[PATCH] OpenMP: Constructors and destructors for "declare target" static aggregates

[PATCH] OpenMP: Constructors and destructors for "declare target" static aggregates

[Julian Brown]

This patch adds support for running constructors and destructors for
static (file-scope) aggregates for C++ objects which are marked with
"declare target" directives on OpenMP offload targets.

At present, space is allocated on the target for such aggregates, but
nothing ever constructs them properly, so they end up zero-initialised.

The approach taken is to generate a set of constructors to run on the
target: this currently works for AMD GCN, but fails on NVPTX due
to lack of constructor/destructor support there so far on mainline.
(See the new test static-aggr-constructor-destructor-3.C for a reason
why running constructors on the target is preferable to e.g. constructing
on the host and then copying the resulting object to the target.)

This patch was previously posted for the og12 branch here:

  https://gcc.gnu.org/pipermail/gcc-patches/2023-March/614710.html
  https://gcc.gnu.org/pipermail/gcc-patches/2023-April/615013.html
  https://gcc.gnu.org/pipermail/gcc-patches/2023-April/615144.html

though needed a fair amount of rework for mainline due to Nathan's
(earlier!) patch:

  https://gcc.gnu.org/pipermail/gcc-patches/2022-June/596402.html

Tested with offloading to AMD GCN and bootstrapped. OK for mainline?

Thanks,

Julian

2023-05-12  Julian Brown  <julian@codesourcery.com>

gcc/cp/
	* decl2.cc (tree-inline.h): Include.
	(static_init_fini_fns): Bump to four entries. Update comment.
	(start_objects, start_partial_init_fini_fn): Add 'omp_target'
	parameter. Support "declare target" decls. Update forward declaration.
	(emit_partial_init_fini_fn): Add 'host_fn' parameter. Return tree for
	the created function. Support "declare target".
	(OMP_SSDF_IDENTIFIER): New macro.
	(partition_vars_for_init_fini): Support partitioning "declare target"
	variables also.
	(generate_ctor_or_dtor_function): Add 'omp_target' parameter. Support
	"declare target" decls.
	(c_parse_final_cleanups): Support constructors/destructors on OpenMP
	offload targets.

gcc/
	* omp-builtins.def (BUILT_IN_OMP_IS_INITIAL_DEVICE): New builtin.
	* tree.cc (get_file_function_name): Support names for on-target
	constructor/destructor functions.

libgomp/
	* testsuite/libgomp.c++/static-aggr-constructor-destructor-1.C: New
	test.
	* testsuite/libgomp.c++/static-aggr-constructor-destructor-2.C: New
	test.
	* testsuite/libgomp.c++/static-aggr-constructor-destructor-3.C: New
	test.
---
 gcc/cp/decl2.cc                               | 243 +++++++++++++++---
 gcc/omp-builtins.def                          |   2 +
 gcc/tree.cc                                   |   6 +-
 .../static-aggr-constructor-destructor-1.C    |  28 ++
 .../static-aggr-constructor-destructor-2.C    |  31 +++
 .../static-aggr-constructor-destructor-3.C    |  36 +++
 6 files changed, 305 insertions(+), 41 deletions(-)
 create mode 100644 libgomp/testsuite/libgomp.c++/static-aggr-constructor-destructor-1.C
 create mode 100644 libgomp/testsuite/libgomp.c++/static-aggr-constructor-destructor-2.C
 create mode 100644 libgomp/testsuite/libgomp.c++/static-aggr-constructor-destructor-3.C

diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
index b510cdac554..ceec681fbeb 100644
--- a/gcc/cp/decl2.cc
+++ b/gcc/cp/decl2.cc
@@ -50,20 +50,22 @@ along with GCC; see the file COPYING3.  If not see
 #include "asan.h"
 #include "optabs-query.h"
 #include "omp-general.h"
+#include "tree-inline.h"
 
 /* Id for dumping the raw trees.  */
 int raw_dump_id;
  
 extern cpp_reader *parse_in;
 
