction({ISD::TRUNCATE, ISD::TRUNCATE_SSAT_S,
+                          ISD::TRUNCATE_SSAT_U, ISD::TRUNCATE_USAT_U},
+                         VT, Custom);
 
       // Custom-lower insert/extract operations to simplify patterns.
       setOperationAction({ISD::INSERT_VECTOR_ELT, ISD::EXTRACT_VECTOR_ELT}, VT,
@@ -1168,7 +1170,9 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
 
         setOperationAction(ISD::SELECT, VT, Custom);
 
-        setOperationAction(ISD::TRUNCATE, VT, Custom);
+        setOperationAction({ISD::TRUNCATE, ISD::TRUNCATE_SSAT_S,
+                            ISD::TRUNCATE_SSAT_U, ISD::TRUNCATE_USAT_U},
+                           VT, Custom);
 
         setOperationAction(ISD::BITCAST, VT, Custom);
 
@@ -6395,6 +6399,9 @@ SDValue RISCVTargetLowering::LowerOperation(SDValue Op,
     return DAG.getNode(RISCVISD::BREV8, DL, VT, BSwap);
   }
   case ISD::TRUNCATE:
+  case ISD::TRUNCATE_SSAT_S:
+  case ISD::TRUNCATE_SSAT_U:
+  case ISD::TRUNCATE_USAT_U:
     // Only custom-lower vector truncates
     if (!Op.getSimpleValueType().isVector())
       return Op;
@@ -8234,7 +8241,8 @@ SDValue RISCVTargetLowering::lowerVectorMaskTruncLike(SDValue Op,
 
 SDValue RISCVTargetLowering::lowerVectorTruncLike(SDValue Op,
                                                   SelectionDAG &DAG) const {
-  bool IsVPTrunc = Op.getOpcode() == ISD::VP_TRUNCATE;
+  unsigned Opc = Op.getOpcode();
+  bool IsVPTrunc = Opc == ISD::VP_TRUNCATE;
   SDLoc DL(Op);
 
   MVT VT = Op.getSimpleValueType();
@@ -8279,11 +8287,18 @@ SDValue RISCVTargetLowering::lowerVectorTruncLike(SDValue Op,
         getDefaultVLOps(SrcVT, ContainerVT, DL, DAG, Subtarget);
   }
 
+  unsigned NewOpc;
+  if (Opc == ISD::TRUNCATE_SSAT_S)
+    NewOpc = RISCVISD::TRUNCATE_VECTOR_VL_SSAT;
+  else if (Opc == ISD::TRUNCATE_SSAT_U || Opc == ISD::TRUNCATE_USAT_U)
+    NewOpc = RISCVISD::TRUNCATE_VECTOR_VL_USAT;
+  else
+    NewOpc = RISCVISD::TRUNCATE_VECTOR_VL;
+
   do {
     SrcEltVT = MVT::getIntegerVT(SrcEltVT.getSizeInBits() / 2);
     MVT ResultVT = ContainerVT.changeVectorElementType(SrcEltVT);
-    Result = DAG.getNode(RISCVISD::TRUNCATE_VECTOR_VL, DL, ResultVT, Result,
-                         Mask, VL);
+    Result = DAG.getNode(NewOpc, DL, ResultVT, Result, Mask, VL);
   } while (SrcEltVT != DstEltVT);
 
   if (SrcVT.isFixedLengthVector())