[flang][OpenMP]: Allow orphaned distribute construct #163546

chandraghale · 2025-10-15T11:56:05Z

If there is a call inside a TEAMS construct, and that call contains a DISTRIBUTE construct, the DISTRIBUTE region is considered to be enclosed by the TEAMS region (based on the dynamic extent of the construct). Currently, Flang diagnoses this as an error, which is incorrect.
For eg :

 subroutine f
  !$omp distribute
  do i = 1, 100
    ...
  end do
end subroutine

subroutine g
  !$omp teams
  call f ! this call is ok, distribute enclosed by teams
  !$omp end teams
end subroutine

This patch adjusts the nesting check for the OpenMP DISTRIBUTE directive. It retains the error for DISTRIBUTE directives that are incorrectly nested lexically but downgrades it to a warning for orphaned directives to allow dynamic nesting, such as when a subroutine with DISTRIBUTE is called from within a TEAMS region.

llvmbot · 2025-10-15T11:56:38Z

@llvm/pr-subscribers-flang-openmp

@llvm/pr-subscribers-flang-semantics

Author: CHANDRA GHALE (chandraghale)

Changes

If there is a call inside a TEAMS construct, and that call contains a DISTRIBUTE construct, the DISTRIBUTE region is considered to be enclosed by the TEAMS region (based on the dynamic extent of the construct). Currently, Flang diagnoses this as an error, which is incorrect.
For eg :

 subroutine f
  !$omp distribute
  do i = 1, 100
    ...
  end do
end subroutine

subroutine g
  !$omp teams
  call f ! this call is ok, distribute enclosed by teams
  !$omp end teams
end subroutine

This patch adjusts the nesting check for the OpenMP DISTRIBUTE directive. It retains the error for DISTRIBUTE directives that are incorrectly nested lexically but downgrades it to a warning for orphaned directives to allow dynamic nesting, such as when a subroutine with DISTRIBUTE is called from within a TEAMS region.

Full diff: https://github.com/llvm/llvm-project/pull/163546.diff

5 Files Affected:

(modified) flang/lib/Semantics/check-omp-loop.cpp (+9-10)
(modified) flang/test/Semantics/OpenMP/combined-constructs.f90 (+1-1)
(modified) flang/test/Semantics/OpenMP/do05.f90 (+2-2)
(modified) flang/test/Semantics/OpenMP/linear-iter.f90 (+3-3)
(modified) flang/test/Semantics/OpenMP/nested-distribute.f90 (+13)

diff --git a/flang/lib/Semantics/check-omp-loop.cpp b/flang/lib/Semantics/check-omp-loop.cpp
index c9d0495850b6e..331397b035cf9 100644
--- a/flang/lib/Semantics/check-omp-loop.cpp
+++ b/flang/lib/Semantics/check-omp-loop.cpp
@@ -127,24 +127,23 @@ using namespace Fortran::semantics::omp;
 
 void OmpStructureChecker::HasInvalidDistributeNesting(
     const parser::OpenMPLoopConstruct &x) {
-  bool violation{false};
   const parser::OmpDirectiveName &beginName{x.BeginDir().DirName()};
   if (llvm::omp::topDistributeSet.test(beginName.v)) {
     // `distribute` region has to be nested
-    if (!CurrentDirectiveIsNested()) {
-      violation = true;
-    } else {
+    if (CurrentDirectiveIsNested()) {
       // `distribute` region has to be strictly nested inside `teams`
       if (!llvm::omp::bottomTeamsSet.test(GetContextParent().directive)) {
-        violation = true;
+        context_.Say(beginName.source,
+            "`DISTRIBUTE` region has to be strictly nested inside `TEAMS` "
+            "region."_err_en_US);
       }
+    } else {
+      // If not lexically nested (orphaned), issue a warning.
+      context_.Say(beginName.source,
+          "`DISTRIBUTE` must be dynamically enclosed in a `TEAMS` "
+          "region."_warn_en_US);
     }
   }
-  if (violation) {
-    context_.Say(beginName.source,
-        "`DISTRIBUTE` region has to be strictly nested inside `TEAMS` "
-        "region."_err_en_US);
-  }
 }
 void OmpStructureChecker::HasInvalidLoopBinding(
     const parser::OpenMPLoopConstruct &x) {
diff --git a/flang/test/Semantics/OpenMP/combined-constructs.f90 b/flang/test/Semantics/OpenMP/combined-constructs.f90
index 49da56298d426..3e9c65434f695 100644
--- a/flang/test/Semantics/OpenMP/combined-constructs.f90
+++ b/flang/test/Semantics/OpenMP/combined-constructs.f90
@@ -7,7 +7,7 @@ program main
   real(8) :: a(256), b(256)
   N = 256
 
