[RISCV] Add statistics for total LMUL spilled/reloaded

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 LMUL for vector register spills and reloads. 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 +44,10 @@ using namespace llvm;
 #define GET_INSTRINFO_NAMED_OPS
 #include "RISCVGenInstrInfo.inc"
 
+#define DEBUG_TYPE "riscv-instr-info"
+STATISTIC(TotalLMULSpilled, "Total LMUL spilled from vector registers");
+STATISTIC(TotalLMULReloaded, "Total LMUL reloaded into vector registers");
+
 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 +662,7 @@ void RISCVInstrInfo::storeRegToStackSlot(MachineBasicBlock &MBB,
         .addFrameIndex(FI)
         .addMemOperand(MMO)
         .setMIFlag(Flags);
+    TotalLMULSpilled += TRI->getRegSizeInBits(*RC) / RISCV::RVVBitsPerBlock;
   } else {
     MachineMemOperand *MMO = MF->getMachineMemOperand(
         MachinePointerInfo::getFixedStack(*MF, FI), MachineMemOperand::MOStore,
@@ -747,6 +753,7 @@ void RISCVInstrInfo::loadRegFromStackSlot(
         .addFrameIndex(FI)
         .addMemOperand(MMO)
         .setMIFlag(Flags);
+    TotalLMULReloaded += TRI->getRegSizeInBits(*RC) / RISCV::RVVBitsPerBlock;
   } else {
     MachineMemOperand *MMO = MF->getMachineMemOperand(
         MachinePointerInfo::getFixedStack(*MF, FI), MachineMemOperand::MOLoad,