Product: GCC
Component: rtl-optimization
Version: 7.3.0
If we add the flag DO_PREDICATION in scheduling ebb, the compiler will try to
predicate the insn when the producer insn has been issued,
and put the consumer insn into suitable queue. For example as shown in
schedule verbose dump file:
;; | insn | prio |
......................
;; | 387 | 27 | t1=a5==0 AGS0|AGS1
;; | 388 | 27 | pc={(t1!=0)?L184:pc} PCU
;; | 459 | 26 | ev10=[a0+0xbc0] AGL0|AGL1
......................
;; 1--> + 387 t1=a5==0 :AGS0|AGS1
deferring rescan insn with uid = 459.
;; dependencies resolved: insn + 459 predicated
;; Ready-->Q: insn + 459: queued for 2 cycles (change queue index)
;; tick updated: insn + 459 into queue with cost=2
insn 387 is a test insn, insn 388 is a jump insn, insn 459 is a load insn.
After predicating, insn 459 convert into this form: [!t1] ev10 = [a0+0xbc0]
and put insn 459 into queue[3]. INSN_TICK (459) = 3;
After issuing jump insn 388, the compiler will try to resotre pattern in insn
459 as shown in the following dump files.
;; Ready list after ready_sort: + 388:94:prio=27
;; Ready list (t = 1): + 388:94:prio=27
[1;1]:388
;; 1--> + 388 pc={(t1!=0)?L184:pc} :PCU
restoring pattern for insn 459
deferring rescan insn with uid = 459.
However, the INSN_TICK of insn 459 doesn't calculate again.
Actually, after restoring pattern, the insn can issue more earlier.
If we recalculate the INSN_TICK of insn 459, we will get INSN_TICK (459) = 2,
then the load insn 459 can issue at clock t = 2 instead of clock t = 3.
So, can we add the following code to recalculate the INSN_TICK in function
restore pattern?
restore_pattern (dep_t dep, bool immediately)
{
rtx_insn *next = DEP_CON (dep);
int tick = INSN_TICK (next);
.........................
if (DEP_TYPE (dep) == REG_DEP_CONTROL)
{
if (sched_verbose >= 5)
fprintf (sched_dump, "restoring pattern for insn %d\n",
INSN_UID (next));
haifa_change_pattern (next, ORIG_PAT (next));
+ update_insn_after_change (next);
+ if ((TODO_SPEC (next) & (HARD_DEP | DEP_POSTPONED)) == 0)
+ {
+ fix_tick_ready (next);
+ tick = INSN_TICK (next);
+ }
}
...........................
I found the similar code in function apply_replacement (dep_t dep, bool
immediately).
I think this patch can improve instruction parallelism.
Best wishes!
