[NFC][CLANG] Fix static code analyzer concerns with dereference null return value

[Manna]

Summary

Reported by Static Analyzer Tool:

Inside "SemaExprMember.cpp" file, in clang::​Sema::​BuildMemberReferenceExpr(clang::​Expr *, clang::​QualType, clang::​SourceLocation, bool, clang::​CXXScopeSpec &, clang::​SourceLocation, clang::​NamedDecl *, clang::​DeclarationNameInfo const &, clang::​TemplateArgumentListInfo const *, clang::​Scope const *, clang::​Sema::​ActOnMemberAccessExtraArgs *): Return value of function which returns null is dereferenced without checking.

//Condition !Base, taking true branch.
if (!Base) {
  TypoExpr *TE = nullptr;
  QualType RecordTy = BaseType;

  //Condition IsArrow, taking true branch.
   if (IsArrow) RecordTy = RecordTy->castAs<PointerType>()->getPointeeType();
  	//returned_null: getAs returns nullptr (checked 279 out of 294 times). 
  	//Condition TemplateArgs != NULL, taking true branch.
  	
   //Dereference null return value (NULL_RETURNS)
   //dereference: Dereferencing a pointer that might be nullptr RecordTy->getAs() when calling LookupMemberExprInRecord. 
   if (LookupMemberExprInRecord(
         *this, R, nullptr, RecordTy->getAs<RecordType>(), OpLoc, IsArrow,
         SS, TemplateArgs != nullptr, TemplateKWLoc, TE))
      return ExprError();
   if (TE)
     return TE;

This patch uses castAs instead of getAs which will assert if the type doesn't match.

[Manna]

Thank you @erichkeane for reviews!

clang/lib/Sema/SemaExprMember.cpp

Sema::BuildMemberReferenceExpr(Expr *Base, QualType BaseType,
   LookupResult R(*this, NameInfo, LookupMemberName);
 
   // Implicit member accesses.
   if (!Base) {
     TypoExpr *TE = nullptr;
     QualType RecordTy = BaseType;
     if (IsArrow) RecordTy = RecordTy->castAs<PointerType>()->getPointeeType();
     if (LookupMemberExprInRecord(
-            *this, R, nullptr, RecordTy->getAs<RecordType>(), OpLoc, IsArrow,
+            *this, R, nullptr, RecordTy->castAs<RecordType>(), OpLoc, IsArrow,
             SS, TemplateArgs != nullptr, TemplateKWLoc, TE))
       return ExprError();
     if (TE)
       return TE;
 
   // Explicit member accesses.
   } else {
     ExprResult BaseResult = Base;