linux-kernel - RE: [PATCH 7/7] minmax: minmax: Add __types_ok3() and optimise defines with 3 arguments

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Message-ID: <f093cc1b170b45839f06b3fbe7df5d2f@AcuMS.aculab.com>
Date: Thu, 25 Jul 2024 09:07:32 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Arnd Bergmann' <arnd@...nel.org>, "'linux-kernel@...r.kernel.org'"
	<linux-kernel@...r.kernel.org>, Linus Torvalds <torvalds@...uxfoundation.org>
CC: Matthew Wilcox <willy@...radead.org>, Christoph Hellwig
	<hch@...radead.org>, Andrew Morton <akpm@...ux-foundation.org>, "Andy
 Shevchenko" <andriy.shevchenko@...ux.intel.com>, Dan Carpenter
	<dan.carpenter@...aro.org>, "Jason A . Donenfeld" <Jason@...c4.com>,
	"'pedro.falcato@...il.com'" <pedro.falcato@...il.com>, Mateusz Guzik
	<mjguzik@...il.com>, "'linux-mm@...ck.org'" <linux-mm@...ck.org>
Subject: RE: [PATCH 7/7] minmax: minmax: Add __types_ok3() and optimise
 defines with 3 arguments

From: Arnd Bergmann
> Sent: 24 July 2024 18:04
> 
> On Wed, Jul 24, 2024, at 16:33, David Laight wrote:
> > min3() and max3() were added to optimise nested min(x, min(y, z))
> > sequences, bit only moved where the expansion was requiested.
> >
> > Add a separate implementation for 3 argument calls.
> > These are never required to generate constant expressiions to
> > remove that logic.
> >
> > Signed-off-by: David Laight <david.laight@...lab.com>
> 
> This brings another 3x improvement in the size of the expansion
> and build speed.
> 
> > +#define __cmp_once3(op, x, y, z, uniq) ({	\
> > +	typeof(x) __x_##uniq = (x);		\
> > +	typeof(x) __y_##uniq = (y);		\
> > +	typeof(x) __z_##uniq = (z);		\
> > +	__cmp(op, __cmp(op, __x_##uniq, __y_##uniq), __z_##uniq); })
> 
> This still has a nested call to __cmp(), which makes the
> resulting expression bigger than necessary.
> 
> The three typeof(x) should be x/y/z, right?

Ooops...

> Using __auto_type
> would avoid the bug and also remove one more variable expansion.

I'd thought that as well.
But hadn't looked up the syntax.

> Using another temporary variable, plus the use of __auto_type
> brings the example line from xen/setup.c down 750KB to 530KB,
> and the compile speed from 0.5s to 0.34s.
> 
>  #define __cmp_once3(op, x, y, z, uniq) ({      \
>        __auto_type __x_##uniq = (x);           \
>        __auto_type __y_##uniq = (y);           \
>        __auto_type __z_##uniq = (z);           \
>        __auto_type __xy##uniq = __cmp(op, __x_##uniq, __y_##uniq); \
>        __cmp(op, __xy_##uniq, __z_##uniq); })
> 
> The __auto_type change can also be applied to the other typeof()
> in this file.

True.

	David

> 
>       Arnd

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