[clang] [compiler-rt] [Clang][Sema] Add -Wstringop-overread warning for source buffer overreads (PR #183004)

[Erich Keane via llvm-commits]

================
@@ -1141,36 +1141,23 @@ static bool ProcessFormatStringLiteral(const Expr *FormatExpr,
   return false;
 }
 
-void Sema::checkFortifiedBuiltinMemoryFunction(FunctionDecl *FD,
-                                               CallExpr *TheCall) {
-  if (TheCall->isValueDependent() || TheCall->isTypeDependent() ||
-      isConstantEvaluatedContext())
-    return;
-
-  bool UseDABAttr = false;
-  const FunctionDecl *UseDecl = FD;
-
-  const auto *DABAttr = FD->getAttr<DiagnoseAsBuiltinAttr>();
-  if (DABAttr) {
-    UseDecl = DABAttr->getFunction();
-    assert(UseDecl && "Missing FunctionDecl in DiagnoseAsBuiltin attribute!");
-    UseDABAttr = true;
+namespace {
+/// Helper class for buffer overflow/overread checking in fortified functions.
+class FortifiedBufferChecker {
+public:
+  FortifiedBufferChecker(Sema &S, FunctionDecl *FD, CallExpr *TheCall)
+      : S(S), TheCall(TheCall), FD(FD),
+        DABAttr(FD ? FD->getAttr<DiagnoseAsBuiltinAttr>() : nullptr) {
+    const TargetInfo &TI = S.getASTContext().getTargetInfo();
+    SizeTypeWidth = TI.getTypeWidth(TI.getSizeType());
   }
 
-  unsigned BuiltinID = UseDecl->getBuiltinID(/*ConsiderWrappers=*/true);
-
-  if (!BuiltinID)
-    return;
-
-  const TargetInfo &TI = getASTContext().getTargetInfo();
-  unsigned SizeTypeWidth = TI.getTypeWidth(TI.getSizeType());
-
-  auto TranslateIndex = [&](unsigned Index) -> std::optional<unsigned> {
+  std::optional<unsigned> TranslateIndex(unsigned Index) {
     // If we refer to a diagnose_as_builtin attribute, we need to change the
     // argument index to refer to the arguments of the called function. Unless
     // the index is out of bounds, which presumably means it's a variadic
     // function.
-    if (!UseDABAttr)
+    if (DABAttr == nullptr) // Not using DABAttr.
----------------
erichkeane wrote:

This entire line of change should probably be reverted... it isn't adding anything (the change to ==nullptr, and the addition of the comment).

https://github.com/llvm/llvm-project/pull/183004