diff --git a/flang/lib/Semantics/check-directive-structure.h b/flang/lib/Semantics/check-directive-structure.h
--- a/flang/lib/Semantics/check-directive-structure.h
+++ b/flang/lib/Semantics/check-directive-structure.h
@@ -197,6 +197,23 @@
     return nullptr;
   }
 
+  DirectiveContext *GetEnclosingDirContext() {
+    CHECK(!dirContext_.empty());
+    auto it{dirContext_.rbegin()};
+    if (++it != dirContext_.rend()) {
+      return &(*it);
+    }
+    return nullptr;
+  }
+
+  const PC *FindClauseInContext(C type, DirectiveContext &dirContext) {
+    auto it{dirContext.clauseInfo.find(type)};
+    if (it != dirContext.clauseInfo.end()) {
+      return it->second;
+    }
+    return nullptr;
+  }
+
   void PushContext(const parser::CharBlock &source, D dir) {
     dirContext_.emplace_back(source, dir);
   }
diff --git a/flang/lib/Semantics/check-omp-structure.h b/flang/lib/Semantics/check-omp-structure.h
--- a/flang/lib/Semantics/check-omp-structure.h
+++ b/flang/lib/Semantics/check-omp-structure.h
@@ -78,6 +78,8 @@
 
 namespace Fortran::semantics {
 
+using SymbolSourceMap = std::multimap<const Symbol *, parser::CharBlock>;
+
 class OmpStructureChecker
     : public DirectiveStructureChecker<llvm::omp::Directive, llvm::omp::Clause,
           parser::OmpClause, llvm::omp::Clause_enumSize> {
@@ -204,8 +206,25 @@
   void CheckIsVarPartOfAnotherVar(const parser::OmpObjectList &objList);
   void CheckIntentInPointer(
       const parser::OmpObjectList &, const llvm::omp::Clause);
-  void GetSymbolsInObjectList(
-      const parser::OmpObjectList &, std::vector<const Symbol *> &);
+  void GetSymbolsInObjectList(const parser::OmpObjectList &, SymbolSourceMap &);
+  void GetSymbolsInDesignatorList(
+      const std::list<parser::Designator> &, SymbolSourceMap &);
+  void CheckDefinableObjects(SymbolSourceMap &, const llvm::omp::Clause);
+  void CheckCommonSymbolsInOuterCxt(SymbolSourceMap &, SymbolSourceMap &,
+      const llvm::omp::Clause, const llvm::omp::Clause);
+
+  bool CheckReductionOperators(const parser::OmpReductionClause &);
+  bool CheckIntrinsicOperator(
+      const parser::DefinedOperator::IntrinsicOperator &);
+  void CheckReductionTypeList(const parser::OmpReductionClause &);
+  void CheckReductionArraySection(
+      const std::list<parser::Designator> &designatorList);
+  void CheckArraySection(const parser::ArrayElement &arrayElement,
+      const parser::Name &name, const llvm::omp::Clause clause);
+  void CheckMultipleAppearanceAcrossContext(
+      SymbolSourceMap &symbols, const llvm::omp::Clause c);
+  void CheckIntentInPointer(const std::list<parser::Designator> &designatorList,
+      const llvm::omp::Clause clause);
 };
 } // namespace Fortran::semantics
 #endif // FORTRAN_SEMANTICS_CHECK_OMP_STRUCTURE_H_
diff --git a/flang/lib/Semantics/check-omp-structure.cpp b/flang/lib/Semantics/check-omp-structure.cpp
--- a/flang/lib/Semantics/check-omp-structure.cpp
+++ b/flang/lib/Semantics/check-omp-structure.cpp
@@ -446,6 +446,126 @@
 
 // Restrictions specific to each clause are implemented apart from the
 // generalized restrictions.
