[Flang][Semantics] Add a semantic check for simd construct (#109089)

Add missing semantic check for the SAFELEN clause in the SIMD Order
construct

Author: Thirumalai-Shaktivel

flang/lib/Semantics/check-omp-structure.cpp

@@ -2285,6 +2285,21 @@ void OmpStructureChecker::Leave(const parser::OmpClauseList &) {
         }
       }
     }
+
+    // 2.11.5 Simd construct restriction (OpenMP 5.1)
+    if (auto *sl_clause{FindClause(llvm::omp::Clause::OMPC_safelen)}) {
+      if (auto *o_clause{FindClause(llvm::omp::Clause::OMPC_order)}) {
+        const auto &orderClause{
+            std::get<parser::OmpClause::Order>(o_clause->u)};
+        if (std::get<parser::OmpOrderClause::Type>(orderClause.v.t) ==
+            parser::OmpOrderClause::Type::Concurrent) {
+          context_.Say(sl_clause->source,
+              "The `SAFELEN` clause cannot appear in the `SIMD` directive "
+              "with `ORDER(CONCURRENT)` clause"_err_en_US);
+        }
+      }
+    }
+
     // Sema checks related to presence of multiple list items within the same
     // clause
     CheckMultListItems();

flang/test/Semantics/OpenMP/clause-validity01.f90

@@ -390,6 +390,12 @@
   enddo
   !$omp end parallel
 
+  !ERROR: The `SAFELEN` clause cannot appear in the `SIMD` directive with `ORDER(CONCURRENT)` clause
+  !$omp simd order(concurrent) safelen(1+2)
+  do i = 1, N
+    a = 3.14
+  enddo
+
 ! 2.11.1 parallel-do-clause -> parallel-clause |
 !                              do-clause