From: Richard Sandiford <richard.sandiford@linaro.org>
Date: Sat, 23 Jun 2018 16:18:36 +0000 (+0000)
Subject: Fix phi backedge detection in backprop (PR85989)
X-Git-Tag: releases/gcc-6.5.0~259
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ea512211f873c42bd120b98b79f04b9612c9314b;p=thirdparty%2Fgcc.git

Fix phi backedge detection in backprop (PR85989)

Backport trunk r261064.

2018-06-23  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	PR tree-optimization/85989
	* gimple-ssa-backprop.c (backprop::m_visited_phis): New member
	variable.
	(backprop::backprop): Initialize it.
	(backprop::~backprop): Free it.
	(backprop::intersect_uses): Check it when deciding whether this
	is a backedge reference.
	(backprop::process_block): Add each phi to m_visited_phis
	after visiting it, then clear it at the end.

gcc/testsuite/
	PR tree-optimization/85989
	* gcc.dg/torture/pr85989.c: New test.

From-SVN: r261985
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 0a6094e4a63f..3ec50a873c00 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,15 @@
+2018-06-23  Richard Sandiford  <richard.sandiford@linaro.org>
+
+	PR tree-optimization/85989
+	* gimple-ssa-backprop.c (backprop::m_visited_phis): New member
+	variable.
+	(backprop::backprop): Initialize it.
+	(backprop::~backprop): Free it.
+	(backprop::intersect_uses): Check it when deciding whether this
+	is a backedge reference.
+	(backprop::process_block): Add each phi to m_visited_phis
+	after visiting it, then clear it at the end.
+
 2018-06-21  Richard Biener  <rguenther@suse.de>
  
 	Backport from mainline
diff --git a/gcc/gimple-ssa-backprop.c b/gcc/gimple-ssa-backprop.c
index d96bccac555f..267761122627 100644
--- a/gcc/gimple-ssa-backprop.c
+++ b/gcc/gimple-ssa-backprop.c
@@ -260,6 +260,11 @@ private:
      post-order walk.  */
   sbitmap m_visited_blocks;
 
+  /* A bitmap of phis that we have finished processing in the initial
+     post-order walk, excluding those from blocks mentioned in
+     M_VISITED_BLOCKS.  */
+  bitmap m_visited_phis;
+
   /* A worklist of SSA names whose definitions need to be reconsidered.  */
   auto_vec <tree, 64> m_worklist;
 
@@ -273,6 +278,7 @@ backprop::backprop (function *fn)
   : m_fn (fn),
     m_info_pool ("usage_info"),
     m_visited_blocks (sbitmap_alloc (last_basic_block_for_fn (m_fn))),
+    m_visited_phis (BITMAP_ALLOC (NULL)),
     m_worklist_names (BITMAP_ALLOC (NULL))
 {
   bitmap_clear (m_visited_blocks);
@@ -281,6 +287,7 @@ backprop::backprop (function *fn)
 backprop::~backprop ()
 {
   BITMAP_FREE (m_worklist_names);
+  BITMAP_FREE (m_visited_phis);
   sbitmap_free (m_visited_blocks);
   m_info_pool.release ();
 }
@@ -501,8 +508,11 @@ backprop::intersect_uses (tree var, usage_info *info)
     {
       if (is_gimple_debug (stmt))
 	continue;
-      if (is_a <gphi *> (stmt)
-	  && !bitmap_bit_p (m_visited_blocks, gimple_bb (stmt)->index))
+      gphi *phi = dyn_cast <gphi *> (stmt);
+      if (phi
+	  && !bitmap_bit_p (m_visited_blocks, gimple_bb (phi)->index)
+	  && !bitmap_bit_p (m_visited_phis,
+			    SSA_NAME_VERSION (gimple_phi_result (phi))))
 	{
 	  /* Skip unprocessed phis.  */
 	  if (dump_file && (dump_flags & TDF_DETAILS))
@@ -510,7 +520,7 @@ backprop::intersect_uses (tree var, usage_info *info)
 	      fprintf (dump_file, "[BACKEDGE] ");
 	      print_generic_expr (dump_file, var, 0);
 	      fprintf (dump_file, " in ");
-	      print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
+	      print_gimple_stmt (dump_file, phi, 0, TDF_SLIM);
 	    }
 	}
       else
@@ -634,7 +644,12 @@ backprop::process_block (basic_block bb)
     }
   for (gphi_iterator gpi = gsi_start_phis (bb); !gsi_end_p (gpi);
        gsi_next (&gpi))
-    process_var (gimple_phi_result (gpi.phi ()));
+    {
+      tree result = gimple_phi_result (gpi.phi ());
+      process_var (result);
+      bitmap_set_bit (m_visited_phis, SSA_NAME_VERSION (result));
+    }
+  bitmap_clear (m_visited_phis);
 }
 
 /* Delete the definition of VAR, which has no uses.  */
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 19a35ad13deb..4b40b0e5631b 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2018-06-23  Richard Sandiford  <richard.sandiford@linaro.org>
+
+	PR tree-optimization/85989
+	* gcc.dg/torture/pr85989.c: New test.
+
 2018-06-21  Richard Biener  <rguenther@suse.de>
  
 	Backport from mainline
diff --git a/gcc/testsuite/gcc.dg/torture/pr85989.c b/gcc/testsuite/gcc.dg/torture/pr85989.c
new file mode 100644
index 000000000000..5cfd7016fb5e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr85989.c
@@ -0,0 +1,31 @@
+/* { dg-do run } */
+
+#define N 9
+
+void __attribute__((noinline, noclone))
+f (double x, double y, double *res)
+{
+  y = -y;
+  for (int i = 0; i < N; ++i)
+    {
+      double tmp = y;
+      y = x;
+      x = tmp;
+      res[i] = i;
+    }
+  res[N] = y * y;
+  res[N + 1] = x;
+}
+
+int
+main (void)
+{
+  double res[N + 2];
+  f (10, 20, res);
+  for (int i = 0; i < N; ++i)
+    if (res[i] != i)
+      __builtin_abort ();
+  if (res[N] != 100 || res[N + 1] != -20)
+    __builtin_abort ();
+  return 0;
+}