[flang] [llvm] [Flang][OpenMP][Sema] Adding parsing and semantic support for scan directive. (PR #102792)

Anchu Rajendran S via llvm-commits llvm-commits at lists.llvm.org
Mon Sep 9 12:45:04 PDT 2024


https://github.com/anchuraj updated https://github.com/llvm/llvm-project/pull/102792

>From c9942ccc492e2c31b4e8d8da7be1e961eba58cc7 Mon Sep 17 00:00:00 2001
From: Anchu Rajendran <asudhaku at amd.com>
Date: Thu, 8 Aug 2024 15:28:26 -0500
Subject: [PATCH 1/6] Adding parsing support for scan directive.

---
 flang/lib/Lower/OpenMP/OpenMP.cpp             |   3 +
 flang/lib/Parser/openmp-parsers.cpp           |   5 +
 flang/lib/Parser/unparse.cpp                  |   3 +
 flang/lib/Semantics/check-omp-structure.cpp   | 113 ++++++++++--------
 flang/lib/Semantics/resolve-directives.cpp    |  16 +++
 flang/test/Parser/OpenMP/scan.f90             |  40 +++++++
 flang/test/Semantics/OpenMP/do05.f90          |   8 +-
 .../test/Semantics/OpenMP/nested-barrier.f90  |   4 +-
 flang/test/Semantics/OpenMP/nested-master.f90 |   2 +-
 flang/test/Semantics/OpenMP/nested-simd.f90   |  34 +++---
 flang/test/Semantics/OpenMP/ordered-simd.f90  |   2 +-
 flang/test/Semantics/OpenMP/scan.f90          |  19 +++
 llvm/include/llvm/Frontend/OpenMP/OMP.td      |   2 +
 13 files changed, 175 insertions(+), 76 deletions(-)
 create mode 100644 flang/test/Parser/OpenMP/scan.f90
 create mode 100644 flang/test/Semantics/OpenMP/scan.f90

diff --git a/flang/lib/Lower/OpenMP/OpenMP.cpp b/flang/lib/Lower/OpenMP/OpenMP.cpp
index 8b77f1ac6b4ff2..c887ae74cc8b08 100644
--- a/flang/lib/Lower/OpenMP/OpenMP.cpp
+++ b/flang/lib/Lower/OpenMP/OpenMP.cpp
@@ -2427,6 +2427,9 @@ static void genOMPDispatch(lower::AbstractConverter &converter,
   case llvm::omp::Directive::OMPD_parallel:
     genStandaloneParallel(converter, symTable, semaCtx, eval, loc, queue, item);
     break;
+  case llvm::omp::Directive::OMPD_scan:
+    TODO(loc, "Unhandled directive " + llvm::omp::getOpenMPDirectiveName(dir));
+    break;
   case llvm::omp::Directive::OMPD_section:
     llvm_unreachable("genOMPDispatch: OMPD_section");
     // Lowered in the enclosing genSectionsOp.
diff --git a/flang/lib/Parser/openmp-parsers.cpp b/flang/lib/Parser/openmp-parsers.cpp
index 52789d6e5f0f6b..5951be846762ab 100644
--- a/flang/lib/Parser/openmp-parsers.cpp
+++ b/flang/lib/Parser/openmp-parsers.cpp
@@ -267,6 +267,8 @@ TYPE_PARSER(
         construct<OmpClause>(construct<OmpClause::DynamicAllocators>()) ||
     "ENTER" >> construct<OmpClause>(construct<OmpClause::Enter>(
                    parenthesized(Parser<OmpObjectList>{}))) ||
+    "EXCLUSIVE" >> construct<OmpClause>(construct<OmpClause::Exclusive>(
+                       parenthesized(Parser<OmpObjectList>{}))) ||
     "FILTER" >> construct<OmpClause>(construct<OmpClause::Filter>(
                     parenthesized(scalarIntExpr))) ||
     "FINAL" >> construct<OmpClause>(construct<OmpClause::Final>(
@@ -286,6 +288,8 @@ TYPE_PARSER(
     "IF" >> construct<OmpClause>(construct<OmpClause::If>(
                 parenthesized(Parser<OmpIfClause>{}))) ||
     "INBRANCH" >> construct<OmpClause>(construct<OmpClause::Inbranch>()) ||
+    "INCLUSIVE" >> construct<OmpClause>(construct<OmpClause::Inclusive>(
+                       parenthesized(Parser<OmpObjectList>{}))) ||
     "IS_DEVICE_PTR" >> construct<OmpClause>(construct<OmpClause::IsDevicePtr>(
                            parenthesized(Parser<OmpObjectList>{}))) ||
     "LASTPRIVATE" >> construct<OmpClause>(construct<OmpClause::Lastprivate>(
@@ -481,6 +485,7 @@ TYPE_PARSER(sourced(construct<OpenMPFlushConstruct>(verbatim("FLUSH"_tok),
 TYPE_PARSER(sourced(construct<OmpSimpleStandaloneDirective>(first(
     "BARRIER" >> pure(llvm::omp::Directive::OMPD_barrier),
     "ORDERED" >> pure(llvm::omp::Directive::OMPD_ordered),
+    "SCAN" >> pure(llvm::omp::Directive::OMPD_scan),
     "TARGET ENTER DATA" >> pure(llvm::omp::Directive::OMPD_target_enter_data),
     "TARGET EXIT DATA" >> pure(llvm::omp::Directive::OMPD_target_exit_data),
     "TARGET UPDATE" >> pure(llvm::omp::Directive::OMPD_target_update),
diff --git a/flang/lib/Parser/unparse.cpp b/flang/lib/Parser/unparse.cpp
index 2511a5dda9d095..f252512a41f655 100644
--- a/flang/lib/Parser/unparse.cpp
+++ b/flang/lib/Parser/unparse.cpp
@@ -2295,6 +2295,9 @@ class UnparseVisitor {
     case llvm::omp::Directive::OMPD_barrier:
       Word("BARRIER ");
       break;
+    case llvm::omp::Directive::OMPD_scan:
+      Word("SCAN ");
+      break;
     case llvm::omp::Directive::OMPD_taskwait:
       Word("TASKWAIT ");
       break;
diff --git a/flang/lib/Semantics/check-omp-structure.cpp b/flang/lib/Semantics/check-omp-structure.cpp
index 643b713b32e29d..fc0c61db2e599e 100644
--- a/flang/lib/Semantics/check-omp-structure.cpp
+++ b/flang/lib/Semantics/check-omp-structure.cpp
@@ -532,62 +532,70 @@ void OmpStructureChecker::CheckSIMDNest(const parser::OpenMPConstruct &c) {
   // current context yet.
   // TODO: Check for declare simd regions.
   bool eligibleSIMD{false};
-  common::visit(Fortran::common::visitors{
-                    // Allow `!$OMP ORDERED SIMD`
-                    [&](const parser::OpenMPBlockConstruct &c) {
-                      const auto &beginBlockDir{
-                          std::get<parser::OmpBeginBlockDirective>(c.t)};
-                      const auto &beginDir{
-                          std::get<parser::OmpBlockDirective>(beginBlockDir.t)};
-                      if (beginDir.v == llvm::omp::Directive::OMPD_ordered) {
-                        const auto &clauses{
-                            std::get<parser::OmpClauseList>(beginBlockDir.t)};
-                        for (const auto &clause : clauses.v) {
-                          if (std::get_if<parser::OmpClause::Simd>(&clause.u)) {
-                            eligibleSIMD = true;
-                            break;
-                          }
-                        }
-                      }
-                    },
-                    [&](const parser::OpenMPSimpleStandaloneConstruct &c) {
-                      const auto &dir{
-                          std::get<parser::OmpSimpleStandaloneDirective>(c.t)};
-                      if (dir.v == llvm::omp::Directive::OMPD_ordered) {
-                        const auto &clauses{
-                            std::get<parser::OmpClauseList>(c.t)};
-                        for (const auto &clause : clauses.v) {
-                          if (std::get_if<parser::OmpClause::Simd>(&clause.u)) {
-                            eligibleSIMD = true;
-                            break;
-                          }
-                        }
-                      }
-                    },
-                    // Allowing SIMD construct
-                    [&](const parser::OpenMPLoopConstruct &c) {
-                      const auto &beginLoopDir{
-                          std::get<parser::OmpBeginLoopDirective>(c.t)};
-                      const auto &beginDir{
-                          std::get<parser::OmpLoopDirective>(beginLoopDir.t)};
-                      if ((beginDir.v == llvm::omp::Directive::OMPD_simd) ||
-                          (beginDir.v == llvm::omp::Directive::OMPD_do_simd)) {
-                        eligibleSIMD = true;
-                      }
-                    },
-                    [&](const parser::OpenMPAtomicConstruct &c) {
-                      // Allow `!$OMP ATOMIC`
-                      eligibleSIMD = true;
-                    },
-                    [&](const auto &c) {},
-                },
+  common::visit(
+      Fortran::common::visitors{
+          // Allow `!$OMP ORDERED SIMD`
+          [&](const parser::OpenMPBlockConstruct &c) {
+            const auto &beginBlockDir{
+                std::get<parser::OmpBeginBlockDirective>(c.t)};
+            const auto &beginDir{
+                std::get<parser::OmpBlockDirective>(beginBlockDir.t)};
+            if (beginDir.v == llvm::omp::Directive::OMPD_ordered) {
+              const auto &clauses{
+                  std::get<parser::OmpClauseList>(beginBlockDir.t)};
+              for (const auto &clause : clauses.v) {
+                if (std::get_if<parser::OmpClause::Simd>(&clause.u)) {
+                  eligibleSIMD = true;
+                  break;
+                }
+              }
+            }
+          },
+          [&](const parser::OpenMPStandaloneConstruct &c) {
+            if (const auto &simpleConstruct =
+                    std::get_if<parser::OpenMPSimpleStandaloneConstruct>(
+                        &c.u)) {
+              const auto &dir{std::get<parser::OmpSimpleStandaloneDirective>(
+                  simpleConstruct->t)};
+              if (dir.v == llvm::omp::Directive::OMPD_ordered) {
+                const auto &clauses{
+                    std::get<parser::OmpClauseList>(simpleConstruct->t)};
+                for (const auto &clause : clauses.v) {
+                  if (std::get_if<parser::OmpClause::Simd>(&clause.u)) {
+                    eligibleSIMD = true;
+                    break;
+                  }
+                }
+              } else if (dir.v == llvm::omp::Directive::OMPD_scan) {
+                eligibleSIMD = true;
+              }
+            }
+          },
+          // Allowing SIMD construct
+          [&](const parser::OpenMPLoopConstruct &c) {
+            const auto &beginLoopDir{
+                std::get<parser::OmpBeginLoopDirective>(c.t)};
+            const auto &beginDir{
+                std::get<parser::OmpLoopDirective>(beginLoopDir.t)};
+            if ((beginDir.v == llvm::omp::Directive::OMPD_simd) ||
+                (beginDir.v == llvm::omp::Directive::OMPD_parallel_do_simd) ||
+                (beginDir.v == llvm::omp::Directive::OMPD_do_simd)) {
+              eligibleSIMD = true;
+            }
+          },
+          [&](const parser::OpenMPAtomicConstruct &c) {
+            // Allow `!$OMP ATOMIC`
+            eligibleSIMD = true;
+          },
+          [&](const auto &c) {},
+      },
       c.u);
   if (!eligibleSIMD) {
     context_.Say(parser::FindSourceLocation(c),
         "The only OpenMP constructs that can be encountered during execution "
         "of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, "
-        "the `SIMD` construct and the `ORDERED` construct with the `SIMD` "
-        "clause."_err_en_US);
+        "the `SIMD` construct, the `SCAN` construct and the `ORDERED` "
+        "construct with the `SIMD` clause."_err_en_US);
   }
 }
 
