From: Martin Uecker

Sent: 07 December 2024 21:06

Am Samstag, dem 07.12.2024 um 21:00 +0000 schrieb David Laight:

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From: Martin Uecker

quoted

Sent: 07 December 2024 19:52

...

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There exist proposals along those lines for C2Y.

From a more near-term solution, I wonder if making it possible (or
easier) to return integer constant expressions from statement
expressions and allowing a restricted form of statement expressions
at file scope would help?

It would help a lot if a #define that just used local variables
to avoid arguments being re-expanded and for CSE could still
generate a constant value.
Does need to be a #define - to get token pasting and 'stringify'.
Although you would need something for reporting detected errors,
and builtin compiler support for const_true() for the detection
itself.

We are super close:

https://godbolt.org/z/Tarq89bha

(The preprocess output is about 500 bytes for each line.)

(if we ignore the grotesque hacks to get there, but this would go
away if the compiler does it internally)

Some of those hacks look excessive.
Isn't IF_CONST(x, y, z) just
	_Generic(0 ? (void *)((x) ? 0L : 0L) : (char *)0, char *: y, void *: z)
and that gets rid some of the grossness.
Just having that as a builtin would simplify some things.
Although you could use:
	__builtin_choose_expr(IS_CONST(x), y, z)
if you need y and z to have different types, and just:
	IS_CONST(x) ? y : z
otherwise.
Since AFAICT they are otherwise equivalent.

	David

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