From: "brian m. carlson" <sandals@crustytoothpaste•net>
To: Sebastian Andrzej Siewior <sebastian@breakpoint•cc>
Cc: git@vger•kernel.org
Subject: Re: [PATCH v2 4/6] bswap.h: Always overwrite ntohl/ ntohll macros
Date: Thu, 12 Jun 2025 00:14:48 +0000 [thread overview]
Message-ID: <aEob-FXAvc2Wqmlr@fruit.crustytoothpaste.net> (raw)
In-Reply-To: <20250611221444.1567638-5-sebastian@breakpoint.cc>
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On 2025-06-11 at 22:14:40, Sebastian Andrzej Siewior wrote:
> The ntohl and htonl macros are redefined because the provided macros were
> not always optimal. Sometimes it was a function call, sometimes it was a
> macro which did the shifting. Using the 'bswap' opcode on x86 provides
> probably better performance than performing the shifting.
I believe that the peephole optimizer will almost always optimize them
to the bswap or equivalent opcode, much like it recognizes how to
generate rotate opcodes from two shifts and an or, so they should
actually be equivalent.
GCC and clang both emit simple bswap instructions with `-O2`, which is
the optimization level we use: https://godbolt.org/z/1r8P1Pqo7.
--
brian m. carlson (they/them)
Toronto, Ontario, CA
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next prev parent reply other threads:[~2025-06-12 0:14 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-06-11 22:14 [PATCH v2 0/6] bswap.h: Rework ntohl handling Sebastian Andrzej Siewior
2025-06-11 22:14 ` [PATCH v2 1/6] Revert "bswap.h: add support for built-in bswap functions" Sebastian Andrzej Siewior
2025-06-12 20:04 ` Junio C Hamano
2025-06-11 22:14 ` [PATCH v2 2/6] bswap.h: Add support for __BYTE_ORDER__ Sebastian Andrzej Siewior
2025-06-12 0:24 ` brian m. carlson
2025-06-12 0:43 ` Collin Funk
2025-06-12 20:10 ` Junio C Hamano
2025-06-11 22:14 ` [PATCH v2 3/6] bswap.h: Define GIT_LITTLE_ENDIAN on msvc as little endian Sebastian Andrzej Siewior
2025-06-12 20:11 ` Junio C Hamano
2025-06-11 22:14 ` [PATCH v2 4/6] bswap.h: Always overwrite ntohl/ ntohll macros Sebastian Andrzej Siewior
2025-06-12 0:14 ` brian m. carlson [this message]
2025-06-12 20:16 ` Junio C Hamano
2025-06-11 22:14 ` [PATCH v2 5/6] bswap.h: Remove optimized x86 version of bswap32/64 Sebastian Andrzej Siewior
2025-06-26 15:55 ` Kristoffer Haugsbakk
2025-07-15 19:02 ` Sebastian Andrzej Siewior
2025-06-11 22:14 ` [PATCH v2 5/6] bswap: " Sebastian Andrzej Siewior
2025-06-11 22:14 ` [PATCH v2 6/6] bswap.h: Provide a built-in based version of bswap32/64 if possible Sebastian Andrzej Siewior
2025-06-12 20:21 ` [PATCH v2 0/6] bswap.h: Rework ntohl handling Junio C Hamano
2025-07-07 22:43 ` Junio C Hamano
2025-07-09 6:04 ` Sebastian Andrzej Siewior
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