[llvm] [PPC] Set minimum of largest number of comparisons to use bit test for switch lowering (PR #155910)

[Eli Friedman via llvm-commits]

================
@@ -206,12 +206,16 @@ bool SwitchCG::SwitchLowering::buildJumpTable(const CaseClusterVector &Clusters,
   for (unsigned I = First; I <= Last; ++I)
     JTProbs[Clusters[I].MBB] = BranchProbability::getZero();
 
+  DenseMap<const BasicBlock *, unsigned int> DestMap;
   for (unsigned I = First; I <= Last; ++I) {
     assert(Clusters[I].Kind == CC_Range);
     Prob += Clusters[I].Prob;
     const APInt &Low = Clusters[I].Low->getValue();
     const APInt &High = Clusters[I].High->getValue();
-    NumCmps += (Low == High) ? 1 : 2;
+    unsigned int NumCmp = (Low == High) ? 1 : 2;
+    const BasicBlock *BB = Clusters[I].MBB->getBasicBlock();
+    DestMap[BB] = DestMap.count(BB) ? (DestMap[BB] + NumCmp) : NumCmp;
----------------
efriedma-quic wrote:

```suggestion
    DestMap[BB] += NumCmp;
```

https://github.com/llvm/llvm-project/pull/155910