BUG #17185: PostgreSQL performance GNU vs LLVM

The following bug has been logged on the website:

Bug reference: 17185
Logged by: arjun shetty
Email address: arjunshetty955(at)gmail(dot)com
PostgreSQL version: 13.4
Operating system: RHEL8.4
Description:

TPCH Results(Query Response Time(Q1 to Q22):
-------------
VU GCC Clang clang-with-llvm Clang(make file code removed -flto
=thin to flto)
vu
1 7185 6349 4410 9984
2 7302 7352 4307 9990
3 6233 6749 4544 9698
4 6701 6328 3701 10878
5 7105 7376 5829 10991

Note: clang-with-llvm: JIT OFF.

TPCC Results(NOPM)
------------------
vu GCC Clang Clang-with-llvm
Clang(make file code removed -flto =thin to flto(regluar flto)
16 921489 967234 946472 963300
52 1655840 1779333 1683924 1713926
68 1765030 1787377 1810060 1835825
170 1894382 1986746 2034823 1938886
192 1739617 1901906 1929656 1912524
210 1610512 1801849 1674440 1715523
230 1830690 1825760 1799097 1708821

1.Regaular LTO not performs better than Thin LTO ? is regular LTO not
supported in postgresql?
2.Is specific reason need to use -flto=thin(clan13)?
3.TPCH(Clang-llvm)performs better than GCC/Clang(others) but why
TPCC(Clang-llvm) not performs better than GCC/Clang-other (performance
deviation is less)

the results captured in bare Metal(HP Environment) and benchmark Env
HammerDbv4.2