[flang-commits] [flang] [Flang][OpenMP] Add diagnosing zero-length depend array sections and … (PR #224168)

[via flang-commits]

https://github.com/laoshd created https://github.com/llvm/llvm-project/pull/224168

…tests.

This PR is to fix #222551.

>From 199759139eddadc95c6ee75228456836cff369a7 Mon Sep 17 00:00:00 2001
From: Shandong Lao <shandong.lao at hpe.com>
Date: Wed, 16 Sep 2026 13:39:10 -0500
Subject: [PATCH] [Flang][OpenMP] Add diagnosing zero-length depend array
 sections and tests.

---
 flang/lib/Semantics/check-omp-structure.cpp | 52 ++++++++++++---------
 flang/test/Semantics/OpenMP/depend01.f90    | 30 ++++++++++--
 2 files changed, 58 insertions(+), 24 deletions(-)

diff --git a/flang/lib/Semantics/check-omp-structure.cpp b/flang/lib/Semantics/check-omp-structure.cpp
index 274efa64d03d0..372634c022ff6 100644
--- a/flang/lib/Semantics/check-omp-structure.cpp
+++ b/flang/lib/Semantics/check-omp-structure.cpp
@@ -6025,7 +6025,9 @@ void OmpStructureChecker::CheckArraySection(
     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) {
           std::optional<int64_t> strideVal{std::nullopt};
           if (const auto &strideExpr = std::get<2>(triplet->t)) {
             // OpenMP 6.0 Section 5.2.5: Array Sections
@@ -6042,28 +6044,36 @@ void OmpStructureChecker::CheckArraySection(
                   "Cannot specify a step for a substring"_err_en_US);
             }
           }
-          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) {
-              int64_t sectionLen = *uval - *lval;
-              if (strideVal) {
-                if (*strideVal == 0) {
-                  continue;
-                }
-                sectionLen = sectionLen / *strideVal;
+          const auto lval{GetIntValue(lower)};
+          const auto uval{GetIntValue(upper)};
+          if (lval && uval) {
+            int64_t sectionLen = *uval - *lval;
+            if (strideVal) {
+              if (*strideVal == 0) {
+                continue;
               }
+              sectionLen = sectionLen / *strideVal;
+            }
 
-              if (sectionLen < 1) {
-                context_.Say(GetContext().clauseSource,
-                    "'%s' in %s clause"
-                    " is a zero size array section"_err_en_US,
-                    name.ToString(),
-                    parser::omp::GetUpperName(clause, version));
-                break;
-              }
+            if (sectionLen < 1) {
+              context_.Say(GetContext().clauseSource,
+                  "'%s' in %s clause"
+                  " is a zero size array section"_err_en_US,
+                  name.ToString(), parser::omp::GetUpperName(clause, version));
+              break;
+            }
+          }
+        } else if (clause == llvm::omp::Clause::OMPC_depend) {
+          if (auto extents{
+                  evaluate::AsConstantExtents(context_.foldingContext(),
+                      evaluate::GetShape(
+                          context_.foldingContext(), *name.symbol))}) {
+            if (llvm::is_contained(*extents, 0)) {
+              context_.Say(GetContext().clauseSource,
+                  "'%s' in %s clause"
+                  " is a zero size array section"_err_en_US,
+                  name.ToString(), parser::omp::GetUpperName(clause, version));
+              break;
             }
           }
         }
diff --git a/flang/test/Semantics/OpenMP/depend01.f90 b/flang/test/Semantics/OpenMP/depend01.f90
index 2b23cc1c4f68c..37eb971cd90ab 100644
--- a/flang/test/Semantics/OpenMP/depend01.f90
+++ b/flang/test/Semantics/OpenMP/depend01.f90
@@ -1,10 +1,11 @@
-! RUN: %python %S/../test_errors.py %s %flang -fopenmp
-! OpenMP Version 4.5
-! 2.13.9 Depend Clause
+! RUN: %python %S/../test_errors.py %s %flang -fopenmp -fopenmp-version=50
+! OpenMP Version 5.0
+! 2.17.11 Depend Clause
 ! List items used in depend clauses cannot be zero-length array sections.
 
 program omp_depend
   integer :: a(10) , b(10,10)
+  integer :: x(0)
   a = 10
   b = 20
 
@@ -35,6 +36,29 @@ program omp_depend
   print *, a(1:10)
   !$omp end task
 
+  !$omp task depend(in: a(:))
+  !$omp end task
+
+  !ERROR: 'x' in DEPEND clause is a zero size array section
+  !$omp task depend(in: x(:))
+  !$omp end task
+
+  !ERROR: 'x' in DEPEND clause is a zero size array section
+  !$omp task depend(out: x(:))
+  !$omp end task
+
+  !ERROR: 'x' in DEPEND clause is a zero size array section
+  !$omp task depend(inout: x(:))
+  !$omp end task
+
+  !ERROR: 'x' in DEPEND clause is a zero size array section
+  !$omp task depend(mutexinoutset: x(:))
+  !$omp end task
+
+  !ERROR: 'x' in DEPEND clause is a zero size array section
+  !$omp task depend(depobj: x(:))
+  !$omp end task
+
   !$omp end single
   !$omp end parallel