[flang-commits] [flang] [flang][OpenMP] Don't allow namelist variables with threadprivate (PR #130957)

[Tom Eccles via flang-commits]

https://github.com/tblah created https://github.com/llvm/llvm-project/pull/130957

While the standard doesn't explicitly mention namelist variables in this case, it does prohibit privatization of namelist variables. Flang decided to also prohibit namelist variables from appearing in a reduction clause.

Variables that are part of a namelist are linked to I/O mechanisms, and their memory association and initialization are managed by the compiler in a way that conflicts with the requirements of threadprivate variables. I propose we should add this restriction.

Fixes #112538

>From 0800f124ee4e2cc8a71bc2f325c5ccf341d6c15e Mon Sep 17 00:00:00 2001
From: Tom Eccles <tom.eccles at arm.com>
Date: Wed, 12 Mar 2025 13:01:59 +0000
Subject: [PATCH] [flang][OpenMP] Don't allow namelist variables with
 threadprivate

While the standard doesn't explicitly mention namelist variables in this
case, it does prohibit privatization of namelist variables. Flang
decided to also prohibit namelist variables from appearing in a
reduction clause.

Variables that are part of a namelist are linked to I/O mechanisms, and
their memory association and initialization are managed by the compiler
in a way that conflicts with the requirements of threadprivate
variables. I propose we should add this restriction.
---
 flang/lib/Semantics/check-omp-structure.cpp     |  9 +++++++++
 flang/test/Semantics/OpenMP/threadprivate09.f90 | 12 ++++++++++++
 2 files changed, 21 insertions(+)
 create mode 100644 flang/test/Semantics/OpenMP/threadprivate09.f90

diff --git a/flang/lib/Semantics/check-omp-structure.cpp b/flang/lib/Semantics/check-omp-structure.cpp
index 5fcebdca0bc5f..e98c9c3091cb4 100644
--- a/flang/lib/Semantics/check-omp-structure.cpp
+++ b/flang/lib/Semantics/check-omp-structure.cpp
@@ -1516,6 +1516,10 @@ void OmpStructureChecker::CheckThreadprivateOrDeclareTargetVar(
                       "A variable in a %s directive cannot appear in an "
                       "EQUIVALENCE statement"_err_en_US,
                       ContextDirectiveAsFortran());
+                } else if (name->symbol->test(Symbol::Flag::InNamelist)) {
+                  context_.Say(name->source,
+                      "A variable in a %s directive cannot appear in a NAMELIST"_err_en_US,
+                      ContextDirectiveAsFortran());
                 } else if (name->symbol->test(Symbol::Flag::OmpThreadprivate) &&
                     GetContext().directive ==
                         llvm::omp::Directive::OMPD_declare_target) {
@@ -1571,6 +1575,11 @@ void OmpStructureChecker::CheckThreadprivateOrDeclareTargetVar(
                           ContextDirectiveAsFortran(), obj->name(),
                           name.symbol->name());
                     }
+                    if (obj->test(Symbol::Flag::InNamelist)) {
+                      context_.Say(name.source,
+                          "A variable in a %s directive cannot appear in a NAMELIST"_err_en_US,
+                          ContextDirectiveAsFortran());
+                    }
                   }
                 }
               }
diff --git a/flang/test/Semantics/OpenMP/threadprivate09.f90 b/flang/test/Semantics/OpenMP/threadprivate09.f90
new file mode 100644
index 0000000000000..02236d19d9d01
--- /dev/null
+++ b/flang/test/Semantics/OpenMP/threadprivate09.f90
@@ -0,0 +1,12 @@
+! RUN: %python %S/../test_errors.py %s %flang_fc1 %openmp_flags
+
+! Check that namelist variables cannot be used with threadprivate
+
+module m
+  integer :: nam1
+  common /com1/nam1
+  namelist /nam/nam1
+
+  !ERROR: A variable in a THREADPRIVATE directive cannot appear in a NAMELIST
+  !$omp threadprivate(/com1/)
+end