| Message ID | 20201009101242.2478660-2-guojiufu@linux.ibm.com |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] correct BB frequencies after loop changed | expand |
guojiufu <guojiufu@linux.ibm.com> writes: Hi Honza, all, Just want to ping this for review. Original messages: [PATCH 2/2] https://gcc.gnu.org/pipermail/gcc-patches/2020-October/555872.html [PATCH 1/2] https://gcc.gnu.org/pipermail/gcc-patches/2020-October/555871.html Thanks, Jiufu Guo. > 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 <guojiufu@linux.ibm.com> > Pat Haugen <pthaugen@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 <guojiufu@linux.ibm.com> > Pat Haugen <pthaugen@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"} } */ > +
On 10/9/20 4:12 AM, guojiufu via Gcc-patches wrote: > 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 <guojiufu@linux.ibm.com> > Pat Haugen <pthaugen@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 <guojiufu@linux.ibm.com> > Pat Haugen <pthaugen@us.ibm.com> > PR rtl-optimization/68212 > * gcc.dg/pr68212.c: New test. OK jeff
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"} } */ +