[SYCL] Allow SYCL_EXTERNAL to be applied to a function with raw pointers

SYCL 1.2.1 specification does not allow SYCL_EXTERNAL to be applied to
a function with a pointer argument or with a pointer return
value. This is required to limit address space inference work to a
single translation unit.

Given that we make inference after we link all translation units
together, it should not really matter now. And there are several cases
where external functions with pointers can be useful, so this patch
tuns an error into a warning.

Signed-off-by: Andrew Savonichev <andrew.savonichev@intel.com>

Author: Andrew Savonichev

clang/include/clang/Basic/DiagnosticGroups.td

@@ -1053,6 +1053,7 @@ def OpenMPLoopForm : DiagGroup<"openmp-loop-form">;
 def OpenMPTarget : DiagGroup<"openmp-target">;
 
 // SYCL warnings
+def Sycl : DiagGroup<"sycl">;
 def SyclTarget : DiagGroup<"sycl-target">;
 
 // Backend warnings.

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -10120,9 +10120,12 @@ def err_conflicting_sycl_kernel_attributes : Error<
 def err_sycl_attibute_cannot_be_applied_here
     : Error<"%0 attribute cannot be applied to a "
             "%select{static function or function in an anonymous namespace"
-            "|class member function"
-            "|function with a raw pointer return type"
-            "|function with a raw pointer parameter type}1">;
+            "|class member function}1">;
+def warn_sycl_attibute_address_space_ext
+    : Warning<"SYCL 1.2.1 specification does not allow %0 attribute applied "
+              "to a %select{function with a raw pointer return type"
+              "|function with a raw pointer parameter type}1">,
+      InGroup<Sycl>;
 def err_ivdep_duplicate_arg : Error<
   "duplicate argument to 'ivdep'. attribute requires one or both of a safelen "
   "and array">;

clang/lib/Sema/SemaDeclAttr.cpp

@@ -4329,15 +4329,13 @@ static void handleSYCLDeviceAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
     return;
   }
   if (FD->getReturnType()->isPointerType()) {
-    S.Diag(AL.getLoc(), diag::err_sycl_attibute_cannot_be_applied_here)
-        << AL << 2 /* function with a raw pointer return type */;
-    return;
+    S.Diag(AL.getLoc(), diag::warn_sycl_attibute_address_space_ext)
+        << AL << 0 /* function with a raw pointer return type */;
   }
   for (const ParmVarDecl *Param : FD->parameters())
     if (Param->getType()->isPointerType()) {
-      S.Diag(AL.getLoc(), diag::err_sycl_attibute_cannot_be_applied_here)
-          << AL << 3 /* function with a raw pointer parameter type */;
-      return;
+      S.Diag(AL.getLoc(), diag::warn_sycl_attibute_address_space_ext)
+          << AL << 1 /* function with a raw pointer parameter type */;
     }
 
   S.addSyclDeviceDecl(D);

clang/test/SemaSYCL/sycl-device.cpp

@@ -25,10 +25,10 @@ class A {
   int func3() {}
 };
 
-__attribute__((sycl_device)) // expected-error {{'sycl_device' attribute cannot be applied to a function with a raw pointer return type}}
+__attribute__((sycl_device)) // expected-warning {{SYCL 1.2.1 specification does not allow 'sycl_device' attribute applied to a function with a raw pointer return type}}
 int* func3() { return nullptr; }
 
-__attribute__((sycl_device)) // expected-error {{'sycl_device' attribute cannot be applied to a function with a raw pointer parameter type}}
+__attribute__((sycl_device)) // expected-warning {{SYCL 1.2.1 specification does not allow 'sycl_device' attribute applied to a function with a raw pointer parameter type}}
 void func3(int *) {}
 
 #else