Hi,
When investigating the issue from
https://gcc.gnu.org/pipermail/gcc-patches/2020-July/549786.html
I find the BB COUNTs of loop seems are not accurate in some case.
For example:
In below figure:
COUNT:268435456 pre-header
|
| ..
| ||
V v|
COUNT:805306369|
/ \ |
33%/ \ |
/ \|
v v |
COUNT:268435456 COUNT:536870911 |
exit-edge | latch |
._.
Those COUNTs have below equations:
COUNT of exit-edge:268435456 = COUNT of pre-header:268435456
COUNT of exit-edge:268435456 = COUNT of header:805306369 * 33
COUNT of header:805306369 = COUNT of pre-header:268435456 + COUNT of
latch:536870911
While after pcom:
COUNT:268435456 pre-header
|
| ..
| ||
V v|
COUNT:268435456|
/ \ |
50%/ \ |
/ \|
v v |
COUNT:134217728 COUNT:134217728 |
exit-edge | latch |
._.
COUNT != COUNT + COUNT
In some cases, the probility of exit-edge is easy to estimate, then
those COUNTs of other BBs in loop can be re-caculated.
Below is a patch to reset COUNTs as above description.
Thanks for comments!!
Jiufu
---
gcc/cfgloopmanip.c| 43 +++
gcc/cfgloopmanip.h| 2 +-
gcc/tree-ssa-loop-manip.c | 28 +++--
3 files changed, 47 insertions(+), 26 deletions(-)
diff --git a/gcc/cfgloopmanip.c b/gcc/cfgloopmanip.c
index 73134a20e33..180916b0974 100644
--- a/gcc/cfgloopmanip.c
+++ b/gcc/cfgloopmanip.c
@@ -1773,3 +1773,46 @@ loop_version (class loop *loop,
return nloop;
}
+
+/* Recacluate the COUNTs of BBs in LOOP, if the probility of exit edge
+ is NEW_EXIT_P. */
+
+bool
+recompute_loop_frequencies (class loop *loop, profile_probability new_exit_p)
+{
+ edge exit = single_exit (loop);
+ if (!exit)
+return false;
+
+ basic_block * bbs;
+ profile_count exit_count = loop_preheader_edge (loop)->count ();
+ profile_probability exit_p = exit_count.probability_in (loop->header->count);
+ profile_count base_count = loop->header->count;
+ profile_count after_num = base_count.apply_probability (exit_p);
+ profile_count after_den = base_count.apply_probability (new_exit_p);
+
+ /* Update BB counts in loop body.
+ COUNT = COUNT
+ COUNT = COUNT * exit_edge_probility
+ The COUNT=COUNT * old_exit_p / new_exit_p. */
+ bbs = get_loop_body (loop);
+ scale_bbs_frequencies_profile_count (bbs, loop->num_nodes, after_num,
+after_den);
+ free (bbs);
+
+ /* Update probability and count of latch. */
+ edge new_nonexit = single_pred_edge (loop->latch);
+ new_nonexit->probability = new_exit_p.invert ();
+ loop->latch->count
+= loop->header->count.apply_probability (new_nonexit->probability);
+
+ /* Update probability and count of exit destination. */
+ edge e;
+ edge_iterator ei;
+ exit->probability = new_exit_p;
+ exit->dest->count = profile_count::zero ();
+ FOR_EACH_EDGE (e, ei, exit->dest->preds)
+exit->dest->count += e->src->count.apply_probability (e->probability);
+
+ return true;
+}
diff --git a/gcc/cfgloopmanip.h b/gcc/cfgloopmanip.h
index 7331e574e2f..d55bab17f65 100644
--- a/gcc/cfgloopmanip.h
+++ b/gcc/cfgloopmanip.h
@@ -62,5 +62,5 @@ class loop * loop_version (class loop *, void *,
basic_block *,
profile_probability, profile_probability,
profile_probability, profile_probability, bool);
-
+extern bool recompute_loop_frequencies (class loop *, profile_probability);
#endif /* GCC_CFGLOOPMANIP_H */
diff --git a/gcc/tree-ssa-loop-manip.c b/gcc/tree-ssa-loop-manip.c
index a2717a411a3..4060d601cf8 100644
--- a/gcc/tree-ssa-loop-manip.c
+++ b/gcc/tree-ssa-loop-manip.c
@@ -1251,7 +1251,6 @@ tree_transform_and_unroll_loop (class loop *loop,
unsigned factor,
bool ok;
unsigned i;
profile_probability prob, prob_entry, scale_unrolled;
- profile_count freq_e, freq_h;
gcov_type new_est_niter = niter_for_unrolled_loop (loop, factor);
unsigned irr = loop_preheader_edge (loop)->flags & EDGE_IRREDUCIBLE_LOOP;
auto_vec to_remove;
@@ -1393,33 +1392,12 @@ tree_transform_and_unroll_loop (class loop *loop,
