[Clang][OpenMP][LoopTransformations] Add support for "#pragma omp fuse" loop transformation directive and "looprange" clause

clang/docs/OpenMPSupport.rst

@@ -376,6 +376,8 @@ implementation.
 +-------------------------------------------------------------+---------------------------+---------------------------+--------------------------------------------------------------------------+
 | loop stripe transformation                                  | :good:`done`              | https://github.com/llvm/llvm-project/pull/119891                                                     |
 +-------------------------------------------------------------+---------------------------+---------------------------+--------------------------------------------------------------------------+
+| loop fuse transformation                                    | :good:`done`              | :none:`unclaimed`         |                                                                          |
++-------------------------------------------------------------+---------------------------+---------------------------+--------------------------------------------------------------------------+
 | work distribute construct                                   | :none:`unclaimed`         | :none:`unclaimed`         |                                                                          |
 +-------------------------------------------------------------+---------------------------+---------------------------+--------------------------------------------------------------------------+
 | task_iteration                                              | :none:`unclaimed`         | :none:`unclaimed`         |                                                                          |

clang/docs/ReleaseNotes.rst

@@ -278,6 +278,7 @@ OpenMP Support
 - Added parsing and semantic analysis support for the ``need_device_addr``
   modifier in the ``adjust_args`` clause.
 - Allow array length to be omitted in array section subscript expression.
+- Added support for 'omp fuse' directive.
 
 Improvements
 ^^^^^^^^^^^^

clang/include/clang-c/Index.h

@@ -2162,6 +2162,10 @@ enum CXCursorKind {
    */
   CXCursor_OMPStripeDirective = 310,
 
+  /** OpenMP fuse directive
+   */
+  CXCursor_OMPFuseDirective = 311,
+
   /** OpenACC Compute Construct.
    */
   CXCursor_OpenACCComputeConstruct = 320,

clang/include/clang/AST/OpenMPClause.h

@@ -1149,6 +1149,80 @@ class OMPFullClause final : public OMPNoChildClause<llvm::omp::OMPC_full> {
   static OMPFullClause *CreateEmpty(const ASTContext &C);
 };
 
+/// This class represents the 'looprange' clause in the
+/// '#pragma omp fuse' directive
+///
+/// \code {c}
+/// #pragma omp fuse looprange(1,2)
+/// {
+///   for(int i = 0; i < 64; ++i)
+///   for(int j = 0; j < 256; j+=2)
+///   for(int k = 127; k >= 0; --k)
+/// \endcode
+class OMPLoopRangeClause final : public OMPClause {
+  friend class OMPClauseReader;
+  /// Location of '('
+  SourceLocation LParenLoc;
+
+  /// Location of first and count expressions
+  SourceLocation FirstLoc, CountLoc;
+
+  /// Number of looprange arguments (always 2: first, count)
+  static constexpr unsigned NumArgs = 2;
+  Stmt *Args[NumArgs] = {nullptr, nullptr};
+
+  /// Set looprange 'first' expression
+  void setFirst(Expr *E) { Args[0] = E; }
+
+  /// Set looprange 'count' expression
+  void setCount(Expr *E) { Args[1] = E; }
+
+  /// Build an empty clause for deserialization.
+  explicit OMPLoopRangeClause()
+      : OMPClause(llvm::omp::OMPC_looprange, {}, {}) {}
+
+public:
+  /// Build a 'looprange' clause AST node.
+  static OMPLoopRangeClause *
+  Create(const ASTContext &C, SourceLocation StartLoc, SourceLocation LParenLoc,
+         SourceLocation FirstLoc, SourceLocation CountLoc,
+         SourceLocation EndLoc, Expr *First, Expr *Count);
+
+  /// Build an empty 'looprange' clause node.
+  static OMPLoopRangeClause *CreateEmpty(const ASTContext &C);
+
+  // Location getters/setters
+  SourceLocation getLParenLoc() const { return LParenLoc; }
+  SourceLocation getFirstLoc() const { return FirstLoc; }
+  SourceLocation getCountLoc() const { return CountLoc; }
+
+  void setLParenLoc(SourceLocation Loc) { LParenLoc = Loc; }
+  void setFirstLoc(SourceLocation Loc) { FirstLoc = Loc; }
+  void setCountLoc(SourceLocation Loc) { CountLoc = Loc; }
+
+  /// Get looprange 'first' expression
+  Expr *getFirst() const { return cast_or_null<Expr>(Args[0]); }
+
+  /// Get looprange 'count' expression
+  Expr *getCount() const { return cast_or_null<Expr>(Args[1]); }
+
+  child_range children() { return child_range(Args, Args + NumArgs); }
+  const_child_range children() const {
+    return const_child_range(Args, Args + NumArgs);
+  }
+
+  child_range used_children() {
+    return child_range(child_iterator(), child_iterator());
+  }
+  const_child_range used_children() const {
+    return const_child_range(const_child_iterator(), const_child_iterator());
+  }
+
+  static bool classof(const OMPClause *T) {
+    return T->getClauseKind() == llvm::omp::OMPC_looprange;
+  }
+};
+
 /// Representation of the 'partial' clause of the '#pragma omp unroll'
 /// directive.
 ///

