[Flang][OpenMP] Update semantics checks for 'teams' nesting

[skatrak]

This patch introduces a directive set for combined constructs where teams is the last leaf. This is used in a couple places to simplify checks, which is NFC, but it also replaces two incorrect uses of topTeamsSet.

Before, these checks would incorrectly skip combined constructs where teams was the last leaf construct when checking for allowed nested constructs inside of a teams region. Similarly, it would also incorrectly perform these checks whenever a compound teams construct where teams was the first leaf construct was found.

[llvmbot]

@llvm/pr-subscribers-flang-semantics

@llvm/pr-subscribers-flang-openmp

Author: Sergio Afonso (skatrak)

Changes

This patch introduces a directive set for combined constructs where teams is the last leaf. This is used in a couple places to simplify checks, which is NFC, but it also replaces two incorrect uses of topTeamsSet.

Before, these checks would incorrectly skip combined constructs where teams was the last leaf construct when checking for allowed nested constructs inside of a teams region. Similarly, it would also incorrectly perform these checks whenever a compound teams construct where teams was the first leaf construct was found.

---

Full diff: https://github.com/llvm/llvm-project/pull/126922.diff

4 Files Affected:

• (modified) flang/include/flang/Semantics/openmp-directive-sets.h (+7)
• (modified) flang/lib/Semantics/check-omp-structure.cpp (+4-6)
• (modified) flang/test/Semantics/OpenMP/nested-target.f90 (+2)
• (modified) flang/test/Semantics/OpenMP/nested-teams.f90 (+1)

diff --git a/flang/include/flang/Semantics/openmp-directive-sets.h b/flang/include/flang/Semantics/openmp-directive-sets.h
index 7cdca1214e749..dd610c9702c28 100644
--- a/flang/include/flang/Semantics/openmp-directive-sets.h
+++ b/flang/include/flang/Semantics/openmp-directive-sets.h
@@ -21,6 +21,8 @@ namespace llvm::omp {
 //===----------------------------------------------------------------------===//
 // - top<Directive>Set: The directive appears alone or as the first in a
 //   compound construct.
+// - bottom<Directive>Set: The directive appears alone or as the last in a
+//   compound construct.
 // - all<Directive>Set: All standalone or compound uses of the directive.
 
 static const OmpDirectiveSet topDistributeSet{
@@ -172,6 +174,11 @@ static const OmpDirectiveSet topTeamsSet{
     Directive::OMPD_teams_loop,
 };
 
+static const OmpDirectiveSet bottomTeamsSet{
+    Directive::OMPD_target_teams,
+    Directive::OMPD_teams,
+};
+
 static const OmpDirectiveSet allTeamsSet{
     OmpDirectiveSet{
         Directive::OMPD_target_teams,
diff --git a/flang/lib/Semantics/check-omp-structure.cpp b/flang/lib/Semantics/check-omp-structure.cpp
index fd2893998205c..1d6fe6c8d4249 100644
--- a/flang/lib/Semantics/check-omp-structure.cpp
+++ b/flang/lib/Semantics/check-omp-structure.cpp
@@ -487,8 +487,7 @@ void OmpStructureChecker::HasInvalidDistributeNesting(
       violation = true;
     } else {
       // `distribute` region has to be strictly nested inside `teams`
-      if (!OmpDirectiveSet{llvm::omp::OMPD_teams, llvm::omp::OMPD_target_teams}
-              .test(GetContextParent().directive)) {
+      if (!llvm::omp::bottomTeamsSet.test(GetContextParent().directive)) {
         violation = true;
       }
     }
@@ -518,8 +517,7 @@ void OmpStructureChecker::HasInvalidLoopBinding(
 
   if (llvm::omp::Directive::OMPD_loop == beginDir.v &&
       CurrentDirectiveIsNested() &&
-      OmpDirectiveSet{llvm::omp::OMPD_teams, llvm::omp::OMPD_target_teams}.test(
-          GetContextParent().directive)) {
+      llvm::omp::bottomTeamsSet.test(GetContextParent().directive)) {
     teamsBindingChecker(
         "`BIND(TEAMS)` must be specified since the `LOOP` region is "
         "strictly nested inside a `TEAMS` region."_err_en_US);
@@ -726,7 +724,7 @@ void OmpStructureChecker::Enter(const parser::OpenMPLoopConstruct &x) {
   HasInvalidDistributeNesting(x);
   HasInvalidLoopBinding(x);
   if (CurrentDirectiveIsNested() &&
-      llvm::omp::topTeamsSet.test(GetContextParent().directive)) {
+      llvm::omp::bottomTeamsSet.test(GetContextParent().directive)) {
     HasInvalidTeamsNesting(beginDir.v, beginDir.source);
   }
   if ((beginDir.v == llvm::omp::Directive::OMPD_distribute_parallel_do_simd) ||
@@ -1169,7 +1167,7 @@ void OmpStructureChecker::Enter(const parser::OpenMPBlockConstruct &x) {
   }
 
   if (CurrentDirectiveIsNested()) {
-    if (llvm::omp::topTeamsSet.test(GetContextParent().directive)) {
+    if (llvm::omp::bottomTeamsSet.test(GetContextParent().directive)) {
       HasInvalidTeamsNesting(beginDir.v, beginDir.source);
     }
     if (GetContext().directive == llvm::omp::Directive::OMPD_master) {
diff --git a/flang/test/Semantics/OpenMP/nested-target.f90 b/flang/test/Semantics/OpenMP/nested-target.f90
index f42b5dde6a08d..6a56a84f4f570 100644
--- a/flang/test/Semantics/OpenMP/nested-target.f90
+++ b/flang/test/Semantics/OpenMP/nested-target.f90
@@ -54,6 +54,7 @@ program main
   n2 = 10
   !$omp target teams map(to:a)
   !PORTABILITY: If TARGET DATA directive is nested inside TARGET region, the behaviour is unspecified
+  !ERROR: Only `DISTRIBUTE`, `PARALLEL`, or `LOOP` regions are allowed to be strictly nested inside `TEAMS` region.
   !$omp target data map(n1,n2)
   do i=1, n1
      do j=1, n2
@@ -65,6 +66,7 @@ program main
 
   !$omp target teams map(to:a) map(from:n1,n2)
   !PORTABILITY: If TARGET TEAMS DISTRIBUTE PARALLEL DO directive is nested inside TARGET region, the behaviour is unspecified
+  !ERROR: Only `DISTRIBUTE`, `PARALLEL`, or `LOOP` regions are allowed to be strictly nested inside `TEAMS` region.
   !$omp target teams distribute parallel do
   do i=1, n1
      do j=1, n2
diff --git a/flang/test/Semantics/OpenMP/nested-teams.f90 b/flang/test/Semantics/OpenMP/nested-teams.f90
index b1a7c92a6906b..974172ee97175 100644
--- a/flang/test/Semantics/OpenMP/nested-teams.f90
+++ b/flang/test/Semantics/OpenMP/nested-teams.f90
@@ -68,6 +68,7 @@ program main
   !$omp end target
 
   !$omp target teams
+  !ERROR: Only `DISTRIBUTE`, `PARALLEL`, or `LOOP` regions are allowed to be strictly nested inside `TEAMS` region.
   !ERROR: TEAMS region can only be strictly nested within the implicit parallel region or TARGET region
   !$omp teams
   a = 3.14

[kparzysz]

LGTM.

The whole top/bottom sets will need to be refactored eventually, but this patch is ok.

[kiranchandramohan]

LG.