[flang][openacc] Add proper TODO for reduction with dynamic shaped array

[clementval]

Summary

Lowering for reduction with dynamic shaped arrays is not implemented yet.
Add a proper TODO for the time being.

[razvanlupusoru]

Thank you for adding a clear TODO here.

flang/lib/Lower/OpenACC.cpp

mlir::acc::ReductionRecipeOp Fortran::lower::createOrGetReductionRecipe(
   mlir::Value v1 = recipe.getCombinerRegion().front().getArgument(0);
   mlir::Value v2 = recipe.getCombinerRegion().front().getArgument(1);
   mlir::Value combinedValue = genCombiner(builder, loc, op, ty, v1, v2);
   builder.create<mlir::acc::YieldOp>(loc, combinedValue);
   builder.restoreInsertionPoint(crtPos);
   return recipe;
 }
 
+/// Determine if the bounds represent a dynamic shape.
+bool hasDynamicShape(llvm::SmallVector<mlir::Value> &bounds) {
+  if (bounds.empty())
+    return false;
+  for (auto b : bounds) {
+    auto op = mlir::dyn_cast<mlir::acc::DataBoundsOp>(b.getDefiningOp());
+    if (((op.getLowerbound() && !fir::getIntIfConstant(op.getLowerbound())) ||
+         (op.getUpperbound() && !fir::getIntIfConstant(op.getUpperbound()))) &&
+        op.getExtent() && !fir::getIntIfConstant(op.getExtent()))
+      return true;
+  }
+  return false;
+}
+
 static void
 genReductions(const Fortran::parser::AccObjectListWithReduction &objectList,
               Fortran::lower::AbstractConverter &converter,
               Fortran::semantics::SemanticsContext &semanticsContext,
               Fortran::lower::StatementContext &stmtCtx,
               llvm::SmallVectorImpl<mlir::Value> &reductionOperands,
               llvm::SmallVector<mlir::Attribute> &reductionRecipes) {
   fir::FirOpBuilder &builder = converter.getFirOpBuilder();
   const auto &objects = std::get<Fortran::parser::AccObjectList>(objectList.t);
   const auto &op =
       std::get<Fortran::parser::AccReductionOperator>(objectList.t);
   mlir::acc::ReductionOperator mlirOp = getReductionOperator(op);
   for (const auto &accObject : objects.v) {
     llvm::SmallVector<mlir::Value> bounds;
     std::stringstream asFortran;
     mlir::Location operandLocation = genOperandLocation(converter, accObject);
     mlir::Value baseAddr = gatherDataOperandAddrAndBounds(
         converter, builder, semanticsContext, stmtCtx, accObject,
         operandLocation, asFortran, bounds);
 
+    if (hasDynamicShape(bounds))
+      TODO(operandLocation, "OpenACC reductions with dynamic shaped array");
+
     mlir::Type reductionTy = fir::unwrapRefType(baseAddr.getType());
     if (auto seqTy = mlir::dyn_cast<fir::SequenceType>(reductionTy))
       reductionTy = seqTy.getEleTy();
 
     if (!fir::isa_trivial(reductionTy))
       TODO(operandLocation, "reduction with unsupported type");
 
     auto op = createDataEntryOp<mlir::acc::ReductionOp>(