The bug resulted in attempt to spill an interval which
has no register assigned.
Initial interval for vreg 20 has use positions at 4 and 29.
Register is available only for positions 4-11 which results
in interval splitting. There are no free registers available
for the new interval (11-29) so it is split at next use position,
which results in new interval 24-29. This interval is marked
as needing to be reloaded. The parent interval however has
no register assigned.
20 (pos: 4-11): ECX non-fixed spill (5) no reload
20 (pos: 11-24): - non-fixed spill (6) reload (5)
20 (pos: 24-29): ESI non-fixed no spill reload (6)
Proposed solution for this problem is to not generate intervals
which do not start with use position in try_to_allocate_free_reg().
In this example, we throw away the interval 11-24 will be dropped.
We can do that because register is not used in this range.
After this fix, we will have the following regalloc:
20 (pos: 4-11): ECX non-fixed spill (5) no reload
20 (pos: 24-29): ESI non-fixed no spill reload (5)
Signed-off-by: Tomek Grabiec <tgrab...@gmail.com>
---
jit/linear-scan.c | 1 +
1 files changed, 1 insertions(+), 0 deletions(-)
diff --git a/jit/linear-scan.c b/jit/linear-scan.c
index 21dd112..d2a3c92 100644
--- a/jit/linear-scan.c
+++ b/jit/linear-scan.c
@@ -315,6 +315,7 @@ static void try_to_allocate_free_reg(struct live_interval
*current,
new = split_interval_at(current, free_until_pos[reg]);
if (has_use_positions(new)) {
+ new = split_interval_at(new, next_use_pos(new, 0));
mark_need_reload(new, current);
insert_to_list(new, unhandled);
}
--
1.6.0.6
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