[clang][dataflow] Avoid MaxIterations overflow

[jkorous]

Summary

In case unsigned is only 16 bits wide MaxIterations wraps around and ends up being zero.

[sgatev]

Thanks!

[tschuett]

clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp

213–214

I would prefer something like uint32_t. long is scary stuff.

clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp

runTypeErasedDataflowAnalysis(const ControlFlowContext &CFCtx,
   Worklist.enqueueSuccessors(&Entry);
 
   // Bugs in lattices and transfer functions can prevent the analysis from
   // converging. To limit the damage (infinite loops) that these bugs can cause,
   // limit the number of iterations.
   // FIXME: Consider making the maximum number of iterations configurable.
   // FIXME: Set up statistics (see llvm/ADT/Statistic.h) to count average number
   // of iterations, number of functions that time out, etc.
-  unsigned Iterations = 0;
-  static constexpr unsigned MaxIterations = 1 << 16;
+  uint32_t Iterations = 0;
+  static constexpr uint32_t MaxIterations = 1 << 16;
   while (const CFGBlock *Block = Worklist.dequeue()) {
     if (++Iterations > MaxIterations) {
       llvm::errs() << "Maximum number of iterations reached, giving up.\n";
       break;
     }
 
     const llvm::Optional<TypeErasedDataflowAnalysisState> &OldBlockState =
         BlockStates[Block->getBlockID()];