+void OmpStructureChecker::Enter(const parser::OmpReductionClause &x) {
+  CheckAllowed(llvm::omp::Clause::OMPC_reduction);
+  if (CheckReductionOperators(x)) {
+    CheckReductionTypeList(x);
+  }
+}
+bool OmpStructureChecker::CheckReductionOperators(
+    const parser::OmpReductionClause &x) {
+  const auto &definedOp{std::get<0>(x.t)};
+  bool ok = false;
+  std::visit(
+      common::visitors{
+          [&](const parser::DefinedOperator &dOpr) {
+            const auto &intrinsicOp{
+                std::get<parser::DefinedOperator::IntrinsicOperator>(dOpr.u)};
+            ok = CheckIntrinsicOperator(intrinsicOp);
+          },
+          [&](const parser::ProcedureDesignator &procD) {
+            const parser::Name *name{std::get_if<parser::Name>(&procD.u)};
+            if (name->symbol) {
+              std::string procName =
+                  parser::ToUpperCaseLetters(name->symbol->name().ToString());
+              if (procName == "MAX" || procName == "MIN" ||
+                  procName == "IAND" || procName == "IOR" ||
+                  procName == "IEOR") {
+                ok = true;
+              } else {
+                context_.Say(GetContext().clauseSource,
+                    "Invalid reduction identifier in REDUCTION clause."_err_en_US,
+                    ContextDirectiveAsFortran());
+              }
+            }
+          },
+      },
+      definedOp.u);
+
+  return ok;
+}
+bool OmpStructureChecker::CheckIntrinsicOperator(
+    const parser::DefinedOperator::IntrinsicOperator &op) {
+
+  switch (op) {
+  case parser::DefinedOperator::IntrinsicOperator::Add:
+  case parser::DefinedOperator::IntrinsicOperator::Subtract:
+  case parser::DefinedOperator::IntrinsicOperator::Multiply:
+  case parser::DefinedOperator::IntrinsicOperator::AND:
+  case parser::DefinedOperator::IntrinsicOperator::OR:
+  case parser::DefinedOperator::IntrinsicOperator::EQV:
+  case parser::DefinedOperator::IntrinsicOperator::NEQV:
+    return true;
+  default:
+    context_.Say(GetContext().clauseSource,
+        "Invalid reduction operator in REDUCTION clause."_err_en_US,
+        ContextDirectiveAsFortran());
+  }
+  return false;
+}
+
+void OmpStructureChecker::CheckReductionTypeList(
+    const parser::OmpReductionClause &x) {
+
+  const auto &designatorList{std::get<1>(x.t)};
+  SymbolSourceMap currSymbols, enclosingSymbols;
+  GetSymbolsInDesignatorList(designatorList, currSymbols);
+  CheckDefinableObjects(currSymbols, llvm::omp::Clause::OMPC_reduction);
+  CheckIntentInPointer(designatorList, llvm::omp::Clause::OMPC_reduction);
+  CheckReductionArraySection(designatorList);
+  CheckMultipleAppearanceAcrossContext(
+      currSymbols, llvm::omp::Clause::OMPC_reduction);
+}
+
+void OmpStructureChecker::CheckReductionArraySection(
+    const std::list<parser::Designator> &designatorList) {
+  for (const auto &designator : designatorList) {
+    if (const auto *dataRef{std::get_if<parser::DataRef>(&designator.u)}) {
+      if (const auto *arrayElement{
+              parser::Unwrap<parser::ArrayElement>(designator)}) {
+        if (arrayElement) {
+          CheckArraySection(*arrayElement, GetLastName(*dataRef),
+              llvm::omp::Clause::OMPC_reduction);
+        }
+      }
+    }
+  }
+}
+
+void OmpStructureChecker::CheckMultipleAppearanceAcrossContext(
+    SymbolSourceMap &currSymbols, const llvm::omp::Clause currClause) {
+  SymbolSourceMap enclosingSymbols;
+  if (auto *enclosingContext{GetEnclosingDirContext()}) {
+    if (const auto *clause{FindClauseInContext(
+            llvm::omp::Clause::OMPC_private, *enclosingContext)}) {
+      const auto &privateClause{
+          std::get<parser::OmpClause::Private>(clause->u)};
+      GetSymbolsInObjectList(privateClause.v, enclosingSymbols);
+      CheckCommonSymbolsInOuterCxt(currSymbols, enclosingSymbols,
+          llvm::omp::Clause::OMPC_reduction, llvm::omp::Clause::OMPC_private);
+    }
+    if (const auto *clause{FindClauseInContext(
+            llvm::omp::Clause::OMPC_firstprivate, *enclosingContext)}) {
+      const auto &firstprivateClause{
+          std::get<parser::OmpClause::Firstprivate>(clause->u)};
+      GetSymbolsInObjectList(firstprivateClause.v, enclosingSymbols);
+      CheckCommonSymbolsInOuterCxt(currSymbols, enclosingSymbols,
+          llvm::omp::Clause::OMPC_reduction,
+          llvm::omp::Clause::OMPC_firstprivate);
+    }
+    if (const auto *clause{FindClauseInContext(
+            llvm::omp::Clause::OMPC_reduction, *enclosingContext)}) {
+      const auto &reductionClause{
+          std::get<parser::OmpReductionClause>(clause->u)};
+      const auto &designators{
+          std::get<std::list<parser::Designator>>(reductionClause.t)};
+      GetSymbolsInDesignatorList(designators, enclosingSymbols);
+      CheckCommonSymbolsInOuterCxt(currSymbols, enclosingSymbols,
+          llvm::omp::Clause::OMPC_reduction, llvm::omp::Clause::OMPC_reduction);
+    }
+  }
+}
+
 void OmpStructureChecker::Enter(const parser::OmpClause::Ordered &x) {
   CheckAllowed(llvm::omp::Clause::OMPC_ordered);
   // the parameter of ordered clause is optional
@@ -493,8 +613,7 @@
         ompObject.u);
   }
 }
-// Following clauses have a seperate node in parse-tree.h.
