[PING] Re: [PATCH] Fix PR50183

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

Hi there,

Ping.  I'm seeking approval for this fix on trunk and 4_6-branch.
Thanks!

Bill

On Tue, 2011-09-13 at 17:55 -0500, William J. Schmidt wrote:
> 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);
> 
>