[clang] [OpenMP 6.0] Parse/Sema support for reduction over private variable with reduction clause. (PR #129938)

[CHANDRA GHALE via cfe-commits]

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@@ -4668,6 +4668,34 @@ bool Parser::ParseOpenMPVarList(OpenMPDirectiveKind DKind,
       assert(Tok.is(tok::comma) && "Expected comma.");
       (void)ConsumeToken();
     }
+    // Handle original(private / shared) Modifier
+    if (Kind == OMPC_reduction && getLangOpts().OpenMP >= 60 &&
+        Tok.is(tok::identifier) && PP.getSpelling(Tok) == "original" &&
+        NextToken().is(tok::l_paren)) {
+      // Parse original(private) modifier.
+      ConsumeToken();
+      BalancedDelimiterTracker ParenT(*this, tok::l_paren, tok::r_paren);
+      ParenT.consumeOpen();
+      if (Tok.is(tok::kw_private)) {
+        Data.OriginalSharingModifier = OMPC_ORIGINAL_SHARING_private;
+        Data.OriginalSharingModifierLoc = Tok.getLocation();
+        ConsumeToken();
+      } else if (Tok.is(tok::identifier) &&
+                 (PP.getSpelling(Tok) == "shared" ||
+                  PP.getSpelling(Tok) == "default")) {
+        Data.OriginalSharingModifier = OMPC_ORIGINAL_SHARING_shared;
+        Data.OriginalSharingModifierLoc = Tok.getLocation();
+        ConsumeToken();
+      } else {
+        Diag(Tok.getLocation(), diag::err_expected)
+            << "'private or shared or default'";
+        SkipUntil(tok::r_paren);
+        return false;
+      }
+      ParenT.consumeClose();
+      assert(Tok.is(tok::comma) && "Expected comma.");
+      (void)ConsumeToken();
+    }
----------------
chandraghale wrote:

@alexey-bataev  "I'm sorry, I didn't understand your comment. The changes are made to consume the newly added original-sharing-modifier [OpenMP 6.0 7.6.10]  For example:
```
#pragma omp parallel reduction(original(private), +: x)
#pragma omp parallel reduction(original(shared), *: y)
```
Isn't it necessary for the parser to recognize the original(...) syntax and record the modifier? I suppose DSAStack does not natively handle this modifier." 

https://github.com/llvm/llvm-project/pull/129938