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Message-ID: <77831c6f-7fc9-c42d-b29b-c3b2f3f5e687@linux-m68k.org>
Date: Mon, 29 Jan 2024 09:34:56 +1100 (AEDT)
From: Finn Thain <fthain@...ux-m68k.org>
To: Vincent MAILHOL <mailhol.vincent@...adoo.fr>
cc: David Laight <David.Laight@...lab.com>,
Andrew Morton <akpm@...ux-foundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Yury Norov <yury.norov@...il.com>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Douglas Anderson <dianders@...omium.org>,
Kees Cook <keescook@...omium.org>, Petr Mladek <pmladek@...e.com>,
Randy Dunlap <rdunlap@...radead.org>,
Zhaoyang Huang <zhaoyang.huang@...soc.com>,
Geert Uytterhoeven <geert+renesas@...der.be>,
Marco Elver <elver@...gle.com>, Brian Cain <bcain@...cinc.com>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
Matthew Wilcox <willy@...radead.org>,
"Paul E . McKenney" <paulmck@...nel.org>,
"linux-m68k@...ts.linux-m68k.org" <linux-m68k@...ts.linux-m68k.org>
Subject: Re: [PATCH v4 2/5] m68k/bitops: use __builtin_{clz,ctzl,ffs} to
evaluate constant expressions
On Sun, 28 Jan 2024, Vincent MAILHOL wrote:
> > > The asm is meant to produce better results when the argument is not
> > > a constant expression.
Is that because gcc's implementation has to satisfy requirements that are
excessively stringent for the kernel's purposes? Or is it a compiler
deficiency only affecting certain architectures?
> ... The only thing I am not ready to do is to compare the produced
> assembly code and confirm whether or not it is better to remove asm
> code.
>
If you do the comparison and find no change, you get to say so in the
commit log, and everyone is happy.
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