[Clang][Sema][OpenMP] Allow num_teams to accept multiple expressions (

#99732)

By the OpenMP standard, `num_teams` clause can only accept one
expression (for now). In this patch, we extend it to allow to accept
multiple expressions when it is used with `target teams ompx_bare`
construct. This will allow to launch a multi-dim grid, same as CUDA/HIP.

clang/docs/OpenMPSupport.rst

@@ -363,5 +363,7 @@ considered for standardization. Please post on the
 | device extension             | `'ompx_bare' clause on 'target teams' construct                                   | :good:`prototyped`       | #66844, #70612                                         |
 |                              | <https://www.osti.gov/servlets/purl/2205717>`_                                    |                          |                                                        |
 +------------------------------+-----------------------------------------------------------------------------------+--------------------------+--------------------------------------------------------+
+| device extension             | Multi-dim `'num_teams' clause on 'target teams ompx_bare' construct               | :good:`partial`          | #99732, #101407                                        |
++------------------------------+-----------------------------------------------------------------------------------+--------------------------+--------------------------------------------------------+
 
 .. _Discourse forums (Runtimes - OpenMP category): https://discourse.llvm.org/c/runtimes/openmp/35

clang/docs/ReleaseNotes.rst

@@ -333,6 +333,9 @@ Improvements
 ^^^^^^^^^^^^
 - Improve the handling of mapping array-section for struct containing nested structs with user defined mappers
 
+- `num_teams` now accepts multiple expressions when it is used along in ``target teams ompx_bare`` construct.
+  This allows the target region to be launched with multi-dim grid on GPUs.
+
 Additional Information
 ======================
 

clang/include/clang/AST/OpenMPClause.h

@@ -6369,60 +6369,77 @@ class OMPMapClause final : public OMPMappableExprListClause<OMPMapClause>,
 /// \endcode
 /// In this example directive '#pragma omp teams' has clause 'num_teams'
 /// with single expression 'n'.
-class OMPNumTeamsClause : public OMPClause, public OMPClauseWithPreInit {
-  friend class OMPClauseReader;
+///
+/// When 'ompx_bare' clause exists on a 'target' directive, 'num_teams' clause
+/// can accept up to three expressions.
+///
+/// \code
+/// #pragma omp target teams ompx_bare num_teams(x, y, z)
+/// \endcode
+class OMPNumTeamsClause final
+    : public OMPVarListClause<OMPNumTeamsClause>,
+      public OMPClauseWithPreInit,
+      private llvm::TrailingObjects<OMPNumTeamsClause, Expr *> {
+  friend OMPVarListClause;
+  friend TrailingObjects;
 
   /// Location of '('.
   SourceLocation LParenLoc;
 
-  /// NumTeams number.
-  Stmt *NumTeams = nullptr;
+  OMPNumTeamsClause(const ASTContext &C, SourceLocation StartLoc,
+                    SourceLocation LParenLoc, SourceLocation EndLoc, unsigned N)
+      : OMPVarListClause(llvm::omp::OMPC_num_teams, StartLoc, LParenLoc, EndLoc,
+                         N),
+        OMPClauseWithPreInit(this) {}
 
-  /// Set the NumTeams number.
-  ///
-  /// \param E NumTeams number.
-  void setNumTeams(Expr *E) { NumTeams = E; }
+  /// Build an empty clause.
+  OMPNumTeamsClause(unsigned N)
+      : OMPVarListClause(llvm::omp::OMPC_num_teams, SourceLocation(),
+                         SourceLocation(), SourceLocation(), N),
+        OMPClauseWithPreInit(this) {}
 
 public:
-  /// Build 'num_teams' clause.
+  /// Creates clause with a list of variables \a VL.
   ///
-  /// \param E Expression associated with this clause.
-  /// \param HelperE Helper Expression associated with this clause.
-  /// \param CaptureRegion Innermost OpenMP region where expressions in this
-  /// clause must be captured.
+  /// \param C AST context.
   /// \param StartLoc Starting location of the clause.
   /// \param LParenLoc Location of '('.
   /// \param EndLoc Ending location of the clause.
-  OMPNumTeamsClause(Expr *E, Stmt *HelperE, OpenMPDirectiveKind CaptureRegion,
-                    SourceLocation StartLoc, SourceLocation LParenLoc,
-                    SourceLocation EndLoc)
-      : OMPClause(llvm::omp::OMPC_num_teams, StartLoc, EndLoc),
-        OMPClauseWithPreInit(this), LParenLoc(LParenLoc), NumTeams(E) {
-    setPreInitStmt(HelperE, CaptureRegion);
-  }
+  /// \param VL List of references to the variables.
+  /// \param PreInit
+  static OMPNumTeamsClause *
+  Create(const ASTContext &C, OpenMPDirectiveKind CaptureRegion,
+         SourceLocation StartLoc, SourceLocation LParenLoc,
+         SourceLocation EndLoc, ArrayRef<Expr *> VL, Stmt *PreInit);
 
