From: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
To: "pb@pbcl.net" <pb@pbcl.net>
Cc: Ramana Radhakrishnan <ramana.gcc@googlemail.com>, nd <nd@arm.com>,
"libc-alpha@sourceware.org" <libc-alpha@sourceware.org>,
"adhemerval.zanella@linaro.org" <adhemerval.zanella@linaro.org>
Subject: Re: [PATCH 4/4] arm: Enable ARM mode for armv6 strlen
Date: Fri, 13 Apr 2018 15:43:00 -0000 [thread overview]
Message-ID: <DB6PR0801MB20535FA1DD3B7E5F01CC0DD383B30@DB6PR0801MB2053.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <DB6PR0801MB205308296F976C0B8B5A634583B30@DB6PR0801MB2053.eurprd08.prod.outlook.com>
Phil Blundell wrote:
> But here we are, two decades later, and the landscape is a bit
> different. It's not entirely clear that -marm/-mthumb are very useful
> options in an ARMv7 world because the user shouldn't need to care. In
> an ideal world the compiler would be able to predict for any given
> function whether T32 or A32 encoding would give the best results
> (either speed or space according to the selected optimisation settings)
> and proceed accordingly. Unfortunately in practice I don't think
> we're quite there yet and for critical code there's still an element of
> "try building it both ways round and see which one runs quickest" which
> means the compiler flags probably are still necessary. Users might
> even legitimately wish to try that experiment with glibc, so forbidding
> them to compile it under -marm would not obviously be the right thing
> to do.
If there are still cases where GCC generates worse code for Thumb-2,
then those can be addressed easily. Our very first Thumb-2 compiler
had performance within 2% on ARM1156T2 more than 2 decades ago!
Things have improved a lot since then, and system wide effects of code
footprint have become more important, so using only Arm on a modern
core just doesn't make any sense today.
Wilco
next prev parent reply other threads:[~2018-04-13 15:43 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-13 15:10 Wilco Dijkstra
2018-04-13 15:43 ` Wilco Dijkstra [this message]
2018-04-13 15:48 ` Florian Weimer
-- strict thread matches above, loose matches on Subject: below --
2018-04-11 21:16 [PATCH 1/4] arm: Fix armv7 neon memchr on ARM mode Adhemerval Zanella
2018-04-11 21:16 ` [PATCH 4/4] arm: Enable ARM mode for armv6 strlen Adhemerval Zanella
2018-04-11 22:12 ` Phil Blundell
2018-04-12 12:42 ` Adhemerval Zanella
2018-04-12 15:33 ` Phil Blundell
2018-04-12 16:16 ` Adhemerval Zanella
2018-04-12 19:20 ` Adhemerval Zanella
2018-04-12 19:28 ` Phil Blundell
[not found] ` <CAJA7tRahZ7L=zBs2z+zgCR=RTuccipdjBXhprjxybErebUwv1A@mail.gmail.com>
2018-04-12 19:41 ` Adhemerval Zanella
2018-04-12 20:31 ` Phil Blundell
2018-04-12 20:49 ` Adhemerval Zanella
2018-04-13 9:56 ` Phil Blundell
2018-04-13 11:56 ` Adhemerval Zanella
2018-04-13 12:06 ` Ramana Radhakrishnan
2018-04-13 12:44 ` Phil Blundell
2018-04-13 14:40 ` Adhemerval Zanella
2018-04-13 15:07 ` Phil Blundell
2018-04-13 16:42 ` Adhemerval Zanella
2018-04-13 19:09 ` Phil Blundell
2018-04-13 20:12 ` Adhemerval Zanella
2018-04-16 14:16 ` Richard Earnshaw (lists)
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