[flang-commits] [flang] [flang][OpenMP] Don't privatize implicit symbols declare by nested `BLOCK`s (PR #152973)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-flang-openmp

Author: Kareem Ergawy (ergawy)

<details>
<summary>Changes</summary>

Fixes a bug when a block variable is marked as implicit 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.

---
Full diff: https://github.com/llvm/llvm-project/pull/152973.diff


3 Files Affected:

- (modified) flang/lib/Lower/OpenMP/DataSharingProcessor.cpp (+18-7) 
- (modified) flang/lib/Lower/OpenMP/DataSharingProcessor.h (+5) 
- (added) flang/test/Lower/OpenMP/block_implicit_privatization.f90 (+31) 


``````````diff
diff --git a/flang/lib/Lower/OpenMP/DataSharingProcessor.cpp b/flang/lib/Lower/OpenMP/DataSharingProcessor.cpp
index 49d8b46beb0eb..e3f792ee296f7 100644
--- a/flang/lib/Lower/OpenMP/DataSharingProcessor.cpp
+++ b/flang/lib/Lower/OpenMP/DataSharingProcessor.cpp
@@ -30,6 +30,7 @@
 #include "flang/Semantics/tools.h"
 #include "llvm/ADT/Sequence.h"
 #include "llvm/ADT/SmallSet.h"
+#include <variant>
 
 namespace Fortran {
 namespace lower {
@@ -44,6 +45,13 @@ bool DataSharingProcessor::OMPConstructSymbolVisitor::isSymbolDefineBy(
       [](const auto &functionParserNode) { return false; }});
 }
 
+bool DataSharingProcessor::OMPConstructSymbolVisitor::
+    isSymbolDefineByNestedDeclaration(const semantics::Symbol *symbol) const {
+  return symDefMap.count(symbol) &&
+         std::holds_alternative<const parser::DeclarationConstruct *>(
+             symDefMap.at(symbol));
+}
+
 static bool isConstructWithTopLevelTarget(lower::pft::Evaluation &eval) {
   const auto *ompEval = eval.getIf<parser::OpenMPConstruct>();
   if (ompEval) {
@@ -550,17 +558,20 @@ void DataSharingProcessor::collectSymbols(
         return false;
       }
 
-      return sym->test(semantics::Symbol::Flag::OmpImplicit);
-    }
-
-    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
+      // Collect implicit symbols only if they are not defined by a nested
+      // `DeclarationConstruct`. 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) &&
+      return !visitor.isSymbolDefineByNestedDeclaration(sym) &&
+             sym->test(semantics::Symbol::Flag::OmpImplicit);
+    }
+
+    if (collectPreDetermined) {
+      // Similar to implicit symbols, collect pre-determined symbols only if
+      // they are not defined by a nested `DeclarationConstruct`
+      return !visitor.isSymbolDefineByNestedDeclaration(sym) &&
              sym->test(semantics::Symbol::Flag::OmpPreDetermined);
     }
 
diff --git a/flang/lib/Lower/OpenMP/DataSharingProcessor.h b/flang/lib/Lower/OpenMP/DataSharingProcessor.h
index 335699577ea84..96c9240017f00 100644
--- a/flang/lib/Lower/OpenMP/DataSharingProcessor.h
+++ b/flang/lib/Lower/OpenMP/DataSharingProcessor.h
@@ -77,6 +77,11 @@ class DataSharingProcessor {
     bool isSymbolDefineBy(const semantics::Symbol *symbol,
                           lower::pft::Evaluation &eval) const;
 
+    // Given a \p symbol, returns true if it is defined by a nested
+    // `DeclarationConstruct`.
+    bool
+    isSymbolDefineByNestedDeclaration(const semantics::Symbol *symbol) const;
+
   private:
     using ConstructPtr = std::variant<const parser::OpenMPConstruct *,
                                       const parser::DeclarationConstruct *>;
diff --git a/flang/test/Lower/OpenMP/block_implicit_privatization.f90 b/flang/test/Lower/OpenMP/block_implicit_privatization.f90
new file mode 100644
index 0000000000000..69956dac3ec70
--- /dev/null
+++ b/flang/test/Lower/OpenMP/block_implicit_privatization.f90
@@ -0,0 +1,31 @@
+! Fixes a bug when a block variable is marked as implicit 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_implicit_privatization
+  implicit none
+  integer :: i
+
+  !$omp task
+  do i=1,10
+    block
+      integer :: j
+      j = 0
+    end block
+  end do
+  !$omp end task
+end subroutine
+
+! CHECK-LABEL: func.func @_QPblock_implicit_privatization() {
+! CHECK:         %[[I_DECL:.*]]:2 = hlfir.declare %{{.*}} {uniq_name = "{{.*}}Ei"}
+! CHECK:         omp.task 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 `task` loop).
+! CHECK:             fir.alloca i32 {bindc_name = "j", {{.*}}}
+! CHECK:           }
+! CHECK:         }
+! CHECK:       }

``````````

</details>


https://github.com/llvm/llvm-project/pull/152973