-  /// Build an empty clause.
-  OMPNumTeamsClause()
-      : OMPClause(llvm::omp::OMPC_num_teams, SourceLocation(),
-                  SourceLocation()),
-        OMPClauseWithPreInit(this) {}
+  /// Creates an empty clause with \a N variables.
+  ///
+  /// \param C AST context.
+  /// \param N The number of variables.
+  static OMPNumTeamsClause *CreateEmpty(const ASTContext &C, unsigned N);
 
   /// Sets the location of '('.
   void setLParenLoc(SourceLocation Loc) { LParenLoc = Loc; }
 
   /// Returns the location of '('.
   SourceLocation getLParenLoc() const { return LParenLoc; }
 
-  /// Return NumTeams number.
-  Expr *getNumTeams() { return cast<Expr>(NumTeams); }
+  /// Return NumTeams expressions.
+  ArrayRef<Expr *> getNumTeams() { return getVarRefs(); }
 
-  /// Return NumTeams number.
-  Expr *getNumTeams() const { return cast<Expr>(NumTeams); }
+  /// Return NumTeams expressions.
+  ArrayRef<Expr *> getNumTeams() const {
+    return const_cast<OMPNumTeamsClause *>(this)->getNumTeams();
+  }
 
-  child_range children() { return child_range(&NumTeams, &NumTeams + 1); }
+  child_range children() {
+    return child_range(reinterpret_cast<Stmt **>(varlist_begin()),
+                       reinterpret_cast<Stmt **>(varlist_end()));
+  }
 
   const_child_range children() const {
-    return const_child_range(&NumTeams, &NumTeams + 1);
+    auto Children = const_cast<OMPNumTeamsClause *>(this)->children();
+    return const_child_range(Children.begin(), Children.end());
   }
 
   child_range used_children() {

clang/include/clang/AST/RecursiveASTVisitor.h

@@ -3828,8 +3828,8 @@ bool RecursiveASTVisitor<Derived>::VisitOMPMapClause(OMPMapClause *C) {
 template <typename Derived>
 bool RecursiveASTVisitor<Derived>::VisitOMPNumTeamsClause(
     OMPNumTeamsClause *C) {
+  TRY_TO(VisitOMPClauseList(C));
   TRY_TO(VisitOMPClauseWithPreInit(C));
-  TRY_TO(TraverseStmt(C->getNumTeams()));
   return true;
 }
 

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -11639,6 +11639,8 @@ def warn_omp_unterminated_declare_target : Warning<
   InGroup<SourceUsesOpenMP>;
 def err_ompx_bare_no_grid : Error<
   "'ompx_bare' clauses requires explicit grid size via 'num_teams' and 'thread_limit' clauses">;
+def err_omp_multi_expr_not_allowed: Error<"only one expression allowed in '%0' clause">;
+def err_ompx_more_than_three_expr_not_allowed: Error<"at most three expressions are allowed in '%0' clause in 'target teams ompx_bare' construct">;
 } // end of OpenMP category
 
 let CategoryName = "Related Result Type Issue" in {

clang/include/clang/Sema/SemaOpenMP.h

@@ -1259,7 +1259,8 @@ class SemaOpenMP : public SemaBase {
       const OMPVarListLocTy &Locs, bool NoDiagnose = false,
       ArrayRef<Expr *> UnresolvedMappers = std::nullopt);
   /// Called on well-formed 'num_teams' clause.
-  OMPClause *ActOnOpenMPNumTeamsClause(Expr *NumTeams, SourceLocation StartLoc,
+  OMPClause *ActOnOpenMPNumTeamsClause(ArrayRef<Expr *> VarList,
+                                       SourceLocation StartLoc,
                                        SourceLocation LParenLoc,
                                        SourceLocation EndLoc);
   /// Called on well-formed 'thread_limit' clause.

clang/lib/AST/OpenMPClause.cpp

@@ -1755,6 +1755,24 @@ OMPContainsClause *OMPContainsClause::CreateEmpty(const ASTContext &C,
   return new (Mem) OMPContainsClause(K);
 }
 
+OMPNumTeamsClause *OMPNumTeamsClause::Create(
+    const ASTContext &C, OpenMPDirectiveKind CaptureRegion,
+    SourceLocation StartLoc, SourceLocation LParenLoc, SourceLocation EndLoc,
+    ArrayRef<Expr *> VL, Stmt *PreInit) {
+  void *Mem = C.Allocate(totalSizeToAlloc<Expr *>(VL.size()));
+  OMPNumTeamsClause *Clause =
+      new (Mem) OMPNumTeamsClause(C, StartLoc, LParenLoc, EndLoc, VL.size());
+  Clause->setVarRefs(VL);
+  Clause->setPreInitStmt(PreInit, CaptureRegion);
+  return Clause;
+}
+
+OMPNumTeamsClause *OMPNumTeamsClause::CreateEmpty(const ASTContext &C,
+                                                  unsigned N) {
+  void *Mem = C.Allocate(totalSizeToAlloc<Expr *>(N));
+  return new (Mem) OMPNumTeamsClause(N);
+}
+
 //===----------------------------------------------------------------------===//
 //  OpenMP clauses printing methods
 //===----------------------------------------------------------------------===//
@@ -2055,9 +2073,11 @@ void OMPClausePrinter::VisitOMPDeviceClause(OMPDeviceClause *Node) {
 }
 
