[clang] [Clang] Generate the GEP instead of adding AST nodes (PR #73730)

[Bill Wendling via cfe-commits]

================
@@ -956,42 +956,70 @@ static llvm::Value *getArrayIndexingBound(CodeGenFunction &CGF,
   return nullptr;
 }
 
-const Expr *
+namespace {
+
+struct MemberExprBaseVisitor
+    : public StmtVisitor<MemberExprBaseVisitor, Expr *> {
+  MemberExprBaseVisitor() = default;
+
+  //===--------------------------------------------------------------------===//
+  //                            Visitor Methods
+  //===--------------------------------------------------------------------===//
+
+  Expr *Visit(Expr *E) {
+    return StmtVisitor<MemberExprBaseVisitor, Expr *>::Visit(E);
+  }
+
+  Expr *VisitArraySubscriptExpr(ArraySubscriptExpr *E) {
+    return Visit(E->getBase());
+  }
+  Expr *VisitCastExpr(CastExpr *E) { return Visit(E->getSubExpr()); }
+  Expr *VisitDeclRefExpr(DeclRefExpr *E) { return E; }
+  Expr *VisitMemberExpr(MemberExpr *E) { return Visit(E->getBase()); }
+  Expr *VisitParenExpr(ParenExpr *E) { return Visit(E->getSubExpr()); }
+  Expr *VisitUnaryOperator(UnaryOperator *E) { return Visit(E->getSubExpr()); }
+};
+
+} // end anonymous namespace
+
+llvm::Value *
 CodeGenFunction::BuildCountedByFieldExpr(const Expr *Base,
                                          const ValueDecl *CountedByVD) {
   // Find the outer struct expr (i.e. p in p->a.b.c.d).
-  Expr *CountedByExpr = const_cast<Expr *>(Base)->IgnoreParenImpCasts();
-
-  // Work our way up the expression until we reach the DeclRefExpr.
-  while (!isa<DeclRefExpr>(CountedByExpr))
-    if (const auto *ME = dyn_cast<MemberExpr>(CountedByExpr))
-      CountedByExpr = ME->getBase()->IgnoreParenImpCasts();
-
-  // Add back an implicit cast to create the required pr-value.
-  CountedByExpr = ImplicitCastExpr::Create(
-      getContext(), CountedByExpr->getType(), CK_LValueToRValue, CountedByExpr,
-      nullptr, VK_PRValue, FPOptionsOverride());
-
-  if (const auto *IFD = dyn_cast<IndirectFieldDecl>(CountedByVD)) {
-    // The counted_by field is inside an anonymous struct / union. The
-    // IndirectFieldDecl has the correct order of FieldDecls to build this
-    // easily. (Yay!)
-    for (NamedDecl *ND : IFD->chain()) {
-      auto *VD = cast<ValueDecl>(ND);
-      CountedByExpr =
-          MemberExpr::CreateImplicit(getContext(), CountedByExpr,
-                                     CountedByExpr->getType()->isPointerType(),
-                                     VD, VD->getType(), VK_LValue, OK_Ordinary);
+  Expr *CountedByExpr = MemberExprBaseVisitor().Visit(const_cast<Expr *>(Base));
----------------
bwendling wrote:

@AaronBallman can correct me if I'm wrong, but I think at this point we should always see a `DeclRefExpr` here. I should probably add an `assert` for that.

https://github.com/llvm/llvm-project/pull/73730