clang/include/clang/AST/RecursiveASTVisitor.h

@@ -3092,6 +3092,9 @@ DEF_TRAVERSE_STMT(OMPUnrollDirective,
 DEF_TRAVERSE_STMT(OMPReverseDirective,
                   { TRY_TO(TraverseOMPExecutableDirective(S)); })
 
+DEF_TRAVERSE_STMT(OMPFuseDirective,
+                  { TRY_TO(TraverseOMPExecutableDirective(S)); })
+
 DEF_TRAVERSE_STMT(OMPInterchangeDirective,
                   { TRY_TO(TraverseOMPExecutableDirective(S)); })
 
@@ -3409,6 +3412,14 @@ bool RecursiveASTVisitor<Derived>::VisitOMPFullClause(OMPFullClause *C) {
   return true;
 }
 
+template <typename Derived>
+bool RecursiveASTVisitor<Derived>::VisitOMPLoopRangeClause(
+    OMPLoopRangeClause *C) {
+  TRY_TO(TraverseStmt(C->getFirst()));
+  TRY_TO(TraverseStmt(C->getCount()));
+  return true;
+}
+
 template <typename Derived>
 bool RecursiveASTVisitor<Derived>::VisitOMPPartialClause(OMPPartialClause *C) {
   TRY_TO(TraverseStmt(C->getFactor()));

clang/include/clang/AST/StmtOpenMP.h

@@ -961,6 +961,9 @@ class OMPLoopTransformationDirective : public OMPLoopBasedDirective {
 
   /// Number of loops generated by this loop transformation.
   unsigned NumGeneratedLoops = 0;
+  /// Number of top level canonical loop nests generated by this loop
+  /// transformation
+  unsigned NumGeneratedLoopNests = 0;
 
 protected:
   explicit OMPLoopTransformationDirective(StmtClass SC,
@@ -973,13 +976,21 @@ class OMPLoopTransformationDirective : public OMPLoopBasedDirective {
   /// Set the number of loops generated by this loop transformation.
   void setNumGeneratedLoops(unsigned Num) { NumGeneratedLoops = Num; }
 
+  /// Set the number of top level canonical loop nests generated by this loop
+  /// transformation
+  void setNumGeneratedLoopNests(unsigned Num) { NumGeneratedLoopNests = 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; }
 
+  /// Return the number of top level canonical loop nests generated by this loop
+  /// transformation
+  unsigned getNumGeneratedLoopNests() const { return NumGeneratedLoopNests; }
+
   /// Get the de-sugared statements after the loop transformation.
   ///
   /// Might be nullptr if either the directive generates no loops and is handled
@@ -994,7 +1005,7 @@ class OMPLoopTransformationDirective : public OMPLoopBasedDirective {
     Stmt::StmtClass C = T->getStmtClass();
     return C == OMPTileDirectiveClass || C == OMPUnrollDirectiveClass ||
            C == OMPReverseDirectiveClass || C == OMPInterchangeDirectiveClass ||
-           C == OMPStripeDirectiveClass;
+           C == OMPStripeDirectiveClass || C == OMPFuseDirectiveClass;
   }
 };
 