@@ -2532,6 +2540,9 @@ void OmpStructureChecker::CheckReductionModifier(
     switch (dirCtx.directive) {
     case llvm::omp::Directive::OMPD_do: // worksharing-loop
     case llvm::omp::Directive::OMPD_do_simd: // worksharing-loop simd
+    case llvm::omp::Directive::
+        OMPD_parallel_do_simd: // worksharing-parallel-loop
+                               // simd
     case llvm::omp::Directive::OMPD_simd: // "simd"
       break;
     default:
diff --git a/flang/lib/Semantics/resolve-directives.cpp b/flang/lib/Semantics/resolve-directives.cpp
index 3b20d9e77e1cfe..a0d7d82de39b3b 100644
--- a/flang/lib/Semantics/resolve-directives.cpp
+++ b/flang/lib/Semantics/resolve-directives.cpp
@@ -1590,9 +1590,11 @@ bool OmpAttributeVisitor::Pre(
     const parser::OpenMPSimpleStandaloneConstruct &x) {
   const auto &standaloneDir{
       std::get<parser::OmpSimpleStandaloneDirective>(x.t)};
+  const auto &parentContext{GetContextIf()};
   switch (standaloneDir.v) {
   case llvm::omp::Directive::OMPD_barrier:
   case llvm::omp::Directive::OMPD_ordered:
+  case llvm::omp::Directive::OMPD_scan:
   case llvm::omp::Directive::OMPD_target_enter_data:
   case llvm::omp::Directive::OMPD_target_exit_data:
   case llvm::omp::Directive::OMPD_target_update:
@@ -1603,6 +1605,20 @@ bool OmpAttributeVisitor::Pre(
   default:
     break;
   }
+  if (standaloneDir.v == llvm::omp::Directive::OMPD_scan) {
+    if ((std::get<parser::OmpClauseList>(x.t).v.size() != 1)) {
+      context_.Say(standaloneDir.source,
+          "Exactly one of `exclusive` or `inclusive` clause is expected"_err_en_US);
+    }
+    if (!parentContext ||
+        (llvm::omp::getDirectiveAssociation(parentContext->directive) !=
+            llvm::omp::Association::Loop)) {
+      context_.Say(standaloneDir.source,
+          "Orphaned `omp scan` directives are prohibited; perhaps you forgot "
+          "to enclose the directive in to a worksharing loop, a worksharing "
+          "loop simd or a simd directive."_err_en_US);
+    }
+  }
   ClearDataSharingAttributeObjects();
   return true;
 }
diff --git a/flang/test/Parser/OpenMP/scan.f90 b/flang/test/Parser/OpenMP/scan.f90
new file mode 100644
index 00000000000000..a6e23ac9404882
--- /dev/null
+++ b/flang/test/Parser/OpenMP/scan.f90
@@ -0,0 +1,40 @@
+! RUN: %flang_fc1 -fdebug-unparse -fopenmp %s | FileCheck --ignore-case %s
+! RUN: %flang_fc1 -fdebug-dump-parse-tree -fopenmp %s | FileCheck --check-prefix="PARSE-TREE" %s
+
+! Check for parsing scan directive
+subroutine test_scan_inclusive()
+  implicit none
+  integer, parameter :: n = 100
+  integer a(n), b(n)
+  integer x, k
+
+  ! initialization
+  x = 0
+  do k = 1, n
+   a(k) = k
+  end do
+
+  ! a(k) is included in the computation of producing results in b(k)
+  !$omp parallel do simd reduction(inscan,+: x)
+  do k = 1, n
+    x = x + a(k)
+    !PARSE-TREE: ExecutionPartConstruct -> ExecutableConstruct -> OpenMPConstruct -> OpenMPStandaloneConstruct -> OpenMPSimpleStandaloneConstruct
+    !PARSE-TREE-NEXT: OmpSimpleStandaloneDirective -> llvm::omp::Directive = scan
+    !PARSE-TREE-NEXT: OmpClauseList -> OmpClause -> Inclusive -> OmpObjectList -> OmpObject -> Designator -> DataRef -> Name = 'x'
+    !CHECK: !$omp scan inclusive(x)
+    !$omp scan inclusive(x)
+      b(k) = x
+  end do
+
+  ! a(k) is not included in the computation of producing results in b(k)
+  !$omp parallel do simd reduction(inscan,+: x)
+  do k = 1, n
+    b(k) = x
+    !PARSE-TREE: ExecutionPartConstruct -> ExecutableConstruct -> OpenMPConstruct -> OpenMPStandaloneConstruct -> OpenMPSimpleStandaloneConstruct
+    !PARSE-TREE-NEXT: OmpSimpleStandaloneDirective -> llvm::omp::Directive = scan
+    !PARSE-TREE-NEXT: OmpClauseList -> OmpClause -> Exclusive -> OmpObjectList -> OmpObject -> Designator -> DataRef -> Name = 'x'
+    !CHECK: !$omp scan exclusive(x)
+    !$omp scan exclusive(x)
+    x = x + a(k)
+  end do
+end subroutine
diff --git a/flang/test/Semantics/OpenMP/do05.f90 b/flang/test/Semantics/OpenMP/do05.f90
index c0f240db57b65b..24844f9fe4f62a 100644
--- a/flang/test/Semantics/OpenMP/do05.f90
+++ b/flang/test/Semantics/OpenMP/do05.f90
@@ -39,7 +39,7 @@ program omp_do
     if( i == 5 ) then
         cycle
     end if
-    !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+    !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
     !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
     !$omp single
     do j=1,10
@@ -70,7 +70,7 @@ program omp_do
     if( i == 3 ) then
         cycle
     end if
-    !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+    !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
     !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
     !$omp single
     do j=1,10
@@ -93,7 +93,7 @@ program omp_do
 
   !$omp target parallel do simd
   do i=1,10
-    !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+    !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
     !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
     !$omp single
     do j=1,10
@@ -116,7 +116,7 @@ program omp_do
 
