Old Postgresql version on i7-1165g7

Good day, hackers.

I've got HP ProBook 640g8 with i7-1165g7. I've installed Ubuntu 20.04
LTS on it
and started to play with PostgreSQL sources.

Occasinally I found I'm not able to `make check` old Postgresql
versions.
At least 9.6 and 10. They are failed at the initdb stage in the call to
postgresql.

Raw postgresql version 9.6.8 and 10.0 fails in boostrap stage:

running bootstrap script ... 2021-04-09 12:33:26.424 MSK [161121]
FATAL: could not find tuple for opclass 1
2021-04-09 12:33:26.424 MSK [161121] PANIC: cannot abort
transaction 1, it was already committed
Aborted (core dumped)
child process exited with exit code 134

Our modified custom version 9.6 fails inside of libc __strncmp_avx2
during post-bootstrap
with segmentation fault:

Program terminated with signal SIGSEGV, Segmentation fault.
#0 __strncmp_avx2 ()
#1 0x0000557168a7eeda in nameeq
#2 0x0000557168b4c4a0 in FunctionCall2Coll
#3 0x0000557168659555 in heapgettup_pagemode
#4 0x000055716865a617 in heap_getnext
#5 0x0000557168678cf1 in systable_getnext
#6 0x0000557168b5651c in GetDatabaseTuple
#7 0x0000557168b574a4 in InitPostgres
#8 0x00005571689dcb7d in PostgresMain
#9 0x00005571688844d5 in main

I've bisected between REL_11_0 and "Rename pg_rewind's
copy_file_range()" and
found 372728b0d49552641f0ea83d9d2e08817de038fa
> Replace our traditional initial-catalog-data format with a better
> design.

https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=372728b0d49552641f0ea83d9d2e08817de038fa

This is first commit where `make check` doesn't fail during initdb on my
machine.
Therefore 02f3e558f21c0fbec9f94d5de9ad34f321eb0e57 is the last one where
`make check` fails.

I've tried with gcc9, gcc10 and clang10.
I've configured either without parameters or with `CFLAGS=-O0
./configure --enable-debug`.

Thing doesn't happen on Intel CPU of 10th series (i7-10510U and
i9-10900K).
Unfortunately, I have no fellows or colleagues with Intel CPU 11
series,
therefore I couldn't tell if this bug of 11 series or bug of concrete
CPU installed
in the notebook.

It will be great if some with i7-11* could try to make check and report
if it also fails or not.

With regards,
Yura Sokolov
PostgresPro