[RISCV] Add statistics for total LMUL spilled/reloaded (llvm#131747)

The cost of a vector spill/reload may vary highly depending on the size
of the vector register being spilled, i.e. LMUL, so the usual
regalloc.NumSpills/regalloc.NumReloads statistics may not be an accurate
reflection of the total cost.

This adds two new statistics for RISCVInstrInfo that collects the total
number of vector registers spilled/reloaded within groups. It can be
used to get a better idea of regalloc changes in e.g. llvm#131176 llvm#113675

Author: lukel97

llvm/lib/Target/RISCV/RISCVInstrInfo.cpp

@@ -18,6 +18,7 @@
 #include "RISCVSubtarget.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/MemoryLocation.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/CodeGen/LiveIntervals.h"
@@ -43,6 +44,12 @@ using namespace llvm;
 #define GET_INSTRINFO_NAMED_OPS
 #include "RISCVGenInstrInfo.inc"
 
+#define DEBUG_TYPE "riscv-instr-info"
+STATISTIC(NumVRegSpilled,
+          "Number of registers within vector register groups spilled");
+STATISTIC(NumVRegReloaded,
+          "Number of registers within vector register groups reloaded");
+
 static cl::opt<bool> PreferWholeRegisterMove(
     "riscv-prefer-whole-register-move", cl::init(false), cl::Hidden,
     cl::desc("Prefer whole register move for vector registers."));
@@ -657,6 +664,7 @@ void RISCVInstrInfo::storeRegToStackSlot(MachineBasicBlock &MBB,
         .addFrameIndex(FI)
         .addMemOperand(MMO)
         .setMIFlag(Flags);
+    NumVRegSpilled += TRI->getRegSizeInBits(*RC) / RISCV::RVVBitsPerBlock;
   } else {
     MachineMemOperand *MMO = MF->getMachineMemOperand(
         MachinePointerInfo::getFixedStack(*MF, FI), MachineMemOperand::MOStore,
@@ -747,6 +755,7 @@ void RISCVInstrInfo::loadRegFromStackSlot(
         .addFrameIndex(FI)
         .addMemOperand(MMO)
         .setMIFlag(Flags);
+    NumVRegReloaded += TRI->getRegSizeInBits(*RC) / RISCV::RVVBitsPerBlock;
   } else {
     MachineMemOperand *MMO = MF->getMachineMemOperand(
         MachinePointerInfo::getFixedStack(*MF, FI), MachineMemOperand::MOLoad,