   !$omp target teams distribute parallel do simd
   do i=1,10
-    !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+    !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
     !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
     !$omp single
     do j=1,10
diff --git a/flang/test/Semantics/OpenMP/nested-barrier.f90 b/flang/test/Semantics/OpenMP/nested-barrier.f90
index aae283229e330d..ed13c98539c93c 100644
--- a/flang/test/Semantics/OpenMP/nested-barrier.f90
+++ b/flang/test/Semantics/OpenMP/nested-barrier.f90
@@ -17,7 +17,7 @@ program omp_nest_barrier
   !$omp do simd
   do i = 1, 10
     k = k + 1
-    !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+    !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
     !ERROR: `BARRIER` region may not be closely nested inside of `WORKSHARING`, `LOOP`, `TASK`, `TASKLOOP`,`CRITICAL`, `ORDERED`, `ATOMIC` or `MASTER` region.
     !$omp barrier
     j = j -1
@@ -34,7 +34,7 @@ program omp_nest_barrier
   !$omp parallel do simd
   do i = 1, 10
     k = k + 1
-    !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+    !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
     !ERROR: `BARRIER` region may not be closely nested inside of `WORKSHARING`, `LOOP`, `TASK`, `TASKLOOP`,`CRITICAL`, `ORDERED`, `ATOMIC` or `MASTER` region.
     !$omp barrier
     j = j -1
diff --git a/flang/test/Semantics/OpenMP/nested-master.f90 b/flang/test/Semantics/OpenMP/nested-master.f90
index 069de67cafae28..0a5118bb947550 100644
--- a/flang/test/Semantics/OpenMP/nested-master.f90
+++ b/flang/test/Semantics/OpenMP/nested-master.f90
@@ -64,7 +64,7 @@ program omp_nest_master
   do i = 1, 10
     k = k + 1
     !WARNING: OpenMP directive 'master' has been deprecated, please use 'masked' instead.
-    !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+    !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
     !ERROR: `MASTER` region may not be closely nested inside of `WORKSHARING`, `LOOP`, `TASK`, `TASKLOOP`, or `ATOMIC` region.
     !$omp master
     j = j -1
diff --git a/flang/test/Semantics/OpenMP/nested-simd.f90 b/flang/test/Semantics/OpenMP/nested-simd.f90
index 4149b6d97e9dc7..c9fb90cdeceb25 100644
--- a/flang/test/Semantics/OpenMP/nested-simd.f90
+++ b/flang/test/Semantics/OpenMP/nested-simd.f90
@@ -40,7 +40,7 @@ SUBROUTINE NESTED_BAD(N)
       !$OMP ORDERED SIMD
       DO J = 1,N
         print *, "Hi"
-        !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+        !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
         !ERROR: TEAMS region can only be strictly nested within the implicit parallel region or TARGET region
         !$omp teams 
          DO K = 1,N
@@ -58,25 +58,25 @@ SUBROUTINE NESTED_BAD(N)
     !$OMP ATOMIC
     K =  K + 1
     IF (I <= 10) THEN
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
       !$omp task 
       do J = 1, N
         K = 2
       end do
       !$omp end task
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
       !$omp target 
       do J = 1, N
         K = 2
       end do
       !$omp end target
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
       !$OMP DO
       DO J = 1,N
         A(J) = J
       END DO
       !$OMP END DO
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
       !$OMP PARALLEL DO
       DO J = 1,N
         A(J) = J
@@ -91,26 +91,26 @@ SUBROUTINE NESTED_BAD(N)
     !$OMP ATOMIC
     K =  K + 1
     IF (I <= 10) THEN
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
       !$omp task 
       do J = 1, N
         K = 2
       end do
       !$omp end task
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
       !$omp target 
       do J = 1, N
         K = 2
       end do
       !$omp end target
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
       !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
       !$OMP DO
       DO J = 1,N
         A(J) = J
       END DO
       !$OMP END DO
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
       !$OMP PARALLEL DO
       DO J = 1,N
         A(J) = J
@@ -125,26 +125,26 @@ SUBROUTINE NESTED_BAD(N)
     !$OMP ATOMIC
     K =  K + 1
     IF (I <= 10) THEN
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
       !$omp task 
       do J = 1, N
         K = 2
       end do
       !$omp end task
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
       !$omp target 
       do J = 1, N
         K = 2
       end do
       !$omp end target
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
       !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
       !$OMP DO
       DO J = 1,N
         A(J) = J
       END DO
       !$OMP END DO
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
       !$OMP PARALLEL DO
       DO J = 1,N
         A(J) = J
@@ -159,25 +159,25 @@ SUBROUTINE NESTED_BAD(N)
     !$OMP ATOMIC
     K =  K + 1
     IF (I <= 10) THEN
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
       !$omp task 
       do J = 1, N
         K = 2
       end do
       !$omp end task
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
       !$omp target 
       do J = 1, N
         K = 2
       end do
       !$omp end target
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
       !$OMP DO
       DO J = 1,N
         A(J) = J
       END DO
       !$OMP END DO
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
       !$OMP PARALLEL DO
       DO J = 1,N
         A(J) = J
diff --git a/flang/test/Semantics/OpenMP/ordered-simd.f90 b/flang/test/Semantics/OpenMP/ordered-simd.f90
index ed52b759491002..0df0471f3db60e 100644
--- a/flang/test/Semantics/OpenMP/ordered-simd.f90
+++ b/flang/test/Semantics/OpenMP/ordered-simd.f90
@@ -25,7 +25,7 @@ SUBROUTINE ORDERED_BAD(N)
   !$OMP DO SIMD
   DO I = 1,N
     IF (I <= 10) THEN
-      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct and the `ORDERED` construct with the `SIMD` clause.
+      !ERROR: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
       !ERROR: An ORDERED directive without the DEPEND clause must be closely nested in a worksharing-loop (or worksharing-loop SIMD) region with ORDERED clause without the parameter
       !$OMP ORDERED 
       CALL WORK(I)
diff --git a/flang/test/Semantics/OpenMP/scan.f90 b/flang/test/Semantics/OpenMP/scan.f90
new file mode 100644
index 00000000000000..76a0379dfec55c
--- /dev/null
+++ b/flang/test/Semantics/OpenMP/scan.f90
@@ -0,0 +1,19 @@
+! RUN: %python %S/../test_errors.py %s %flang_fc1 -fopenmp
+
+subroutine test_scan()
+ integer x, k
+ 
+ !ERROR: Orphaned `omp scan` directives are prohibited; perhaps you forgot to enclose the directive in to a worksharing loop, a worksharing loop simd or a simd directive.
+ !$omp scan inclusive(x)
+ !$omp parallel do simd reduction(inscan,+: x)
+ do k = 1, n
+ !ERROR: UNTIED clause is not allowed on the SCAN directive
+   !$omp scan untied
+ end do
+ 
+ !$omp parallel do simd reduction(inscan,+: x)
+ do k = 1, n
+ !ERROR: Exactly one of `exclusive` or `inclusive` clause is expected
+   !$omp scan
+ end do
+end subroutine
diff --git a/llvm/include/llvm/Frontend/OpenMP/OMP.td b/llvm/include/llvm/Frontend/OpenMP/OMP.td
index 2cbcbd883fb2e3..6a96fe1d82abef 100644
--- a/llvm/include/llvm/Frontend/OpenMP/OMP.td
+++ b/llvm/include/llvm/Frontend/OpenMP/OMP.td
@@ -156,6 +156,7 @@ def OMPC_Enter : Clause<"enter"> {
 }
 def OMPC_Exclusive : Clause<"exclusive"> {
   let clangClass = "OMPExclusiveClause";
+  let flangClass = "OmpObjectList";
 }
 def OMPC_Fail : Clause<"fail"> {
   let clangClass = "OMPFailClause";
@@ -213,6 +214,7 @@ def OMPC_Inbranch : Clause<"inbranch"> {
 }
 def OMPC_Inclusive : Clause<"inclusive"> {
   let clangClass = "OMPInclusiveClause";
+  let flangClass = "OmpObjectList";
 }
 def OMPC_Indirect : Clause<"indirect"> {
 }

>From e061e42798e78036b565b4b1f781a35fb7a0144c Mon Sep 17 00:00:00 2001
From: Anchu Rajendran <asudhaku at amd.com>
Date: Wed, 28 Aug 2024 17:17:14 -0500
Subject: [PATCH 2/6] R2: Addressing review comments

---
 .../flang/Semantics/openmp-directive-sets.h   |   1 +
 flang/lib/Semantics/check-omp-structure.cpp   | 123 ++++++++----------
 flang/lib/Semantics/resolve-directives.cpp    |   3 +-
 flang/test/Parser/OpenMP/scan.f90             |  36 +++--
 flang/test/Semantics/OpenMP/out               |  37 ++++++
 flang/test/Semantics/OpenMP/scan.f90          |   8 +-
 6 files changed, 130 insertions(+), 78 deletions(-)
 create mode 100644 flang/test/Semantics/OpenMP/out

diff --git a/flang/include/flang/Semantics/openmp-directive-sets.h b/flang/include/flang/Semantics/openmp-directive-sets.h
index 8eb736bb098fe4..0df4e992d793bc 100644
--- a/flang/include/flang/Semantics/openmp-directive-sets.h
+++ b/flang/include/flang/Semantics/openmp-directive-sets.h
@@ -194,6 +194,7 @@ static const OmpDirectiveSet allDistributeParallelDoSimdSet{
 static const OmpDirectiveSet allDistributeSimdSet{
     allDistributeSet & allSimdSet};
 static const OmpDirectiveSet allDoSimdSet{allDoSet & allSimdSet};
+static const OmpDirectiveSet scanAllowedSet{allDoSet | allSimdSet};
 static const OmpDirectiveSet allTaskloopSimdSet{allTaskloopSet & allSimdSet};
 
 static const OmpDirectiveSet compositeConstructSet{
diff --git a/flang/lib/Semantics/check-omp-structure.cpp b/flang/lib/Semantics/check-omp-structure.cpp
index fc0c61db2e599e..372a28c1428fc0 100644
--- a/flang/lib/Semantics/check-omp-structure.cpp
+++ b/flang/lib/Semantics/check-omp-structure.cpp
@@ -10,6 +10,7 @@
 #include "definable.h"
 #include "flang/Parser/parse-tree.h"
 #include "flang/Semantics/tools.h"
+#include <variant>
 
 namespace Fortran::semantics {
 
@@ -532,63 +533,61 @@ void OmpStructureChecker::CheckSIMDNest(const parser::OpenMPConstruct &c) {
   // current context yet.
   // TODO: Check for declare simd regions.
   bool eligibleSIMD{false};
-  common::visit(
-      Fortran::common::visitors{
-          // Allow `!$OMP ORDERED SIMD`
-          [&](const parser::OpenMPBlockConstruct &c) {
-            const auto &beginBlockDir{
-                std::get<parser::OmpBeginBlockDirective>(c.t)};
-            const auto &beginDir{
-                std::get<parser::OmpBlockDirective>(beginBlockDir.t)};
-            if (beginDir.v == llvm::omp::Directive::OMPD_ordered) {
-              const auto &clauses{
-                  std::get<parser::OmpClauseList>(beginBlockDir.t)};
-              for (const auto &clause : clauses.v) {
-                if (std::get_if<parser::OmpClause::Simd>(&clause.u)) {
-                  eligibleSIMD = true;
-                  break;
-                }
-              }
-            }
-          },
-          [&](const parser::OpenMPStandaloneConstruct &c) {
-            if (const auto &simpleConstruct =
-                    std::get_if<parser::OpenMPSimpleStandaloneConstruct>(
-                        &c.u)) {
-              const auto &dir{std::get<parser::OmpSimpleStandaloneDirective>(
-                  simpleConstruct->t)};
-              if (dir.v == llvm::omp::Directive::OMPD_ordered) {
-                const auto &clauses{
-                    std::get<parser::OmpClauseList>(simpleConstruct->t)};
-                for (const auto &clause : clauses.v) {
-                  if (std::get_if<parser::OmpClause::Simd>(&clause.u)) {
-                    eligibleSIMD = true;
-                    break;
-                  }
-                }
-              } else if (dir.v == llvm::omp::Directive::OMPD_scan) {
-                eligibleSIMD = true;
-              }
-            }
-          },
-          // Allowing SIMD construct
-          [&](const parser::OpenMPLoopConstruct &c) {
-            const auto &beginLoopDir{
-                std::get<parser::OmpBeginLoopDirective>(c.t)};
-            const auto &beginDir{
-                std::get<parser::OmpLoopDirective>(beginLoopDir.t)};
-            if ((beginDir.v == llvm::omp::Directive::OMPD_simd) ||
-                (beginDir.v == llvm::omp::Directive::OMPD_parallel_do_simd) ||
-                (beginDir.v == llvm::omp::Directive::OMPD_do_simd)) {
-              eligibleSIMD = true;
-            }
-          },
-          [&](const parser::OpenMPAtomicConstruct &c) {
-            // Allow `!$OMP ATOMIC`
-            eligibleSIMD = true;
-          },
-          [&](const auto &c) {},
-      },
+  common::visit(Fortran::common::visitors{
+                    // Allow `!$OMP ORDERED SIMD`
+                    [&](const parser::OpenMPBlockConstruct &c) {
+                      const auto &beginBlockDir{
+                          std::get<parser::OmpBeginBlockDirective>(c.t)};
+                      const auto &beginDir{
+                          std::get<parser::OmpBlockDirective>(beginBlockDir.t)};
+                      if (beginDir.v == llvm::omp::Directive::OMPD_ordered) {
+                        const auto &clauses{
+                            std::get<parser::OmpClauseList>(beginBlockDir.t)};
+                        for (const auto &clause : clauses.v) {
+                          if (std::get_if<parser::OmpClause::Simd>(&clause.u)) {
+                            eligibleSIMD = true;
+                            break;
+                          }
+                        }
+                      }
+                    },
+                    [&](const parser::OpenMPStandaloneConstruct &c) {
+                      if (const auto &simpleConstruct =
+                              std::get_if<parser::OpenMPSimpleStandaloneConstruct>(
+                                  &c.u)) {
+                        const auto &dir{std::get<parser::OmpSimpleStandaloneDirective>(
+                            simpleConstruct->t)};
+                        if (dir.v == llvm::omp::Directive::OMPD_ordered) {
+                          const auto &clauses{
+                              std::get<parser::OmpClauseList>(simpleConstruct->t)};
+                          for (const auto &clause : clauses.v) {
+                            if (std::get_if<parser::OmpClause::Simd>(&clause.u)) {
+                              eligibleSIMD = true;
+                              break;
+                            }
+                          }
+                        } else if (dir.v == llvm::omp::Directive::OMPD_scan) {
+                          eligibleSIMD = true;
+                        }
+                      }
+                    },
+                    // Allowing SIMD construct
+                    [&](const parser::OpenMPLoopConstruct &c) {
+                      const auto &beginLoopDir{
+                          std::get<parser::OmpBeginLoopDirective>(c.t)};
+                      const auto &beginDir{
+                          std::get<parser::OmpLoopDirective>(beginLoopDir.t)};
+                      if ((beginDir.v == llvm::omp::Directive::OMPD_simd) ||
+                          (beginDir.v == llvm::omp::Directive::OMPD_do_simd)) {
+                        eligibleSIMD = true;
+                      }
+                    },
+                    [&](const parser::OpenMPAtomicConstruct &c) {
+                      // Allow `!$OMP ATOMIC`
+                      eligibleSIMD = true;
+                    },
+                    [&](const auto &c) {},
+                },
       c.u);
   if (!eligibleSIMD) {
     context_.Say(parser::FindSourceLocation(c),
@@ -2537,15 +2536,7 @@ void OmpStructureChecker::CheckReductionModifier(
     // or "simd" directive.
     // The worksharing-loop directives are OMPD_do and OMPD_for. Only the
     // former is allowed in Fortran.
-    switch (dirCtx.directive) {
-    case llvm::omp::Directive::OMPD_do: // worksharing-loop
-    case llvm::omp::Directive::OMPD_do_simd: // worksharing-loop simd
-    case llvm::omp::Directive::
-        OMPD_parallel_do_simd: // worksharing-parallel-loop
-                               // simd
-    case llvm::omp::Directive::OMPD_simd: // "simd"
-      break;
-    default:
+    if (!llvm::omp::scanAllowedSet.test(dirCtx.directive)) {
       context_.Say(GetContext().clauseSource,
           "Modifier 'INSCAN' on REDUCTION clause is only allowed with "
           "worksharing-loop, worksharing-loop simd, "
diff --git a/flang/lib/Semantics/resolve-directives.cpp b/flang/lib/Semantics/resolve-directives.cpp
index a0d7d82de39b3b..fd71667264cc8e 100644
--- a/flang/lib/Semantics/resolve-directives.cpp
+++ b/flang/lib/Semantics/resolve-directives.cpp
@@ -1611,8 +1611,7 @@ bool OmpAttributeVisitor::Pre(
           "Exactly one of `exclusive` or `inclusive` clause is expected"_err_en_US);
     }
     if (!parentContext ||
-        (llvm::omp::getDirectiveAssociation(parentContext->directive) !=
-            llvm::omp::Association::Loop)) {
+        (!llvm::omp::scanAllowedSet.test(parentContext->directive))) {
       context_.Say(standaloneDir.source,
           "Orphaned `omp scan` directives are prohibited; perhaps you forgot "
           "to enclose the directive in to a worksharing loop, a worksharing "
diff --git a/flang/test/Parser/OpenMP/scan.f90 b/flang/test/Parser/OpenMP/scan.f90
index a6e23ac9404882..6bc970c922160f 100644
--- a/flang/test/Parser/OpenMP/scan.f90
+++ b/flang/test/Parser/OpenMP/scan.f90
@@ -2,17 +2,11 @@
 ! RUN: %flang_fc1 -fdebug-dump-parse-tree -fopenmp %s | FileCheck --check-prefix="PARSE-TREE" %s
 
 ! Check for parsing scan directive
-subroutine test_scan_inclusive()
+subroutine test_scan(n, a, b)
   implicit none
-  integer, parameter :: n = 100
+  integer n
   integer a(n), b(n)
-  integer x, k
-
-  ! initialization
-  x = 0
-  do k = 1, n
-   a(k) = k
-  end do
+  integer x,y,k
 
   ! a(k) is included in the computation of producing results in b(k)
   !$omp parallel do simd reduction(inscan,+: x)
@@ -37,4 +31,28 @@ subroutine test_scan_inclusive()
     !$omp scan exclusive(x)
     x = x + a(k)
   end do
+
+  !$omp parallel do simd reduction(inscan,+: x)
+  do k = 1, n
+    x = x + a(k)
+    !PARSE-TREE: ExecutionPartConstruct -> ExecutableConstruct -> OpenMPConstruct -> OpenMPStandaloneConstruct -> OpenMPSimpleStandaloneConstruct
+    !PARSE-TREE-NEXT: OmpSimpleStandaloneDirective -> llvm::omp::Directive = scan
+    !PARSE-TREE-NEXT: OmpClauseList -> OmpClause -> Inclusive -> OmpObjectList -> OmpObject -> Designator -> DataRef -> Name = 'x'
+    !PARSE-TREE-NEXT: OmpObject -> Designator -> DataRef -> Name = 'y'
+    !CHECK: !$omp scan inclusive(x,y)
+    !$omp scan inclusive(x, y)
+      b(k) = x
+  end do
+
+  !$omp parallel do simd reduction(inscan,+: x)
+  do k = 1, n
+    x = x + a(k)
+    !PARSE-TREE: ExecutionPartConstruct -> ExecutableConstruct -> OpenMPConstruct -> OpenMPStandaloneConstruct -> OpenMPSimpleStandaloneConstruct
+    !PARSE-TREE-NEXT: OmpSimpleStandaloneDirective -> llvm::omp::Directive = scan
+    !PARSE-TREE-NEXT: OmpClauseList -> OmpClause -> Exclusive -> OmpObjectList -> OmpObject -> Designator -> DataRef -> Name = 'x'
+    !PARSE-TREE-NEXT: OmpObject -> Designator -> DataRef -> Name = 'y'
+    !CHECK: !$omp scan exclusive(x,y)
+    !$omp scan exclusive(x, y)
+      b(k) = x
+  end do
 end subroutine
diff --git a/flang/test/Semantics/OpenMP/out b/flang/test/Semantics/OpenMP/out
new file mode 100644
index 00000000000000..d63b909cdd6c6c
--- /dev/null
+++ b/flang/test/Semantics/OpenMP/out
@@ -0,0 +1,37 @@
+error: Semantic errors in nested-simd.f90
+./nested-simd.f90:45:15: error: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
+          !$omp teams 
+                ^
+./nested-simd.f90:45:15: error: TEAMS region can only be strictly nested within the implicit parallel region or TARGET region
+          !$omp teams 
+                ^
+./nested-simd.f90:62:13: error: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
+        !$omp task 
+              ^
+./nested-simd.f90:68:13: error: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
+        !$omp target 
+              ^
+./nested-simd.f90:95:13: error: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
+        !$omp task 
+              ^
+./nested-simd.f90:101:13: error: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
+        !$omp target 
+              ^
+./nested-simd.f90:108:13: error: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
+        !$OMP DO
+              ^^
+./nested-simd.f90:129:13: error: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
+        !$omp task 
+              ^
+./nested-simd.f90:135:13: error: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
+        !$omp target 
+              ^
+./nested-simd.f90:142:13: error: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
+        !$OMP DO
+              ^^
+./nested-simd.f90:163:13: error: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
+        !$omp task 
+              ^
+./nested-simd.f90:169:13: error: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
+        !$omp target 
+              ^
diff --git a/flang/test/Semantics/OpenMP/scan.f90 b/flang/test/Semantics/OpenMP/scan.f90
index 76a0379dfec55c..fe154c2fa74cd3 100644
--- a/flang/test/Semantics/OpenMP/scan.f90
+++ b/flang/test/Semantics/OpenMP/scan.f90
@@ -1,7 +1,7 @@
 ! RUN: %python %S/../test_errors.py %s %flang_fc1 -fopenmp
 
 subroutine test_scan()
- integer x, k
+ integer x, y, k
  
  !ERROR: Orphaned `omp scan` directives are prohibited; perhaps you forgot to enclose the directive in to a worksharing loop, a worksharing loop simd or a simd directive.
  !$omp scan inclusive(x)
@@ -16,4 +16,10 @@ subroutine test_scan()
  !ERROR: Exactly one of `exclusive` or `inclusive` clause is expected
    !$omp scan
  end do
+
+!$omp parallel do simd reduction(inscan,+: x)
+ do k = 1, n
+ !ERROR: Exactly one of `exclusive` or `inclusive` clause is expected
+   !$omp scan inclusive(x) exclusive(y)
+ end do
 end subroutine

>From d6873392ba0d69f7686851f3f3c4be7c990fe3f7 Mon Sep 17 00:00:00 2001
From: Anchu Rajendran <asudhaku at amd.com>
Date: Wed, 28 Aug 2024 18:54:32 -0500
Subject: [PATCH 3/6] R3: Adding formatted file

---
 flang/lib/Semantics/check-omp-structure.cpp | 111 ++++++++++----------
 1 file changed, 56 insertions(+), 55 deletions(-)

diff --git a/flang/lib/Semantics/check-omp-structure.cpp b/flang/lib/Semantics/check-omp-structure.cpp
index 372a28c1428fc0..f130b35a8359b2 100644
--- a/flang/lib/Semantics/check-omp-structure.cpp
+++ b/flang/lib/Semantics/check-omp-structure.cpp
@@ -533,61 +533,62 @@ void OmpStructureChecker::CheckSIMDNest(const parser::OpenMPConstruct &c) {
   // current context yet.
   // TODO: Check for declare simd regions.
   bool eligibleSIMD{false};
-  common::visit(Fortran::common::visitors{
-                    // Allow `!$OMP ORDERED SIMD`
-                    [&](const parser::OpenMPBlockConstruct &c) {
-                      const auto &beginBlockDir{
-                          std::get<parser::OmpBeginBlockDirective>(c.t)};
-                      const auto &beginDir{
-                          std::get<parser::OmpBlockDirective>(beginBlockDir.t)};
-                      if (beginDir.v == llvm::omp::Directive::OMPD_ordered) {
-                        const auto &clauses{
-                            std::get<parser::OmpClauseList>(beginBlockDir.t)};
-                        for (const auto &clause : clauses.v) {
-                          if (std::get_if<parser::OmpClause::Simd>(&clause.u)) {
-                            eligibleSIMD = true;
-                            break;
-                          }
-                        }
-                      }
-                    },
-                    [&](const parser::OpenMPStandaloneConstruct &c) {
-                      if (const auto &simpleConstruct =
-                              std::get_if<parser::OpenMPSimpleStandaloneConstruct>(
-                                  &c.u)) {
-                        const auto &dir{std::get<parser::OmpSimpleStandaloneDirective>(
-                            simpleConstruct->t)};
-                        if (dir.v == llvm::omp::Directive::OMPD_ordered) {
-                          const auto &clauses{
-                              std::get<parser::OmpClauseList>(simpleConstruct->t)};
-                          for (const auto &clause : clauses.v) {
-                            if (std::get_if<parser::OmpClause::Simd>(&clause.u)) {
-                              eligibleSIMD = true;
-                              break;
-                            }
-                          }
-                        } else if (dir.v == llvm::omp::Directive::OMPD_scan) {
-                          eligibleSIMD = true;
-                        }
-                      }
-                    },
-                    // Allowing SIMD construct
-                    [&](const parser::OpenMPLoopConstruct &c) {
-                      const auto &beginLoopDir{
-                          std::get<parser::OmpBeginLoopDirective>(c.t)};
-                      const auto &beginDir{
-                          std::get<parser::OmpLoopDirective>(beginLoopDir.t)};
-                      if ((beginDir.v == llvm::omp::Directive::OMPD_simd) ||
-                          (beginDir.v == llvm::omp::Directive::OMPD_do_simd)) {
-                        eligibleSIMD = true;
-                      }
-                    },
-                    [&](const parser::OpenMPAtomicConstruct &c) {
-                      // Allow `!$OMP ATOMIC`
-                      eligibleSIMD = true;
-                    },
-                    [&](const auto &c) {},
-                },
+  common::visit(
+      Fortran::common::visitors{
+          // Allow `!$OMP ORDERED SIMD`
+          [&](const parser::OpenMPBlockConstruct &c) {
+            const auto &beginBlockDir{
+                std::get<parser::OmpBeginBlockDirective>(c.t)};
+            const auto &beginDir{
+                std::get<parser::OmpBlockDirective>(beginBlockDir.t)};
+            if (beginDir.v == llvm::omp::Directive::OMPD_ordered) {
+              const auto &clauses{
+                  std::get<parser::OmpClauseList>(beginBlockDir.t)};
+              for (const auto &clause : clauses.v) {
+                if (std::get_if<parser::OmpClause::Simd>(&clause.u)) {
+                  eligibleSIMD = true;
+                  break;
+                }
+              }
+            }
+          },
+          [&](const parser::OpenMPStandaloneConstruct &c) {
+            if (const auto &simpleConstruct =
+                    std::get_if<parser::OpenMPSimpleStandaloneConstruct>(
+                        &c.u)) {
+              const auto &dir{std::get<parser::OmpSimpleStandaloneDirective>(
+                  simpleConstruct->t)};
+              if (dir.v == llvm::omp::Directive::OMPD_ordered) {
+                const auto &clauses{
+                    std::get<parser::OmpClauseList>(simpleConstruct->t)};
+                for (const auto &clause : clauses.v) {
+                  if (std::get_if<parser::OmpClause::Simd>(&clause.u)) {
+                    eligibleSIMD = true;
+                    break;
+                  }
+                }
+              } else if (dir.v == llvm::omp::Directive::OMPD_scan) {
+                eligibleSIMD = true;
+              }
+            }
+          },
+          // Allowing SIMD construct
+          [&](const parser::OpenMPLoopConstruct &c) {
+            const auto &beginLoopDir{
+                std::get<parser::OmpBeginLoopDirective>(c.t)};
+            const auto &beginDir{
+                std::get<parser::OmpLoopDirective>(beginLoopDir.t)};
+            if ((beginDir.v == llvm::omp::Directive::OMPD_simd) ||
+                (beginDir.v == llvm::omp::Directive::OMPD_do_simd)) {
+              eligibleSIMD = true;
+            }
+          },
+          [&](const parser::OpenMPAtomicConstruct &c) {
+            // Allow `!$OMP ATOMIC`
+            eligibleSIMD = true;
+          },
+          [&](const auto &c) {},
+      },
       c.u);
   if (!eligibleSIMD) {
     context_.Say(parser::FindSourceLocation(c),

>From 7087dcf6c0ba92e75170cec6cfdd4a913c2e5a74 Mon Sep 17 00:00:00 2001
From: Anchu Rajendran <asudhaku at amd.com>
Date: Thu, 29 Aug 2024 13:19:04 -0500
Subject: [PATCH 4/6] R4: Addressing review comments

---
 .../flang/Semantics/openmp-directive-sets.h   |  6 ++-
 flang/lib/Semantics/resolve-directives.cpp    |  4 +-
 flang/test/Parser/OpenMP/scan.f90             |  4 +-
 flang/test/Semantics/OpenMP/out               | 37 -------------------
 flang/test/Semantics/OpenMP/scan.f90          |  2 +-
 5 files changed, 9 insertions(+), 44 deletions(-)
 delete mode 100644 flang/test/Semantics/OpenMP/out

diff --git a/flang/include/flang/Semantics/openmp-directive-sets.h b/flang/include/flang/Semantics/openmp-directive-sets.h
index 0df4e992d793bc..90ce28e450ea46 100644
--- a/flang/include/flang/Semantics/openmp-directive-sets.h
+++ b/flang/include/flang/Semantics/openmp-directive-sets.h
@@ -186,7 +186,10 @@ static const OmpDirectiveSet allTeamsSet{
 // Directive sets for groups of multiple directives
 //===----------------------------------------------------------------------===//
 
-// Composite constructs
+// Directive sets for parent directives that do allow/not allow a construct
+static const OmpDirectiveSet scanAllowedSet{allDoSet | allSimdSet};
+
+// Directive sets that form Composite constructs
 static const OmpDirectiveSet allDistributeParallelDoSet{
     allDistributeSet & allParallelSet & allDoSet};
 static const OmpDirectiveSet allDistributeParallelDoSimdSet{
@@ -194,7 +197,6 @@ static const OmpDirectiveSet allDistributeParallelDoSimdSet{
 static const OmpDirectiveSet allDistributeSimdSet{
     allDistributeSet & allSimdSet};
 static const OmpDirectiveSet allDoSimdSet{allDoSet & allSimdSet};
-static const OmpDirectiveSet scanAllowedSet{allDoSet | allSimdSet};
 static const OmpDirectiveSet allTaskloopSimdSet{allTaskloopSet & allSimdSet};
 
 static const OmpDirectiveSet compositeConstructSet{
diff --git a/flang/lib/Semantics/resolve-directives.cpp b/flang/lib/Semantics/resolve-directives.cpp
index fd71667264cc8e..12abf3ecc2c0b8 100644
--- a/flang/lib/Semantics/resolve-directives.cpp
+++ b/flang/lib/Semantics/resolve-directives.cpp
@@ -1606,12 +1606,12 @@ bool OmpAttributeVisitor::Pre(
     break;
   }
   if (standaloneDir.v == llvm::omp::Directive::OMPD_scan) {
-    if ((std::get<parser::OmpClauseList>(x.t).v.size() != 1)) {
+    if (std::get<parser::OmpClauseList>(x.t).v.size() != 1) {
       context_.Say(standaloneDir.source,
           "Exactly one of `exclusive` or `inclusive` clause is expected"_err_en_US);
     }
     if (!parentContext ||
-        (!llvm::omp::scanAllowedSet.test(parentContext->directive))) {
+        !llvm::omp::scanAllowedSet.test(parentContext->directive)) {
       context_.Say(standaloneDir.source,
           "Orphaned `omp scan` directives are prohibited; perhaps you forgot "
           "to enclose the directive in to a worksharing loop, a worksharing "
diff --git a/flang/test/Parser/OpenMP/scan.f90 b/flang/test/Parser/OpenMP/scan.f90
index 6bc970c922160f..02fa09b6ef3505 100644
--- a/flang/test/Parser/OpenMP/scan.f90
+++ b/flang/test/Parser/OpenMP/scan.f90
@@ -32,7 +32,7 @@ subroutine test_scan(n, a, b)
     x = x + a(k)
   end do
 
-  !$omp parallel do simd reduction(inscan,+: x)
+  !$omp parallel do simd reduction(inscan,+: x, y)
   do k = 1, n
     x = x + a(k)
     !PARSE-TREE: ExecutionPartConstruct -> ExecutableConstruct -> OpenMPConstruct -> OpenMPStandaloneConstruct -> OpenMPSimpleStandaloneConstruct
@@ -44,7 +44,7 @@ subroutine test_scan(n, a, b)
       b(k) = x
   end do
 
-  !$omp parallel do simd reduction(inscan,+: x)
+  !$omp parallel do simd reduction(inscan,+: x, y)
   do k = 1, n
     x = x + a(k)
     !PARSE-TREE: ExecutionPartConstruct -> ExecutableConstruct -> OpenMPConstruct -> OpenMPStandaloneConstruct -> OpenMPSimpleStandaloneConstruct
diff --git a/flang/test/Semantics/OpenMP/out b/flang/test/Semantics/OpenMP/out
deleted file mode 100644
index d63b909cdd6c6c..00000000000000
--- a/flang/test/Semantics/OpenMP/out
+++ /dev/null
@@ -1,37 +0,0 @@
-error: Semantic errors in nested-simd.f90
-./nested-simd.f90:45:15: error: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
-          !$omp teams 
-                ^
-./nested-simd.f90:45:15: error: TEAMS region can only be strictly nested within the implicit parallel region or TARGET region
-          !$omp teams 
-                ^
-./nested-simd.f90:62:13: error: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
-        !$omp task 
-              ^
-./nested-simd.f90:68:13: error: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
-        !$omp target 
-              ^
-./nested-simd.f90:95:13: error: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
-        !$omp task 
-              ^
-./nested-simd.f90:101:13: error: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
-        !$omp target 
-              ^
-./nested-simd.f90:108:13: error: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
-        !$OMP DO
-              ^^
-./nested-simd.f90:129:13: error: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
-        !$omp task 
-              ^
-./nested-simd.f90:135:13: error: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
-        !$omp target 
-              ^
-./nested-simd.f90:142:13: error: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
-        !$OMP DO
-              ^^
-./nested-simd.f90:163:13: error: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
-        !$omp task 
-              ^
-./nested-simd.f90:169:13: error: The only OpenMP constructs that can be encountered during execution of a 'SIMD' region are the `ATOMIC` construct, the `LOOP` construct, the `SIMD` construct, the `SCAN` construct and the `ORDERED` construct with the `SIMD` clause.
-        !$omp target 
-              ^
diff --git a/flang/test/Semantics/OpenMP/scan.f90 b/flang/test/Semantics/OpenMP/scan.f90
index fe154c2fa74cd3..e82982f60b9021 100644
--- a/flang/test/Semantics/OpenMP/scan.f90
+++ b/flang/test/Semantics/OpenMP/scan.f90
@@ -17,7 +17,7 @@ subroutine test_scan()
    !$omp scan
  end do
 
-!$omp parallel do simd reduction(inscan,+: x)
+!$omp parallel do simd reduction(inscan,+: x, y)
  do k = 1, n
  !ERROR: Exactly one of `exclusive` or `inclusive` clause is expected
    !$omp scan inclusive(x) exclusive(y)

>From 23fd9635590da7e898eca52347f5d5746386069a Mon Sep 17 00:00:00 2001
From: Anchu Rajendran <asudhaku at amd.com>
Date: Thu, 29 Aug 2024 14:43:18 -0500
Subject: [PATCH 5/6] R5: Addressing a few more review comments

---
 flang/include/flang/Semantics/openmp-directive-sets.h | 8 +++++---
 flang/lib/Semantics/check-omp-structure.cpp           | 2 +-
 flang/lib/Semantics/resolve-directives.cpp            | 2 +-
 3 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/flang/include/flang/Semantics/openmp-directive-sets.h b/flang/include/flang/Semantics/openmp-directive-sets.h
index 90ce28e450ea46..271f4c4697c6d2 100644
--- a/flang/include/flang/Semantics/openmp-directive-sets.h
+++ b/flang/include/flang/Semantics/openmp-directive-sets.h
@@ -186,9 +186,6 @@ static const OmpDirectiveSet allTeamsSet{
 // Directive sets for groups of multiple directives
 //===----------------------------------------------------------------------===//
 
-// Directive sets for parent directives that do allow/not allow a construct
-static const OmpDirectiveSet scanAllowedSet{allDoSet | allSimdSet};
-
 // Directive sets that form Composite constructs
 static const OmpDirectiveSet allDistributeParallelDoSet{
     allDistributeSet & allParallelSet & allDoSet};
@@ -289,6 +286,11 @@ static const OmpDirectiveSet workShareSet{
     } | allDoSet,
 };
 
+//===----------------------------------------------------------------------===//
+// Directive sets for parent directives that do allow/not allow a construct
+static const OmpDirectiveSet scanParentAllowedSet{allDoSet | allSimdSet};
+//===----------------------------------------------------------------------===//
+
 //===----------------------------------------------------------------------===//
 // Directive sets for allowed/not allowed nested directives
 //===----------------------------------------------------------------------===//
diff --git a/flang/lib/Semantics/check-omp-structure.cpp b/flang/lib/Semantics/check-omp-structure.cpp
index f130b35a8359b2..d8c37f8df37b49 100644
--- a/flang/lib/Semantics/check-omp-structure.cpp
+++ b/flang/lib/Semantics/check-omp-structure.cpp
@@ -2537,7 +2537,7 @@ void OmpStructureChecker::CheckReductionModifier(
     // or "simd" directive.
     // The worksharing-loop directives are OMPD_do and OMPD_for. Only the
     // former is allowed in Fortran.
-    if (!llvm::omp::scanAllowedSet.test(dirCtx.directive)) {
+    if (!llvm::omp::scanParentAllowedSet.test(dirCtx.directive)) {
       context_.Say(GetContext().clauseSource,
           "Modifier 'INSCAN' on REDUCTION clause is only allowed with "
           "worksharing-loop, worksharing-loop simd, "
diff --git a/flang/lib/Semantics/resolve-directives.cpp b/flang/lib/Semantics/resolve-directives.cpp
index 12abf3ecc2c0b8..c669bba9a40e24 100644
--- a/flang/lib/Semantics/resolve-directives.cpp
+++ b/flang/lib/Semantics/resolve-directives.cpp
@@ -1611,7 +1611,7 @@ bool OmpAttributeVisitor::Pre(
           "Exactly one of `exclusive` or `inclusive` clause is expected"_err_en_US);
     }
     if (!parentContext ||
-        !llvm::omp::scanAllowedSet.test(parentContext->directive)) {
+        !llvm::omp::scanParentAllowedSet.test(parentContext->directive)) {
       context_.Say(standaloneDir.source,
           "Orphaned `omp scan` directives are prohibited; perhaps you forgot "
           "to enclose the directive in to a worksharing loop, a worksharing "

>From d71e947022f3bcbdbce36fa8c145501054b9cc52 Mon Sep 17 00:00:00 2001
From: Anchu Rajendran <asudhaku at amd.com>
Date: Mon, 9 Sep 2024 13:25:58 -0500
Subject: [PATCH 6/6] R6: Reworked to add a few more semantic checks and moved
 checks to check-omp-structure

---
 .../lib/Semantics/check-directive-structure.h |   4 +
 flang/lib/Semantics/check-omp-structure.cpp   | 148 ++++++++++++++++--
 flang/lib/Semantics/check-omp-structure.h     |   7 +-
 flang/lib/Semantics/resolve-directives.cpp    |  14 --
 .../Lower/OpenMP/Todo/reduction-modifiers.f90 |   1 +
 .../Semantics/OpenMP/reduction-modifiers.f90  |   3 +
 flang/test/Semantics/OpenMP/scan.f90          |  14 +-
 7 files changed, 156 insertions(+), 35 deletions(-)

diff --git a/flang/lib/Semantics/check-directive-structure.h b/flang/lib/Semantics/check-directive-structure.h
index b32c10b0f3330b..9e16d4af832ae6 100644
--- a/flang/lib/Semantics/check-directive-structure.h
+++ b/flang/lib/Semantics/check-directive-structure.h
@@ -198,6 +198,10 @@ class DirectiveStructureChecker : public virtual BaseChecker {
     ClauseMapTy clauseInfo;
     std::list<C> actualClauses;
     std::list<C> crtGroup;
+    std::set<std::string> usedInScanDirective;
+
+    using ReductionModifier = parser::OmpReductionClause::ReductionModifier;
+    std::map<const std::string, ReductionModifier> reductionMod;
     Symbol *loopIV{nullptr};
   };
 
diff --git a/flang/lib/Semantics/check-omp-structure.cpp b/flang/lib/Semantics/check-omp-structure.cpp
index d8c37f8df37b49..cf981d7beb42f8 100644
--- a/flang/lib/Semantics/check-omp-structure.cpp
+++ b/flang/lib/Semantics/check-omp-structure.cpp
@@ -759,7 +759,43 @@ void OmpStructureChecker::CheckDistLinear(
   }
 }
 
-void OmpStructureChecker::Leave(const parser::OpenMPLoopConstruct &) {
+void OmpStructureChecker::Leave(const parser::OpenMPLoopConstruct &x) {
+  const auto &beginLoopDir = std::get<parser::OmpBeginLoopDirective>(x.t);
+  const auto &clauseList{std::get<parser::OmpClauseList>(beginLoopDir.t)};
+  for (const auto &clause : clauseList.v) {
+    if (const auto *reductionClause{
+            std::get_if<parser::OmpClause::Reduction>(&clause.u)}) {
+      using ReductionModifier = parser::OmpReductionClause::ReductionModifier;
+      const auto &maybeModifier{
+          std::get<std::optional<ReductionModifier>>(reductionClause->v.t)};
+      if (maybeModifier && *maybeModifier == ReductionModifier::Inscan) {
+
+        const auto &objectList{
+            std::get<parser::OmpObjectList>(reductionClause->v.t)};
+        for (const auto &ompObj : objectList.v) {
+          common::visit(
+              common::visitors{
+                  [&](const parser::Designator &designator) {
+                    if (const auto *name{semantics::getDesignatorNameIfDataRef(
+                            designator)}) {
+                      std::string nameStr = name->symbol->name().ToString();
+                      if (GetContext().usedInScanDirective.find(nameStr) ==
+                          GetContext().usedInScanDirective.end()) {
+                        context_.Say(name->source,
+                            "List item %s must appear in 'inclusive' or "
+                            "'exclusive' clause of an "
+                            "enclosed scan directive"_err_en_US,
+                            nameStr);
+                      }
+                    }
+                  },
+                  [&](const auto &name) {},
+              },
+              ompObj.u);
+        }
+      }
+    }
+  }
   if (llvm::omp::allSimdSet.test(GetContext().directive)) {
     ExitDirectiveNest(SIMDNest);
   }
@@ -1391,19 +1427,32 @@ void OmpStructureChecker::Leave(const parser::OpenMPAllocatorsConstruct &x) {
   dirContext_.pop_back();
 }
 
+void OmpStructureChecker::CheckScan(
+    const parser::OpenMPSimpleStandaloneConstruct &x) {
+  if (std::get<parser::OmpClauseList>(x.t).v.size() != 1) {
+    context_.Say(x.source,
+        "Exactly one of `exclusive` or `inclusive` clause is expected"_err_en_US);
+  }
+  if (!CurrentDirectiveIsNested() ||
+      !llvm::omp::scanParentAllowedSet.test(GetContextParent().directive)) {
+    context_.Say(x.source,
+        "Orphaned `omp scan` directives are prohibited; perhaps you forgot "
+        "to enclose the directive in to a worksharing loop, a worksharing "
+        "loop simd or a simd directive."_err_en_US);
+  }
+}
+
 void OmpStructureChecker::CheckBarrierNesting(
     const parser::OpenMPSimpleStandaloneConstruct &x) {
   // A barrier region may not be `closely nested` inside a worksharing, loop,
   // task, taskloop, critical, ordered, atomic, or master region.
   // TODO:  Expand the check to include `LOOP` construct as well when it is
   // supported.
-  if (GetContext().directive == llvm::omp::Directive::OMPD_barrier) {
-    if (IsCloselyNestedRegion(llvm::omp::nestedBarrierErrSet)) {
-      context_.Say(parser::FindSourceLocation(x),
-          "`BARRIER` region may not be closely nested inside of `WORKSHARING`, "
-          "`LOOP`, `TASK`, `TASKLOOP`,"
-          "`CRITICAL`, `ORDERED`, `ATOMIC` or `MASTER` region."_err_en_US);
-    }
+  if (IsCloselyNestedRegion(llvm::omp::nestedBarrierErrSet)) {
+    context_.Say(parser::FindSourceLocation(x),
+        "`BARRIER` region may not be closely nested inside of `WORKSHARING`, "
+        "`LOOP`, `TASK`, `TASKLOOP`,"
+        "`CRITICAL`, `ORDERED`, `ATOMIC` or `MASTER` region."_err_en_US);
   }
 }
 
@@ -1524,7 +1573,16 @@ void OmpStructureChecker::Enter(
     const parser::OpenMPSimpleStandaloneConstruct &x) {
   const auto &dir{std::get<parser::OmpSimpleStandaloneDirective>(x.t)};
   PushContextAndClauseSets(dir.source, dir.v);
-  CheckBarrierNesting(x);
+  switch (dir.v) {
+  case llvm::omp::Directive::OMPD_barrier:
+    CheckBarrierNesting(x);
+    break;
+  case llvm::omp::Directive::OMPD_scan:
+    CheckScan(x);
+    break;
+  default:
+    break;
+  }
 }
 
 void OmpStructureChecker::Leave(
@@ -2241,7 +2299,6 @@ CHECK_SIMPLE_CLAUSE(Destroy, OMPC_destroy)
 CHECK_SIMPLE_CLAUSE(Detach, OMPC_detach)
 CHECK_SIMPLE_CLAUSE(DeviceType, OMPC_device_type)
 CHECK_SIMPLE_CLAUSE(DistSchedule, OMPC_dist_schedule)
-CHECK_SIMPLE_CLAUSE(Exclusive, OMPC_exclusive)
 CHECK_SIMPLE_CLAUSE(Final, OMPC_final)
 CHECK_SIMPLE_CLAUSE(Flush, OMPC_flush)
 CHECK_SIMPLE_CLAUSE(From, OMPC_from)
@@ -2249,7 +2306,6 @@ CHECK_SIMPLE_CLAUSE(Full, OMPC_full)
 CHECK_SIMPLE_CLAUSE(Hint, OMPC_hint)
 CHECK_SIMPLE_CLAUSE(Holds, OMPC_holds)
 CHECK_SIMPLE_CLAUSE(InReduction, OMPC_in_reduction)
-CHECK_SIMPLE_CLAUSE(Inclusive, OMPC_inclusive)
 CHECK_SIMPLE_CLAUSE(Match, OMPC_match)
 CHECK_SIMPLE_CLAUSE(Nontemporal, OMPC_nontemporal)
 CHECK_SIMPLE_CLAUSE(Order, OMPC_order)
@@ -2322,7 +2378,24 @@ void OmpStructureChecker::Enter(const parser::OmpClause::Reduction &x) {
   if (CheckReductionOperators(x)) {
     CheckReductionTypeList(x);
   }
-  CheckReductionModifier(x);
+  using ReductionModifier = parser::OmpReductionClause::ReductionModifier;
+  if (const auto &maybeModifier{
+          std::get<std::optional<ReductionModifier>>(x.v.t)}) {
+    ReductionModifier modifier{*maybeModifier};
+    const auto &ompObjectList{std::get<parser::OmpObjectList>(x.v.t)};
+    addModifiertoMap(ompObjectList, modifier);
+    CheckReductionModifier(modifier);
+  }
+}
+
+void OmpStructureChecker::Enter(const parser::OmpClause::Inclusive &x) {
+  CheckAllowed(llvm::omp::Clause::OMPC_inclusive);
+  checkAndAddSymbolsToUsedInScanList(x.v);
+}
+
+void OmpStructureChecker::Enter(const parser::OmpClause::Exclusive &x) {
+  CheckAllowed(llvm::omp::Clause::OMPC_exclusive);
+  checkAndAddSymbolsToUsedInScanList(x.v);
 }
 
 bool OmpStructureChecker::CheckReductionOperators(
@@ -2365,6 +2438,49 @@ bool OmpStructureChecker::CheckReductionOperators(
 
