[PATCH] PR/17635

[Devang Patel]

On Sep 24, 2004, at 2:54 PM, Richard Henderson wrote:

> On Fri, Sep 24, 2004 at 09:49:34AM -0700, Devang Patel wrote:
>> 	* tree-if-conv.c (if_convertable_loop_p): Check for loop with zero
>> exits.
>
> It strikes me as likely that you're papering over some bug.
> I don't see any reason why a zero exit loop shouldn't be
> handled by your pass.

If-conversion pass does not allow loops with non-empty
basic blocks after exit edge. So latch is either empty or
bb with exit edge. However, in this case there is no exit
and latch is non-empty.

Alternatives
1) Reject such loops
2) Take care of non-empty latch in such cases and update
    loop structure after blocks are merged.

Following patch implements 2). Bootstrapped on powerpc-darwin
with -ftree-vectorize (to enable if-conversion during bootstrap).
DejaGNU run is in progress.

      * tree-if-conv.c (process_phi_nodes): Process latch block.
	(combine_blocks): Process latch block and update loop structure.

thoughts?
-
Devang

Index: tree-if-conv.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-if-conv.c,v
retrieving revision 2.10
diff -Idpatel.pbxuser -c -3 -p -r2.10 tree-if-conv.c
*** tree-if-conv.c      28 Sep 2004 07:59:51 -0000      2.10
--- tree-if-conv.c      5 Oct 2004 16:03:18 -0000
*************** process_phi_nodes (struct loop *loop)
*** 815,821 ****
         basic_block true_bb = NULL;
         bb = ifc_bbs[i];

!       if (bb == loop->header || bb == loop->latch)
         continue;

         phi = phi_nodes (bb);
--- 815,821 ----
         basic_block true_bb = NULL;
         bb = ifc_bbs[i];

!       if (bb == loop->header)
         continue;

         phi = phi_nodes (bb);
*************** combine_blocks (struct loop *loop)
*** 863,871 ****

         bb = ifc_bbs[i];

-       if (bb == loop->latch)
-       continue;
-
         if (!exit_bb && bb_with_exit_edge_p (bb))
           exit_bb = bb;

--- 863,868 ----
*************** combine_blocks (struct loop *loop)
*** 891,896 ****
--- 888,896 ----
           continue;
         }

+       if (bb == loop->latch && empty_block_p (bb))
+       continue;
+
         /* It is time to remove this basic block.        First remove 
edges.  */
         while (EDGE_COUNT (bb->succs) > 0)
         ssa_remove_edge (EDGE_SUCC (bb, 0));
*************** combine_blocks (struct loop *loop)
*** 921,926 ****
--- 921,928 ----
         delete_from_dominance_info (CDI_POST_DOMINATORS, bb);

         /* Remove basic block.  */
+       if (bb == loop->latch)
+       loop->latch = merge_target_bb;
         remove_bb_from_loops (bb);
         expunge_block (bb);
       }
*************** combine_blocks (struct loop *loop)
*** 928,934 ****
     /* Now if possible, merge loop header and block with exit edge.
        This reduces number of basic blocks to 2. Auto vectorizer 
addresses
        loops with two nodes only.  FIXME: Use cleanup_tree_cfg().  */
!   if (exit_bb != loop->latch && empty_block_p (loop->latch))
       {
         if (can_merge_blocks_p (loop->header, exit_bb))
         {
--- 930,939 ----
     /* Now if possible, merge loop header and block with exit edge.
        This reduces number of basic blocks to 2. Auto vectorizer 
addresses
        loops with two nodes only.  FIXME: Use cleanup_tree_cfg().  */
!   if (exit_bb
!       && loop->header != loop->latch
!       && exit_bb != loop->latch
!       && empty_block_p (loop->latch))
       {
         if (can_merge_blocks_p (loop->header, exit_bb))
         {