On Fri, 29 Sep 2023, Jakub Jelinek wrote:
> Hi!
>
> As reported by Jonathan on IRC, my vec.h patch broke build with GCC 4.8.x
> or 4.9.x as system compiler, e.g. on CFarm.
> The problem is that while all of
> std::is_trivially_{destructible,copyable,default_constructible} traits
> are in C++, only std::is_trivially_destructible has been implemented in GCC
> 4.8, the latter two were added only in GCC 5.
> Only std::is_trivially_destructible is the really important one though,
> which is used to decide what pop returns and whether to invoke the
> destructors or not. The rest are solely used in static_asserts and as such
> I think it is acceptable if we don't assert those when built with GCC 4.8
> or 4.9, anybody doing bootstrap from those system compilers or doing builds
> with newer GCC will catch that.
>
> So, the following patch guards those for 5+.
> If we switch to C++14 later on and start requiring newer version of system
> GCC as well (do we require GCC >= 5 which claims the last C++14 language
> features, or what provides all C++14 library features, or GCC >= 6 which
> uses -std=c++14 by default?), this patch then can be reverted.
I'd say we can recommend a compiler with all language and library features
but "support" the oldest working compiler. For us it's practically
GCC 4.8 (doesn't work) or GCC 7 (new enough anyway).
> Ok for trunk?
OK.
Richard.
> 2023-09-29 Jakub Jelinek <ja...@redhat.com>
>
> * vec.h (quick_insert, ordered_remove, unordered_remove,
> block_remove, qsort, sort, stablesort, quick_grow): Guard
> std::is_trivially_{copyable,default_constructible} and
> vec_detail::is_trivially_copyable_or_pair static assertions
> with GCC_VERSION >= 5000.
> (vec_detail::is_trivially_copyable_or_pair): Guard definition
> with GCC_VERSION >= 5000.
>
> --- gcc/vec.h.jj 2023-09-29 10:59:09.830551963 +0200
> +++ gcc/vec.h 2023-09-29 12:29:32.676428677 +0200
> @@ -1086,7 +1086,12 @@ vec<T, A, vl_embed>::quick_insert (unsig
> {
> gcc_checking_assert (length () < allocated ());
> gcc_checking_assert (ix <= length ());
> +#if GCC_VERSION >= 5000
> + /* GCC 4.8 and 4.9 only implement std::is_trivially_destructible,
> + but not std::is_trivially_copyable nor
> + std::is_trivially_default_constructible. */
> static_assert (std::is_trivially_copyable <T>::value, "");
> +#endif
> T *slot = &address ()[ix];
> memmove (slot + 1, slot, (m_vecpfx.m_num++ - ix) * sizeof (T));
> *slot = obj;
> @@ -1102,7 +1107,9 @@ inline void
> vec<T, A, vl_embed>::ordered_remove (unsigned ix)
> {
> gcc_checking_assert (ix < length ());
> +#if GCC_VERSION >= 5000
> static_assert (std::is_trivially_copyable <T>::value, "");
> +#endif
> T *slot = &address ()[ix];
> memmove (slot, slot + 1, (--m_vecpfx.m_num - ix) * sizeof (T));
> }
> @@ -1150,7 +1157,9 @@ inline void
> vec<T, A, vl_embed>::unordered_remove (unsigned ix)
> {
> gcc_checking_assert (ix < length ());
> +#if GCC_VERSION >= 5000
> static_assert (std::is_trivially_copyable <T>::value, "");
> +#endif
> T *p = address ();
> p[ix] = p[--m_vecpfx.m_num];
> }
> @@ -1164,13 +1173,16 @@ inline void
> vec<T, A, vl_embed>::block_remove (unsigned ix, unsigned len)
> {
> gcc_checking_assert (ix + len <= length ());
> +#if GCC_VERSION >= 5000
> static_assert (std::is_trivially_copyable <T>::value, "");
> +#endif
> T *slot = &address ()[ix];
> m_vecpfx.m_num -= len;
> memmove (slot, slot + len, (m_vecpfx.m_num - ix) * sizeof (T));
> }
>
>
> +#if GCC_VERSION >= 5000
> namespace vec_detail
> {
> /* gcc_{qsort,qsort_r,stablesort_r} implementation under the hood
> @@ -1189,6 +1201,7 @@ namespace vec_detail
> : std::integral_constant<bool, std::is_trivially_copyable<T>::value
> && std::is_trivially_copyable<U>::value> { };
> }
> +#endif
>
> /* Sort the contents of this vector with qsort. CMP is the comparison
> function to pass to qsort. */
> @@ -1197,7 +1210,9 @@ template<typename T, typename A>
> inline void
> vec<T, A, vl_embed>::qsort (int (*cmp) (const void *, const void *))
> {
> +#if GCC_VERSION >= 5000
> static_assert (vec_detail::is_trivially_copyable_or_pair <T>::value, "");
> +#endif
> if (length () > 1)
> gcc_qsort (address (), length (), sizeof (T), cmp);
> }
> @@ -1210,7 +1225,9 @@ inline void
> vec<T, A, vl_embed>::sort (int (*cmp) (const void *, const void *, void *),
> void *data)
> {
> +#if GCC_VERSION >= 5000
> static_assert (vec_detail::is_trivially_copyable_or_pair <T>::value, "");
> +#endif
> if (length () > 1)
> gcc_sort_r (address (), length (), sizeof (T), cmp, data);
> }
> @@ -1223,7 +1240,9 @@ inline void
> vec<T, A, vl_embed>::stablesort (int (*cmp) (const void *, const void *,
> void *), void *data)
> {
> +#if GCC_VERSION >= 5000
> static_assert (vec_detail::is_trivially_copyable_or_pair <T>::value, "");
> +#endif
> if (length () > 1)
> gcc_stablesort_r (address (), length (), sizeof (T), cmp, data);
> }
> @@ -1396,7 +1415,9 @@ inline void
> vec<T, A, vl_embed>::quick_grow (unsigned len)
> {
> gcc_checking_assert (length () <= len && len <= m_vecpfx.m_alloc);
> +#if GCC_VERSION >= 5000
> // static_assert (std::is_trivially_default_constructible <T>::value, "");
> +#endif
> m_vecpfx.m_num = len;
> }
>
>
> 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)
