[PATCH 2/n] OpenMP 4.0 offloading infrastructure: LTO streaming

[Ilya Verbin <iverbin at gmail dot com>]

Hello,

This patch enables the streaming of LTO bytecode, needed by offload target,
using existing LTO infrastructure.  It creates new prefix for the section names
(.gnu.target_lto_) and streams out the functions and variables with "omp declare
target" attribute, including the functions for outlined '#pragma omp target'
regions.  The offload compiler (under ifdef ACCEL_COMPILER) reads and compiles
these new sections.

But I have doubts regarding the offload_lto_mode switch.  Why I added it:
The outlined target regions (say omp_fn0) contains references from the parent
functions.  And that's correct for the case when we stream out the host-side
version of omp_fn0.  But for the target version there are no parent functions,
node->used_from_other_partition gets incorrect value (always 1), and offload
compiler crashes on streaming in.

Another solution is to remain referenced_from_other_partition_p and
reachable_from_other_partition_p unchanged, then used_from_other_partition will
have incorrect value for target regions, but the offload compiler will just
ignore it.  Which approach is better?
Anyway, now it's bootstrapped and regtested on i686-linux and x86_64-linux.


2014-09-27  Ilya Verbin  <ilya.verbin@intel.com>
	    Ilya Tocar  <ilya.tocar@intel.com>
	    Andrey Turetskiy  <andrey.turetskiy@intel.com>
	    Bernd Schmidt  <bernds@codesourcery.com>
gcc/
	* cgraph.h (symtab_node): Add need_dump flag.
	* cgraphunit.c: Include lto-section-names.h.
	(initialize_offload): New function.
	(ipa_passes): Initialize offload and call ipa_write_summaries if there
	is something to write to OMP_SECTION_NAME_PREFIX sections.
	(symbol_table::compile): Call lto_streamer_hooks_init under flag_openmp.
	* ipa-inline-analysis.c (inline_generate_summary): Do not exit under
	flag_openmp.
	(inline_free_summary): Always remove hooks.
	* lto-cgraph.c (lto_set_symtab_encoder_in_partition): Exit if there is
	no need to encode the node.
	(referenced_from_other_partition_p, reachable_from_other_partition_p):
	Ignore references from non-target functions to target functions if we
	are streaming out target-side bytecode (offload lto mode).
	(select_what_to_dump): New function.
	* lto-section-names.h (OMP_SECTION_NAME_PREFIX): Define.
	(section_name_prefix): Declare.
	* lto-streamer.c (offload_lto_mode): New variable.
	(section_name_prefix): New variable.
	(lto_get_section_name): Use section_name_prefix instead of
	LTO_SECTION_NAME_PREFIX.
	* lto-streamer.h (select_what_to_dump): Declare.
	(offload_lto_mode): Declare.
	* omp-low.c (is_targetreg_ctx): New function.
	(create_omp_child_function, check_omp_nesting_restrictions): Use it.
	(expand_omp_target): Set mark_force_output for the target functions.
	(lower_omp_critical): Add target attribute for omp critical symbol.
	* passes.c (ipa_write_summaries): Call select_what_to_dump.
gcc/lto/
	* lto-object.c (lto_obj_add_section): Use section_name_prefix instead of
	LTO_SECTION_NAME_PREFIX.
	* lto-partition.c (add_symbol_to_partition_1): Always set
	node->need_dump to true.
	(lto_promote_cross_file_statics): Call select_what_to_dump.
	* lto.c (lto_section_with_id): Use section_name_prefix instead of
	LTO_SECTION_NAME_PREFIX.
	(read_cgraph_and_symbols): Read OMP_SECTION_NAME_PREFIX sections, if
	being built as an offload compiler.

Thanks,
  -- Ilya

---

diff --git a/gcc/cgraph.h b/gcc/cgraph.h
index 7481906..9ab970d 100644
--- a/gcc/cgraph.h
+++ b/gcc/cgraph.h
@@ -444,6 +444,11 @@ public:
   /* Set when init priority is set.  */
   unsigned in_init_priority_hash : 1;
 
+  /* Set when symbol needs to be dumped into LTO bytecode for LTO,
+     or in pragma omp target case, for separate compilation targeting
+     a different architecture.  */
+  unsigned need_dump : 1;
+
 
