[PATCH] Fix parloops gimple_uid usage

[Tom de Vries]

Hi,

In tree-parloops.c:gather_scalar_reductions, we find the comment:
...
  /* As gimple_uid is used by the vectorizer in between
     vect_analyze_loop_form and destroy_loop_vec_info, we can set
     gimple_uid of reduc_phi stmts only now.  */
  reduction_list->traverse <void *, set_reduc_phi_uids> (NULL);
...
However, the usage of gimple_uid seems to extend until the 
free_stmt_vec_info_vec call at the end of parallelize_loops (the pass 
top-level function). During free_stmt_vec_info_vec we test for 
gimple_uid == 0 in vinfo_for_stmt.

By initializing all the phis in the function with -1 before using them 
in the reduct_phi stmts:
...
   destroy_loop_vec_info (simple_loop_info, true);
   destroy_loop_vec_info (simple_inner_loop_info, true);



   /* As gimple_uid is used by the vectorizer in between
      vect_analyze_loop_form and destroy_loop_vec_info, we can set
      gimple_uid of reduc_phi stmts only now. */
+  basic_block bb;
+  FOR_EACH_BB_FN (bb, cfun)
+    for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+      gimple_set_uid (gsi_stmt (gsi), (unsigned int)-1);
 reduction_list->traverse <void *, set_reduc_phi_uids> (NULL);
...
we trigger a sigsegv in vinfo_for_stmt while trying to access 
stmt_vec_info_vec[4294967295 - 1].

This patch fixes that by moving the calls to init_stmt_vec_info_vec and
free_stmt_vec_info_vec from parallelize_loops and gather_scalar_reductions.

Furthermore, now that the gimple_uids are properly initialized, we can 
in reduction_phi:
- handle 0 (new phi) and -1 (initialized) values, both meaning the
  phi's not in the table, and
- assert that returned entries in fact match the phi argument.

OK for trunk if bootstrap and reg-test passes?

Thanks,
- Tom

Fix parloops gimple_uid usage

2015-10-09  Tom de Vries  <t...@codesourcery.com>

	* tree-parloops.c (reduction_phi): Handle cases that gimple_uid is 0 or
	-1.  Add assert that returned entry matches phi argument.
	(parallelize_loops): Move calls to init_stmt_vec_info_vec and
	free_stmt_vec_info_vec ...
	(gather_scalar_reductions): ... here.  Initialize gimple_uids of phis
	with -1.
---
 gcc/tree-parloops.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/gcc/tree-parloops.c b/gcc/tree-parloops.c
index 741392b..7366318 100644
--- a/gcc/tree-parloops.c
+++ b/gcc/tree-parloops.c
@@ -237,9 +237,14 @@ reduction_phi (reduction_info_table_type *reduction_list, gimple *phi)
   if (reduction_list->elements () == 0 || phi == NULL)
     return NULL;
 
+  if (gimple_uid (phi) == (unsigned int)-1
+      || gimple_uid (phi) == 0)
+    return NULL;
+
   tmpred.reduc_phi = phi;
   tmpred.reduc_version = gimple_uid (phi);
   red = reduction_list->find (&tmpred);
+  gcc_assert (red == NULL || red->reduc_phi == phi);
 
   return red;
 }
@@ -2392,6 +2397,9 @@ gather_scalar_reductions (loop_p loop, reduction_info_table_type *reduction_list
   loop_vec_info simple_inner_loop_info = NULL;
   bool allow_double_reduc = true;
 
+  if (!stmt_vec_info_vec.exists ())
+    init_stmt_vec_info_vec ();
+
   simple_loop_info = vect_analyze_loop_form (loop);
   if (simple_loop_info == NULL)
     return;
@@ -2453,9 +2461,16 @@ gather_scalar_reductions (loop_p loop, reduction_info_table_type *reduction_list
   destroy_loop_vec_info (simple_loop_info, true);
   destroy_loop_vec_info (simple_inner_loop_info, true);
 
+  /* Release the claim on gimple_uid.  */
+  free_stmt_vec_info_vec ();
+
   /* As gimple_uid is used by the vectorizer in between vect_analyze_loop_form
-     and destroy_loop_vec_info, we can set gimple_uid of reduc_phi stmts
-     only now.  */
+     and free_stmt_vec_info_vec, we can set gimple_uid of reduc_phi stmts only
+     now.  */
+  basic_block bb;
+  FOR_EACH_BB_FN (bb, cfun)
+    for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+      gimple_set_uid (gsi_stmt (gsi), (unsigned int)-1);
   reduction_list->traverse <void *, set_reduc_phi_uids> (NULL);
 }
 
@@ -2603,7 +2618,6 @@ parallelize_loops (void)
 
   gcc_obstack_init (&parloop_obstack);
   reduction_info_table_type reduction_list (10);
-  init_stmt_vec_info_vec ();
 
   FOR_EACH_LOOP (loop, 0)
     {
@@ -2695,7 +2709,6 @@ parallelize_loops (void)
 			 n_threads, &niter_desc);
     }
 
-  free_stmt_vec_info_vec ();
   obstack_free (&parloop_obstack, NULL);
 
   /* Parallelization will cause new function calls to be inserted through
-- 
1.9.1