linux-kernel - Re: [PATCH v4 2/5] m68k/bitops: use __builtin_{clz,ctzl,ffs} to evaluate constant expressions

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Date: Mon, 5 Feb 2024 19:43:17 +0900
From: Vincent MAILHOL <mailhol.vincent@...adoo.fr>
To: Finn Thain <fthain@...ux-m68k.org>
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 Mon. 5 Feb. 2024 at 18:48, Finn Thain <fthain@...ux-m68k.org> wrote:
> On Mon, 5 Feb 2024, Vincent MAILHOL wrote:
>
> >
> > This is why I am asking whether or not clang support is important or not
> > for m68k. If you tell me it is not, then fine, I will remove all the asm
> > (by the way, the patch is already ready). But if there are even a few
> > users who care about clang for m68k, then I do not think we should
> > penalize them and I would not sign-off a change which negatively impacts
> > some users.
> >
>
> If clang support is important then clang's builtins are important. So why
> not improve those instead? That would resolve the issue in a win-win.

I am deeply sorry, but with all your respect, this request is unfair.
I will not fix the compiler.

Let me repeat my question for the third time: are you (or any other
m68k maintainer) ready to acknowledge that we can degrade the
performance for clang m68k users? With that acknowledgement, I will
remove the asm and replace it with the builtins.


Yours sincerely,
Vincent Mailhol