RE: [PATCH 3/7] compiler.h: Add __if_constexpr(expr, if_const, if_not_const)

[David Laight <David.Laight@ACULAB.COM>]

From: Arnd Bergmann
> Sent: 24 July 2024 18:32
> 
> On Wed, Jul 24, 2024, at 16:29, David Laight wrote:
> 
> > +#define __if_constexpr(expr, if_const, if_not_const)		\
> > +	_Generic(0 ? ((void *)((long)(expr) * 0l)) : (char *)0,	\
> > +		char *: (if_const),				\
> > +		void *: (if_not_const))
> > +
> > -#define __is_constexpr(x) \
> > -	(sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
> > +#define __is_constexpr(expr) __if_constexpr((expr), 1, 0)
> 
> I don't immediately see anything wrong with this, but I'm
> still scared of any change to it, especially if this is
> meant to go straight into mainline.

Well it would be -rc1 (or maybe -rc2).

> Would it be possible to do patch 4/7 without the new
> __if_constexpr() and instead still using __builtin_choose_expr()?

The safer option would be to add __if_constexpr() but leave the
change to __is_constexpr() for 'next'.

	David

> 
>      Arnd

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