[PATCH] Fix PR50183

["William J. Schmidt" <wschmidt at linux dot vnet dot ibm dot com>]

Greetings,

The code to build scops (static control parts) for graphite first
rewrites loops into canonical loop-closed SSA form.  PR50183 identifies
a scenario where the results do not fulfill all required invariants of
this form.  In particular, a value defined inside a loop and used
outside that loop must reach exactly one definition, which must be a
single-argument PHI node called a close-phi.  When nested loops exist,
it is possible that, following the rewrite, a definition may reach two
close-phis.  This patch corrects that problem.

The problem arises because loops are processed from outside in.  While
processing a loop, duplicate close-phis are eliminated.  However,
eliminating duplicate close-phis for an inner loop can sometimes create
duplicate close-phis for an already-processed outer loop.  This patch
detects when this may have occurred and repeats the removal of duplicate
close-phis as necessary.

The problem was noted on ibm/4_6-branch and 4_6-branch; it is apparently
latent on trunk.  The same patch can be applied to all three branches.

Bootstrapped and regression-tested on powerpc64-linux.  OK to commit to
these three branches?

Thanks,
Bill


2011-09-13  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

	* graphite-scop-detection.c (make_close_phi_nodes_unique):  New
	forward declaration.
	(remove_duplicate_close_phi): Detect and repair creation of
	duplicate close-phis for a containing loop.


Index: gcc/graphite-scop-detection.c
===================================================================
--- gcc/graphite-scop-detection.c	(revision 178829)
+++ gcc/graphite-scop-detection.c	(working copy)
@@ -30,6 +30,9 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree-pass.h"
 #include "sese.h"
 
+/* Forward declarations.  */
+static void make_close_phi_nodes_unique (basic_block);
+
 #ifdef HAVE_cloog
 #include "ppl_c.h"
 #include "graphite-ppl.h"
@@ -1231,6 +1234,13 @@ remove_duplicate_close_phi (gimple phi, gimple_stm
 	SET_USE (use_p, res);
 
       update_stmt (use_stmt);
+      
+      /* It is possible that we just created a duplicate close-phi
+	 for an already-processed containing loop.  Check for this
+	 case and clean it up.  */
+      if (gimple_code (use_stmt) == GIMPLE_PHI
+	  && gimple_phi_num_args (use_stmt) == 1)
+	make_close_phi_nodes_unique (gimple_bb (use_stmt));
     }
 
   remove_phi_node (gsi, true);