-static tree start_objects (bool, unsigned, bool);
+static tree start_objects (bool, unsigned, bool, bool);
 static tree finish_objects (bool, unsigned, tree, bool = true);
-static tree start_partial_init_fini_fn (bool, unsigned, unsigned);
+static tree start_partial_init_fini_fn (bool, unsigned, unsigned, bool);
 static void finish_partial_init_fini_fn (tree);
-static void emit_partial_init_fini_fn (bool, unsigned, tree,
-				       unsigned, location_t);
+static tree emit_partial_init_fini_fn (bool, unsigned, tree,
+				       unsigned, location_t, tree);
 static void one_static_initialization_or_destruction (bool, tree, tree);
-static void generate_ctor_or_dtor_function (bool, unsigned, tree, location_t);
+static void generate_ctor_or_dtor_function (bool, unsigned, tree, location_t,
+					    bool);
 static tree prune_vars_needing_no_initialization (tree *);
 static void write_out_vars (tree);
 static void import_export_class (tree);
@@ -165,9 +167,10 @@ struct priority_map_traits
 typedef hash_map<unsigned/*Priority*/, tree/*List*/,
 		 priority_map_traits> priority_map_t;
 
-/* A pair of such hash tables, indexed by initp -- one for fini and
-   one for init.  The fini table is only ever used when !cxa_atexit.  */
-static GTY(()) priority_map_t *static_init_fini_fns[2];
+/* Two pairs of such hash tables, for the host and an OpenMP offload device.
+   Each pair has one priority map for fini and one for init.  The fini tables
+   are only ever used when !cxa_atexit.  */
+static GTY(()) priority_map_t *static_init_fini_fns[4];
 
 /* Nonzero if we're done parsing and into end-of-file activities.  */
 
@@ -3867,7 +3870,8 @@ generate_tls_wrapper (tree fn)
 /* Start a global constructor or destructor function.  */
 
 static tree
-start_objects (bool initp, unsigned priority, bool has_body)
+start_objects (bool initp, unsigned priority, bool has_body,
+	       bool omp_target = false)
 {
   bool default_init = initp && priority == DEFAULT_INIT_PRIORITY;
   bool is_module_init = default_init && module_global_init_needed ();
@@ -3881,7 +3885,15 @@ start_objects (bool initp, unsigned priority, bool has_body)
 
       /* We use `I' to indicate initialization and `D' to indicate
 	 destruction.  */
-      unsigned len = sprintf (type, "sub_%c", initp ? 'I' : 'D');
+      unsigned len;
+      if (omp_target)
+	/* Use "off_" signifying "offload" here.  The name must be distinct
+	   from the non-offload case.  The format of the name is scanned in
+	   tree.cc/get_file_function_name, so stick to the same length for
+	   both name variants.  */
+	len = sprintf (type, "off_%c", initp ? 'I' : 'D');
+      else
+	len = sprintf (type, "sub_%c", initp ? 'I' : 'D');
       if (priority != DEFAULT_INIT_PRIORITY)
 	{
 	  char joiner = '_';
@@ -3896,6 +3908,17 @@ start_objects (bool initp, unsigned priority, bool has_body)
 
   tree fntype =	build_function_type (void_type_node, void_list_node);
   tree fndecl = build_lang_decl (FUNCTION_DECL, name, fntype);
+
+  if (omp_target)
+    {
+      DECL_ATTRIBUTES (fndecl)
+	= tree_cons (get_identifier ("omp declare target"), NULL_TREE,
+		     DECL_ATTRIBUTES (fndecl));
+      DECL_ATTRIBUTES (fndecl)
+	= tree_cons (get_identifier ("omp declare target nohost"), NULL_TREE,
+		     DECL_ATTRIBUTES (fndecl));
+    }
+
   DECL_CONTEXT (fndecl) = FROB_CONTEXT (global_namespace);
   if (is_module_init)
     {
@@ -3980,34 +4003,63 @@ finish_objects (bool initp, unsigned priority, tree body, bool startp)
 /* The name of the function we create to handle initializations and
    destructions for objects with static storage duration.  */
 #define SSDF_IDENTIFIER "__static_initialization_and_destruction"
+#define OMP_SSDF_IDENTIFIER "__omp_target_static_init_and_destruction"
 
 /* Begins the generation of the function that will handle all
    initialization or destruction of objects with static storage
    duration at PRIORITY.
 
