[clang][dataflow] Convert nonnull pointer parameter to a reference.

[ymandel]

Summary

The parameter in question belongs to a function that is only called once. This patch updates the API to use a reference and changes the caller accordingly.

[ymandel]

Just realized this is actually more complicated to change, assuming I also want to update all the derived classes. For now, I'll limit the scope of the change to these files, but I'll follow up with an overload-based solution to admit either kind of derived class until we can port them all over to then new signature.

[ymandel]

add fixme and fix compilation error

clang/include/clang/Analysis/FlowSensitive/DataflowAnalysis.h

public:
 
   bool isEqualTypeErased(const TypeErasedLattice &E1,
                          const TypeErasedLattice &E2) final {
     const Lattice &L1 = llvm::any_cast<const Lattice &>(E1.Value);
     const Lattice &L2 = llvm::any_cast<const Lattice &>(E2.Value);
     return L1 == L2;
   }
 
-  void transferTypeErased(const CFGElement *Element, TypeErasedLattice &E,
+  void transferTypeErased(const CFGElement &Element, TypeErasedLattice &E,
                           Environment &Env) final {
     Lattice &L = llvm::any_cast<Lattice &>(E.Value);
-    static_cast<Derived *>(this)->transfer(Element, L, Env);
+    // FIXME: change the contract of `transfer` to take a reference.
+    static_cast<Derived *>(this)->transfer(&Element, L, Env);
   }
 
   void transferBranchTypeErased(bool Branch, const Stmt *Stmt,
                                 TypeErasedLattice &E, Environment &Env) final {
     transferBranchInternal(Rank0{}, *static_cast<Derived *>(this), Branch, Stmt,
                            E, Env);
   }
 

clang/include/clang/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.h

public:
 
   /// Returns true if and only if the two given type-erased lattice elements are
   /// equal.
   virtual bool isEqualTypeErased(const TypeErasedLattice &,
                                  const TypeErasedLattice &) = 0;
 
   /// Applies the analysis transfer function for a given control flow graph
   /// element and type-erased lattice element.
-  virtual void transferTypeErased(const CFGElement *, TypeErasedLattice &,
+  virtual void transferTypeErased(const CFGElement &, TypeErasedLattice &,
                                   Environment &) = 0;
 
   /// Applies the analysis transfer function for a given edge from a CFG block
   /// of a conditional statement.
   /// @param Stmt The condition which is responsible for the split in the CFG.
   /// @param Branch True if the edge goes to the basic block where the
   /// condition is true.
   virtual void transferBranchTypeErased(bool Branch, const Stmt *,

clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp

transferCFGBlock(const CFGBlock &Block, AnalysisContext &AC,
   auto State = computeBlockInputState(Block, AC);
   for (const auto &Element : Block) {
     // Built-in analysis
     if (AC.Analysis.builtinOptions()) {
       builtinTransfer(Element, State, AC);
     }
 
     // User-provided analysis
-    AC.Analysis.transferTypeErased(&Element, State.Lattice, State.Env);
+    AC.Analysis.transferTypeErased(Element, State.Lattice, State.Env);
 
     // Post processing
     if (PostVisitCFG) {
       PostVisitCFG(Element, State);
     }
   }
   return State;
 }