-CHECK_SIMPLE_PARSER_CLAUSE(OmpReductionClause, OMPC_reduction)
+
 // Atomic-clause
 CHECK_SIMPLE_PARSER_CLAUSE(OmpAtomicRead, OMPC_read)
 CHECK_SIMPLE_PARSER_CLAUSE(OmpAtomicWrite, OMPC_write)
@@ -703,7 +822,8 @@
         if (const auto *arr{
                 std::get_if<common::Indirection<parser::ArrayElement>>(
                     &dataRef->u)}) {
-          CheckDependArraySection(*arr, GetLastName(*dataRef));
+          CheckArraySection(arr->value(), GetLastName(*dataRef),
+              llvm::omp::Clause::OMPC_depend);
         }
       }
     }
@@ -768,12 +888,80 @@
     }
   }
 }
+// Called from both Reduction and Depend clause.
+void OmpStructureChecker::CheckArraySection(
+    const parser::ArrayElement &arrayElement, const parser::Name &name,
+    const llvm::omp::Clause clause) {
+  if (!arrayElement.subscripts.empty()) {
+    for (const auto &subscript : arrayElement.subscripts) {
+      if (const auto *triplet{
+              std::get_if<parser::SubscriptTriplet>(&subscript.u)}) {
+        if (std::get<0>(triplet->t) && std::get<1>(triplet->t)) {
+          const auto &lower{std::get<0>(triplet->t)};
+          const auto &upper{std::get<1>(triplet->t)};
+          if (lower && upper) {
+            const auto lval{GetIntValue(lower)};
+            const auto uval{GetIntValue(upper)};
+
+            if (lval && uval && *uval < *lval) {
+              context_.Say(GetContext().clauseSource,
+                  "'%s' in %s clause"
+                  " cannot have a zero-length array section."_err_en_US,
+                  name.ToString(),
+                  parser::ToUpperCaseLetters(getClauseName(clause).str()));
+              break;
+            } else if (std::get<2>(triplet->t)) {
+              const auto &strideExpr{std::get<2>(triplet->t)};
+              if (strideExpr) {
+                if (clause == llvm::omp::Clause::OMPC_depend) {
+                  context_.Say(GetContext().clauseSource,
+                      "Stride should not be specified for array section in "
+                      "DEPEND "
+                      "clause"_err_en_US);
+                }
+                const auto stride{GetIntValue(strideExpr)};
+                if ((stride && stride != 1)) {
+                  context_.Say(GetContext().clauseSource,
+                      "A list item that appears in a REDUCTION clause"
+                      " should have a contiguos storage array section."_err_en_US,
+                      ContextDirectiveAsFortran());
+                  break;
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+}
 
 void OmpStructureChecker::CheckIntentInPointer(
     const parser::OmpObjectList &objectList, const llvm::omp::Clause clause) {
-  std::vector<const Symbol *> symbols;
+  SymbolSourceMap symbols;
   GetSymbolsInObjectList(objectList, symbols);
-  for (const auto *symbol : symbols) {
+  for (auto it{symbols.begin()}; it != symbols.end(); ++it) {
+    const auto *symbol{it->first};
+    const auto source{it->second};
+    if (IsPointer(*symbol) && IsIntentIn(*symbol)) {
+      context_.Say(GetContext().clauseSource,
+          "Pointer '%s' with the INTENT(IN) attribute may not appear "
+          "in a %s clause"_err_en_US,
+          symbol->name(),
+          parser::ToUpperCaseLetters(getClauseName(clause).str()));
+    }
+  }
+}
+
+void OmpStructureChecker::CheckIntentInPointer(
+    const std::list<parser::Designator> &designatorList,
+    const llvm::omp::Clause clause) {
+  SymbolSourceMap symbols;
+  GetSymbolsInDesignatorList(designatorList, symbols);
+  for (auto it{symbols.begin()}; it != symbols.end(); ++it) {
+    const auto *symbol{it->first};
+    const auto source{it->second};
+
     if (IsPointer(*symbol) && IsIntentIn(*symbol)) {
       context_.Say(GetContext().clauseSource,
           "Pointer '%s' with the INTENT(IN) attribute may not appear "
@@ -785,22 +973,66 @@
 }
 
 void OmpStructureChecker::GetSymbolsInObjectList(
-    const parser::OmpObjectList &objectList,
-    std::vector<const Symbol *> &symbols) {
+    const parser::OmpObjectList &objectList, SymbolSourceMap &symbols) {
   for (const auto &ompObject : objectList.v) {
