[flang-commits] [flang] [flang][OpenMP] Don't allow DO CONCURRENT inside of a loop nest (PR #144506)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-flang-openmp

Author: Tom Eccles (tblah)

<details>
<summary>Changes</summary>

I don't think DO CONCURRENT fits the definition of a Canonical Loop Nest (OpenMP 6.0 section 6.4.1).

Fixes #<!-- -->144178

---
Full diff: https://github.com/llvm/llvm-project/pull/144506.diff


2 Files Affected:

- (modified) flang/lib/Semantics/resolve-directives.cpp (+7) 
- (added) flang/test/Semantics/OpenMP/do-concurrent-collapse.f90 (+19) 


``````````diff
diff --git a/flang/lib/Semantics/resolve-directives.cpp b/flang/lib/Semantics/resolve-directives.cpp
index b5f8667fe36f2..05568cc0ba0ae 100644
--- a/flang/lib/Semantics/resolve-directives.cpp
+++ b/flang/lib/Semantics/resolve-directives.cpp
@@ -1952,6 +1952,13 @@ void OmpAttributeVisitor::PrivatizeAssociatedLoopIndexAndCheckLoopLevel(
   const auto &outer{std::get<std::optional<parser::DoConstruct>>(x.t)};
   if (outer.has_value()) {
     for (const parser::DoConstruct *loop{&*outer}; loop && level > 0; --level) {
+      // DO CONCURRENT is allowed for loop constructs but not loop nests
+      if (loop->IsDoConcurrent() && GetContext().associatedLoopLevel != 1) {
+        auto &stmt =
+            std::get<parser::Statement<parser::NonLabelDoStmt>>(loop->t);
+        context_.Say(stmt.source,
+            "DO CONCURRENT loops cannot form part of a loop nest."_err_en_US);
+      }
       // go through all the nested do-loops and resolve index variables
       const parser::Name *iv{GetLoopIndex(*loop)};
       if (iv) {
diff --git a/flang/test/Semantics/OpenMP/do-concurrent-collapse.f90 b/flang/test/Semantics/OpenMP/do-concurrent-collapse.f90
new file mode 100644
index 0000000000000..71e1928e1f245
--- /dev/null
+++ b/flang/test/Semantics/OpenMP/do-concurrent-collapse.f90
@@ -0,0 +1,19 @@
+!RUN: %python %S/../test_errors.py %s %flang -fopenmp
+
+integer :: i, j
+!$omp parallel do collapse(2)
+do i = 1, 1
+  ! ERROR: DO CONCURRENT loops cannot form part of a loop nest.
+  do concurrent (j = 1:2)
+    print *, j
+  end do
+end do
+
+!$omp parallel do
+do i = 1, 1
+  ! This should not lead to an error because it is not part of a loop nest:
+  do concurrent (j = 1:2)
+    print *, j
+  end do
+end do
+end

``````````

</details>


https://github.com/llvm/llvm-project/pull/144506