[OpenMP 60] Update parsing and semantic support for nowait clause to accept optional argument (#159628)

This PR enhances the OpenMP `nowait` clause implementation by adding
support for optional argument in both parsing and semantic analysis
phases.

Reference:
1. OpenMP 6.0 Specification, page 481

Author: mdfazlay

clang/docs/OpenMPSupport.rst

@@ -505,7 +505,7 @@ implementation.
 +-------------------------------------------------------------+---------------------------+---------------------------+--------------------------------------------------------------------------+
 | pure directives in DO CONCURRENT                            |                           | :none:`unclaimed`         |                                                                          |
 +-------------------------------------------------------------+---------------------------+---------------------------+--------------------------------------------------------------------------+
-| Optional argument for all clauses                           | :none:`unclaimed`         | :none:`unclaimed`         |                                                                          |
+| Optional argument for all clauses                           | :none:`partial`           | :none:`In Progress`       | Parse/Sema (nowait): https://github.com/llvm/llvm-project/pull/159628    |
 +-------------------------------------------------------------+---------------------------+---------------------------+--------------------------------------------------------------------------+
 | Function references for locator list items                  | :none:`unclaimed`         | :none:`unclaimed`         |                                                                          |
 +-------------------------------------------------------------+---------------------------+---------------------------+--------------------------------------------------------------------------+

clang/docs/ReleaseNotes.rst

@@ -641,6 +641,8 @@ OpenMP Support
 - Added support for ``defaultmap`` directive implicit-behavior ``private``.
 - Added parsing and semantic analysis support for ``groupprivate`` directive.
 - Added support for 'omp fuse' directive.
+- Updated parsing and semantic analysis support for ``nowait`` clause to accept
+  optional argument in OpenMP >= 60.
 
 Improvements
 ^^^^^^^^^^^^

clang/include/clang/AST/OpenMPClause.h

@@ -2291,18 +2291,68 @@ class OMPOrderedClause final
 /// This represents 'nowait' clause in the '#pragma omp ...' directive.
 ///
 /// \code
-/// #pragma omp for nowait
+/// #pragma omp for nowait (cond)
 /// \endcode
-/// In this example directive '#pragma omp for' has 'nowait' clause.
-class OMPNowaitClause final : public OMPNoChildClause<llvm::omp::OMPC_nowait> {
+/// In this example directive '#pragma omp for' has simple 'nowait' clause with
+/// condition 'cond'.
+class OMPNowaitClause final : public OMPClause {
+  friend class OMPClauseReader;
+
+  /// Location of '('.
+  SourceLocation LParenLoc;
+
+  /// Condition of the 'nowait' clause.
+  Stmt *Condition = nullptr;
+
+  /// Set condition.
+  void setCondition(Expr *Cond) { Condition = Cond; }
+
 public:
-  /// Build 'nowait' clause.
+  /// Build 'nowait' clause with condition \a Cond.
   ///
+  /// \param Cond Condition of the clause.
   /// \param StartLoc Starting location of the clause.
+  /// \param LParenLoc Location of '('.
   /// \param EndLoc Ending location of the clause.
-  OMPNowaitClause(SourceLocation StartLoc = SourceLocation(),
-                  SourceLocation EndLoc = SourceLocation())
-      : OMPNoChildClause(StartLoc, EndLoc) {}
+  OMPNowaitClause(Expr *Cond, SourceLocation StartLoc, SourceLocation LParenLoc,
+                  SourceLocation EndLoc)
+      : OMPClause(llvm::omp::OMPC_nowait, StartLoc, EndLoc),
+        LParenLoc(LParenLoc), Condition(Cond) {}
+
+  /// Build an empty clause.
+  OMPNowaitClause()
+      : OMPClause(llvm::omp::OMPC_nowait, SourceLocation(), SourceLocation()) {}
+
+  /// Sets the location of '('.
+  void setLParenLoc(SourceLocation Loc) { LParenLoc = Loc; }
+
+  /// Returns the location of '('.
+  SourceLocation getLParenLoc() const { return LParenLoc; }
+
+  /// Returns condition.
+  Expr *getCondition() const { return cast_or_null<Expr>(Condition); }
+
+  child_range children() {
+    if (Condition)
+      return child_range(&Condition, &Condition + 1);
+    return child_range(child_iterator(), child_iterator());
+  }
+
+  const_child_range children() const {
+    if (Condition)
+      return const_child_range(&Condition, &Condition + 1);
+    return const_child_range(const_child_iterator(), const_child_iterator());
+  }
+
+  child_range used_children();
+  const_child_range used_children() const {
+    auto Children = const_cast<OMPNowaitClause *>(this)->used_children();
+    return const_child_range(Children.begin(), Children.end());
+  }
+
+  static bool classof(const OMPClause *T) {
+    return T->getClauseKind() == llvm::omp::OMPC_nowait;
+  }
 };
 
