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

[Alexey Bataev via llvm-commits]

================
@@ -14175,27 +14222,350 @@ bool SemaOpenMP::checkTransformableLoopNest(
         return false;
       },
       [&OriginalInits](OMPLoopBasedDirective *Transform) {
-        Stmt *DependentPreInits;
-        if (auto *Dir = dyn_cast<OMPTileDirective>(Transform))
-          DependentPreInits = Dir->getPreInits();
-        else if (auto *Dir = dyn_cast<OMPStripeDirective>(Transform))
-          DependentPreInits = Dir->getPreInits();
-        else if (auto *Dir = dyn_cast<OMPUnrollDirective>(Transform))
-          DependentPreInits = Dir->getPreInits();
-        else if (auto *Dir = dyn_cast<OMPReverseDirective>(Transform))
-          DependentPreInits = Dir->getPreInits();
-        else if (auto *Dir = dyn_cast<OMPInterchangeDirective>(Transform))
-          DependentPreInits = Dir->getPreInits();
-        else
-          llvm_unreachable("Unhandled loop transformation");
-
-        appendFlattenedStmtList(OriginalInits.back(), DependentPreInits);
+        updatePreInits(Transform, OriginalInits);
       });
   assert(OriginalInits.back().empty() && "No preinit after innermost loop");
   OriginalInits.pop_back();
   return Result;
 }
 
+// Counts the total number of nested loops, including the outermost loop (the
+// original loop). PRECONDITION of this visitor is that it must be invoked from
+// the original loop to be analyzed. The traversal is stop for Decl's and
+// Expr's given that they may contain inner loops that must not be counted.
+//
+// Example AST structure for the code:
+//
+// int main() {
+//     #pragma omp fuse
+//     {
+//         for (int i = 0; i < 100; i++) {    <-- Outer loop
+//             []() {
+//                 for(int j = 0; j < 100; j++) {}  <-- NOT A LOOP
+//             };
+//             for(int j = 0; j < 5; ++j) {}    <-- Inner loop
+//         }
+//         for (int r = 0; i < 100; i++) {    <-- Outer loop
+//             struct LocalClass {
+//                 void bar() {
+//                     for(int j = 0; j < 100; j++) {}  <-- NOT A LOOP
+//                 }
+//             };
+//             for(int k = 0; k < 10; ++k) {}    <-- Inner loop
+//             {x = 5; for(k = 0; k < 10; ++k) x += k; x}; <-- NOT A LOOP
+//         }
+//     }
+// }
+// Result: Loop 'i' contains 2 loops, Loop 'r' also contains 2 loops
+class NestedLoopCounterVisitor : public DynamicRecursiveASTVisitor {
+private:
+  unsigned NestedLoopCount = 0;
+
+public:
+  explicit NestedLoopCounterVisitor() {}
+
+  unsigned getNestedLoopCount() const { return NestedLoopCount; }
+
+  bool VisitForStmt(ForStmt *FS) override {
+    ++NestedLoopCount;
+    return true;
+  }
+
+  bool VisitCXXForRangeStmt(CXXForRangeStmt *FRS) override {
+    ++NestedLoopCount;
+    return true;
+  }
+
+  bool TraverseStmt(Stmt *S) override {
+    if (!S)
+      return true;
+
+    // Skip traversal of all expressions, including special cases like
+    // LambdaExpr, StmtExpr, BlockExpr, and RequiresExpr. These expressions
+    // may contain inner statements (and even loops), but they are not part
+    // of the syntactic body of the surrounding loop structure.
+    //  Therefore must not be counted
+    if (isa<Expr>(S))
+      return true;
+
+    // Only recurse into CompoundStmt (block {}) and loop bodies
+    if (isa<CompoundStmt>(S) || isa<ForStmt>(S) || isa<CXXForRangeStmt>(S)) {
+      return DynamicRecursiveASTVisitor::TraverseStmt(S);
+    }
----------------
alexey-bataev wrote:

```suggestion
    if (isa<CompoundStmt, ForStmt, CXXForRangeStmt>(S))
      return DynamicRecursiveASTVisitor::TraverseStmt(S);
```


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