-   It is assumed that this function will only be called once.  */
+   It is assumed that this function will be called once for the host, and once
+   for an OpenMP offload target.  */
 
 static tree
-start_partial_init_fini_fn (bool initp, unsigned priority, unsigned count)
+start_partial_init_fini_fn (bool initp, unsigned priority, unsigned count,
+			    bool omp_target)
 {
-  char id[sizeof (SSDF_IDENTIFIER) + 1 /* '\0' */ + 32];
+  tree name;
 
-  /* Create the identifier for this function.  It will be of the form
-     SSDF_IDENTIFIER_<number>.  */
-  sprintf (id, "%s_%u", SSDF_IDENTIFIER, count);
+  if (omp_target)
+    {
+      char id[sizeof (OMP_SSDF_IDENTIFIER) + 1 /* \0 */ + 32];
+
+      /* Create the identifier for this function.  It will be of the form
+	 OMP_SSDF_IDENTIFIER_<number>.  */
+      sprintf (id, "%s_%u", OMP_SSDF_IDENTIFIER, count);
+      name = get_identifier (id);
+    }
+  else
+    {
+      char id[sizeof (SSDF_IDENTIFIER) + 1 /* '\0' */ + 32];
+      /* Create the identifier for this function.  It will be of the form
+	 SSDF_IDENTIFIER_<number>.  */
+      sprintf (id, "%s_%u", SSDF_IDENTIFIER, count);
+      name = get_identifier (id);
+    }
 
   tree type = build_function_type (void_type_node, void_list_node);
 
   /* Create the FUNCTION_DECL itself.  */
-  tree fn = build_lang_decl (FUNCTION_DECL, get_identifier (id), type);
+  tree fn = build_lang_decl (FUNCTION_DECL, name, type);
   TREE_PUBLIC (fn) = 0;
   DECL_ARTIFICIAL (fn) = 1;
 
+  if (omp_target)
+    {
+      DECL_ATTRIBUTES (fn)
+	= tree_cons (get_identifier ("omp declare target"), NULL_TREE,
+		     DECL_ATTRIBUTES (fn));
+      DECL_ATTRIBUTES (fn)
+	= tree_cons (get_identifier ("omp declare target nohost"), NULL_TREE,
+		     DECL_ATTRIBUTES (fn));
+    }
+
+  int idx = initp + 2 * omp_target;
+
   /* Put this function in the list of functions to be called from the
      static constructors and destructors.  */
-  if (!static_init_fini_fns[initp])
-    static_init_fini_fns[initp] = priority_map_t::create_ggc ();
-  auto &slot = static_init_fini_fns[initp]->get_or_insert (priority);
+  if (!static_init_fini_fns[idx])
+    static_init_fini_fns[idx] = priority_map_t::create_ggc ();
+  auto &slot = static_init_fini_fns[idx]->get_or_insert (priority);
   slot = tree_cons (fn, NULL_TREE, slot);
 
   /* Put the function in the global scope.  */
@@ -4203,22 +4255,76 @@ one_static_initialization_or_destruction (bool initp, tree decl, tree init)
    a TREE_LIST of VAR_DECL with static storage duration.
    Whether initialization or destruction is performed is specified by INITP.  */
 
-static void
+static tree
 emit_partial_init_fini_fn (bool initp, unsigned priority, tree vars,
-			   unsigned counter, location_t locus)
+			   unsigned counter, location_t locus, tree host_fn)
 {
   input_location = locus;
-  tree body = start_partial_init_fini_fn (initp, priority, counter);
+  bool omp_target = (host_fn != NULL_TREE);
+  tree body = start_partial_init_fini_fn (initp, priority, counter, omp_target);
+  tree fndecl = current_function_decl;
+
+  tree nonhost_if_stmt = NULL_TREE;
+  if (omp_target)
+    {
+      nonhost_if_stmt = begin_if_stmt ();
+      /* We add an "omp declare target nohost" attribute, but (for
+	 now) we still get a copy of the constructor/destructor on
+	 the host.  Make sure it does nothing unless we're on the
+	 target device.  */
+      tree fn
+	= builtin_decl_explicit (BUILT_IN_OMP_IS_INITIAL_DEVICE);
+      tree initial_dev = build_call_expr (fn, 0);
+      tree target_dev_p
+	= cp_build_binary_op (input_location, NE_EXPR, initial_dev,
+			      build_int_cst (NULL_TREE, 1),
+			      tf_warning_or_error);
+      finish_if_stmt_cond (target_dev_p, nonhost_if_stmt);
+    }
 
