Made stall_enable disgnostic more descriptive.

Author: rdeodhar

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -3192,6 +3192,9 @@ def warn_dllimport_dropped_from_inline_function : Warning<
   InGroup<IgnoredAttributes>;
 def warn_attribute_ignored : Warning<"%0 attribute ignored">,
   InGroup<IgnoredAttributes>;
+def warn_attribute_on_direct_kernel_callee_only : Warning<"%0 attribute allowed"
+  " only on function directly called from kernel; attribute ignored">,
+  InGroup<IgnoredAttributes>;
 def warn_nothrow_attribute_ignored : Warning<"'nothrow' attribute conflicts with"
   " exception specification; attribute ignored">,
   InGroup<IgnoredAttributes>;

clang/lib/Sema/SemaSYCL.cpp

@@ -328,7 +328,9 @@ static void collectSYCLAttributes(Sema &S, FunctionDecl *FD,
     if (DirectlyCalled) {
       Attrs.push_back(A);
     } else {
-      S.Diag(A->getLocation(), diag::warn_attribute_ignored) << A;
+      S.Diag(A->getLocation(),
+             diag::warn_attribute_on_direct_kernel_callee_only)
+          << A;
       FD->dropAttr<SYCLIntelUseStallEnableClustersAttr>();
     }
   }

clang/test/SemaSYCL/stall_enable.cpp

@@ -6,7 +6,7 @@
 using namespace cl::sycl;
 queue q;
 
-[[intel::use_stall_enable_clusters]] void test() {} //expected-warning{{'use_stall_enable_clusters' attribute ignored}}
+[[intel::use_stall_enable_clusters]] void test() {} //expected-warning{{'use_stall_enable_clusters' attribute allowed only on function directly called from kernel}}
 
 #ifdef TRIGGER_ERROR
 [[intel::use_stall_enable_clusters(1)]] void bar1() {} // expected-error{{'use_stall_enable_clusters' attribute takes no arguments}}