   /* Ordering of all symtab entries.  */
   int order;
diff --git a/gcc/cgraphunit.c b/gcc/cgraphunit.c
index b854e4b..4ab4c57 100644
--- a/gcc/cgraphunit.c
+++ b/gcc/cgraphunit.c
@@ -211,6 +211,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree-nested.h"
 #include "gimplify.h"
 #include "dbgcnt.h"
+#include "lto-section-names.h"
 
 /* Queue of cgraph nodes scheduled to be added into cgraph.  This is a
    secondary queue used during optimization to accommodate passes that
@@ -1994,9 +1995,40 @@ output_in_order (bool no_reorder)
   free (nodes);
 }
 
+/* Check whether there is at least one function or global variable to offload.
+   */
+
+static bool
+initialize_offload (void)
+{
+  bool have_offload = false;
+  struct cgraph_node *node;
+  struct varpool_node *vnode;
+
+  FOR_EACH_DEFINED_FUNCTION (node)
+    if (lookup_attribute ("omp declare target", DECL_ATTRIBUTES (node->decl)))
+      {
+	have_offload = true;
+	break;
+      }
+
+  FOR_EACH_DEFINED_VARIABLE (vnode)
+    {
+      if (!lookup_attribute ("omp declare target",
+			     DECL_ATTRIBUTES (vnode->decl))
+	  || TREE_CODE (vnode->decl) != VAR_DECL
+	  || DECL_SIZE (vnode->decl) == 0)
+	continue;
+      have_offload = true;
+    }
+
+  return have_offload;
+}
+
 static void
 ipa_passes (void)
 {
+  bool have_offload = false;
   gcc::pass_manager *passes = g->get_passes ();
 
   set_cfun (NULL);
@@ -2004,6 +2036,14 @@ ipa_passes (void)
   gimple_register_cfg_hooks ();
   bitmap_obstack_initialize (NULL);
 
+  if (!in_lto_p && flag_openmp)
+    {
+      have_offload = initialize_offload ();
+      /* OpenMP offloading requires LTO infrastructure.  */
+      if (have_offload)
+	flag_generate_lto = 1;
+    }
+
   invoke_plugin_callbacks (PLUGIN_ALL_IPA_PASSES_START, NULL);
 
   if (!in_lto_p)
@@ -2041,7 +2081,20 @@ ipa_passes (void)
     targetm.asm_out.lto_start ();
 
   if (!in_lto_p)
-    ipa_write_summaries ();
+    {
+      if (have_offload)
+	{
+	  offload_lto_mode = true;
+	  section_name_prefix = OMP_SECTION_NAME_PREFIX;
+	  ipa_write_summaries ();
+	}
+      if (flag_lto)
+	{
+	  offload_lto_mode = false;
+	  section_name_prefix = LTO_SECTION_NAME_PREFIX;
+	  ipa_write_summaries ();
+	}
+    }
 
   if (flag_generate_lto)
     targetm.asm_out.lto_end ();
@@ -2122,7 +2175,7 @@ symbol_table::compile (void)
   state = IPA;
 
   /* If LTO is enabled, initialize the streamer hooks needed by GIMPLE.  */
-  if (flag_lto)
+  if (flag_lto || flag_openmp)
     lto_streamer_hooks_init ();
 
   /* Don't run the IPA passes if there was any error or sorry messages.  */
diff --git a/gcc/ipa-inline-analysis.c b/gcc/ipa-inline-analysis.c
index 38f56d2..076a1e8 100644
--- a/gcc/ipa-inline-analysis.c
+++ b/gcc/ipa-inline-analysis.c
@@ -4010,7 +4010,7 @@ inline_generate_summary (void)
 
   /* When not optimizing, do not bother to analyze.  Inlining is still done
      because edge redirection needs to happen there.  */
-  if (!optimize && !flag_lto && !flag_wpa)
+  if (!optimize && !flag_lto && !flag_wpa && !flag_openmp)
     return;
 