     if (const auto *name{parser::Unwrap<parser::Name>(ompObject)}) {
       if (const auto *symbol{name->symbol}) {
         if (const auto *commonBlockDetails{
                 symbol->detailsIf<CommonBlockDetails>()}) {
           for (const auto &object : commonBlockDetails->objects()) {
-            symbols.emplace_back(&object->GetUltimate());
+            symbols.emplace(&object->GetUltimate(), name->source);
           }
         } else {
-          symbols.emplace_back(&symbol->GetUltimate());
+          symbols.emplace(&symbol->GetUltimate(), name->source);
         }
       }
     }
   }
 }
 
+void OmpStructureChecker::GetSymbolsInDesignatorList(
+    const std::list<parser::Designator> &designatorList,
+    SymbolSourceMap &symbols) {
+  for (const auto &designator : designatorList) {
+    if (const auto *name{parser::Unwrap<parser::Name>(designator)}) {
+      if (const auto *symbol{name->symbol}) {
+        symbols.emplace(&symbol->GetUltimate(), name->source);
+      }
+    }
+  }
+}
+
+void OmpStructureChecker::CheckDefinableObjects(
+    SymbolSourceMap &symbols, const llvm::omp::Clause clause) {
+  for (auto it{symbols.begin()}; it != symbols.end(); ++it) {
+    const auto *symbol{it->first};
+    const auto source{it->second};
+    const auto msg{WhyNotModifiable(*symbol, context_.FindScope(source))};
+    if (IsNamedConstant(*symbol) || msg) {
+      context_
+          .Say(source,
+              "Variable '%s' on the %s clause is not definable"_err_en_US,
+              symbol->name(),
+              parser::ToUpperCaseLetters(getClauseName(clause).str()))
+          .Attach(source, std::move(*msg), symbol->name());
+    }
+  }
+}
+
+void OmpStructureChecker::CheckCommonSymbolsInOuterCxt(
+    SymbolSourceMap &currSymbols, SymbolSourceMap &outerSymbols,
+    const llvm::omp::Clause currClause, const llvm::omp::Clause outerClause) {
+  for (auto it{currSymbols.begin()}; it != currSymbols.end(); ++it) {
+    const auto *symbol{it->first};
+    const auto source{it->second};
+    if (outerSymbols.find(symbol) != outerSymbols.end()) {
+      context_.Say(source,
+          "%s variable '%s' is %s in outer context must be shared in the parallel regions to which any of the worksharing regions arising from the worksharing construct bind."_err_en_US,
+          parser::ToUpperCaseLetters(getClauseName(currClause).str()),
+          symbol->name(),
+          parser::ToUpperCaseLetters(getClauseName(outerClause).str()));
+    }
+  }
+}
+
 } // namespace Fortran::semantics
diff --git a/flang/lib/Semantics/resolve-directives.cpp b/flang/lib/Semantics/resolve-directives.cpp
--- a/flang/lib/Semantics/resolve-directives.cpp
+++ b/flang/lib/Semantics/resolve-directives.cpp
@@ -316,6 +316,49 @@
         x.u);
     return false;
   }
+
+  bool Pre(const parser::OmpReductionClause &x) {
+    const parser::OmpReductionOperator &opr{
+        std::get<parser::OmpReductionOperator>(x.t)};
+    std::visit(
+        common::visitors{
+            [&](const parser::DefinedOperator &dOP) {},
+            [&](const parser::ProcedureDesignator &procD) {
+              std::visit(
+                  common::visitors{
+                      [&](const parser::Name &name) {
+                        if (!name.symbol) {
+                          const auto namepair{currScope().try_emplace(
+                              name.source, Attrs{}, ProcEntityDetails{})};
+                          auto &symbol{*namepair.first->second};
+                          name.symbol = &symbol;
+                          name.symbol->set(Symbol::Flag::OmpReduction);
+                          AddToContextObjectWithDSA(
+                              *name.symbol, Symbol::Flag::OmpReduction);
+                        }
+                      },
+                      [&](const parser::ProcComponentRef &procRef) {
+                        ResolveOmp(*procRef.v.thing.component.symbol,
+                            Symbol::Flag::OmpReduction, currScope());
+                      },
+                  },
+                  procD.u);
+            },
+        },
+        opr.u);
+
+    // To check Multiple appearances of a symbol on the same context.