   for (tree node = vars; node; node = TREE_CHAIN (node))
-    /* Do one initialization or destruction.  */
-    one_static_initialization_or_destruction (initp, TREE_VALUE (node),
-					      TREE_PURPOSE (node));
+    {
+      tree decl = TREE_VALUE (node);
+      tree init = TREE_PURPOSE (node);
+	/* We will emit 'init' twice, and it is modified in-place during
+	   gimplification.  Make a copy here.  */
+      if (omp_target)
+	{
+	  /* We've already emitted INIT in the host version of the ctor/dtor
+	     function.  We need to deep-copy it (including new versions of
+	     local variables introduced, etc.) for use in the target
+	     ctor/dtor function.  */
+	  copy_body_data id;
+	  hash_map<tree, tree> decl_map;
+	  memset (&id, 0, sizeof (id));
+	  id.src_fn = host_fn;
+	  id.dst_fn = current_function_decl;
+	  id.src_cfun = DECL_STRUCT_FUNCTION (id.src_fn);
+	  id.decl_map = &decl_map;
+	  id.copy_decl = copy_decl_no_change;
+	  id.transform_call_graph_edges = CB_CGE_DUPLICATE;
+	  id.transform_new_cfg = true;
+	  id.transform_return_to_modify = false;
+	  id.eh_lp_nr = 0;
+	  walk_tree (&init, copy_tree_body_r, &id, NULL);
+	}
+      /* Do one initialization or destruction.  */
+      one_static_initialization_or_destruction (initp, decl, init);
+    }
+
+  if (omp_target)
+    {
+      /* Finish up nonhost if-stmt body.  */
+      finish_then_clause (nonhost_if_stmt);
+      finish_if_stmt (nonhost_if_stmt);
+    }
 
   /* Finish up the static storage duration function for this
      round.  */
   input_location = locus;
   finish_partial_init_fini_fn (body);
+
+  return fndecl;
 }
 
 /* VARS is a list of variables with static storage duration which may
@@ -4281,7 +4387,7 @@ prune_vars_needing_no_initialization (tree *vars)
    This reverses the variable ordering.  */
 
 void
-partition_vars_for_init_fini (tree var_list, priority_map_t *(&parts)[2])
+partition_vars_for_init_fini (tree var_list, priority_map_t *(&parts)[4])
 {
   for (auto node = var_list; node; node = TREE_CHAIN (node))
     {
@@ -4307,6 +4413,30 @@ partition_vars_for_init_fini (tree var_list, priority_map_t *(&parts)[2])
 	  auto &slot = parts[false]->get_or_insert (priority);
 	  slot = tree_cons (NULL_TREE, decl, slot);
 	}
+
+      if (flag_openmp
+	   && lookup_attribute ("omp declare target", DECL_ATTRIBUTES (decl)))
+	{
+	  priority_map_t **omp_parts = parts + 2;
+
+	  if (init || (flag_use_cxa_atexit && has_cleanup))
+	    {
+	      // Add to initialization list.
+	      if (!omp_parts[true])
+		omp_parts[true] = priority_map_t::create_ggc ();
+	      auto &slot = omp_parts[true]->get_or_insert (priority);
+	      slot = tree_cons (init, decl, slot);
+	    }
+
+	  if (!flag_use_cxa_atexit && has_cleanup)
+	    {
+	      // Add to finalization list.
+	      if (!omp_parts[false])
+		omp_parts[false] = priority_map_t::create_ggc ();
+	      auto &slot = omp_parts[false]->get_or_insert (priority);
+	      slot = tree_cons (NULL_TREE, decl, slot);
+	    }
+	}
     }
 }
 
