[SelectionDAGBuilder] Add const to relevant places

[hans]

Looks good to me, thanks!

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h

struct BitTestBlock {
     MachineBasicBlock *Parent;
     MachineBasicBlock *Default;
     BitTestInfo Cases;
     BranchProbability Prob;
     BranchProbability DefaultProb;
   };
 
   /// Check whether a range of clusters is dense enough for a jump table.
-  bool isDense(const CaseClusterVector &Clusters, unsigned *TotalCases,
-               unsigned First, unsigned Last, unsigned MinDensity);
+  bool isDense(const CaseClusterVector &Clusters,
+               const SmallVectorImpl<unsigned> &TotalCases,
+               unsigned First, unsigned Last, unsigned MinDensity) const;
 
   /// Build a jump table cluster from Clusters[First..Last]. Returns false if it
   /// decides it's not a good idea.
-  bool buildJumpTable(CaseClusterVector &Clusters, unsigned First,
+  bool buildJumpTable(const CaseClusterVector &Clusters, unsigned First,
                       unsigned Last, const SwitchInst *SI,
                       MachineBasicBlock *DefaultMBB, CaseCluster &JTCluster);
 
   /// Find clusters of cases suitable for jump table lowering.
   void findJumpTables(CaseClusterVector &Clusters, const SwitchInst *SI,
                       MachineBasicBlock *DefaultMBB);
 
   /// Check whether the range [Low,High] fits in a machine word.

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

void SelectionDAGBuilder::updateDAGForMaybeTailCall(SDValue MaybeTC) {
   // If the node is null, we do have a tail call.
   if (MaybeTC.getNode() != nullptr)
     DAG.setRoot(MaybeTC);
   else
     HasTailCall = true;
 }
 
 bool SelectionDAGBuilder::isDense(const CaseClusterVector &Clusters,
-                                  unsigned *TotalCases, unsigned First,
-                                  unsigned Last,
-                                  unsigned Density) {
+                                  const SmallVectorImpl<unsigned> &TotalCases,
+                                  unsigned First, unsigned Last,
+                                  unsigned Density) const {
   assert(Last >= First);
   assert(TotalCases[Last] >= TotalCases[First]);
 
-  APInt LowCase = Clusters[First].Low->getValue();
-  APInt HighCase = Clusters[Last].High->getValue();
+  const APInt &LowCase = Clusters[First].Low->getValue();
+  const APInt &HighCase = Clusters[Last].High->getValue();
   assert(LowCase.getBitWidth() == HighCase.getBitWidth());
 
   // FIXME: A range of consecutive cases has 100% density, but only requires one
   // comparison to lower. We should discriminate against such consecutive ranges
   // in jump tables.
 
   uint64_t Diff = (HighCase - LowCase).getLimitedValue((UINT64_MAX - 1) / 100);
   uint64_t Range = Diff + 1;
static inline bool areJTsAllowed(const TargetLowering &TLI,
   const Function *Fn = SI->getParent()->getParent();
   if (Fn->getFnAttribute("no-jump-tables").getValueAsString() == "true")
     return false;
 
   return TLI.isOperationLegalOrCustom(ISD::BR_JT, MVT::Other) ||
          TLI.isOperationLegalOrCustom(ISD::BRIND, MVT::Other);
 }
 
-bool SelectionDAGBuilder::buildJumpTable(CaseClusterVector &Clusters,
+bool SelectionDAGBuilder::buildJumpTable(const CaseClusterVector &Clusters,
                                          unsigned First, unsigned Last,
                                          const SwitchInst *SI,
                                          MachineBasicBlock *DefaultMBB,
                                          CaseCluster &JTCluster) {
   assert(First <= Last);
 
   auto Prob = BranchProbability::getZero();
   unsigned NumCmps = 0;
   std::vector<MachineBasicBlock*> Table;
   DenseMap<MachineBasicBlock*, BranchProbability> JTProbs;
 
