[PATCH] Fix spurious valgrind errors in irred loop verification

[Richard Biener via Gcc-patches]

The sbitmap bitmap_{set,clear}_bit changes trigger spurious
uninit value use reportings from valgrind since we now
read the old value before setting/clearing a bit so
verify_loop_structures optimization to not clear the sbitmap is reported.

Fixed by using a temporary BB flag which should also be more
efficient in terms of cache re-use.

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

2021-11-08  Richard Biener  <rguent...@suse.de>

        * cfgloop.c (verify_loop_structure): Use a temporary BB flag
        instead of an sbitmap to cache irreducible state.
---
 gcc/cfgloop.c | 23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/gcc/cfgloop.c b/gcc/cfgloop.c
index 2ba9918bfa2..20c24c13c36 100644
--- a/gcc/cfgloop.c
+++ b/gcc/cfgloop.c
@@ -1567,19 +1567,17 @@ verify_loop_structure (void)
   /* Check irreducible loops.  */
   if (loops_state_satisfies_p (LOOPS_HAVE_MARKED_IRREDUCIBLE_REGIONS))
     {
-      auto_edge_flag saved_irr_mask (cfun);
-      /* Record old info.  */
-      auto_sbitmap irreds (last_basic_block_for_fn (cfun));
+      auto_edge_flag saved_edge_irr (cfun);
+      auto_bb_flag saved_bb_irr (cfun);
+      /* Save old info.  */
       FOR_EACH_BB_FN (bb, cfun)
        {
          edge_iterator ei;
          if (bb->flags & BB_IRREDUCIBLE_LOOP)
-           bitmap_set_bit (irreds, bb->index);
-         else
-           bitmap_clear_bit (irreds, bb->index);
+           bb->flags |= saved_bb_irr;
          FOR_EACH_EDGE (e, ei, bb->succs)
            if (e->flags & EDGE_IRREDUCIBLE_LOOP)
-             e->flags |= saved_irr_mask;
+             e->flags |= saved_edge_irr;
        }
 
       /* Recount it.  */
@@ -1591,34 +1589,35 @@ verify_loop_structure (void)
          edge_iterator ei;
 
          if ((bb->flags & BB_IRREDUCIBLE_LOOP)
-             && !bitmap_bit_p (irreds, bb->index))
+             && !(bb->flags & saved_bb_irr))
            {
              error ("basic block %d should be marked irreducible", bb->index);
              err = 1;
            }
          else if (!(bb->flags & BB_IRREDUCIBLE_LOOP)
-             && bitmap_bit_p (irreds, bb->index))
+                  && (bb->flags & saved_bb_irr))
            {
              error ("basic block %d should not be marked irreducible", 
bb->index);
              err = 1;
            }
+         bb->flags &= ~saved_bb_irr;
          FOR_EACH_EDGE (e, ei, bb->succs)
            {
              if ((e->flags & EDGE_IRREDUCIBLE_LOOP)
-                 && !(e->flags & saved_irr_mask))
+                 && !(e->flags & saved_edge_irr))
                {
                  error ("edge from %d to %d should be marked irreducible",
                         e->src->index, e->dest->index);
                  err = 1;
                }
              else if (!(e->flags & EDGE_IRREDUCIBLE_LOOP)
-                      && (e->flags & saved_irr_mask))
+                      && (e->flags & saved_edge_irr))
                {
                  error ("edge from %d to %d should not be marked irreducible",
                         e->src->index, e->dest->index);
                  err = 1;
                }
-             e->flags &= ~saved_irr_mask;
+             e->flags &= ~saved_edge_irr;
            }
        }
     }
-- 
2.31.1