[gcc/devel/gccgo] tree-optimization/95172 - avoid mixing conditionalized and ordered SM

[Ian Lance Taylor]

https://gcc.gnu.org/g:52a0f83980082c9995f2d8ec9b88548520fb8a5f

commit 52a0f83980082c9995f2d8ec9b88548520fb8a5f
Author: Richard Biener <rguenther@suse.de>
Date:   Mon May 18 09:17:24 2020 +0200

    tree-optimization/95172 - avoid mixing conditionalized and ordered SM
    
    The following testcase shows a missed optimization that then leads to
    wrong-code when issueing SMed stores on exits.  When we were able to
    compute an ordered sequence of stores for an exit we need to emit
    that in the correct order and we can emit it disregarding to any
    conditional for whether a store actually happened (we know it did).
    We can also improve detection as of whether we need conditional
    processing at all.  Both parts fix the testcase.
    
    2020-05-18  Richard Biener  <rguenther@suse.de>
    
            PR tree-optimization/95172
            * tree-ssa-loop-im.c (execute_sm): Get flag whether we
            eventually need the conditional processing.
            (execute_sm_exit): When processing an orderd sequence
            avoid doing any conditional processing.
            (hoist_memory_references): Pass down whether all edges
            have ordered processing for a ref to execute_sm.
    
            * gcc.dg/torture/pr95172.c: New testcase.

Diff:
---
 gcc/ChangeLog                          | 10 ++++++++++
 gcc/testsuite/ChangeLog                |  5 +++++
 gcc/testsuite/gcc.dg/torture/pr95172.c | 17 +++++++++++++++++
 gcc/tree-ssa-loop-im.c                 | 11 ++++++-----
 4 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 3a090452a96..491293d77df 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,13 @@
+2020-05-18  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/95172
+	* tree-ssa-loop-im.c (execute_sm): Get flag whether we
+	eventually need the conditional processing.
+	(execute_sm_exit): When processing an orderd sequence
+	avoid doing any conditional processing.
+	(hoist_memory_references): Pass down whether all edges
+	have ordered processing for a ref to execute_sm.
+
 2020-05-17 Jeff Law  <law@redhat.com>
 
 	* config/h8300/predicates.md (pc_or_label_operand): New predicate.
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 54fbdb08b66..1123599b9a7 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-05-18  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/95172
+	* gcc.dg/torture/pr95172.c: New testcase.
+
 2020-05-17  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR target/95021
diff --git a/gcc/testsuite/gcc.dg/torture/pr95172.c b/gcc/testsuite/gcc.dg/torture/pr95172.c
new file mode 100644
index 00000000000..b39de69f08e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr95172.c
@@ -0,0 +1,17 @@
+/* { dg-do run } */
+
+int a, d;
+int *b = &a;
+short c;
+int main()
+{
+  for (; c <= 4; c--) {
+    for (; d;)
+      ;
+    a = 1;
+    *b = 0;
+  }
+  if (a != 0)
+    __builtin_abort ();
+  return 0;
+}
diff --git a/gcc/tree-ssa-loop-im.c b/gcc/tree-ssa-loop-im.c
index 0d77aaa08a5..63f4ef8883c 100644
--- a/gcc/tree-ssa-loop-im.c
+++ b/gcc/tree-ssa-loop-im.c
@@ -2130,7 +2130,7 @@ struct sm_aux
 
 static void
 execute_sm (class loop *loop, im_mem_ref *ref,
-	    hash_map<im_mem_ref *, sm_aux *> &aux_map)
+	    hash_map<im_mem_ref *, sm_aux *> &aux_map, bool maybe_mt)
 {
   gassign *load;
   struct fmt_data fmt_data;
@@ -2154,8 +2154,9 @@ execute_sm (class loop *loop, im_mem_ref *ref,
   for_each_index (&ref->mem.ref, force_move_till, &fmt_data);
 
   bool always_stored = ref_always_accessed_p (loop, ref, true);
-  if (bb_in_transaction (loop_preheader_edge (loop)->src)
-      || (! flag_store_data_races && ! always_stored))
+  if (maybe_mt
+      && (bb_in_transaction (loop_preheader_edge (loop)->src)
+	  || (! flag_store_data_races && ! always_stored)))
     multi_threaded_model_p = true;
 
   if (multi_threaded_model_p)
@@ -2244,7 +2245,7 @@ execute_sm_exit (class loop *loop, edge ex, vec<seq_entry> &seq,
       else
 	{
 	  sm_aux *aux = *aux_map.get (ref);
-	  if (!aux->store_flag)
+	  if (!aux->store_flag || kind == sm_ord)
 	    {
 	      gassign *store;
 	      store = gimple_build_assign (unshare_expr (ref->mem.ref),
@@ -2630,7 +2631,7 @@ hoist_memory_references (class loop *loop, bitmap mem_refs,
   EXECUTE_IF_SET_IN_BITMAP (mem_refs, 0, i, bi)
     {
       ref = memory_accesses.refs_list[i];
-      execute_sm (loop, ref, aux_map);
+      execute_sm (loop, ref, aux_map, bitmap_bit_p (refs_not_supported, i));
     }
 
   /* Materialize ordered store sequences on exits.  */