git: 23408297fbf3 - main - Merge llvm-project 12.0.1 rc2

[Dimitry Andric]

On 20 Jun 2021, at 14:49, Dmitry Chagin <dchagin at freebsd.org> wrote:
> 
> On Sat, Jun 19, 2021 at 06:11:04PM +0000, Dimitry Andric wrote:
>> The branch main has been updated by dim:
>> 
>> URL: https://cgit.FreeBSD.org/src/commit/?id=23408297fbf3089f0388a8873b02fa75ab3f5bb9
>> 
>> commit 23408297fbf3089f0388a8873b02fa75ab3f5bb9
>> Merge: cac129e60300 e4bbddaec868
>> Author:     Dimitry Andric <dim at FreeBSD.org>
>> AuthorDate: 2021-06-19 10:06:00 +0000
>> Commit:     Dimitry Andric <dim at FreeBSD.org>
>> CommitDate: 2021-06-19 18:09:28 +0000
>> 
>>    Merge llvm-project 12.0.1 rc2
>> 
>>    This updates llvm, clang, compiler-rt, libc++, libunwind, lld, lldb and
>>    openmp to llvmorg-12.0.1-rc2-0-ge7dac564cd0e, a.k.a. 12.0.1 rc2.
>> 
>>    PR:             255570
>>    MFC after:      6 weeks
>> 
> hi! with 11 clang kernel build time is about 60 sec, with 12.0.0 and
> 12.0.1 rc2 build time increased to 500 sec.

Did you previously have llvm/clang assertions turned off (via
MK_LLVM_ASSERTIONS=no)?

I did a few measurements of "make -j32 buildkernel", on
main-n247475-9d1cafb3049, with clang 11.0.1 and clang 12.0.1 (both with
assertions turned off, and statically linked:

clang 11.0.1 (n=5):

real user sys
138.65 3145.23 285.25
129.00 3240.73 290.61
126.38 3244.03 284.76
128.90 3250.95 268.71
136.42 3250.73 267.93

clang 12.0.1 (n=5):

real user sys
129.16 3306.13 291.84
128.18 3308.14 284.32
128.77 3301.35 281.90
141.37 3293.22 282.20
129.93 3304.08 284.47

$ ministat -A clang1101-real.txt clang1201-real.txt
x clang1101-real.txt
+ clang1201-real.txt
    N           Min           Max        Median           Avg        Stddev
x   5        126.38        138.65           129        131.87     5.3354662
+   5        128.18        141.37        129.16       131.482     5.5639707
No difference proven at 95.0% confidence

$ ministat -A clang1101-user.txt clang1201-user.txt
x clang1101-user.txt
+ clang1201-user.txt
    N           Min           Max        Median           Avg        Stddev
x   5       3145.23       3250.95       3244.03      3226.334     45.550423
+   5       3293.22       3308.14       3304.08      3302.584     5.8070759
Difference at 95.0% confidence
        76.25 +/- 47.3552
        2.36336% +/- 1.50191%
        (Student's t, pooled s = 32.4697)

Before I merged 12.0.1, I did the same sort of measurement, but for
"make -j32 buildworld buildkernel" (with CROSS_TOOLCHAIN set so the
bootstrap compiler isn't built), and this showed roughly similar
results:

$ ministat -A clang1101-real.txt clang1200-real.txt
x clang1101-real.txt
+ clang1200-real.txt
    N           Min           Max        Median           Avg        Stddev
x   5       1410.24       1461.04        1434.2      1435.296     18.210247
+   5       1461.54       1499.69       1462.07      1469.976     16.667199
Difference at 95.0% confidence
        34.68 +/- 25.4583
        2.41623% +/- 1.79718%
        (Student's t, pooled s = 17.4558)

$ ministat -A clang1101-user.txt clang1200-user.txt
x clang1101-user.txt
+ clang1200-user.txt
    N           Min           Max        Median           Avg        Stddev
x   5      37495.09       37913.2      37750.64     37750.734     165.00886
+   5      38133.12      38396.77      38390.77     38324.132     113.63363
Difference at 95.0% confidence
        573.398 +/- 206.617
        1.51891% +/- 0.552972%
        (Student's t, pooled s = 141.67)

So basically ~2% slower. It's would be a little tricky to find out if
there is any particular upstream commit that might be responsible,
as the difference is so small.

I think I'll also compare the performance with assertions enabled, and
MK_SHARED_TOOLCHAIN=yes, which should be worse than the above, but still
comparable between 11.0 and 12.0.

-Dimitry

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