From: "Timur Safin" <tsafin@tarantool.org>
To: 'Aleksandr Lyapunov' <alyapunov@tarantool.org>,
'Vladislav Shpilevoy' <v.shpilevoy@tarantool.org>,
tarantool-patches@dev.tarantool.org, gorcunov@gmail.com
Subject: Re: [Tarantool-patches] [PATCH 2/2] uuid: fix unaligned memory access
Date: Tue, 19 May 2020 11:34:24 +0300 [thread overview]
Message-ID: <353d01d62db8$4dc09f30$e941dd90$@tarantool.org> (raw)
In-Reply-To: <f0774d12-0fdd-c922-05e3-e299640d6187@tarantool.org>
: From: Aleksandr Lyapunov <alyapunov@tarantool.org>
:
:
: > Could you please show the benchmark? I did my own, and I can't see any
: > significant difference. The present difference is so small, that it
: > looks like jitter. Both in is_nil and is_eq.
: >
: > I did a very simple bench in Lua, without any GCed objects.
:
: I fear that Lua is not suitable for performance tests.
: Here you are: https://pastebin.com/VXkS1v6M
: Also please take a look at disasm: https://godbolt.org/z/s6Cti4
Haha, good example - love it! One may assume that this is awkward C++ aliasing rules (where only std::byte_t, char, and unsigned char are aliasing) and
should look differently in C mode, but no - it's the same for C enforced
https://godbolt.org/z/fdbBLf
So I'd agree - memcmp is the simplest way to do the fastest comparison while
Keeping that picky aliasing analysis in compiler happy.
Regards,
Timur
next prev parent reply other threads:[~2020-05-19 8:34 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-15 23:03 [Tarantool-patches] [PATCH 0/2] Sanitize uuid and bit alignment Vladislav Shpilevoy
2020-05-15 23:03 ` [Tarantool-patches] [PATCH 1/2] bit: fix unaligned memory access and UB bit shift Vladislav Shpilevoy
2020-05-21 14:37 ` Timur Safin
2020-05-15 23:03 ` [Tarantool-patches] [PATCH 2/2] uuid: fix unaligned memory access Vladislav Shpilevoy
2020-05-18 12:55 ` Aleksandr Lyapunov
2020-05-18 21:17 ` Vladislav Shpilevoy
2020-05-19 7:28 ` Aleksandr Lyapunov
2020-05-19 8:34 ` Timur Safin [this message]
2020-05-19 21:24 ` Vladislav Shpilevoy
2020-05-20 8:18 ` Aleksandr Lyapunov
2020-05-20 21:38 ` Vladislav Shpilevoy
2020-05-21 8:28 ` Aleksandr Lyapunov
2020-05-21 14:37 ` Timur Safin
2020-05-21 19:33 ` [Tarantool-patches] [PATCH 0/2] Sanitize uuid and bit alignment Vladislav Shpilevoy
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