[4.1 PATCH] Fix tree-ssa/loop-14.c test case failure, take 3

[Ulrich Weigand]

I wrote:

> Do you think it would be less risk for 4.1 to backport this part of
> your recent patch only, instead of changing the cost computation?

This would be something like the following patch, which also fixes
the loop-14.c regression on s390(x).

Bootstrapped/regtested on s390-ibm-linux/s390x-ibm-linux.
OK for 4.1 branch?

Bye,
Ulrich


ChangeLog:

	Backport from mainline:
	2006-01-06  Zdenek Dvorak  <dvorakz@suse.cz>
	* tree-scalar-evolution.c (scev_const_prop): Evaluate expensiveness
	of computing # of iterations instead of the final expression.


Index: gcc/tree-scalar-evolution.c
===================================================================
*** gcc/tree-scalar-evolution.c	(revision 109753)
--- gcc/tree-scalar-evolution.c	(working copy)
*************** scev_const_prop (void)
*** 2723,2729 ****
    for (i = current_loops->num - 1; i > 0; i--)
      {
        edge exit;
!       tree def, rslt, ass;
        block_stmt_iterator bsi;
  
        loop = current_loops->parray[i];
--- 2723,2729 ----
    for (i = current_loops->num - 1; i > 0; i--)
      {
        edge exit;
!       tree def, rslt, ass, niter;
        block_stmt_iterator bsi;
  
        loop = current_loops->parray[i];
*************** scev_const_prop (void)
*** 2733,2740 ****
        /* If we do not know exact number of iterations of the loop, we cannot
  	 replace the final value.  */
        exit = loop->single_exit;
!       if (!exit
! 	  || number_of_iterations_in_loop (loop) == chrec_dont_know)
  	continue;
  
        /* Ensure that it is possible to insert new statements somewhere.  */
--- 2733,2746 ----
        /* If we do not know exact number of iterations of the loop, we cannot
  	 replace the final value.  */
        exit = loop->single_exit;
!       if (!exit)
! 	continue;
! 
!       niter = number_of_iterations_in_loop (loop);
!       if (niter == chrec_dont_know
! 	  /* If computing the number of iterations is expensive, it may be
! 	     better not to introduce computations involving it.  */
! 	  || expression_expensive_p (niter))
  	continue;
  
        /* Ensure that it is possible to insert new statements somewhere.  */
*************** scev_const_prop (void)
*** 2763,2773 ****
  	      || chrec_contains_symbols_defined_in_loop (def, ex_loop->num))
  	    continue;
  
- 	  /* If computing the expression is expensive, let it remain in the
- 	     loop.  */
- 	  if (expression_expensive_p (def))
- 	    continue;
- 
  	  /* Eliminate the phi node and replace it by a computation outside
  	     the loop.  */
  	  def = unshare_expr (def);
--- 2769,2774 ----


-- 
  Dr. Ulrich Weigand
  Linux on zSeries Development
  Ulrich.Weigand@de.ibm.com