[clang] [OpenACC] Implement `self` clause for compute constructs (PR #88760)

[Alexey Bataev via cfe-commits]

================
@@ -160,12 +169,58 @@ SemaOpenACC::ActOnClause(ArrayRef<const OpenACCClause *> ExistingClauses,
     // The parser has ensured that we have a proper condition expr, so there
     // isn't really much to do here.
 
-    // TODO OpenACC: When we implement 'self', this clauses causes us to
-    // 'ignore' the self clause, so we should implement a warning here.
+    // If the 'if' clause is true, it makes the 'self' clause have no effect,
+    // diagnose that here.
+    // TODO OpenACC: When we add these two to other constructs, we might not
+    // want to warn on this (for example, 'update').
+    const auto *Itr =
+        llvm::find_if(ExistingClauses, [](const OpenACCClause *C) {
+          return C->getClauseKind() == OpenACCClauseKind::Self;
+        });
+    if (Itr != ExistingClauses.end()) {
+      Diag(Clause.getBeginLoc(), diag::warn_acc_if_self_conflict);
+      Diag((*Itr)->getBeginLoc(), diag::note_acc_previous_clause_here);
+    }
+
     return OpenACCIfClause::Create(
         getASTContext(), Clause.getBeginLoc(), Clause.getLParenLoc(),
         Clause.getConditionExpr(), Clause.getEndLoc());
   }
+
+  case OpenACCClauseKind::Self: {
+    // 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 (!isOpenACCComputeDirectiveKind(Clause.getDirectiveKind()))
+      break;
+
+    // TODO OpenACC: When we implement this for 'update', this takes a
+    // 'var-list' instead of a condition expression, so semantics/handling has
+    // to happen differently here.
+
+    // There is no prose in the standard that says duplicates aren't allowed,
+    // but this diagnostic is present in other compilers, as well as makes
+    // sense.
+    if (checkAlreadyHasClauseOfKind(*this, ExistingClauses, Clause))
+      return nullptr;
+
+    // If the 'if' clause is true, it makes the 'self' clause have no effect,
+    // diagnose that here.
+    // TODO OpenACC: When we add these two to other constructs, we might not
+    // want to warn on this (for example, 'update').
+    const auto *Itr =
+        llvm::find_if(ExistingClauses, [](const OpenACCClause *C) {
+          return C->getClauseKind() == OpenACCClauseKind::If;
+        });
----------------
alexey-bataev wrote:

```suggestion
        llvm::find_if(ExistingClauses, IsaPred<OpenACCIfClause>);
```
???

https://github.com/llvm/llvm-project/pull/88760