From: Linus Torvalds
> Sent: 28 July 2024 18:25
...
> But I think even if we don't do that, I wonder if we can just do this:
>
> #define __cmp_once(op, x, y, unique_x, unique_y) ({ \
> typeof(x) unique_x = (x); \
> typeof(y) unique_y = (y); \
> static_assert(__types_ok(x, y), \
> ...
>
> and change it to
>
> #define __cmp_once(op, x, y, unique_x, unique_y) ({ \
> __auto_type unique_x = (x); \
> __auto_type unique_y = (y); \
> static_assert(__types_ok(unique_x, unique_y), \
> ...
>
> because while that may screw up the "constant integer" case (because
> it now goes through that "unique_XY" variable, maybe it doesn't? At
> least gcc has been known to deal with things like arguments to inline
> functions well enough (ie a constant argument means that the arguments
> shows as __builtin_constant_p(), and we already depend on that).
>
> That single change would cut down on duplication of 'x' and 'y'
> _enormously_. No?
IIRC the unique_x values can be tested with __builtin_constantp()
but will never be 'constant integer expressions' so can't be used
with static_assert() (etc).
I have thought about using typeof(unique_x) but the value 'x'.
That would be messy but only have one expansion of 'x'.
Might be doable if __COUNTER__ is passed as I did for min3().
I think it would be better to build on these changes - since they help.
David
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