https://gcc.gnu.org/g:5cd4605141b8b45cab95e4de8005c69273071107
commit r15-7078-g5cd4605141b8b45cab95e4de8005c69273071107
Author: Denis Chertykov <cherty...@gmail.com>
Date: Tue Jan 21 00:27:04 2025 +0400
[PR117868][LRA]: Restrict the reuse of spill slots
This is an LRA bug derived from reuse spilling slots after frame pointer
spilling.
The slot was created for QImode (1 byte) and it was reused after spilling
of the
frame pointer for TImode register (16 bytes long) and it overlaps other
slots.
Wrong things happened while `lra_spill ()'
---------------------------- part of lra-spills.cc
----------------------------
n = assign_spill_hard_regs (pseudo_regnos, n);
slots_num = 0;
assign_stack_slot_num_and_sort_pseudos (pseudo_regnos, n); <--- first
call ---
for (i = 0; i < n; i++)
if (pseudo_slots[pseudo_regnos[i]].mem == NULL_RTX)
assign_mem_slot (pseudo_regnos[i]);
if ((n2 = lra_update_fp2sp_elimination (pseudo_regnos)) > 0)
{
/* Assign stack slots to spilled pseudos assigned to fp. */
assign_stack_slot_num_and_sort_pseudos (pseudo_regnos, n2); <---
second call ---
for (i = 0; i < n2; i++)
if (pseudo_slots[pseudo_regnos[i]].mem == NULL_RTX)
assign_mem_slot (pseudo_regnos[i]);
}
------------------------------------------------------------------------------
In a first call of `assign_stack_slot_num_and_sort_pseudos(...)' LRA
allocates slot #17
for r93 (QImode - 1 byte).
In a second call of `assign_stack_slot_num_and_sort_pseudos(...)' LRA reuse
slot #17 for
r114 (TImode - 16 bytes).
It's wrong. We can't reuse 1 byte slot #17 for 16 bytes register.
The code in patch does reuse slots only without allocated memory or only
with equal or
smaller registers with equal or smaller alignment.
Also, a small fix for debugging output of slot width.
Print slot size as width, not a 0 as a size of (mem/c:BLK (...)).
PR rtl-optimization/117868
gcc/
* lra-spills.cc (assign_stack_slot_num_and_sort_pseudos): Reuse
slots
only without allocated memory or only with equal or smaller
registers
with equal or smaller alignment.
(lra_spill): Print slot size as width.
Diff:
---
gcc/lra-spills.cc | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/gcc/lra-spills.cc b/gcc/lra-spills.cc
index db78dcd28a35..93a0c92db9fa 100644
--- a/gcc/lra-spills.cc
+++ b/gcc/lra-spills.cc
@@ -386,7 +386,18 @@ assign_stack_slot_num_and_sort_pseudos (int
*pseudo_regnos, int n)
&& ! (lra_intersected_live_ranges_p
(slots[j].live_ranges,
lra_reg_info[regno].live_ranges)))
- break;
+ {
+ /* A slot without allocated memory can be shared. */
+ if (slots[j].mem == NULL_RTX)
+ break;
+
+ /* A slot with allocated memory can be shared only with equal
+ or smaller register with equal or smaller alignment. */
+ if (slots[j].align >= spill_slot_alignment (mode)
+ && compare_sizes_for_sort (slots[j].size,
+ GET_MODE_SIZE (mode)) != -1)
+ break;
+ }
}
if (j >= slots_num)
{
@@ -656,8 +667,7 @@ lra_spill (void)
for (i = 0; i < slots_num; i++)
{
fprintf (lra_dump_file, " Slot %d regnos (width = ", i);
- print_dec (GET_MODE_SIZE (GET_MODE (slots[i].mem)),
- lra_dump_file, SIGNED);
+ print_dec (slots[i].size, lra_dump_file, SIGNED);
fprintf (lra_dump_file, "):");
for (curr_regno = slots[i].regno;;
curr_regno = pseudo_slots[curr_regno].next - pseudo_slots)
