[tree-ssa] Speed up dominator and out-of-ssa passes

[law at redhat dot com]

This is something I noticed while evaluating the compile-time performance
of the incremental SSA updating scheme I've been working on.

When the dominator optimizer threads a jump, it takes a set of variables out
of SSA form (and the time is charged to the dominator optimizer). 

This out-of-ssa code has a rather expensive sanity check which walks through
all the PHI arguments to see if any of them are assigned to a partition
when the PHI result is not assigned to a partition (eliminate_build).  The
problem is the placement of that code resulted in us examining each PHI
multiple times.

Moving the code to a better location so that each PHI is only sanity
checked once is about a .3% improvement across the components of cc1.
Nothing radical, but nice for simply moving a hunk of code to a better
location within the compiler.  Note this is inside an ENABLE_CHECKING
block, so this only improves ENABLE_CHECKING compile times.


[ You might ask if this code is relevant if we have a true incremental
  SSA updating scheme.  The answer is no, it would not be relevant.

  However, I'm pretty confident we're still a long way from being
  able to completely eliminate this code.  There's a number of very
  nasty problems that have to be solved before we can have a real
  incremental update of the SSA graph in response to jump threading. ]


	* tree-outof-ssa.c (eliminate_build): Move code which verifies
	that all of a PHI's arguments do not have a partition if the
	result does not have a partition from here to...
	(rewrite_trees): Here.

Index: tree-outof-ssa.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/Attic/tree-outof-ssa.c,v
retrieving revision 1.1.2.4
diff -c -p -r1.1.2.4 tree-outof-ssa.c
*** tree-outof-ssa.c	16 Apr 2004 17:13:36 -0000	1.1.2.4
--- tree-outof-ssa.c	30 Apr 2004 19:44:39 -0000
*************** eliminate_build (elim_graph g, basic_blo
*** 349,374 ****
        
        /* Ignore results which are not in partitions.  */
        if (T0 == NULL_TREE)
!         {
! #ifdef ENABLE_CHECKING
! 	  /* There should be no arguments of this PHI which are in
! 	     the partition list, or we get incorrect results.  */
! 	  for (pi = 0; pi < PHI_NUM_ARGS (phi); pi++)
! 	    {
! 	      tree arg = PHI_ARG_DEF (phi, pi);
! 	      if (TREE_CODE (arg) == SSA_NAME
! 		  && var_to_partition (g->map, arg) != NO_PARTITION)
! 		{
! 		  fprintf (stderr, "Argument of PHI is in a partition :(");
! 		  print_generic_expr (stderr, arg, TDF_SLIM);
! 		  fprintf (stderr, "), but the result is not :");
! 		  print_generic_stmt (stderr, phi, TDF_SLIM);
! 		  abort();
! 		}
! 	    }
! #endif
! 	  continue;
! 	}
  
        if (PHI_ARG_EDGE (phi, i) == g->e)
  	Ti = PHI_ARG_DEF (phi, i);
--- 349,355 ----
        
        /* Ignore results which are not in partitions.  */
        if (T0 == NULL_TREE)
! 	continue;
  
        if (PHI_ARG_EDGE (phi, i) == g->e)
  	Ti = PHI_ARG_DEF (phi, i);
*************** rewrite_trees (var_map map, tree *values
*** 1796,1801 ****
--- 1777,1817 ----
    edge e;
    tree phi;
    bool changed;
+  
+ #ifdef ENABLE_CHECKING
+   /* Search for PHIs where the destination has no partition, but one
+      or more arguments has a partition.  This should not happen and can
+      create incorrect code.  */
+   FOR_EACH_BB (bb)
+     {
+       tree phi;
+ 
+       for (phi = phi_nodes (bb); phi; phi = TREE_CHAIN (phi))
+ 	{
+ 	  tree T0 = var_to_partition_to_var (map, PHI_RESULT (phi));
+       
+ 	  if (T0 == NULL_TREE)
+ 	    {
+ 	      int i;
+ 
+ 	      for (i = 0; i < PHI_NUM_ARGS (phi); i++)
+ 		{
+ 		  tree arg = PHI_ARG_DEF (phi, i);
+ 
+ 		  if (TREE_CODE (arg) == SSA_NAME
+ 		      && var_to_partition (map, arg) != NO_PARTITION)
+ 		    {
+ 		      fprintf (stderr, "Argument of PHI is in a partition :(");
+ 		      print_generic_expr (stderr, arg, TDF_SLIM);
+ 		      fprintf (stderr, "), but the result is not :");
+ 		      print_generic_stmt (stderr, phi, TDF_SLIM);
+ 		      abort();
+ 		    }
+ 		}
+ 	    }
+ 	}
+     }
+ #endif
  
    /* Replace PHI nodes with any required copies.  */
    g = new_elim_graph (map->num_partitions);