Re: [patch] Fix PR43464: update loop closed SSA form once copy prop is done

[Zdenek Dvorak <rakdver at kam dot mff dot cuni dot cz>]

Hi,

> > sure -- just check whether at least one predecessor edge of the block in that the phi node is located
> > is a loop exit (this is unnecessarily conservative, of course, but so is the current code),
> 
> Something like the following?  (I don't want to rely on recorded
> loop exits)

almost -- this would also return true for loop entry edges.  I'd suggest
loop_exit_edge_p (e->src->loop_father, e)

Zdenek

> Sebastian - does this fix your testcase?
> 
> Thanks,
> Richard.
> 
> Index: gcc/tree-ssa-copy.c
> ===================================================================
> --- gcc/tree-ssa-copy.c	(revision 157820)
> +++ gcc/tree-ssa-copy.c	(working copy)
> @@ -749,6 +749,7 @@ init_copy_prop (void)
>      {
>        gimple_stmt_iterator si;
>        int depth = bb->loop_depth;
> +      bool loop_exit_p = false;
>  
>        for (si = gsi_start_bb (bb); !gsi_end_p (si); gsi_next (&si))
>  	{
> @@ -786,6 +787,18 @@ init_copy_prop (void)
>  	      cached_last_copy_of[SSA_NAME_VERSION (def)] = def;
>  	}
>  
> +      /* In loop-closed SSA form do not copy-propagate through
> +	 PHI nodes in blocks with a loop exit edge predecessor.  */
> +      if (current_loops
> +	  && loops_state_satisfies_p (LOOP_CLOSED_SSA))
> +	{
> +	  edge_iterator ei;
> +	  edge e;
> +	  FOR_EACH_EDGE (e, ei, bb->preds)
> +	    if (e->src->loop_father != e->dest->loop_father)
> +	      loop_exit_p = true;
> +	}
> +
>        for (si = gsi_start_phis (bb); !gsi_end_p (si); gsi_next (&si))
>  	{
>            gimple phi = gsi_stmt (si);
> @@ -793,12 +806,7 @@ init_copy_prop (void)
>  
>  	  def = gimple_phi_result (phi);
>  	  if (!is_gimple_reg (def)
> -	      /* In loop-closed SSA form do not copy-propagate through
> -	         PHI nodes.  Technically this is only needed for loop
> -		 exit PHIs, but this is difficult to query.  */
> -	      || (current_loops
> -		  && gimple_phi_num_args (phi) == 1
> -		  && loops_state_satisfies_p (LOOP_CLOSED_SSA)))
> +	      || loop_exit_p)
>              prop_set_simulate_again (phi, false);
>  	  else
>              prop_set_simulate_again (phi, true);