[PATCH] Fix parts of PR61607

[Richard Biener <rguenther@suse.de>]

This removes prematurely killing loops during jump threading
and moves it to a spot where we know we didn't cancel the
jump thread.

Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.

Ok?

Thanks,
Richard.

2014-06-25  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/61607
	* tree-ssa-threadupdate.c (ssa_redirect_edges): Cancel the
	loop if we redirected its latch edge.
	(thread_block_1): Do not cancel loops prematurely.

Index: gcc/tree-ssa-threadupdate.c
===================================================================
*** gcc/tree-ssa-threadupdate.c	(revision 211978)
--- gcc/tree-ssa-threadupdate.c	(working copy)
*************** ssa_redirect_edges (struct redirection_d
*** 764,769 ****
--- 764,777 ----
  	  if ((*path)[1]->type != EDGE_COPY_SRC_JOINER_BLOCK)
  	    EDGE_SUCC (rd->dup_blocks[0], 0)->count += e->count;
  
+ 	  /* If we redirect a loop latch edge cancel its loop.  */
+ 	  if (e->src == e->src->loop_father->latch)
+ 	    {
+ 	      e->src->loop_father->header = NULL;
+ 	      e->src->loop_father->latch = NULL;
+ 	      loops_state_set (LOOPS_NEED_FIXUP);
+ 	    }
+ 
  	  /* Redirect the incoming edge (possibly to the joiner block) to the
  	     appropriate duplicate block.  */
  	  e2 = redirect_edge_and_branch (e, rd->dup_blocks[0]);
*************** thread_block_1 (basic_block bb, bool nol
*** 844,850 ****
    edge e, e2;
    edge_iterator ei;
    ssa_local_info_t local_info;
-   struct loop *loop = bb->loop_father;
  
    /* To avoid scanning a linear array for the element we need we instead
       use a hash table.  For normal code there should be no noticeable
--- 852,857 ----
*************** thread_block_1 (basic_block bb, bool nol
*** 853,884 ****
    redirection_data
      = new hash_table<struct redirection_data> (EDGE_COUNT (bb->succs));
  
-   /* If we thread the latch of the loop to its exit, the loop ceases to
-      exist.  Make sure we do not restrict ourselves in order to preserve
-      this loop.  */
-   if (loop->header == bb)
-     {
-       e = loop_latch_edge (loop);
-       vec<jump_thread_edge *> *path = THREAD_PATH (e);
- 
-       if (path
- 	  && (((*path)[1]->type == EDGE_COPY_SRC_JOINER_BLOCK && joiners)
- 	      || ((*path)[1]->type == EDGE_COPY_SRC_BLOCK && !joiners)))
- 	{
- 	  for (unsigned int i = 1; i < path->length (); i++)
- 	    {
- 	      edge e2 = (*path)[i]->e;
- 
- 	      if (loop_exit_edge_p (loop, e2))
- 		{
- 		  loop->header = NULL;
- 		  loop->latch = NULL;
- 		  loops_state_set (LOOPS_NEED_FIXUP);
- 		}
- 	    }
- 	}
-     }
- 
    /* Record each unique threaded destination into a hash table for
       efficient lookups.  */
    FOR_EACH_EDGE (e, ei, bb->preds)
--- 860,865 ----