[SYCL] the first kernel function declaration should be added with attribute

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -12676,7 +12676,8 @@ def err_free_function_variadic_args : Error<
   "free function kernel cannot be a variadic function">;
 def err_free_function_return_type : Error<
   "SYCL free function kernel should have return type 'void'">;
-
+def err_free_function_first_occurrence_missing_attr: Error<
+  "the first occurrence of kernel free function should be declared with attribute add_ir_attributes_function with 'sycl-nd-range-kernel' or 'sycl-single-task-kernel'">;
 
 // SYCL kernel entry point diagnostics
 def err_sycl_entry_point_invalid : Error<

clang/lib/Sema/SemaSYCL.cpp

@@ -1160,14 +1160,33 @@ static target getAccessTarget(QualType FieldTy,
 }
 
 bool SemaSYCL::isFreeFunction(const FunctionDecl *FD) {
-  for (auto *IRAttr : FD->specific_attrs<SYCLAddIRAttributesFunctionAttr>()) {
-    SmallVector<std::pair<std::string, std::string>, 4> NameValuePairs =
-        IRAttr->getAttributeNameValuePairs(getASTContext());
-    for (const auto &NameValuePair : NameValuePairs) {
-      if (NameValuePair.first == "sycl-nd-range-kernel" ||
-          NameValuePair.first == "sycl-single-task-kernel") {
+  clang::SourceLocation Loc = FD->getLocation();
+  bool NextDeclaredWithAttr = false;
+  for (clang::FunctionDecl *Redecl : FD->redecls()) {
+    bool IsFreeFunctionAttr = false;
+    for (auto *IRAttr :
+         Redecl->specific_attrs<SYCLAddIRAttributesFunctionAttr>()) {
+      SmallVector<std::pair<std::string, std::string>, 4> NameValuePairs =
+          IRAttr->getAttributeNameValuePairs(getASTContext());
+      const auto it = std::find_if(
+          NameValuePairs.begin(), NameValuePairs.end(),
+          [](const auto &NameValuePair) {
+            return NameValuePair.first == "sycl-nd-range-kernel" ||
+                   NameValuePair.first == "sycl-single-task-kernel";
+          });
+      IsFreeFunctionAttr = it != NameValuePairs.end();
+    }
+    if (Redecl->isFirstDecl()) {
+      if (IsFreeFunctionAttr)
         return true;
+      if (NextDeclaredWithAttr) {
+        Diag(Loc, diag::err_free_function_first_occurrence_missing_attr);
+        Diag(Redecl->getLocation(), diag::note_previous_declaration);
+        return false;
       }
+    } else {
+      Loc = Redecl->getLocation();
+      NextDeclaredWithAttr = IsFreeFunctionAttr;
     }
   }
   return false;

clang/test/SemaSYCL/free_function_negative.cpp

@@ -10,6 +10,22 @@ foo(int start, ...) { // expected-error {{free function kernel cannot be a varia
 foo1(int start, ...) { // expected-error {{free function kernel cannot be a variadic function}}
 }
 
+// expected-note@+1 {{conflicting attribute is here}}
+[[__sycl_detail__::add_ir_attributes_function("sycl-single-task-kernel", 1)]] void
+foo2(int start);
+
+// expected-error@+1 {{attribute 'add_ir_attributes_function' is already applied with different arguments}}
+[[__sycl_detail__::add_ir_attributes_function("sycl-single-task-kernel", 2)]] void 
+foo2(int start) {
+}
+
+// expected-note@+1 {{previous declaration is here}}
+void foo3(int start, int *ptr);
+
+// expected-error@+2 {{the first occurrence of kernel free function should be declared with attribute add_ir_attributes_function with 'sycl-nd-range-kernel' or 'sycl-single-task-kernel'}}
+[[__sycl_detail__::add_ir_attributes_function("sycl-single-task-kernel", 2)]] void 
+foo3(int start, int *ptr){}
+
 // expected-error@+2 {{a function with a default argument value cannot be used to define SYCL free function kernel}}
 [[__sycl_detail__::add_ir_attributes_function("sycl-single-task-kernel", 2)]] void 
 singleTaskKernelDefaultValues(int Value = 1) {

