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* [Bug c++/111379] New: comparison between unequal pointers to void should be illegal during constant evaluation @ 2023-09-11 22:16 pkeir at outlook dot com 2023-09-12 1:20 ` [Bug c++/111379] " de34 at live dot cn ` (2 more replies) 0 siblings, 3 replies; 4+ messages in thread From: pkeir at outlook dot com @ 2023-09-11 22:16 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111379 Bug ID: 111379 Summary: comparison between unequal pointers to void should be illegal during constant evaluation Product: gcc Version: 14.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: pkeir at outlook dot com Target Milestone: --- [DR 2526](https://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#2526) clarifies that in C++23 comparison between unequal pointers to void has unspecified result. As unspecified behaviour cannot be executed in a constant expression, the code below should not compile. In fact without DR 2526, the comparison would have undefined behaviour, which also cannot be executed in a constant expression. constexpr bool compare_void_pointers() { int a[2]; void* vp1 = &a[0], * vp2 = &a[1]; return vp1 < vp2; } static_assert(compare_void_pointers()); ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/111379] comparison between unequal pointers to void should be illegal during constant evaluation 2023-09-11 22:16 [Bug c++/111379] New: comparison between unequal pointers to void should be illegal during constant evaluation pkeir at outlook dot com @ 2023-09-12 1:20 ` de34 at live dot cn 2023-09-13 8:39 ` xry111 at gcc dot gnu.org 2023-09-13 8:41 ` xry111 at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: de34 at live dot cn @ 2023-09-12 1:20 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111379 Jiang An <de34 at live dot cn> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |de34 at live dot cn --- Comment #1 from Jiang An <de34 at live dot cn> --- There's (or will be) a new DR CWG2749 which tentatively ready now. https://cplusplus.github.io/CWG/issues/2749.html It seems that the old resolution in CWG2526 was wrong, and the comparison should be constexpr-friendly. BTW I don't think there was anything specifying that "the comparison would have *undefined* behaviour" before CWG2526. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/111379] comparison between unequal pointers to void should be illegal during constant evaluation 2023-09-11 22:16 [Bug c++/111379] New: comparison between unequal pointers to void should be illegal during constant evaluation pkeir at outlook dot com 2023-09-12 1:20 ` [Bug c++/111379] " de34 at live dot cn @ 2023-09-13 8:39 ` xry111 at gcc dot gnu.org 2023-09-13 8:41 ` xry111 at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: xry111 at gcc dot gnu.org @ 2023-09-13 8:39 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111379 Xi Ruoyao <xry111 at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |xry111 at gcc dot gnu.org --- Comment #2 from Xi Ruoyao <xry111 at gcc dot gnu.org> --- (In reply to Jiang An from comment #1) > There's (or will be) a new DR CWG2749 which tentatively ready now. > https://cplusplus.github.io/CWG/issues/2749.html > > It seems that the old resolution in CWG2526 was wrong, and the comparison > should be constexpr-friendly. > > BTW I don't think there was anything specifying that "the comparison would > have *undefined* behaviour" before CWG2526. It is (or was) unspecified, not undefined. And the standard explicitly disallows "a relational operator where the result is unspecified" in [expr.const]. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/111379] comparison between unequal pointers to void should be illegal during constant evaluation 2023-09-11 22:16 [Bug c++/111379] New: comparison between unequal pointers to void should be illegal during constant evaluation pkeir at outlook dot com 2023-09-12 1:20 ` [Bug c++/111379] " de34 at live dot cn 2023-09-13 8:39 ` xry111 at gcc dot gnu.org @ 2023-09-13 8:41 ` xry111 at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: xry111 at gcc dot gnu.org @ 2023-09-13 8:41 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111379 --- Comment #3 from Xi Ruoyao <xry111 at gcc dot gnu.org> --- If CWG 2749 is accepted we should just close this as WONTFIX. ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2023-09-13 8:41 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2023-09-11 22:16 [Bug c++/111379] New: comparison between unequal pointers to void should be illegal during constant evaluation pkeir at outlook dot com 2023-09-12 1:20 ` [Bug c++/111379] " de34 at live dot cn 2023-09-13 8:39 ` xry111 at gcc dot gnu.org 2023-09-13 8:41 ` xry111 at gcc dot gnu.org
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