On 2021/12/13 17:25, Jan Hubicka wrote:
>> r12-4526 cancelled jump thread path rotates loop. It exposes a issue in
>> profile-estimate when predict_extra_loop_exits, outer loop's exit edge
>> is marked as inner loop's extra loop exit and set with incorrect
>> prediction, then a hot inner loop will become cold loop finally through
>> optimizations, this patch add loop check when searching extra exit edges
>> to avoid unexpected predict_edge from predict_paths_for_bb.
>>
>> Regression tested on P8LE, OK for master?
>>
>> gcc/ChangeLog:
>>
>> PR middle-end/103270
>> * predict.c (predict_extra_loop_exits): Add loop parameter.
>> (predict_loops): Call with loop argument.
>
> With changes to branch predictors it is useful to re-test their
> effectivity on spec and see if their hitrates are still mathcing
> reality. You can do it by buiding spec with -fprofile-generate, train
> it and then build with -fprofile-use -fdump-tree-ipa-profile-details
> and use contrib/analyze_brprob.py that will collect info on how they
> work.
>
> This patch looks good to me, but it would be nice to have things reality
> checked (and since we did not do the stats for some time, there may be
> surprises) so if you could run the specs and post results of
> analyze_brprob, it would be great. I will also try to get to that soon,
> but currently I am bit swamped by other problems I noticed on clang
> builds.
>
> Thanks a lot for working on profile fixes - I am trying now to get
> things into shape. With Martin we added basic testing infrastructure
> for keeping track of profile updates and I am trying to see how it works
> in practice now. Hopefully it will make it easier to judge on profile
> updating patches. I would welcome list of patches I should look at.
>
> I will write separate mail on this.
> Honza
With the patch, the analyze_brprob.py outputs below data with PGO build,
there is no verification code in the script, so how to check whether it
is correct? Run it again without the patch and compare "extra loop exit"
field?
./contrib/analyze_brprob.py ~/workspace/tests/spec2017/dump_file_all
HEURISTICS BRANCHES (REL) BR. HITRATE
HITRATE COVERAGE COVERAGE (REL) predict.def (REL) HOT branches (>10%)
noreturn call 1 0.0% 100.00% 50.00%
/ 50.00% 2 2.00 0.0% 100%:1
Fortran zero-sized array 3 0.0% 66.67% 41.71%
/ 60.50% 362 362.00 0.0% 100%:3
loop iv compare 16 0.0% 93.75% 98.26%
/ 98.76% 279847 279.85k 0.0% 93%:4
__builtin_expect 35 0.0% 97.14% 78.09%
/ 78.35% 17079558 17.08M 0.0%
loop guard with recursion 45 0.1% 86.67% 85.13%
/ 85.14% 6722424412 6.72G 1.3% 74%:4
extra loop exit 80 0.1% 58.75% 81.49%
/ 89.21% 438470261 438.47M 0.1% 86%:3
guess loop iv compare 235 0.3% 80.85% 52.83%
/ 73.97% 148558247 148.56M 0.0% 47%:3
negative return 241 0.3% 71.37% 25.33%
/ 92.61% 250402383 250.40M 0.0% 69%:2
loop exit with recursion 315 0.4% 74.60% 85.07%
/ 85.71% 9403136858 9.40G 1.8% 59%:4
const return 320 0.4% 51.88% 90.45%
/ 95.63% 925341727 925.34M 0.2% 76%:5
indirect call 377 0.5% 51.46% 84.72%
/ 91.14% 2133772848 2.13G 0.4% 69%:1
polymorphic call 410 0.5% 44.15% 31.26%
/ 79.37% 3272688244 3.27G 0.6% 53%:2
recursive call 506 0.7% 39.53% 44.97%
/ 83.92% 1211036806 1.21G 0.2% 10%:1
goto 618 0.8% 64.24% 65.37%
/ 83.57% 702446178 702.45M 0.1% 20%:1
null return 800 1.1% 64.62% 56.59%
/ 77.70% 603952067 603.95M 0.1% 28%:2
continue 956 1.3% 63.70% 65.65%
/ 79.97% 3780303799 3.78G 0.7% 52%:3
loop guard 1177 1.6% 56.33% 42.54%
/ 80.32% 7373601457 7.37G 1.4% 50%:2
