The following replaces
/* Skip bits that are zero. */
for (; (word & 1) == 0; word >>= 1)
bit_num++;
idioms in ira-int.h in the attempt to speedup update_conflict_hard_regno_costs
which we're bound on in PR104686. The trick is to use ctz_hwi here
which should pay off even with dense bitmaps on architectures that
have HW support for this.
For the PR in question this speeds up compile-time from 31s to 24s for
me.
Bootstrapped and tested on x86_64-unknown-linux-gnu.
OK for trunk?
Thanks,
Richard.
2022-02-25 Richard Biener
PR rtl-optimization/104686
* ira-int.h (minmax_set_iter_cond): Use ctz_hwi to elide loop
skipping bits that are zero.
(ira_object_conflict_iter_cond): Likewise.
---
gcc/ira-int.h | 10 ++
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/gcc/ira-int.h b/gcc/ira-int.h
index 957604b22e9..f42a314fa7f 100644
--- a/gcc/ira-int.h
+++ b/gcc/ira-int.h
@@ -764,8 +764,9 @@ minmax_set_iter_cond (minmax_set_iterator *i, int *n)
}
/* Skip bits that are zero. */
- for (; (i->word & 1) == 0; i->word >>= 1)
-i->bit_num++;
+ int off = ctz_hwi (i->word);
+ i->bit_num += off;
+ i->word >>= off;
*n = (int) i->bit_num + i->start_val;
@@ -1379,8 +1380,9 @@ ira_object_conflict_iter_cond
(ira_object_conflict_iterator *i,
}
/* Skip bits that are zero. */
- for (; (word & 1) == 0; word >>= 1)
- bit_num++;
+ int off = ctz_hwi (word);
+ bit_num += off;
+ word >>= off;
obj = ira_object_id_map[bit_num + i->base_conflict_id];
i->bit_num = bit_num + 1;
--
2.34.1