 /// This represents 'untied' clause in the '#pragma omp ...' directive.

clang/include/clang/AST/RecursiveASTVisitor.h

@@ -3594,7 +3594,8 @@ bool RecursiveASTVisitor<Derived>::VisitOMPOrderedClause(OMPOrderedClause *C) {
 }
 
 template <typename Derived>
-bool RecursiveASTVisitor<Derived>::VisitOMPNowaitClause(OMPNowaitClause *) {
+bool RecursiveASTVisitor<Derived>::VisitOMPNowaitClause(OMPNowaitClause *C) {
+  TRY_TO(TraverseStmt(C->getCondition()));
   return true;
 }
 

clang/include/clang/Sema/SemaOpenMP.h

@@ -1022,7 +1022,8 @@ class SemaOpenMP : public SemaBase {
                                SourceLocation EndLoc);
   /// Called on well-formed 'nowait' clause.
   OMPClause *ActOnOpenMPNowaitClause(SourceLocation StartLoc,
-                                     SourceLocation EndLoc);
+                                     SourceLocation EndLoc,
+                                     SourceLocation LParenLoc, Expr *Condition);
   /// Called on well-formed 'untied' clause.
   OMPClause *ActOnOpenMPUntiedClause(SourceLocation StartLoc,
                                      SourceLocation EndLoc);

clang/lib/AST/OpenMPClause.cpp

@@ -309,6 +309,12 @@ OMPClause::child_range OMPIfClause::used_children() {
   return child_range(&Condition, &Condition + 1);
 }
 
+OMPClause::child_range OMPNowaitClause::used_children() {
+  if (Condition)
+    return child_range(&Condition, &Condition + 1);
+  return children();
+}
+
 OMPClause::child_range OMPGrainsizeClause::used_children() {
   if (Stmt **C = getAddrOfExprAsWritten(getPreInitStmt()))
     return child_range(C, C + 1);
@@ -2113,8 +2119,13 @@ void OMPClausePrinter::VisitOMPOrderedClause(OMPOrderedClause *Node) {
   }
 }
 
-void OMPClausePrinter::VisitOMPNowaitClause(OMPNowaitClause *) {
+void OMPClausePrinter::VisitOMPNowaitClause(OMPNowaitClause *Node) {
   OS << "nowait";
+  if (auto *Cond = Node->getCondition()) {
+    OS << "(";
+    Cond->printPretty(OS, nullptr, Policy, 0);
+    OS << ")";
+  }
 }
 
 void OMPClausePrinter::VisitOMPUntiedClause(OMPUntiedClause *) {

clang/lib/AST/StmtProfile.cpp

@@ -585,7 +585,10 @@ void OMPClauseProfiler::VisitOMPOrderedClause(const OMPOrderedClause *C) {
     Profiler->VisitStmt(Num);
 }
 
-void OMPClauseProfiler::VisitOMPNowaitClause(const OMPNowaitClause *) {}
+void OMPClauseProfiler::VisitOMPNowaitClause(const OMPNowaitClause *C) {
+  if (C->getCondition())
+    Profiler->VisitStmt(C->getCondition());
+}
 
 void OMPClauseProfiler::VisitOMPUntiedClause(const OMPUntiedClause *) {}
 

clang/lib/Parse/ParseOpenMP.cpp

@@ -3311,7 +3311,11 @@ OMPClause *Parser::ParseOpenMPClause(OpenMPDirectiveKind DKind,
       ErrorFound = true;
     }
 
-    Clause = ParseOpenMPClause(CKind, WrongDirective);
+    if (CKind == OMPC_nowait && PP.LookAhead(/*N=*/0).is(tok::l_paren) &&
+        getLangOpts().OpenMP >= 60)
+      Clause = ParseOpenMPSingleExprClause(CKind, WrongDirective);
+    else
+      Clause = ParseOpenMPClause(CKind, WrongDirective);
     break;
   case OMPC_self_maps:
     // OpenMP [6.0, self_maps clause]

