[clang] [flang] [llvm] [openmp] [Clang][OpenMP][LoopTransformations] Add support for "#pragma omp fuse" loop transformation directive and "looprange" clause (PR #139293)

[Roger Ferrer Ibáñez via cfe-commits]

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@@ -1479,7 +1492,85 @@ class SemaOpenMP : public SemaBase {
   bool checkTransformableLoopNest(
       OpenMPDirectiveKind Kind, Stmt *AStmt, int NumLoops,
       SmallVectorImpl<OMPLoopBasedDirective::HelperExprs> &LoopHelpers,
-      Stmt *&Body, SmallVectorImpl<SmallVector<Stmt *, 0>> &OriginalInits);
+      Stmt *&Body, SmallVectorImpl<SmallVector<Stmt *>> &OriginalInits);
+
+  /// Categories of loops encountered during semantic OpenMP loop
+  /// analysis.
+  ///
+  /// This enumeration identifies the structural category of a loop or sequence
+  /// of loops analyzed in the context of OpenMP transformations and directives.
+  /// This categorization helps differentiate between original source loops
+  /// and the structures resulting from applying OpenMP loop transformations.
+  enum class OMPLoopCategory {
+    /// @var OMPLoopCategory::RegularLoop
+    /// Represents a standard canonical loop nest found in the
+    /// original source code or an intact loop after transformations
+    /// (i.e Post/Pre loops of a loopranged fusion).
+    RegularLoop,
+
+    /// @var OMPLoopCategory::TransformSingleLoop
+    /// Represents the resulting loop structure when an OpenMP loop
+    /// transformation, generates a single, top-level loop.
+    TransformSingleLoop,
+  };
+
+  /// Holds the result of the analysis of a (possibly canonical) loop.
+  struct LoopAnalysis {
+    /// Category of the analyzed loop.
+    OMPLoopCategory Category;
+    /// Loop analyses results.
+    OMPLoopBasedDirective::HelperExprs HelperExprs;
+    /// The for-statement of the loop.
+    Stmt *ForStmt;
+    /// Initialization statements before transformations.
+    SmallVector<Stmt *> OriginalInits;
+    /// Initialization statements required after transformation of this loop.
+    SmallVector<Stmt *> TransformsPreInits;
+
+    explicit LoopAnalysis(OMPLoopCategory Category) : Category(Category) {}
+  };
+
+  /// Holds the result of the analysis of a (possibly canonical) loop sequence.
+  struct LoopSequenceAnalysis {
+    /// Number of top level canonical loops.
+    unsigned LoopSeqSize = 0;
+    /// Number of canonical loops, including nested.
+    unsigned NumLoops = 0;
+    /// For each loop results of the analysis.
+    std::vector<LoopAnalysis> Loops;
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rofirrim wrote:

I had to use `SmallVector<LoopAnalysis, 2>` or a static assertion triggers about `LoopAnalysis` being too large.

https://github.com/llvm/llvm-project/pull/139293