 void OMPClausePrinter::VisitOMPNumTeamsClause(OMPNumTeamsClause *Node) {
-  OS << "num_teams(";
-  Node->getNumTeams()->printPretty(OS, nullptr, Policy, 0);
-  OS << ")";
+  if (!Node->varlist_empty()) {
+    OS << "num_teams";
+    VisitOMPClauseList(Node, '(');
+    OS << ")";
+  }
 }
 
 void OMPClausePrinter::VisitOMPThreadLimitClause(OMPThreadLimitClause *Node) {

clang/lib/AST/StmtProfile.cpp

@@ -857,9 +857,8 @@ void OMPClauseProfiler::VisitOMPAllocateClause(const OMPAllocateClause *C) {
   VisitOMPClauseList(C);
 }
 void OMPClauseProfiler::VisitOMPNumTeamsClause(const OMPNumTeamsClause *C) {
+  VisitOMPClauseList(C);
   VistOMPClauseWithPreInit(C);
-  if (C->getNumTeams())
-    Profiler->VisitStmt(C->getNumTeams());
 }
 void OMPClauseProfiler::VisitOMPThreadLimitClause(
     const OMPThreadLimitClause *C) {

clang/lib/CodeGen/CGOpenMPRuntime.cpp

@@ -6036,8 +6036,9 @@ const Expr *CGOpenMPRuntime::getNumTeamsExprForTargetDirective(
             dyn_cast_or_null<OMPExecutableDirective>(ChildStmt)) {
       if (isOpenMPTeamsDirective(NestedDir->getDirectiveKind())) {
         if (NestedDir->hasClausesOfKind<OMPNumTeamsClause>()) {
-          const Expr *NumTeams =
-              NestedDir->getSingleClause<OMPNumTeamsClause>()->getNumTeams();
+          const Expr *NumTeams = NestedDir->getSingleClause<OMPNumTeamsClause>()
+                                     ->getNumTeams()
+                                     .front();
           if (NumTeams->isIntegerConstantExpr(CGF.getContext()))
             if (auto Constant =
                     NumTeams->getIntegerConstantExpr(CGF.getContext()))
@@ -6062,7 +6063,7 @@ const Expr *CGOpenMPRuntime::getNumTeamsExprForTargetDirective(
   case OMPD_target_teams_distribute_parallel_for_simd: {
     if (D.hasClausesOfKind<OMPNumTeamsClause>()) {
       const Expr *NumTeams =
-          D.getSingleClause<OMPNumTeamsClause>()->getNumTeams();
+          D.getSingleClause<OMPNumTeamsClause>()->getNumTeams().front();
       if (NumTeams->isIntegerConstantExpr(CGF.getContext()))
         if (auto Constant = NumTeams->getIntegerConstantExpr(CGF.getContext()))
           MinTeamsVal = MaxTeamsVal = Constant->getExtValue();

clang/lib/CodeGen/CGStmtOpenMP.cpp

@@ -6859,7 +6859,7 @@ static void emitCommonOMPTeamsDirective(CodeGenFunction &CGF,
   const auto *NT = S.getSingleClause<OMPNumTeamsClause>();
   const auto *TL = S.getSingleClause<OMPThreadLimitClause>();
   if (NT || TL) {
-    const Expr *NumTeams = NT ? NT->getNumTeams() : nullptr;
+    const Expr *NumTeams = NT ? NT->getNumTeams().front() : nullptr;
     const Expr *ThreadLimit = TL ? TL->getThreadLimit() : nullptr;
 
     CGF.CGM.getOpenMPRuntime().emitNumTeamsClause(CGF, NumTeams, ThreadLimit,

clang/lib/Parse/ParseOpenMP.cpp

@@ -3175,7 +3175,6 @@ OMPClause *Parser::ParseOpenMPClause(OpenMPDirectiveKind DKind,
   case OMPC_simdlen:
   case OMPC_collapse:
   case OMPC_ordered:
-  case OMPC_num_teams:
   case OMPC_thread_limit:
   case OMPC_priority:
   case OMPC_grainsize:
@@ -3332,6 +3331,13 @@ OMPClause *Parser::ParseOpenMPClause(OpenMPDirectiveKind DKind,
                  ? ParseOpenMPSimpleClause(CKind, WrongDirective)
                  : ParseOpenMPClause(CKind, WrongDirective);
     break;
+  case OMPC_num_teams:
+    if (!FirstClause) {
+      Diag(Tok, diag::err_omp_more_one_clause)
+          << getOpenMPDirectiveName(DKind) << getOpenMPClauseName(CKind) << 0;
+      ErrorFound = true;
+    }
+    [[clang::fallthrough]];
   case OMPC_private:
   case OMPC_firstprivate:
   case OMPC_lastprivate: