[flang-commits] [flang] [Flang][OpenMP] Added diagnostic for ORDERED THREADS SIMD inside plain SIMD region (PR #205723)

[Urvi Rav via flang-commits]

https://github.com/ravurvi20 updated https://github.com/llvm/llvm-project/pull/205723

>From b2992683d4fd433aab202a09199f05240477d49b Mon Sep 17 00:00:00 2001
From: Urvi Rav <urvi.rav20 at gmail.com>
Date: Thu, 25 Jun 2026 00:14:55 -0500
Subject: [PATCH 1/2] Added diagnostic for ORDERED THREADS SIMD inside plain
 SIMD region

---
 flang/lib/Semantics/check-omp-structure.cpp |  7 +++++++
 flang/test/Semantics/OpenMP/ordered02.f90   | 19 +++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/flang/lib/Semantics/check-omp-structure.cpp b/flang/lib/Semantics/check-omp-structure.cpp
index d87b2f1983de6..ea7027d55953e 100644
--- a/flang/lib/Semantics/check-omp-structure.cpp
+++ b/flang/lib/Semantics/check-omp-structure.cpp
@@ -1486,6 +1486,13 @@ void OmpStructureChecker::ChecksOnOrderedAsBlock() {
       context_.Say(GetContext().directiveSource,
           "An ORDERED directive with SIMD clause must be closely nested in a "
           "SIMD or worksharing-loop SIMD region"_err_en_US);
+    } else if (CurrentDirectiveIsNested() &&
+        FindClause(llvm::omp::Clause::OMPC_simd) &&
+        FindClause(llvm::omp::Clause::OMPC_threads) && isNestedInSIMD &&
+        !isNestedInDoSIMD) {
+      context_.Say(GetContext().directiveSource,
+          "An ORDERED directive with SIMD and THREADS clauses must be closely "
+          "nested in a worksharing-loop SIMD region"_err_en_US);
     }
     if (isNestedInDo && (noOrderedClause || isOrderedClauseWithPara)) {
       context_.Say(GetContext().directiveSource,
diff --git a/flang/test/Semantics/OpenMP/ordered02.f90 b/flang/test/Semantics/OpenMP/ordered02.f90
index ed320c82a9794..ad3e2b3428115 100644
--- a/flang/test/Semantics/OpenMP/ordered02.f90
+++ b/flang/test/Semantics/OpenMP/ordered02.f90
@@ -143,4 +143,23 @@ subroutine sub1()
     !$omp end ordered
   end do
   !$omp end target parallel do
+
+  ! THREADS+SIMD inside a plain SIMD (not DO SIMD) region must be rejected
+  !$omp simd
+  do i = 1, N
+    !ERROR: An ORDERED directive with SIMD and THREADS clauses must be closely nested in a worksharing-loop SIMD region
+    !$omp ordered threads simd
+    arrayA(i) = foo(i)
+    !$omp end ordered
+  end do
+  !$omp end simd
+
+  ! THREADS+SIMD inside a DO SIMD region is valid
+  !$omp do simd ordered
+  do i = 1, N
+    !$omp ordered threads simd
+    arrayA(i) = foo(i)
+    !$omp end ordered
+  end do
+  !$omp end do simd
 end

>From 2194a05764a56121972f514c0cd5bd59cdb4eb46 Mon Sep 17 00:00:00 2001
From: Urvi Rav <urvi.rav20 at gmail.com>
Date: Thu, 9 Jul 2026 04:31:00 -0500
Subject: [PATCH 2/2] Addressed comment-added regression test

---
 flang/test/Semantics/OpenMP/ordered02.f90 | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/flang/test/Semantics/OpenMP/ordered02.f90 b/flang/test/Semantics/OpenMP/ordered02.f90
index ad3e2b3428115..649e008f7cb54 100644
--- a/flang/test/Semantics/OpenMP/ordered02.f90
+++ b/flang/test/Semantics/OpenMP/ordered02.f90
@@ -163,3 +163,20 @@ subroutine sub1()
   end do
   !$omp end do simd
 end
+
+! No diagnostic when ORDERED THREADS SIMD is in a called routine (enclosing
+! DO SIMD region is not visible to the static checker).
+subroutine contains_ordered_threads_simd()
+  !$omp ordered threads simd
+  !$omp end ordered
+end subroutine
+
+subroutine sub2()
+  integer :: i, N = 10
+  external :: contains_ordered_threads_simd
+  !$omp do simd ordered
+  do i = 1, N
+    call contains_ordered_threads_simd()
+  end do
+  !$omp end do simd
+end subroutine