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

 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);