[clang] [Clang][Sema] Add fortify warnings for vsprintf (PR #230672)

[George Burgess IV via cfe-commits]

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@@ -1406,9 +1406,17 @@ void Sema::checkFortifiedBuiltinMemoryFunction(FunctionDecl *FD,
   }
 
   case Builtin::BIsprintf:
-  case Builtin::BI__builtin___sprintf_chk: {
-    size_t FormatIndex = BuiltinID == Builtin::BIsprintf ? 1 : 3;
-    auto *FormatExpr = TheCall->getArg(FormatIndex)->IgnoreParenImpCasts();
+  case Builtin::BI__builtin_sprintf:
+  case Builtin::BI__builtin___sprintf_chk:
+  case Builtin::BIvsprintf:
+  case Builtin::BI__builtin_vsprintf:
+  case Builtin::BI__builtin___vsprintf_chk: {
+    bool IsChk = BuiltinID == Builtin::BI__builtin___sprintf_chk ||
+                 BuiltinID == Builtin::BI__builtin___vsprintf_chk;
+    std::optional<unsigned> FormatIndex = Checker.TranslateIndex(IsChk ? 3 : 1);
+    if (!FormatIndex)
+      return;
+    auto *FormatExpr = TheCall->getArg(*FormatIndex)->IgnoreParenImpCasts();
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gburgessiv wrote:

nit: i understand it's the way this was previously written, but please `const auto *` while we're here - makes it a bit clearer that we don't need a mutable pointee

https://github.com/llvm/llvm-project/pull/230672