+    // ResolveObjectList()
+    const auto &designatorList{std::get<std::list<parser::Designator>>(x.t)};
+    for (const auto &designator : designatorList) {
+      if (const auto *name{GetDesignatorNameIfDataRef(designator)}) {
+        CheckMultipleAppearances(
+            *name, *name->symbol, Symbol::Flag::OmpReduction);
+      }
+    }
+    return false;
+  }
+
   bool Pre(const parser::OmpAlignedClause &x) {
     const auto &alignedNameList{std::get<std::list<parser::Name>>(x.t)};
     ResolveOmpNameList(alignedNameList, Symbol::Flag::OmpAligned);
diff --git a/flang/test/Semantics/omp-depend01.f90 b/flang/test/Semantics/omp-depend01.f90
--- a/flang/test/Semantics/omp-depend01.f90
+++ b/flang/test/Semantics/omp-depend01.f90
@@ -11,8 +11,8 @@
   !$omp parallel
   !$omp single
 
-  !ERROR: 'a' in DEPEND clause is a zero size array section
-  !ERROR: 'b' in DEPEND clause is a zero size array section
+  !ERROR: 'a' in DEPEND clause cannot have a zero-length array section.
+  !ERROR: 'b' in DEPEND clause cannot have a zero-length array section.
   !$omp task shared(a,b) depend(out: a(2:1), b(3:1, 1:-1))
   a(2:1) = b(2, 2)
   !$omp end task
diff --git a/flang/test/Semantics/omp-reduction01.f90 b/flang/test/Semantics/omp-reduction01.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/omp-reduction01.f90
@@ -0,0 +1,14 @@
+! RUN: %S/test_errors.sh %s %t %f18 -fopenmp
+! OpenMP Version 4.5
+! 2.15.3.6 Reduction Clause
+program omp_reduction
+  integer :: i
+  integer :: k = 10
+
+  !ERROR: Invalid reduction operator in REDUCTION clause.
