------------------------------------------------------------------------

r186424 | vries | 2012-04-13 18:44:18 +0200 (Fri, 13 Apr 2012) | 12 lines

2012-04-13  Tom de Vries  <tom@codesourcery.com>

	Backport from mainline r186418.

	2012-04-13  Tom de Vries  <tom@codesourcery.com>

	* tree-ssa-tail-merge.c (gsi_advance_bw_nondebug_nonlocal): Add

	parameters vuse and vuse_escaped.

	(find_duplicate): Init vuse1, vuse2 and vuse_escaped.  Pass to

	gsi_advance_bw_nondebug_nonlocal.  Return if vuse_escaped and

	vuse1 != vuse2.

------------------------------------------------------------------------

Index: gcc/tree-ssa-tail-merge.c

===================================================================

--- gcc-4.7.0/gcc/tree-ssa-tail-merge.c	(revision 186423)

+++ gcc-4.7.0/gcc/tree-ssa-tail-merge.c	(revision 186424)

@@ -1123,18 +1123,31 @@

     }

 }

-/* Let GSI skip backwards over local defs.  */

+/* Let GSI skip backwards over local defs.  Return the earliest vuse in VUSE.

+   Return true in VUSE_ESCAPED if the vuse influenced a SSA_OP_DEF of one of the

+   processed statements.  */

 static void

-gsi_advance_bw_nondebug_nonlocal (gimple_stmt_iterator *gsi)

+gsi_advance_bw_nondebug_nonlocal (gimple_stmt_iterator *gsi, tree *vuse,

+				  bool *vuse_escaped)

 {

   gimple stmt;

+  tree lvuse;

   while (true)

     {

       if (gsi_end_p (*gsi))

 	return;

       stmt = gsi_stmt (*gsi);

+

+      lvuse = gimple_vuse (stmt);

+      if (lvuse != NULL_TREE)

+	{

+	  *vuse = lvuse;

+	  if (!ZERO_SSA_OPERANDS (stmt, SSA_OP_DEF))

+	    *vuse_escaped = true;

+	}

+

       if (!(is_gimple_assign (stmt) && local_def (gimple_get_lhs (stmt))

 	    && !gimple_has_side_effects (stmt)))

 	return;

@@ -1150,9 +1163,11 @@

 {

   gimple_stmt_iterator gsi1 = gsi_last_nondebug_bb (bb1);

   gimple_stmt_iterator gsi2 = gsi_last_nondebug_bb (bb2);

+  tree vuse1 = NULL_TREE, vuse2 = NULL_TREE;

+  bool vuse_escaped = false;

-  gsi_advance_bw_nondebug_nonlocal (&gsi1);

-  gsi_advance_bw_nondebug_nonlocal (&gsi2);

+  gsi_advance_bw_nondebug_nonlocal (&gsi1, &vuse1, &vuse_escaped);

+  gsi_advance_bw_nondebug_nonlocal (&gsi2, &vuse2, &vuse_escaped);

   while (!gsi_end_p (gsi1) && !gsi_end_p (gsi2))

     {

@@ -1161,13 +1176,20 @@

       gsi_prev_nondebug (&gsi1);

       gsi_prev_nondebug (&gsi2);

-      gsi_advance_bw_nondebug_nonlocal (&gsi1);

-      gsi_advance_bw_nondebug_nonlocal (&gsi2);

+      gsi_advance_bw_nondebug_nonlocal (&gsi1, &vuse1, &vuse_escaped);

+      gsi_advance_bw_nondebug_nonlocal (&gsi2, &vuse2, &vuse_escaped);

     }

   if (!(gsi_end_p (gsi1) && gsi_end_p (gsi2)))

     return;

+  /* If the incoming vuses are not the same, and the vuse escaped into an

+     SSA_OP_DEF, then merging the 2 blocks will change the value of the def,

+     which potentially means the semantics of one of the blocks will be changed.

+     TODO: make this check more precise.  */

+  if (vuse_escaped && vuse1 != vuse2)

+    return;

+

   if (dump_file)

     fprintf (dump_file, "find_duplicates: <bb %d> duplicate of <bb %d>\n",

 	     bb1->index, bb2->index);