[Clang][OpenMP] Add an additional class to hold data that will be shared between all loop transformations (#155849)

This is preparatory work for the implementation of `#pragma omp fuse` in
#139293

**Note**: this change builds on top of
#155848

This change adds an additional class to hold data that will be shared
between all loop transformations: those that apply to canonical loop
nests (the majority) and those that apply to canonical loop sequences
(`fuse` in OpenMP 6.0).
    
This class is not a statement by itself and its goal is to avoid having
to replicate information between classes.
    
Also simplfiy the way we handle the "generated loops" information as we
currently only need to know if it is zero or non-zero.

Author: rofirrim

clang/include/clang/AST/StmtOpenMP.h

@@ -956,30 +956,46 @@ class OMPLoopBasedDirective : public OMPExecutableDirective {
   }
 };
 
+/// Common class of data shared between
+/// OMPCanonicalLoopNestTransformationDirective and transformations over
+/// canonical loop sequences.
+class OMPLoopTransformationDirective {
+  /// Number of (top-level) generated loops.
+  /// This value is 1 for most transformations as they only map one loop nest
+  /// into another.
+  /// Some loop transformations (like a non-partial 'unroll') may not generate
+  /// a loop nest, so this would be 0.
+  /// Some loop transformations (like 'fuse' with looprange and 'split') may
+  /// generate more than one loop nest, so the value would be >= 1.
+  unsigned NumGeneratedTopLevelLoops = 1;
+
+protected:
+  void setNumGeneratedTopLevelLoops(unsigned N) {
+    NumGeneratedTopLevelLoops = N;
+  }
+
+public:
+  unsigned getNumGeneratedTopLevelLoops() const {
+    return NumGeneratedTopLevelLoops;
+  }
+};
+
 /// The base class for all transformation directives of canonical loop nests.
 class OMPCanonicalLoopNestTransformationDirective
-    : public OMPLoopBasedDirective {
+    : public OMPLoopBasedDirective,
+      public OMPLoopTransformationDirective {
   friend class ASTStmtReader;
 
-  /// Number of loops generated by this loop transformation.
-  unsigned NumGeneratedLoops = 0;
-
 protected:
   explicit OMPCanonicalLoopNestTransformationDirective(
       StmtClass SC, OpenMPDirectiveKind Kind, SourceLocation StartLoc,
       SourceLocation EndLoc, unsigned NumAssociatedLoops)
       : OMPLoopBasedDirective(SC, Kind, StartLoc, EndLoc, NumAssociatedLoops) {}
 
-  /// Set the number of loops generated by this loop transformation.
-  void setNumGeneratedLoops(unsigned Num) { NumGeneratedLoops = Num; }
-
 public:
   /// Return the number of associated (consumed) loops.
   unsigned getNumAssociatedLoops() const { return getLoopsNumber(); }
 
-  /// Return the number of loops generated by this loop transformation.
-  unsigned getNumGeneratedLoops() const { return NumGeneratedLoops; }
-
   /// Get the de-sugared statements after the loop transformation.
   ///
   /// Might be nullptr if either the directive generates no loops and is handled
@@ -5560,9 +5576,7 @@ class OMPTileDirective final
                             unsigned NumLoops)
       : OMPCanonicalLoopNestTransformationDirective(
             OMPTileDirectiveClass, llvm::omp::OMPD_tile, StartLoc, EndLoc,
-            NumLoops) {
-    setNumGeneratedLoops(2 * NumLoops);
-  }
+            NumLoops) {}
 
   void setPreInits(Stmt *PreInits) {
     Data->getChildren()[PreInitsOffset] = PreInits;
@@ -5638,9 +5652,7 @@ class OMPStripeDirective final
                               unsigned NumLoops)
       : OMPCanonicalLoopNestTransformationDirective(
             OMPStripeDirectiveClass, llvm::omp::OMPD_stripe, StartLoc, EndLoc,
-            NumLoops) {
-    setNumGeneratedLoops(2 * NumLoops);
-  }
+            NumLoops) {}
 