   function_insertion_hook_holder =
@@ -4325,11 +4325,6 @@ void
 inline_free_summary (void)
 {
   struct cgraph_node *node;
-  if (!inline_edge_summary_vec.exists ())
-    return;
-  FOR_EACH_DEFINED_FUNCTION (node)
-    if (!node->alias)
-      reset_inline_summary (node);
   if (function_insertion_hook_holder)
     symtab->remove_cgraph_insertion_hook (function_insertion_hook_holder);
   function_insertion_hook_holder = NULL;
@@ -4345,6 +4340,11 @@ inline_free_summary (void)
   if (edge_duplication_hook_holder)
     symtab->remove_edge_duplication_hook (edge_duplication_hook_holder);
   edge_duplication_hook_holder = NULL;
+  if (!inline_edge_summary_vec.exists ())
+    return;
+  FOR_EACH_DEFINED_FUNCTION (node)
+    if (!node->alias)
+      reset_inline_summary (node);
   vec_free (inline_summary_vec);
   inline_edge_summary_vec.release ();
   if (edge_predicate_pool)
diff --git a/gcc/lto-cgraph.c b/gcc/lto-cgraph.c
index 0584946..78b7fc8 100644
--- a/gcc/lto-cgraph.c
+++ b/gcc/lto-cgraph.c
@@ -239,6 +239,9 @@ void
 lto_set_symtab_encoder_in_partition (lto_symtab_encoder_t encoder,
 				     symtab_node *node)
 {
+  /* Ignore not needed nodes.  */
+  if (!node->need_dump)
+    return;
   int index = lto_symtab_encoder_encode (encoder, node);
   encoder->nodes[index].in_partition = true;
 }
@@ -321,6 +324,12 @@ referenced_from_other_partition_p (symtab_node *node, lto_symtab_encoder_t encod
 
   for (i = 0; node->iterate_referring (i, ref); i++)
     {
+      /* Ignore references from non-target functions in offload lto mode.  */
+      if (offload_lto_mode
+	  && !lookup_attribute ("omp declare target",
+				DECL_ATTRIBUTES (ref->referring->decl)))
+	continue;
+
       if (ref->referring->in_other_partition
           || !lto_symtab_encoder_in_partition_p (encoder, ref->referring))
 	return true;
@@ -339,9 +348,17 @@ reachable_from_other_partition_p (struct cgraph_node *node, lto_symtab_encoder_t
   if (node->global.inlined_to)
     return false;
   for (e = node->callers; e; e = e->next_caller)
-    if (e->caller->in_other_partition
-	|| !lto_symtab_encoder_in_partition_p (encoder, e->caller))
-      return true;
+    {
+      /* Ignore references from non-target functions in offload lto mode.  */
+      if (offload_lto_mode
+	  && !lookup_attribute ("omp declare target",
+				DECL_ATTRIBUTES (e->caller->decl)))
+	continue;
+
+      if (e->caller->in_other_partition
+	  || !lto_symtab_encoder_in_partition_p (encoder, e->caller))
+	return true;
+    }
   return false;
 }
 
@@ -802,6 +819,18 @@ create_references (lto_symtab_encoder_t encoder, symtab_node *node)
       lto_symtab_encoder_encode (encoder, ref->referred);
 }
 
+/* Select what needs to be streamed out.  In regular lto mode stream everything.
+   In offload lto mode stream only stuff marked with an attribute.  */
+void
+select_what_to_dump (void)
+{
+  struct symtab_node *snode;
+  FOR_EACH_SYMBOL (snode)
+    snode->need_dump = !offload_lto_mode
+		       || lookup_attribute ("omp declare target",
+					    DECL_ATTRIBUTES (snode->decl));
+}
+
 /* Find all symbols we want to stream into given partition and insert them
    to encoders.
 
diff --git a/gcc/lto-section-names.h b/gcc/lto-section-names.h
index cb75230..06d2caf 100644
--- a/gcc/lto-section-names.h
+++ b/gcc/lto-section-names.h
@@ -25,6 +25,11 @@ along with GCC; see the file COPYING3.  If not see
    name for the functions and static_initializers.  For other types of
    sections a '.' and the section type are appended.  */
 #define LTO_SECTION_NAME_PREFIX ".gnu.lto_"
+#define OMP_SECTION_NAME_PREFIX ".gnu.target_lto_"
+
+/* Can be either OMP_SECTION_NAME_PREFIX when we stream 'pragma omp target'
+   stuff, or LTO_SECTION_NAME_PREFIX for LTO case.  */
+extern const char *section_name_prefix;
 
 /* Segment name for LTO sections.  This is only used for Mach-O.  */
 
diff --git a/gcc/lto-streamer.c b/gcc/lto-streamer.c
index 3480723..95232f9 100644
--- a/gcc/lto-streamer.c
+++ b/gcc/lto-streamer.c
@@ -48,6 +48,8 @@ struct lto_stats_d lto_stats;
 static bitmap_obstack lto_obstack;
 static bool lto_obstack_initialized;
 
