Liveness analysis can produce intervals with range not ending at a use
position. When splitting such interval after last use position we get
the new interval with non-zero range length and without use positions.
We should not add such intervals to the "unhandled" list.
This bug led to incorrect compilation of
java/lang/Thread.<init>(Ljava/lang/ThreadGroup;Ljava/lang/Runnable;)V
because of splitting an interval with no use position. The bug didn't
produce noticeable runtime effects when jato was compiled with
-Os. When compiled with -O0 or -O2 it was failing in assertion:
jit/spill-reload.c:51: last_insn: Assertion `ret != ((void *)0)' failed.
Signed-off-by: Tomek Grabiec <tgrab...@gmail.com>
---
include/jit/vars.h | 5 +++++
jit/linear-scan.c | 25 +++++++++++++++++++------
2 files changed, 24 insertions(+), 6 deletions(-)
diff --git a/include/jit/vars.h b/include/jit/vars.h
index a697b1c..1f73c48 100644
--- a/include/jit/vars.h
+++ b/include/jit/vars.h
@@ -88,6 +88,11 @@ struct live_interval {
bool fixed_reg;
};
+static inline bool has_use_positions(struct live_interval *it)
+{
+ return !list_is_empty(&it->use_positions);
+}
+
static inline void
mark_need_reload(struct live_interval *it, struct live_interval *parent)
{
diff --git a/jit/linear-scan.c b/jit/linear-scan.c
index ca3053b..e67a733 100644
--- a/jit/linear-scan.c
+++ b/jit/linear-scan.c
@@ -149,8 +149,11 @@ static void __spill_interval_intersecting(struct
live_interval *current,
return;
new = split_interval_at(new, next_pos);
- mark_need_reload(new, it);
+ if (!has_use_positions(new))
+ return;
+
+ mark_need_reload(new, it);
insert_to_list(new, unhandled);
}
@@ -238,8 +241,12 @@ static void allocate_blocked_reg(struct live_interval
*current,
*/
pos = next_use_pos(current, current->range.start);
new = split_interval_at(current, pos);
- mark_need_reload(new, current);
- insert_to_list(new, unhandled);
+
+ if (has_use_positions(new)) {
+ mark_need_reload(new, current);
+ insert_to_list(new, unhandled);
+ }
+
current->need_spill = 1;
} else if (block_pos[reg] > current->range.end) {
/* Spilling made a register free for the whole current */
@@ -248,7 +255,9 @@ static void allocate_blocked_reg(struct live_interval
*current,
inactive, unhandled);
} else {
new = split_interval_at(current, block_pos[reg]);
- insert_to_list(new, unhandled);
+
+ if (has_use_positions(new))
+ insert_to_list(new, unhandled);
current->reg = reg;
spill_all_intervals_intersecting(current, reg, active,
@@ -300,8 +309,12 @@ static void try_to_allocate_free_reg(struct live_interval
*current,
* Register available for the first part of the interval.
*/
new = split_interval_at(current, free_until_pos[reg]);
- mark_need_reload(new, current);
- insert_to_list(new, unhandled);
+
+ if (has_use_positions(new)) {
+ mark_need_reload(new, current);
+ insert_to_list(new, unhandled);
+ }
+
current->reg = reg;
current->need_spill = 1;
}
--
1.6.0.6
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