[Clang][OpenMP][LoopTransformations] Fix incorrect number of generated loops for Tile and Reverse directives (llvm#140532)

This patch is closely related to llvm#139293 and addresses an existing issue
in the loop transformation codebase. Specifically, it corrects the
handling of the `NumGeneratedLoops` variable in
`OMPLoopTransformationDirective` AST nodes and its inheritors (such as
OMPUnrollDirective, OMPTileDirective, etc.).

Previously, this variable was inaccurately set for certain
transformations like reverse or tile. While this did not lead to
functional bugs, since the value was only checked to determine whether
it was greater than zero or equal to zero, the inconsistency could
introduce problems when supporting more complex directives in the
future.

Author: eZWALT

clang/include/clang/AST/StmtOpenMP.h

@@ -5787,10 +5787,13 @@ class OMPReverseDirective final : public OMPLoopTransformationDirective {
     TransformedStmtOffset,
   };
 
-  explicit OMPReverseDirective(SourceLocation StartLoc, SourceLocation EndLoc)
+  explicit OMPReverseDirective(SourceLocation StartLoc, SourceLocation EndLoc,
+                               unsigned NumLoops)
       : OMPLoopTransformationDirective(OMPReverseDirectiveClass,
                                        llvm::omp::OMPD_reverse, StartLoc,
-                                       EndLoc, 1) {}
+                                       EndLoc, NumLoops) {
+    setNumGeneratedLoops(NumLoops);
+  }
 
   void setPreInits(Stmt *PreInits) {
     Data->getChildren()[PreInitsOffset] = PreInits;
@@ -5806,19 +5809,23 @@ class OMPReverseDirective final : public OMPLoopTransformationDirective {
   /// \param C         Context of the AST.
   /// \param StartLoc  Location of the introducer (e.g. the 'omp' token).
   /// \param EndLoc    Location of the directive's end (e.g. the tok::eod).
+  /// \param NumLoops Number of affected loops
   /// \param AssociatedStmt  The outermost associated loop.
   /// \param TransformedStmt The loop nest after tiling, or nullptr in
   ///                        dependent contexts.
   /// \param PreInits   Helper preinits statements for the loop nest.
-  static OMPReverseDirective *
-  Create(const ASTContext &C, SourceLocation StartLoc, SourceLocation EndLoc,
-         Stmt *AssociatedStmt, Stmt *TransformedStmt, Stmt *PreInits);
+  static OMPReverseDirective *Create(const ASTContext &C,
+                                     SourceLocation StartLoc,
+                                     SourceLocation EndLoc,
+                                     Stmt *AssociatedStmt, unsigned NumLoops,
+                                     Stmt *TransformedStmt, Stmt *PreInits);
 
   /// Build an empty '#pragma omp reverse' AST node for deserialization.
   ///
   /// \param C          Context of the AST.
-  /// \param NumClauses Number of clauses to allocate.
-  static OMPReverseDirective *CreateEmpty(const ASTContext &C);
+  /// \param NumLoops   Number of associated loops to allocate
+  static OMPReverseDirective *CreateEmpty(const ASTContext &C,
+                                          unsigned NumLoops);
 
   /// Gets/sets the associated loops after the transformation, i.e. after
   /// de-sugaring.
@@ -5857,7 +5864,7 @@ class OMPInterchangeDirective final : public OMPLoopTransformationDirective {
       : OMPLoopTransformationDirective(OMPInterchangeDirectiveClass,
                                        llvm::omp::OMPD_interchange, StartLoc,
                                        EndLoc, NumLoops) {
-    setNumGeneratedLoops(3 * NumLoops);
+    setNumGeneratedLoops(NumLoops);
   }
 
   void setPreInits(Stmt *PreInits) {

clang/lib/AST/StmtOpenMP.cpp

@@ -471,18 +471,21 @@ OMPUnrollDirective *OMPUnrollDirective::CreateEmpty(const ASTContext &C,
 OMPReverseDirective *
 OMPReverseDirective::Create(const ASTContext &C, SourceLocation StartLoc,
                             SourceLocation EndLoc, Stmt *AssociatedStmt,
-                            Stmt *TransformedStmt, Stmt *PreInits) {
+                            unsigned NumLoops, Stmt *TransformedStmt,
+                            Stmt *PreInits) {
   OMPReverseDirective *Dir = createDirective<OMPReverseDirective>(
-      C, {}, AssociatedStmt, TransformedStmtOffset + 1, StartLoc, EndLoc);
+      C, {}, AssociatedStmt, TransformedStmtOffset + 1, StartLoc, EndLoc,
+      NumLoops);
   Dir->setTransformedStmt(TransformedStmt);
   Dir->setPreInits(PreInits);
   return Dir;
 }
 
-OMPReverseDirective *OMPReverseDirective::CreateEmpty(const ASTContext &C) {
+OMPReverseDirective *OMPReverseDirective::CreateEmpty(const ASTContext &C,
+                                                      unsigned NumLoops) {
   return createEmptyDirective<OMPReverseDirective>(
       C, /*NumClauses=*/0, /*HasAssociatedStmt=*/true,
-      TransformedStmtOffset + 1, SourceLocation(), SourceLocation());
+      TransformedStmtOffset + 1, SourceLocation(), SourceLocation(), NumLoops);
 }
 
 OMPInterchangeDirective *OMPInterchangeDirective::Create(

clang/lib/Sema/SemaOpenMP.cpp

@@ -15140,7 +15140,7 @@ StmtResult SemaOpenMP::ActOnOpenMPReverseDirective(Stmt *AStmt,
   // instantiated.
   if (SemaRef.CurContext->isDependentContext())
     return OMPReverseDirective::Create(Context, StartLoc, EndLoc, AStmt,
-                                       nullptr, nullptr);
+                                       NumLoops, nullptr, nullptr);
 
   assert(LoopHelpers.size() == NumLoops &&
          "Expecting a single-dimensional loop iteration space");
@@ -15299,7 +15299,7 @@ StmtResult SemaOpenMP::ActOnOpenMPReverseDirective(Stmt *AStmt,
       ForStmt(Context, Init.get(), Cond.get(), nullptr, Incr.get(),
               ReversedBody, LoopHelper.Init->getBeginLoc(),
               LoopHelper.Init->getBeginLoc(), LoopHelper.Inc->getEndLoc());
-  return OMPReverseDirective::Create(Context, StartLoc, EndLoc, AStmt,
+  return OMPReverseDirective::Create(Context, StartLoc, EndLoc, AStmt, NumLoops,
                                      ReversedFor,
                                      buildPreInits(Context, PreInits));
 }

clang/lib/Serialization/ASTReaderStmt.cpp

@@ -3602,11 +3602,10 @@ Stmt *ASTReader::ReadStmtFromStream(ModuleFile &F) {
     }
 
     case STMT_OMP_REVERSE_DIRECTIVE: {
-      assert(Record[ASTStmtReader::NumStmtFields] == 1 &&
-             "Reverse directive accepts only a single loop");
+      unsigned NumLoops = Record[ASTStmtReader::NumStmtFields];
       assert(Record[ASTStmtReader::NumStmtFields + 1] == 0 &&
              "Reverse directive has no clauses");
-      S = OMPReverseDirective::CreateEmpty(Context);
+      S = OMPReverseDirective::CreateEmpty(Context, NumLoops);
       break;
     }