Avoid unevaluated implicit private

[SunilKuravinakop]

For every variable used under #pragma omp task directive (DeclRefExpr) an ImplicitPrivateVariable is created in the AST, if private or shared clauses are not present. If the variable has the property of non_odr_use_unevaluated e.g. for statements which use sizeof( i ) i will have non_odr_use_unevaluated . In such cases CodeGen was asserting by avoiding emitting of LLVM IR for such variables. To prevent this assertion this checkin avoids adding the ImplicitPrivateVariable for variables with non_odr_use_unevaluated.

[llvmbot]

@llvm/pr-subscribers-clang

Author: None (SunilKuravinakop)

Changes

For every variable used under #pragma omp task directive (DeclRefExpr) an ImplicitPrivateVariable is created in the AST, if private or shared clauses are not present. If the variable has the property of non_odr_use_unevaluated e.g. for statements which use sizeof( i ) i will have non_odr_use_unevaluated . In such cases CodeGen was asserting by avoiding emitting of LLVM IR for such variables. To prevent this assertion this checkin avoids adding the ImplicitPrivateVariable for variables with non_odr_use_unevaluated.

---

Full diff: https://github.com/llvm/llvm-project/pull/92055.diff

2 Files Affected:

• (modified) clang/lib/Sema/SemaOpenMP.cpp (+2-1)
• (modified) clang/test/OpenMP/task_ast_print.cpp (+34)

diff --git a/clang/lib/Sema/SemaOpenMP.cpp b/clang/lib/Sema/SemaOpenMP.cpp
index 7d00cf6fb5b6a..6110e5229b076 100644
--- a/clang/lib/Sema/SemaOpenMP.cpp
+++ b/clang/lib/Sema/SemaOpenMP.cpp
@@ -3757,7 +3757,8 @@ class DSAAttrChecker final : public StmtVisitor<DSAAttrChecker, void> {
   void VisitDeclRefExpr(DeclRefExpr *E) {
     if (TryCaptureCXXThisMembers || E->isTypeDependent() ||
         E->isValueDependent() || E->containsUnexpandedParameterPack() ||
-        E->isInstantiationDependent())
+        E->isInstantiationDependent() ||
+        E->isNonOdrUse() == clang::NOUR_Unevaluated)
       return;
     if (auto *VD = dyn_cast<VarDecl>(E->getDecl())) {
       // Check the datasharing rules for the expressions in the clauses.
diff --git a/clang/test/OpenMP/task_ast_print.cpp b/clang/test/OpenMP/task_ast_print.cpp
index 12923e6ab4244..9d545c5f6716c 100644
--- a/clang/test/OpenMP/task_ast_print.cpp
+++ b/clang/test/OpenMP/task_ast_print.cpp
@@ -5,6 +5,7 @@
 // RUN: %clang_cc1 -verify -Wno-vla -fopenmp-simd -ast-print %s | FileCheck %s
 // RUN: %clang_cc1 -fopenmp-simd -x c++ -std=c++11 -emit-pch -o %t %s
 // RUN: %clang_cc1 -fopenmp-simd -std=c++11 -include-pch %t -verify -Wno-vla %s -ast-print | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -fopenmp -ast-dump  %s | FileCheck %s --check-prefix=DUMP
 // expected-no-diagnostics
 
 #ifndef HEADER
@@ -208,4 +209,37 @@ int main(int argc, char **argv) {
 extern template int S<int>::TS;
 extern template long S<long>::TS;
 
+int
+implicit_firstprivate() {
+
+#pragma omp parallel num_threads(1)
+  {
+    int i = 0;
+    // DUMP : OMPTaskDirective
+    // DUMP-NEXT : OMPFirstprivateClause
+    // DUMP-NEXT : DeclRefExpr {{.+}} 'i' {{.+}} refers_to_enclosing_variable_or_capture
+    #pragma omp task
+    {
+	int j = sizeof(i);
+	j = i;
+    }
+  }
+}
+
+int
+no_implicit_firstprivate() {
+
+#pragma omp parallel num_threads(1)
+  {
+    int i = 0;
+    // DUMP : OMPTaskDirective
+    // DUMP-NEXT : CapturedStmt
+    // DUMP : DeclRefExpr {{.+}} 'i' {{.+}} non_odr_use_unevaluated refers_to_enclosing_variable_or_capture
+    #pragma omp task
+    {
+	int j = sizeof(i);
+    }
+  }
+}
+
 #endif

[dreachem]

This could still match if non_odr_use_unevaluated shows up, can't it? Can we add a check that non_odr_use_unevaluated should not be part of the DeclRefRexpr under this firstprivate clause?

[alexey-bataev]

LG

[SunilKuravinakop]

Alexey,
My colleagues (in my company), having contribution rights, are not around. Can you please merge this change to master?