sycl/test-e2e/Experimental/free_functions/redeclaration.cpp

@@ -0,0 +1,82 @@
+// REQUIRES: aspect-usm_shared_allocations
+// RUN: %{build} -o %t.out
+// RUN: %{run} %t.out
+
+// The name mangling for free function kernels currently does not work with PTX.
+// UNSUPPORTED: cuda, hip
+// UNSUPPORTED-INTENDED: Not implemented yet for Nvidia/AMD backends.
+
+#include <iostream>
+#include <sycl/detail/core.hpp>
+#include <sycl/ext/oneapi/free_function_queries.hpp>
+#include <sycl/kernel_bundle.hpp>
+#include <sycl/usm.hpp>
+
+namespace syclext = sycl::ext::oneapi;
+namespace syclexp = sycl::ext::oneapi::experimental;
+
+static constexpr size_t NUM = 1024;
+static constexpr size_t WGSIZE = 16;
+
+int check_result(int *ptr) {
+  for (size_t i = 0; i < NUM; ++i) {
+    const float expected = 3 + static_cast<int>(i);
+    if (ptr[i] != expected) {
+      std::cout << "Kernel execution did not produce the expected result\n";
+      return 1;
+    }
+  }
+  return 0;
+}
+
+SYCL_EXT_ONEAPI_FUNCTION_PROPERTY((syclexp::nd_range_kernel<1>))
+void free_func(int start, int *ptr);
+
+SYCL_EXT_ONEAPI_FUNCTION_PROPERTY((syclexp::nd_range_kernel<1>))
+void free_func(int start, int *ptr);
+
+SYCL_EXT_ONEAPI_FUNCTION_PROPERTY((syclexp::nd_range_kernel<1>))
+void free_func1(int start, int *ptr);
+
+void free_func1(int start, int *ptr);
+
+static int call_kernel_code(sycl::queue &q, sycl::kernel &kernel) {
+  int *ptr = sycl::malloc_shared<int>(NUM, q);
+  q.submit([&](sycl::handler &cgh) {
+     cgh.set_args(3, ptr);
+     sycl::nd_range ndr{{NUM}, {WGSIZE}};
+     cgh.parallel_for(ndr, kernel);
+   }).wait();
+  const int ret = check_result(ptr);
+  sycl::free(ptr, q);
+  return ret;
+}
+
+template <auto Func>
+int test_declarations(sycl::queue &q, sycl::context &ctxt) {
+  auto exe_bndl =
+      syclexp::get_kernel_bundle<Func, sycl::bundle_state::executable>(ctxt);
+  sycl::kernel k_func = exe_bndl.template ext_oneapi_get_kernel<Func>();
+  return call_kernel_code(q, k_func);
+}
+
+#define KERNEL_CODE(start, ptr)                                                \
+  size_t id =                                                                  \
+      syclext::this_work_item::get_nd_item<1>().get_global_linear_id();        \
+  ptr[id] = start + static_cast<int>(id);
+
+SYCL_EXT_ONEAPI_FUNCTION_PROPERTY((syclexp::nd_range_kernel<1>))
+void free_func(int start, int *ptr) { KERNEL_CODE(start, ptr); }
+
+SYCL_EXT_ONEAPI_FUNCTION_PROPERTY((syclexp::nd_range_kernel<1>))
+void free_func1(int start, int *ptr) { KERNEL_CODE(start, ptr); }
+
+int main() {
+  sycl::queue q;
+  sycl::context ctxt = q.get_context();
+
+  int result{0};
+  result |= test_declarations<free_func>(q, ctxt);
+  result |= test_declarations<free_func1>(q, ctxt);
+  return result;
+}