[patch] O(1) PHI argument look-up - Part 13/n

[Kazu Hirata <kazu at cs dot umass dot edu>]

Hi,

Attached is a patch to part 13 of my O(1) PHI argument look-up patch.

cprop_into_successor_phis has ugly code to find the index of a PHI
argument.  Specifically, given an edge E, it caches the index of a PHI
argument for E, hoping that the same index in another PHI will also
correspond to E.

The patch removes the ugly code and uses e->dest_idx instead.

Tested on i686-pc-linux-gnu.  OK to apply?

p.s.
Perhaps the variable name "hint" isn't a good name any more because we
know for sure that "hint = e->dest_idx;" gives us the correct index.
If you feel that the naming does not make sense, I'd like to address
that in a separate patch.  I'd like this patch to address the index
calculation only.

Kazu Hirata

2004-11-23  Kazu Hirata  <kazu@cs.umass.edu>

	* tree-ssa-dom.c (cprop_into_successor_phis): Remove code to
	find the index of a PHI argument.  Use e->dest_idx instead.

Index: tree-ssa-dom.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-ssa-dom.c,v
retrieving revision 2.68
diff -u -d -p -r2.68 tree-ssa-dom.c
--- tree-ssa-dom.c	19 Nov 2004 18:21:42 -0000	2.68
+++ tree-ssa-dom.c	23 Nov 2004 13:59:38 -0000
@@ -2296,7 +2296,6 @@ cprop_into_successor_phis (basic_block b
   FOR_EACH_EDGE (e, ei, bb->succs)
     {
       tree phi;
-      int phi_num_args;
       int hint;
 
       /* If this is an abnormal edge, then we do not want to copy propagate
@@ -2308,43 +2307,13 @@ cprop_into_successor_phis (basic_block b
       if (! phi)
 	continue;
 
-      /* There is no guarantee that for any two PHI nodes in a block that
-	 the phi alternative associated with a particular edge will be
-	 at the same index in the phi alternative array.
-
-	 However, it is very likely they will be the same.  So we keep
-	 track of the index of the alternative where we found the edge in
-	 the previous phi node and check that index first in the next
-	 phi node.  If that hint fails, then we actually search all
-	 the entries.  */
-      phi_num_args = PHI_NUM_ARGS (phi);
-      hint = phi_num_args;
+      hint = e->dest_idx;
       for ( ; phi; phi = PHI_CHAIN (phi))
 	{
-	  int i;
 	  tree new;
 	  use_operand_p orig_p;
 	  tree orig;
 
-	  /* If the hint is valid (!= phi_num_args), see if it points
-	     us to the desired phi alternative.  */
-	  if (hint != phi_num_args && PHI_ARG_EDGE (phi, hint) == e)
-	    ;
-	  else
-	    {
-	      /* The hint was either invalid or did not point to the
-		 correct phi alternative.  Search all the alternatives
-		 for the correct one.  Update the hint.  */
-	      for (i = 0; i < phi_num_args; i++)
-		if (PHI_ARG_EDGE (phi, i) == e)
-		  break;
-	      hint = i;
-	    }
-
-	  /* If we did not find the proper alternative, then something is
-	     horribly wrong.  */
-	  gcc_assert (hint != phi_num_args);
-
 	  /* The alternative may be associated with a constant, so verify
 	     it is an SSA_NAME before doing anything with it.  */
 	  orig_p = PHI_ARG_DEF_PTR (phi, hint);