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

Arnd Bergmann
2024-07-24T17:03:55Z

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

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.

Arnd