[SYCL] Report compile time error for recursion in a SYCL kernel (#3390)

According to SYCL 2020 spec(https://www.khronos.org/registry/SYCL/specs/sycl-2020/html/sycl-2020.html#sec:language.restrictions.kernels), recursion is not allowed in SYCL kernel, we had better report compiling error for this illegal behavior. Moving runtime crash to compiling error is more friendly to users too.

Signed-off-by: gejin <ge.jin@intel.com>

Author: jinge90

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -11299,9 +11299,6 @@ def warn_sycl_implicit_decl
               "declaration for a kernel type name; your program may not "
               "be portable">,
       InGroup<SyclStrict>, ShowInSystemHeader, DefaultIgnore;
-def warn_sycl_restrict_recursion
-    : Warning<"SYCL kernel cannot call a recursive function">,
-      InGroup<SyclStrict>, DefaultError;
 def err_ivdep_duplicate_arg : Error<
   "duplicate argument to 'ivdep'; attribute requires one or both of a safelen "
   "and array">;

clang/lib/Sema/SemaSYCL.cpp

@@ -387,7 +387,8 @@ class MarkDeviceFunction : public RecursiveASTVisitor<MarkDeviceFunction> {
       // all functions used by kernel have already been parsed and have
       // definitions.
       if (RecursiveSet.count(Callee) && !ConstexprDepth) {
-        SemaRef.Diag(e->getExprLoc(), diag::warn_sycl_restrict_recursion);
+        SemaRef.Diag(e->getExprLoc(), diag::err_sycl_restrict)
+            << Sema::KernelCallRecursiveFunction;
         SemaRef.Diag(Callee->getSourceRange().getBegin(),
                      diag::note_sycl_recursive_function_declared_here)
             << Sema::KernelCallRecursiveFunction;

clang/test/SemaSYCL/restrict-recursion3.cpp

@@ -34,7 +34,7 @@ template <typename name, typename Func>
 __attribute__((sycl_kernel)) void kernel_single_task2(const Func &kernelFunc) {
   // expected-note@+1 {{called by 'kernel_single_task2}}
   kernelFunc();
-  // expected-warning@+1 2{{SYCL kernel cannot call a recursive function}}
+  // expected-error@+1 2{{SYCL kernel cannot call a recursive function}}
   kernel_single_task2<name, Func>(kernelFunc);
 }
 

clang/test/SemaSYCL/restrict-recursion4.cpp

@@ -10,7 +10,7 @@ int fib(int n) {
 
 // expected-note@+1 2{{function implemented using recursion declared here}}
 void kernel2(void) {
-  // expected-warning@+1 {{SYCL kernel cannot call a recursive function}}
+  // expected-error@+1 {{SYCL kernel cannot call a recursive function}}
   kernel2();
 }
 
@@ -24,7 +24,7 @@ void *operator new(size_t);
 void usage2(myFuncDef functionPtr) {
   // expected-error@+1 {{SYCL kernel cannot allocate storage}}
   int *ip = new int;
-  // expected-warning@+1 {{SYCL kernel cannot call a recursive function}}
+  // expected-error@+1 {{SYCL kernel cannot call a recursive function}}
   kernel2();
 }