Revert "[Flang][OpenMP] Add semantic check for OpenMP Private, Firstprivate and Lastprivate clauses."

[kiranchandramohan]

Summary

This reverts commit a2ca6bbda6160c1b474fffd6204bcac9456c7eb1.

D93213 performs some checks to ensure that variables that appear in
statement functions are not in privatisation clauses. The point at
which this check is currently performed, there can be misparses that
cause more constructs to be identified as statement functions. This
can lead to various kinds of errors, hence reverting.

This revert hopefully fixes:
https://github.com/llvm/llvm-project/issues/54477
https://github.com/llvm/llvm-project/issues/54161
https://github.com/llvm/llvm-project/issues/54163

[shraiysh]

I believe the original semantic restriction has been removed in OpenMP 5.0.

[kiranchandramohan]

In D122650#3414032, @shraiysh wrote:

I believe the original semantic restriction has been removed in OpenMP 5.0.

This restriction is still present in the OpenMP 5.2 standard.
The OpenMP 5.2 standard (page 108, Section 4.3) says that "Variables that appear in namelist statements, in variable format expressions, and in expressions for statement function definitions, must not be privatized."
https://www.openmp.org/wp-content/uploads/OpenMP-API-Specification-5-2.pdf

I have filed a ticket to implement this check (https://github.com/llvm/llvm-project/issues/54677).

flang/lib/Semantics/resolve-directives.cpp

bool Pre(const parser::ModuleSubprogram &) {
     return true;
   }
 
   bool Pre(const parser::SpecificationPart &x) {
     Walk(std::get<std::list<parser::OpenMPDeclarativeConstruct>>(x.t));
     return true;
   }
 
-  bool Pre(const parser::StmtFunctionStmt &x) {
-    const auto &parsedExpr{std::get<parser::Scalar<parser::Expr>>(x.t)};
-    if (const auto *expr{GetExpr(parsedExpr)}) {
-      for (const Symbol &symbol : evaluate::CollectSymbols(*expr)) {
-        if (!IsStmtFunctionDummy(symbol)) {
-          stmtFunctionExprSymbols_.insert(symbol.GetUltimate());
-        }
-      }
-    }
-    return true;
-  }
-
   bool Pre(const parser::OpenMPBlockConstruct &);
   void Post(const parser::OpenMPBlockConstruct &);
 
   void Post(const parser::OmpBeginBlockDirective &) {
     GetContext().withinConstruct = true;
   }
 
   bool Pre(const parser::OpenMPSimpleStandaloneConstruct &);
private:
   Symbol *DeclareOrMarkOtherAccessEntity(const parser::Name &, Symbol::Flag);
   Symbol *DeclareOrMarkOtherAccessEntity(Symbol &, Symbol::Flag);
   void CheckMultipleAppearances(
       const parser::Name &, const Symbol &, Symbol::Flag);
 
   void CheckDataCopyingClause(
       const parser::Name &, const Symbol &, Symbol::Flag);
   void CheckAssocLoopLevel(std::int64_t level, const parser::OmpClause *clause);
-  void CheckPrivateDSAObject(
+  void CheckObjectInNamelist(
       const parser::Name &, const Symbol &, Symbol::Flag);
   void CheckSourceLabel(const parser::Label &);
   void CheckLabelContext(const parser::CharBlock, const parser::CharBlock,
       std::optional<DirContext>, std::optional<DirContext>);
   void ClearLabels() {
     sourceLabels_.clear();
     targetLabels_.clear();
   };
std::visit(
                 if (dataCopyingAttributeFlags.test(ompFlag)) {
                   CheckDataCopyingClause(*name, *symbol, ompFlag);
                 } else {
                   AddToContextObjectWithDSA(*symbol, ompFlag);
                   if (dataSharingAttributeFlags.test(ompFlag)) {
                     CheckMultipleAppearances(*name, *symbol, ompFlag);
                   }
                   if (privateDataSharingAttributeFlags.test(ompFlag)) {
-                    CheckPrivateDSAObject(*name, *symbol, ompFlag);
+                    CheckObjectInNamelist(*name, *symbol, ompFlag);
                   }
 
                   if (ompFlag == Symbol::Flag::OmpAllocate) {
                     AddAllocateName(name);
                   }
                 }
                 if (ompFlag == Symbol::Flag::OmpDeclarativeAllocateDirective &&
                     IsAllocatable(*symbol)) {
if (IsObjectWithDSA(symbol) &&
             "COPYPRIVATE variable '%s' is not PRIVATE or THREADPRIVATE in "
             "outer context"_err_en_US,
             symbol.name());
       }
     }
   }
 }
 
-void OmpAttributeVisitor::CheckPrivateDSAObject(
+void OmpAttributeVisitor::CheckObjectInNamelist(
     const parser::Name &name, const Symbol &symbol, Symbol::Flag ompFlag) {
   const auto &ultimateSymbol{symbol.GetUltimate()};
   llvm::StringRef clauseName{"PRIVATE"};
   if (ompFlag == Symbol::Flag::OmpFirstPrivate) {
     clauseName = "FIRSTPRIVATE";
   } else if (ompFlag == Symbol::Flag::OmpLastPrivate) {
     clauseName = "LASTPRIVATE";
   }
 
   if (ultimateSymbol.test(Symbol::Flag::InNamelist)) {
     context_.Say(name.source,
         "Variable '%s' in NAMELIST cannot be in a %s clause"_err_en_US,
         name.ToString(), clauseName.str());
   }
-
-  if (stmtFunctionExprSymbols_.find(ultimateSymbol) !=
-      stmtFunctionExprSymbols_.end()) {
-    context_.Say(name.source,
-        "Variable '%s' in STATEMENT FUNCTION expression cannot be in a "
-        "%s clause"_err_en_US,
-        name.ToString(), clauseName.str());
-  }
 }
 
 void OmpAttributeVisitor::CheckSourceLabel(const parser::Label &label) {
   // Get the context to check if the statement causing a jump to the 'label' is
   // in an enclosing OpenMP construct
   std::optional<DirContext> thisContext{GetContextIf()};
   sourceLabels_.emplace(
       label, std::make_pair(currentStatementSource_, thisContext));

flang/test/Semantics/omp-private03.f90

-! RUN: %python %S/test_errors.py %s %flang -fopenmp
-! OpenMP Version 4.5
-! Variables that appear in expressions for statement function definitions
-! may not appear in private, firstprivate or lastprivate clauses.
-
-subroutine stmt_function(temp)
-
-  integer :: i, p, q, r
-  real :: c, f, s, v, t(10)
-  real, intent(in) :: temp
-
-  c(temp) = p * (temp - q) / r
-  f(temp) = q + (temp * r/p)
-  v(temp) = c(temp) + f(temp)/2 - s
-
-  p = 5
-  q = 32
-  r = 9
-
-  !ERROR: Variable 'p' in STATEMENT FUNCTION expression cannot be in a PRIVATE clause
-  !$omp parallel private(p)
-  s = c(temp)
-  !$omp end parallel
-
-  !ERROR: Variable 's' in STATEMENT FUNCTION expression cannot be in a FIRSTPRIVATE clause
-  !$omp parallel firstprivate(s)
-  s = s + f(temp)
-  !$omp end parallel
-
-  !ERROR: Variable 's' in STATEMENT FUNCTION expression cannot be in a LASTPRIVATE clause
-  !$omp parallel do lastprivate(s, t)
-  do i = 1, 10
-    t(i) = v(temp) + i - s
-  end do
-  !$omp end parallel do
-
-  print *, t
-
-end subroutine stmt_function