[clang] [llvm] [IR] Make dead_on_return attribute optionally sized (PR #171712)

[Antonio Frighetto via cfe-commits]

================
@@ -2468,31 +2482,38 @@ bool LLParser::parseOptionalCodeModel(CodeModel::Model &model) {
   return false;
 }
 
-/// parseOptionalDerefAttrBytes
+/// parseOptionalAttrBytes
 ///   ::= /* empty */
 ///   ::= AttrKind '(' 4 ')'
 ///
-/// where AttrKind is either 'dereferenceable' or 'dereferenceable_or_null'.
-bool LLParser::parseOptionalDerefAttrBytes(lltok::Kind AttrKind,
-                                           uint64_t &Bytes) {
+/// where AttrKind is either 'dereferenceable', 'dereferenceable_or_null', or
+/// 'dead_on_return'
+bool LLParser::parseOptionalAttrBytes(lltok::Kind AttrKind,
+                                      std::optional<uint64_t> &Bytes,
+                                      bool ErrorNoBytes) {
   assert((AttrKind == lltok::kw_dereferenceable ||
-          AttrKind == lltok::kw_dereferenceable_or_null) &&
+          AttrKind == lltok::kw_dereferenceable_or_null ||
+          AttrKind == lltok::kw_dead_on_return) &&
          "contract!");
 
   Bytes = 0;
   if (!EatIfPresent(AttrKind))
     return false;
   LocTy ParenLoc = Lex.getLoc();
-  if (!EatIfPresent(lltok::lparen))
-    return error(ParenLoc, "expected '('");
+  if (!EatIfPresent(lltok::lparen)) {
+    if (ErrorNoBytes)
----------------
antoniofrighetto wrote:

```suggestion
    if (!ErrorNoBytes)
```
Or meant to pass ErrorNoBytes true as default?

https://github.com/llvm/llvm-project/pull/171712