+bool offload_lto_mode = false;
+const char *section_name_prefix = LTO_SECTION_NAME_PREFIX;
 
 /* Return a string representing LTO tag TAG.  */
 
@@ -177,7 +179,7 @@ lto_get_section_name (int section_type, const char *name, struct lto_file_decl_d
     sprintf (post, "." HOST_WIDE_INT_PRINT_HEX_PURE, f->id);
   else
     sprintf (post, "." HOST_WIDE_INT_PRINT_HEX_PURE, get_random_seed (false)); 
-  return concat (LTO_SECTION_NAME_PREFIX, sep, add, post, NULL);
+  return concat (section_name_prefix, sep, add, post, NULL);
 }
 
 
diff --git a/gcc/lto-streamer.h b/gcc/lto-streamer.h
index 4bec969..0016eef 100644
--- a/gcc/lto-streamer.h
+++ b/gcc/lto-streamer.h
@@ -831,6 +831,7 @@ bool referenced_from_this_partition_p (symtab_node *,
 bool reachable_from_this_partition_p (struct cgraph_node *,
 				      lto_symtab_encoder_t);
 lto_symtab_encoder_t compute_ltrans_boundary (lto_symtab_encoder_t encoder);
+void select_what_to_dump (void);
 
 
 /* In lto-symtab.c.  */
@@ -846,6 +847,9 @@ extern void lto_write_options (void);
 /* Statistics gathered during LTO, WPA and LTRANS.  */
 extern struct lto_stats_d lto_stats;
 
+/* Regular or offload mode of LTO.  */
+extern bool offload_lto_mode;
+
 /* Section names corresponding to the values of enum lto_section_type.  */
 extern const char *lto_section_name[];
 
diff --git a/gcc/lto/lto-object.c b/gcc/lto/lto-object.c
index 323f7b2..4ee752f 100644
--- a/gcc/lto/lto-object.c
+++ b/gcc/lto/lto-object.c
@@ -230,8 +230,7 @@ lto_obj_add_section (void *data, const char *name, off_t offset,
   void **slot;
   struct lto_section_list *list = loasd->list;
 
-  if (strncmp (name, LTO_SECTION_NAME_PREFIX,
-	       strlen (LTO_SECTION_NAME_PREFIX)) != 0)
+  if (strncmp (name, section_name_prefix, strlen (section_name_prefix)))
     return 1;
 
   new_name = xstrdup (name);
diff --git a/gcc/lto/lto-partition.c b/gcc/lto/lto-partition.c
index 0451a66..332562f 100644
--- a/gcc/lto/lto-partition.c
+++ b/gcc/lto/lto-partition.c
@@ -134,6 +134,7 @@ add_symbol_to_partition_1 (ltrans_partition part, symtab_node *node)
   gcc_assert (c != SYMBOL_EXTERNAL
 	      && (c == SYMBOL_DUPLICATE || !symbol_partitioned_p (node)));
 
+  node->need_dump = true;
   lto_set_symtab_encoder_in_partition (part->encoder, node);
 
   if (symbol_partitioned_p (node))
@@ -920,6 +921,8 @@ lto_promote_cross_file_statics (void)
 
   gcc_assert (flag_wpa);
 
+  select_what_to_dump ();
+
   /* First compute boundaries.  */
   n_sets = ltrans_partitions.length ();
   for (i = 0; i < n_sets; i++)
diff --git a/gcc/lto/lto.c b/gcc/lto/lto.c
index 6cbb178..f23d997 100644
--- a/gcc/lto/lto.c
+++ b/gcc/lto/lto.c
@@ -2125,7 +2125,7 @@ lto_section_with_id (const char *name, unsigned HOST_WIDE_INT *id)
 {
   const char *s;
 
-  if (strncmp (name, LTO_SECTION_NAME_PREFIX, strlen (LTO_SECTION_NAME_PREFIX)))
+  if (strncmp (name, section_name_prefix, strlen (section_name_prefix)))
     return 0;
   s = strrchr (name, '.');
   return s && sscanf (s, "." HOST_WIDE_INT_PRINT_HEX_PURE, id) == 1;
@@ -2899,6 +2899,10 @@ read_cgraph_and_symbols (unsigned nfiles, const char **fnames)
 
   timevar_push (TV_IPA_LTO_DECL_IN);
 