-  !ERROR: `DISTRIBUTE` region has to be strictly nested inside `TEAMS` region.
+  !WARNING: `DISTRIBUTE` must be dynamically enclosed in a `TEAMS` region.
   !$omp distribute simd
   do i = 1, N
      a(i) = 3.14d0
diff --git a/flang/test/Semantics/OpenMP/do05.f90 b/flang/test/Semantics/OpenMP/do05.f90
index 24844f9fe4f62..d8320520879ef 100644
--- a/flang/test/Semantics/OpenMP/do05.f90
+++ b/flang/test/Semantics/OpenMP/do05.f90
@@ -49,7 +49,7 @@ program omp_do
   end do
   !$omp end parallel do simd
 
-  !ERROR: `DISTRIBUTE` region has to be strictly nested inside `TEAMS` region.
+  !WARNING: `DISTRIBUTE` must be dynamically enclosed in a `TEAMS` region.
   !$omp distribute parallel do
   do i=1,10
     if( i == 3 ) then
@@ -64,7 +64,7 @@ program omp_do
   end do
   !$omp end distribute parallel do
 
-  !ERROR: `DISTRIBUTE` region has to be strictly nested inside `TEAMS` region.
+  !WARNING: `DISTRIBUTE` must be dynamically enclosed in a `TEAMS` region.
   !$omp distribute parallel do simd
   do i=1,10
     if( i == 3 ) then
diff --git a/flang/test/Semantics/OpenMP/linear-iter.f90 b/flang/test/Semantics/OpenMP/linear-iter.f90
index 1f40228be92ad..5c9f2d5fb34c4 100644
--- a/flang/test/Semantics/OpenMP/linear-iter.f90
+++ b/flang/test/Semantics/OpenMP/linear-iter.f90
@@ -53,7 +53,7 @@ SUBROUTINE LINEAR_BAD(N)
   !$omp end teams
   !$omp end target 
 
-  !ERROR: `DISTRIBUTE` region has to be strictly nested inside `TEAMS` region.
+  !WARNING: `DISTRIBUTE` must be dynamically enclosed in a `TEAMS` region.
   !ERROR: Variable 'j' not allowed in LINEAR clause, only loop iterator can be specified in LINEAR clause of a construct combined with DISTRIBUTE
   !$omp distribute simd linear(i,j)
    do i = 1, N
@@ -63,7 +63,7 @@ SUBROUTINE LINEAR_BAD(N)
    enddo
    !$omp end distribute simd
 
-   !ERROR: `DISTRIBUTE` region has to be strictly nested inside `TEAMS` region.
+   !WARNING: `DISTRIBUTE` must be dynamically enclosed in a `TEAMS` region.
    !ERROR: Variable 'j' not allowed in LINEAR clause, only loop iterator can be specified in LINEAR clause of a construct combined with DISTRIBUTE
    !$omp distribute simd linear(i,j) collapse(1)
    do i = 1, N
@@ -73,7 +73,7 @@ SUBROUTINE LINEAR_BAD(N)
    enddo
    !$omp end distribute simd
 
-   !ERROR: `DISTRIBUTE` region has to be strictly nested inside `TEAMS` region.
+   !WARNING: `DISTRIBUTE` must be dynamically enclosed in a `TEAMS` region.
    !$omp distribute simd linear(i,j) collapse(2)
    do i = 1, N
       do j = 1, N
diff --git a/flang/test/Semantics/OpenMP/nested-distribute.f90 b/flang/test/Semantics/OpenMP/nested-distribute.f90
index cb4aea3bcdffa..4134ced7d81f6 100644
--- a/flang/test/Semantics/OpenMP/nested-distribute.f90
+++ b/flang/test/Semantics/OpenMP/nested-distribute.f90
@@ -1,6 +1,15 @@
 ! RUN: %python %S/../test_errors.py %s %flang -fopenmp
 ! Check OpenMP clause validity for the following directives:
 !     2.10 Device constructs
+
+subroutine f
+  integer :: i
+  !WARNING: `DISTRIBUTE` must be dynamically enclosed in a `TEAMS` region.
+  !$omp distribute
+  do i = 1, 100
+     print *, "hello"
+  end do
+end subroutine
 program main
 