   void setPreInits(Stmt *PreInits) {
     Data->getChildren()[PreInitsOffset] = PreInits;
@@ -5744,7 +5756,8 @@ class OMPUnrollDirective final
   static OMPUnrollDirective *
   Create(const ASTContext &C, SourceLocation StartLoc, SourceLocation EndLoc,
          ArrayRef<OMPClause *> Clauses, Stmt *AssociatedStmt,
-         unsigned NumGeneratedLoops, Stmt *TransformedStmt, Stmt *PreInits);
+         unsigned NumGeneratedTopLevelLoops, Stmt *TransformedStmt,
+         Stmt *PreInits);
 
   /// Build an empty '#pragma omp unroll' AST node for deserialization.
   ///
@@ -5794,9 +5807,7 @@ class OMPReverseDirective final
                                unsigned NumLoops)
       : OMPCanonicalLoopNestTransformationDirective(
             OMPReverseDirectiveClass, llvm::omp::OMPD_reverse, StartLoc, EndLoc,
-            NumLoops) {
-    setNumGeneratedLoops(NumLoops);
-  }
+            NumLoops) {}
 
   void setPreInits(Stmt *PreInits) {
     Data->getChildren()[PreInitsOffset] = PreInits;
@@ -5867,9 +5878,7 @@ class OMPInterchangeDirective final
                                    SourceLocation EndLoc, unsigned NumLoops)
       : OMPCanonicalLoopNestTransformationDirective(
             OMPInterchangeDirectiveClass, llvm::omp::OMPD_interchange, StartLoc,
-            EndLoc, NumLoops) {
-    setNumGeneratedLoops(NumLoops);
-  }
+            EndLoc, NumLoops) {}
 
   void setPreInits(Stmt *PreInits) {
     Data->getChildren()[PreInitsOffset] = PreInits;

clang/lib/AST/StmtOpenMP.cpp

@@ -139,13 +139,14 @@ bool OMPLoopBasedDirective::doForAllLoops(
 
       Stmt *TransformedStmt = Dir->getTransformedStmt();
       if (!TransformedStmt) {
-        unsigned NumGeneratedLoops = Dir->getNumGeneratedLoops();
-        if (NumGeneratedLoops == 0) {
+        unsigned NumGeneratedTopLevelLoops =
+            Dir->getNumGeneratedTopLevelLoops();
+        if (NumGeneratedTopLevelLoops == 0) {
           // May happen if the loop transformation does not result in a
           // generated loop (such as full unrolling).
           break;
         }
-        if (NumGeneratedLoops > 0) {
+        if (NumGeneratedTopLevelLoops > 0) {
           // The loop transformation construct has generated loops, but these
           // may not have been generated yet due to being in a dependent
           // context.
@@ -447,16 +448,16 @@ OMPStripeDirective *OMPStripeDirective::CreateEmpty(const ASTContext &C,
       SourceLocation(), SourceLocation(), NumLoops);
 }
 
-OMPUnrollDirective *
-OMPUnrollDirective::Create(const ASTContext &C, SourceLocation StartLoc,
-                           SourceLocation EndLoc, ArrayRef<OMPClause *> Clauses,
-                           Stmt *AssociatedStmt, unsigned NumGeneratedLoops,
-                           Stmt *TransformedStmt, Stmt *PreInits) {
-  assert(NumGeneratedLoops <= 1 && "Unrolling generates at most one loop");
+OMPUnrollDirective *OMPUnrollDirective::Create(
+    const ASTContext &C, SourceLocation StartLoc, SourceLocation EndLoc,
+    ArrayRef<OMPClause *> Clauses, Stmt *AssociatedStmt,
+    unsigned NumGeneratedTopLevelLoops, Stmt *TransformedStmt, Stmt *PreInits) {
+  assert(NumGeneratedTopLevelLoops <= 1 &&
+         "Unrolling generates at most one loop");
 
