[TailDuplication] Split up NumInstrDups statistic.

[gberry]

Summary

Split NumInstrDups statistic into separate added/removed counts to avoid
negative stat being printed as unsigned.

[mcrosier]

LGTM.

lib/CodeGen/TailDuplicator.cpp

 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
 using namespace llvm;
 
 #define DEBUG_TYPE "tailduplication"
 
 STATISTIC(NumTails, "Number of tails duplicated");
 STATISTIC(NumTailDups, "Number of tail duplicated blocks");
-STATISTIC(NumInstrDups, "Additional instructions due to tail duplication");
+STATISTIC(NumTailDupAdded,
+          "Number of instructions added due to tail duplication");
+STATISTIC(NumTailDupRemoved,
+          "Number of instructions removed due to tail duplication");
 STATISTIC(NumDeadBlocks, "Number of dead blocks removed");
 STATISTIC(NumAddedPHIs, "Number of phis added");
 
 // Heuristic for tail duplication.
 static cl::opt<unsigned> TailDuplicateSize(
     "tail-dup-size",
     cl::desc("Maximum instructions to consider tail duplicating"), cl::init(2),
     cl::Hidden);
bool TailDuplicator::tailDuplicateAndUpdate(MachineFunction &MF, bool IsSimple,
   // which duplicated TailBB. Add the predecessors as sources to the PHI
   // instructions.
   bool isDead = MBB->pred_empty() && !MBB->hasAddressTaken();
   if (PreRegAlloc)
     updateSuccessorsPHIs(MBB, isDead, TDBBs, Succs);
 
   // If it is dead, remove it.
   if (isDead) {
-    NumInstrDups -= MBB->size();
+    NumTailDupRemoved += MBB->size();
     removeDeadBlock(MBB);
     ++NumDeadBlocks;
   }
 
   // Update SSA form.
   if (!SSAUpdateVRs.empty()) {
     for (unsigned i = 0, e = SSAUpdateVRs.size(); i != e; ++i) {
       unsigned VReg = SSAUpdateVRs[i];
while (I != TailBB->instr_end()) {
         duplicateInstruction(MI, TailBB, PredBB, MF, LocalVRMap, UsedByPhi);
       }
     }
     appendCopies(PredBB, CopyInfos, Copies);
 
     // Simplify
     TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true);
 
-    NumInstrDups += TailBB->size() - 1; // subtract one for removed branch
+    NumTailDupAdded += TailBB->size() - 1; // subtract one for removed branch
 
     // Update the CFG.
     PredBB->removeSuccessor(PredBB->succ_begin());
     assert(PredBB->succ_empty() &&
            "TailDuplicate called on block with multiple successors!");
     for (MachineBasicBlock::succ_iterator I = TailBB->succ_begin(),
                                           E = TailBB->succ_end();
          I != E; ++I)