[flang-commits] [flang] [flang][OpenMP][Semantics] Disallow NOWAIT and ORDERED with CANCEL (PR #135991)

via flang-commits flang-commits at lists.llvm.org
Wed Apr 16 10:09:32 PDT 2025 

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-flang-semantics

Author: Tom Eccles (tblah)

<details>
<summary>Changes</summary>

NOWAIT was a tricky one because the clause can be on either the start or the end directive. I couldn't find a convenient way to access the end directive from the CANCEL directive nested inside of the construct, but there are convenient ways to access the start directive. I have added a list to the start directive context containing the clauses from the end directive.

---
Full diff: https://github.com/llvm/llvm-project/pull/135991.diff


4 Files Affected:

- (modified) flang/lib/Semantics/check-directive-structure.h (+1) 
- (modified) flang/lib/Semantics/check-omp-structure.cpp (+45-1) 
- (modified) flang/lib/Semantics/check-omp-structure.h (+2) 
- (modified) flang/test/Semantics/OpenMP/cancel.f90 (+51) 


``````````diff
diff --git a/flang/lib/Semantics/check-directive-structure.h b/flang/lib/Semantics/check-directive-structure.h
index 91ffda6404c23..4a4893fe805a2 100644
--- a/flang/lib/Semantics/check-directive-structure.h
+++ b/flang/lib/Semantics/check-directive-structure.h
@@ -202,6 +202,7 @@ class DirectiveStructureChecker : public virtual BaseChecker {
     const PC *clause{nullptr};
     ClauseMapTy clauseInfo;
     std::list<C> actualClauses;
+    std::list<C> endDirectiveClauses;
     std::list<C> crtGroup;
     Symbol *loopIV{nullptr};
   };
diff --git a/flang/lib/Semantics/check-omp-structure.cpp b/flang/lib/Semantics/check-omp-structure.cpp
index 717982f66027c..7b26e20620269 100644
--- a/flang/lib/Semantics/check-omp-structure.cpp
+++ b/flang/lib/Semantics/check-omp-structure.cpp
@@ -15,6 +15,7 @@
 #include "flang/Semantics/expression.h"
 #include "flang/Semantics/openmp-modifiers.h"
 #include "flang/Semantics/tools.h"
+#include "llvm/ADT/STLExtras.h"
 #include <variant>
 
 namespace Fortran::semantics {
@@ -682,11 +683,20 @@ void OmpStructureChecker::Leave(const parser::OpenMPDeclarativeConstruct &x) {
   ExitDirectiveNest(DeclarativeNest);
 }
 
+void OmpStructureChecker::AddEndStatementClauses(
+    const parser::OmpClauseList &clauses) {
+  for (const parser::OmpClause &clause : clauses.v) {
+    GetContext().endDirectiveClauses.push_back(clause.Id());
+  }
+}
+
 void OmpStructureChecker::Enter(const parser::OpenMPLoopConstruct &x) {
   loopStack_.push_back(&x);
   const auto &beginLoopDir{std::get<parser::OmpBeginLoopDirective>(x.t)};
   const auto &beginDir{std::get<parser::OmpLoopDirective>(beginLoopDir.t)};
 
+  PushContextAndClauseSets(beginDir.source, beginDir.v);
+
   // check matching, End directive is optional
   if (const auto &endLoopDir{
           std::get<std::optional<parser::OmpEndLoopDirective>>(x.t)}) {
@@ -694,9 +704,10 @@ void OmpStructureChecker::Enter(const parser::OpenMPLoopConstruct &x) {
         std::get<parser::OmpLoopDirective>(endLoopDir.value().t)};
 
     CheckMatching<parser::OmpLoopDirective>(beginDir, endDir);
+
+    AddEndStatementClauses(std::get<parser::OmpClauseList>(endLoopDir->t));
   }
 
-  PushContextAndClauseSets(beginDir.source, beginDir.v);
   if (llvm::omp::allSimdSet.test(GetContext().directive)) {
     EnterDirectiveNest(SIMDNest);
   }
@@ -1429,6 +1440,8 @@ void OmpStructureChecker::Enter(const parser::OpenMPSectionsConstruct &x) {
   CheckMatching<parser::OmpSectionsDirective>(beginDir, endDir);
 
   PushContextAndClauseSets(beginDir.source, beginDir.v);
+  AddEndStatementClauses(std::get<parser::OmpClauseList>(endSectionsDir.t));
+
   const auto &sectionBlocks{std::get<parser::OmpSectionBlocks>(x.t)};
   for (const parser::OpenMPConstruct &block : sectionBlocks.v) {
     CheckNoBranching(std::get<parser::OpenMPSectionConstruct>(block.u).v,
@@ -2288,6 +2301,37 @@ void OmpStructureChecker::Enter(const parser::OpenMPCancelConstruct &x) {
