Hi,
PR68212 mentioned that the COUNT of unrolled loop was not correct, and
comments of this PR also mentioned that loop become 'cold'.
This patch fixes the wrong COUNT/PROB of unrolled loop. And the
patch handles the case where unrolling in unreliable count number can
cause a loop to no longer look hot and therefor not get aligned. This
patch scale by profile_probability::likely () if unrolled count gets
unrealistically small.
Bootstrap/regtest on powerpc64le with no new regressions. Ok for trunk?
Jiufu Guo
gcc/ChangeLog:
2020-10-09 Jiufu Guo <guoji...@linux.ibm.com>
Pat Haugen <pthau...@us.ibm.com>
PR rtl-optimization/68212
* cfgloopmanip.c (duplicate_loop_to_header_edge): Reset probablity
of unrolled/peeled loop.
testsuite/ChangeLog:
2020-10-09 Jiufu Guo <guoji...@linux.ibm.com>
Pat Haugen <pthau...@us.ibm.com>
PR rtl-optimization/68212
* gcc.dg/pr68212.c: New test.
---
gcc/cfgloopmanip.c | 31 +++++++++++++++++++++++++++++--
gcc/testsuite/gcc.dg/pr68212.c | 13 +++++++++++++
2 files changed, 42 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/pr68212.c
diff --git a/gcc/cfgloopmanip.c b/gcc/cfgloopmanip.c
index b0ca82a67fd..d3c95498402 100644
--- a/gcc/cfgloopmanip.c
+++ b/gcc/cfgloopmanip.c
@@ -1260,14 +1260,30 @@ duplicate_loop_to_header_edge (class loop *loop, edge e,
/* If original loop is executed COUNT_IN times, the unrolled
loop will account SCALE_MAIN_DEN times. */
scale_main = count_in.probability_in (scale_main_den);
+
+ /* If we are guessing at the number of iterations and count_in
+ becomes unrealistically small, reset probability. */
+ if (!(count_in.reliable_p () || loop->any_estimate))
+ {
+ profile_count new_count_in = count_in.apply_probability
(scale_main);
+ profile_count preheader_count = loop_preheader_edge (loop)->count
();
+ if (new_count_in.apply_scale (1, 10) < preheader_count)
+ scale_main = profile_probability::likely ();
+ }
+
scale_act = scale_main * prob_pass_main;
}
else
{
+ profile_count new_loop_count;
profile_count preheader_count = e->count ();
- for (i = 0; i < ndupl; i++)
- scale_main = scale_main * scale_step[i];
scale_act = preheader_count.probability_in (count_in);
+ /* Compute final preheader count after peeling NDUPL copies. */
+ for (i = 0; i < ndupl; i++)
+ preheader_count = preheader_count.apply_probability (scale_step[i]);
+ /* Subtract out exit(s) from peeled copies. */
+ new_loop_count = count_in - (e->count () - preheader_count);
+ scale_main = new_loop_count.probability_in (count_in);
}
}
@@ -1383,6 +1399,17 @@ duplicate_loop_to_header_edge (class loop *loop, edge e,
scale_bbs_frequencies (new_bbs, n, scale_act);
scale_act = scale_act * scale_step[j];
}
+
+ /* Need to update PROB of exit edge and corresponding COUNT. */
+ if (orig && is_latch && (!bitmap_bit_p (wont_exit, j + 1))
+ && bbs_to_scale)
+ {
+ edge new_exit = new_spec_edges[SE_ORIG];
+ profile_count new_count = new_exit->src->count;
+ profile_count exit_count = loop_preheader_edge (loop)->count ();
+ profile_probability prob = exit_count.probability_in (new_count);
+ recompute_loop_frequencies (loop, prob);
+ }
}
free (new_bbs);
free (orig_loops);
diff --git a/gcc/testsuite/gcc.dg/pr68212.c b/gcc/testsuite/gcc.dg/pr68212.c
new file mode 100644
index 00000000000..e0cf71d5202
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr68212.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-tree-vectorize -funroll-loops --param
max-unroll-times=4 -fdump-rtl-alignments" } */
+
+void foo(long int *a, long int *b, long int n)
+{
+ long int i;
+
+ for (i = 0; i < n; i++)
+ a[i] = *b;
+}
+
+/* { dg-final { scan-rtl-dump-times "internal loop alignment added" 1
"alignments"} } */
+
--
2.25.1