   return ok;
 }
+
+void OmpStructureChecker::addModifiertoMap(const parser::OmpObjectList &x,
+    parser::OmpReductionClause::ReductionModifier &modifier) {
+  for (const auto &ompObject : x.v) {
+    if (const auto *name{parser::Unwrap<parser::Name>(ompObject)}) {
+      if (const auto *symbol{name->symbol}) {
+        GetContext().reductionMod[symbol->name().ToString()] = modifier;
+      }
+    }
+  }
+}
+
+void OmpStructureChecker::checkAndAddSymbolsToUsedInScanList(
+    const parser::OmpObjectList &x) {
+  for (const auto &ompObj : x.v) {
+    common::visit(
+        common::visitors{
+            [&](const parser::Designator &designator) {
+              if (const auto *name{
+                      semantics::getDesignatorNameIfDataRef(designator)}) {
+                if (name->symbol) {
+                  if (CurrentDirectiveIsNested()) {
+                    std::string nameStr = name->symbol->name().ToString();
+                    if (GetContextParent().reductionMod.find(nameStr) ==
+                        GetContextParent().reductionMod.end()) {
+
+                      context_.Say(name->source,
+                          "List item %s must appear in 'reduction' clause "
+                          "with the 'inscan' modifier of the parent "
+                          "directive"_err_en_US,
+                          nameStr);
+                    }
+                    GetContextParent().usedInScanDirective.insert(nameStr);
+                  }
+                }
+              }
+            },
+            [&](const auto &name) {},
+        },
+        ompObj.u);
+  }
+}
+
 bool OmpStructureChecker::CheckIntrinsicOperator(
     const parser::DefinedOperator::IntrinsicOperator &op) {
 
@@ -2499,14 +2615,12 @@ void OmpStructureChecker::CheckReductionTypeList(
 }
 
 void OmpStructureChecker::CheckReductionModifier(
-    const parser::OmpClause::Reduction &x) {
+    const parser::OmpReductionClause::ReductionModifier &modifier) {
   using ReductionModifier = parser::OmpReductionClause::ReductionModifier;
-  const auto &maybeModifier{std::get<std::optional<ReductionModifier>>(x.v.t)};
-  if (!maybeModifier || *maybeModifier == ReductionModifier::Default) {
-    // No modifier, or the default one is always ok.
+  if (modifier == ReductionModifier::Default) {
+    // the default one is always ok.
     return;
   }
-  ReductionModifier modifier{*maybeModifier};
   const DirectiveContext &dirCtx{GetContext()};
   if (dirCtx.directive == llvm::omp::Directive::OMPD_loop) {
     // [5.2:257:33-34]
diff --git a/flang/lib/Semantics/check-omp-structure.h b/flang/lib/Semantics/check-omp-structure.h
index 2cc1a78068f540..4319623f8ce0e6 100644
--- a/flang/lib/Semantics/check-omp-structure.h
+++ b/flang/lib/Semantics/check-omp-structure.h
@@ -205,10 +205,12 @@ class OmpStructureChecker
   bool CheckIntrinsicOperator(
       const parser::DefinedOperator::IntrinsicOperator &);
   void CheckReductionTypeList(const parser::OmpClause::Reduction &);
-  void CheckReductionModifier(const parser::OmpClause::Reduction &);
+  void CheckReductionModifier(
+      const parser::OmpReductionClause::ReductionModifier &);
   void CheckMasterNesting(const parser::OpenMPBlockConstruct &x);
   void ChecksOnOrderedAsBlock();
   void CheckBarrierNesting(const parser::OpenMPSimpleStandaloneConstruct &x);
+  void CheckScan(const parser::OpenMPSimpleStandaloneConstruct &x);
   void ChecksOnOrderedAsStandalone();
   void CheckOrderedDependClause(std::optional<std::int64_t> orderedValue);
   void CheckReductionArraySection(const parser::OmpObjectList &ompObjectList);
@@ -223,6 +225,9 @@ class OmpStructureChecker
       const parser::OmpObjectList &ompObjectList);
   void CheckPredefinedAllocatorRestriction(
       const parser::CharBlock &source, const parser::Name &name);
+  void checkAndAddSymbolsToUsedInScanList(const parser::OmpObjectList &x);
+  void addModifiertoMap(const parser::OmpObjectList &x,
+      parser::OmpReductionClause::ReductionModifier &modifier);
   bool isPredefinedAllocator{false};
 
   void CheckAllowedRequiresClause(llvmOmpClause clause);
diff --git a/flang/lib/Semantics/resolve-directives.cpp b/flang/lib/Semantics/resolve-directives.cpp
index c669bba9a40e24..5cc570d579b6af 100644
--- a/flang/lib/Semantics/resolve-directives.cpp
+++ b/flang/lib/Semantics/resolve-directives.cpp
@@ -1590,7 +1590,6 @@ bool OmpAttributeVisitor::Pre(
     const parser::OpenMPSimpleStandaloneConstruct &x) {
   const auto &standaloneDir{
       std::get<parser::OmpSimpleStandaloneDirective>(x.t)};
-  const auto &parentContext{GetContextIf()};
   switch (standaloneDir.v) {
   case llvm::omp::Directive::OMPD_barrier:
   case llvm::omp::Directive::OMPD_ordered:
@@ -1605,19 +1604,6 @@ bool OmpAttributeVisitor::Pre(
   default:
     break;
   }
-  if (standaloneDir.v == llvm::omp::Directive::OMPD_scan) {
-    if (std::get<parser::OmpClauseList>(x.t).v.size() != 1) {
-      context_.Say(standaloneDir.source,
-          "Exactly one of `exclusive` or `inclusive` clause is expected"_err_en_US);
-    }
-    if (!parentContext ||
-        !llvm::omp::scanParentAllowedSet.test(parentContext->directive)) {
-      context_.Say(standaloneDir.source,
-          "Orphaned `omp scan` directives are prohibited; perhaps you forgot "
-          "to enclose the directive in to a worksharing loop, a worksharing "
-          "loop simd or a simd directive."_err_en_US);
-    }
-  }
   ClearDataSharingAttributeObjects();
   return true;
 }
diff --git a/flang/test/Lower/OpenMP/Todo/reduction-modifiers.f90 b/flang/test/Lower/OpenMP/Todo/reduction-modifiers.f90
index 5e566466492ceb..82625ed8c5f31c 100644
--- a/flang/test/Lower/OpenMP/Todo/reduction-modifiers.f90
+++ b/flang/test/Lower/OpenMP/Todo/reduction-modifiers.f90
@@ -8,6 +8,7 @@ subroutine foo()
   j = 0
   !$omp do reduction (inscan, *: j)
   do i = 1, 10
+    !$omp scan inclusive(j)
     j = j + 1
   end do
 end subroutine
diff --git a/flang/test/Semantics/OpenMP/reduction-modifiers.f90 b/flang/test/Semantics/OpenMP/reduction-modifiers.f90
index cf38200ba0a83e..31d21e9d4189cb 100644
--- a/flang/test/Semantics/OpenMP/reduction-modifiers.f90
+++ b/flang/test/Semantics/OpenMP/reduction-modifiers.f90
@@ -39,6 +39,7 @@ subroutine mod_inscan1(x)
   !Correct: worksharing-loop directive
   !$omp do reduction(inscan, +:x)
   do i = 1, 100
+    !$omp scan inclusive(x)
     x = foo(i)
   enddo
   !$omp end do
@@ -50,6 +51,7 @@ subroutine mod_inscan2(x)
   !Correct: worksharing-loop simd directive
   !$omp do simd reduction(inscan, +:x)
   do i = 1, 100
+    !$omp scan inclusive(x)
     x = foo(i)
   enddo
   !$omp end do simd
@@ -61,6 +63,7 @@ subroutine mod_inscan3(x)
   !Correct: "simd" directive
   !$omp simd reduction(inscan, +:x)
   do i = 1, 100
+    !$omp scan inclusive(x)
     x = foo(i)
   enddo
   !$omp end simd
diff --git a/flang/test/Semantics/OpenMP/scan.f90 b/flang/test/Semantics/OpenMP/scan.f90
index e82982f60b9021..c7526d31df4acb 100644
--- a/flang/test/Semantics/OpenMP/scan.f90
+++ b/flang/test/Semantics/OpenMP/scan.f90
@@ -1,17 +1,17 @@
 ! RUN: %python %S/../test_errors.py %s %flang_fc1 -fopenmp
 
 subroutine test_scan()
- integer x, y, k
+ integer x, y, k, z
  
  !ERROR: Orphaned `omp scan` directives are prohibited; perhaps you forgot to enclose the directive in to a worksharing loop, a worksharing loop simd or a simd directive.
  !$omp scan inclusive(x)
- !$omp parallel do simd reduction(inscan,+: x)
+ !$omp parallel do simd
  do k = 1, n
  !ERROR: UNTIED clause is not allowed on the SCAN directive
    !$omp scan untied
  end do
  
- !$omp parallel do simd reduction(inscan,+: x)
+ !$omp parallel do simd
  do k = 1, n
  !ERROR: Exactly one of `exclusive` or `inclusive` clause is expected
    !$omp scan
@@ -22,4 +22,12 @@ subroutine test_scan()
  !ERROR: Exactly one of `exclusive` or `inclusive` clause is expected
    !$omp scan inclusive(x) exclusive(y)
  end do
+
+!ERROR: List item y must appear in 'inclusive' or 'exclusive' clause of an enclosed scan directive
+!$omp parallel do simd reduction(inscan,+: x, y)
+ do k = 1, n
+ !ERROR: Exactly one of `exclusive` or `inclusive` clause is expected
+ !ERROR: List item z must appear in 'reduction' clause with the 'inscan' modifier of the parent directive
+   !$omp scan inclusive(x) exclusive(z)
+ end do
 end subroutine



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