+  !$omp parallel do reduction(**:k)
+  do i = 1, 10
+    k = k ** 1
+  end do
+  !$omp end parallel do
+end program omp_reduction
diff --git a/flang/test/Semantics/omp-reduction02.f90 b/flang/test/Semantics/omp-reduction02.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/omp-reduction02.f90
@@ -0,0 +1,31 @@
+! RUN: %S/test_errors.sh %s %t %f18 -fopenmp
+! OpenMP Version 4.5
+! 2.15.3.6 Reduction Clause
+program omp_reduction
+
+  integer :: i
+  integer :: k = 10
+  integer :: j = 10
+
+  !ERROR: 'k' appears in more than one data-sharing clause on the same OpenMP directive
+  !$omp parallel do reduction(+:k), reduction(-:k)
+  do i = 1, 10
+    k = k + 1
+  end do
+  !$omp end parallel do
+
+  !ERROR: 'k' appears in more than one data-sharing clause on the same OpenMP directive
+  !$omp parallel do reduction(+:k), reduction(-:j), reduction(+:k)
+  do i = 1, 10
+    k = k + 1
+  end do
+  !$omp end parallel do
+
+  !ERROR: 'k' appears in more than one data-sharing clause on the same OpenMP directive
+  !$omp parallel do reduction(+:j), reduction(-:k), reduction(+:k)
+  do i = 1, 10
+    k = k + 1
+  end do
+  !$omp end parallel do
+
+end program omp_reduction
diff --git a/flang/test/Semantics/omp-reduction03.f90 b/flang/test/Semantics/omp-reduction03.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/omp-reduction03.f90
@@ -0,0 +1,19 @@
+! RUN: %S/test_errors.sh %s %t %f18 -fopenmp
+! OpenMP Version 4.5
+! 2.15.3.6 Reduction Clause
+
+subroutine omp_target(p)
+  integer, pointer, intent(in) :: p
+
+  integer :: i
+  integer :: k = 10
+
+  !ERROR: Pointer 'p' with the INTENT(IN) attribute may not appear in a REDUCTION clause
+  !ERROR: Variable 'p' on the REDUCTION clause is not definable
+  !$omp parallel do reduction(+:p)
+  do i = 1, 10
+    k= k + 1
+  end do
+  !$omp end parallel do
+
+end subroutine omp_target
diff --git a/flang/test/Semantics/omp-reduction04.f90 b/flang/test/Semantics/omp-reduction04.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/omp-reduction04.f90
@@ -0,0 +1,16 @@
+! RUN: %S/test_errors.sh %s %t %f18 -fopenmp
+! OpenMP Version 4.5
+! 2.15.3.6 Reduction Clause
+
+program omp_Reduction
+  integer :: i
+  integer, parameter :: k = 10
+
+  !ERROR: Variable 'k' on the REDUCTION clause is not definable
+  !$omp parallel do reduction(+:k)
+  do i = 1, 10
+    l = k + 1
+  end do
+  !$omp end parallel do
+
+end program omp_Reduction
diff --git a/flang/test/Semantics/omp-reduction05.f90 b/flang/test/Semantics/omp-reduction05.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/omp-reduction05.f90
@@ -0,0 +1,38 @@
+! RUN: %S/test_errors.sh %s %t %f18 -fopenmp
+! OpenMP Version 4.5
+! 2.15.3.6 Reduction Clause
+
+program omp_reduction
+
+  integer :: i
+  integer :: k = 10
+  integer :: a(10),b(10,10,10)
+
+  !ERROR: 'a' in REDUCTION clause cannot have a zero-length array section.
+  !$omp parallel do reduction(+:a(1:0:2))
+  do i = 1, 10
+    k = k + 1
+  end do
+  !$omp end parallel do
+
+  !ERROR: 'a' in REDUCTION clause cannot have a zero-length array section.
+  !$omp parallel do reduction(+:a(1:0))
+  do i = 1, 10
+    k = k + 1
+  end do
+  !$omp end parallel do
+
+  !ERROR: 'b' in REDUCTION clause cannot have a zero-length array section.
+  !$omp parallel do reduction(+:b(1:6,5,1:0))
+  do i = 1, 10
+    k = k + 1
+  end do
+  !$omp end parallel do
+
+  !ERROR: 'b' in REDUCTION clause cannot have a zero-length array section.
+  !$omp parallel do reduction(+:b(1:6,1:0:5,1:10))
+  do i = 1, 10
+    k = k + 1
+  end do
+  !$omp end parallel do
+end program omp_reduction
diff --git a/flang/test/Semantics/omp-reduction06.f90 b/flang/test/Semantics/omp-reduction06.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/omp-reduction06.f90
@@ -0,0 +1,31 @@
+! RUN: %S/test_errors.sh %s %t %f18 -fopenmp
+! OpenMP Version 4.5
+! 2.15.3.6 Reduction Clause
+
+program omp_reduction
+
+  integer :: i
+  integer :: k = 10
+  integer :: a(10), b(10,10,10)
+
+  !ERROR: A list item that appears in a REDUCTION clause should have a contiguos storage array section.
+  !$omp parallel do reduction(+:a(1:10:3))
+  do i = 1, 10
+    k = k + 1
+  end do
+  !$omp end parallel do
+
+  !ERROR: A list item that appears in a REDUCTION clause should have a contiguos storage array section.
+  !$omp parallel do reduction(+:b(1:10:3,1:8:1,1:5:1))
+  do i = 1, 10
+    k = k + 1
+  end do
+  !$omp end parallel do
+
+  !ERROR: A list item that appears in a REDUCTION clause should have a contiguos storage array section.
