[flang-commits] [flang] [Flang][OpenMP] Reject array sections and subobjects in LINEAR clause (PR #197430)

[CHANDRA GHALE via flang-commits]

https://github.com/chandraghale created https://github.com/llvm/llvm-project/pull/197430

Array sections like a(:,1,1) and array elements like a(1) in a LINEAR clause cause a crash during MLIR-to-LLVM IR translation because the semantic checker doesn't catch them. 

This adds a call to CheckVarIsNotPartOfAnotherVar for the LINEAR clause, which is the same check used by PRIVATE and FIRSTPRIVATE to reject subobject designators.

Fixes : [https://github.com/llvm/llvm-project/issues/196068](https://github.com/llvm/llvm-project/issues/196068)

>From df212050d6da66a79601727c55ba5d06716132c6 Mon Sep 17 00:00:00 2001
From: Chandra Ghale <ghale at pe34genoa.hpc.amslabs.hpecorp.net>
Date: Wed, 13 May 2026 07:13:32 -0500
Subject: [PATCH] Reject array sections and subobjects in LINEAR clause

---
 flang/lib/Semantics/check-omp-loop.cpp        |  1 +
 .../OpenMP/linear-clause-array-section.f90    | 64 +++++++++++++++++++
 2 files changed, 65 insertions(+)
 create mode 100644 flang/test/Semantics/OpenMP/linear-clause-array-section.f90

diff --git a/flang/lib/Semantics/check-omp-loop.cpp b/flang/lib/Semantics/check-omp-loop.cpp
index 50fbcc20a98aa..1ef84feebfe55 100644
--- a/flang/lib/Semantics/check-omp-loop.cpp
+++ b/flang/lib/Semantics/check-omp-loop.cpp
@@ -722,6 +722,7 @@ void OmpStructureChecker::Enter(const parser::OmpClause::Linear &x) {
 
   SymbolSourceMap symbols;
   auto &objects{std::get<parser::OmpObjectList>(x.v.t)};
+  CheckVarIsNotPartOfAnotherVar(GetContext().clauseSource, objects, "LINEAR");
   CheckCrayPointee(objects, "LINEAR", false);
   GetSymbolsInObjectList(objects, symbols);
   CheckAssumedSizeArray(symbols, llvm::omp::Clause::OMPC_linear);
diff --git a/flang/test/Semantics/OpenMP/linear-clause-array-section.f90 b/flang/test/Semantics/OpenMP/linear-clause-array-section.f90
new file mode 100644
index 0000000000000..cdcf9df723334
--- /dev/null
+++ b/flang/test/Semantics/OpenMP/linear-clause-array-section.f90
@@ -0,0 +1,64 @@
+! RUN: %python %S/../test_errors.py %s %flang_fc1 %openmp_flags
+! Verify that array sections and array elements in LINEAR clause are rejected.
+! The LINEAR clause requires a scalar variable name (OpenMP 4.5 §2.15.3.7).
+
+subroutine test_array_section_in_linear()
+  implicit none
+  integer :: i
+  integer, dimension(0:99, -99:10, 200) :: a, b, c
+
+  !$omp parallel
+    !ERROR: A variable that is part of another variable (as an array or structure element) cannot appear in a LINEAR clause
+    !$omp do linear(a(:,1,1))
+    do i = 0, 99
+      c(i, 1, 1) = a(i, 1, 1) + b(i, 1, 1)
+    end do
+    !$omp end do
+  !$omp end parallel
+end subroutine
+
+subroutine test_array_element_in_linear()
+  implicit none
+  integer :: i
+  integer :: arr(10)
+
+  !$omp parallel
+    !ERROR: A variable that is part of another variable (as an array or structure element) cannot appear in a LINEAR clause
+    !$omp do linear(arr(1))
+    do i = 1, 10
+      arr(i) = i
+    end do
+    !$omp end do
+  !$omp end parallel
+end subroutine
+
+subroutine test_structure_component_in_linear()
+  implicit none
+  integer :: i
+  type :: my_type
+    integer :: field
+  end type
+  type(my_type) :: obj
+
+  !$omp parallel
+    !ERROR: A variable that is part of another variable (as an array or structure element) cannot appear in a LINEAR clause
+    !$omp do linear(obj%field)
+    do i = 1, 10
+    end do
+    !$omp end do
+  !$omp end parallel
+end subroutine
+
+subroutine test_valid_scalar_in_linear()
+  implicit none
+  integer :: i, j
+
+  !$omp parallel
+    !$omp do linear(j)
+    do i = 1, 10
+      j = i
+    end do
+    !$omp end do
+  !$omp end parallel
+end subroutine
+