[RISCV] Add Enum for CSR encodings. (#121674)

This allows us to use them in C++ code without needing to do a table
lookup.

Author: topperc

llvm/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.h

@@ -480,6 +480,7 @@ struct SysReg {
   }
 };
 
+#define GET_SysRegEncodings_DECL
 #define GET_SysRegsList_DECL
 #include "RISCVGenSearchableTables.inc"
 } // end namespace RISCVSysReg

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -12663,8 +12663,7 @@ SDValue RISCVTargetLowering::lowerGET_ROUNDING(SDValue Op,
   const MVT XLenVT = Subtarget.getXLenVT();
   SDLoc DL(Op);
   SDValue Chain = Op->getOperand(0);
-  SDValue SysRegNo = DAG.getTargetConstant(
-      RISCVSysReg::lookupSysRegByName("FRM")->Encoding, DL, XLenVT);
+  SDValue SysRegNo = DAG.getTargetConstant(RISCVSysReg::frm, DL, XLenVT);
   SDVTList VTs = DAG.getVTList(XLenVT, MVT::Other);
   SDValue RM = DAG.getNode(RISCVISD::READ_CSR, DL, VTs, Chain, SysRegNo);
 
@@ -12695,8 +12694,7 @@ SDValue RISCVTargetLowering::lowerSET_ROUNDING(SDValue Op,
   SDLoc DL(Op);
   SDValue Chain = Op->getOperand(0);
   SDValue RMValue = Op->getOperand(1);
-  SDValue SysRegNo = DAG.getTargetConstant(
-      RISCVSysReg::lookupSysRegByName("FRM")->Encoding, DL, XLenVT);
+  SDValue SysRegNo = DAG.getTargetConstant(RISCVSysReg::frm, DL, XLenVT);
 
   // Encoding used for rounding mode in RISC-V differs from that used in
   // FLT_ROUNDS. To convert it the C rounding mode is used as an index in
@@ -12899,15 +12897,11 @@ void RISCVTargetLowering::ReplaceNodeResults(SDNode *N,
     SDValue LoCounter, HiCounter;
     MVT XLenVT = Subtarget.getXLenVT();
     if (N->getOpcode() == ISD::READCYCLECOUNTER) {
-      LoCounter = DAG.getTargetConstant(
-          RISCVSysReg::lookupSysRegByName("CYCLE")->Encoding, DL, XLenVT);
-      HiCounter = DAG.getTargetConstant(
-          RISCVSysReg::lookupSysRegByName("CYCLEH")->Encoding, DL, XLenVT);
+      LoCounter = DAG.getTargetConstant(RISCVSysReg::cycle, DL, XLenVT);
+      HiCounter = DAG.getTargetConstant(RISCVSysReg::cycleh, DL, XLenVT);
     } else {
-      LoCounter = DAG.getTargetConstant(
-          RISCVSysReg::lookupSysRegByName("TIME")->Encoding, DL, XLenVT);
-      HiCounter = DAG.getTargetConstant(
-          RISCVSysReg::lookupSysRegByName("TIMEH")->Encoding, DL, XLenVT);
+      LoCounter = DAG.getTargetConstant(RISCVSysReg::time, DL, XLenVT);
+      HiCounter = DAG.getTargetConstant(RISCVSysReg::timeh, DL, XLenVT);
     }
     SDVTList VTs = DAG.getVTList(MVT::i32, MVT::i32, MVT::Other);
     SDValue RCW = DAG.getNode(RISCVISD::READ_COUNTER_WIDE, DL, VTs,

llvm/lib/Target/RISCV/RISCVSystemOperands.td

@@ -48,6 +48,12 @@ def SysRegsList : GenericTable {
   let PrimaryKeyReturnRange = true;
 }
 
+def SysRegEncodings : GenericEnum {
+  let FilterClass = "SysReg";
+  let NameField = "Name";
+  let ValueField = "Encoding";
+}
+
 def lookupSysRegByName : SearchIndex {
   let Table = SysRegsList;
   let Key = [ "Name" ];