+#ifdef ACCEL_COMPILER
+    section_name_prefix = OMP_SECTION_NAME_PREFIX;
+#endif
+
   real_file_decl_data
     = decl_data = ggc_cleared_vec_alloc<lto_file_decl_data_ptr> (nfiles + 1);
   real_file_count = nfiles;
diff --git a/gcc/omp-low.c b/gcc/omp-low.c
index 82651ea..7d587b3 100644
--- a/gcc/omp-low.c
+++ b/gcc/omp-low.c
@@ -257,6 +257,16 @@ is_parallel_ctx (omp_context *ctx)
 }
 
 
+/* Return true if CTX is for an omp target region.  */
+
+static inline bool
+is_targetreg_ctx (omp_context *ctx)
+{
+  return gimple_code (ctx->stmt) == GIMPLE_OMP_TARGET
+	 && gimple_omp_target_kind (ctx->stmt) == GF_OMP_TARGET_KIND_REGION;
+}
+
+
 /* Return true if CTX is for an omp task.  */
 
 static inline bool
@@ -1930,9 +1940,7 @@ create_omp_child_function (omp_context *ctx, bool task_copy)
     {
       omp_context *octx;
       for (octx = ctx; octx; octx = octx->outer)
-	if (gimple_code (octx->stmt) == GIMPLE_OMP_TARGET
-	    && gimple_omp_target_kind (octx->stmt)
-	       == GF_OMP_TARGET_KIND_REGION)
+	if (is_targetreg_ctx (octx))
 	  {
 	    target_p = true;
 	    break;
@@ -2588,8 +2596,7 @@ check_omp_nesting_restrictions (gimple stmt, omp_context *ctx)
       break;
     case GIMPLE_OMP_TARGET:
       for (; ctx != NULL; ctx = ctx->outer)
-	if (gimple_code (ctx->stmt) == GIMPLE_OMP_TARGET
-	    && gimple_omp_target_kind (ctx->stmt) == GF_OMP_TARGET_KIND_REGION)
+	if (is_targetreg_ctx (ctx))
 	  {
 	    const char *name;
 	    switch (gimple_omp_target_kind (stmt))
@@ -8206,6 +8213,7 @@ expand_omp_target (struct omp_region *region)
   if (kind == GF_OMP_TARGET_KIND_REGION)
     {
       unsigned srcidx, dstidx, num;
+      struct cgraph_node *node;
 
       /* If the target region needs data sent from the parent
 	 function, then the very first statement (except possible
@@ -8337,6 +8345,11 @@ expand_omp_target (struct omp_region *region)
       push_cfun (child_cfun);
       cgraph_edge::rebuild_edges ();
 
+      /* Prevent IPA from removing child_fn as unreachable, since there are no
+	 refs from the parent function to the target side child_fn.  */
+      node = cgraph_node::get (child_fn);
+      node->mark_force_output ();
+
       /* Some EH regions might become dead, see PR34608.  If
 	 pass_cleanup_cfg isn't the first pass to happen with the
 	 new child, these dead EH edges might cause problems.
@@ -9207,6 +9220,19 @@ lower_omp_critical (gimple_stmt_iterator *gsi_p, omp_context *ctx)
 	  DECL_COMMON (decl) = 1;
 	  DECL_ARTIFICIAL (decl) = 1;
 	  DECL_IGNORED_P (decl) = 1;
+
+	  /* If '#pragma omp critical' is inside target region, the symbol must
+	     have an 'omp declare target' attribute.  */
+	  omp_context *octx;
+	  for (octx = ctx->outer; octx; octx = octx->outer)
+	    if (is_targetreg_ctx (octx))
+	      {
+		DECL_ATTRIBUTES (decl)
+		  = tree_cons (get_identifier ("omp declare target"),
+			       NULL_TREE, DECL_ATTRIBUTES (decl));
+		break;
+	      }
+
 	  varpool_node::finalize_decl (decl);
 
 	  splay_tree_insert (critical_name_mutexes, (splay_tree_key) name,
diff --git a/gcc/passes.c b/gcc/passes.c
index 5001c3d..d63c913 100644
--- a/gcc/passes.c
+++ b/gcc/passes.c
@@ -2308,6 +2308,8 @@ ipa_write_summaries (void)
   if (!flag_generate_lto || seen_error ())
     return;
 
+  select_what_to_dump ();
+
   encoder = lto_symtab_encoder_new (false);
 
   /* Create the callgraph set in the same order used in
-- 
1.7.1