Re: [PATCH 10/12] mode-switching: Use 1-based edge aux fields

[Richard Sandiford <richard.sandiford@arm.com>]

Jeff Law <jlaw@ventanamicro.com> writes:
> On 11/7/23 17:35, Richard Sandiford wrote:
>
>> I could have sworn that there was something that checked that passes
>> left edge aux fields clear, but it looks like I misremembered.  So I
>> probably need to stick a clear_aux_for_edges () call above the first
>> main loop (for 12/12) and keep the initialisation here as well.
> That does sound vaguely familiar.   Maybe it was a one-off test someone 
> did.
>
>> 
>> That kind-of takes away the point of shifting to 1-based values
>> in the first place.  Ah well...
> Your call.  I'd tend to lean towards inserting the clear_aux call if we 
> don't have something that's consistently verifying aux state. 

Agreed.  A convention that isn't tested isn't strong enough to rely on.

> Alternately we can return to the -1 handling.  I doubt it's all that 
> important from a compile-time standpoint.

I dithered about it a bit, but in the end, zero does still seem to work
out a bit more nicely.

I think you'd basically OKed the patch with this change, but I'm feeling
extra risk-averse at the moment :) so, here's an updated patch.
Tested as before.  OK to install?

Thanks for catching this.

Richard


gcc/
	* mode-switching.cc (commit_mode_sets): Use 1-based edge aux values.
---
 gcc/mode-switching.cc | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/gcc/mode-switching.cc b/gcc/mode-switching.cc
index 7a5c4993d65..6b5661131e3 100644
--- a/gcc/mode-switching.cc
+++ b/gcc/mode-switching.cc
@@ -106,10 +106,10 @@ commit_mode_sets (struct edge_list *edge_list, int e, struct bb_info *info)
   for (int ed = NUM_EDGES (edge_list) - 1; ed >= 0; ed--)
     {
       edge eg = INDEX_EDGE (edge_list, ed);
-      int mode;
 
-      if ((mode = (int)(intptr_t)(eg->aux)) != -1)
+      if (eg->aux)
 	{
+	  int mode = (int) (intptr_t) eg->aux - 1;
 	  HARD_REG_SET live_at_edge;
 	  basic_block src_bb = eg->src;
 	  int cur_mode = info[src_bb->index].mode_out;
@@ -728,14 +728,14 @@ optimize_mode_switching (void)
 	{
 	  edge eg = INDEX_EDGE (edge_list, ed);
 
-	  eg->aux = (void *)(intptr_t)-1;
+	  eg->aux = (void *) (intptr_t) 0;
 
 	  for (i = 0; i < no_mode; i++)
 	    {
 	      int m = targetm.mode_switching.priority (entity_map[j], i);
 	      if (mode_bit_p (insert[ed], j, m))
 		{
-		  eg->aux = (void *)(intptr_t)m;
+		  eg->aux = (void *) (intptr_t) (m + 1);
 		  break;
 		}
 	    }
-- 
2.25.1