   real(8) :: arrayA(256), arrayB(256)
@@ -108,4 +117,8 @@ program main
       end do
       !$omp end distribute
   !$omp end task
+
+  !$omp teams
+    call foo
+  !$omp end teams
 end program main

tblah

Thanks! Just one question.

flang/lib/Semantics/check-omp-loop.cpp

Stylie777

I am concerned about the changes to some of the tests in this PR. It looks like errors, that should still be genuine errors, are being changed to warnings. We are not testing the error at all so at the very least, tests for that need adding.

EDIT: Sorry, I have resolved my threads as I originally misunderstood some aims of this PR.

Is there a case we will now hit the original error message? If so we should still test this but if not, is there a case for removing it and only having the new warning in the code.

flang/test/Semantics/OpenMP/combined-constructs.f90

flang/test/Semantics/OpenMP/do05.f90

flang/test/Semantics/OpenMP/linear-iter.f90

chandraghale · 2025-10-17T10:31:45Z

I am concerned about the changes to some of the tests in this PR. It looks like errors, that should still be genuine errors, are being changed to warnings. We are not testing the error at all so at the very least, tests for that need adding.

EDIT: Sorry, I have resolved my threads as I originally misunderstood some aims of this PR.

Is there a case we will now hit the original error message? If so we should still test this but if not, is there a case for removing it and only having the new warning in the code.

Thanks @Stylie777
Yes, there are cases where the original error message is emitted. For example lexical violations (e.g., distribute directly under, or after, a non-teams context) still produce the original error, in code like:

!$omp end parallel
  !ERROR: `DISTRIBUTE` region has to be strictly nested inside `TEAMS` region.
  !$omp distribute firstprivate(a)
  do i = 1, 10
     j = j + 1
  end do

Original error message is still relevant so kept it.

Stylie777

Thanks @chandraghale. LGTM!

tblah

LGTM

If there is a call inside a TEAMS construct, and that call contains a DISTRIBUTE construct, the DISTRIBUTE region is considered to be enclosed by the TEAMS region (based on the dynamic extent of the construct). Currently, Flang diagnoses this as an error, which is incorrect. For eg : ``` subroutine f !$omp distribute do i = 1, 100 ... end do end subroutine subroutine g !$omp teams call f ! this call is ok, distribute enclosed by teams !$omp end teams end subroutine ``` This patch adjusts the nesting check for the OpenMP DISTRIBUTE directive. It retains the error for DISTRIBUTE directives that are incorrectly nested lexically but downgrades it to a warning for orphaned directives to allow dynamic nesting, such as when a subroutine with DISTRIBUTE is called from within a TEAMS region. Co-authored-by: Chandra Ghale <ghale@pe31.hpc.amslabs.hpecorp.net>

Allow orphaned distribute construct

15d695d

llvmbot added flang Flang issues not falling into any other category flang:openmp flang:semantics labels Oct 15, 2025

chandraghale requested review from Stylie777 and tblah October 15, 2025 13:29

tblah reviewed Oct 15, 2025

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chandraghale requested a review from tblah October 16, 2025 08:37

Stylie777 requested changes Oct 17, 2025

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flang/test/Semantics/OpenMP/combined-constructs.f90 Show resolved Hide resolved

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chandraghale requested a review from Stylie777 October 17, 2025 10:31

Stylie777 approved these changes Oct 17, 2025

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tblah approved these changes Oct 20, 2025

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chandraghale merged commit 6dda3b1 into llvm:main Oct 20, 2025
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[flang][OpenMP]: Allow orphaned distribute construct #163546

[flang][OpenMP]: Allow orphaned distribute construct #163546

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[flang][OpenMP]: Allow orphaned distribute construct #163546

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