// Insert a call to the reducer in the region of the mhlo op.
    mlir::SymbolRefAttr func = op.getComputation();
    auto func_op = cast<mlir::func::FuncOp>(SymbolTable::lookupSymbolIn(
        op->getParentOfType<mlir::ModuleOp>(), func));
    auto func_ty = func_op.getFunctionType();
    BuildBodyWithCall(rewriter, loc, func, func_ty,
                      &reduce_window_op.getBody());