@@ -5560,7 +5571,10 @@ class OMPTileDirective final : public OMPLoopTransformationDirective {
       : OMPLoopTransformationDirective(OMPTileDirectiveClass,
                                        llvm::omp::OMPD_tile, StartLoc, EndLoc,
                                        NumLoops) {
+    // Tiling doubles the original number of loops
     setNumGeneratedLoops(2 * NumLoops);
+    // Produces a single top-level canonical loop nest
+    setNumGeneratedLoopNests(1);
   }
 
   void setPreInits(Stmt *PreInits) {
@@ -5638,6 +5652,8 @@ class OMPStripeDirective final : public OMPLoopTransformationDirective {
                                        llvm::omp::OMPD_stripe, StartLoc, EndLoc,
                                        NumLoops) {
     setNumGeneratedLoops(2 * NumLoops);
+    // Similar to Tile, it only generates a single top level loop nest
+    setNumGeneratedLoopNests(1);
   }
 
   void setPreInits(Stmt *PreInits) {
@@ -5791,7 +5807,9 @@ class OMPReverseDirective final : public OMPLoopTransformationDirective {
       : OMPLoopTransformationDirective(OMPReverseDirectiveClass,
                                        llvm::omp::OMPD_reverse, StartLoc,
                                        EndLoc, NumLoops) {
+    // Reverse produces a single top-level canonical loop nest
     setNumGeneratedLoops(NumLoops);
+    setNumGeneratedLoopNests(1);
   }
 
   void setPreInits(Stmt *PreInits) {
@@ -5863,7 +5881,10 @@ class OMPInterchangeDirective final : public OMPLoopTransformationDirective {
       : OMPLoopTransformationDirective(OMPInterchangeDirectiveClass,
                                        llvm::omp::OMPD_interchange, StartLoc,
                                        EndLoc, NumLoops) {
+    // Interchange produces a single top-level canonical loop
+    // nest, with the exact same amount of total loops
     setNumGeneratedLoops(NumLoops);
+    setNumGeneratedLoopNests(1);
   }
 
   void setPreInits(Stmt *PreInits) {
@@ -5914,6 +5935,90 @@ class OMPInterchangeDirective final : public OMPLoopTransformationDirective {
   }
 };
 
+/// Represents the '#pragma omp fuse' loop transformation directive
+///
+/// \code{c}
+/// #pragma omp fuse
+/// {
+///   for(int i = 0; i < m1; ++i) {...}
+///   for(int j = 0; j < m2; ++j) {...}
+///   ...
+/// }
+/// \endcode
+class OMPFuseDirective final : public OMPLoopTransformationDirective {
+  friend class ASTStmtReader;
+  friend class OMPExecutableDirective;
+
+  // Offsets of child members.
+  enum {
+    PreInitsOffset = 0,
+    TransformedStmtOffset,
+  };
+
+  explicit OMPFuseDirective(SourceLocation StartLoc, SourceLocation EndLoc,
+                            unsigned NumLoops)
+      : OMPLoopTransformationDirective(OMPFuseDirectiveClass,
+                                       llvm::omp::OMPD_fuse, StartLoc, EndLoc,
+                                       NumLoops) {
+    // This default initialization assumes simple loop fusion.
+    // If a 'looprange' clause is specified, these values must be explicitly set
+    setNumGeneratedLoopNests(1);
+    setNumGeneratedLoops(NumLoops);
+  }
+
+  void setPreInits(Stmt *PreInits) {
+    Data->getChildren()[PreInitsOffset] = PreInits;
+  }
+
+  void setTransformedStmt(Stmt *S) {
+    Data->getChildren()[TransformedStmtOffset] = S;
+  }
+
+public:
+  /// Create a new AST node representation for #pragma omp fuse'
+  ///
+  /// \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 Clauses The directive's clauses
+  /// \param NumLoops Number of total affected loops
+  /// \param NumLoopNests Number of affected top level canonical loops
+  ///                 (number of items in the 'looprange' clause if present)
+  /// \param AssociatedStmt The outermost associated loop
+  /// \param TransformedStmt The loop nest after fusion, or nullptr in
+  ///                        dependent
+  /// \param PreInits Helper preinits statements for the loop nest
+  static OMPFuseDirective *Create(const ASTContext &C, SourceLocation StartLoc,
+                                  SourceLocation EndLoc,
+                                  ArrayRef<OMPClause *> Clauses,
+                                  unsigned NumLoops, unsigned NumLoopNests,
+                                  Stmt *AssociatedStmt, Stmt *TransformedStmt,
+                                  Stmt *PreInits);
+
+  /// Build an empty '#pragma omp fuse' AST node for deserialization
+  ///
+  /// \param C Context of the AST
+  /// \param NumClauses Number of clauses to allocate
+  /// \param NumLoops Number of associated loops to allocate
+  /// \param NumLoopNests Number of top level loops to allocate
+  static OMPFuseDirective *CreateEmpty(const ASTContext &C, unsigned NumClauses,
+                                       unsigned NumLoops,
+                                       unsigned NumLoopNests);
+
+  /// Gets the associated loops after the transformation. This is the de-sugared
+  /// replacement or nulltpr in dependent contexts.
+  Stmt *getTransformedStmt() const {
+    return Data->getChildren()[TransformedStmtOffset];
+  }
+
+  /// Return preinits statement.
+  Stmt *getPreInits() const { return Data->getChildren()[PreInitsOffset]; }
+
+  static bool classof(const Stmt *T) {
+    return T->getStmtClass() == OMPFuseDirectiveClass;
+  }
+};
+
 /// This represents '#pragma omp scan' directive.
 ///
 /// \code

