[flang-commits] [flang] 98ffdf3 - [flang][OpenMP] Don't privatize pre-determined symbols declare by nested `BLOCK`s (#152652)

[via flang-commits]

Author: Kareem Ergawy
Date: 2025-08-11T10:21:07+02:00
New Revision: 98ffdf3958ddff704a520b590c879c9289378e3b

URL: https://github.com/llvm/llvm-project/commit/98ffdf3958ddff704a520b590c879c9289378e3b
DIFF: https://github.com/llvm/llvm-project/commit/98ffdf3958ddff704a520b590c879c9289378e3b.diff

LOG: [flang][OpenMP] Don't privatize pre-determined symbols declare by nested `BLOCK`s (#152652)

Fixes a bug when a block variable is marked as pre-determined private.
In such case, we can simply ignore privatizing that symbol within the
context of the currrent OpenMP construct since the "private" allocation
for the symbol will be emitted within the nested block anyway.

Added: 
    flang/test/Lower/OpenMP/block_predetermined_privatization.f90

Modified: 
    flang/lib/Lower/OpenMP/DataSharingProcessor.cpp
    flang/lib/Lower/OpenMP/DataSharingProcessor.h

Removed: 
    


################################################################################
diff  --git a/flang/lib/Lower/OpenMP/DataSharingProcessor.cpp b/flang/lib/Lower/OpenMP/DataSharingProcessor.cpp
index 67a9a4675f115..49d8b46beb0eb 100644
--- a/flang/lib/Lower/OpenMP/DataSharingProcessor.cpp
+++ b/flang/lib/Lower/OpenMP/DataSharingProcessor.cpp
@@ -36,12 +36,12 @@ namespace lower {
 namespace omp {
 bool DataSharingProcessor::OMPConstructSymbolVisitor::isSymbolDefineBy(
     const semantics::Symbol *symbol, lower::pft::Evaluation &eval) const {
-  return eval.visit(
-      common::visitors{[&](const parser::OpenMPConstruct &functionParserNode) {
-                         return symDefMap.count(symbol) &&
-                                symDefMap.at(symbol) == &functionParserNode;
-                       },
-                       [](const auto &functionParserNode) { return false; }});
+  return eval.visit(common::visitors{
+      [&](const parser::OpenMPConstruct &functionParserNode) {
+        return symDefMap.count(symbol) &&
+               symDefMap.at(symbol) == ConstructPtr(&functionParserNode);
+      },
+      [](const auto &functionParserNode) { return false; }});
 }
 
 static bool isConstructWithTopLevelTarget(lower::pft::Evaluation &eval) {
@@ -553,8 +553,16 @@ void DataSharingProcessor::collectSymbols(
       return sym->test(semantics::Symbol::Flag::OmpImplicit);
     }
 
-    if (collectPreDetermined)
-      return sym->test(semantics::Symbol::Flag::OmpPreDetermined);
+    if (collectPreDetermined) {
+      // Collect pre-determined symbols only if they are defined by the current
+      // OpenMP evaluation. If `sym` is not defined by the current OpenMP
+      // evaluation then it is defined by a block nested within the OpenMP
+      // construct. This, in turn, means that the private allocation for the
+      // symbol will be emitted as part of the nested block and there is no need
+      // to privatize it within the OpenMP construct.
+      return visitor.isSymbolDefineBy(sym, eval) &&
+             sym->test(semantics::Symbol::Flag::OmpPreDetermined);
+    }
 
     return !sym->test(semantics::Symbol::Flag::OmpImplicit) &&
            !sym->test(semantics::Symbol::Flag::OmpPreDetermined);

diff  --git a/flang/lib/Lower/OpenMP/DataSharingProcessor.h b/flang/lib/Lower/OpenMP/DataSharingProcessor.h
index 96e7fa6d5d93c..335699577ea84 100644
--- a/flang/lib/Lower/OpenMP/DataSharingProcessor.h
+++ b/flang/lib/Lower/OpenMP/DataSharingProcessor.h
@@ -19,6 +19,7 @@
 #include "flang/Parser/parse-tree.h"
 #include "flang/Semantics/symbol.h"
 #include "mlir/Dialect/OpenMP/OpenMPDialect.h"
+#include <variant>
 
 namespace mlir {
 namespace omp {
@@ -58,13 +59,18 @@ class DataSharingProcessor {
     }
 
     void Post(const parser::Name &name) {
-      auto *current = !constructs.empty() ? constructs.back() : nullptr;
+      auto current = !constructs.empty() ? constructs.back() : ConstructPtr();
       symDefMap.try_emplace(name.symbol, current);
     }
 
-    llvm::SmallVector<const parser::OpenMPConstruct *> constructs;
-    llvm::DenseMap<semantics::Symbol *, const parser::OpenMPConstruct *>
-        symDefMap;
+    bool Pre(const parser::DeclarationConstruct &decl) {
+      constructs.push_back(&decl);
+      return true;
+    }
+
+    void Post(const parser::DeclarationConstruct &decl) {
+      constructs.pop_back();
+    }
 
     /// Given a \p symbol and an \p eval, returns true if eval is the OMP
     /// construct that defines symbol.
@@ -72,6 +78,11 @@ class DataSharingProcessor {
                           lower::pft::Evaluation &eval) const;
 
   private:
+    using ConstructPtr = std::variant<const parser::OpenMPConstruct *,
+                                      const parser::DeclarationConstruct *>;
+    llvm::SmallVector<ConstructPtr> constructs;
+    llvm::DenseMap<semantics::Symbol *, ConstructPtr> symDefMap;
+
     unsigned version;
   };
 

diff  --git a/flang/test/Lower/OpenMP/block_predetermined_privatization.f90 b/flang/test/Lower/OpenMP/block_predetermined_privatization.f90
new file mode 100644
index 0000000000000..12346c14ef5d9
--- /dev/null
+++ b/flang/test/Lower/OpenMP/block_predetermined_privatization.f90
@@ -0,0 +1,32 @@
+! Fixes a bug when a block variable is marked as pre-determined private. In such
+! case, we can simply ignore privatizing that symbol within the context of the
+! currrent OpenMP construct since the "private" allocation for the symbol will
+! be emitted within the nested block anyway.
+
+! RUN: %flang_fc1 -emit-hlfir -fopenmp %s -o - | FileCheck %s
+
+subroutine block_predetermined_privatization
+  implicit none
+  integer :: i
+
+  !$omp parallel
+  do i=1,10
+    block
+      integer :: j
+      do j=1,10
+      end do
+    end block
+  end do
+  !$omp end parallel
+end subroutine
+
+! CHECK-LABEL: func.func @_QPblock_predetermined_privatization() {
+! CHECK:         %[[I_DECL:.*]]:2 = hlfir.declare %{{.*}} {uniq_name = "{{.*}}Ei"}
+! CHECK:         omp.parallel private(@{{.*}}Ei_private_i32 %[[I_DECL]]#0 -> %{{.*}} : !fir.ref<i32>) {
+! CHECK:           fir.do_loop {{.*}} {
+! Verify that `j` is allocated whithin the same scope of its block (i.e. inside
+! the `parallel` loop).
+! CHECK:             fir.alloca i32 {bindc_name = "j", {{.*}}}
+! CHECK:           }
+! CHECK:         }
+! CHECK:       }