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

David Laight
2024-07-25T09:08:15Z

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@aculab.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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