The following patch fixes the case where unrolling in the absence of profile
information can cause a loop to no longer look hot and therefor not get
aligned. In this case, instead of dividing by the unroll factor we now just
scale by profile_probability::likely (). The diff looks worse than what really
changed, just the addition of an if test and putting the existing 'scalemain'
setting code into the else leg. Bootstrap/regtest on powerpc64le with no new
regressions. I also ran a CPU2006 comparison, there were 4 benchmarks that
improved 2-3% with the others in the noise range.
Ok for trunk?
-Pat
2018-11-28 Pat Haugen <pthau...@us.ibm.com>
PR rtl-optimization/68212
* cfgloopmanip.c (duplicate_loop_to_header_edge): Adjust scale factor.
testsuite/ChangeLog:
2018-11-28 Pat Haugen <pthau...@us.ibm.com>
PR rtl-optimization/68212
* gcc.dg/pr68212.c: New test.
Index: gcc/cfgloopmanip.c
===================================================================
--- gcc/cfgloopmanip.c (revision 266522)
+++ gcc/cfgloopmanip.c (working copy)
@@ -1242,16 +1242,25 @@ duplicate_loop_to_header_edge (struct lo
profile_probability prob_pass_main = bitmap_bit_p (wont_exit, 0)
? prob_pass_wont_exit
: prob_pass_thru;
- profile_probability p = prob_pass_main;
- profile_count scale_main_den = count_in;
- for (i = 0; i < ndupl; i++)
+
+ /* If not using real profile data then don't scale the loop by ndupl.
+ This can lead to the loop no longer looking hot wrt surrounding
+ code. */
+ if (profile_status_for_fn (cfun) == PROFILE_GUESSED)
+ scale_main = profile_probability::likely ();
+ else
{
- scale_main_den += count_in.apply_probability (p);
- p = p * scale_step[i];
+ profile_probability p = prob_pass_main;
+ profile_count scale_main_den = count_in;
+ for (i = 0; i < ndupl; i++)
+ {
+ scale_main_den += count_in.apply_probability (p);
+ p = p * scale_step[i];
+ }
+ /* 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 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);
scale_act = scale_main * prob_pass_main;
}
else
Index: gcc/testsuite/gcc.dg/pr68212.c
===================================================================
--- gcc/testsuite/gcc.dg/pr68212.c (nonexistent)
+++ gcc/testsuite/gcc.dg/pr68212.c (working copy)
@@ -0,0 +1,12 @@
+/* { 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"} } */
