diff -r 000000000000 -r a8cb9039fade patches/gcc/4.7.0/100-PR52734-tree-ssa-tail-merge.patch
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/patches/gcc/4.7.0/100-PR52734-tree-ssa-tail-merge.patch	Tue Feb 11 21:34:48 2014 +0100
@@ -0,0 +1,91 @@
+------------------------------------------------------------------------
+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);