+  !$omp parallel do reduction(+:b(1:10:1,1:8:2,1:5:1))
+  do i = 1, 10
+    k = k + 1
+  end do
+  !$omp end parallel do
+end program omp_reduction
diff --git a/flang/test/Semantics/omp-reduction07.f90 b/flang/test/Semantics/omp-reduction07.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/omp-reduction07.f90
@@ -0,0 +1,35 @@
+! RUN: %S/test_errors.sh %s %t %f18 -fopenmp
+! OpenMP Version 4.5
+! 2.15.3.6 Reduction Clause
+program omp_reduction
+
+  integer :: i,j
+  integer :: k = 10
+  !$omp parallel private(k)
+  !ERROR: REDUCTION variable 'k' is PRIVATE in outer context must be shared in the parallel regions to which any of the worksharing regions arising from the worksharing construct bind.
+  !$omp do reduction(+:k)
+  do i = 1, 10
+    k = k + 1
+  end do
+  !$omp end do
+  !$omp end parallel
+
+
+  !$omp parallel private(j),reduction(-:k)
+  !ERROR: REDUCTION variable 'k' is REDUCTION in outer context must be shared in the parallel regions to which any of the worksharing regions arising from the worksharing construct bind.
+  !$omp do reduction(+:k)
+  do i = 1, 10
+    k = k + 1
+  end do
+  !$omp end do
+  !$omp end parallel
+
+  !$omp parallel private(j),firstprivate(k)
+  !ERROR: REDUCTION variable 'k' is FIRSTPRIVATE in outer context must be shared in the parallel regions to which any of the worksharing regions arising from the worksharing construct bind.
+  !$omp do reduction(+:k)
+  do i = 1, 10
+    k = k + 1
+  end do
+  !$omp end do
+  !$omp end parallel
+end program omp_reduction
diff --git a/flang/test/Semantics/omp-reduction08.f90 b/flang/test/Semantics/omp-reduction08.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/omp-reduction08.f90
@@ -0,0 +1,63 @@
+! RUN: %S/test_symbols.sh %s %t %f18 -fopenmp
+! OpenMP Version 4.5
+! 2.15.3.6 Reduction Clause Positive cases
+
+!DEF: /omp_reduction MainProgram
+program omp_reduction
+  !DEF: /omp_reduction/i ObjectEntity INTEGER(4)
+  integer i
+  !DEF: /omp_reduction/k ObjectEntity INTEGER(4)
+  integer :: k = 10
+  !DEF: /omp_reduction/m ObjectEntity INTEGER(4)
+  integer :: m = 12
+  !$omp parallel do  reduction(max:k)
+  !DEF: /omp_reduction/Block1/i (OmpPrivate, OmpPreDetermined) HostAssoc INTEGER(4)
+  do i=1,10
+    !REF: /omp_reduction/k
+    !DEF: /omp_reduction/max INTRINSIC (Function) ProcEntity
+    !REF: /omp_reduction/m
+    k = max(k, m)
+  end do
+  !$omp end parallel do
+
+  !$omp parallel do  reduction(min:k)
+  !DEF: /omp_reduction/Block2/i (OmpPrivate, OmpPreDetermined) HostAssoc INTEGER(4)
+  do i=1,10
+    !REF: /omp_reduction/k
+    !DEF: /omp_reduction/min INTRINSIC (Function) ProcEntity
+    !REF: /omp_reduction/m
+    k = min(k, m)
+  end do
+  !$omp end parallel do
+
+  !$omp parallel do  reduction(iand:k)
+  !DEF: /omp_reduction/Block3/i (OmpPrivate, OmpPreDetermined) HostAssoc INTEGER(4)
+  do i=1,10
+    !REF: /omp_reduction/k
+    !DEF: /omp_reduction/iand INTRINSIC (Function) ProcEntity
+    !REF: /omp_reduction/m
+    k = iand(k, m)
+  end do
+  !$omp end parallel do
+
+  !$omp parallel do  reduction(ior:k)
+  !DEF: /omp_reduction/Block4/i (OmpPrivate, OmpPreDetermined) HostAssoc INTEGER(4)
+  do i=1,10
+    !REF: /omp_reduction/k
+    !DEF: /omp_reduction/ior INTRINSIC (Function) ProcEntity
+    !REF: /omp_reduction/m
+    k = ior(k, m)
+  end do
+  !$omp end parallel do
+
+  !$omp parallel do  reduction(ieor:k)
+  !DEF: /omp_reduction/Block5/i (OmpPrivate, OmpPreDetermined) HostAssoc INTEGER(4)
+  do i=1,10
+    !REF: /omp_reduction/k
+    !DEF: /omp_reduction/ieor INTRINSIC (Function) ProcEntity
+    !REF: /omp_reduction/m
+    k = ieor(k,m)
+  end do
+  !$omp end parallel do
+
+end program omp_reduction
diff --git a/flang/test/Semantics/omp-reduction09.f90 b/flang/test/Semantics/omp-reduction09.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/omp-reduction09.f90
@@ -0,0 +1,70 @@
+! RUN: %S/test_symbols.sh %s %t %f18 -fopenmp
+! OpenMP Version 4.5
+! 2.15.3.6 Reduction Clause Positive cases.