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -11691,6 +11691,17 @@ def note_omp_implicit_dsa : Note<
   "implicitly determined as %0">;
 def err_omp_loop_var_dsa : Error<
   "loop iteration variable in the associated loop of 'omp %1' directive may not be %0, predetermined as %2">;
+def err_omp_not_canonical_loop : Error<
+  "loop after '#pragma omp %0' is not in canonical form">;
+def err_omp_not_a_loop_sequence : Error<
+  "statement after '#pragma omp %0' must be a loop sequence containing canonical loops or loop-generating constructs">;
+def err_omp_empty_loop_sequence : Error<
+  "loop sequence after '#pragma omp %0' must contain at least 1 canonical loop or loop-generating construct">;
+def err_omp_invalid_looprange : Error<
+  "looprange clause selects loops from %1 to %2 but this exceeds the number of loops (%3) in the loop sequence">;
+def warn_omp_redundant_fusion : Warning<
+  "looprange clause selects a single loop, resulting in redundant fusion">,
+  InGroup<OpenMPClauses>;
 def err_omp_not_for : Error<
   "%select{statement after '#pragma omp %1' must be a for loop|"
   "expected %2 for loops after '#pragma omp %1'%select{|, but found only %4}3}0">;

clang/include/clang/Basic/StmtNodes.td

@@ -233,6 +233,7 @@ def OMPStripeDirective : StmtNode<OMPLoopTransformationDirective>;
 def OMPUnrollDirective : StmtNode<OMPLoopTransformationDirective>;
 def OMPReverseDirective : StmtNode<OMPLoopTransformationDirective>;
 def OMPInterchangeDirective : StmtNode<OMPLoopTransformationDirective>;
+def OMPFuseDirective : StmtNode<OMPLoopTransformationDirective>;
 def OMPForDirective : StmtNode<OMPLoopDirective>;
 def OMPForSimdDirective : StmtNode<OMPLoopDirective>;
 def OMPSectionsDirective : StmtNode<OMPExecutableDirective>;

clang/include/clang/Parse/Parser.h

@@ -6759,6 +6759,9 @@ class Parser : public CodeCompletionHandler {
                                                 OpenMPClauseKind Kind,
                                                 bool ParseOnly);
 
+  /// Parses the 'looprange' clause of a '#pragma omp fuse' directive.
+  OMPClause *ParseOpenMPLoopRangeClause();
+
   /// Parses the 'sizes' clause of a '#pragma omp tile' directive.
   OMPClause *ParseOpenMPSizesClause();