[flang-commits] [flang] [flang][OpenMP][Semantics] resolve objects in the flush arg list (PR #139522)

[Tom Eccles via flang-commits]

https://github.com/tblah created https://github.com/llvm/llvm-project/pull/139522

Fixes #136583

Normally the flush argument list would contain a DataRef to some variable. All DataRefs are handled generically in resolve-names and so the problem wasn't observed. But when a common block name is specified, this is not parsed as a DataRef. There was already handling in resolve-directives for OmpObjectList but not for argument lists. I've added a visitor for FLUSH which ensures all of the arguments have been resolved.

The test is there to make sure the compiler doesn't crashed encountering the unresolved symbol. It shows that we currently deny flushing a common block. I'm not sure that it is right to restrict common blocks from flush argument lists, but fixing that can come in a different patch. This one is fixing an ICE.

>From a64751019f3eab8a7d6d678ad76fdb8c31b86e54 Mon Sep 17 00:00:00 2001
From: Tom Eccles <tom.eccles at arm.com>
Date: Mon, 12 May 2025 09:38:01 +0000
Subject: [PATCH] [flang][OpenMP][Semantics] resolve objects in the flush arg
 list

Fixes #136583

Normally the flush argument list would contain a DataRef to some
variable. All DataRefs are handled generically in resolve-names and so
the problem wasn't observed. But when a common block name is specified,
this is not parsed as a DataRef. There was already handling in
resolve-directives for OmpObjectList but not for argument lists. I've
added a visitor for FLUSH which ensures all of the arguments have been
resolved.

The test is there to make sure the compiler doesn't crashed encountering
the unresolved symbol. It shows that we currently deny flushing a common
block. I'm not sure that it is right to restrict common blocks from flush
argument lists, but fixing that can come in a different patch. This one
is fixing an ICE.
---
 flang/lib/Semantics/resolve-directives.cpp | 13 +++++++++++++
 flang/test/Semantics/OpenMP/flush04.f90    | 11 +++++++++++
 2 files changed, 24 insertions(+)
 create mode 100644 flang/test/Semantics/OpenMP/flush04.f90

diff --git a/flang/lib/Semantics/resolve-directives.cpp b/flang/lib/Semantics/resolve-directives.cpp
index 8b1caca34a6a7..68f8cf9f17620 100644
--- a/flang/lib/Semantics/resolve-directives.cpp
+++ b/flang/lib/Semantics/resolve-directives.cpp
@@ -409,6 +409,19 @@ class OmpAttributeVisitor : DirectiveAttributeVisitor<llvm::omp::Directive> {
   }
   void Post(const parser::OpenMPDepobjConstruct &) { PopContext(); }
 
+  bool Pre(const parser::OpenMPFlushConstruct &x) {
+    PushContext(x.source, llvm::omp::Directive::OMPD_flush);
+    for (auto &arg : x.v.Arguments().v) {
+      if (auto *locator{std::get_if<parser::OmpLocator>(&arg.u)}) {
+        if (auto *object{std::get_if<parser::OmpObject>(&locator->u)}) {
+          ResolveOmpObject(*object, Symbol::Flag::OmpDependObject);
+        }
+      }
+    }
+    return true;
+  }
+  void Post(const parser::OpenMPFlushConstruct &) { PopContext(); }
+
   bool Pre(const parser::OpenMPRequiresConstruct &x) {
     using Flags = WithOmpDeclarative::RequiresFlags;
     using Requires = WithOmpDeclarative::RequiresFlag;
diff --git a/flang/test/Semantics/OpenMP/flush04.f90 b/flang/test/Semantics/OpenMP/flush04.f90
new file mode 100644
index 0000000000000..ffc2273b692dc
--- /dev/null
+++ b/flang/test/Semantics/OpenMP/flush04.f90
@@ -0,0 +1,11 @@
+! RUN: %python %S/../test_errors.py %s %flang_fc1 -fopenmp
+
+! Regression test to ensure that the name /c/ in the flush argument list is
+! resolved to the common block symbol.
+
+  common /c/ x
+  real :: x
+!ERROR: FLUSH argument must be a variable list item
+  !$omp flush(/c/)
+end
+