[RISCV] Add statistic support for VSETVL insertion pass (#78543)

This patch make vsetvl insertion pass could track the number of
inserted/removed vsetvl instruction from `-stats` option.

Author: BeMg

llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp

@@ -26,6 +26,7 @@
 
 #include "RISCV.h"
 #include "RISCVSubtarget.h"
+#include "llvm/ADT/Statistic.h"
 #include "llvm/CodeGen/LiveIntervals.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include <queue>
@@ -34,6 +35,9 @@ using namespace llvm;
 #define DEBUG_TYPE "riscv-insert-vsetvli"
 #define RISCV_INSERT_VSETVLI_NAME "RISC-V Insert VSETVLI pass"
 
+STATISTIC(NumInsertedVSETVL, "Number of VSETVL inst inserted");
+STATISTIC(NumRemovedVSETVL, "Number of VSETVL inst removed");
+
 static cl::opt<bool> DisableInsertVSETVLPHIOpt(
     "riscv-disable-insert-vsetvl-phi-opt", cl::init(false), cl::Hidden,
     cl::desc("Disable looking through phis when inserting vsetvlis."));
@@ -911,6 +915,7 @@ void RISCVInsertVSETVLI::insertVSETVLI(MachineBasicBlock &MBB,
                      MachineBasicBlock::iterator InsertPt, DebugLoc DL,
                      const VSETVLIInfo &Info, const VSETVLIInfo &PrevInfo) {
 
+  ++NumInsertedVSETVL;
   if (PrevInfo.isValid() && !PrevInfo.isUnknown()) {
     // Use X0, X0 form if the AVL is the same and the SEW+LMUL gives the same
     // VLMAX.
@@ -1578,6 +1583,7 @@ void RISCVInsertVSETVLI::doLocalPostpass(MachineBasicBlock &MBB) {
     Used = getDemanded(MI, MRI, ST);
   }
 
+  NumRemovedVSETVL += ToDelete.size();
   for (auto *MI : ToDelete)
     MI->eraseFromParent();
 }