[NFC][SYCL] Add todo comment for validation of group-local variables definintion (#3437)

Signed-off-by: Mikhail Lychkov <mikhail.lychkov@intel.com>

Author: mlychkov

llvm/lib/SYCLLowerIR/LowerWGLocalMemory.cpp

@@ -52,12 +52,14 @@ ModulePass *llvm::createSYCLLowerWGLocalMemoryLegacyPass() {
   return new SYCLLowerWGLocalMemoryLegacy();
 }
 
-// Static local memory allocation should be allowed only in a scope of a kernel
-// (not a device function) and shouldn't be called inside loop or if statement
+// TODO: It should be checked that __sycl_allocateLocalMemory (or its source
+// form - group_local_memory) does not occur:
+//  - in a function (other than user lambda/functor)
+//  - in a loop
+//  - in a non-convergent control flow
 // to make it consistent with OpenCL restriction.
-// TODO: Relax that restriction for SYCL or modify this pass to move allocation
-// of memory up to a kernel scope at the beginning for each nested device
-// function call, loop or if statement.
+// But LLVM pass is not the best place to diagnose these cases.
+// Error checking should be done in the front-end compiler.
 static void lowerAllocaLocalMemCall(CallInst *CI, Module &M) {
   assert(CI);