   if (auto maybeConstruct{GetCancelType(
           llvm::omp::Directive::OMPD_cancel, x.source, maybeClauses)}) {
     CheckCancellationNest(dirName.source, *maybeConstruct);
+
+    if (CurrentDirectiveIsNested()) {
+      // nowait can be put on the end directive rather than the start directive
+      // so we need to check both
+      auto getParentClauses{[&]() {
+        const DirectiveContext &parent{GetContextParent()};
+        return llvm::concat<const llvm::omp::Clause>(
+            parent.actualClauses, parent.endDirectiveClauses);
+      }};
+
+      if (llvm::omp::nestedCancelDoAllowedSet.test(*maybeConstruct)) {
+        for (llvm::omp::Clause clause : getParentClauses()) {
+          if (clause == llvm::omp::Clause::OMPC_nowait) {
+            context_.Say(dirName.source,
+                "The CANCEL construct cannot be nested inside of a worksharing construct with the NOWAIT clause"_err_en_US);
+          }
+          if (clause == llvm::omp::Clause::OMPC_ordered) {
+            context_.Say(dirName.source,
+                "The CANCEL construct cannot be nested inside of a worksharing construct with the ORDERED clause"_err_en_US);
+          }
+        }
+      } else if (llvm::omp::nestedCancelSectionsAllowedSet.test(
+                     *maybeConstruct)) {
+        for (llvm::omp::Clause clause : getParentClauses()) {
+          if (clause == llvm::omp::Clause::OMPC_nowait) {
+            context_.Say(dirName.source,
+                "The CANCEL construct cannot be nested inside of a worksharing construct with the NOWAIT clause"_err_en_US);
+          }
+        }
+      }
+    }
   }
 }
 
diff --git a/flang/lib/Semantics/check-omp-structure.h b/flang/lib/Semantics/check-omp-structure.h
index a8869561cf5ea..dd9d3ee306b84 100644
--- a/flang/lib/Semantics/check-omp-structure.h
+++ b/flang/lib/Semantics/check-omp-structure.h
@@ -318,6 +318,8 @@ class OmpStructureChecker
 
   void CheckAlignValue(const parser::OmpClause &);
 
+  void AddEndStatementClauses(const parser::OmpClauseList &clauses);
+
   void EnterDirectiveNest(const int index) { directiveNest_[index]++; }
   void ExitDirectiveNest(const int index) { directiveNest_[index]--; }
   int GetDirectiveNest(const int index) { return directiveNest_[index]; }
diff --git a/flang/test/Semantics/OpenMP/cancel.f90 b/flang/test/Semantics/OpenMP/cancel.f90
index 581c4bdb97646..6f3a255312ccf 100644
--- a/flang/test/Semantics/OpenMP/cancel.f90
+++ b/flang/test/Semantics/OpenMP/cancel.f90
@@ -27,3 +27,54 @@ subroutine f03
 !$omp cancellation point parallel parallel
 !$omp end parallel
 end
+
+subroutine do_nowait1
+!$omp parallel
+!$omp do nowait
+  do i=1,2
+!ERROR: The CANCEL construct cannot be nested inside of a worksharing construct with the NOWAIT clause
+    !$omp cancel do
+  enddo
+!$omp end do
+!$omp end parallel
+end subroutine
+
+subroutine do_nowait2
+!$omp parallel
+!$omp do
+  do i=1,2
+!ERROR: The CANCEL construct cannot be nested inside of a worksharing construct with the NOWAIT clause
+    !$omp cancel do
+  enddo
+!$omp end do nowait
+!$omp end parallel
+end subroutine
+
+subroutine do_ordered
+!$omp parallel do ordered
+  do i=1,2
+!ERROR: The CANCEL construct cannot be nested inside of a worksharing construct with the ORDERED clause
+    !$omp cancel do
+  enddo
+!$omp end parallel do
+end subroutine
+
+subroutine sections_nowait1
+!$omp parallel
+!$omp sections nowait
+  !$omp section
+!ERROR: The CANCEL construct cannot be nested inside of a worksharing construct with the NOWAIT clause
+    !$omp cancel sections
+!$omp end sections
+!$omp end parallel
+end subroutine
+
+subroutine sections_nowait2
+!$omp parallel
+!$omp sections
+  !$omp section
+!ERROR: The CANCEL construct cannot be nested inside of a worksharing construct with the NOWAIT clause
+    !$omp cancel sections
+!$omp end sections nowait
+!$omp end parallel
+end subroutine

``````````

</details>


https://github.com/llvm/llvm-project/pull/135991

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