+
+!DEF: /omp_reduction MainProgram
+program omp_reduction
+  !DEF: /omp_reduction/i ObjectEntity INTEGER(4)
+  integer i
+  !DEF: /omp_reduction/k ObjectEntity INTEGER(4)
+  integer :: k = 10
+  !DEF: /omp_reduction/a ObjectEntity INTEGER(4)
+  integer a(10)
+  !DEF: /omp_reduction/b ObjectEntity INTEGER(4)
+  integer b(10,10,10)
+
+  !$omp parallel  shared(k)
+  !$omp do  reduction(+:k)
+  !DEF: /omp_reduction/Block1/Block1/i (OmpPrivate, OmpPreDetermined) HostAssoc INTEGER(4)
+  do i=1,10
+    !REF: /omp_reduction/k
+    k = k+1
+  end do
+  !$omp end do
+  !$omp end parallel
+
+
+  !$omp parallel do  reduction(+:a(10))
+  !DEF: /omp_reduction/Block2/i (OmpPrivate, OmpPreDetermined) HostAssoc INTEGER(4)
+  do i=1,10
+    !REF: /omp_reduction/k
+    k = k+1
+  end do
+  !$omp end parallel do
+
+
+  !$omp parallel do  reduction(+:a(1:10:1))
+  !DEF: /omp_reduction/Block3/i (OmpPrivate, OmpPreDetermined) HostAssoc INTEGER(4)
+  do i=1,10
+    !REF: /omp_reduction/k
+    k = k+1
+  end do
+  !$omp end parallel do
+
+  !$omp parallel do  reduction(+:a(1:10:1,1:5,2))
+  !DEF: /omp_reduction/Block4/i (OmpPrivate, OmpPreDetermined) HostAssoc INTEGER(4)
+  do i=1,10
+    !REF: /omp_reduction/k
+    k = k+1
+  end do
+  !$omp end parallel do
+
+  !$omp parallel do  reduction(+:a(1:10:1,1:5,2:5:1))
+  !DEF: /omp_reduction/Block5/i (OmpPrivate, OmpPreDetermined) HostAssoc INTEGER(4)
+  do i=1,10
+    !REF: /omp_reduction/k
+    k = k+1
+  end do
+  !$omp end parallel do
+
+  !$omp parallel  private(i)
+  !$omp do reduction(+:k) reduction(+:j)
+  !DEF: /omp_reduction/Block6/Block1/i (OmpPrivate, OmpPreDetermined) HostAssoc INTEGER(4)
+  do i=1,10
+    !REF: /omp_reduction/k
+    k = k+1
+  end do
+  !$omp end do
+  !$omp end parallel
+
+end program omp_reduction
diff --git a/flang/test/Semantics/omp-reduction10.f90 b/flang/test/Semantics/omp-reduction10.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/omp-reduction10.f90
@@ -0,0 +1,15 @@
+! RUN: %S/test_errors.sh %s %t %f18 -fopenmp
+! OpenMP Version 4.5
+! 2.15.3.6 Reduction Clause
+program omp_reduction
+
+  integer :: i
+  integer :: k = 10
+
+  !ERROR: Invalid reduction identifier in REDUCTION clause.
+  !$omp parallel do reduction(foo:k)
+  do i = 1, 10
+    k = foo(k)
+  end do
+  !$omp end parallel do
+end program omp_reduction