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

[Alexey Bataev via llvm-commits]

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@@ -14219,27 +14262,320 @@ 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 stops 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 {
----------------
alexey-bataev wrote:

```suggestion
class NestedLoopCounterVisitor final: public DynamicRecursiveASTVisitor {
```


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