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From: "dave.rodgman at arm dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug other/110946] 3x perf regression with -Os on M1 Pro
Date: Tue, 08 Aug 2023 12:40:32 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110946

--- Comment #5 from Dave Rodgman <dave.rodgman at arm dot com> ---
(In reply to Richard Biener from comment #3)
> Note you shouldn't use -Os if you care about performance.  GCC is quite
> reasonable with code size increases at -O2 (as compared to other compiler=
s).
> Instead I suggest you use -flto with -O2 to decrease the size of the final
> executable/library and give GCC better knowledge on unit growth.

Understood, but I think it depends on the magnitude of the perf difference.=
 I'd
expect a smallish perf drop, say 10%, from -Os to be reasonable, but I'd
consider a 3x perf difference to be a compiler issue.(In reply to Alexander
Monakov from comment #2)
> So basically missed inlining at -Os, even memcpy wrappers are not inlined.
>=20
> Can you provide a reproducible testcase?
>=20
> Note that inline functions in mbedtls/library/alignment.h all miss the
> 'static' qualifier, which affects inlining decisions, and looks like a
> mistake anyway (if they are really meant to be non-static inlines, should=
n't
> there be a comment?)
>=20
> Does making them 'static inline' rectify the problem?

The easiest way to reproduce is to use the benchmark tool:

make programs/test/benchmark CC=3Dgcc CFLAGS=3D"-Os"
programs/test/benchmark aes_xts

I don't have a compact reproducer, sorry.=