[PATCH 05/12] mode-switching: Simplify recording of transparency

[Richard Sandiford]

For a given block, an entity is either transparent for
all modes or for none.  Each update to the transparency set
therefore used a loop like:

                for (i = 0; i < no_mode; i++)
                  clear_mode_bit (transp[bb->index], j, i);

This patch instead starts out with a bit-per-block bitmap
and updates the main bitmap at the end.

This isn't much of a simplification on its own.  The main
purpose is to simplify later patches.

gcc/
        * mode-switching.cc (optimize_mode_switching): Initially
        compute transparency in a bit-per-block bitmap.
---
 gcc/mode-switching.cc | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/gcc/mode-switching.cc b/gcc/mode-switching.cc
index 12ddbd6adfa..03dd4c1ebe4 100644
--- a/gcc/mode-switching.cc
+++ b/gcc/mode-switching.cc
@@ -556,6 +556,8 @@ optimize_mode_switching (void)
   bitmap_vector_clear (antic, last_basic_block_for_fn (cfun));
   bitmap_vector_clear (comp, last_basic_block_for_fn (cfun));
 
+  auto_sbitmap transp_all (last_basic_block_for_fn (cfun));
+
   for (j = n_entities - 1; j >= 0; j--)
     {
       int e = entity_map[j];
@@ -563,6 +565,8 @@ optimize_mode_switching (void)
       struct bb_info *info = bb_info[j];
       rtx_insn *insn;
 
+      bitmap_ones (transp_all);
+
       /* Determine what the first use (if any) need for a mode of entity E is.
         This will be the mode that is anticipatable for this block.
         Also compute the initial transparency settings.  */
@@ -595,8 +599,7 @@ optimize_mode_switching (void)
                  ins_pos = NEXT_INSN (ins_pos);
                ptr = new_seginfo (no_mode, no_mode, ins_pos, live_now);
                add_seginfo (&tail_ptr, ptr);
-               for (i = 0; i < no_mode; i++)
-                 clear_mode_bit (transp[bb->index], j, i);
+               bitmap_clear_bit (transp_all, bb->index);
              }
          }
 
@@ -611,8 +614,7 @@ optimize_mode_switching (void)
                    {
                      ptr = new_seginfo (last_mode, mode, insn, live_now);
                      add_seginfo (&tail_ptr, ptr);
-                     for (i = 0; i < no_mode; i++)
-                       clear_mode_bit (transp[bb->index], j, i);
+                     bitmap_clear_bit (transp_all, bb->index);
                      any_set_required = true;
                      last_mode = mode;
                    }
@@ -643,8 +645,7 @@ optimize_mode_switching (void)
              ptr = new_seginfo (last_mode, no_mode, BB_END (bb), live_now);
              add_seginfo (&tail_ptr, ptr);
              if (last_mode != no_mode)
-               for (i = 0; i < no_mode; i++)
-                 clear_mode_bit (transp[bb->index], j, i);
+               bitmap_clear_bit (transp_all, bb->index);
            }
        }
       if (targetm.mode_switching.entry && targetm.mode_switching.exit)
@@ -667,8 +668,7 @@ optimize_mode_switching (void)
                 an extra check in make_preds_opaque.  We also
                 need this to avoid confusing pre_edge_lcm when
                 antic is cleared but transp and comp are set.  */
-             for (i = 0; i < no_mode; i++)
-               clear_mode_bit (transp[bb->index], j, i);
+             bitmap_clear_bit (transp_all, bb->index);
 
              /* Insert a fake computing definition of MODE into entry
                 blocks which compute no mode. This represents the mode on
@@ -688,6 +688,9 @@ optimize_mode_switching (void)
 
          FOR_EACH_BB_FN (bb, cfun)
            {
+             if (!bitmap_bit_p (transp_all, bb->index))
+               clear_mode_bit (transp[bb->index], j, m);
+
              if (info[bb->index].seginfo->mode == m)
                set_mode_bit (antic[bb->index], j, m);
 
-- 
2.25.1