[SYCL] Fix error with type aliases used as free function kernel args (#20123)

This PR fixes type name that is being printed as free function kernel
argument type in its forward-declaration in the integration header.

Before the change, we used the original argument type name, which could
be an alias - this patch makes use of the canonical type's name to make
sure that all type aliases are "unwrapped".

Author: AlexeySachkov

clang/lib/Sema/SemaSYCL.cpp

@@ -6822,13 +6822,13 @@ class FreeFunctionPrinter {
         continue;
       }
 
-      TemplateName TN = TST->getTemplateName();
+      TemplateName CTN = CTST->getTemplateName();
+      CTN.getAsTemplateDecl()->printQualifiedName(ParmListOstream);
+      ParmListOstream << "<";
+
       auto SpecArgs = TST->template_arguments();
       auto DeclArgs = CTST->template_arguments();
 
-      TN.getAsTemplateDecl()->printQualifiedName(ParmListOstream);
-      ParmListOstream << "<";
-
       for (size_t I = 0, E = std::max(DeclArgs.size(), SpecArgs.size()),
                   SE = SpecArgs.size();
            I < E; ++I) {

clang/test/CodeGenSYCL/free-function-kernel-type-alias-arg.cpp

@@ -0,0 +1,63 @@
+// RUN: %clang_cc1 -fsycl-is-device -internal-isystem %S/Inputs -triple spir64-unknown-unknown -sycl-std=2020 -fsycl-int-header=%t.h %s
+// RUN: FileCheck -input-file=%t.h %s
+//
+// The purpose of this test is to ensure that forward declarations of free
+// function kernels are emitted properly.
+// However, this test checks a specific scenario:
+// - free function arguments are type aliases (through using or typedef)
+
+namespace ns {
+
+using IntUsing = int;
+typedef int IntTypedef;
+
+template <typename T>
+struct Foo {};
+
+using FooIntUsing = Foo<int>;
+typedef Foo<int> FooIntTypedef;
+
+template <typename T1, typename T2>
+struct Bar {};
+
+template<typename T1>
+using BarUsing = Bar<T1, float>;
+
+class Baz {
+public:
+  using type = BarUsing<double>;
+};
+
+} // namespace ns
+
+[[__sycl_detail__::add_ir_attributes_function("sycl-nd-range-kernel", 2)]]
+void int_using(ns::IntUsing Arg) {}
+
+// CHECK: void int_using(int Arg);
+
+[[__sycl_detail__::add_ir_attributes_function("sycl-nd-range-kernel", 2)]]
+void int_typedef(ns::IntTypedef Arg) {}
+
+// CHECK: void int_typedef(int Arg);
+
+[[__sycl_detail__::add_ir_attributes_function("sycl-nd-range-kernel", 2)]]
+void foo_using(ns::FooIntUsing Arg) {}
+
+// CHECK: void foo_using(ns::Foo<int> Arg);
+
+[[__sycl_detail__::add_ir_attributes_function("sycl-nd-range-kernel", 2)]]
+void foo_typedef(ns::FooIntTypedef Arg) {}
+
+// CHECK: void foo_typedef(ns::Foo<int> Arg);
+
+template<typename T>
+[[__sycl_detail__::add_ir_attributes_function("sycl-nd-range-kernel", 2)]]
+void bar_using(ns::BarUsing<T> Arg) {}
+template void bar_using(ns::BarUsing<int>);
+
+// CHECK: template <typename T> void bar_using(ns::Bar<T, float>);
+
+[[__sycl_detail__::add_ir_attributes_function("sycl-nd-range-kernel", 2)]]
+void baz_type(ns::Baz::type Arg) {}
+
+// CHECK: void baz_type(ns::Bar<double, float> Arg);