From: Richard Biener <rguenther@suse.de>
Date: Tue, 5 May 2020 09:00:09 +0000 (+0200)
Subject: tree-optimization/94949 - fix load eliding in SM
X-Git-Tag: misc/first-auto-changelog~555
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0424a5ece5307cc22bbc0fe97edf4707d7a798ed;p=thirdparty%2Fgcc.git

tree-optimization/94949 - fix load eliding in SM

This fixes the case of not using the multithreaded model when
only conditionally storing to the destination.  We cannot elide
the load in this case.

2020-05-05  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/94949
	* tree-ssa-loop-im.c (execute_sm): Check whether we use
	the multithreaded model or always compute the stored value
	before eliding a load.

	* gcc.dg/torture/pr94949.c: New testcase.
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 6a419757bf89..2267a63bca13 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2020-05-05  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/94949
+	* tree-ssa-loop-im.c (execute_sm): Check whether we use
+	the multithreaded model or always compute the stored value
+	before eliding a load.
+
 2020-05-05  Alex Coplan  <alex.coplan@arm.com>
 
 	* config/aarch64/aarch64.md (*one_cmpl_zero_extend): New.
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index e06bcf862123..2ffa0f8f4341 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-05-05  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/94949
+	* gcc.dg/torture/pr94949.c: New testcase.
+
 2020-05-05  Alex Coplan  <alex.coplan@arm.com>
 
 	* gcc.target/aarch64/mvn_zero_ext.c: New test.
diff --git a/gcc/testsuite/gcc.dg/torture/pr94949.c b/gcc/testsuite/gcc.dg/torture/pr94949.c
new file mode 100644
index 000000000000..6182d77b3cda
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr94949.c
@@ -0,0 +1,17 @@
+/* { dg-do run } */
+/* { dg-additional-options "-fallow-store-data-races" } */
+
+static int x = 1;
+static volatile int y = -1;
+int
+main()
+{
+  for (int i = 0; i < 128; ++i)
+    {
+      if (i == y)
+	x = i;
+    }
+  if (x != 1)
+    __builtin_abort ();
+  return 0;
+}
diff --git a/gcc/tree-ssa-loop-im.c b/gcc/tree-ssa-loop-im.c
index 18e5c18c17eb..554dd4be5bbc 100644
--- a/gcc/tree-ssa-loop-im.c
+++ b/gcc/tree-ssa-loop-im.c
@@ -2128,9 +2128,9 @@ execute_sm (class loop *loop, vec<edge> exits, im_mem_ref *ref)
   fmt_data.orig_loop = loop;
   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
-	  && ! ref_always_accessed_p (loop, ref, true)))
+      || (! flag_store_data_races && ! always_stored))
     multi_threaded_model_p = true;
 
   if (multi_threaded_model_p)
@@ -2145,8 +2145,10 @@ execute_sm (class loop *loop, vec<edge> exits, im_mem_ref *ref)
 
   /* Avoid doing a load if there was no load of the ref in the loop.
      Esp. when the ref is not always stored we cannot optimize it
-     away later.  */
-  if (ref->loaded && bitmap_bit_p (ref->loaded, loop->num))
+     away later.  But when it is not always stored we must use a conditional
+     store then.  */
+  if ((!always_stored && !multi_threaded_model_p)
+      || (ref->loaded && bitmap_bit_p (ref->loaded, loop->num)))
     {
       load = gimple_build_assign (tmp_var, unshare_expr (ref->mem.ref));
       lim_data = init_lim_data (load);