[Flang][OpenMP] Add semantic checks for Worshare construct (#111358)

Add missing semantic checks for the Workshare construct:
OpenMP 5.2: 11.4 Workshare Construct
- The construct must not contain any user-defined function calls unless
either the function is pure and elemental or the function call is
contained inside a parallel construct that is nested inside the
workshare construct. (Flang-new used to check only the elemental function, 
but now it needs to be an impure elemental function)
- At most one NoWait clause can appear in the Workshare construct.
- Add tests for the same.

Author: Thirumalai-Shaktivel

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

@@ -68,11 +68,23 @@ class OmpWorkshareBlockChecker {
     if (const auto *e{GetExpr(context_, expr)}) {
       for (const Symbol &symbol : evaluate::CollectSymbols(*e)) {
         const Symbol &root{GetAssociationRoot(symbol)};
-        if (IsFunction(root) && !IsElementalProcedure(root)) {
-          context_.Say(expr.source,
-              "User defined non-ELEMENTAL function "
-              "'%s' is not allowed in a WORKSHARE construct"_err_en_US,
-              root.name());
+        if (IsFunction(root)) {
+          std::string attrs{""};
+          if (!IsElementalProcedure(root)) {
+            attrs = " non-ELEMENTAL";
+          }
+          if (root.attrs().test(Attr::IMPURE)) {
+            if (attrs != "") {
+              attrs = "," + attrs;
+            }
+            attrs = " IMPURE" + attrs;
+          }
+          if (attrs != "") {
+            context_.Say(expr.source,
+                "User defined%s function '%s' is not allowed in a "
+                "WORKSHARE construct"_err_en_US,
+                attrs, root.name());
+          }
         }
       }
     }

flang/test/Semantics/OpenMP/workshare02.f90

@@ -9,6 +9,14 @@ module my_mod
   integer function my_func()
     my_func = 10
   end function my_func
+
+  impure integer function impure_my_func()
+    impure_my_func = 20
+  end function impure_my_func
+
+  impure elemental integer function impure_ele_my_func()
+    impure_ele_my_func = 20
+  end function impure_ele_my_func
 end module my_mod
 
 subroutine workshare(aa, bb, cc, dd, ee, ff, n)
@@ -61,6 +69,16 @@ subroutine workshare(aa, bb, cc, dd, ee, ff, n)
   j = j - my_func()
   !$omp end atomic
 
+  !ERROR: User defined IMPURE, non-ELEMENTAL function 'impure_my_func' is not allowed in a WORKSHARE construct
+  cc = impure_my_func()
+  !ERROR: User defined IMPURE function 'impure_ele_my_func' is not allowed in a WORKSHARE construct
+  aa(1) = impure_ele_my_func()
+
   !$omp end workshare
 
+  !$omp workshare
+    j = j + 1
+  !ERROR: At most one NOWAIT clause can appear on the END WORKSHARE directive
+  !$omp end workshare nowait nowait
+
 end subroutine workshare

llvm/include/llvm/Frontend/OpenMP/OMP.td

@@ -1170,7 +1170,7 @@ def OMP_Workshare : Directive<"workshare"> {
   let category = CA_Executable;
 }
 def OMP_EndWorkshare : Directive<"end workshare"> {
-  let allowedClauses = [
+  let allowedOnceClauses = [
     VersionedClause<OMPC_NoWait>,
   ];
   let leafConstructs = OMP_Workshare.leafConstructs;