   // Initialize probabilities in JTProbs.
   for (unsigned I = First; I <= Last; ++I)
     JTProbs[Clusters[I].MBB] = BranchProbability::getZero();
 
   for (unsigned I = First; I <= Last; ++I) {
     assert(Clusters[I].Kind == CC_Range);
     Prob += Clusters[I].Prob;
-    APInt Low = Clusters[I].Low->getValue();
-    APInt High = Clusters[I].High->getValue();
+    const APInt &Low = Clusters[I].Low->getValue();
+    const APInt &High = Clusters[I].High->getValue();
     NumCmps += (Low == High) ? 1 : 2;
     if (I != First) {
       // Fill the gap between this and the previous cluster.
-      APInt PreviousHigh = Clusters[I - 1].High->getValue();
+      const APInt &PreviousHigh = Clusters[I - 1].High->getValue();
       assert(PreviousHigh.slt(Low));
       uint64_t Gap = (Low - PreviousHigh).getLimitedValue() - 1;
       for (uint64_t J = 0; J < Gap; J++)
         Table.push_back(DefaultMBB);
     }
     uint64_t ClusterSize = (High - Low).getLimitedValue() + 1;
     for (uint64_t J = 0; J < ClusterSize; ++J)
       Table.push_back(Clusters[I].MBB);
#endif
 
   const int64_t N = Clusters.size();
   const unsigned MinJumpTableSize = TLI.getMinimumJumpTableEntries();
 
   // TotalCases[i]: Total nbr of cases in Clusters[0..i].
   SmallVector<unsigned, 8> TotalCases(N);
 
   for (unsigned i = 0; i < N; ++i) {
-    APInt Hi = Clusters[i].High->getValue();
-    APInt Lo = Clusters[i].Low->getValue();
+    const APInt &Hi = Clusters[i].High->getValue();
+    const APInt &Lo = Clusters[i].Low->getValue();
     TotalCases[i] = (Hi - Lo).getLimitedValue() + 1;
     if (i != 0)
       TotalCases[i] += TotalCases[i - 1];
   }
 
   unsigned MinDensity = JumpTableDensity;
   if (DefaultMBB->getParent()->getFunction()->optForSize())
     MinDensity = OptsizeJumpTableDensity;
   if (N >= MinJumpTableSize
-      && isDense(Clusters, &TotalCases[0], 0, N - 1, MinDensity)) {
+      && isDense(Clusters, TotalCases, 0, N - 1, MinDensity)) {
     // Cheap case: the whole range might be suitable for jump table.
     CaseCluster JTCluster;
     if (buildJumpTable(Clusters, 0, N - 1, SI, DefaultMBB, JTCluster)) {
       Clusters[0] = JTCluster;
       Clusters.resize(1);
       return;
     }
   }
for (int64_t i = N - 2; i >= 0; i--) {
     // Baseline: Put Clusters[i] into a partition on its own.
     MinPartitions[i] = MinPartitions[i + 1] + 1;
     LastElement[i] = i;
     NumTables[i] = NumTables[i + 1];
 
     // Search for a solution that results in fewer partitions.
     for (int64_t j = N - 1; j > i; j--) {
       // Try building a partition from Clusters[i..j].
-      if (isDense(Clusters, &TotalCases[0], i, j, MinDensity)) {
+      if (isDense(Clusters, TotalCases, i, j, MinDensity)) {
         unsigned NumPartitions = 1 + (j == N - 1 ? 0 : MinPartitions[j + 1]);
         bool IsTable = j - i + 1 >= MinJumpTableSize;
         unsigned Tables = IsTable + (j == N - 1 ? 0 : NumTables[j + 1]);
 
         // If this j leads to fewer partitions, or same number of partitions
         // with more lookup tables, it is a better partitioning.
         if (NumPartitions < MinPartitions[i] ||
             (NumPartitions == MinPartitions[i] && Tables > NumTables[i])) {