On Wed, Jun 27, 2007 at 09:34:55AM -0700, Josh Triplett wrote:
> > is actually nice code for something like the kernel, but it turns out that
> > in order to make this work, you have to do it as
> >
> > #define htons(x) (__builtin_constant_p(x) ? constant_htons(x) : __htons(x))
That's not quite right. In principle, __builtin_choose_expr() could be
used for that kind of stuff and builtins can change the rules.
> Also agreed. Same goes for other short-circuiting operations like &&,
> ||, and ?: without the center argument; if you can determine at
> compilation time that it does not need to evaluate part of the
> expression at all, go ahead and ignore that part of the expression even
> if it does not constitute an integer constant expression. If you want
> to optionally check for this case and issue a diagnostic, put it under
> -Wstrict-constant-expressions or similar.
That actually means extra work for evaluate_expression(). Unfortunately.
The thing is, we want to typecheck all branches, even ones not taken.
_However_, we don't want to expand all of them. Having extra places
where we have to do expansion means extra work.
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