@@ -4334,10 +4464,10 @@ write_out_vars (tree vars)
 
 static void
 generate_ctor_or_dtor_function (bool initp, unsigned priority,
-				tree fns, location_t locus)
+				tree fns, location_t locus, bool omp_target)
 {
   input_location = locus;
-  tree body = start_objects (initp, priority, bool (fns));
+  tree body = start_objects (initp, priority, bool (fns), omp_target);
 
   if (fns)
     {
@@ -4979,7 +5109,7 @@ c_parse_final_cleanups (void)
   auto_vec<tree> consteval_vtables;
 
   int retries = 0;
-  unsigned ssdf_count = 0;
+  unsigned ssdf_count = 0, omp_ssdf_count = 0;
   for (bool reconsider = true; reconsider; retries++)
     {
       reconsider = false;
@@ -5042,8 +5172,9 @@ c_parse_final_cleanups (void)
 	  write_out_vars (vars);
 
 	  function_depth++; // Disable GC
-	  priority_map_t *parts[2] = {nullptr, nullptr};
+	  priority_map_t *parts[4] = {nullptr, nullptr, nullptr, nullptr};
 	  partition_vars_for_init_fini (vars, parts);
+	  tree host_init_fini[2] = { NULL_TREE, NULL_TREE };
 
 	  for (unsigned initp = 2; initp--;)
 	    if (parts[initp])
@@ -5054,10 +5185,32 @@ c_parse_final_cleanups (void)
 		    // Partitioning kept the vars in reverse order.
 		    // We only want that for dtors.
 		    list = nreverse (list);
-		  emit_partial_init_fini_fn (initp, iter.first, list,
-					     ssdf_count++,
-					     locus_at_end_of_parsing);
+		  host_init_fini[initp]
+		    = emit_partial_init_fini_fn (initp, iter.first, list,
+						 ssdf_count++,
+						 locus_at_end_of_parsing,
+						 NULL_TREE);
 		}
+
+	  if (flag_openmp)
+	    {
+	      priority_map_t **omp_parts = parts + 2;
+	      for (unsigned initp = 2; initp--;)
+		if (omp_parts[initp])
+		  for (auto iter : *omp_parts[initp])
+		    {
+		      auto list = iter.second;
+		      if (initp)
+			// Partitioning kept the vars in reverse order.
+			// We only want that for dtors.
+			list = nreverse (list);
+		      emit_partial_init_fini_fn (initp, iter.first, list,
+						 omp_ssdf_count++,
+						 locus_at_end_of_parsing,
+						 host_init_fini[initp]);
+		  }
+	    }
+
 	  function_depth--; // Re-enable GC
 
 	  /* All those initializations and finalizations might cause
@@ -5223,7 +5376,11 @@ c_parse_final_cleanups (void)
   if (static_init_fini_fns[true])
     for (auto iter : *static_init_fini_fns[true])
       iter.second = nreverse (iter.second);
-  
+
+  if (flag_openmp && static_init_fini_fns[2 + true])
+    for (auto iter : *static_init_fini_fns[2 + true])
+      iter.second = nreverse (iter.second);
+
   /* Then, do the Objective-C stuff.  This is where all the
      Objective-C module stuff gets generated (symtab,
      class/protocol/selector lists etc).  This must be done after C++
@@ -5238,7 +5395,7 @@ c_parse_final_cleanups (void)
     {
       input_location = locus_at_end_of_parsing;
       tree body = start_partial_init_fini_fn (true, DEFAULT_INIT_PRIORITY,
-					      ssdf_count++);
+					      ssdf_count++, false);
       /* For Objective-C++, we may need to initialize metadata found
 	 in this module.  This must be done _before_ any other static
 	 initializations.  */
@@ -5257,18 +5414,26 @@ c_parse_final_cleanups (void)
 	static_init_fini_fns[true] = priority_map_t::create_ggc ();
       if (static_init_fini_fns[true]->get_or_insert (DEFAULT_INIT_PRIORITY))
 	has_module_inits = true;
+
+      if (flag_openmp)
+	{
+	  if (!static_init_fini_fns[2 + true])
+	    static_init_fini_fns[2 + true] = priority_map_t::create_ggc ();
+	  static_init_fini_fns[2 + true]->get_or_insert (DEFAULT_INIT_PRIORITY);
+	}
     }
 