opcode values positive (on trees) 2020 2.7% 62.38% 64.16%
/ 84.44% 31695571761 31.70G 6.0% 21%:2
loop exit 3293 4.4% 76.19% 87.18%
/ 88.35% 50377138963 50.38G 9.6% 18%:1
loop iterations 4761 6.3% 99.98% 84.27%
/ 84.27% 73463634555 73.46G 13.9%
pointer (on trees) 8076 10.7% 56.23% 69.36%
/ 83.15% 12322099991 12.32G 2.3%
call 11396 15.1% 64.14% 74.13%
/ 89.82% 25197949198 25.20G 4.8% 34%:1
opcode values nonequal (on trees) 12237 16.3% 70.70% 70.86%
/ 83.54% 36638772333 36.64G 6.9%
guessed loop iterations 16760 22.3% 99.78% 91.49%
/ 91.49% 162952747918 162.95G 30.9%
HEURISTICS BRANCHES (REL) BR. HITRATE
HITRATE COVERAGE COVERAGE (REL) predict.def (REL) HOT branches (>10%)
no prediction 12730 16.9% 39.29% 33.32%
/ 79.93% 121106031835 121.11G 23.0%
first match 25261 33.6% 92.17% 88.33%
/ 88.98% 296652487962 296.65G 56.3%
DS theory 28333 37.7% 63.03% 72.05%
/ 85.00% 109563734005 109.56G 20.8%
combined 75232 100.0% 73.17% 72.32%
/ 86.08% 527351738575 527.35G 100.0%
Loop count: 37870
avg. # of iter: 8444.77
median # of iter: 7.00
avg. (1% cutoff) # of iter: 174.68
avg. (5% cutoff) # of iter: 55.14
avg. (10% cutoff) # of iter: 35.21
avg. (20% cutoff) # of iter: 26.23
avg. (30% cutoff) # of iter: 21.70
>>
>> gcc/testsuite/ChangeLog:
>>
>> PR middle-end/103270
>> * gcc.dg/pr103270.c: New test.
>> ---
>> gcc/predict.c | 10 ++++++----
>> gcc/testsuite/gcc.dg/pr103270.c | 19 +++++++++++++++++++
>> 2 files changed, 25 insertions(+), 4 deletions(-)
>> create mode 100644 gcc/testsuite/gcc.dg/pr103270.c
>>
>> diff --git a/gcc/predict.c b/gcc/predict.c
>> index 3cb4e3c0eb5..5b6e0cf722b 100644
>> --- a/gcc/predict.c
>> +++ b/gcc/predict.c
>> @@ -1859,7 +1859,7 @@ predict_iv_comparison (class loop *loop, basic_block
>> bb,
>> exits to predict them using PRED_LOOP_EXTRA_EXIT. */
>>
>> static void
>> -predict_extra_loop_exits (edge exit_edge)
>> +predict_extra_loop_exits (class loop *loop, edge exit_edge)
>> {
>> unsigned i;
>> bool check_value_one;
>> @@ -1912,12 +1912,14 @@ predict_extra_loop_exits (edge exit_edge)
>> continue;
>> if (EDGE_COUNT (e->src->succs) != 1)
>> {
>> - predict_paths_leading_to_edge (e, PRED_LOOP_EXTRA_EXIT, NOT_TAKEN);
>> + predict_paths_leading_to_edge (e, PRED_LOOP_EXTRA_EXIT, NOT_TAKEN,
>> + loop);
>> continue;
>> }
>>
>> FOR_EACH_EDGE (e1, ei, e->src->preds)
>> - predict_paths_leading_to_edge (e1, PRED_LOOP_EXTRA_EXIT, NOT_TAKEN);
>> + predict_paths_leading_to_edge (e1, PRED_LOOP_EXTRA_EXIT, NOT_TAKEN,
>> + loop);
>> }
>> }
>>
>> @@ -2008,7 +2010,7 @@ predict_loops (void)
>> ex->src->index, ex->dest->index);
>> continue;
>> }
>> - predict_extra_loop_exits (ex);
>> + predict_extra_loop_exits (loop, ex);
>>
>> if (number_of_iterations_exit (loop, ex, &niter_desc, false, false))
>> niter = niter_desc.niter;
>> diff --git a/gcc/testsuite/gcc.dg/pr103270.c
>> b/gcc/testsuite/gcc.dg/pr103270.c
>> new file mode 100644
>> index 00000000000..819310e360e
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/pr103270.c
>> @@ -0,0 +1,19 @@
>> +/* { dg-do compile } */
>> +/* { dg-options "-O2 -fdump-tree-profile_estimate" } */
>> +
>> +void test(int a, int* i)
>> +{
>> + for (; a < 5; ++a)
>> + {
>> + int b = 0;
>> + int c = 0;
>> + for (; b != -11; b--)
>> + for (int d = 0; d ==0; d++)
>> + {
>> + *i += c & a;
>> + c = b;
>> + }
>> + }
>> +}
>> +
>> +/* { dg-final { scan-tree-dump-not "extra loop exit heuristics of
>> edge\[^:\]*:" "profile_estimate"} } */
>> --
>> 2.25.1
>>
--
Thanks,
Xionghu