clang/lib/Sema/SemaOpenMP.cpp

@@ -16491,6 +16491,9 @@ OMPClause *SemaOpenMP::ActOnOpenMPSingleExprClause(OpenMPClauseKind Kind,
   case OMPC_ordered:
     Res = ActOnOpenMPOrderedClause(StartLoc, EndLoc, LParenLoc, Expr);
     break;
+  case OMPC_nowait:
+    Res = ActOnOpenMPNowaitClause(StartLoc, EndLoc, LParenLoc, Expr);
+    break;
   case OMPC_priority:
     Res = ActOnOpenMPPriorityClause(Expr, StartLoc, LParenLoc, EndLoc);
     break;
@@ -16546,7 +16549,6 @@ OMPClause *SemaOpenMP::ActOnOpenMPSingleExprClause(OpenMPClauseKind Kind,
   case OMPC_aligned:
   case OMPC_copyin:
   case OMPC_copyprivate:
-  case OMPC_nowait:
   case OMPC_untied:
   case OMPC_mergeable:
   case OMPC_threadprivate:
@@ -17955,7 +17957,9 @@ OMPClause *SemaOpenMP::ActOnOpenMPClause(OpenMPClauseKind Kind,
     Res = ActOnOpenMPOrderedClause(StartLoc, EndLoc);
     break;
   case OMPC_nowait:
-    Res = ActOnOpenMPNowaitClause(StartLoc, EndLoc);
+    Res = ActOnOpenMPNowaitClause(StartLoc, EndLoc,
+                                  /*LParenLoc=*/SourceLocation(),
+                                  /*Condition=*/nullptr);
     break;
   case OMPC_untied:
     Res = ActOnOpenMPUntiedClause(StartLoc, EndLoc);
@@ -18107,9 +18111,24 @@ OMPClause *SemaOpenMP::ActOnOpenMPClause(OpenMPClauseKind Kind,
 }
 
 OMPClause *SemaOpenMP::ActOnOpenMPNowaitClause(SourceLocation StartLoc,
-                                               SourceLocation EndLoc) {
+                                               SourceLocation EndLoc,
+                                               SourceLocation LParenLoc,
+                                               Expr *Condition) {
+  Expr *ValExpr = Condition;
+  if (Condition && LParenLoc.isValid()) {
+    if (!Condition->isValueDependent() && !Condition->isTypeDependent() &&
+        !Condition->isInstantiationDependent() &&
+        !Condition->containsUnexpandedParameterPack()) {
+      ExprResult Val = SemaRef.CheckBooleanCondition(StartLoc, Condition);
+      if (Val.isInvalid())
+        return nullptr;
+
+      ValExpr = Val.get();
+    }
+  }
   DSAStack->setNowaitRegion();
-  return new (getASTContext()) OMPNowaitClause(StartLoc, EndLoc);
+  return new (getASTContext())
+      OMPNowaitClause(ValExpr, StartLoc, LParenLoc, EndLoc);
 }
 
 OMPClause *SemaOpenMP::ActOnOpenMPUntiedClause(SourceLocation StartLoc,

clang/lib/Sema/TreeTransform.h

@@ -1865,6 +1865,17 @@ class TreeTransform {
                                                        LParenLoc, Num);
   }
 
+  /// Build a new OpenMP 'nowait' clause.
+  ///
+  /// By default, performs semantic analysis to build the new OpenMP clause.
+  /// Subclasses may override this routine to provide different behavior.
+  OMPClause *RebuildOMPNowaitClause(Expr *Condition, SourceLocation StartLoc,
+                                    SourceLocation LParenLoc,
+                                    SourceLocation EndLoc) {
+    return getSema().OpenMP().ActOnOpenMPNowaitClause(StartLoc, EndLoc,
+                                                      LParenLoc, Condition);
+  }
+
   /// Build a new OpenMP 'private' clause.
   ///
   /// By default, performs semantic analysis to build the new OpenMP clause.
@@ -10612,8 +10623,14 @@ TreeTransform<Derived>::TransformOMPDetachClause(OMPDetachClause *C) {
 template <typename Derived>
 OMPClause *
 TreeTransform<Derived>::TransformOMPNowaitClause(OMPNowaitClause *C) {
-  // No need to rebuild this clause, no template-dependent parameters.
-  return C;
+  ExprResult Cond;
+  if (auto *Condition = C->getCondition()) {
+    Cond = getDerived().TransformExpr(Condition);
+    if (Cond.isInvalid())
+      return nullptr;
+  }
+  return getDerived().RebuildOMPNowaitClause(Cond.get(), C->getBeginLoc(),
+                                             C->getLParenLoc(), C->getEndLoc());
 }
 
 template <typename Derived>