   /* Generate initialization and destruction functions for all
      priorities for which they are required.  They have C-language
      linkage.  */
   push_lang_context (lang_name_c);
-  for (unsigned initp = 2; initp--;)
+  for (unsigned initp = 4; initp--;)
     if (static_init_fini_fns[initp])
       {
 	for (auto iter : *static_init_fini_fns[initp])
-	  generate_ctor_or_dtor_function (initp, iter.first, iter.second,
-					  locus_at_end_of_parsing);
+	  generate_ctor_or_dtor_function (initp & 1, iter.first, iter.second,
+					  locus_at_end_of_parsing,
+					  (initp & 2) != 0);
 	static_init_fini_fns[initp] = nullptr;
       }
   pop_lang_context ();
diff --git a/gcc/omp-builtins.def b/gcc/omp-builtins.def
index e0f03263db0..a80158f5c14 100644
--- a/gcc/omp-builtins.def
+++ b/gcc/omp-builtins.def
@@ -68,6 +68,8 @@ DEF_GOACC_BUILTIN_ONLY (BUILT_IN_GOACC_SINGLE_COPY_START, "GOACC_single_copy_sta
 DEF_GOACC_BUILTIN_ONLY (BUILT_IN_GOACC_SINGLE_COPY_END, "GOACC_single_copy_end",
 			BT_FN_VOID_PTR, ATTR_NOTHROW_LEAF_LIST)
 
+DEF_GOMP_BUILTIN (BUILT_IN_OMP_IS_INITIAL_DEVICE, "omp_is_initial_device",
+		  BT_FN_INT, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_GOMP_BUILTIN (BUILT_IN_OMP_GET_THREAD_NUM, "omp_get_thread_num",
 		  BT_FN_INT, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_GOMP_BUILTIN (BUILT_IN_OMP_GET_NUM_THREADS, "omp_get_num_threads",
diff --git a/gcc/tree.cc b/gcc/tree.cc
index 7e6de288886..097806e9875 100644
--- a/gcc/tree.cc
+++ b/gcc/tree.cc
@@ -8806,9 +8806,11 @@ get_file_function_name (const char *type)
      will be local to this file and the name is only necessary for
      debugging purposes. 
      We also assign sub_I and sub_D sufixes to constructors called from
-     the global static constructors.  These are always local.  */
+     the global static constructors.  These are always local.
+     OpenMP "declare target" offloaded constructors/destructors use "off_I" and
+     "off_D" for the same purpose.  */
   else if (((type[0] == 'I' || type[0] == 'D') && targetm.have_ctors_dtors)
-	   || (startswith (type, "sub_")
+	   || ((startswith (type, "sub_") || startswith (type, "off_"))
 	       && (type[4] == 'I' || type[4] == 'D')))
     {
       const char *file = main_input_filename;
diff --git a/libgomp/testsuite/libgomp.c++/static-aggr-constructor-destructor-1.C b/libgomp/testsuite/libgomp.c++/static-aggr-constructor-destructor-1.C
new file mode 100644
index 00000000000..91d8469a150
--- /dev/null
+++ b/libgomp/testsuite/libgomp.c++/static-aggr-constructor-destructor-1.C
@@ -0,0 +1,28 @@
+// { dg-do run }
+
+#include <cassert>
+
+#pragma omp declare target
+
+struct str {
+  str(int x) : _x(x) { }
+  int add(str o) { return _x + o._x; }
+  int _x;
+} v1(5);
+
+#pragma omp end declare target
+
+int main()
+{
+  int res = -1;
+  str v2(2);
+
+#pragma omp target map(from:res)
+  {
+    res = v1.add(v2);
+  }
+
+  assert (res == 7);
+
+  return 0;
+}
diff --git a/libgomp/testsuite/libgomp.c++/static-aggr-constructor-destructor-2.C b/libgomp/testsuite/libgomp.c++/static-aggr-constructor-destructor-2.C
new file mode 100644
index 00000000000..1bf3ee8e31c
--- /dev/null
+++ b/libgomp/testsuite/libgomp.c++/static-aggr-constructor-destructor-2.C
@@ -0,0 +1,31 @@
+// { dg-do run }
+
+#include <cassert>
+
+#pragma omp declare target
+
+template<typename T>
+struct str {
+  str(T x) : _x(x) { }
+  T add(str o) { return _x + o._x; }
+  T _x;
+};
+
+str<long> v1(5);
+
+#pragma omp end declare target
+
+int main()
+{
+  long res = -1;
+  str<long> v2(2);
+
+#pragma omp target map(from:res)
+  {
+    res = v1.add(v2);
+  }
+
+  assert (res == 7);
+
+  return 0;
+}
diff --git a/libgomp/testsuite/libgomp.c++/static-aggr-constructor-destructor-3.C b/libgomp/testsuite/libgomp.c++/static-aggr-constructor-destructor-3.C
new file mode 100644
index 00000000000..8d4aff21cd7
--- /dev/null
+++ b/libgomp/testsuite/libgomp.c++/static-aggr-constructor-destructor-3.C
@@ -0,0 +1,36 @@
+// { dg-do run }
+
+#include <cassert>
+
+#pragma omp declare target
+
+struct item {
+  item(item *p, int v) : prev(p), val(v) { }
+  int get() { return prev ? prev->get() * val : val; }
+  item *prev;
+  int val;
+};
+
+/* This case demonstrates why constructing on the host and then copying to
+   the target would be less desirable.  With on-target construction, "prev"
+   for each 'item' will be a device pointer, not a host pointer.  */
+item hubert1(nullptr, 3);
+item hubert2(&hubert1, 5);
+item hubert3(&hubert2, 7);
+item hubert4(&hubert3, 11);
+
+#pragma omp end declare target
+
+int main()
+{
+  int res = -1;
+
+#pragma omp target map(from:res)
+  {
+    res = hubert4.get ();
+  }
+
+  assert (res == 1155);
+
+  return 0;
+}
-- 
2.25.1