   auto *Dir = createDirective<OMPUnrollDirective>(
       C, Clauses, AssociatedStmt, TransformedStmtOffset + 1, StartLoc, EndLoc);
-  Dir->setNumGeneratedLoops(NumGeneratedLoops);
+  Dir->setNumGeneratedTopLevelLoops(NumGeneratedTopLevelLoops);
   Dir->setTransformedStmt(TransformedStmt);
   Dir->setPreInits(PreInits);
   return Dir;

clang/lib/Sema/SemaOpenMP.cpp

@@ -14983,12 +14983,13 @@ StmtResult SemaOpenMP::ActOnOpenMPUnrollDirective(ArrayRef<OMPClause *> Clauses,
                                   Body, OriginalInits))
     return StmtError();
 
-  unsigned NumGeneratedLoops = PartialClause ? 1 : 0;
+  unsigned NumGeneratedTopLevelLoops = PartialClause ? 1 : 0;
 
   // Delay unrolling to when template is completely instantiated.
   if (SemaRef.CurContext->isDependentContext())
     return OMPUnrollDirective::Create(Context, StartLoc, EndLoc, Clauses, AStmt,
-                                      NumGeneratedLoops, nullptr, nullptr);
+                                      NumGeneratedTopLevelLoops, nullptr,
+                                      nullptr);
 
   assert(LoopHelpers.size() == NumLoops &&
          "Expecting a single-dimensional loop iteration space");
@@ -15011,9 +15012,10 @@ StmtResult SemaOpenMP::ActOnOpenMPUnrollDirective(ArrayRef<OMPClause *> Clauses,
   // The generated loop may only be passed to other loop-associated directive
   // when a partial clause is specified. Without the requirement it is
   // sufficient to generate loop unroll metadata at code-generation.
-  if (NumGeneratedLoops == 0)
+  if (NumGeneratedTopLevelLoops == 0)
     return OMPUnrollDirective::Create(Context, StartLoc, EndLoc, Clauses, AStmt,
-                                      NumGeneratedLoops, nullptr, nullptr);
+                                      NumGeneratedTopLevelLoops, nullptr,
+                                      nullptr);
 
   // Otherwise, we need to provide a de-sugared/transformed AST that can be
   // associated with another loop directive.
@@ -15228,7 +15230,7 @@ StmtResult SemaOpenMP::ActOnOpenMPUnrollDirective(ArrayRef<OMPClause *> Clauses,
               LoopHelper.Init->getBeginLoc(), LoopHelper.Inc->getEndLoc());
 
   return OMPUnrollDirective::Create(Context, StartLoc, EndLoc, Clauses, AStmt,
-                                    NumGeneratedLoops, OuterFor,
+                                    NumGeneratedTopLevelLoops, OuterFor,
                                     buildPreInits(Context, PreInits));
 }
 

clang/lib/Serialization/ASTReaderStmt.cpp

@@ -2450,7 +2450,7 @@ void ASTStmtReader::VisitOMPSimdDirective(OMPSimdDirective *D) {
 void ASTStmtReader::VisitOMPCanonicalLoopNestTransformationDirective(
     OMPCanonicalLoopNestTransformationDirective *D) {
   VisitOMPLoopBasedDirective(D);
-  D->setNumGeneratedLoops(Record.readUInt32());
+  D->setNumGeneratedTopLevelLoops(Record.readUInt32());
 }
 
 void ASTStmtReader::VisitOMPTileDirective(OMPTileDirective *D) {

clang/lib/Serialization/ASTWriterStmt.cpp

@@ -2459,7 +2459,7 @@ void ASTStmtWriter::VisitOMPSimdDirective(OMPSimdDirective *D) {
 void ASTStmtWriter::VisitOMPCanonicalLoopNestTransformationDirective(
     OMPCanonicalLoopNestTransformationDirective *D) {
   VisitOMPLoopBasedDirective(D);
-  Record.writeUInt32(D->getNumGeneratedLoops());
+  Record.writeUInt32(D->getNumGeneratedTopLevelLoops());
 }
 
 void ASTStmtWriter::VisitOMPTileDirective(OMPTileDirective *D) {