[RISCV] Store only VNInfo val no in VSETVLIInfo. NFC

The VNInfo id (called val no elsewhere it seems) and register is enough
to uniquely identify AVL values, so try to store as little state as
possible.

This may also allow us to use dummy val nos in an upcoming patch when we
don't have LiveIntervals.

Author: lukel97

llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp

@@ -504,7 +504,7 @@ DemandedFields getDemanded(const MachineInstr &MI, const RISCVSubtarget *ST) {
 class VSETVLIInfo {
   struct AVLDef {
     // Every AVLDef should have a VNInfo.
-    const VNInfo *ValNo;
+    unsigned ValNo;
     Register DefReg;
   };
   union {
@@ -543,9 +543,9 @@ class VSETVLIInfo {
   void setUnknown() { State = Unknown; }
   bool isUnknown() const { return State == Unknown; }
 
-  void setAVLRegDef(const VNInfo *VNInfo, Register AVLReg) {
-    assert(VNInfo && AVLReg.isVirtual());
-    AVLRegDef.ValNo = VNInfo;
+  void setAVLRegDef(unsigned ValNo, Register AVLReg) {
+    assert(AVLReg.isVirtual());
+    AVLRegDef.ValNo = ValNo;
     AVLRegDef.DefReg = AVLReg;
     State = AVLIsReg;
   }
@@ -571,7 +571,7 @@ class VSETVLIInfo {
     assert(hasAVLImm());
     return AVLImm;
   }
-  const VNInfo *getAVLVNInfo() const {
+  unsigned getAVLValNo() const {
     assert(hasAVLReg());
     return AVLRegDef.ValNo;
   }
@@ -580,8 +580,10 @@ class VSETVLIInfo {
   // boundary slot.
   const MachineInstr *getAVLDefMI(const LiveIntervals *LIS) const {
     assert(hasAVLReg());
-    auto *MI = LIS->getInstructionFromIndex(getAVLVNInfo()->def);
-    assert(!(getAVLVNInfo()->isPHIDef() && MI));
+    const VNInfo *VNI =
+        LIS->getInterval(getAVLReg()).getValNumInfo(getAVLValNo());
+    auto *MI = LIS->getInstructionFromIndex(VNI->def);
+    assert(!(VNI->isPHIDef() && MI));
     return MI;
   }
 
@@ -590,7 +592,7 @@ class VSETVLIInfo {
     if (Info.isUnknown())
       setUnknown();
     else if (Info.hasAVLReg())
-      setAVLRegDef(Info.getAVLVNInfo(), Info.getAVLReg());
+      setAVLRegDef(Info.getAVLValNo(), Info.getAVLReg());
     else if (Info.hasAVLVLMAX())
       setAVLVLMAX();
     else if (Info.hasAVLIgnored())
@@ -629,7 +631,7 @@ class VSETVLIInfo {
 
   bool hasSameAVL(const VSETVLIInfo &Other) const {
     if (hasAVLReg() && Other.hasAVLReg())
-      return getAVLVNInfo()->id == Other.getAVLVNInfo()->id &&
+      return getAVLValNo() == Other.getAVLValNo() &&
              getAVLReg() == Other.getAVLReg();
 
     if (hasAVLImm() && Other.hasAVLImm())
@@ -927,7 +929,7 @@ static VSETVLIInfo getInfoForVSETVLI(const MachineInstr &MI,
     if (AVLReg == RISCV::X0)
       NewInfo.setAVLVLMAX();
     else if (VNInfo *VNI = getVNInfoFromReg(AVLReg, MI, LIS))
-      NewInfo.setAVLRegDef(VNI, AVLReg);
+      NewInfo.setAVLRegDef(VNI->id, AVLReg);
     else {
       assert(MI.getOperand(1).isUndef());
       NewInfo.setAVLIgnored();
@@ -1003,7 +1005,7 @@ static VSETVLIInfo computeInfoForInstr(const MachineInstr &MI, uint64_t TSFlags,
       else
         InstrInfo.setAVLImm(Imm);
     } else if (VNInfo *VNI = getVNInfoFromReg(VLOp.getReg(), MI, LIS)) {
-      InstrInfo.setAVLRegDef(VNI, VLOp.getReg());
+      InstrInfo.setAVLRegDef(VNI->id, VLOp.getReg());
     } else {
       assert(VLOp.isUndef());
       InstrInfo.setAVLIgnored();
@@ -1255,7 +1257,7 @@ void RISCVInsertVSETVLI::transferAfter(VSETVLIInfo &Info,
     auto &LI = LIS->getInterval(MI.getOperand(1).getReg());
     SlotIndex SI = LIS->getSlotIndexes()->getInstructionIndex(MI).getRegSlot();
     VNInfo *VNI = LI.getVNInfoAt(SI);
-    Info.setAVLRegDef(VNI, MI.getOperand(1).getReg());
+    Info.setAVLRegDef(VNI->id, MI.getOperand(1).getReg());
     return;
   }
 
@@ -1350,7 +1352,8 @@ bool RISCVInsertVSETVLI::needVSETVLIPHI(const VSETVLIInfo &Require,
     return true;
 
   // We need the AVL to have been produced by a PHI node in this basic block.
-  const VNInfo *Valno = Require.getAVLVNInfo();
+  const VNInfo *Valno = LIS->getInterval(Require.getAVLReg())
+                            .getValNumInfo(Require.getAVLValNo());
   if (!Valno->isPHIDef() || LIS->getMBBFromIndex(Valno->def) != &MBB)
     return true;
 
@@ -1514,7 +1517,8 @@ void RISCVInsertVSETVLI::doPRE(MachineBasicBlock &MBB) {
   // we need to prove the value is available at the point we're going
   // to insert the vsetvli at.
   if (AvailableInfo.hasAVLReg()) {
-    SlotIndex SI = AvailableInfo.getAVLVNInfo()->def;
+    const LiveInterval &LI = LIS->getInterval(AvailableInfo.getAVLReg());
+    SlotIndex SI = LI.getValNumInfo(AvailableInfo.getAVLValNo())->def;
     // This is an inline dominance check which covers the case of
     // UnavailablePred being the preheader of a loop.
     if (LIS->getMBBFromIndex(SI) != UnavailablePred)