Re: [PATCH] OpenMP: Constructors and destructors for "declare target" static aggregates

[Tobias Burnus]

Hi Julian, hi all,

(I have not (yet) looked at the patch/testcase in depth - and I prefer
that someone knowledgeable with C++ constructors comments. However:)

Regarding only nvptx - and the testcase on nvptx:

On 12.05.23 14:02, Julian Brown wrote:
> The approach taken is to generate a set of constructors to run on the
> target: this currently works for AMD GCN, but fails on NVPTX due
> to lack of constructor/destructor support there so far on mainline.
> (See the new test static-aggr-constructor-destructor-3.C for a reason
> why running constructors on the target is preferable to e.g. constructing
> on the host and then copying the resulting object to the target.)

(I think also the wording in OpenMP implies that it is constructed
on the device and not copied over from the host, albeit the wording
is not very clear.)

For nvptx constructor/destructor support, see email thread
"nvptx: Support global constructors/destructors via 'collect2' for offloading",
e.g., https://gcc.gnu.org/pipermail/gcc-patches/2023-January/609711.html
* * *

If I run the testcase manually with nvptx offloading and -O0, I get:
   libgomp/testsuite/libgomp.c++/static-aggr-constructor-destructor-3.C:8:3: error:
     alias definitions not supported in this configuration

and with -O1 and higher:
   libgomp/testsuite/libgomp.c++/static-aggr-constructor-destructor-3.C:36:1:
      sorry, unimplemented: global constructors not supported on this target

As DEFAULT_CFLAGS is -O2 checking for the proper error works, i.e. something
like (untested and ... to be filled in):

   /* { dg-message "sorry, ..." "..." target { offload_target_nvptx } } }
   /* { dg-excess-errors "Follow-up errors from mkoffload and lto-wrapper" { target { offload_target_nvptx } } */


Tobias

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