On Mon, 20 Nov 2023, Jakub Jelinek wrote: > On Mon, Nov 20, 2023 at 08:37:55AM +0000, Richard Biener wrote: > > > I'm not sure about that, it would be nice for them to be usable there, > > > > Btw, I think that {( .. )} should be made usable in sizeof () and > > possibly even in at least C++ constant expressions (not sure about C). > > I believe the problkem is having new VAR_DECLs in those which actually > aren't file scope/namespace scope variables but there is no function > DECL_CONTEXT to attach to them. So, it probably wouldn't be one afternoon > change to allow that. > > > > but I think e.g. none of Joseph's implementation of those macros > > > made them usable there (except inside of sizeof/typeof/typeof_unquall) > > > and I don't see a requirement in the C23 standard that they must be usable > > > in constant expressions. > > > The versions I've posted on Thursday were usable there except for > > > stdc_has_single_bit (but that actually can be implemented that way too) > > > and stdc_bit_floor. And the version I haven't posted that used the 3 > > > patches posted on Saturday would have all functions usable when the > > > argument to those macros is a constant expression. > > > > > > BTW, if we go route of implementing all of the stdc_ type-generic macros > > > as builtins, we could as well not implement that way the following 4 > > > # define stdc_first_leading_one(x) (__builtin_clzg (x, -1) + 1U) > > > # define stdc_first_trailing_one(x) (__builtin_ctzg (x, -1) + 1U) > > > # define stdc_count_ones(x) ((unsigned int) __builtin_popcountg (x)) > > > # define stdc_has_single_bit(x) ((_Bool) (__builtin_popcountg (x) == 1)) > > > which are implementable without any new extensions. > > > > I'd rather do all of those necessary as builtins instead of hacking > > around limitations. If we don't want to solve those limitations in > > a more generic way. > > Ok, I can prepare a patch for that, shouldn't be that hard. > Do you want all 14, or just the 10 and leave the above 4 with the > above definitions?
I'd say all of them for consistency, we can parse/gimplify them to the open-coded variants then. > > And of course nobody would write > > > > const int x = sizeof (stdc_first_leading_one (5)); > > > > that's just stupid ... (but oh well). > > Well, standard testsuite needs to include that at least. > But of course, if it is usable in constant expressions, > unsigned a = stdc_bit_width ((unsigned _BitInt(824)) > 435987349856735489657489657468954768954674589674598uwb * > 49876558967549867548967548967548967549867548967456uwb); > etc. can be useful in constant expressions. > > Jakub > > -- Richard Biener <rguent...@suse.de> SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg, Germany; GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)