[clang] [OpenACC] Implement Default clause for Compute Constructs (PR #88135)

[via cfe-commits]

================
@@ -63,8 +79,43 @@ SemaOpenACC::ActOnClause(ArrayRef<const OpenACCClause *> ExistingClauses,
     return nullptr;
   }
 
-  // TODO OpenACC: Switch over the clauses we implement here and 'create'
-  // them.
+  switch (Clause.getClauseKind()) {
+  case OpenACCClauseKind::Default: {
+    // Restrictions only properly implemented on 'compute' constructs, and
+    // 'compute' constructs are the only construct that can do anything with
+    // this yet, so skip/treat as unimplemented in this case.
+    if (Clause.getDirectiveKind() != OpenACCDirectiveKind::Parallel &&
+        Clause.getDirectiveKind() != OpenACCDirectiveKind::Serial &&
+        Clause.getDirectiveKind() != OpenACCDirectiveKind::Kernels)
+      break;
+
+    // Don't add an invalid clause to the AST.
+    if (Clause.getDefaultClauseKind() == OpenACCDefaultClauseKind::Invalid)
+      return nullptr;
+
+    // OpenACC 3.3, Section 2.5.4:
+    // At most one 'default' clause may appear, and it must have a value of
+    // either 'none' or 'present'.
+    // Second half of the sentence is diagnosed during parsing.
+    auto Itr = llvm::find_if(ExistingClauses, [](const OpenACCClause *C) {
+      return C->getClauseKind() == OpenACCClauseKind::Default;
+    });
+
+    if (Itr != ExistingClauses.end()) {
+      SemaRef.Diag(Clause.getBeginLoc(),
+                   diag::err_acc_duplicate_clause_diallowed)
----------------
Sirraide wrote:

```suggestion
                   diag::err_acc_duplicate_clause_disallowed)
```

https://github.com/llvm/llvm-project/pull/88135