[flang-commits] [flang] c7e1ec9 - [flang][OpenMP] Implicitly capture variables in enclosing task for nested firstprivate (#183770)

[via flang-commits]

Author: Ritanya-B-Bharadwaj
Date: 2026-03-02T15:08:04+05:30
New Revision: c7e1ec97b9794da3154f44ad198d9b8eaddc7dfd

URL: https://github.com/llvm/llvm-project/commit/c7e1ec97b9794da3154f44ad198d9b8eaddc7dfd
DIFF: https://github.com/llvm/llvm-project/commit/c7e1ec97b9794da3154f44ad198d9b8eaddc7dfd.diff

LOG: [flang][OpenMP] Implicitly capture variables in enclosing task for nested firstprivate (#183770)

Fixes https://github.com/llvm/llvm-project/issues/181271
If a variable is marked firstprivate in a nested task but not actually
used in the outer task body, we still need the outer task to capture it
as firstprivate. Otherwise the nested task can end up pointing to the
parallel region’s stack frame, which might already be gone when the
deferred task runs, causing a use-after-free.

Added: 
    flang/test/Lower/OpenMP/task-implicit-firstprivate.f90

Modified: 
    flang/lib/Semantics/resolve-directives.cpp

Removed: 
    


################################################################################
diff  --git a/flang/lib/Semantics/resolve-directives.cpp b/flang/lib/Semantics/resolve-directives.cpp
index 7e11be509cd02..22f66aafea941 100644
--- a/flang/lib/Semantics/resolve-directives.cpp
+++ b/flang/lib/Semantics/resolve-directives.cpp
@@ -3148,6 +3148,12 @@ void OmpAttributeVisitor::ResolveOmpDesignator(
         AddAllocateName(name);
       }
     }
+    // Save the original symbol. For privatizing clauses, ensure enclosing
+    // constructs properly capture the variable.
+    const Symbol *origSymbol{name->symbol};
+    if (origSymbol && privateDataSharingAttributeFlags.test(ompFlag)) {
+      CreateImplicitSymbols(origSymbol);
+    }
     if (ompFlag == Symbol::Flag::OmpReduction) {
       // Using variables inside of a namelist in OpenMP reductions
       // is allowed by the standard, but is not allowed for

diff  --git a/flang/test/Lower/OpenMP/task-implicit-firstprivate.f90 b/flang/test/Lower/OpenMP/task-implicit-firstprivate.f90
new file mode 100644
index 0000000000000..ae37082b389b6
--- /dev/null
+++ b/flang/test/Lower/OpenMP/task-implicit-firstprivate.f90
@@ -0,0 +1,25 @@
+! RUN: %flang_fc1 -emit-hlfir -fopenmp -o - %s 2>&1 | FileCheck %s
+
+! CHECK-LABEL: omp.private
+! CHECK-SAME:      {type = firstprivate} @[[B_FIRSTPRIVATE:.*firstprivate.*]] : !fir.box<!fir.array<2xi32>>
+
+! CHECK-LABEL: func @_QPtest_nested_task_firstprivate
+! CHECK:         omp.parallel
+! CHECK:           omp.task private(@[[B_FIRSTPRIVATE]] %{{.*}} -> %[[OUTER_TASK_B:.*]] :
+! CHECK:             %[[OUTER_TASK_B_DECL:.*]]:2 = hlfir.declare %[[OUTER_TASK_B]]
+! CHECK:             omp.task private(@[[B_FIRSTPRIVATE]] %[[OUTER_TASK_B_DECL]]#0 -> %[[INNER_TASK_B:.*]] :
+! CHECK:               hlfir.declare %[[INNER_TASK_B]]
+! CHECK:               omp.terminator
+! CHECK:             omp.terminator
+! CHECK:           omp.terminator
+subroutine test_nested_task_firstprivate
+  integer :: b(2)
+  b = 1
+  !$omp parallel private(b)
+    b = 2
+    !$omp task
+      !$omp task firstprivate(b)
+      !$omp end task
+    !$omp end task
+  !$omp end parallel
+end subroutine